CN103824896A - High-throughput printing of semiconductor precursor layers from intermetallic nanoflake particles - Google Patents

Abstract

The present invention relates to high-throughput printing of semiconductor precursor layers from intermetallic nanoplatelet particles, in particular to the following method and apparatus: which transforms a non-planar or planar precursor material in a suitable carrier under suitable conditions, resulting in a dispersion of planar particles with an elemental stoichiometric ratio equal to that in the feed or precursor material, even after selective forced settling. In particular, planar particles are more easily dispersed, form a much denser coating (or form a coating with a greater interparticle contact area), and anneal to a molten dense film at a lower temperature and/or for a shorter time than coatings made with their spherical nanoparticles. These planar particles may be nanoflakes with high aspect ratios. The resulting dense films formed from nanoflakes are particularly useful in forming photovoltaic devices. In one embodiment, at least one set of particles in the ink may be intermetallic flake particles (microflakes or nanoflakes) containing at least one group IB-IIIA intermetallic alloy phase.

Description

High-throughput printing of semiconductor precursor layers from intermetallic nanoflake particles

The present invention is the priority of the Chinese Invention Patent Application No. 200780014617.7 (International Patent Application No. PCT/US2007) dated February 23, 2006, entitled "High-throughput Printing of Semiconductor Precursor Layer from Intermetallic Nanoflake Particles" /062766) divisional application.

technical field

The present invention relates generally to semiconductor films, and more particularly to the fabrication of solar cells using semiconductor films based on IB-IIIA-VIA compounds.

Background technique

Solar cells and solar modules convert sunlight into electricity. These electronic devices have traditionally been fabricated in relatively expensive production processes using silicon (Si) as the light-absorbing semiconductor material. To make solar cells more economically viable, solar cell device structures have been developed that can inexpensively utilize thin-film, light-absorbing semiconductor materials such as copper indium gallium sulfide diselenide, Cu(In,Ga)(S,Se ) ₂ , also known as CI(G)S(S). Such solar cells typically have a p-type absorber layer sandwiched between a back electrode layer and an n-type junction pair. The back electrode layer is often Mo and the junction pair is often CdS. A transparent conductive oxide (TCO) such as zinc oxide (ZnO _x ) is formed on the junction pair layer, which is often used as a transparent electrode. CIS-based solar cells have demonstrated power conversion efficiencies exceeding 19%.

A central challenge in the cost-effective construction of large-area CIGS-based solar cells or modules is that the elements of the CIGS layer must be within narrow stoichiometric ratios at nano-, meso-, and macro-length scales in all three dimensions in order to produce The battery or module has high efficiency. However, it is difficult to achieve precise stoichiometric composition over relatively large substrate areas using conventional vacuum-based deposition processes. For example, it is difficult to deposit compounds and/or alloys containing more than one element by sputtering or evaporation. Both techniques rely on deposition methods limited by line-of-sight and limited-area sources, which tend to yield poor surface coverage. Line-of-sight trajectories and finite area sources can produce non-uniform three-dimensional distribution of elements in all three dimensions and/or poor film thickness uniformity over large areas. These inhomogeneities can occur on nano, meso and/or macro scales. Such non-uniformities also alter the local stoichiometry of the absorber layer, reducing the potential power conversion efficiency of the complete cell or module.

Alternatives to conventional vacuum-based deposition techniques have been developed. In particular, the fabrication of solar cells on flexible substrates using non-vacuum semiconductor printing techniques offers a highly cost-effective alternative to conventional vacuum-deposited solar cells. For example, T. Arita and co-workers [20th IEEE PV Specialists Conference, 1988, p. 1650] describe a non-vacuum screen-printing technique consisting of pure Cu, In and Se powders in a composition ratio of 1:1:2 Mix and grind and form a screen printable paste, screen print the paste on a substrate, and sinter the film to form the compound layer. They reported that although they started with elemental Cu, In, and Se powders, after the milling step, the paste contained a Cu-In- _Se2 phase. However, solar cells fabricated from sintered layers have very low efficiencies due to the poor structural and electronic properties of these absorbers.

A.Vervaet et al also reported the deposition of thin film screen printing Cu-In-Se ₂ [9thEuropean Communities PV Solar Energy Conference, 1989, p. 480], in which micron-sized Cu-In-Se ₂ powder and micron-sized used with Se powder to prepare a screen-printable paste. The layer formed by non-vacuum screen printing is sintered at high temperature. The difficulty of this approach is to find suitable flux for dense Cu-In- _Se2 film formation. Although the solar cells thus produced have poor conversion efficiencies, the use of printing and other non-vacuum techniques to fabricate solar cells remains promising.

There is a general notion in said field, and certainly in the field of CIGS non-vacuum precursors, that the optimal dispersions and coatings contain spherical particles and that in terms of dispersion stability and film filling, especially when nanoparticles are involved , any other shape is less desirable. Therefore, the processes and theories that dispersion chemists and coatings engineers are targeting involve spherical particles. Due to the high density of metals used in CIGS non-vacuum precursors, especially those containing pure metals, the use of spherical particles requires very small sizes in order to obtain a well dispersed medium. This then requires that each component be of a similar size in order to maintain the desired stoichiometric ratio, since otherwise the larger particles would settle first. Additionally, spheroids are thought to be useful for achieving high packed unit/volume based packing densities, but even at high densities, spheroids touch only at tangent points, representing a very small fraction of interparticle surface area. Furthermore, minimal flocculation is desired to reduce aggregation if good atomic mixing is desired in the resulting film.

Because of the above problems, many experts in the non-vacuum precursor CIGS community desire spherical nanoparticles as small in size as they can achieve. Although the use of conventional spherical nanoparticles remains promising, many fundamental challenges remain, such as the difficulty or availability of sufficiently small spherical nanoparticles in high yield and low cost, especially from CIGS precursor materials. Difficulties in obtaining high quality membranes reproducibly. Furthermore, the small interparticle surface area at the contact points between spherical particles may hinder the rapid processing of these particles, since the reaction kinetics depend in many ways on the amount of surface area contact between particles.

Contents of the invention

Embodiments of the present invention address at least some of the above-mentioned disadvantages. The present invention provides for the use of non-spherical particles in the formation of high quality precursor layers processed into dense films. The resulting dense films can be useful in a variety of industries and applications including, but not limited to, the fabrication of photovoltaic devices and solar cells. More specifically, the invention finds particular application in the formation of precursor layers for thin-film solar cells. The present invention provides more efficient and simplified preparation of dispersions and resulting coatings. It should be understood that the present invention is generally applicable to any process involving the deposition of material from dispersion. At least some of these and other objects described herein will be met by various embodiments of the present invention.

In one embodiment of the present invention, a method is provided for transforming non-planar and/or planar precursor metals in suitable supports under suitable conditions to produce elemental stoichiometric ratios identical to those of the feedstock even after selective precipitation. Or a dispersion of equal planar particles in the precursor metal. In particular, it has been found that the planar particles described herein are readily dispersed, form much denser coatings and at lower temperatures and/or Or less time to anneal to form a film. In one embodiment of the invention, a stable dispersion is a dispersion that remains dispersed for a period of time sufficient to allow the substrate to be coated. In one embodiment, this may involve the use of agitation to keep the particles dispersed in the dispersion. In other embodiments, this may involve a dispersion that settles but can be redispersed by stirring and/or other means when the time of use comes.

In another embodiment of the invention there is provided a method comprising formulating a particle ink wherein substantially all of the particles are nanoflakes. In one embodiment, at least about 95% of all particles (based on the total weight of all particles) are nanoflakes. In one embodiment, at least about 99% of all particles (based on the total weight of all particles) are nanoflakes. In one embodiment, all particles are nanoflakes. In another embodiment, all particles are microflakes and/or nanoflakes. Substantially each nanoflake contains at least one element from groups IB, IIIA and/or VIA, wherein the total amount of group IB, IIIA and/or VIA elements contained in the ink is such that the ink is at least for groups IB and IIIA The elements have desired or near-desired stoichiometric ratios of elements. The method includes coating a substrate with the ink to form a precursor layer and treating the precursor layer in a suitable atmosphere to form a dense film. The dense film can be used in the formation of semiconductor absorbers for photovoltaic devices. The film may consist of a molten form of a precursor layer comprising a plurality of non-fused individual particles.

In another embodiment of the present invention there is provided a material comprising a plurality of nanoflakes whose material composition comprises at least one element from groups IB, IIIA and/or VIA. The nanoflakes are prepared by grinding or comminuting precursor particles characterized by a precursor composition that provides sufficient ductility (better ductility, see patent below) to dissociate from non-planar and/or or a planar starting shape forming a planar shape, and wherein the total amount of group IB, IIIA and/or VIA elements contained in the combined precursor particles is at or near the desired elemental chemistry for at least the group IB and IIIA elements Under the measurement ratio. In one embodiment, planar includes those instances of particles that are broad in two dimensions and thin in all other dimensions. Milling can convert substantially all of the precursor particles into nanoflakes. Alternatively, milling converts at least 50% of the precursor particles into nanoflakes. Milling can be performed in an oxygen-free atmosphere to produce oxygen-free nanoflakes. Milling can be performed in an inert gas environment to produce oxygen-free nanoflakes. These non-spherical particles may be nanoflakes with a largest dimension (thickness and/or length and/or width) greater than about 20 nm, as sizes smaller than this tend to produce less efficient solar cells. Grinding may also be quenched and performed at temperatures below room temperature to allow grinding of particles composed of low melting point materials. In other embodiments, milling may be performed at room temperature. Alternatively, grinding may be performed at temperatures above room temperature to obtain the desired ductility of the material. In one embodiment of the present invention, the material composition of the feed particles preferably exhibits ductility such that non-planar feed particles are shaped into substantially planar nanoflakes at appropriate temperatures. In one embodiment, the nanoflakes have at least one substantially planar surface.

In another embodiment of the present invention, there is provided a solar cell comprising a substrate, a back electrode formed on the substrate, a p-type semiconductor thin film formed on the back electrode, formed so as to communicate with the The p-type semiconductor thin film together constitutes the n-type semiconductor thin film of the pn junction, and the transparent electrode formed on the n-type semiconductor thin film. The p-type semiconductor thin film is produced by processing a dense film formed of a plurality of nanoflakes whose material composition contains at least one element from groups IB, IIIA and/or VIA, wherein the produced film has 26% or less void volume. In one embodiment, this value can be based on the free volume of spheres packed with different diameters to minimize void volume. In another embodiment of the invention, the dense membrane has a void volume of about 30% or less. In other embodiments, the void volume is about 20% or less. In other embodiments, the void volume is about 10% or less.

In another embodiment of the present invention, a method of forming a film by using particles having specific properties is provided. The properties may be based on interparticle size, shape, composition and morphology distribution. As a non-limiting example, the particles may be nanoflakes in a desired size range. In nanoflakes, the morphology can include amorphous particles, crystalline particles, particles that are more crystalline than amorphous, and particles that are more amorphous than crystalline. The properties can also be based on interparticle composition and morphological distribution. In one embodiment of the invention, it is understood that the flakes produced have a morphology in which the flakes are less crystalline than the feed material from which they were formed. Flakes are particles having at least one substantially planar surface and may include nanoflakes and/or microflakes.

In another embodiment of the present invention, the method comprises formulating a particle ink wherein about 50% or more of the particles (based on the total weight of all particles) are each containing at least one compound from IB, IIIA and/or VIA Group IB, IIIA and/or VIA elements are included in the ink in an amount such that the ink has a desired stoichiometric ratio of the elements. In another embodiment, the term "50% or more" may be based on the number of particles relative to the total number of particles in the ink. In another embodiment, at least about 75% or more of the particles (by weight or number) are nanoflakes. The method includes coating a substrate with the ink to form a precursor layer and treating the precursor layer under suitable processing conditions to form a film. The films can be used in the formation of semiconductor absorbers for photovoltaic devices. It should be understood that suitable processing conditions may include, but are not limited to, atmosphere composition, pressure and/or temperature. In one embodiment, substantially all of the particles are flakes having a non-spherical planar shape. In one embodiment, at least about 95% of all particles (by weight of all particles combined) are flakes. In another embodiment, at least 99% of all particles (by weight of all particles combined) are flakes. The flakes may consist of nanoflakes. In other embodiments, the flakes may consist of microflakes and nanoflakes.

It should be appreciated that the planar shape of the nanoflakes can provide a number of advantages. As a non-limiting example, the planar shape can create greater surface area contact between adjacent nanoflakes, which enables films compared to films made using precursor layers of inks with spherical nanoparticles having With substantially similar material composition and otherwise substantially the same as the inks of the present invention, dense films are formed at lower temperatures and/or shorter times. The planar shape of the nanoflakes can also create greater surface area contact between adjacent nanoflakes, which allows for the use of spherical nanoparticle ink precursor layers that are otherwise substantially the same as the inks of the present invention. The dense film is formed at an annealing temperature at least 50° C. lower than that of the thin film.

The planar shape of the nanoflakes can result in greater surface area contact between adjacent nanoflakes relative to adjacent spherical nanoparticles, and thus compared to films made from precursor layers formed from inks of the present invention Promotes enhanced atomic mixing. The planar shape of the nanoflakes produces a higher packing density in a dense film compared to a film made using a precursor layer formed from a spherical nanoparticle ink of the same composition that is otherwise substantially the same as the ink of the invention.

The planar shape of the nanoflakes can also result in a packing density of at least about 76% in the precursor layer. The planar shape of the nanoflakes can result in a packing density of at least 80% in the precursor layer. The planar shape of the nanoflakes can produce a packing density of at least 90% in the precursor layer. The planar shape of the nanoflakes can produce a packing density of at least 95% in the precursor layer. Bulk density can be mass/volume, solids/volume or non-voided/volume.

The planar shape of the nanoflakes produces a grain size of at least about 1 μm in the semiconductor absorber of the photovoltaic device. The planar shape of the nanoflakes can produce a grain size of at least about 2.0 μm in at least one dimension in a semiconductor absorber of a photovoltaic device. In additional embodiments, the nanoflakes produce a grain size of at least about 1.0 μm in at least one dimension in a semiconductor absorber of a photovoltaic device. In additional embodiments, the nanoflakes produce a grain size of at least about 0.5 μm in at least one dimension in a semiconductor absorber of a photovoltaic device. The planar shape of the nanoflakes can produce a grain size of at least about 0.3 μm wide in a semiconductor absorber of a photovoltaic device. In additional embodiments, the planar shape of the nanoflakes can be produced in a semiconductor absorber of a photovoltaic device when the nanoflakes are formed from one or more of copper selenide, indium selenide, or gallium selenide A grain size of at least about 0.3 μm wide.

The planar shape of the nanoflakes provides material properties that avoid rapid and/or preferential settling of particles when forming the precursor layer. The planar shape of the nanoflakes provides a material property that avoids rapid and/or preferential settling of nanoflakes with different material compositions when forming the precursor layer. The planar shape of the nanoflakes provides a material property that avoids rapid and/or preferential settling of nanoflakes with different particle sizes when forming the precursor layer. The planar shape of the nanoflakes provides a material property that avoids aggregation of the nanoflakes in the ink and thus enables a finely dispersed solution of the nanoflakes.

The planar shape of the nanoflakes provides a material property that avoids undesired aggregation of certain kinds of nanoflakes in the ink and thus enables a homogeneously dispersed solution of the nanoflakes. The planar shape of the nanoflakes provides a material property that avoids undesired aggregation of nanoflakes of a particular material composition in the ink and thus enables a homogeneously dispersed solution of the nanoflakes. The planar shape of the nanoflakes provides a material property that avoids aggregation of specific phase-separated nanoflakes in the ink-generated precursor layer. The nanoflakes have the material property of reducing the surface tension at the interface between the nanoflakes in the ink and the carrier liquid to improve dispersion quality.

In one embodiment of the invention, the ink can be formulated by utilizing a low molecular weight dispersant whose inclusion is effective due to its favorable interaction with the planar shape of the nanoflakes. Inks can be formulated by using a carrier liquid without a dispersant. The planar shape of the nanoflakes provides a material property that allows for a more uniform dispersion of the Group IIIA material throughout the dense film compared to films made from precursor layers of spherical nanoparticle inks that are otherwise substantially the same as the inks of the invention . In another embodiment, the nanoflakes may have a random planar shape and/or a random size distribution.

The nanoflakes may have a non-random planar shape and/or a non-random size distribution. The nanoflakes can each have a length and/or largest lateral dimension of less than about 500 nm and greater than about 20 nm. The nanoflakes can each have a length and/or largest lateral dimension of from about 300 nm to about 50 nm. The nanoflakes may each have a thickness of about 100 nm or less. In other embodiments, the planar nanoflakes are about 500 nm to about 1 nm in length. As a non-limiting example, the nanoflakes can have a length and/or largest lateral dimension of about 300 nm to about 10 nm. In other embodiments, the nanoflakes may have a thickness of from about 200 nm to about 20 nm. In another embodiment, the nanoflakes may have a thickness from about 100 nm to about 10 nm. In one embodiment, the nanoflakes may have a thickness from about 200 nm to about 20 nm. The nanoflakes can each have a thickness of less than about 50 nm. The nanoflakes can have a thickness of less than about 20 nm. The nanoflakes can have an aspect ratio of at least about 5 or greater. The nanoflakes can have an aspect ratio of at least about 10 or greater. The nanoflakes have an aspect ratio of at least about 15 or greater.

The nanoflakes may be free of oxygen. The nanoflakes can be a single metal. The nano flakes may be alloys of group IB and IIIA elements. The nano flakes may be binary alloys of group IB and IIIA elements. The nano flakes may be ternary alloys of group IB and IIIA elements. The nanoflakes may be quaternary alloys of group IB, IIIA and/or VIA elements. The nanoflakes may be Group IB-chalcogenide particles and/or Group IIIA-chalcogenide particles. Additionally, the particles may be substantially oxygen-free particles, which may include those containing less than about 1 wt% oxygen. Additional embodiments may use materials having less than about 5 wt% oxygen. Additional embodiments may use materials having less than about 3 wt% oxygen. Additional embodiments may use materials having less than about 2 wt% oxygen. Additional embodiments may use materials having less than about 0.5 wt% oxygen. Additional embodiments may use materials having less than about 0.1 wt% oxygen.

In one embodiment of the invention, said coating step is performed at room temperature. This coating step can be performed at atmospheric pressure. The method may further include depositing a selenium film on the dense film. This treatment step may be facilitated by heat treatment techniques using at least one of the following: pulsed heat treatment, exposure to a laser beam, or heating by IR lamps, and/or similar or related methods. The processing may comprise heating the precursor layer to a temperature greater than about 375°C but less than the melting temperature of the substrate for a time of less than 15 minutes. The processing may comprise heating the precursor layer to a temperature greater than about 375°C but less than the melting temperature of the substrate for a period of 1 minute or less.

In another embodiment of the invention, the processing may comprise heating the precursor layer to an annealing temperature but less than the substrate melting temperature for a time of 1 minute or less. The suitable atmosphere may include a hydrogen atmosphere. In another embodiment of the present invention, said suitable atmosphere comprises a nitrogen atmosphere. In another embodiment, the suitable atmosphere comprises a carbon monoxide atmosphere. The suitable atmosphere may consist of an atmosphere having less than about 10% hydrogen. The suitable atmosphere may consist of a selenium-containing atmosphere. The suitable atmosphere may consist of a non-oxygen chalcogen atmosphere. In one embodiment of the invention, said suitable atmosphere may consist of a selenium atmosphere providing a partial pressure greater than or equal to the selenium vapor pressure in the precursor layer. In another embodiment, the suitable atmosphere may consist of a non-oxygen atmosphere containing a chalcogen vapor at a concentration of the chalcogen component greater than or equal to the chalcogen vapor pressure at the process temperature and process pressure. Press down to minimize loss of chalcogen from the precursor layer, wherein the process pressure is a non-vacuum pressure. In another embodiment, a chalcogen atmosphere may be used with one or more binary chalcogenides (in any shape or form) at greater than or equal to the chalcogen vapor at process temperature and process pressure The partial pressure of the chalcogen to minimize the loss of the precursor layer chalcogen, wherein optionally the process pressure is a non-vacuum pressure.

In another embodiment of the present invention, prior to the step of formulating the ink, a step of producing nanoflakes is included. The manufacturing step comprises providing feed particles comprising at least one Group IB, IIIA, and/or VIA element, wherein substantially each feed particle has a sufficiently ductile composition to form a planar shape from a non-planar starting shape, and The feed particles are ground to at least reduce the thickness of each particle to less than 100 nm. The milling step can be performed in an oxygen-free atmosphere to produce substantially oxygen-free nanoflakes. The substrate may be a rigid substrate. The substrate may be a flexible substrate. The substrate can be an aluminum foil substrate or a polymer substrate, which is a flexible substrate in a roll-to-roll process (continuous or segmented) using a commercially available screen coating system. The rigid substrate may consist of at least one material selected from the group consisting of glass, solar glass, low iron glass, green glass, soda lime glass, steel, stainless steel, aluminum, polymer, ceramic, metal plate, metallized ceramic plate, Metallized polymer panels, metallized glass panels, and/or any single or multiple combinations of the foregoing. The substrate may be at a different temperature than the precursor layer during processing. This may enable the substrate to use materials that would melt or become unstable at the processing temperature of the precursor layer. Optionally, this may involve actively cooling the substrate during processing.

In another embodiment of the present invention there is provided a method of formulating a particle ink wherein the majority of the particles are nanoflakes each containing at least one element from groups IB, IIIA and/or VIA and having a non-spherical planar shape , wherein the total amount of group IB, IIIA and/or VIA elements contained in the ink is such that the ink has a desired stoichiometric ratio of the elements. The method may include coating a substrate with the ink to form a precursor layer and processing the precursor layer to form a dense film for semiconductor absorber growth for a photovoltaic device. In one embodiment, at least 60% of the particles (by weight or by number) are nanoflakes. In another embodiment, at least 70% of the particles (by weight or by number) are nanoflakes. In another embodiment, at least 80% of the particles (by weight or by number) are nanoflakes. In another embodiment, at least 90% of the particles (by weight or by number) are nanoflakes. In another embodiment, at least 95% of the particles (by weight or by number) are nanoflakes.

