CN103337547A - Photovoltaic cells with treated surfaces and related applications - Google Patents

Abstract

The invention provides a photovoltaic cell and process that mitigate recombination losses of photogenerated carriers. To reduce recombination losses, a diffuse doping layer in an active photovoltaic PV element is coated with a pattern of dielectric material that reduces contact between metal contacts and the active PV element. Various patterns may be utilized, and one or more surfaces of the PV element may be coated with one or more dielectrics. Vertical multi-junction photovoltaic cells can be produced with patterned PV elements or cells. While patterned PV elements can increase the series resistance of VMJ photovoltaic cells, and patterning one or more surfaces in the PV elements can add complexity to the process for producing VMJ photovoltaic cells, reducing carrier loss at diffuse doping layers in PV elements increases the efficiency of photovoltaic cells, and thus provides PV operational advantages over increased manufacturing complexity. A system for fabricating the photovoltaic cell is provided.

Description

Photovoltaic cells with treated surfaces and related applications

This application is a divisional application of a patent application with the international application number PCT/US2009/053576 and the Chinese application number 200980139221.4 entitled "Photovoltaic cells with treated surfaces and related applications". The international filing date of the original application is 2009 August 12th.

technical field

This application claims benefit to U.S. Provisional Application No. 61/089,389, filed August 15, 2008, and entitled "SOLAR CELL WITH PATTERNED CONTACTS" claiming priority to U.S. Patent Application No. 12/535,952, filed August 5, 2009, and entitled "PHOTOVOLTAIC CELL WITH PATTERNED CONTACTS"; in 2009 U.S. Patent Application No. 12/536,982, filed August 6, and entitled "VERTICAL MULTI JUNCTION CELL WITH TEXTURED SURFACE," which was filed on August 14, 2008 Priority to U.S. Provisional Application No. 61/088,921, filed August 6, 2009, and titled "VERTICAL MULTIJUNCTION CELL WITH TEXTURED SURFACE" US Patent Application No. 12/536,987 for "PHOTOVOLTAIC CELL WITH BUFFER ZONE," filed August 14, 2008, and entitled "SOLAR CELL WITH BUFFER ZONE 61/088,936, filed on August 6, 2009 and entitled "ELECTROLYSIS VIA VERTICAL MULTI-JUNCTION PHOTOVOLTAIC CELL" US Patent Application No. 12/536,992, which petitions for 61/092,531 filed August 28, 2008 and entitled "ELECTROLYSIS VIA VERTICAL MULTI-JUNCTION SOLAR CELL" Priority of U.S. Provisional Application No. Each of the applications referenced above is incorporated herein by reference in its entirety.

Background technique

The limited supply and increasing demand for fossil energy sources and the associated global environmental damage have driven global efforts to diversify the use of energy sources and related technologies. One such resource is solar energy, which employs photovoltaic (PV) technology to convert light into electricity. In addition, solar energy can be used for heat generation (eg, in solar furnaces, steam generators, etc.). Solar energy technology is typically implemented in a series of PV cells or solar cells or panels thereof, which receive sunlight and convert it into electricity, which can then be delivered into the power grid. Significant advances have been made in the design and production of solar panels that have effectively increased efficiency while reducing their manufacturing costs. As more efficient solar cells are developed, the size of the cells decreases, leading to a substantial increase in the adoption of solar panels to provide competing renewable energy to replace dwindling and highly demanded non-renewable sources. To this end, solar energy harvesting systems like solar concentrators can be deployed to convert solar energy into electricity that can be delivered to the power grid and also harvest heat. In addition to the development of solar concentrator technology, the development of solar cells using solar concentrators has also begun.

A high-intensity solar cell technology known as vertical multi-junction VMJ solar cells is an integrally bonded series-connected array of small vertical junction cells that are edge-illuminated and have electrical contacts on the ends. The unique VMJ solar cell design can inherently provide high voltage low series resistance output characteristics, making it ideally suited for high efficiency performance in high intensity photovoltaic concentrators. Another key feature of VMJ solar cells is their design simplicity leading to low manufacturing costs.