In another embodiment, liquid inks can be made from one or more liquid metals. For example, inks can be manufactured starting from liquid and/or molten mixtures of gallium and/or indium. Copper nanoparticles can then be added to the mixture, which can then be used as an ink/paste. Copper nanoparticles are commercially available. Alternatively, the temperature of the Cu-Ga-In mixture can be adjusted (eg, cooled) until a solid forms. The solid can be ground at this temperature until small nanoparticles (eg less than 5 nm) are present. Selenium may be added to the ink and/or the film formed from the ink, for example, by exposure to selenium vapor before, during or after annealing.

In another embodiment of the present invention, a process is described comprising formulating a dispersion of solid and/or liquid particles comprising a group IB and/or IIIA element and optionally at least one group VIA element. The process includes depositing the dispersion onto a substrate to form a layer on the substrate and reacting the layer in a suitable atmosphere to form a film. In the process, at least one set of particles are intermetallic particles comprising at least one Group IB-IIIA intermetallic phase. Any of the above embodiments may use flakes (microflakes or nanoflakes) containing intermetallic phases as described herein.

In another embodiment of the present invention there is provided a composition comprising a plurality of particles comprising a group IB and/or IIIA element and optionally at least one group VIA element. At least one set of particles contains at least one Group IB-IIIA intermetallic phase.

In another embodiment of the present invention, the method may comprise formulating a dispersion of particles comprising a Group IB and/or IIIA element and optionally at least one Group VIA element. The method may include depositing the dispersion onto a substrate to form a layer on the substrate and reacting the layer in a suitable atmosphere to form a film. At least one set of particles contains a Group IB-IIIA alloy phase depleted in Group IB. In some embodiments, Group IB-depleted particles contribute less than about 50 mol % of the Group IB elements present in all particles. The Group IB-depleted Group IB-IIIA alloy phase particles may be the sole source of one of the Group IIIA elements. The Group IB-depleted Group IB-IIIA alloy phase particles may contain an intermetallic phase and may be the sole source of one of the Group IIIA elements. The Group IB-depleted Group IB-IIIA alloy phase particles may contain an intermetallic phase and be the sole source of one of the Group IIIA elements. The Group IB-depleted Group IB-IIIA alloy phase particles may be Cu ₁ In ₂ particles and be the only source of indium in the material.

It should be understood that any of the foregoing films and/or final compounds may include Group IB-IIIA-VIA compounds. The reacting step may comprise heating the layer in a suitable atmosphere. The depositing step may include coating the substrate with the dispersion. At least one set of particles in the dispersion may be in the form of nanospheres. At least one set of particles in the dispersion may be in the form of nanospheres and contain at least one Group IIIA element. At least one set of particles in the dispersion may be in the form of nanoglobules comprising a Group IIIA element in elemental form. In some embodiments of the invention, the intermetallic phase is not a terminal solid solution phase. In some embodiments of the invention, the intermetallic phase is not a solid solution phase. The intermetallic particles may contribute less than about 50 mol % of Group IB elements present in all particles. The intermetallic particles may contribute less than about 50 mol % of the Group IIIA element present in all particles. The intermetallic particles may contribute less than about 50 mol % of the Group IB element and less than about 50 mol % of the Group IIIA element in the dispersion deposited on the substrate. The intermetallic particles may contribute less than about 50 mol % of the Group IB element and more than about 50 mol % of the Group IIIA element in the dispersion deposited on the substrate. The intermetallic particles may contribute more than about 50 mol % of the Group IB element and less than about 50 mol % of the Group IIIA element in the dispersion deposited on the substrate. The mole percentages for any of the foregoing may be based on the total molar amount of the element in all particles present in the dispersion. In some embodiments, at least some of the particles have a platelet shape. In some embodiments, a majority of the particles have a platelet shape. In other embodiments, substantially all of the particles have a platelet shape.

For any of the preceding embodiments, the intermetallic material used under the present invention is a binary material. The intermetallic material may be a ternary material. The intermetallic material may contain Cu ₁ In ₂ . The intermetallic material may comprise a delta phase composition of Cu ₁ In ₂ . The intermetallic material may comprise a composition between the delta phase _{of Cu1In2} and the phase defined by Cu16In9. The intermetallic material may contain Cu ₁ Ga ₂ . The intermetallic material may comprise an intermediate solid solution of Cu ₁ Ga ₂ . The intermetallic material may contain Cu ₆₈ Ga ₃₈ . The intermetallic material may contain Cu ₇₀ Ga ₃₀ . The intermetallic material may contain Cu ₇₅ Ga ₂₅ . The intermetallic material may comprise a Cu-Ga composition of the phase between the terminal solid solution and the intermediate solid solution next to it. The intermetallic material may comprise a Cu-Ga composition (about 31.8 to about 39.8 wt% Ga) of the γ1 phase. The intermetallic material may comprise a Cu—Ga composition (about 36.0 to about 39.9 wt% Ga) in the γ2 phase. The intermetallic material may comprise a Cu-Ga composition (about 39.7 to about 44.9 wt% Ga) of the γ3 phase. The intermetallic material may comprise a Cu-Ga composition of a phase between γ2 and γ3. The intermetallic material may comprise a Cu-Ga composition of the phase between the terminal solid solution and γ1. The intermetallic material may comprise a theta phase Cu—Ga composition (about 66.7 to about 68.7 wt% Ga). The intermetallic material may include Cu-rich Cu—Ga. Gallium can be introduced as a Group IIIA element in a suspension of nanospheres. Gallium nanospheres can be formed by creating an emulsion of liquid gallium in solution. Gallium nanospheres can be produced by quenching below room temperature.

The process according to any of the preceding embodiments of the invention may include maintaining or enhancing the dispersion of liquid gallium in solution by stirring, mechanical means, electromagnetic means, ultrasonic means and/or addition of dispersants and/or emulsifiers. The process may include adding a mixture of one or more elemental particles selected from the group consisting of aluminum, tellurium, or sulfur. The suitable atmosphere may contain selenium, sulfur, tellurium, _H2 , CO, _H2Se , _H2S , Ar, _N2, or combinations or mixtures thereof. The suitable atmosphere may contain at least one of the following: _H2 , CO, Ar and _N2 . One or more types of particles may be doped with one or more inorganic materials. Optionally, one or more types of particles are doped with one or more inorganic materials selected from aluminum (Al), sulfur (S), sodium (Na), potassium (K) or lithium (Li).

Optionally, embodiments of the present invention may include having a copper source that does not immediately alloy with In and/or Ga. One option would be to use (slightly) oxidized copper. Another option would be to use CuxSey. Note that for (slightly) oxidized copper pathways, a reduction step may be required. Basically, if elemental copper is used in liquid In and/or Ga, the speed of the process between ink preparation and coating should be sufficient so that the particles do not grow to a size that would produce a coating of uneven thickness.

It should be understood that the temperature range may only be that of the substrate, since the substrate is usually the only one that should not be heated above its melting point. This applies to the lowest melting material in the substrate, ie Al, and other suitable substrates.

Further understanding of the nature and advantages of the present invention will become apparent by reference to the remaining portions of the specification and drawings.

Description of drawings

Figures 1A-1D are schematic cross-sectional views illustrating membrane fabrication according to one embodiment of the present invention.

2A and 2B are enlarged side and top views of nanoflakes according to one embodiment of the present invention.

Figure 2C is an enlarged top view of a microflake according to one embodiment of the present invention.

Figure 3 shows a schematic diagram of a milling system according to one embodiment of the present invention.

Figure 4 shows a schematic diagram of a roll-to-roll manufacturing system according to one embodiment of the present invention.

Figure 5 shows a cross-sectional view of a photovoltaic device according to one embodiment of the present invention.

Figure 6 shows a flow diagram of a method according to one embodiment of the present invention.

Figure 7 shows a module with a plurality of photovoltaic devices according to one embodiment of the invention.

8A-8C show schematic representations of planar particles for use with spherical particles according to one embodiment of the invention.

9A-9D show schematic diagrams of discrete printed layers of a chalcogen source used with planar particles according to one embodiment of the present invention.

Figure 9E shows a particle having a chalcogen shell according to one embodiment of the invention.

10A-10C illustrate the use of chalcogenide planar particles according to one embodiment of the present invention.

11A-11C show a nucleation layer according to one embodiment of the invention.

12A-12C show schematic diagrams of apparatus that can be used to prepare nucleation layers via thermal gradients.

Figures 13A-13F illustrate the use of chemical gradients according to one embodiment of the invention.

Figure 14 shows a roll-to-roll system according to the present invention.

Figure 15A shows a schematic diagram of a system using a chalcogen vapor environment according to one embodiment of the invention.

Figure 15B shows a schematic diagram of a system using a chalcogen vapor environment according to one embodiment of the invention.

Figure 15C shows a schematic diagram of a system using a chalcogen vapor environment according to one embodiment of the invention.

Figure 16A shows an embodiment of a system for use with a rigid substrate according to an embodiment of the present invention.

Figure 16B shows an embodiment of a system for use with a rigid substrate according to an embodiment of the present invention.

17-19 illustrate the use of intermetallic materials to form films according to embodiments of the present invention.

Figure 20 is a cross-sectional view showing the use of multiple layers to form a film according to an embodiment of the present invention.

Figure 21 shows feed material treated in accordance with an embodiment of the invention.

22A and 22B show features of flakes according to embodiments of the invention.

Figures 23A and 23B show the characteristics of lamellar crystals.

Detailed ways

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the claimed invention. It may be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a material" may include mixtures of materials, reference to "a compound" may include compounds, and so forth. References cited herein are hereby incorporated by reference in their entirety, except to the extent they conflict with the teachings expressly set forth in this specification.

In this specification and the following claims, reference will be made to several terms which shall be defined to have the following meanings:

"Optional" or "optionally" means that the subsequently described circumstance may or may not occur, and thus the description includes instances where it occurs and instances where it does not. For example, if a device optionally includes a barrier film feature, this means that the barrier film feature may or may not be present, and, thus, the description includes both structures in which the device has a barrier film feature and structures in which the barrier film feature does not. the structure that exists.

According to an embodiment of the present invention, a precursor layer is formed by first formulating inks each containing at least one non-spherical particle of an element from groups IB, IIIA and/or VIA, coating a substrate with the ink, and heating the precursor layer to form a dense film that can be used to fabricate the active layers of photovoltaic devices. Optionally, it should be understood that in some embodiments, densification of the precursor layer may not be required, especially if the precursor material is oxygen-free and/or substantially oxygen-free. Thus, the heating step may optionally be skipped if the particles are processed in the absence of air and oxygen. In a preferred embodiment, the non-spherical particles are nanoflakes that are substantially planar in shape. Dense films can be treated in a suitable atmosphere to form Group IB-IIIA-VIA compounds. The resulting group IB-IIIA-VIA compound is preferably a compound of Cu, In, _Ga and selenium (Se) or sulfur S of the formula CuIn _{(1-x) GaxS2(1-y) Se2y} , where 0≤ x≤1 and 0≤y≤1. It should also be understood that the resulting Group IB-IIIA-VIA compound may be Cu, In, Ga, and selenium (Se) or sulfur S of the formula Cu _z In _(1-x) Ga _x S _{2 (1-y)} Se _2y Compounds where 0.5≤z≤1.5, 0≤x≤1.0 and 0≤y≤1.0.

It should be understood that Group IB, IIIA, and VIA elements other than Cu, In, Ga, Se, and S may also be included in the descriptions of IB-IIIA-VIA materials described herein, and that hyphens ("-" for example, in Cu- The use of Se or Cu-In-Se) does not denote a compound, but rather a coexisting mixture of elements linked by this hyphen. It is also understood that Group IB is sometimes referred to as Group 11, Group IIIA is sometimes referred to as Group 13, and Group VIA is sometimes referred to as Group 16. Additionally, Group VIA(16) elements are sometimes referred to as chalcogens. In an embodiment of the invention, where several elements may be combined or substituted for each other, such as In and Ga, or Se, and S, it is common in the art to include within a set of parentheses those elements that may be combined or interchanged elements such as (In,Ga) or (Se,S). The descriptions in this specification sometimes employ this convenience. Finally, and also for convenience, the elements are discussed in terms of their commonly accepted chemical symbols. Group IB elements suitable for use in the method of the present invention include copper (Cu), silver (Ag) and gold (Au). Preferably, the Group IB element is copper (Cu). Group IIIA elements suitable for use in the method of the present invention include gallium (Ga), indium (In), aluminum (Al) and thallium (Tl). Preferably, the group IIIA element is gallium (Ga) or indium (In). Group VIA elements of interest include selenium (Se), sulfur (S) and tellurium (Te), preferably the group VIA elements are Se and/or S. It should be understood that mixtures of any of the foregoing may also be used, such as, but not limited to, alloys, solid solutions, and compounds.

film forming method

Referring now to FIG. 1, a method of forming a semiconductor film according to the present invention will be described. It should be understood that this embodiment of the invention uses non-vacuum techniques to form the semiconductor film. However, other embodiments can form the film in a vacuum environment, and the invention using non-spherical particles is not limited to non-vacuum coating techniques.

As seen in FIG. 1A , a substrate 102 is provided on which a precursor layer 106 will be formed (see FIG. 1B ). As a non-limiting example, substrate 102 may be made of a metal such as aluminum. In other embodiments, metals such as, but not limited to, stainless steel, molybdenum, titanium, copper, metalized plastic films, or combinations of the foregoing may be used as the substrate 102 . Alternative substrates include, but are not limited to, ceramics, glass, and the like. Any of these substrates may be in the form of foils, sheets, rolls, etc. or combinations thereof. Depending on the material of substrate 102, it may be useful to cover the surface of substrate 102 with a contact layer 104, thereby facilitating electrical contact between substrate 102 and an absorber layer to be formed thereon, and/or thereby confining substrate 102 reactivity in subsequent steps, and/or to promote higher quality absorber growth. As a non-limiting example, when the substrate 102 is made of aluminum, the contact layer 104 may be, but is not limited to, a molybdenum layer. For the purposes of the present discussion, the contact layer 104 may be considered part of the substrate. Thus, any discussion of forming or disposing a material or layer of material on substrate 102 includes disposing or forming said material or layer on contact layer 104 if contact layer 104 is used. Optionally, other material layers may also be used with the contact layer 104 for insulation or other purposes and still be considered part of the substrate 102 . It should be understood that the contact layer 104 may comprise more than one type or more than one discrete layer of material. Optionally, some embodiments may use any one and/or combination of the following for the contact layer: copper, aluminum, chromium, molybdenum, vanadium, etc. and/or iron-cobalt alloys. Optionally, a diffusion barrier layer 103 (shown in phantom) may be included and layer 103 may be conductive or non-conductive. As non-limiting examples, layer 103 may be composed of any of a variety of materials including, but not limited to, chromium, vanadium, tungsten, or compounds such as nitrides (including tantalum nitride, tungsten nitride, titanium nitride, nitrogen silicon nitride, zirconium nitride and/or hafnium nitride), oxides (including Al2O3 or SiO2), carbides (including SiC) and/or any single or multiple combinations of the foregoing. Optionally, a diffusion barrier layer 105 (shown in phantom) may be on the underside of the substrate 102 and be composed of materials such as, but not limited to, chromium, vanadium, tungsten, or compounds such as nitrides (including tantalum nitride , tungsten nitride, titanium nitride, silicon nitride, zirconium nitride and/or hafnium nitride), oxides (including Al2O3 or SiO2), carbides (including SiC) and/or any single or multiple combinations of the foregoing. Layers 103 and/or 105 may be adapted for use with any of the embodiments described herein.

Referring now to FIG. 1B , precursor layer 106 is formed on substrate 102 by coating substrate 102 with a dispersion such as, but not limited to, ink. As a non-limiting example, the ink may comprise a carrier liquid mixed with the nanoflakes 108 and have a rheology that renders the ink coatable on the substrate 102 . In one embodiment, the invention may use a dry powder that is mixed with a carrier and sonicated prior to coating. Optionally, the ink may have been formulated directly from the mill. In the case of mixing multiple flake compositions, the product can be mixed by various mills. This mixing can be sonicated, but other forms of agitation and/or additional mills can be used. The ink used to form precursor layer 106 may contain non-spherical particles 108 such as, but not limited to, nanoflakes. It should also be understood that the ink may optionally employ both non-spherical and spherical particles in any of various relative proportions.

Figure IB includes a close-up view of nanoflakes 108 in precursor layer 106, as seen in the enlarged image. The nanoflakes have a non-spherical shape and are substantially flat on at least one side. A more detailed view of one embodiment of nanoflakes 108 can be found in Figures 2A and 2B. Nanoflakes can be defined as particles having at least one substantially planar surface having a length and/or largest lateral dimension of about 500 nm or less, and the particles have an aspect ratio of about 2 or greater. In one embodiment, the length and/or largest lateral dimension is from about 400 nm to about 1 nm. In another embodiment, the length and/or largest lateral dimension is from about 300 nm to about 10 nm. In another embodiment, the length and/or largest lateral dimension is from about 200 nm to about 20 nm. In another embodiment, the length and/or largest lateral dimension is from about 500 nm to about 200 nm. In other embodiments, the nanoflakes are substantially planar structures having a thickness of about 10 to about 100 nm and a length of about 20 nm to about 500 nm.

It should be understood that different types of nanoflakes 108 may be used to form precursor layer 106 . In a non-limiting example, the nanoflakes are elemental nanoflakes, ie nanoflakes having only a single atomic species. The nanoflakes can be single metallic particles of Cu, Ga, In or Se. Some inks can have only one type of nanoflakes. Other inks may have two or more nanoflakes that may differ in material composition and/or other properties such as, but not limited to, shape, size, internal structure (e.g., a central core surrounded by one or more shells), Exterior coatings (to be more descriptive at this point, wording such as core-shell could be used), etc. In one embodiment, the ink used in precursor layer 106 may contain nanoflakes comprising one or more Group IB elements and nanoflakes comprising one or more different Group IIIA elements. Preferably, the precursor layer (106) contains copper, indium and gallium. In another embodiment, precursor layer 106 may be an oxygen-free copper, indium, and gallium-containing layer. Optionally, the ratio of elements in the precursor layer may be such that the layer forms a compound of _{CuInxGai -x} , where 0≤x≤1, when processed. Those skilled in the art will recognize that other Group IB elements may be substituted for Cu and other Group IIIA elements may be substituted for In and Ga. Optionally, the precursor may also contain Se, such as but not limited to Cu-In-Ga-Se flakes. This is feasible if the precursor is oxygen-free and does not require densification. In additional embodiments, the precursor material may contain nanoflakes of group IB, IIIA and VIA elements. In one non-limiting example, the precursor may contain Cu-In-Ga-Se nanoflakes, which would be particularly advantageous if the nanoflakes were formed without air and without densification prior to film formation.

Optionally, the nanoflakes 108 in the ink may be alloy nanoflakes. In a non-limiting example, the nanoflakes may be binary alloy nanoflakes such as Cu-In, In-Ga, or Cu-Ga. Alternatively, the nanoflakes may be binary alloys of elements from groups IB, IIIA, binary alloys of elements from groups IB, VIA and/or binary alloys of elements from groups IIIA, VIA. In other embodiments, the particles may be ternary alloys of Group IB, IIIA and/or VIA elements. For example, the particles may be ternary alloy particles of any of the above elements such as but not limited to Cu-In-Ga. In further embodiments, the ink may contain particles that are quaternary alloys of Group IB, IIIA and/or VIA elements. Some embodiments may have quaternary or multicomponent nanoflakes. The ink can also combine different kinds of nanoflakes such as but not limited to simple nanoflakes and alloy nanoflakes. In one embodiment, the nanoflakes used to form precursor layer 106 are preferably free of oxygen other than those amounts that are unavoidably present as impurities. Optionally, the nanoflakes contain less than about 0.1 wt% oxygen. In other embodiments, the nanoflakes contain less than about 0.5 wt% oxygen. In other embodiments, the nanoflakes contain less than about 1.0 wt% oxygen. In another embodiment, the nanoflakes contain less than about 3.0 wt% oxygen. In other embodiments, the nanoflakes contain less than about 5.0 wt% oxygen.

Optionally, the nanoflakes 108 in the ink may be chalcogenide particles such as, but not limited to, Group IB or Group IIIA selenides. In a non-limiting example, the nanoflakes may be Group IB chalcogenides formed with one or more Group IB (new style: Group 11) elements such as copper (Cu), silver (Ag), and gold (Au). elemental compounds. Examples include, but are not limited to _{, CuxSey} , where x is about 1-10 and y is about 1-10. In some embodiments of the invention, x<y. Alternatively, some embodiments may have more selenium-rich selenides, such as but not limited to Cu ₁ Se _x (where x > 1). This may provide an increased source of selenium, as discussed in commonly assigned, co-pending U.S. Patent Application 11/243,522 (Attorney Docket No. NSL-046), filed February 23, 2006 and incorporated herein by reference in its entirety like that. In another non-limiting example, the nanoflakes can be formed with one or more group IIIA (new style: group 16) elements such as aluminum (Al), indium (In), gallium (Ga) and thallium (Tl) Group IIIA chalcogenides. Examples include In _x Se _y and Ga _x Se _y , where x is about 1-10 and y is about 1-10. Still further, the nanoflakes may be Group IB-IIIA-chalcogenide compounds of one or more Group IB elements, one or more Group IIIA elements, and one or more chalcogen elements. Examples include CuInGa-Se ₂ . Additional embodiments may replace the selenide component with another Group VIA element such as, but not limited to, sulfur, or a combination of Group VIA elements such as both sulfur and selenium.

It should be understood that inks useful in the present invention may include more than one type of chalcogenide nanoflakes. For example, some may include nanoflakes from Group IB-chalcogenides and Group IIIA-chalcogenides. Additional ones may include nanoflakes from different Group IB-chalcogenides with different stoichiometric ratios. Additional ones may include nanoflakes from different Group IIIA-chalcogenides with different stoichiometric ratios.

Optionally, the nanoflakes 108 in the ink may also be particles of at least one solid solution. In a non-limiting example, the nanopowder may contain copper-gallium solid solution particles, and at least one of indium particles, indium-gallium solid solution particles, copper-indium solid solution particles, and copper particles. Alternatively, the nanopowder may contain copper particles and indium-gallium solid solution particles.

One of the advantages of using nanoflake-based dispersions is that the concentration of elements in the precursor layer 106 can be varied from top to bottom by forming the precursor layers in the order of the thinner sublayers that, when combined, form the precursor layer. Materials may be deposited to form the first, second or subsequent sub-layers and reacted in at least one suitable atmosphere to form the corresponding components of the active layer. In another embodiment, the sublayer can be reacted as it is deposited. The relative elemental concentrations of the nanoflakes making up the ink for each sublayer can vary. Thus, for example, the gallium concentration within the absorber layer may vary with depth within the absorber layer. Precursor layer 106 (or selected molecular layers, if any) may be deposited from precursor materials having a controlled bulk composition configuration of a desired stoichiometry. More details on one method of composing layers in sublayer order can be found in commonly assigned, co-pending U.S. Patent Application 11/243,492, filed October 3, 2005 and incorporated herein by reference in its entirety for all purposes ( Attorney Docket No. NSL-040).

It should be understood that the film may be a layer made from a dispersion such as but not limited to ink, paste or paint. A layer of the dispersion may be coated onto a substrate and annealed to form precursor layer 106 . For example, the dispersion can be prepared by forming oxygen-free nanoflakes containing group IB, group IIIA elements, mixing these nanoflakes and adding them to a carrier, which may contain a carrier liquid (such as but not limited to a solvent) and any additives.

In general, inks can be formed by dispersing the nanoflakes, along with (optionally) some combination of other ingredients commonly used to make inks, in a vehicle containing a dispersant such as a surfactant or a polymer. In some of the above aspects of the invention, the inks are formulated without dispersants or other additives. Carrier fluids can be aqueous (water-based) or non-aqueous (organic) solvents. Other ingredients include without limitation dispersants, binders, emulsifiers, defoamers, desiccants, solvents, fillers, extenders, thickeners, film regulators, antioxidants, flow and leveling agents, plasticizers and preservatives. These ingredients can be added in various combinations to improve film quality and optimize the coating performance of the nanoflake dispersion. An alternative method of mixing nanoflakes and then preparing dispersions from these mixed nanoflakes would be to prepare separate dispersions of each individual type of nanoflakes and then mix these dispersions. It should be appreciated that some embodiments of the ink can be formulated by using a carrier liquid and without a dispersing agent due to the favorable interaction of the planar shape of the nanoflakes with the carrier liquid.

Precursor layer 106 may be formed from a dispersion on substrate 102 by any of a variety of solution-based coating techniques including, but not limited to, wet coating, spray coating, spin coating, doctor blade coating, contact printing, Top-fed reverse printing, bottom-fed reverse printing, nozzle-fed reverse printing, gravure printing, micro-gravure printing, reverse micro-gravure printing, comma direct printing, roll coating, slot die coating Coating, Meyer rod coating, lip direct coating, double-bed direct coating, capillary coating, inkjet printing, jet deposition, spray deposition, etc., and combinations of the above and/or related technologies . Regardless of particle size or dimensions, the foregoing may apply to any of the embodiments herein.

In some embodiments, additional chalcogen, alloy particles, or elemental particles such as micron or submicron sized chalcogen powders can be mixed into the nanoflake-containing dispersion so that the nanoflakes are deposited simultaneously with the additional chalcogen . Alternatively the chalcogen powder may be deposited on the substrate in a separate solution-based coating step before or after deposition of the nanoflake-containing dispersion. In another embodiment, droplets of a Group IIIA elemental material such as but not limited to gallium may be mixed with the flakes. This is more fully described in commonly assigned, co-pending US Patent Application 11/243,522 (Attorney Docket No. NSL-046), filed February 23, 2006 and incorporated herein by reference in its entirety. This can result in an additional layer 107 (shown in phantom in Figure 1C). Optionally, additional chalcogens can be added by any combination of: (1) any source of chalcogens capable of solution deposition, such as Se or S nanometer or micrometer size mixed into the precursor layer or deposited as a separate layer powder, (2) chalcogen (such as Se or S) evaporation, (3) _H2Se ( _H2S ) atmosphere, (4) chalcogen (such as Se or S) atmosphere, (5) _H2 atmosphere, (6) an organic selenium atmosphere, such as diethyl selenium or another organometallic material, (7) another reducing atmosphere, such as CO, and (8) heat treatment. The stoichiometric ratio of nanoflakes to additional chalcogen given as Se/(Cu+In+Ga+Se) can be from about 0 to about 1000.

Note that solution-based deposition of the proposed nanoflake mixtures does not necessarily have to be performed by depositing these mixtures in a single step. In some embodiments of the invention, the coating step may be performed by depositing nanoflake dispersions of IB-, IIIA- and chalcogen-based microparticles with different compositions sequentially in two or more steps. For example, the method may first deposit a dispersion containing indium selenide nanoflakes (e.g., having an In/Se ratio of about 1), and subsequently deposit copper selenide nanoflakes (e.g., having a Cu/Se ratio of about 1) and A dispersion of gallium selenide nanoflakes (eg, having a Ga/Se ratio of about 1), followed by optionally depositing a dispersion of Se. This produces a stack of three solution-based deposited layers, which can be sintered together. Alternatively, each layer may be heated or sintered before the next layer is deposited. Many different sequences are possible. For example, In _x can be formed above a uniform, dense layer of Cu _w In _x Ga _y where w ≥ 0 (greater than or equal to zero), x ≥ 0 (greater than or equal to zero), and y ≥ 0 (greater than or equal to zero), as described above Ga _y Se _z layer, where x ≥ 0 (greater than or equal to zero), y ≥ 0 (greater than or equal to zero) and z ≥ 0 (greater than or equal to zero), and subsequently convert (sinter) these two layers into CIGS. Alternatively, _a layer _{of CuwInxGay} can be formed over a uniform _, dense layer of _InxGaySez and _the two layers subsequently converted (sintered) into CIGS.

In alternative embodiments, nanoflake-based dispersions as described above may further comprise elemental IB and/or IIIA nanoparticles (eg, in metallic form). These nanoparticles may be in the form of nanoflakes, or optionally take other shapes such as, but not limited to, spherical, spheroidal, elliptical, cubic, or other non-planar shapes. These particles may include emulsions, molten materials, mixtures, etc. in addition to solids. For example Cu _x In _y Ga _z Se _u material, where u>0 (greater than zero), x≥0 (greater than or equal to zero), y≥0 (greater than or equal to zero) and z≥0 (greater than or equal to zero), can be combined with additional A source of selenium (or other chalcogens) and gallium metal are combined into a dispersion that is sintered to form a film on a substrate. Gallium metal nanoparticles and/or nanoglobules and/or nanodroplets may be formed, for example, by initially creating an emulsion of liquid gallium in solution. Gallium metal or gallium metal in a solvent with or without an emulsifier can be heated to liquefy the metal, which is then sonicated and/or otherwise mechanically stirred in the presence of the solvent. Agitation can be performed mechanically, electromagnetically or acoustically in the presence of solvents with or without surfactants, dispersants and/or emulsifiers. The gallium nanoglobules and/or nanoliquid droplets can then be manipulated as solid particles by quenching in an environment at or below room temperature to convert the liquid gallium nanoglobules into solid gallium nanoparticles. This technique is described in detail in commonly assigned US patent application Ser. No. 11/081,163, entitled "Metallic Dispersion," by Matthew R. Robinson and Martin R. Roscheisen, the entire disclosure of which is incorporated herein by reference.

Note that this method can be optimized by using any combination of the following before, during, or after solution deposition and/or sintering of one or more precursor layers: (1) any chalcogen source capable of solution deposition, e.g. Se or S nanopowder deposited in or as a separate layer, (2) chalcogen (e.g. Se or S) evaporation, (3) _H2Se ( _H2S ) atmosphere, (4) chalcogen (e.g. Se or S) atmosphere, (5) an atmosphere containing organoselenium, such as diethylselenium, (6) an atmosphere of _H2 , (7) an additional reducing atmosphere, such as CO, (8) a wet chemical reduction step, and (9) heat treatment.

Referring now to FIG. 1C , precursor layer 106 may then be processed in a suitable atmosphere to form a film. The membrane may be a dense membrane. In one embodiment, this includes heating precursor layer 106 to a temperature sufficient to convert the ink (deposited ink). Note that solvent and possible dispersants have been removed by drying. The temperature may be from about 375°C to about 525°C (safe temperature range for processing on aluminum foil or high temperature polymer substrates). Treatment can be performed at various temperatures within this range, such as but not limited to 450°C. In other embodiments, the temperature at the substrate may be from about 400°C to about 600°C at the level of the precursor layer, but at a lower temperature on the substrate. The duration of the process can also be reduced by at least about 20% if certain steps are eliminated. Heating can be performed in the range of about 4 minutes to about 10 minutes. In one embodiment, treating comprises heating the precursor layer to a temperature greater than about 375°C but less than the melting temperature of the substrate for a time of less than about 15 minutes. In another embodiment, the processing comprises heating the precursor layer to a temperature greater than about 375° C. but less than the melting temperature of the substrate for a period of 1 minute or less. In another embodiment, the processing comprises heating the precursor layer to an annealing temperature but less than the substrate melting temperature for a time of about 1 minute or less. The processing step may also be facilitated by heat treatment techniques using at least one of the following processes: pulsed heat treatment, exposure to a laser beam, or heating by IR lamps, and/or similar or related processes.

The atmosphere associated with the annealing step in Figure 1C can also be varied. In one embodiment, suitable atmospheres include atmospheres containing greater than about 10% hydrogen. In another embodiment the suitable atmosphere comprises a carbon monoxide atmosphere. However, in other embodiments where very low or no oxygen is present in the particles, a suitable atmosphere may be a nitrogen atmosphere, an argon atmosphere, or an atmosphere having less than about 10% hydrogen. These other atmospheres may be advantageous to enable and improve material handling during fabrication.

While pulsed heat treatment generally remains promising, certain pulsed heat treatment instruments, such as directional plasma arc systems, face a number of challenges. In this particular example, a directional plasma arc system sufficient to provide pulsed heat treatment is an inherently cumbersome system that is costly to operate. The directional plasma arc system requires a level of power that makes the overall system energy costly and adds considerable cost to the manufacturing process. Directional plasma arcs also exhibit long lag times between pulses and thus make the system difficult to coordinate and synchronize with continuous roll-to-roll systems. The time such a system takes to recharge between pulses also results in a very slow system or a system using a more directional plasma arc, which adds up rapidly in system cost.

In some embodiments of the invention, other devices suitable for rapid thermal processing can be used, including pulsed layers used in adiabatic mode for annealing (Shtyrokov EI, Sov. Phys. Semicond. 91309), continuous wave lasers (usually 10-30W) (Ferris S D1979Laser-Solid Interactions and LaserProcessing (New York: AIP)), pulsed electron beam device (Kamins T I1979Appl.Phys.Leti.35282-5), scanning electron beam system (McMahon R A1979J.Vac. Sci.Techno.161840-2) (Regolini J L1979Appl.Phys.Lett.34410), other beam systems (Hodgson R T1980Appl.Phys.Lett.37187-9), graphite plate heaters (Fan J C C1983Mater.Res. Soc.Proc.4751-8) (M W Geis1980Appl.Phys.Lett.37454), lamp system (Cohen R L1978Appl.Phys.Lett.33751-3), and scanning hydrogen flame system (Downey D F1982Solid State Technol.2587- 93). In some embodiments of the invention, non-directional low density systems may be used. Alternatively, other known pulsed heating processes are also described in US Pat. Nos. 4,350,537 and 4,356,384. Additionally, it should be understood that references to solar cell processing and fast electron beam pulsing as described in expired U.S. Patents 3,950,187 (“Method and apparatus involving pulsed electron beam processing of semiconductor devices”) and 4,082,958 (“Apparatus involving pulsed electron beam processing of semiconductor devices”) Methods and equipment for heat treatment are in the public domain and are well known. US Patent 4,729,962 also describes another known method for rapid thermal processing of solar cells. The above may be applied alone or in single or multiple combinations with the above or other similar processing techniques and various embodiments of the present invention.

It should be noted that the use of nanoflakes generally results in precursor layers that sinter into solid layers at temperatures up to 50 °C lower than corresponding layers of spherical nanoparticles. This is partly due to the greater surface area contact between the particles.

In certain embodiments of the invention, precursor layer 106 (or any of its sublayers) may be annealed sequentially or simultaneously. The annealing may be accomplished by rapid heating of the substrate 102 and precursor layer 106 from ambient temperature to a plateau temperature range of about 200°C to about 600°C. Treatment includes annealing with a ramp rate of 1-5°C/sec, preferably more than 5°C/sec, to a temperature of about 200°C to about 600°C. The temperature is maintained at a plateau for a period of time ranging from about a fraction of a second to about 60 minutes, followed by cooling down. Optionally, the treatment further comprises subjecting the Se vapor to a temperature of about 225°C to about 575°C for a period of about 60 seconds to about 10 minutes at a ramp rate of 1-5°C/sec, preferably greater than 5°C/sec. Annealing layer selenization, where the plateau temperature does not necessarily remain constant in time, to form a thin film comprising one or more chalcogenides containing Cu, In, Ga and Se. Optionally, the treatment comprises selenization without a separate annealing step in an atmosphere containing hydrogen, but can be performed in an atmosphere containing _H2Se or a mixture of _H2 and Se vapor at 1-5 °C/sec, preferably more than 5 The ramp rate of °C/sec to a temperature of about 225°C to about 575°C for a period of about 120 seconds to about 20 minutes densifies and selenizes in one step.

Alternatively, the annealing temperature can be adjusted to swing over a range of temperatures rather than remain at a particular plateau temperature. This technique (referred to herein as rapid thermal processing or RTA) is particularly suitable for forming photovoltaically active layers (sometimes referred to as "absorber" layers) on metal foil substrates such as, but not limited to, aluminum foil. Other suitable substrates include, but are not limited to, other metals such as stainless steel, copper, titanium or molybdenum, metallized plastic foils, glass, ceramic films, and mixtures, alloys, and blends of these and similar or related materials. The substrate can be flexible, such as in the form of a foil, or rigid, such as in the form of a plate, or a combination of these. Additional details of this technique are described in US Patent Application 10/943,685, which is incorporated herein by reference.

The atmosphere associated with the annealing step can also vary. In one embodiment, the suitable atmosphere comprises a hydrogen atmosphere. However, in other embodiments where very low or no oxygen is present in the nanoflakes, a suitable atmosphere may be a nitrogen atmosphere, an argon atmosphere, a carbon monoxide atmosphere, or an atmosphere with less than about 10% hydrogen. These other atmospheres would be advantageous to enable and improve material handling during fabrication.

Referring now to FIG. 1D , precursor layer 106 is processed to form dense film 110 . The dense film 110 may actually have a reduced thickness compared to the thickness of the wet precursor layer 106 because the carrier fluid and other materials have been removed during processing. In one embodiment, membrane 110 may have a thickness of about 0.5 μm to about 2.5 μm. In other embodiments, the thickness of the membrane 110 may be from about 1.5 μm to about 2.25 μm. In one embodiment, the resulting dense film 110 can be substantially void-free. In some embodiments, dense membrane 110 has a void volume of about 5% or less. In other embodiments, the void volume is about 10% or less. In another embodiment, the void volume is about 20% or less. In another embodiment, the void volume is about 24% or less. In another embodiment, the void volume is about 30% or less. Treatment of the precursor layer 106 fuses the nanoflakes together and in most cases removes void spaces and thereby reduces the thickness of the resulting dense film.

Depending on the type of material used to form film 110, film 110 may be suitable for use as an absorbent layer or further processed to become an absorbent layer. More particularly, the membrane 110 may be a membrane produced in a one-step process, or a membrane used in another subsequent one-step process making it a two-step process, or a membrane used in a multi-step process. In a one-step process, film 110 is formed to include Group IB-IIIA-VIA compounds and may be an absorber film suitable for use in photovoltaic devices. In a two-step process, the film 110 may be a solid and/or densified film that will have further processing to be suitable for use as an absorber film for use in photovoltaic devices. As a non-limiting example, the film 110 in the two-step process may not contain any and/or a sufficient amount of Group VIA elements to act as an absorber layer. Adding Group VIA elements or other materials can be the second step of this two-step process. A mixture of two or more VIA elements can be used, or a third step can be added using another VIA element as used in the second step. Various methods of adding this material include printing of Group VIA elements, use of VIA element vapor, and/or other techniques. It should also be understood that the process atmospheres may be different in the two-step process. As a non-limiting example, one atmosphere may optionally be a Group VIA-based atmosphere. As another non-limiting example, an atmosphere can be an inert atmosphere as described herein. Additional processing steps for the multi-step process may be wet chemical surface treatments to improve the IB-IIIA-VIA film surface, and/or additional rapid thermal treatments to improve the volume and surface properties of the IB-IIIA-VIA film.

nanoflakes

Referring now to Figures 2A and 2B, an embodiment of the nanoflakes 108 of the present invention will be described in more detail. Nanoflakes 108 can have various shapes and sizes. In one embodiment, the nanoflakes 108 can have a large aspect ratio in terms of particle thickness to particle length. Figure 2A shows particle packing density. Figure 2A shows that some nanoflakes have a thickness of about 20 to about 100 nm. Some may have a length of about 500 nm or less. In some embodiments the aspect ratio of the nanoflakes may be about 10:1 or greater (the ratio of the longest dimension to the shortest dimension of the particle). Additional embodiments may have aspect ratios of about 30:1 or greater. Additionally may have an aspect ratio of about 50:1 or greater. An increase in aspect ratio indicates that the longest dimension increases relative to the shortest dimension or the shortest dimension decreases relative to the longest dimension. Thus, the aspect ratio here relates to the longest transverse dimension (its length or width) relative to the shortest dimension which is usually the thickness of the sheet. These dimensions are measured along the edge or along the long axis to provide measurements of dimensions such as, but not limited to, length, width, depth and/or diameter. When referring to a plurality of nanoflakes having a specified aspect ratio, it is meant that all nanoflakes of the composition collectively have the specified average aspect ratio. It should be understood that there may be a particle aspect ratio distribution around an average aspect ratio.

As seen in FIG. 2A , although the size and shape of the nanoflakes 108 can vary, most include at least one substantially planar surface 120 . The at least one planar surface 120 allows for greater surface contact between adjacent nanoflakes 108 . This greater surface contact provides several benefits. Greater contact allows for improved atomic mixing between adjacent particles. For nanoflakes containing more than one element, the intimate contact in the film allows easy subsequent diffusion even though there may already be a proper atomic mixing for the particles. Thus, increased contact favors a more uniform distribution of the element in the resulting dense film if the particles are slightly enriched in one element. In addition, larger interparticle interfacial areas lead to faster reaction rates. The planar shape of the particles maximizes the interparticle contact area. The interparticle contact area allows chemical reactions (such as those based on atomic diffusion) to be initiated, catalyzed, and/or performed relatively quickly and simultaneously over a large area. Thus, not only does the shape improve mixing, but the larger interfacial area and interparticle contact area also increases the reaction rate.

Still referring to FIG. 2A , the planar shape also allows for increased packing density. As seen in FIG. 2A , nanoflakes 108 may be oriented substantially parallel to the surface of substrate 102 and stacked one above the other to form precursor layer 106 . Inherently, the geometry of the nanoflakes allows for more intimate contact in the precursor layer than spherical particles or nanoparticles. In fact, it is possible that 100% of the flat surfaces of a nanoflake are in contact with another nanoflake. Thus, the planar shape of the nanoflakes produces a higher packing density in a dense film than a film made using an otherwise substantially identical precursor layer of spherical nanoparticle ink of the same composition. In some embodiments, the planar shape of the nanoflakes produces a packing density of at least about 70% in the precursor layer. In other embodiments, the nanoflakes create a packing density of at least about 80% in the precursor layer. In other embodiments, the nanoflakes create a packing density of at least about 90% in the precursor layer. In other embodiments, the nanoflakes produce a packing density of at least about 95% in the precursor layer.

As seen in Figure 2B, the nanoflakes 108 can have various shapes. In some embodiments, the nanoflakes in the ink can include those of random size and/or random shape. Conversely, particle size is extremely important for standard spherical nanoparticles, and those of different sizes and compositions will produce dispersions with unstable atomic compositions. The flat surface 120 of the nanoflakes allows for easier suspension of the particles in the carrier liquid. Thus, even though the nanoflakes may not be monodisperse in size, having the constituent metals flake-like provides a means of suspending particles in a carrier liquid without rapid and/or preferential settling of any constituent elements. Additionally, Figure 2C is an enlarged top view of a microflake 121 according to one embodiment of the present invention.

It should be appreciated that the nanoflakes 108 of the present invention may be formed and/or sized to provide a more controlled size and shape distribution. The size distribution of the nanoflakes can be such that one standard deviation from the mean length and/or width of the nanoflakes is less than about 250 nm. In another embodiment, the size distribution of the nanoflakes can be such that one standard deviation from the mean length and/or width of the nanoflakes is less than about 200 nm. In another embodiment, the size distribution of the nanoflakes can be such that one standard deviation from the mean length and/or width of the nanoflakes is less than about 150 nm. In another embodiment, the size distribution of the nanoflakes can be such that one standard deviation from the mean length and/or width of the nanoflakes is less than about 100 nm. In another embodiment, one standard deviation from the mean length of the nanoflakes is less than about 50 nm. In another embodiment, one standard deviation from the average thickness of the nanoflakes is less than about 10 nm. In another embodiment of the invention, one standard deviation from the mean thickness of the nanoflakes is less than about 5 nm. The nanoflakes each have a thickness of less than about 250 nm. In another embodiment, the nanoflakes each have a thickness of less than about 100 nm. In another embodiment, the nanoflakes each have a thickness of less than about 50 nm. In another embodiment, the nanoflakes each have a thickness of less than about 20 nm. In terms of their shape, the nanoflakes can have an aspect ratio of at least about 10 or greater. In another embodiment, the nanoflakes have an aspect ratio of at least about 15 or greater. The nanoflakes have a random planar shape and/or a random size distribution. In other embodiments, the nanoflakes have a non-random planar shape and/or a non-random size distribution.