The efficacy of VMJ solar cells can be demonstrated from performance data obtained on experimental VMJ solar cells with 40 series-connected junctions in the range of 100 to 2500 suns of concentration, with output power densities in excess of 400,000 watts at 25 volts /m ² , its efficiency is close to 20%. It will be appreciated that the above properties in VMJ solar cells are achieved by low manufacturing cost and complexity. It is believed that such aspects are the required boosters of the practical technical performance and economic efficiency needed to make photovoltaic concentrator systems significantly more cost-effective and feasible in solving global energy problems. Furthermore, any increase in cell efficiency (eg, outputting more watts) directly reduces concentrator system size (eg, lower costs associated with bill of materials), resulting in a lower $/watt cost of photovoltaic electricity.

It should be noted that lower $/W cost is substantially related to solar cell technology adoption and market penetration as global energy demand is steadily increasing (not only in emerging countries but also in developed countries) while traditional fossil fuel costs are escalating . In addition, there are broadly increased concerns over all associated issues such as environmental pollution, global warming, and national security and economic dangers associated with dependence on foreign fuel supplies. These environmental, economic and safety factors associated with increasing public awareness are driving strong interest in finding more cost-effective and environmentally friendly renewable energy solutions. Of all available renewable energy sources, solar energy has roughly the greatest potential to meet demand in an efficient and sustainable manner. In fact, the earth receives more energy in the form of sunlight every few minutes' cycle than humans can consume from roughly all other sources in an entire year.

Even though photovoltaic power is widely regarded as an ideal renewable energy technology, its associated costs can be a major barrier to adoption and market penetration. Before gaining market share and adoption, photovoltaic-based electricity needs to become cost-competitive with traditional power sources, including coal-fired electricity, which is well developed, used in consumers, and generally cost-effective. Furthermore, the availability of low-cost electricity is considered essential in all global economies; therefore terawatts (eg, tens of gigawatts) of photovoltaic power systems may be required. Market research shows that installed PV power systems must fall to a baseline cost of $3/W to be considered cost-competitive without subsidies in large utility-scale applications. With installed photovoltaic system costs currently exceeding $6/watt, substantial cost improvements are still needed.

Trying to achieve lower $/Watt performance has been the primary goal of much research and development in photovoltaic technology over the past few decades. Although the industry is spending billions of dollars pursuing various technologies (with the goal of making photovoltaic energy more cost-efficient), the existing photovoltaic industry still requires considerable subsidies to support sales, which can be a disadvantage for market development and industry development index of.

Currently, silicon solar cells (which remain about the same as when they were originally discovered and developed in the 1960s) dominate -93% of the photovoltaic market. The existing photovoltaic industry, which seeks to reduce costs, relies heavily on the availability of low-cost scrap-grade semiconductor silicon to manufacture conventional solar cells. It should be noted that this tailings grade silicon (often referred to as solar grade silicon) is primarily an ingot head and tail leftover from wafer production and rejected material by semiconductor device manufacturers requiring higher quality Class A silicon wafers . Despite rapid growth in PV sales, growing ~40% annually over the past decade (with production estimated at 3.8 gigawatts (GW) in 2007), sales are now hampered by shortages and higher prices of solar-grade silicon. Despite Grade A silicon is available, but it is not considered an option as it further increases the manufacturing cost several times.

For a typical conventional solar cell, more than half of the manufacturing cost is the raw semiconductor polysilicon used to produce the wafers for the solar cell. Thus, a typical 14% efficient solar cell is rated at 0.014 W/cm ² and has a silicon wafer cost above $3/watt (or $0.042/cm ² ) before any additional fabrication. Therefore, the existing photovoltaic industry must address and address the fact that the cost of silicon material only to begin with exceeds the benchmark price utility needs for large-scale applications. In contrast, semiconductor manufacturers producing microprocessor chips that sell at over $100/ ^cm2 on an area basis can afford the costs associated with utilizing Grade A silicon wafers.