The stoichiometric ratio of the elements can vary between individual nanoflakes so long as the total amount in all combined particles is at or close to the desired stoichiometric ratio of the precursor layer and/or resulting dense film. According to a preferred embodiment of the process, the total amount of elements in the resulting film has a Cu/(In+Ga) composition ranging from about 0.7 to about 1.0 and a Ga/(In+Ga) composition ranging from about 0.05 to about 0.30 scope. Optionally, the Se/(In+Ga) composition may range from about 0.00 to about 4.00 such that a subsequent step involving the use of an additional Se source may or may not be required.

nanoflake formation

Referring now to FIG. 3, one embodiment of an apparatus for forming nanoflakes 108 will be described. Nanoflakes 108 can be obtained by applying the following various techniques, including but not limited to comminution techniques such as ball milling, bead milling, Small media milling, agitator ball milling, planetary milling, horizontal ball milling, pebble milling, attrition, hammer milling, dry milling, wet milling, jet milling, or other types of milling. Figure 3 shows one embodiment of a milling system 130 using a mill 132 containing balls or beads or other material used in the milling process. System 130 may be a closed system to provide an oxygen-free environment for processing of feed materials. A source of inert gas 134 can be connected to the closed system to maintain an oxygen-free environment. The milling system 130 may also be configured to allow cryogenic milling by providing liquid nitrogen or other cooling source 136 (shown in phantom). Alternatively, grinding system 130 may also be configured to provide heating during the grinding process. It is also possible to perform heating and/or cooling cycles during the milling process. Optionally, milling may also include mixing a carrier liquid and/or dispersant with the powder or feed to be processed. In one embodiment of the invention, the nanoflakes 108 produced by milling can have various dimensions such as, but not limited to, about 20 nm to about 500 nm thick. In another embodiment, the nanoflakes may be about 75nm-100nm thick.

It should be understood that milling may use beads or microbeads made of a harder and/or higher mass density material than the feed particles to convert the feed particles to a suitable size and shape. In one embodiment, the beads are glass, ceramic, alumina, porcelain, silicon carbide, or tungsten carbide beads, stainless steel balls with ceramic shells, iron balls with ceramic shells, etc., thereby reducing the risk of contamination of the nanoflakes Minimize. The grinder itself or components of the grinder may also have a ceramic lining or be lined with another inert material, or components of the grinder may be entirely ceramic or rendered inert chemically and mechanically so that the slurry containing the nanoflakes Pollution is minimized. The beads can also be sieved periodically during the process.

Ball milling can be performed in an oxygen-free environment. This may involve using a grinder that is closed from the outside environment and purged of air. Grinding may then be performed under an inert atmosphere or other oxygen-free environment. Some embodiments may involve placing the grinder in an enclosure or chamber that provides a seal for an oxygen-free environment. The process can include drying and degassing the support or choosing an anhydrous, oxygen-free solvent to start and feed without exposure to air. Oxygen-free milling can produce oxygen-free nanoflakes, which in turn reduces the need for particle oxygen removal steps. This can significantly reduce the annealing time associated with the transformation of the nanoflake precursor layer into a dense film. In some embodiments, the annealing time is in the range of about 30 seconds. With respect to air-free nanoflake fabrication (shredding), it should be understood that the present invention may also include air-free dispersion fabrication as well as air-free coating, storage and/or handling.

Grinding can be performed at various temperatures. In one embodiment of the invention, grinding is performed at room temperature. In another embodiment, milling is performed at low temperature such as but not limited to ≤ -175°C. This allows the grind to work on particles that may be liquid at room temperature or not brittle enough to pulverize. Milling can also be performed at a desired milling temperature where all of the precursor particles are solid and at which the precursor particles are sufficiently ductile to form a planar shape from a non-planar or planar starting shape. The desired temperature may be room temperature, above or below room temperature and/or cycling between different temperatures. In one embodiment, the milling temperature may be less than about 15°C. In another embodiment, the temperature is less than about -175°C. In another embodiment, the grinding can be cooled by liquid nitrogen at 80K, ie -193°C. Temperature control during milling can control possible chemical reactions between solvents, dispersants, feed materials and/or mill components. It should be understood that in addition to the above, the temperature may also be varied during different periods of the milling process. As a non-limiting example, grinding may be performed at a first temperature for an initial grinding period and to an additional temperature for subsequent periods during grinding.

Milling can convert substantially all of the precursor particles into nanoflakes. In some embodiments, milling converts at least about 50% (by weight of all precursor particles) of the precursor particles into nanoflakes. In additional embodiments, at least 50% by volume of all precursor particles are converted into nanoflakes. Additionally, it should be understood that the temperature may be constant or varied during milling. This can be useful to adjust the material properties of the feed material or part of the ground material to produce particles of desired shape, size and/or composition.

Although the present invention discloses a "top down" method of forming nanoflakes, it should be understood that other techniques may also be used. For example, the material is quenched from the melt on a surface such as a liquid cooling bath. Indium (and possibly gallium and selenium) nanoflakes can be formed by emulsifying molten indium while stirring and quenching on the surface of a cooling bath. It should be understood that any wet chemical, dry chemical, dry physical and/or wet physical technique for making flakes may be used with the present invention (other than dry or wet comminution). Thus, the invention is not limited to wet physical top-down methods (grinding), but may also include dry/wet bottom-up methods. It should also be noted that comminution can optionally be a multi-step process. In one non-limiting example, this may first involve taking millimeter-sized chunks/pieces which are dry ground to <100 μm, followed by grinding in one, two, three or more steps, and subsequently reducing Bead size to nanoflakes.

It should be understood that the feed particles for use in the present invention can be prepared by a variety of methods. For example and without limitation, US Patent No. 5,985,691 to B.M. Basol et al. describes a particle-based method to form Group IB-IIIA-VIA compound films. Eberspacher and Pauls in US Pat. No. 6,821,559 describe a process for making phase stable precursors in the form of fine particles, such as submicron multinary metal particles, and heterogeneous mixed metal particles comprising at least one metal oxide. Bulent Basol describes in US Published Patent Application 20040219730 a process for forming a compound film that involves formulating a nanopowder material with a controlled overall composition and a single solid solution particle. Using the solid solution approach, gallium can be incorporated into metal dispersions in non-oxide form—but only with relative atomic percents up to about 18 (Subramanian, P.R., Laughlin, D.E., Binary AlloyPhase Diagrams. Second Edition, edited by Massalski, T.B. 1990. ASM international, Materials Park, OH, pp. 1410-1412; Hansen, M., Constitution of Binary Alloys. 1958. Second edition, McGraw Hill, pp. 582-584). US Patent Application 11/081,163 describes a process for forming compound films by formulating a mixture of elemental nanoparticles composed of Group IB, IIIA, and optionally Group VIA elements, the mixture having a controlled overall composition. A discussion of chalcogenide powders can also be found in: [(1) Vervaet, A. et al., E.C. Photovoltaic Sol. Energy Conf., Proc. Int. Conf., 10th(1991), 900-3.; (2) Journal of Electronic Materials, Vol.27, No.5, 1998, p. 433; Ginley et al; (3) WO99,378,32; Ginley et al; (4) US6,126,740]. These methods can be used to make feed to be comminuted. Additional methods can form precursor submicron sized particles ready for solution deposition. All documents listed above are hereby incorporated by reference in their entirety for all purposes.

ink preparation

To formulate the dispersion for use in precursor layer 106, nanoflakes 108 are mixed together and mixed with one or more chemicals including, but not limited to, dispersants, surfactants, polymers, binders Agents, crosslinking agents, emulsifiers, defoamers, desiccants, solvents, fillers, extenders, thickeners, film regulators, antioxidants, flow agents, leveling agents, and preservatives.

Inks made with the present invention may optionally include a dispersant. Some embodiments may not include any dispersants. Dispersants (also known as wetting agents) are surface active substances used to prevent particle aggregation or flocculation, thus facilitating the suspension of solid materials in a liquid medium and stabilizing the dispersions thus produced. If particle surfaces attract each other, flocculation occurs, which tends to cause aggregation and reduce stability and/or uniformity. If the particle surfaces repel each other, stabilization occurs where the particles do not aggregate and tend not to settle out of solution very quickly.

Effective dispersants are generally capable of pigment wetting, dispersion and stabilization. Dispersants vary according to the nature of the ink/coating. Polyphosphates, styrene-maleates and polyacrylates are often used in aqueous formulations, while fatty acid derivatives and low molecular weight modified alkyd and polyester resins are often used in organic formulations.

Surfactants are surface active agents that lower the surface tension of the solvent in which they are dissolved, act as wetting agents, and keep the surface tension of the (aqueous) medium low for the ink to interact with the substrate surface. Certain types of surfactants are also used as dispersants. Surfactants usually contain hydrophobic carbon chains and hydrophilic polar groups. The polar group may be nonionic. If the polar group is ionic, the charge can be positive or negative, resulting in a cationic or anionic surfactant. Zwitterionic surfactants contain both positive and negative charges within the same molecule; an example is N-n-dodecyl-N,N-dimethylbetaine. Certain surfactants are often used as dispersants in aqueous solutions. Representative classes include acetylene glycols, fatty acid derivatives, phosphate esters, polyacrylic acid sodium salt, polyacrylic acid, soybean lecithin, trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO).

Binders and resins are often used to hold adjacent particles together in nascent or formed dispersions. Examples of common binders include acrylic monomers (as monofunctional diluents and polyfunctional reactive agents), acrylic resins (e.g., acrylic polyols, amine synergists, epoxy acrylics, poly ester acrylic, polyether acrylic, styrene/acrylic, urethane acrylic or vinyl acrylic), alkyds (such as long oil, medium oil, short oil or tall oil), adhesion promoters Such as but not limited to polyvinylpyrrolidone (PVP), amide resins, amino resins (such as but not limited to melamine-based or urea-based compounds), asphalt/bitumen, butadiene acrylonitrile, cellulose resins (such as but not limited to butyl acetate cellulose acetate (CAB), cellulose acetate propionate (CAP), ethyl cellulose (EC), nitrocellulose (NC) or organic cellulose esters), chlorinated rubber, dimer fatty acid, epoxy resin (e.g. acrylates, bisphenol-A based resins, epoxy UV curable resins, esters, phenols and cresols (novolaks) or phenoxy based compounds), ethylene co-terpolymers such as ethylene acrylic acid/methyl Acrylic, E/AA, E/M/AA, or ethylene vinyl acetate (EVA), fluoropolymers, gelatin (such as Pluronic F-68 from BASF Corporation of Florham Park, NJ), glycol monomers, hydrocarbon resins (e.g. aliphatic, aromatic or coumaronyl such as indene), maleic resins, modified ureas, natural rubber, natural resins and gums, rosins, modified phenolic resins, resole resins, polyamides, polybutadiene (liquid hydroxyl terminated), polyesters (saturated and unsaturated), polyolefins, polyurethane (PU) isocyanates (e.g. hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), alicyclic diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI) or trimethylhexamethylene diisocyanate (TMDI)), polyurethane (PU) polyols (e.g. caprolactone, dimer-based polyester, polyester, or polyether), polyurethane (PU) dispersions (PUDs) such as those based on polyester or polyether, polyurethane prepolymers (e.g. caprolactone, dimer-based polyester, polyester, polyethers and urethane acrylate based compounds), polyurethane thermoplastics (TPU) such as polyesters or polyethers, silicates (e.g. alkyl silicates or water glass based compounds), silicones (amine functional , epoxy-functional, ethoxy-functional, hydroxyl-functional, methoxy-functional, silanol-functional, or vinyl (cinyl)-functional), styrenes (such as styrene-butadiene emulsions, styrene/vinyltoluene polymers and copolymers) or vinyl compounds such as polyolefins and polyolefin derivatives, polystyrene and styrene copolymers, or polyvinyl acetate (PVAC)).

Emulsifiers are dispersants that allow a liquid to blend with other liquids by facilitating the breakup of aggregated material into small droplets and thus stabilize the suspension in solution. For example, sorbitan esters are used as emulsifiers in the preparation of water-in-oil (w/o) emulsions, in the preparation of oil-absorbing substrates (w/o), in the preparation of w/o pomades, in As a reabsorbent and as a non-toxic anti-foaming agent. Examples of emulsifiers are sorbitan esters such as sorbitan sesquioleate (Arlacel 60), sorbitan sesquioleate (Arlacel 83), sorbitan monolaurate (Span 20), dehydrated Sorbitan monopalmitate (Span40), sorbitan monostearate (Span60), sorbitan tristearate (Span65), sorbitan monooleate (Span80) and anhydrous Sorbitan trioleate (Span 85), all of which are commercially available, for example, from Uniqema of New Castle, Delaware. Other polymeric emulsifiers include polyoxyethylene monostearate (Myrj45), polyoxyethylene monostearate (Myrj49), polyoxyl (40) stearate (Myrj52), polyoxyethylene monolaurate ester (PEG400), polyoxyethylene monooleate (PEG400 monooleate) and polyoxyethylene monostearate (PEG400 monostearate), and Tween series surfactants, including but not limited to poly Oxyethylene sorbitan monolaurate (Tween20), polyoxyethylene sorbitan monolaurate (Tween21), polyoxyethylene sorbitan monopalmitate (Tween40), polyoxyethylene sorbitan Alcohol monostearate (Tween60), polyoxyethylene sorbitan tristearate (Tween61), polyoxyethylene sorbitan monooleate (Tween80), polyoxyethylene sorbitan mono-oil (Tween 81), and polyoxyethylene sorbitan trioleate (Tween 85), all of which are commercially available, for example, from Uniqema of New Castle, Delaware. Arlacel, Myrj and Tween are registered trademarks of ICI Americans Inc. of Wilmington, Delaware.

Foaming may be formed by the release of various Ga-Ses during the coating/printing process, especially if the printing process is performed at high speed. Surfactants may adsorb and stabilize the liquid-air interface, promoting foam formation. Anti-foaming agents prevent foam from starting, while anti-foaming agents minimize or remove pre-formed foam. Antifoam agents include hydrophobic solids, fatty oils, and certain surfactants, all of which penetrate the liquid-air interface to slow down foam formation. Antifoams also include silicates, silicones, and silicone-free materials. Silicone-free materials include microcrystalline waxes, mineral oils, polymeric materials, and silica- and surfactant-based materials.

Solvents can be aqueous (water-based) or non-aqueous (organic). However, environmentally friendly water-based solutions have the disadvantage of relatively higher surface tension than organic solvents, making it more difficult to wet substrates, especially plastic substrates. To improve substrate wetting when using polymeric substrates, surfactants can be added to lower ink surface tension (while minimizing surfactant-stabilized foaming), while the substrate surface is modified to increase its surface energy (e.g. by corona treatment). Common organic solvents include acetates, acrylates, alcohols (butanol, ethanol, isopropanol, or methanol), aldehydes, benzene, methylene bromide, chloroform, methylene chloride, dichloroethane, trichloroethane, cyclic compounds such as cyclopentanone or cyclohexanone, esters such as butyl acetate or ethyl acetate, ethers, glycols such as ethylene glycol or propylene glycol, hexane, heptane, aliphatic hydrocarbons, aromatic hydrocarbons, Ketones (such as acetone, methyl ethyl ketone or methyl isobutyl ketone), natural oils, terpenes, terpineol, toluene.

Additional components may include fillers/extenders, thickeners, rheology modifiers, surface modifiers (including adhesion promoters/bonding), anti-gelling agents, anti-blocking agents, antistatic agents, chelating agents Compounding/compounding agent, corrosion inhibitor, flame retardant/rust inhibitor, flame retardant, wetting agent, heat stabilizer, light stabilizer/UV absorber, lubricant, pH stabilizer, slip control material, antioxidant, Flow and leveling agent. It should be understood that all components may be added alone or in combination with other components.

roll-to-roll manufacturing

Referring now to FIG. 4, a roll-to-roll manufacturing process in accordance with the present invention will be described. Embodiments of the invention using nanoflakes are well suited for roll-to-roll manufacturing. Specifically, in roll-to-roll manufacturing system 200 , a flexible substrate 201 , such as aluminum foil, travels from a supply roll 202 to a take-up roll 204 . Between the supply roll and the take-up roll, the substrate 201 passes through several coaters 206A, 206B, 206C, microgravure rollers and heating means 208A, 208B, 208C. Each applicator deposits a different layer or sublayer of the precursor layer, such as those described above. A heating device is used to anneal the various layers and/or sublayers to form a dense film. In the example depicted in FIG. 4 , coaters 206A and 206B can coat different sublayers of a precursor layer (eg, precursor layer 106 ). Heating devices 208A and 208B may anneal each sublayer before depositing the next sublayer. Alternatively, both sublayers can be annealed simultaneously. Applicator 206C may optionally apply additional layers of material containing chalcogen or alloy or elemental particles as described above. The heating device 208C heats the optional layer and the aforementioned precursor layer. Note that it is also possible to deposit the precursor layer (or sub-layers) followed by any additional layers and then heat all three layers together to form the IB-IIIA-chalcogenide compound film for the photovoltaic absorber layer. The roll-to-roll system may be a continuous roll-to-roll and/or a segmented roll-to-roll and/or a batch-mode processed roll-to-roll system.

Photovoltaic device

Referring now to Figure 5, films made as described above can serve as absorber layers in photovoltaic devices, modules, or solar panels. An example of the photovoltaic device 300 is shown in FIG. 4 . The device 300 comprises a base substrate 302, an optional adhesion layer 303, a base or back electrode 304, a p-type absorber layer 306 comprising films of the type described above, an n-type semiconductor thin film 308 and a transparent electrode 310. For example, base substrate 302 may be made of metal foil, polymers such as polyimide (PI), polyamide, polyetheretherketone (PEEK), polyethersulfone (PES), polyetherimide (PEI), poly Polyethylene naphthalate (PEN), polyester (PET), related polymers, or metallized plastics. Related polymers include, by way of non-limiting example, those polymers having similar structural and/or functional properties and/or material properties. The base 304 is made of a conductive material. For example, base 304 may be a metal layer having a thickness selected from about 0.1 μm to about 25 μm. An optional intermediate layer 303 may be introduced between the electrode 304 and the substrate 302 . Optionally, layer 303 may be a diffusion barrier layer to prevent diffusion of material between substrate 302 and electrode 304 . Diffusion barrier layer 303 may be a conductive layer or it may be a non-conductive layer. As non-limiting examples, layer 303 may be composed of any of a variety of materials including, but not limited to, chromium, vanadium, tungsten, and glass, or compounds such as nitrides (including tantalum nitride, tungsten nitride, titanium, silicon nitride, zirconium nitride and/or hafnium nitride), oxides, carbides and/or any single or multiple combinations of the foregoing. Although not limited to the following, the thickness of this layer may be 100 nm to 500 nm. In some embodiments, this layer may be 100nm-300nm. Optionally, the thickness may be from about 150 nm to about 250 nm. Optionally, the thickness may be about 200 nm. In some embodiments, two barrier layers may be used, one on each side of the substrate 302 . Optionally, an interfacial layer may be disposed over electrode 304 and be composed of materials such as including but not limited to chromium, vanadium, tungsten, and glass, or compounds such as nitrides (including tantalum nitride, tungsten nitride, nitrogen titanium nitride, silicon nitride, zirconium nitride and/or hafnium nitride), oxides, carbides and/or any single or multiple combinations of the foregoing.

The transparent electrode 310 may include a transparent conductive layer 309 and a metal (eg, Al, Ag, Cu, or Ni) finger layer 311 to reduce sheet resistance.

The n-type semiconductor thin film 308 serves as a junction pair between the compound film and the transparent conductive layer 309 . For example, n-type semiconductor thin film 308 (sometimes referred to as a junction pair layer) may include inorganic materials such as cadmium sulfide (CdS), zinc sulfide (ZnS), zinc hydroxide, zinc selenide (ZnSe), n-type organic materials, or Some combination of two or more of these or similar materials, or organic materials such as n-type polymers and/or small molecules. Layers of these materials can be deposited, for example, by chemical bath deposition (CBD) and/or chemical surface deposition (and/or related methods) to a thickness of from about 2 nm to about 1000 nm, more preferably from about 5 nm to about 500 nm and most preferably from about 10 nm to about 300nm. This can also be configured for continuous roll-to-roll and/or staging roll-to-roll and/or batch mode systems.

The transparent conductive layer 309 may be inorganic such as a transparent conductive oxide (TCO) such as but not limited to indium tin oxide (ITO), fluorinated indium tin oxide, zinc oxide (ZnO) or aluminum doped zinc oxide or related materials , which can be deposited by any of a variety of methods including but not limited to: sputtering, evaporation, CBD, electroplating, sol-gel based coating, spray coating, chemical vapor deposition (CVD), physical vapor deposition ( PVD), atomic layer deposition (ALD), etc. Alternatively, the transparent conductive layer may comprise a transparent conductive polymer layer such as doped PEDOT (poly-3,4-ethylenedioxythiophene), carbon nanotubes or related structures, or other transparent organic materials, alone or in combination. layer, which may be deposited by spin-coating, dip-coating, or spray-coating, etc., or by any of a variety of vapor deposition techniques. Optionally, it should be understood that intrinsic (non-conductive) i-ZnO can be used between CdS and Al doped ZnO. Optionally, an insulating layer may be included between layer 308 and transparent conductive layer 309 . Combinations of inorganic and organic materials can also be used to form hybrid transparent conductive layers. Thus, layer 309 may optionally be organic (polymer or hybrid polymer molecules) or hybrid (organic-inorganic). Examples of such transparent conductive layers are described, for example, in commonly assigned US Patent Application Publication 20040187917, which is incorporated herein by reference.

Those skilled in the art will be able to devise modifications within the scope of these teachings based on the above described embodiments. For example, note that in embodiments of the invention, portions of the IB-IIIA precursor layer (or certain sublayers of the precursor layer or other layers in the stack) may be deposited using techniques other than nanoflake-based inks. For example, precursor layers or constituent sublayers can be deposited using any of a number of alternative deposition techniques including, but not limited to, solution deposition of spherical nanopowder based inks, vapor deposition techniques such as ALD, evaporation, sputtering, CVD , PVD, electroplating and so on.

Referring now to Figure 6, a flow chart showing one embodiment of the method of the present invention will be described. Figure 6 shows that at step 350, nanoflakes 108 may be fabricated using one of the processes described herein. Optionally, there may be a washing step 351 to remove any undesired residues. Once the nanoflakes 108 are made, step 352 shows that an ink can be formulated with the nanoflakes and at least one other component such as, but not limited to, a carrier liquid. Optionally, it should be understood that some embodiments of the invention may combine steps 350 and 352 into one process step, as indicated by block 353 (shown in phantom), if the manufacturing steps result in a coatable formulation. As a non-limiting example, this would be the case if the dispersants and/or solvents used during forming could also be used to form a good coating. At step 354 , substrate 102 may be coated with ink to form precursor layer 106 . Optionally, there may be a step 355 of removing dispersants and/or other residues of the freshly applied layer 106 by methods such as, but not limited to, heating, washing, and the like. Optionally, step 355 may include a step of removing solvent after ink deposition by using a drying device such as, but not limited to, a drying tunnel/oven. Step 356 shows processing the precursor layer to form a dense film, which can then be further processed at step 358 to form an absorber layer. Optionally, it is understood that some embodiments of the invention may combine steps 356 and 358 into one process step if the dense film is the absorbing layer and no further processing of the film is required. Step 360 shows that an N-type junction may be formed on and/or in contact with the absorber layer. Step 362 shows that a transparent electrode can be formed over the N-type junction layer to produce a stack capable of functioning as a solar cell.