The shortage of solar-grade silicon and the photovoltaic industry's inability to meet important cost benchmarks, together with the advent of novel, more efficient triple-junction solar cells being developed for space applications, has recently revived a great deal of interest in photovoltaic concentrators. The obvious advantage of photovoltaic concentrators is the potential cost-effectiveness of using large areas of inexpensive materials (glass mirror reflectors or plastic lenses) to concentrate sunlight on expensive solar cells of much smaller areas, thereby using inexpensive materials to Replace expensive materials. A photovoltaic concentrator designed for 1000 sun concentration intensity would significantly reduce the need for expensive semiconducting silicon by ~99.9%, meaning that 1000MW of VMJ solar cells is possible using the same amount of expensive semiconducting silicon currently required for 1MW of conventional solar cells of. Pragmatically, this is seen as a practical way to alleviate any silicon shortage problems.

Considerable work on solar concentrators has mostly focused on developing silicon concentrator solar cell designs for high intensity; although a great deal of fruitful development work had been done during the energy crisis of the 1970s, the results were cost-effective at the time Performance is mediocre and unsatisfactory. Research and development was carried out on silicon cells originally targeted for use in concentrator systems operating at 500 sun concentration intensities; however, when trying to overcome the series resistance problem in the solar cell design under study encountered Unresolved development difficulty when said target was lowered to 250 sunspots. For example, high series resistance losses in concentrator solar cells were indeed seen as a major problem addressed and solved by conventional VMJ solar cell technology. It should be noted that a considerable majority of solar cells developed for concentrator technology are rather complex and expensive to manufacture through 6 or 7 high temperature steps (>1000°C) and 6 or 7 photolithographic masking steps. This complexity is due to design attempts to minimize the series resistance losses that essentially limit the maximum intensity operation of the best of these designs to no higher than 250 suns of concentration. Such complexity and associated costs hinder substantial development of concentrator technology and associated solar cell technology, while promoting the development of alternative technologies like thin film solar cell technology.

Vertical multi-junction VMJ solar cell technology differs substantially from conventional concentrator solar cells. The VMJ solar cell technology offers at least two advantages over other technologies: (1) it does not require photolithography, and (2) a single high temperature diffusion step at temperatures greater than 1000°C can be used to form both junctions. Therefore, lower manufacturing costs are taken for granted. Furthermore, VMJ solar cells can be operated at high intensity; for example at 2500 suns concentrated. It is evident from this operation that series resistance is not a problem in VMJ solar cell design; not even at intensities orders of magnitude higher than conventional wisdom, even if this is not economically feasible. Furthermore, the current density of a VMJ cell at 2500 suns concentration is typically close to 70 A/cm ² , a level of radiation that can be roughly harmful to most solar cells based on other technologies.

As mentioned above, the renewed interest in photovoltaic concentrators is mainly due to triple-junction solar cells through III to V materials including gallium (Ga), phosphorus (P), arsenide (As), indium (In) and germanium (Ge) ) made for development. A triple-junction cell can use 20 to 30 different semiconductors layered in series on a germanium wafer: doped _GaInP2 and GaAs layers grown in a metal-organic chemical vapor deposition (MOCVD) reactor, where each type of semiconductor will Has a characteristic bandgap energy that causes it to absorb sunlight most efficiently in a certain color. The semiconductor layers are carefully selected to absorb nearly the entire solar spectrum, generating electricity from as much sunlight as possible. These multijunction devices are the most efficient solar cells to date, achieving a record high efficiency of 40.7% under moderate solar concentration and laboratory conditions. But since it is expensive to manufacture, it needs to be applied in photovoltaic concentrators.

However, the demand for III to V solar cell materials and their cost are rapidly increasing. As an example, in 12 months (12/2006 to 12/2007), the cost of pure gallium increased from about $350/Kg to $680/kg and the price of germanium increased roughly to $1000 to $1200/Kg. Indium, which was priced at $94/Kg in 2002, increased to nearly $1000/Kg in 2007. In addition, demand for indium is expected to continue to increase with the start of large-scale fabrication of thin-film CIGS (CuInGaSe) solar cells in 2007 by several new companies. Furthermore, indium is a rare element widely used to form transparent electrical coatings in the form of indium tin oxide for liquid crystal displays and large flat panel monitors. Practically speaking, these materials do not appear to be viable long-term photovoltaic (PV) solutions needed to provide terawatts of low-cost electricity to solve major global energy problems.

Although a III to V semiconductor solar cell with an area of 0.26685 ^cm2 can produce 2.6 watts (or about 10W/ ^cm2 ), and it has been estimated that this technology can eventually generate electricity at 8 to 10 fen/kWh, it is roughly similar to The price of electricity from conventional sources may require further analysis to support such estimates. However, VMJ solar cells exhibit output powers exceeding 40 W/cm ² at an intensity of 2500 suns concentrated by low-cost fabrication using the lowest-cost semiconductor materials. (This output exceeds 400,000 W/ ^m2 .) In addition to complex PV technologies based on advanced materials, Si-based solar cell technologies remain largely dominant in photovoltaic elements and applications. Furthermore, silicon is the only semiconductor material with an existing industry base that will be able to supply terawatts of photovoltaic power in the foreseeable future of widespread global application if global demand arises.

Contents of the invention

A simplified summary is presented below to provide a basic understanding of some aspects described herein. This summary is not an exhaustive overview, nor is it intended to identify key/critical elements or to delineate the scope of the various aspects described herein. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

The present invention provides semiconductor-based photovoltaic cells and processes for mitigating recombination losses of photogenerated carriers. In one aspect, to reduce recombination losses, the diffusely doped layer in the active PV element is coated with a pattern of dielectric material that reduces contact between the metal contacts and the active PV element. Various patterns can be utilized, and one or more surfaces of the PV element can be coated with one or more dielectrics. Vertical multi-junction VMJ solar cells can be created from patterned PV elements or cells. Patterned PV elements can increase the series resistance of a VMJ solar cell, and patterning one or more surfaces in the PV element can add complexity to the process used to create a VMJ solar cell; furthermore, reducing the diffusion doping layer Loss of carriers at can increase the efficiency of the solar cell and thus provide PV operating advantages that outweigh the increased manufacturing complexity. Also provided are systems enabling the fabrication of semiconductor-based PV cells.

Aspects or features described herein and associated advantages, such as reduced recombination losses of photogenerated carriers, can be utilized in any type of photovoltaic cell (eg, solar cells, thermal photovoltaic cells, or cells excited by a laser source of photons). Additionally, aspects of the invention may also be implemented in other types of energy conversion cells (eg, betavoltaic cells).

The present invention mitigates bulk weight loss in vertical multi-junction VMJ photovoltaic cells via texturing on the light receiving surface of the vertical multi-junction VMJ photovoltaic cells. The texture may be in the form of cavity-shaped grooves (e.g., "V" shaped cross-sectional configuration, "U" shaped cross-sectional configuration, etc.), wherein the plane comprising such cross-sectional configuration is approximately perpendicular to the cells stacked to form a VMJ photovoltaic cell The orientation of the unit. In one aspect, a plane comprising a substantially repeating cross-section (eg, transverse to a direction in which a groove extends) is substantially perpendicular to a direction in which the battery cells are stacked. This arrangement facilitates directing refracted light away from the p+ and n+ diffusely doped regions of the VMJ photovoltaic cell while generating the desired carriers in a reduced volume. Accordingly, incident light may be refracted in a plane including the cross-sectional configuration and substantially perpendicular to the direction in which the battery cells are stacked.