Referring now to FIG. 7 , it should additionally be appreciated that multiple devices 300 may be incorporated into a module 400 to form a solar module that includes various packaging, durability, and environmental protection features to enable installation of devices 300 in outdoor environments. In one embodiment, the module 400 may include a frame 402 that supports a substrate 404 on which the device 300 may be mounted. The module 400 simplifies the mounting process by allowing multiple devices 300 to be mounted at one time. Alternatively, flexible form factors are also available. It should also be understood that encapsulating devices and/or layers may serve to protect from the environment. As a non-limiting example, encapsulating the device and/or layer can block the ingress of moisture and/or oxygen and/or acid rain into the device, especially during prolonged environmental exposure.

Additional sources of chalcogen

It should be understood that the present invention using nanoflakes may also employ an additional source of chalcogen in a manner similar to that described in co-pending U.S. Patent Application 11/290,633 (Attorney Docket No. NSL-045), wherein the precursor material contains 1 ) chalcogenides such as but not limited to copper selenide, and/or indium selenide and/or gallium selenide and/or 2) sources of additional chalcogens, such as but not limited to, Se or S having a size of less than about 200 nm nanoparticles. In one non-limiting example, the chalcogenide and/or additional chalcogen can be in the form of nanoflakes and/or nanoflakes, while the additional source of chalcogen can be flakes and/or non-flakes. The chalcogenide nanoflakes may be one or more binary alloy chalcogenides such as but not limited to Group IB binary chalcogenide nanoparticles (e.g. Group IB non-oxide chalcogenides such as Cu- Se, CuS, or CuTe) and/or group IIIA chalcogenide nanoparticles (e.g., group IIIA non-oxide chalcogenides such as Ga(Se,S,Te), In(Se,S,Te) and Al( Se, S, Te)). In further embodiments, the nanoflakes may be non-chalcogenides such as, but not limited to, Group IB and/or IIIA materials such as CuIn, CuGa, and/or InGa. If the chalcogen melts at a relatively low temperature (eg, 220°C for Se, 120°C for S), the chalcogen is already in a liquid state and makes good contact with the nanoflakes. If the nanoflakes and chalcogen are then heated sufficiently (eg, at about 375° C.), the chalcogen reacts with the chalcogenide to form the desired IB-IIIA-chalcogenide material. Referring now to FIGS. 8A-8C , chalcogenide nanoflakes 502 and a source 504 of additional chalcogen, for example in the form of a powder containing chalcogen particles, may be supported on a substrate 501 . As a non-limiting example, the chalcogen particles may be micron and/or submicron sized non-oxychalcogen (eg Se, S or Te) particles, for example hundreds of nanometers or smaller down to microns in size. A mixture of chalcogenide nanoflakes 502 and chalcogen particles 504 is placed on a substrate 501 and heated to a temperature sufficient to melt the additional chalcogen particles 504 to form liquid chalcogen 506 as shown in FIG. 8B . The liquid chalcogen 506 and the chalcogenide 502 are heated to a temperature sufficient for the liquid chalcogen 506 to react with the chalcogenide 502 to form a dense group IB-IIIA-chalcogenide compound as shown in FIG. 1C Film 508. The dense film of the Group IB-IIIA-chalcogenide compound is then allowed to cool.

Although not limited to the following, the chalcogenide particles 502 may be obtained starting from a binary chalcogenide feed material, such as micron-sized particles or larger. Examples of commercially available chalcogenide materials are listed in Table 1 below.

Table I

chemical components chemical formula Typical purity% Aluminum selenide Al ₂ Se ₃ 99.5 Aluminum sulfide Al ₂ S ₃ 98 Aluminum sulfide Al ₂ S ₃ 99.9 aluminum telluride Al ₂ Te ₃ 99.5 copper selenide Cu-Se 99.5 copper selenide Cu ₂ Se 99.5 gallium selenide Ga ₂ Se ₃ 99.999 copper sulfide Cu ₂ S (can be Cu1.8-2S) 99.5 copper sulfide CuS 99.5 copper sulfide CuS 99.99 copper telluride CuTe (typically Cu _1.4 Te) 99.5 copper telluride Cu ₂ Te 99.5 gallium sulfide Ga ₂ S ₃ 99.95 gallium sulfide GaS 99.95 gallium telluride GaTe 99.999 gallium telluride Ga ₂ Te ₃ 99.999 indium selenide In ₂ Se ₃ 99.999 indium selenide In ₂ Se ₃ 99.99% indium selenide In ₂ Se ₃ 99.9 indium selenide In ₂ Se ₃ 99.9 indium sulfide InS 99.999 indium sulfide In ₂ S ₃ 99.99 indium telluride In ₂ Te ₃ 99.999 indium telluride In ₂ Te ₃ 99.999

Examples of chalcogen powders and other commercially available feeds are listed in Table II below.

Table II

chemical components chemical formula Typical purity % selenium metal Se 99.99 selenium metal Se 99.6 selenium metal Se 99.6 selenium metal Se 99.999 selenium metal Se 99.999 sulfur S 99.999 tellurium metal Te 99.95 tellurium metal Te 99.5 tellurium metal Te 99.5 tellurium metal Te 99.9999 tellurium metal Te 99.99 tellurium metal Te 99.999 tellurium metal Te 99.999 tellurium metal Te 99.95 tellurium metal Te 99.5

Printing additional layers of chalcogen source

Referring now to Figures 9A-9E, another embodiment of the present invention using nanoflakes will be described. Figure 9A shows a substrate 602 with a contact layer 604 on which a nanoflake precursor layer 606 is formed. The additional source of chalcogen may be provided on the nanoflake precursor layer 606 as a discrete layer 608 containing the additional source of chalcogen such as, but not limited to, elemental chalcogen particles 607 . For example, and without loss of generality, the chalcogen particles may be particles of selenium, sulfur or tellurium. As shown in FIG. 9B, heat 609 is applied to the nanoflake precursor layer 606 and the layer 608 containing chalcogen particles to heat them sufficiently to melt the chalcogen particles 607 and separate the chalcogen particles 607 from the precursor layer 606. The temperature at which the elements in the reaction react. It should be understood that the nanoflakes may be made from a variety of materials including, but not limited to, Group IB elements, Group IIIA elements, and/or Group VIA elements. The reaction of the chalcogen particles 607 with the elements of the precursor layer 606 forms a compound film 610 of an IB-IIIA chalcogenide compound as shown in FIG. 9C . Preferably, the IB-IIIA-chalcogenide compound has the form CuIn _1-x Ga _x Se _2(1-y) S _2y , where 0≤x≤1 and 0≤y≤1. It should be understood that in some embodiments, the precursor layer 106 may be sintered prior to the application of the layer 108 with the additional chalcogen source. In other embodiments, precursor layer 106 is not preheated but layers 106 and 108 are heated together.

In one embodiment of the invention, precursor layer 606 may be about 4.0 to about 0.5 μm thick. Layer 608 containing chalcogen particles 607 may have a thickness of about 4.0 μm to about 0.5 μm. The chalcogen particles 607 in layer 608 may range in size from about 1 nm to about 25 μm, with a preferred size ranging from about 25 nm to about 300 nm. Note that the chalcogen particles 607 may initially be larger than the final thickness of the IB-IIIA-VIA compound film 610 . Chalcogen particles 607 may be mixed with solvents, carriers, dispersants, etc. to prepare an ink or paste suitable for wet deposition on precursor layer 606 to form layer 608 . Alternatively, chalcogen particles 607 may be prepared for dry deposition on the substrate to form layer 608 . Note also that the heating of the layer 608 containing the chalcogen particles 607 may be performed by, for example, the RTA process described above.

Chalcogen particles 607 (eg, Se or S) can be formed in a number of different ways. For example, Se or S particles can be formed starting from a commercially available fine-mesh powder (eg, 200 mesh/75 μm) and ball milling the powder to the desired size. A typical ball milling process may use a ceramic grinding jar filled with ground ceramic balls in a liquid medium and a feed material which may be in powder form. When the tank is rotated or shaken, the balls vibrate in the liquid medium and grind the powder to reduce the particle size of the feed material. Optionally, the process may include dry (pre)grinding larger pieces of material such as but not limited to Se. Dry grinding can use 2-6mm and smaller pieces, but will also be able to handle larger pieces. Note that this applies to all comminutions where the process may start with a larger feed material, dry mill, followed by wet milling (such as but not limited to ball milling). The grinders themselves can range from small media grinders to horizontal rotary ceramic jars.

Referring now to FIG. 9D , it should additionally be understood that in some embodiments, a layer 608 of chalcogen particles may be formed below the precursor layer 606 . This location of layer 608 still allows the chalcogen particles to provide sufficient excess chalcogen to precursor layer 606 to fully react with the group IB and group IIIA elements in layer 606 . Additionally, such a location of layer 608 below layer 606 may be beneficial in creating greater mixing between the elements since the chalcogen elements liberated in layer 608 may rise through layer 606 . The thickness of layer 608 may be from about 4.0 μm to about 0.5 μm. In other embodiments, the thickness of layer 608 may be from about 500 nm to about 50 nm. In one non-limiting example, a single Se layer of about 100 nm or larger would be sufficient. Coating of chalcogens may include (alone or in combination) the use of powder coating, Se evaporation or other Se deposition methods such as but not limited to chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD ), electroplating, and/or similar or related methods. Other types of material deposition techniques can be used to obtain Se layers with a thickness of less than 0.5 μm or less than 1.0 μm. It should also be understood that in some embodiments, the additional source of chalcogen is not limited to only elemental chalcogen, but may be alloys and/or solutions of one or more chalcogens in some embodiments.

Optionally, it should be understood that additional sources of chalcogen may be mixed with and/or deposited in the precursor layer rather than as a separate layer. In one embodiment of the invention, oxygen-free or substantially oxygen-free particles of chalcogen may be used. If chalcogens are used with nanoflakes and/or sheet-like precursor materials, densification may not end the problem of higher densities achieved by using planar particles, so there is no reason to rule out discrete layers as opposed to discrete layers in the precursor layer Se and/or other chalcogen sources are internally printed. This may involve not having to heat the precursor layer to a previous processing temperature. In some embodiments, this may involve forming the film without heating above about 400°C. In some embodiments, this may involve not necessarily heating above about 300°C.

In additional embodiments of the invention, multiple layers of material may be printed and reacted with chalcogen before the next layer is deposited. A non-limiting example would be to deposit a Cu-In-Ga layer, anneal it, then deposit a Se layer, then treat with RTA, then deposit another Ga-rich precursor layer, then deposit Se again, and finally the first Secondary RTA treatment. More generally, this can involve forming a precursor layer (with or without heat), then applying an additional chalcogen source layer (with or without heat), followed by forming another layer of more precursor (with or without heat). heated), followed by another layer of additional chalcogen source (then heated or not), and repeated as many times as desired to either step the composition or nucleate the desired crystal size. In one non-limiting example, this can be used to grade the gallium concentration. In another embodiment, this can be used to gradually vary the copper concentration. In another embodiment, this can be used to gradually vary the indium concentration. In another embodiment, this can be used to gradually vary the selenium concentration. In another embodiment, this can be used to vary the selenium concentration gradually. Another reason is to grow the copper-rich film first to obtain large crystals and then start adding copper-poor layers to restore stoichiometry. Of course such embodiments can be combined to allow chalcogen deposition in the precursor layer for either of the steps involved.

Referring now to FIG. 9E , an alternative approach to exploit the low melting point of chalcogens such as but not limited to Se and S is to form core-shell nanoflakes where the core is the nanoflake 607 and the shell 620 is the chalcogen coating. The chalcogens 620 melt and react rapidly with the material of the core nanoflakes 607 . As a non-limiting example, the core may be a mixture of elemental particles of Group IB (e.g., Cu) and/or Group IIIA (e.g., Ga and In), which may be obtained by ball milling elemental feedstock to the desired size . Examples of useful elemental feed materials are listed in Table III below. The core may also be a chalcogenide core or other materials described herein.

Table III

Chalcogen-rich chalcogenide particles

Referring now to Figures 10A-10C, it should be understood that another embodiment of the present invention includes wherein the nanoflake particles may be chalcogen-rich chalcogenide particles (whether they are Group IB chalcogenides, Group IIIA chalcogenides) or other chalcogenides) embodiments. In these embodiments, it may not be necessary to use a separate source of chalcogen due to the excess chalcogen contained within the chalcogenide particles themselves. In one non-limiting example of a Group IB chalcogenide, the chalcogenide may be copper selenide, wherein the material comprises Cu _x Se _y , where x<y. So this is a chalcogen-rich chalcogenide, which provides an excess of selenium when processing the particles of the precursor material.

The purpose of providing an additional source of chalcogen is to create a liquid first to expand the contact area between the initial solid particles (flakes) and the liquid. Second, when working with chalcogen-depleted membranes, this additional source adds chalcogen to achieve the stoichiometrically desired amount of chalcogen. Third, chalcogens such as Se are volatile and inevitably lose some during processing. Therefore, the main purpose is to generate liquid. There are also various other routes to increase the amount of liquid when processing the precursor layer. These routes include but are not limited to: 1) Cu-Se that is more Se-rich than Cu _2-x Se (>377 °C, more liquid above >523 °C); 2) equal to Cu ₂ Se or when additional Se Cu-Se (>220℃) which is more Se-rich than it; 3) composition In ₄ Se ₃ , or In-Se between In ₄ Se ₃ and In ₁ Se ₁ (>550℃); 4) and In-Se that is equal to In ₄ Se ₃ or richer than it when additional Se is added (>220°C); 5) In-Se between In and In ₄ Se ₃ (>156°C due to the generation of In preferably in an oxygen-free environment); 6) Ga emulsions (>29°C, preferably without oxygen); and rarely (but possible) Ga-Se. Even when cooperating with Se vapor, it can still be very advantageous to generate additional liquid in the precursor layer itself using one of the above methods or by an equivalent method.

Referring now to FIG. 1OA, it should be understood that inks may contain various types of particles. In FIG. 1OA, particle 704 is a first type of particle and particle 706 is a second type of particle. In one non-limiting example, an ink may have multiple types of particles where only one type of particle is chalcogenide and also chalcogen-rich. In further embodiments, the ink may have particles wherein at least two types of chalcogenides in the ink are chalcogen-rich. As a non-limiting example, an ink may have _Cux Se _y (where x<y) and In _a Se _b (where a<b). In further embodiments, the ink may have particles 704, 706, and 708 (shown in phantom) with at least three types of chalcogenide particles in the ink. As non-limiting examples, the chalcogen-rich chalcogenide particles may be Cu-Se, In-Se, and/or Ga-Se. All three can be rich in chalcogen. Various combinations are possible to obtain the desired excess of chalcogen. If the ink has three types of particles, it should be understood that not all particles need be chalcogenide or chalcogen-rich. Even in inks with only one type of particle, such as Cu-Se, there can be chalcogen-rich particles such as Cu _x Se _y where x<y and particles that are not rich in chalcogen such as where x>y Mixture of Cu _x Se _y . As a non-limiting example, the mixture may contain copper selenide particles, which may have the following composition: Cu ₁ Se ₁ and Cu ₁ Se ₂ .

Still referring to FIG. 10A , it should additionally be understood that even in the case of chalcogen-rich particles, an additional layer 710 (shown in phantom) may additionally be printed or coated onto the ink to provide additional chalcogen element source. The material in this layer may be pure chalcogen, a chalcogenide, or a chalcogen-containing compound. As shown in Figure 10C, an additional layer 710 (shown in phantom) can also be printed onto the resulting film if further treatment with chalcogen is desired.

Referring now to FIG. 10B, heat may be applied to particles 704 and 706 to begin transforming them. Due to the different melting temperatures of the materials in the particles, some materials may begin to assume liquid form sooner than others. In the present invention it is particularly advantageous if the particles in liquid form also release excess chalcogen as liquid 712 which may surround other materials and/or elements in the layer such as 714 and 716 . FIG. 10B includes a view with an enlarged view of liquid 712 and materials and/or elements 714 and 716 .

The amount of additional chalcogen provided by all particles collectively is at a level equal to or above the stoichiometric level present in the compound after treatment. In one embodiment of the invention, the excess of chalcogen comprises an amount greater than the sum of: 1) the stoichiometric amount present in the final IB-IIIA chalcogenide film and 2) formed with the desired The minimum amount of chalcogen necessary due to loss during processing of the stoichiometric final IB-IIIA-chalcogenide. Although not limited to the following, the excess chalcogen may act as a flux that will liquefy at processing temperatures and promote greater atomic mixing of the particles provided by the liquefied excess chalcogen. The liquefied excess chalcogen also ensures that enough chalcogen is present to react with the group IB and IIIA elements. Excess chalcogen helps to "digest" or "dissolve" the particles or flakes. Excess chalcogen will strip out of the layer before the desired film is fully formed.

Referring now to FIG. 10C , application of heat may continue until Group IB-IIIA chalcogenide film 720 is formed. Another layer 722 (shown in phantom) can be applied for further processing of the film 720 if specific features are desired. As a non-limiting example, an additional source of gallium can be added to the top layer and further reacted with film 720 . Other sources can provide additional selenium to improve selenization on the top surface of membrane 720 .

It should be understood that various chalcogenide particles may also be combined with non-chalcogenide particles to achieve the desired oversupply of chalcogen in the precursor layer. The following table (Table IV) provides a non-limiting array of some possible combinations between chalcogenide particles listed in rows and non-chalcogenide particles listed in columns.

Table IV

In another embodiment, the present invention may combine various chalcogenide particles with other chalcogenide particles. The following table (Table V) provides a non-limiting array of some possible combinations between the chalcogenide particles listed in the rows and the chalcogenide particles listed in the columns.

Table V

nucleation layer

Referring now to Figures 11A-11C, another embodiment of the invention using flakes such as but not limited to nanoflakes will be described. This embodiment provides a method for film growth by depositing a thin layer of a Group IB-IIIA chalcogenide on a substrate to serve as a precursor layer formed over the thin layer of a Group IB-IIIA chalcogenide nucleation plane to improve crystal growth on the substrate. The Group IB-IIIA chalcogenide nucleation layer may be deposited, coated, or formed prior to forming the precursor layer. The nucleation layer can be formed using vacuum or non-vacuum techniques. The precursor layer formed over the nucleation layer can be formed by a variety of techniques including, but not limited to, using an ink containing a plurality of nanoflakes as described herein.

FIG. 11A shows that an absorber layer may be formed on a substrate 812, as shown in FIG. 11A. The surface of the substrate 812 may be coated with a contact layer 814 to facilitate electrical contact between the substrate 812 and an absorber layer formed thereon. For example, an aluminum substrate 812 may be coated with a molybdenum contact layer 814 . As discussed herein, forming or arranging a material or layer of material on substrate 812 includes arranging or forming such a material or layer on contact layer 814 if a contact layer is used.

As shown in FIG. 11B , a nucleation layer 816 is formed on a substrate 812 . The nucleation layer may comprise a Group IB-IIIA chalcogenide and may be deposited, coated or formed prior to forming the precursor layer. As a non-limiting example, this could be a CIGS layer, a Ga-Se layer, any other high melting point IB-IIIA chalcogenide layer, or even a thin layer of gallium.

Referring now to FIG. 11C, once the nucleation layer is formed, a precursor layer 818 may be formed over the nucleation layer. In some embodiments, the nucleation layer and precursor layer can be formed simultaneously. Precursor layer 818 may contain one or more Group IB elements and one or more Group IIIA elements. Preferably, the one or more Group IB elements include copper. The one or more group IIIA elements may include indium and/or gallium. The precursor layer may be formed from a film, for example by any of the techniques described above.

Still referring to FIG. 11C , it should additionally be understood that the structure of alternating nucleation and precursor layers may be repeated in the stack. Figure 11C shows that optionally another nucleation layer 820 (shown in phantom) can be formed on the precursor layer 818 to continue the structure of alternating nucleation and precursor layers. Another precursor layer 822 can then be formed on the nucleation layer 820 to continue the stack, which can be repeated as desired. Although not limited to the following, there may be 2, 3, 4, 5, 6, 7, 8, 9, 10 or more sets of alternating nucleation and precursor layers to establish the desired properties. Each group may have a different material or amount of material than the other groups in the stack. Alternating layers may be solution deposited, vacuum deposited, etc. The different layers can be deposited by different techniques. In one embodiment, this may involve solution deposition (or vacuum deposition) of a precursor layer (optionally with a desired ratio of Cu to In to Ga), followed by addition of the chalcogen (solution-based, vacuum-based, or otherwise such as but not limited to steam or _H2Se , etc.), optionally thermally treating the stack (during or after introduction of the chalcogen source), followed by deposition of additional precursor layers (optionally with desired Cu and In and Ga ratio), and a final heat treatment of the final stack (during or after the introduction of additional chalcogen). The goal is to produce planar nucleation so that there are no holes or regions where the substrate is not covered by subsequent film formation and/or crystal growth. Optionally, the chalcogen source can also be introduced before adding the first Cu+In+Ga containing precursor layer. It should also be understood that in some other embodiments, layer 820 may be a chalcogen-containing layer, such as but not limited to a selenium layer, and be heated with each precursor layer (or eventually after all precursor layers are formed).

Nucleation layer by means of thermal gradient

Referring now to FIGS. 12A-12B , it should be understood that the nucleation layer used with the nanoflake-based precursor material can also be formed by creating a thermal gradient in the precursor layer 850 . As a non-limiting example, nucleation layer 852 may be formed from the upper portion of the precursor layer, or optionally by forming nucleation layer 854 from the lower portion of the precursor layer. In one embodiment of the invention, the nucleation layer can be considered as the layer in which the initial IB-IIIA-VIA compound crystal growth is preferential to crystal growth at another location in the precursor layer and/or precursor layer stack . Nucleation layer 852 or 854 is formed by creating a thermal gradient in the precursor layer such that a portion of the layer reaches a temperature sufficient to initiate crystal growth. The nucleation layer may be in the form of a nucleation plane having a substantially planar structure to promote more uniform crystal growth across the substrate while minimizing the formation of pinholes and other irregularities.