It will be appreciated that the texturing of VMJ photovoltaic cells of the present invention differs from prior art techniques for conventional silicon photovoltaic cell texturing in both the orientation of the PN junction and/or interaction with incident light. For example, conventional silicon photovoltaic cells are usually textured to block the penetration of light so that more of the longer wavelengths are absorbed closer to the PN junction (horizontally positioned) for better carrier current collection and thereby lessen the impact on the sun. The differential spectral response at longer wavelengths in the spectrum. In contrast, this is not required in the VMJ photovoltaic cells of the present invention which include vertical junctions and thus already provide an enhanced spectral response to longer wavelengths in the solar spectrum.

In particular aspects, the result of implementing the inventive grooves (e.g., V-grooves) is to mitigate weight weight loss by reducing volume—(as opposed to using textured conventional solar surfaces, which reduce reflection, or cause reflected or refracted light becomes closer to the knot). In particular, the VMJ photovoltaic cells have exhibited better carrier current collection for both short and long wavelengths, wherein the short wavelength response is due to the elimination of highly doped horizontal junctions at the top surface, and the The long wavelength response is due to the enhanced collection efficiency of the vertical junction. ) As another example, if instead of the cavity-shaped groove texture of the present invention, other textures (e.g., random, pyramidal, domed, and similar raised configurations) are implemented as part of a VMJ photovoltaic cell, then the incident light becomes direction, resulting in light absorption in the p+ and n+ diffused regions and thus reduced efficiency.

According to a related approach, a VMJ photovoltaic cell may initially be formed by stacking multiple battery cells, where each cell may itself include multiple parallel semiconductor substrates or layers stacked together. Each layer may consist of an impurity-doped semiconductor material forming a PN junction, and further includes a "built-in" electrostatic drift field that enhances movement of minority carriers towards such a PN junction. Subsequently, multiple such cells are integrated to form a VMJ photovoltaic cell. Next, on the light-receiving surface of the VMJ photovoltaic cell, a cavity-shaped groove can be formed (eg, via a dicing saw), wherein the plane comprising the cross-sectional configuration is approximately perpendicular to the stack forming the VMJ photovoltaic cell orientation of the battery cell. Accordingly, incident light may be refracted in a plane comprising said repeated cross-sectional configuration and generally perpendicular to said direction of stacking said battery cells (eg, thereby providing higher absorption for a given depth.) Furthermore, the present invention may be combined Various aspects of the invention are implemented with various rear and side surfaces having reflective coatings.

In a related aspect, the grooved surfaces of the present invention further improve carrier collection while reducing bulk weight loss. For example, the V-groove can be positioned perpendicular to the p+nn+ (or n+pp+) cell to increase the optical absorption path for longer wavelengths in the solar spectrum and enable light absorption to be roughly localized to p +nn+ in the n-type body region of the battery cell. Additionally, such V-grooves may have anti-reflective coatings applied to improve incident light absorption in the cell.

In a related aspect, the present invention mitigates bulk weight loss in vertical multi-junction VMJ photovoltaic cells via texturing on the light receiving surface of the vertical multi-junction VMJ photovoltaic cells. The texture may be in the form of cavity-shaped grooves (e.g., "V" shaped cross-sectional configuration, "U" shaped cross-sectional configuration, etc.), wherein the plane comprising such cross-sectional configuration is approximately perpendicular to the cells stacked to form a VMJ photovoltaic cell The orientation of the unit. In one aspect, a plane comprising a substantially repeating cross-section (eg, transverse to a direction in which a groove extends) is substantially perpendicular to said direction of stacking said battery cells. This arrangement facilitates directing refracted light away from the p+ and n+ diffusely doped regions of the VMJ photovoltaic cell while generating the desired carriers in a reduced volume. Accordingly, incident light may be refracted in a plane including the cross-sectional configuration and substantially perpendicular to the direction in which the battery cells are stacked.