As can be seen in Figure 12A, in one embodiment of the invention, the thermal gradient used to form the nucleation layer 852 can be created by using a laser 856 to raise only the upper portion of the precursor layer 850 to the processing temperature. Laser 856 may be pulsed or otherwise controlled so as not to heat the entire thickness of the precursor layer to processing temperatures. The backside 858 of the precursor layer and the substrate 860 supporting it may be in contact with a chill roll 862, a cooled flat contact surface, or a cooling drum that provides an external source of cooling to prevent the lower portion of the layer from reaching processing temperatures. A cooling gas 864 may additionally be provided on one side of the substrate and adjacent portions of the precursor layer to reduce the temperature of the precursor layer below the processing temperature at which nucleation of the final IB-IIIA chalcogenide compound begins. It should be understood that other means may be used to heat the upper portion of the precursor layer, such as, but not limited to, pulsed heat treatment, plasma heating, or heating via IR lamps.

As can be seen in Figure 12B, in another embodiment of the invention, a nucleation layer 854 may be formed in the lower portion of the precursor layer 850 using techniques similar to those described above. Since the substrate 860, which may optionally be used in the present invention, is thermally conductive, heating of the underside of the substrate will also result in heating of the lower portion of the precursor layer. A nucleation plane would then form along the bottom of the lower part. The upper portion of the precursor layer can be cooled by various techniques such as, but not limited to, cooling gas, chilled rolls, or other cooling devices.

After formation of the nucleation layer, which preferably consists of a material identical to or close to the final IB-IIIA chalcogenide compound, the entire precursor layer, or optionally only the precursor layer, remains more or less untreated Those parts will be heated to the processing temperature so that the remaining material will start to convert to the final IB-IIIA chalcogenide compound in contact with the nucleation layer. The nucleation layer guides crystal formation and minimizes the possibility of forming pinholes or having other irregular substrate regions due to non-uniform crystal growth.

It should be understood that in addition to the above, the temperature may also be varied during different periods of precursor layer processing. As a non-limiting example, heating may be at a first temperature for an initial treatment period and to an additional temperature for subsequent treatment periods. Optionally, the method may include intentionally producing one or more temperature drops such that, as a non-limiting example, the method comprises heating, cooling, heating followed by cooling. In one embodiment of the invention, this may involve reducing the temperature by about 50°C to about 200°C from the temperature in the initial period of time.

nucleation layer via chemical gradient

Referring now to Figures 13A-13F, another method of forming a nucleation layer using the nanoflake precursor material of the present invention will be described in more detail. In this embodiment of the invention, the composition of the layers of precursor material may be chosen such that crystal formation begins sooner in some layers than in others. It should be understood that different methods of forming a nucleation layer may be combined to facilitate layer formation. As a non-limiting example, thermal gradient and chemical gradient methods can be combined to promote nucleation layer formation. It is conceivable that single or multiple combinations of thermal gradients, chemical gradients and/or thin film nucleation layers could be used in combination.

Referring now to FIG. 13A, an absorber layer may be formed on a substrate 912, as shown in FIG. 13A. One surface of the substrate 912 may be coated with a contact layer 914 to facilitate electrical contact between the substrate 912 and an absorber layer formed thereon. For example, an aluminum substrate 912 may be coated with a molybdenum contact layer 914 . As discussed herein, forming or arranging a material or layer of material on substrate 912 includes arranging or forming such a material or layer on contact layer 914 if a contact layer is used. Optionally, it is additionally understood that layer 915 may also be formed over contact layer 914 and/or directly on substrate 912 . This layer can be solution coated, evaporated and/or deposited using vacuum based techniques. Although not limited to the following, layer 915 may have a thickness that is less than precursor layer 916 . In one non-limiting example, the layer may be about 1 to about 100 nm thick. Layer 915 may be composed of a variety of materials including but not limited to at least one of the following: Group IB elements, Group IIIA elements, Group VIA elements, Group IA elements (new style: Group 1), binary and/or Multicomponent alloys, solid solutions of any of the foregoing elements, copper, indium, gallium, selenium, copper indium, copper gallium, indium gallium, sodium, sodium compounds, sodium fluoride, sodium indium sulfide, copper selenide, copper sulfide, indium selenide, Indium sulfide, gallium selenide, gallium sulfide, copper indium selenide, copper indium sulfide, copper gallium selenide, copper gallium sulfide, indium gallium selenide, indium gallium sulfide, copper gallium indium selenide, and/or copper gallium indium sulfide.

As shown in Figure 13B, a precursor layer 916 is formed on the substrate. Precursor layer 916 contains one or more Group IB elements and one or more Group IIIA elements. Preferably, the one or more Group IB elements include copper. The one or more group IIIA elements may include indium and/or gallium. The precursor layer can be formed using any of the techniques described above. In one embodiment, the precursor layer is free of oxygen other than those oxygens that are unavoidably present as impurities or incidentally present in film components other than the nanoflakes themselves. While non-vacuum methods are preferred for forming precursor layer 916, it should be understood that it may optionally be formed by other methods such as evaporation, sputtering, ALD, and the like. For example, precursor layer 916 may be an oxygen-free compound containing copper, indium, and gallium. In one embodiment, the non-vacuum system operates at a pressure above about 3.2 kPa (24 Torr). Optionally, it is additionally understood that layer 917 may also be formed over precursor layer 916 . It should be understood that the stack can have both layers 915 and 917, only one of them, or neither. Although not limited to the following, layer 917 may have a thickness that is less than precursor layer 916 . In one non-limiting example, the layer may be about 1 to about 100 nm thick. Layer 917 may be composed of a variety of materials including, but not limited to, at least one of the following: Group IB elements, Group IIIA elements, Group VIA elements, Group IA elements (new style: Group 1), binary and/or Multicomponent alloys, solid solutions of any of the foregoing elements, copper, indium, gallium, selenium, copper indium, copper gallium, indium gallium, sodium, sodium compounds, sodium fluoride, sodium indium sulfide, copper selenide, copper sulfide, indium selenide, Indium sulfide, gallium selenide, gallium sulfide, copper indium selenide, copper indium sulfide, copper gallium selenide, copper gallium sulfide, indium gallium selenide, indium gallium sulfide, copper gallium indium selenide, and/or copper gallium indium sulfide.

Referring now to FIG. 13C, a second precursor layer 918 of a second precursor material may optionally be applied over the precursor layer. The second precursor material may have an overall composition that is richer in chalcogen than the first precursor material in precursor layer 916 . As a non-limiting example, by creating two coatings (preferably with only one heating process in the stack after deposition of the two precursor coatings), wherein the first coating contains relatively Selenide with less selenium (but still enough), which allows a gradient of available Se to be produced. For example, the precursor to the first coating may contain Cu _x Se _y , where x is greater than in the second coating. Or it can contain a mixture of Cu _x Se _y particles in which there is a greater concentration (by weight) of x-large selenide particles. In the current embodiment, each layer preferably has a target stoichiometry since the C/I/G ratio remains the same for each precursor layer. Also, while the second precursor layer 918 is preferably formed using a non-vacuum method, it should be understood that it can optionally be formed by other methods such as evaporation, sputtering, ALD, and the like.

The rationale for using a chalcogen step change, or more generally a bottom-up step change in melting temperature, is to deeply control the relative rates of crystallization and to have crystallization occur more quickly, for example, at the bottom of the precursor layer stack than at the top of the precursor layer stack. . An additional rationale is that the pervasive grain structure in a generally efficient solution-deposited CIGS cell with large grains on top of the photoactive film and small grains on the backside still has appreciable energy conversion efficiencies. The membrane is the part of the photoactive membrane that is primarily photoactive. It should be understood that in alternative embodiments, multiples of a number of different precursor material layers may be used to establish the desired chalcogen gradient, or more generally at the melting temperature and/or subsequent solidification into the final IB-IIIA-sulfur Desired gradients in the chalcogenide compound, or more generally due to the creation of chemical (compositional) and/or thermal gradients in the resulting film, upon melting and/or subsequent solidification to the final IB-IIIA-chalcogenide The desired gradient in the compound. As _a non-limiting example, the present invention may use particles and/or microflakes and/or nanoflakes with different melting points, such as but not limited to lower melting point materials compared to higher melting point materials _In2Se3 , _Cu2Se Se, In ₄ Se ₃ , Ga, and Cu ₁ Se ₁ .

Referring now to FIG. 13C , heat 920 is applied to sinter the first precursor layer 916 and the second precursor layer 918 into a Group IB-IIIA compound film 922 . Heat 920 may be supplied, for example, in a rapid thermal annealing process as described above. Specifically, substrate 912 and precursor layers 916 and/or 918 may be heated from ambient temperature to a plateau temperature range of about 200°C to about 600°C. The temperature is maintained in this plateau range for a period of about a fraction of a second to about 60 minutes, followed by cooling down.

Optionally, as shown in Figure 13D, it is understood that a layer 924 containing elemental chalcogen particles may be applied to the precursor layers 916 and/or 918 prior to heating. Of course, layer 924 is formed on precursor layer 916 if the material stack does not include a second precursor layer. For example, and without loss of generality, the chalcogen particles may be particles of selenium, sulfur or tellurium. These particles can be produced as described above. The chalcogen particle size in layer 924 may be from about 1 nm to about 25 μm, preferably from 50 nm to 500 nm. Chalcogen particles may be mixed with solvents, carriers, dispersants, etc. to prepare an ink or paste suitable for wet deposition on precursor layers 916 and/or 918 to form layer 924 . Alternatively, chalcogen particles may be prepared for dry deposition on the substrate to form layer 924 .

Optionally, as shown in FIG. 13E , a layer 926 containing an additional source of chalcogen and/or an atmosphere containing a source of chalcogen may optionally be applied to layer 922, especially if layer 924 is not applied in FIG. 13D if. Heat 928 may optionally be applied to layer 922 and layer 926 and/or the atmosphere containing the chalcogen source to heat them sufficiently to melt the chalcogen source and to combine the chalcogen source with the Group IB elements in precursor layer 922 and The temperature at which group IIIA elements react. Heat 928 may be applied during a rapid thermal annealing process such as described above. The reaction of the chalcogen source with the Group IB and IIIA elements forms a compound film 930 of Group IB-IIIA chalcogenide compounds as shown in FIG. 13F . Preferably, the Group IB-IIIA chalcogenide compound has the formula Cu _z In _1-x Ga _x Se _2(1-y) S _2y , where 0≤x≤1, 0≤y≤1 and 0.5≤y≤ 1.5.

Still referring to FIGS. 13A-13F , it should be understood that sodium can also be used with the precursor material to improve the properties of the resulting film. In a first approach, one or more layers of sodium-containing material may be formed above and/or below precursor layer 916 as discussed with respect to FIGS. 13A and 13B . The formation may be by solution coating and/or other techniques such as but not limited to sputtering, evaporation, CBD, electroplating, sol-gel based coating, spray coating, chemical vapor deposition (CVD), physical vapor deposition (PVD) , atomic layer deposition (ALD), etc.

Optionally, in the second approach, sodium can also be introduced into the stack by doping the nanoflakes and/or particles in the precursor layer 916 . As a non-limiting example, the nanoflakes and/or other particles in the precursor layer 916 may be a sodium-containing material such as, but not limited to, Cu-Na, In-Na, Ga-Na, Cu-In-Na, Cu -Ga-Na, In-Ga-Na, Na-Se, Cu-Se-Na, In-Se-Na, Ga-Se-Na, Cu-In-Se-Na, Cu-Ga-Se-Na, In -Ga-Se-Na, Cu-In-Ga-Se-Na, Na-S, Cu-S-Na, In-S-Na, Ga-S-Na, Cu-In-S-Na, Cu-Ga - S-Na, In-Ga-S-Na and/or Cu-In-Ga-S-Na. In one embodiment of the invention, the sodium content of the nanoflakes and/or other particles may be less than about 1 atomic % or less. In another embodiment, the sodium content may be about 0.5 atomic percent or less. In another embodiment, the sodium content may be about 0.1 atomic percent or less. It should be understood that the doped particles and/or flakes can be made by a variety of methods including milling the feed material with sodium-containing material and/or elemental sodium.

Optionally, in the third method, sodium can be incorporated into the ink itself, regardless of the type of particles, nanoparticles, microflakes and/or nanoflakes dispersed in the ink. As a non-limiting example, the ink may include nanoflakes (Na-doped or undoped) and a sodium compound with an organic counterion (such as but not limited to sodium acetate) and/or a sodium compound with an inorganic counterion (such as but not limited to sodium sulfide). It should be understood that the sodium compound added to the ink (as a separate compound) may be present as particles (eg nanoparticles) or dissolved. Sodium can be in "aggregate" form of sodium compounds (eg dispersed particles) as well as in "molecularly dissolved" form.

None of the above three methods are mutually exclusive and may be applied alone or in any single or multiple combination to provide the desired amount of sodium to the stack containing the precursor material. In addition, sodium and/or sodium-containing compounds may also be added to the substrate (eg, to the molybdenum target). Additionally, if multiple precursor layers (using the same or different materials) are used, a sodium-containing layer may be formed between one or more precursor layers. It should also be understood that the source of sodium is not limited to those previously listed materials. As a non-limiting example, basically, any deprotonated alcohol in which the protons are replaced by sodium, any deprotonated organic and inorganic acids, sodium salts of (deprotonated) acids, sodium hydroxide, sodium acetate , and the sodium salts of the following acids: butyric acid, caproic acid, caprylic acid, capric acid, dodecanoic acid, myristic acid, hexadecanoic acid, 9-hexadecenoic acid, octadecanoic acid, 9-decanoic acid Octadecenoic acid, 11-octadecenoic acid, 9,12-octadecadienoic acid, 9,12,15-octadecatrienoic acid and/or 6,9,12-octadecatriene acid.

Optionally, as seen in Figure 13F, it is additionally understood that sodium and/or sodium compounds may be added to the treated chalcogenide film after the precursor layer has been sintered or otherwise processed. This embodiment of the invention thus modifies the membrane after CIGS formation. In the presence of sodium, the carrier trap levels associated with the grain boundaries are lowered, allowing improved electronic properties in the film. CIGS films can be treated by depositing various sodium-containing materials such as those listed above as layer 932 onto the treated film followed by annealing.

In addition, the sodium material may be combined with other elements capable of providing a bandgap broadening effect. Two elements that can achieve this effect include gallium and sulfur. The use of one or more of these elements in addition to sodium can further improve the properties of the absorbent layer. The use of sodium compounds such as but not limited to _Na2S , _NaInS2 , etc. provides both Na and S to the membrane and can be advanced with annealing such as but not limited to an RTA step to provide a different bandgap than that of the unmodified CIGS layer or membrane. layer.

Referring now to FIG. 14, embodiments of the present invention may be compatible with roll-to-roll manufacturing. Specifically, in roll-to-roll manufacturing system 1000 , a flexible substrate 1001 , such as aluminum foil, travels from a supply roll 1002 to a take-up roll 1004 . Between the supply roll and the take-up roll, the substrate 1001 passes through several coaters 1006A, 1006B, 1006C, such as microgravure rollers, and heating means 1008A, 1008B, 1008C. Each coater deposits a different layer or sublayer of the active layer of the photovoltaic device, such as those described above. The heating means are used to anneal the different sublayers. In the example depicted in FIG. 14 , coaters 1006A and 1006B can coat different sub-layers of a precursor layer (eg, precursor layer 106 , precursor layer 916 , or precursor layer 918 ). Heating devices 1008A and 1008B may anneal each sublayer before depositing the next sublayer. Alternatively, both sublayers can be annealed simultaneously. Applicator 1006C may apply a layer of material containing chalcogen particles as described above. The heating device 1008C heats the chalcogen layer and the aforementioned precursor layer. Note that it is also possible to deposit a precursor layer (or sub-layer) followed by a chalcogen-containing layer and then heat all three layers together to form an IB-IIIA-chalcogenide compound film for the photovoltaic absorber layer.

The total number of printing steps can be varied to construct absorbing layers with different orders of bandgaps. For example, additional layers (4 layers, 5 layers, 6 layers, etc.) can be printed (and optionally annealed between printing steps) to create a more finely graded bandgap within the absorbing layer. Alternatively, fewer films can be printed (eg double-layer printing) to produce a less subdivided bandgap. For any of the above embodiments, it is also possible to have different amounts of chalcogen in each layer to alter crystal growth which may be affected by the amount of chalcogen present.

Additionally, it should be understood that many combinations of flake and non-flake particles in different layers may be used in accordance with the present invention. As a non-limiting example, the combination may include but is not limited to the following:

Table VI

Although not limited to the following, these chalcogenide and non-chalcogenide materials may be selected from any of those listed in Tables IV and V.

reduced melting temperature

In another embodiment of the invention, the ratios of elements within the particles or flakes can be altered to produce more desirable material properties. In one non-limiting example, this embodiment includes using a desired stoichiometric ratio of elements so that the particles used in the ink have a reduced melting temperature. As a non-limiting example, for Group IB chalcogenides, the amount of Group IB element and the amount of chalcogen are controlled to shift the resulting material to a portion of the phase diagram with a reduced melting temperature. Thus for _CuxSey , the values of x and y are chosen to produce a material with a reduced melting temperature, as determined with reference to the phase diagram of _the material. Phase diagrams for the following materials can be found in ASM Handbook, Volume 3 Alloy Phase Diagrams (1992), ASM International, incorporated herein by reference in its entirety for all purposes. Some specific examples can be found on pages 2-168, 2-170, 2-176, 2-178, 2-208, 2-214, 2-257 and/or 2-259.

As a non-limiting example, copper selenide has various melting temperatures depending on the ratio of copper to selenium in the material. Everything composed of solid solution Cu _2-x Se richer in Se (that is, pure Cu on the left and pure Se on the right side of the binary phase diagram) would yield liquid selenium. Depending on the composition, melting temperatures can be as low as 221°C (more Se-rich than Cu ₁ Se ₂ ), as low as 332°C (for compositions between Cu ₁ Se ₁ and Cu ₁ Se ₂ ), and as low as 377°C (for Cu _{2 -x} Se and Cu ₁ Se ₁ composition). At 523 °C and above, the material is all liquid for Cu-Se, which is more Se-rich than the eutectic (∼57.9 wt% Se). For compositions between solid solution Cu _2-x Se and eutectic (˜57.9 wt% Se), solid solid solution Cu _2-x Se and liquid eutectic (˜57.9 wt% Se) will result at 523 °C and just above.

Another non-limiting example includes gallium selenide, which can have various melting temperatures depending on the ratio of gallium to selenium in the material. _Everything composed primarily of pure Se that is more Se-rich than _Ga2Se3 (that is, pure Ga on the left and pure Se on the right side of the binary phase diagram) will produce a liquid above 220°C. Ga-Se richer in Se than Ga ₁ Se ₁ can be prepared by preparing e.g. the compound Ga ₂ Se ₃ (or any compound richer in Se than Ga ₁ Se ₁ ), but only when other selenium sources are added, as in Ga ₁ Cooperation between Se ₁ and Ga ₂ Se ₃ or with their same composition, which is an additional source of selenium or Se-rich Cu-Se, will liquefy Ga-Se at processing temperatures. Therefore, an additional source of Se can be provided to facilitate the production of liquids comprising gallium selenide.

Another non-limiting example includes indium selenide, which can have various melting temperatures depending on the ratio of indium to selenium in the material. Everything composed primarily of pure Se that is more Se-rich than _In2Se3 (that is _, pure In on the left and pure Se on the right side of a binary phase diagram) will produce a liquid above 220°C. Making In-Se richer in Se than In ₁ Se ₁ would yield a liquid of In ₂ Se ₃ as well as In ₆ Se ₇ (or an overall composition between In ₁ Se ₁ and Se), but when treated at In ₁ Se ₁ and In ₂ Se ₃ or at the same composition as them, only by adding other Se sources, either additional Se sources or Se-enriched Cu-Se, the In-Se will liquefy at the processing temperature. Optionally for In-Se, there is another way to produce more liquid by going in the "other" direction and using a composition that is less Se rich (ie on the left side of the binary phase diagram). By using a material composition between pure In and In ₄ Se ₃ (or between In and In ₁ Se ₁ or In and In ₆ Se ₇ depending on temperature), it is possible to produce pure liquid In at 156 °C as well as at 520 °C ( Or at higher temperatures when a more Se-rich shift is performed from the eutectic point of ~24.0 wt% Se to In ₁ Se ₁ ) yields more liquid. Basically, for an overall composition less Se-rich than the In-Se eutectic (~24.0 wt% Se), all In-Se would become liquid at 520°C. Of course, for these types of Se-poor materials, one of the other particles (such as but not limited to Cu ₁ Se ₂ and/or Se) or another Se source will be required to increase the Se content.

Therefore, liquids can be generated at our processing temperature by: 1) adding an independent source of selenium, 2) using Cu-Se which is more Se-rich than Cu _2-x Se, 3) using Ga-emulsion (or In-Ga emulsion) or In (in an air-free environment), or 4) use In-Se that is less Se-rich than In ₁ Se ₁ , although this may also require an air-free environment. When copper selenide is used, the composition may be Cu _x Se _y , where x is from about 2 to about 1 and y is from about 1 to about 2. When indium selenide is used, the composition may be In _x Se _y , where x is from about 1 to about 6 and y is from about 0 to about 7. When gallium selenide is used, the composition may be Ga _x Se _y , where x is from about 1 to about 2 and y is from about 1 to about 3.

It will be appreciated that addition of a separate source of selenium will cause the composition to initially appear more Se-rich at the interface of the selenide particles and liquid selenium at the processing temperature.

Chalcogen Vapor Environment

Referring now to Figure 15A, another embodiment of the present invention will be described. In this embodiment used with nanoflake precursor materials, it is understood that the overpressure from the chalcogen vapor is used to provide a chalcogen atmosphere to improve film handling and crystal growth. FIG. 15A shows a chamber 1050 together with a substrate 1052 having a contact layer 1054 and a precursor layer 1056 . An additional chalcogen source 1058 is included within the chamber and brought to a temperature that produces chalcogen vapor represented by line 1060 . In one embodiment of the invention, the chalcogen vapor is provided such that the partial pressure of the chalcogen present in the atmosphere is greater than or equal to the vapor pressure at which the partial pressure of the chalcogen is maintained at the process temperature and process pressure to Minimizing the loss of chalcogen from the precursor layer and, if desired, providing the chalcogen vapor pressure required for the precursor layer with additional chalcogen. This partial pressure is determined based in part on the temperature at which chamber 1050 or precursor layer 1056 is located. It should also be understood that chalcogen vapor is used in chamber 1050 at non-vacuum pressures. In one embodiment, the pressure in the chamber is about atmospheric pressure. From the ideal gas law PV=nRT, it should be understood that temperature affects vapor pressure. In one embodiment, the chalcogen vapor may be provided by using a partially or fully enclosed chamber having a chalcogen source 1062 therein or connected to the chamber. In another embodiment using a more open chamber, the chalcogen atmosphere may be provided by supplying a source that produces chalcogen vapor. Chalcogen vapor can be used to help maintain chalcogen in the film or to provide chalcogen to convert the precursor layer. Thus, chalcogen vapor may or may not be used to provide excess chalcogen. In some embodiments, this may serve more to maintain the chalcogen present in the membrane than to provide more chalcogen into the membrane. Optionally, this can be used as chalcogen to be introduced into an otherwise chalcogen-free or selenium-free precursor layer. Exposure to chalcogen vapors can occur at atmospheric pressure. These conditions may apply to any of the embodiments described herein. Chalcogen can be brought into the chamber via the carrier gas. The carrier gas may be an inert gas such as nitrogen, argon, or the like. The chalcogen atmosphere system can be adapted for roll-to-roll systems.

Referring now to FIG. 15B , it is shown that the present invention may be adapted for use with a roll-to-roll system, wherein a substrate 1070 with precursor layers may be flexible and configured as rolls 1072 and 1074 . Chamber 1076 may be under vacuum or non-vacuum pressure. The chamber 1076 can be designed to include a differential valve design to minimize the loss of chalcogen vapor at the chamber entry and chamber exit points of the roll-to-roll substrate 1070 .

Referring now to FIG. 15C, another embodiment of the present invention uses a chamber 1090 of sufficient size to contain the entire substrate, including any rolls 1072 or 1074 associated with using a roll-to-roll configuration.

Referring now to FIG. 16A , it should additionally be understood that embodiments of the present invention may also be used on rigid substrates 1100 . As non-limiting examples, rigid substrate 1100 may be glass, solar glass, low-iron glass, green glass, soda lime glass, steel, stainless steel, aluminum, polymer, ceramic, coated polymer, or suitable for use as a solar cell Or other rigid materials for solar module substrates. A high speed pick and place robot 1102 may be used to move the rigid substrate 1100 from a stack or other storage area onto a processing area. In Figure 16A, substrates 1100 are placed on a conveyor belt which then moves them through the different processing chambers. Optionally, the substrate 1100 may have undergone some processing at this point and may already include a precursor layer on the substrate 1100 . Other embodiments of the invention may form the precursor layer as the substrate 1100 passes through the chamber 1106 .

FIG. 16B shows another embodiment of the present system in which a pick-and-place robot 1110 is used to place a plurality of rigid substrates on a transport device 1112 which can then be moved as indicated by arrow 1114 to the processing area. This allows multiple substrates 1100 to be loaded and then moved all together to undergo processing.

Referring now to Figure 17, another embodiment of the present invention will be described. In one embodiment, the particles used to form precursor layer 1500 may include particles that are intermetallic particles 1502 . In one embodiment, the intermetallic material is a material containing at least two elements, wherein the amount of one element in the intermetallic material is less than that of the total molar amount of the intermetallic material and/or the precursor material About 50 mol% of the total molar amount of elements. The amount of the second element is variable and can range from less than about 50 mole percent to about 50 mole percent or more of the total molar amount of that element in the intermetallic material and/or precursor material. Alternatively, the intermetallic phase material may consist of two or more metals in which the materials are mixed in a ratio between the upper limit of the terminal solid solution and an alloy comprising about 50% of one of the elements in the intermetallic material. The particle distribution shown in the enlarged view of Figure 10 is purely exemplary and non-limiting. It should be understood that some embodiments may have particles that all contain intermetallic materials, mixtures of metallic materials and intermetallic materials, metallic particles and intermetallic particles, or combinations thereof.

It should be understood that intermetallic phase materials are compounds and/or intermediate solid solutions containing two or more metals that have different properties and crystal structures than pure metals or terminal solid solutions. Intermetallic phase materials are caused by the diffusion of one material into another via lattice vacancies made available by defects, contamination, impurities, grain boundaries and mechanical stress. After the two or more metals diffuse into each other, an intermediate metal species is created that is a combination of the two materials. Subclasses of intermetallic compounds include electron compounds and interstitial compounds.

Electronic compounds are created if two or more mixed metals have different crystal structures, valence states, or electropositivity relative to each other, examples include but are not limited to copper selenide, gallium selenide, indium selenide, copper telluride , gallium telluride, indium telluride, and similar and/or related materials and/or blends or mixtures of these materials.

Interstitial compounds arise from metals or mixtures of metals and nonmetallic elements with atomic dimensions similar enough to allow the formation of an interstitial crystal structure in which atoms of one material fit into the spaces between atoms of another material. For intermetallic materials where each material has a single crystal phase, the two materials typically show two diffraction peaks superimposed on the same spectrum, each representing each individual material. Intermetallics therefore generally contain the crystal structure of the two materials contained within the same volume. Examples include, but are not limited to, Cu-Ga, Cu-In, and similar and/or related materials and/or blends or mixtures of these materials where the compositional ratios of each element to the other elements place the material in its phase diagram In regions other than the terminal solid solution region.

Intermetallic materials are useful in the formation of precursor materials for CIGS photovoltaic devices in which metals are interspersed among each other in a highly uniform and consistent manner, and where each material is present in substantially similar amounts relative to the other, thereby allowing Fast reaction kinetics, which result in high-quality absorber films that are substantially homogeneous in all three dimensions and on the nano, micro and meso scales.

Absent the addition of indium nanoparticles, which are difficult to synthesize and process, terminal solid solutions do not readily allow a sufficiently large range of precursor materials to be incorporated into the precursor film in the correct ratio (e.g. Cu/(In+Ga) = 0.85) to allow available Forms a photoactive absorber layer that is highly light absorbing. Furthermore, terminal solid solutions may have different mechanical properties than intermetallic materials and/or intermediate solid solutions (terminal solid solutions and/or solid solutions between elements). As a non-limiting example, some terminal solid solutions are not brittle enough to be ground for comminution. Other embodiments may be too hard to grind. The use of intermetallic materials and/or intermediate solid solutions can address some of these disadvantages.

The advantages of particles 1502 having an intermetallic phase are numerous. As a non-limiting example, precursor materials suitable for use in thin film solar cells may contain Group IB and Group IIIA elements such as copper and indium, respectively. If an intermetallic phase of Cu—In such as Cu ₁ In ₂ is used, the indium is part of the In-rich Cu material and is not added as pure indium. Adding pure indium as metal particles is challenging due to the difficulty in achieving In particle synthesis in high yield, small and narrow nanoparticle size distribution, and the need for particle size determination that adds more cost. The use of intermetallic In-rich Cu particles avoids pure elemental In as a precursor material. In addition, since the intermetallic material is Cu-depleted, this also advantageously allows the addition of Cu alone to precisely achieve the desired amount of Cu in the precursor material. Cu does not depend on a fixed ratio in alloys or solid solutions that can be produced from Cu and In. The amount of intermetallic material and Cu can be refined as needed to achieve the desired stoichiometric ratio. Ball milling of these particles results in no need for particle size determination, which reduces cost and increases throughput of the material preparation process.

In some specific embodiments of the invention, having an intermetallic material provides a wider range of flexibility. Since it is difficult to manufacture elemental indium particles economically, it would be advantageous to have a more economically interesting source of indium. In addition, it would be advantageous if the indium source also allowed changing Cu/(In+Ga) and Ga/(In+Ga) in the layers independently of each other. As a non-limiting example, an intermetallic phase can be used to differentiate between Cu ₁₁ In ₉ and Cu ₁ In ₂ . This is especially true if only one layer of precursor material is used. For this particular example, there are more constraints on the stoichiometry that can be produced in the final Group IB-IIIA-VIA compound if only the indium is provided by Cu ₁₁ In ₉ . However, with Cu ₁ In ₂ as the sole indium source, a much larger range of ratios can be produced in the final Group IB-IIIA-VIA compound. Cu ₁ In ₂ allows independent changes of Cu/(In+Ga) and Ga/(In+Ga) over a wide range, while Cu ₁₁ In ₉ cannot. For example, Cu ₁₁ In ₉ only allows Ga/(In+Ga)=0.25 at Cu/(In+Ga)>0.92. As another example, Cu ₁₁ In ₉ only allows Ga/(In+Ga)=0.20 at Cu/(In+Ga)>0.98. As another example, Cu ₁₁ In ₉ only allows Ga/(In+Ga)=0.15 at Cu/(In+Ga)>1.04. Thus for intermetallic materials, especially when the intermetallic material is the sole source of one of the elements in the final compound, the final compound can be produced in a stoichiometric ratio: This stoichiometric ratio explores a broader compositional range of about 0.7 to about 1.0 Cu/(In+Ga) bound and compositions ranging from about 0.05 to about 0.3 Ga/(In+Ga) bound. In other embodiments, the Cu/(In+Ga) composition may range from about 0.01 to about 1.0. In other embodiments, the Cu/(In+Ga) composition may range from about 0.01 to about 1.1. In other embodiments, the Cu/(In+Ga) composition may range from about 0.01 to about 1.5. This usually creates extra _Cux Se _y which may be removed later if it is on the top surface. It should be understood that these ratios may apply to any of the embodiments described herein above.

Furthermore, it should be understood that intermetallic materials may generate more liquid during processing than other compounds. As _a non-limiting example, _Cu1In2 will form more liquid than Cu11In9 when heated during processing. More liquid promotes more intermixing of atoms because materials move and mix more easily when they are in a liquid state.

In addition, particular advantages exist _for certain types of intermetallic particles such as, but not limited to, _Cu1In2 . Cu ₁ In ₂ is a metastable material. This material is more prone to decomposition, which would advantageously increase the reaction rate (kinetically) for the present invention. Furthermore, the material is less prone to oxidation (compared to eg pure In) and this further simplifies handling. The material can also be single-phase, which would make it more homogeneous as a precursor material, leading to better yields.

As seen in FIGS. 18 and 19 , after depositing layer 1500 on substrate 1506 , heating may follow under a suitable atmosphere to react layer 1500 in FIG. 18 and form film 1510 shown in FIG. 19 . It should be understood that layer 1500 may be used in combination with layers 915 and 917 . Layer 915 may be composed of various materials including but not limited to at least one of the following: Group IB elements, Group IIIA elements, Group VIA elements, Group IA elements (new style: Group 1), binary and/or Multiple alloys, solid solutions of any of the foregoing elements. It should be understood that sodium or sodium-based materials such as, but not limited to, sodium, sodium compounds, sodium fluoride, and/or sodium indium sulfide may also be used in layer 915 along with precursor materials to improve the properties of the resulting film. Figure 19 shows that layer 932 can also be used as described with respect to Figure 6F. Any of the previously suggested methods regarding sodium content may also be adapted for use with the embodiments shown in Figures 17-19.

It should be understood that additional embodiments of the present invention also disclose materials comprising at least two elements, wherein the amount of at least one element in the material is less than about 50 mole percent of the total molar amount of the element in the precursor material. This includes embodiments wherein the amount of Group IB element is less than the amount of Group IIIA element in the intermetallic material. As a _non -limiting example, this may include other Group IB-depleted Group IB-IIIA materials such as Cu-depleted _CuxIny particles (where x<y). The amount of Group IIIA material can be in any desired range (more than about 50 mol% or less than 50 mol% of this element in the precursor material). In another non-limiting example, Cu ₁ Ga ₂ can be used with elemental Cu and elemental In. Although the material is not an intermetallic material, the material is an intermediate solid solution and is distinct from a terminal solid solution. All solid particles are produced based on Cu ₁ Ga ₂ precursors. In this embodiment, no emulsion is used.

In additional embodiments of the invention, Group IB-enriched Group IB-IIIA materials may be used to form other viable precursor materials. As a non-limiting example, various intermediate solid solutions can be used. Cu—Ga (38 atomic % Ga) may be used in the precursor layer 1500 together with elemental indium and elemental copper. In another embodiment, Cu—Ga (30 atomic % Ga) may be used in the precursor layer 1500 together with elemental copper and elemental indium. Both of these embodiments describe Cu-rich materials in which the Group IIIA element is less than about 50 mol% of that element in the precursor material. In additional embodiments, Cu-Ga (heterogeneous, 25 atomic % Ga) can be used with elemental copper and indium to form the desired precursor layer. It should be understood that nanoparticles of these materials may be produced by mechanical milling or other comminution methods. In additional embodiments, these particles can be produced by electro-explosive wire (EEW) processing, evaporative condensation (EC), pulsed plasma processing, or other methods. Although not limited to the following, the particle size may be from about 10 nm to about 1 μm. They can have any shape described herein.

Referring now to FIG. 19, in another embodiment of the invention, two or more layers of material may be coated, printed, or otherwise formed to provide precursor layers with a desired stoichiometric ratio. As a non-limiting example, layer 1530 may comprise a precursor material having Cu ₁₁ In ₉ and a Ga source such as elemental Ga and/or Ga _x Se _y . A copper-rich precursor layer 1532 containing Cu ₇₈ In ₂₈ (solid solution) and elemental indium or In _x Se _y may be printed on layer 1530 . In such an embodiment, the resulting overall ratios may have Cu/(In+Ga)=0.85 and Ga/(In+Ga)0.19. In one embodiment of the resulting film, the film has a Cu/(In+Ga) stoichiometry in the composition range from about 0.7 to about 1.0 and a Ga/(In+Ga) stoichiometry in the composition range from about 0.05 to about 0.3 Compare.

Referring now to FIG. 21 , it will be appreciated that in some embodiments of the invention, intermetallic materials are used as feedstock or raw materials from which particles and/or nanoparticles may be formed. As a non-limiting example, Figure 21 shows an intermetallic feed particle 1550 that is processed to form other particles. Any method for comminution and/or shape change may be suitable including, but not limited to, milling, EEW, EC, pulsed plasma treatment, or combinations thereof. Particles 552, 554, 556, and 558 may be formed. The particles may have varying shapes and some particles may contain only the intermetallic phase while others may contain this phase as well as other material phases.

Referring now to FIGS. 22A and 22B , flakes 1600 (microflakes and/or nanoflakes) offer certain advantages over other non-spherical shapes such as, but not limited to, platelets. Flakes 1600 provide very efficient stacking (due to uniform thickness in the Z axis) and high surface area (in the X and Y axes). This results in faster reactions, better kinetics, and more uniform products/films/compounds (with less side spread). The lamellae 1602 seen in Figures 23A and 23B do not have all of the above advantages.

While the invention has been described and illustrated with reference to certain specific embodiments thereof, those skilled in the art will recognize that various modifications and changes in process and procedures can be made without departing from the spirit and scope of the invention. , improve, replace, omit, or add to. For example, for any of the above embodiments, the nanoflakes may be replaced by and/or mixed with microflakes, wherein the planar microflakes have a length and/or largest lateral dimension of about 500 nm or greater. The microflakes may each have a length less than about 5 μm and greater than about 500 nm. The microflakes may each have a length from about 3 μm to about 500 nm. The particles may be microflakes with a length greater than 500 nm. The particles may be microflakes with a length greater than 750 nm. The microflakes may each have a thickness of about 100 nm or less. The particles may be microflakes having a thickness of about 75 nm or less. The particles may be microflakes with a thickness of about 50 nm or less. The microflakes may each have a thickness of less than about 20 nm. The microflakes may have a length of less than about 2 μm and a thickness of less than 100 nm. The microflakes may have a length of less than about 1 μm and a thickness of less than 50 nm. The microflakes can have an aspect ratio of at least about 10 or greater. The microflakes have an aspect ratio of at least about 15 or greater.

As mentioned, some embodiments of the invention may include both nanoflakes and microflakes. Other embodiments may include flakes exclusively in the nanoflake size range or in the microflake size range. For any of the above embodiments, the microflakes may be replaced by microrods, which are elongated substantially linear bodies. For any of the above embodiments, the nanoflakes may be replaced by nanorods, which are substantially linear elongated materials. Additional embodiments may combine nanorods with nanoflakes in the precursor layer. Any of the above-described embodiments may be used on rigid substrates, flexible substrates, or a combination of both, such as, but not limited to, flexible substrates that become rigid during processing due to their material properties. In one embodiment of the invention, the particles may be plates and/or discs and/or flakes and/or wires and/or rods with micron-sized fractions. In another embodiment of the invention, the particles may be nanoplates and/or nanodisks and/or nanoflakes and/or nanowires and/or nanorods with nanosized portions.

As with any of the above embodiments, it should be understood that in addition to the above, the temperature may also be varied over different periods of time during the processing of the precursor layer. As a non-limiting example, heating may be at a first temperature for an initial treatment period and to an additional temperature for subsequent treatment periods. Optionally, the method may include intentionally producing one or more temperature drops such that, as a non-limiting example, the method comprises heating, cooling, heating and then cooling. As with any of the above embodiments, it is also possible to have two or more IB elements in the chalcogenide particles and/or the resulting film.

Additionally, concentrations, amounts, and other numerical data may be presented herein in range format. It should be understood that this range format is used for convenience and brevity only, and should be construed flexibly to include not only the values expressly recited as the boundaries of the stated range, but also all individual values or subranges subsumed within that range, as if each Both numerical values and subranges are explicitly stated. For example, a size range of about 1 nm to about 200 nm should be interpreted to include not only the expressly stated boundaries of about 1 nm and about 200 nm, but also individual sizes such as 2 nm, 3 nm, 4 nm and sub-ranges such as 10 nm to 50 nm, 20 nm to 100 nm, etc. .

For example, additional embodiments of the present invention may use Cu-In precursor materials where Cu-In contributes less than about 50% of both Cu and In present in the precursor material. The remaining amount is introduced in elemental form or from non-IB-IIIA alloys. Therefore, Cu ₁₁ In ₉ can be used with elemental Cu, In, and Ga to form the resulting film. In another embodiment, other materials such as Cu-Se, In-Se and/or Ga-Se may replace elemental Cu, In and Ga as the source of Group IB or IIIA materials. Optionally, in another embodiment, the source of IB can be any particle (Cu, Cu—Se) comprising Cu that is not alloyed with In and Ga. The IIIA source can be any particle containing In without Cu (In-Se, In-Ga-Se) or any particle containing Ga without Cu (Ga, Ga-Se or In-Ga-Se). Additional embodiments may have these combinations of IB materials in either nitride or oxide form. Additional embodiments may have these combinations of IIIA materials in either nitride or oxide form. The present invention may use any combination of elements and/or may use selenides (binary, ternary or polynary). Optionally, some other embodiments may use oxides such as In ₂ O ₃ to add the desired amount of material. It should be understood that more than one solid solution may be used for any of the above-described embodiments, and that multi-phase alloys and/or alloys more generally may also be used. For any of the above embodiments, the annealing process may also include exposing the compound film to a gas, such as _H2 , CO, _N2 , Ar, _H2Se , Se vapor, or a combination or blend of these gases. It should also be understood that Se may be evaporated or printed onto the stack of layers for processing.

It should also be understood that several intermediate solid solutions may also be suitable for use in accordance with the present invention. As non-limiting examples, compositions in the delta phase of Cu-In (about 42.52 to about 44.3 wt% In) and/or compositions between the delta phase of Cu-In and Cu ₁₆ In ₉ may be suitable for use with the present invention Suitable intermetallic materials used together to form Group IB-IIIA-VIA compounds. It should be understood that these intermetallic materials may be mixed with elemental or other materials such as Cu-Se, In-Se and/or Ga-Se to provide a source of Group IB or IIIA materials to achieve the desired stoichiometric ratio in the final compound. Other non-limiting examples of intermetallic materials include Cu-Ga compositions containing the following phases: γ1 (about 31.8 to about 39.8 wt% Ga), γ2 (about 36.0 to about 39.9 wt% Ga), γ3 (about 39.7 to about 44.9 wt% Ga), a phase between γ2 and γ3, a phase between terminal solid solution and γ1, and θ (about 66.7 to about 68.7 wt% Ga). For Cu-Ga, the suitable composition also exists in the range between the terminal solid solution and the intermediate solid solution next to it. Advantageously, some of these intermetallic materials may be heterogeneous, which are more likely to result in a brittle material capable of mechanical grinding. Phase diagrams for the following materials can be found in ASM Handbook, Volume 3 Alloy Phase Diagrams (1992), ASM International, incorporated herein by reference in its entirety for all purposes. Some specific examples (incorporated by reference herein in their entirety) can be found at pages 2-168, 2-170, 2-176, 2-178, 2-208, 2-214, 2-257, and/or 2-259.

Publications discussed or referenced herein are provided only for their disclosure prior to the filing date of the present application. Nothing here should be construed as an admission that the present invention is not entitled to antedate these publications by prior invention. In addition, the dates of publication provided may differ from the actual publication dates, which need to be independently confirmed. All publications mentioned herein are incorporated herein by reference to disclose and describe the structures and/or methods in connection with which the publications are cited. The following applications are also incorporated herein by reference for all purposes: U.S. Patent Application 11/290,633, filed November 29, 2005, and titled "CHALCOGENIDE SOLAR CELLS," and U.S. Patent Application 10/782,017, filed February 19, 2004 , entitled "SOLUTION-BASED FABRICATION OF PHOTOVOLTAIC CELLS," U.S. Patent Application 10/943,657, filed September 18, 2004, and titled "COATED NANOPARTICLES AND QUANTUMDOTS FOR SOLUTION-BASED FABRICATION OF PHOTOVOLTAIC CELLS," and March 16, 2005 U.S. Patent Application 11/081,163, filed September 18, 2004, entitled "METALLIC DISPERSION," and U.S. Patent Application 10/943,685, filed September 18, 2004, entitled "FORMATION OF CIGS ABSORBER LAYERS ON FOIL SUBSTRATES," February 23, 2006 11/361,433, filed March 30, 2006, and 11/394,849, filed March 30, 2006, the entire disclosures of which are incorporated herein by reference.