It will be appreciated that the texturing of VMJ photovoltaic cells of the present invention differs from prior art techniques for conventional silicon photovoltaic cell texturing in both the orientation of the PN junction and/or interaction with incident light. For example, conventional silicon photovoltaic cells are usually textured to block the penetration of light so that more of the longer wavelengths are absorbed closer to the PN junction (horizontally positioned) for better carrier current collection and thereby lessen the impact on the sun. The differential spectral response at longer wavelengths in the spectrum. In contrast, this is not required in the VMJ photovoltaic cells of the present invention which include vertical junctions and thus already provide an enhanced spectral response to longer wavelengths in the solar spectrum.

In particular aspects, the result of implementing the inventive grooves (e.g., V-grooves) is to mitigate weight weight loss by reducing volume—(as opposed to using textured conventional solar surfaces, which reduce reflection, or cause reflected or refracted light becomes closer to the knot). In particular, the VMJ photovoltaic cells have exhibited better carrier current collection for both short and long wavelengths, wherein the short wavelength response is due to the elimination of highly doped horizontal junctions at the top surface, and the The long wavelength response is due to the enhanced collection efficiency of the vertical junction. ) As another example, if instead of the cavity-shaped groove texture of the present invention, other textures (e.g., random, pyramidal, domed, and similar raised configurations) are implemented as part of a VMJ photovoltaic cell, then the incident light becomes direction, resulting in light absorption in the p+ and n+ diffused regions and thus reduced efficiency.

According to a related approach, a VMJ photovoltaic cell may initially be formed by stacking multiple battery cells, where each cell may itself include multiple parallel semiconductor substrates or layers stacked together. Each layer may consist of an impurity-doped semiconductor material forming a PN junction, and further includes an "internal" electrostatic drift field that enhances minority carrier movement towards such a PN junction. Subsequently, multiple such cells are integrated to form a VMJ photovoltaic cell. Next, on the light-receiving surface of the VMJ photovoltaic cell, a cavity-shaped groove can be formed (eg, via a dicing saw), wherein the plane comprising the cross-sectional configuration is approximately perpendicular to the stack forming the VMJ photovoltaic cell orientation of the battery cell. Accordingly, incident light may be refracted in a plane comprising said repeated cross-sectional configuration and generally perpendicular to said direction of stacking said battery cells (eg, thereby providing higher absorption for a given depth.) Furthermore, the present invention may be combined Various aspects of the invention are implemented with various rear and side surfaces having reflective coatings.

In a related aspect, the grooved surfaces of the present invention further improve carrier collection while reducing bulk weight loss. For example, the V-groove can be positioned perpendicular to the p+nn+ (or n+pp+) cell to increase the optical absorption path for longer wavelengths in the solar spectrum and enable light absorption to be roughly localized to p +nn+ in the n-type body region of the battery cell. Additionally, such V-grooves may have anti-reflective coatings applied to improve incident light absorption in the cell.

In another aspect, the present invention supplies one or more buffer strips at the terminal layers of a high voltage silicon vertical multi-junction VMJ photovoltaic cell to provide a barrier protecting the active layer while providing an ohmic contact. Such buffer strips may be in the form of an arrangement of inactive layers that are additionally stacked above and/or below the terminal layers of the VMJ photovoltaic cell cells. The VMJ photovoltaic cell itself may comprise multiple cells, where each cell employs several active layers (e.g., three) to form a PN junction and an "internal" electrostatic drift field (which enhances the minority load towards the PN junction). submove).

Thus, the various active layers (e.g., nn+ and/or p+n junctions) located at either end of a VMJ photovoltaic cell (and as part of its cell) can be protected from detrimental forms of stress and/or strain (e.g. , thermal/mechanical stresses, torques, moments, shear forces, etc. that may be induced in the VMJ photovoltaic cell during its fabrication and/or operation). Furthermore, the buffer strip can be formed via a material (metal or semiconductor) with a substantially low-resistivity ohmic contact such that it will not contribute any substantial series resistance losses in the photovoltaic cell under operating conditions. For example, the buffer zone can be formed by employing a p-type doped low-resistivity silicon wafer such that when other p-type dopants (e.g., aluminum alloys) are used in fabricating the VMJ photovoltaic cell, it will Mitigates the risk of auto-doping (compared to using n-type wafers which can create undesired pn junctions - when the goal is to create substantially low-resistivity ohmic contacts). It should be appreciated that the present invention may be implemented as part of any type of photovoltaic cell (eg, a solar cell or a thermophotovoltaic cell). Additionally, aspects of the invention may also be implemented in other types of energy conversion cells (eg, beta voltaic cells).