While the above is a complete description of the preferred embodiment of the invention, various alternatives, modifications and equivalents may be used. The scope of the invention, therefore, should be determined not with reference to the above description, but should be determined in accordance with the appended claims, along with their full scope of equivalents. Any feature, whether preferred or not, may be combined with any other feature, whether preferred or not. In the following claims, the indefinite article "a", or "an" means that the number of the item following said article is one or more, unless expressly stated otherwise. The appended claims should not be construed to include means-plus-function limitations, unless such limitation is expressly indicated in a given claim using the phrase "means for".

In summary, the invention provides the following technical solutions:

1. A method comprising:

forming a precursor layer on a substrate; and

The precursor layer is reacted in one or more steps to form the absorber layer.

2. A method comprising:

Formulated particle inks wherein about 50% or more of the particles are flakes each containing at least one element from Groups IB, IIIA and/or VIA and having a non-spherical planar shape, wherein said ink contains elements from Groups IB, The total amount of elements of groups IIIA and/or VIA is such that the ink has a desired stoichiometric ratio of elements;

coating a substrate with the ink to form a precursor layer; and

treating the precursor layer in a suitable atmosphere to form a dense film;

Wherein at least one set of particles in the ink are intermetallic flake particles comprising at least one Group IB-IIIA intermetallic alloy phase.

3. The method of technical scheme 1, wherein at least one group of particles in the dispersion is in the form of nanospheres.

4. The method of technical scheme 1, wherein at least one group of particles in the dispersion is in the form of nanospheres and contains at least one group IIIA element.

5. The method of technical scheme 1, wherein at least one group of particles in the dispersion is in the form of nanospheres comprising group IIIA elements in elemental form.

6. The method of technical scheme 1, wherein the intermetallic phase is not a terminal solid solution phase.

7. The method of technical scheme 1, wherein the intermetallic phase is not a solid solution phase.

8. The method of claim 1, wherein the intermetallic particles contribute less than about 50 mol% of the group IB elements present in all the particles.

9. The method of claim 1, wherein the intermetallic particles contribute less than about 50 mol% of the group IIIA elements present in all the particles.

10. The method of embodiment 1, wherein the intermetallic particles contribute less than about 50 mol% of group IB elements and less than about 50 mol% of group IIIA elements in the dispersion deposited on the substrate.

11. The method of embodiment 1, wherein the intermetallic particles contribute less than about 50 mol% of group IB elements and more than about 50 mol% of group IIIA elements in the dispersion deposited on the substrate.

12. The method of claim 1, wherein the intermetallic particles contribute more than about 50 mol% of group IB elements and less than about 50 mol% of group IIIA elements in the dispersion deposited on the substrate.

13. The method of technical scheme 10, wherein the molar percentage is based on the total molar amount of elements in all particles present in the dispersion.

14. The method of technical solution 1, wherein at least some of the particles have a lamellar shape.

15. The method of technical scheme 1, wherein most of the particles have a lamellar shape.

16. The method of technical scheme 1, wherein all the particles have a lamellar shape.

17. The method of claim 1, wherein the step of depositing comprises coating the substrate with the dispersion.

18. The method of technical scheme 1, wherein the dispersion comprises an emulsion.

19. The method of technical scheme 1, wherein the intermetallic material is a binary material.

20. The method of technical solution 1, wherein the intermetallic material is a ternary material.

21. The method of technical scheme 1, wherein the intermetallic material comprises Cu ₁ In ₂ .

22. The method of technical scheme 1, wherein the intermetallic material comprises a composition of Cu ₁ In ₂ δ phase.

23. The method of technical solution 1, wherein the intermetallic material comprises a composition between the δ phase of Cu ₁ In ₂ and the phase defined by Cu ₁₆ In ₉ .

24. The method of technical solution 1, wherein the intermetallic material comprises Cu ₁ Ga ₂ .

25. The method of technical solution 1, wherein the intermetallic material comprises an intermediate solid solution of Cu ₁ Ga ₂ .

26. The method of technical solution 1, wherein the intermetallic material comprises Cu ₆₈ Ga ₃₈ .

27. The method of technical solution 1, wherein the intermetallic material comprises Cu ₇₀ Ga ₃₀ .

28. The method of technical solution 1, wherein the intermetallic material comprises Cu ₇₅ Ga ₂₅ .

29. The method of technical solution 1, wherein the intermetallic material comprises a Cu-Ga composition of the phase between the terminal solid solution and the intermediate solid solution next to it.

30. The method of technical scheme 1, wherein the intermetallic material comprises a Cu-Ga composition of γ ₁ phase (about 31.8 to about 39.8 wt% Ga).

31. The method of technical scheme 1, wherein the intermetallic material comprises a Cu-Ga composition of γ ₂ phase (about 36.0 to about 39.9 wt% Ga).

32. The method of technical scheme 1, wherein the intermetallic material comprises a Cu-Ga composition of γ ₃ phase (about 39.7 to about 44.9 wt% Ga).

33. The method of claim 1, wherein the intermetallic material comprises a Cu-Ga composition of theta phase (about 66.7 to about 68.7 wt% Ga).

34. The method of claim 1, wherein the intermetallic material comprises a Cu-Ga composition of a phase between _γ2 and _γ3 .

35. The method of technical scheme 1, wherein the intermetallic material comprises a Cu-Ga composition of a phase between the terminal solid solution and _γ1 .

36. The method of technical scheme 1, wherein the intermetallic material comprises Cu-rich Cu-Ga.

37. The method of technical scheme 1, wherein gallium is introduced as a group IIIA element in the form of a suspension of nanospheres.

38. The method of technical solution 37, wherein the gallium nanospheres are formed by producing an emulsion of liquid gallium in a solution.

39. The method of technical scheme 37, wherein the gallium is quenched below room temperature.

40. The method of technical solution 37, further comprising maintaining or improving the dispersion of liquid gallium in the solution by stirring, mechanical device, electromagnetic device, ultrasonic device and/or adding dispersant and/or emulsifier.

41. The method of technical solution 1, further comprising adding a mixture of one or more elemental particles selected from the group consisting of aluminum, tellurium, or sulfur.

42. The method of technical solution 1, wherein the suitable atmosphere contains at least one of the following: selenium, sulfur, tellurium, H ₂ , CO, H ₂ Se, H ₂ S, Ar, N ₂ or combinations or mixtures thereof.

43. The method of technical solution 1, wherein the suitable atmosphere contains at least one of the following: H ₂ , CO, Ar and N ₂ .

44. The method of technical solution 1, wherein one or more types of particles are doped with one or more inorganic materials.

45. The method of technical scheme 1, wherein one or more types of particles are doped with one or more inorganic substances selected from aluminum (Al), sulfur (S), sodium (Na), potassium (K) or lithium (Li) Material.

46. A method comprising:

Formulating particle inks wherein the majority of the particles are nanoflakes each containing at least one element from groups IB, IIIA and/or VIA and having a non-spherical planar shape, wherein the ink comprises elements from groups IB, IIIA and/or The total amount of elements of Group VIA is such that the ink has a desired stoichiometric ratio of elements;

coating a substrate with the ink to form a precursor layer; and

processing the precursor layer to form a dense film for semiconductor absorber growth for photovoltaic devices;

Wherein at least one set of particles in the ink are intermetallic nanoflake particles comprising at least one Group IB-IIIA intermetallic alloy phase.

47. A method comprising:

Formulated particle inks wherein about 50% or more of the particles are flakes each containing at least one element from Groups IB, IIIA and/or VIA and having a non-spherical planar shape, wherein said ink contains elements from Groups IB, The total amount of elements of groups IIIA and/or VIA is such that the ink has a desired stoichiometric ratio of elements;

coating a substrate with the ink to form a precursor layer; and

The precursor layer is treated in a suitable atmosphere to form a dense film.

48. The method of technical solution 47, wherein at least one group of particles in the dispersion is in the form of nanospheres.

49. The method according to claim 47, wherein at least one group of particles in the dispersion is in the form of nanospheres and contains at least one group IIIA element.

50. The method according to technical solution 47, wherein at least one group of particles in the dispersion is in the form of nanospheres containing group IIIA elements in elemental form.

51. The method of technical solution 47, wherein the intermetallic phase is not a terminal solid solution phase.

52. The method according to technical solution 47, wherein the intermetallic phase is not a solid solution phase.

53. The method of technical scheme 47, wherein the intermetallic particles contribute less than about 50 mol% of group IB elements present in all particles.

54. A method comprising:

Formulating particle inks wherein the majority of the particles are nanoflakes each containing at least one element from groups IB, IIIA and/or VIA and having a non-spherical planar shape, wherein the ink comprises elements from groups IB, IIIA and/or The total amount of elements of Group VIA is such that the ink has a desired stoichiometric ratio of elements;

coating a substrate with the ink to form a precursor layer; and

processing the precursor layer to form a dense film for semiconductor absorber growth for photovoltaic devices;

Wherein at least one set of particles in the ink are intermetallic nanoflake particles comprising at least one Group IB-IIIA intermetallic alloy phase.

55. The method of technical scheme 54, wherein at least 80% of the particles are nanoflakes.

56. The method of technical scheme 54, wherein at least 90% of the particles are nanoflakes.

57. A composition comprising:

a plurality of particles comprising a group IB and/or IIIA element and optionally at least one group VIA element;

Wherein at least one set of particles are nanoflakes containing at least one Group IB-IIIA intermetallic alloy phase.

58. A material comprising:

The material composition comprises a plurality of nanoflakes of at least one element from groups IB, IIIA and/or VIA;

wherein the nanoflakes are prepared by milling precursor particles characterized by a precursor composition that provides sufficient ductility to form a planar shape from a non-planar starting shape upon milling, and wherein the combined The total amount of group IB, IIIA and/or VIA elements contained in the precursor particle is at a desired stoichiometric ratio of elements.

59. The material of technical scheme 1, wherein grinding converts at least 50% of the precursor particles into nanoflakes.

60. The material of technical scheme 1, wherein milling converts at least 95% of the precursor particles into nanoflakes.

61. The material of claim 1, wherein milling converts substantially all of the precursor particles into nanoflakes.

62. The material of claim 1, wherein the precursor particles are 10 μm or larger when measured along their longest dimension.

63. The material of technical solution 1, wherein the milling is performed in an oxygen-free atmosphere to produce oxygen-free nanoflakes.

64. The material of technical scheme 1, wherein the milling is performed in an inert gas atmosphere to produce oxygen-free nanoflakes.

65. The material according to technical scheme 1, wherein the grinding is performed at room temperature.

66. The material according to technical scheme 1, wherein grinding is performed at a low temperature.

67. The material of technical scheme 1, wherein grinding is carried out under the grinding temperature where all elements in the precursor particles are solid, and the precursor particles have sufficient ductility at the grinding temperature to start from non-planar The shape forms a flat shape.

68. The material of technical solution 1, wherein the grinding is performed at a temperature lower than 15°C.

69. The material according to technical solution 1, wherein the grinding is carried out at a temperature lower than -200°C.

70. The material of technical scheme 1, wherein the precursor particle is a single metal particle.

71. The material of technical solution 1, wherein the precursor particles are elemental particles.

72. The material of technical solution 1, wherein the precursor particles are alloy particles.

73. The material of technical solution 1, wherein the precursor particles are binary alloy particles.

74. The material of technical solution 1, wherein the precursor particles are ternary alloy particles.

75. The material of technical solution 1, wherein the precursor particles are quaternary alloy particles.

76. The material of technical solution 1, wherein the precursor particles are solid solution particles.

77. The material of technical solution 1, wherein the nanoflakes only contain group IIIA materials.

78. The material of technical solution 1, wherein the nanoflakes only contain group IB and group IIIA materials.

79. The material of technical solution 1, wherein the nanoflakes only contain group IB and group VIA materials.

80. The material of technical solution 1, wherein the nanoflakes only contain group IIIA and group VIA materials.

81. The material of technical solution 1, wherein the molar ratio of group IB material to group IIIA material in the plurality of nanoflakes is greater than 1.0.

82. The material of technical scheme 1, wherein the precursor particles are elemental particles and wherein the alloy nanoflakes are milled from the elemental particles.

83. The material of technical scheme 1, wherein the precursor particles are chalcogenide particles, the particles are characterized by a stoichiometric ratio of the elements: the stoichiometric ratio provides sufficient ductility to the precursor particles from non-planar The original shape forms a flat shape.

84. The material of technical solution 1, wherein the precursor particles are selected from one of the following: copper selenide, indium selenide or gallium selenide.

85. The material of technical scheme 1, wherein the stoichiometric ratio of elements between nanoflakes varies as long as the total amount in all combined nanoflakes is at the desired stoichiometric ratio.

86. The material of claim 1, further comprising performing size determination on the nanoflakes to exclude nanoflakes larger than a desired length.

87. The material of claim 1, further comprising performing size determination on the nanoflakes to exclude nanoflakes larger than a desired thickness.

88. The material of technical solution 1, which further comprises determining the size of the nanoflakes to control the size change of the nanoflakes to the following deviation: less than about 30% of the average length and about 30% of the average thickness.

89. The material of technical solution 1, wherein one standard deviation from the average thickness of the nanoflakes is less than 10 nm.

90. The material of technical solution 1, wherein one standard deviation from the average thickness of the nanoflakes is less than 5 nm.

91. The material according to technical solution 1, further comprising coating the nanoflakes with at least one layer of a material containing a group VIA element.

92. The material of technical solution 1, further comprising coating the nanoflakes with at least one layer of material containing selenium and/or selenide.

93. The material of technical solution 1, wherein the nano flakes are formed into a dry powder.

94. The material of claim 1, wherein the nanoflakes have an aspect ratio of at least about 10 or greater.

95. The material of claim 1, wherein the nanoflakes have an aspect ratio of at least about 15 or greater.

96. The material according to technical solution 1, wherein the nanoflakes contain sodium.

97. The material of technical scheme 1, wherein the nano flakes contain at least one of the following materials: Cu-Na, In-Na, Ga-Na, Cu-In-Na, Cu-Ga-Na, In-Ga-Na, Na-Se, Cu-Se-Na, In-Se-Na, Ga-Se-Na, Cu-In-Se-Na, Cu-Ga-Se-Na, In-Ga-Se-Na, Cu-In- Ga-Se-Na, Na-S, Cu-S-Na, In-S-Na, Ga-S-Na, Cu-In-S-Na, Cu-Ga-S-Na, In-Ga-S- Na or Cu-In-Ga-S-Na.

98. The material according to claim 1, further comprising an ink comprising a sodium compound having an organic counter ion or a sodium compound having an inorganic counter ion.

99. A method of using the material of claim 1, comprising heating nanoflakes in a non-oxygen chalcogen atmosphere to form a dense film.

100. A method of using the material of claim 1, further comprising heating the material on the substrate to form a film and then forming a layer of the sodium-containing material on the film.

101. A solar cell comprising:

Substrate;

a back electrode formed on the substrate;

a p-type semiconductor thin film formed on the back electrode;

an n-type semiconductor film formed so as to constitute a pn junction with the p-type semiconductor film; and

a transparent electrode formed on the n-type semiconductor film;

wherein said p-type semiconductor thin film is produced by processing a dense film formed of a plurality of nanoflakes whose material composition contains at least one element from groups IB, IIIA and/or VIA, wherein the dense film has about 26% or smaller void volume.

102. The solar cell of technical solution 1, wherein the dense film is a substantially void-free film.

103. The solar cell of embodiment 1, wherein a molar ratio of group IB material to group IIIA material in the plurality of nanoflakes is greater than about 1.0.

104. The solar cell of technical solution 1, wherein the nanoflakes are oxygen-free nanoflakes.

105. The solar cell of technical solution 1, wherein the nanoflakes are single metal particles.

106. The solar cell of technical solution 1, wherein the nano flakes are elemental particles.

107. The solar cell of technical solution 1, wherein the nano flakes are alloy particles.

108. The solar cell of technical solution 1, wherein the nano flakes are binary alloy particles.

109. The solar cell of technical solution 1, wherein the nano flakes are ternary alloy particles.

110. The solar cell of technical solution 1, wherein the nano flakes are quaternary alloy particles.

111. The solar cell of technical solution 1, wherein the nano flakes are solid solution particles.

112. The solar cell of technical solution 1, wherein the nanoflakes only contain group IIIA materials.

113. The solar cell of technical solution 1, wherein the nanoflakes only contain group IB and group IIIA materials.

114. The solar cell of technical solution 1, wherein the nanoflakes only contain group IB and group VIA materials.

115. The solar cell of technical solution 1, wherein the nanoflakes only contain group IIIA and group VIA materials.

116. The solar cell of technical solution 1, wherein the nanoflakes are selected from one of the following: copper selenide, indium selenide or gallium selenide.

117. The solar cell of technical solution 1, wherein one standard deviation from the average thickness of the nanoflakes is less than 10 nm.

118. The solar cell of technical solution 1, wherein one standard deviation from the average thickness of the nanoflakes is less than 5 nm.

119. The solar cell of technical scheme 1, wherein the stoichiometric ratio of elements between the nanoflakes varies as long as the total amount in all combined particles is at the desired stoichiometric ratio.

120. The solar cell of embodiment 1, wherein the nanoflakes have an aspect ratio of at least about 10 or greater.

121. The solar cell of embodiment 1, wherein the nanoflakes have an aspect ratio of at least about 15 or greater.

122. The solar cell of technical solution 1, wherein the nanoflakes have a random planar shape and/or a random size distribution.

123. The solar cell of technical solution 1, wherein the nanoflakes have a non-random planar shape and/or a non-random size distribution.

124. The solar cell of embodiment 1, wherein each of the nanoflakes has a thickness of less than about 20 nm.

125. The solar cell of embodiment 1, wherein the dense film is formed by heating a precursor layer of nanoflakes to a temperature greater than about 375° C. but less than the melting temperature of the substrate for 1 minute or less.

126. The solar cell of technical solution 1, wherein the dense film is formed by heating the precursor layer of nanoflakes to an annealing temperature but less than the substrate melting temperature for 1 minute or less.

127. The solar cell according to claim 1, wherein the dense film formation is promoted by a heat treatment technique using at least one of the following: pulse heat treatment, laser beam, or heating by an IR lamp.

128. The solar cell according to claim 1, wherein the substrate is a flexible substrate.

129. The solar cell of technical solution 1, wherein the substrate is a rigid substrate.

130. The solar cell of embodiment 1, wherein the film is formed from a precursor layer of nanoflakes and a layer of sodium-containing material in contact with the precursor layer.

131. The solar cell of technical scheme 1, wherein said film is formed by a precursor layer of nanoflakes and a layer contacting the precursor layer and containing at least one of the following materials: IB group elements, IIIA group elements, VIA group elements, Group IA elements, binary and/or multiple alloys of any of the foregoing elements, solid solutions of any of the foregoing elements, copper, indium, gallium, selenium, copper indium, copper gallium, indium gallium, sodium, sodium compounds, sodium fluoride, indium sulfide Sodium, copper selenide, copper sulfide, indium selenide, indium sulfide, gallium selenide, gallium sulfide, copper indium selenide, copper indium sulfide, copper gallium selenide, copper gallium sulfide, gallium indium selenide, gallium indium sulfide, Gallium indium copper selenide, and/or gallium indium copper sulfide.

132. The solar cell of technical solution 1, wherein the nanosheets contain sodium.

133. The solar cell of technical scheme 1, wherein the nanosheets contain at least one of the following materials: Cu-Na, In-Na, Ga-Na, Cu-In-Na, Cu-Ga-Na, In-Ga-Na , Na-Se, Cu-Se-Na, In-Se-Na, Ga-Se-Na, Cu-In-Se-Na, Cu-Ga-Se-Na, In-Ga-Se-Na, Cu-In -Ga-Se-Na, Na-S, Cu-S-Na, In-S-Na, Ga-S-Na, Cu-In-S-Na, Cu-Ga-S-Na, In-Ga-S -Na or Cu-In-Ga-S-Na.

134. The solar cell of claim 1, wherein the film is formed from a precursor layer of nanoflakes and an ink comprising a sodium compound with an organic counterion or a sodium compound with an inorganic counterion.

135. The solar cell of technical solution 1, wherein said film is formed from a precursor layer of nanoflakes and a layer of a sodium-containing material in contact with the precursor layer and/or nanoflakes containing at least one of the following materials: Cu -Na, In-Na, Ga-Na, Cu-In-Na, Cu-Ga-Na, In-Ga-Na, Na-Se, Cu-Se-Na, In-Se-Na, Ga-Se-Na , Cu-In-Se-Na, Cu-Ga-Se-Na, In-Ga-Se-Na, Cu-In-Ga-Se-Na, Na-S, Cu-S-Na, In-S-Na , Ga-S-Na, Cu-In-S-Na, Cu-Ga-S-Na, In-Ga-S-Na or Cu-In-Ga-S-Na; and/or containing nanoflakes and having organic An ink of a sodium compound as a counterion or a sodium compound with an inorganic counterion.

Claims (10)

1. a method, it comprises:

On substrate, form precursor layer; With

In one or more steps, make this precursor layer react to form absorbed layer.

2. a method, it comprises:

Preparation particle ink, wherein approximately 50% or more particle be contain separately at least one from the element of IB, IIIA and/or VIA family and there is the thin slice of aspheric flat shape, the total amount of the element from IB, IIIA and/or VIA family comprising in wherein said ink makes this ink have the element chemistry metering ratio of expectation;

With this ink coats substrate with form precursor layer; With

In appropriate atmosphere, process this precursor layer to form dense film;

Wherein at least one group of particle in this ink is the intermetallic plane particle that contains at least one IB-IIIA family intermetallic alloy phase.

3. the process of claim 1 wherein that at least one group of particle in dispersion is nanometer bead form.

4. the process of claim 1 wherein that at least one group of particle in dispersion is nanometer bead form and contains at least one IIIA family element.

5. the process of claim 1 wherein that at least one group of particle in dispersion is the nanometer bead form of the IIIA family element that comprises simple substance form.

6. the process of claim 1 wherein that intermetallic phase is not end border solid solution phase.

7. the process of claim 1 wherein that intermetallic phase is not solid solution phase.

8. the process of claim 1 wherein that the contribution of intermetallic particle is less than the IB family element existing in all particles of about 50mol%.

9. the process of claim 1 wherein that the contribution of intermetallic particle is less than the IIIA family element existing in all particles of about 50mol%.

10. the process of claim 1 wherein that intermetallic particle contributes the IB family element that is less than about 50mol% and the IIIA family element that is less than about 50mol% in the dispersion being deposited on substrate.

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