In a related aspect, the buffer strip may be in the form of a rim on the surface of the terminal layer of the cell, which acts as a protective boundary for such active layers and further forms the frame of the VMJ photovoltaic cell for ease of handling and transportation. Also, by enabling a secure grip on the VMJ photovoltaic cell, such edge formations also facilitate handling associated with anti-reflective coatings (e.g., when holding the cell securely during operation (e.g., by Coating can be applied evenly when held by mechanical clamping). In addition, the buffer strips (e.g., non-active layers positioned at the ends of the VMJ photovoltaic cells) can be physically positioned adjacent to other buffer strips during deposition, and thus can be removed without damaging active cells. Any undesired dielectric coating material that inadvertently penetrates down onto the contact surface is easily removed. The buffer strips can be formed from substantially low resistivity and highly doped silicon (e.g., about 0.008" thick). Such buffer strips can then be contacted to separate a VMJ photovoltaic cell from another VMJ photovoltaic cell in a photovoltaic cell array. or separate conductive leads.

According to a further aspect, the buffer tape may be sandwiched between an electrical contact and an active layer of the VMJ photovoltaic cell. In addition, such buffer strips may have thermal expansion characteristics that generally match those of the active layer, thereby mitigating performance degradation (eg, stress/strain relief from soldering or soldering leads during fabrication). For example, a highly doped low-resistivity silicon layer matching the coefficient of thermal expansion (3x10 ⁻⁶ /° C.) of all active cells can be employed. Accordingly, substantially strong ohmic contacts may be provided to the active cell, which additionally alleviates stress problems caused by soldering/soldering and/or from mismatched coefficients of thermal expansion in the contact materials. Other examples include the introduction of metal layers such as tungsten (4.5x10 ^–6 /°C) or molybdenum (5.3x10 ^–6 /°C) due to their thermal expansion coefficient being roughly similar to that of active silicon (3x10 ^–6 /°C) p+nn+ cells And was chosen. The outer layer of the low-resistivity silicon layer applied to the buffer strip or the metal applied to the electrodes fused to the active cell can be welded or soldered without introducing detrimental stress to high-strength solar cells or photovoltaic cells Metallization of layers where such outer layers serve as ohmic contacts; rather than segments of cells in series with other cells.

Various aspects of the present invention can be implemented as part of a wafer having a Miller index (111) for the orientation of the associated crystal planes of the buffer zone, which is considered to be higher than that typically used to fabricate functional VMJ photovoltaic cells. The (100) crystalline oriented silicon is mechanically stronger and etches slower. Accordingly, the low-resistivity silicon layer may have a different crystallographic orientation than that of the active cell, wherein by employing such an alternate orientation, a device with improved mechanical strength/terminal contacts is provided. In other words, the edges of a (100) oriented cell typically etch faster and substantially trim the corners of an active cell with this crystallographic orientation compared to a non-active (111) oriented end layer, resulting in a cell with a useful A more stable device structure with higher mechanical strength for soldering or otherwise connecting end contacts.

To the accomplishment of the foregoing and related ends, certain illustrative aspects are described herein in conjunction with the following description and drawings. These aspects represent various ways in which it can be practiced, and all such aspects are intended to be covered herein. Other advantages and novel features may become apparent when the following detailed description is considered in conjunction with the accompanying drawings.

Description of drawings

Figure 1 illustrates a schematic perspective view of a textured or grooved surface as part of a vertical multi-junction VMJ photovoltaic cell according to one aspect of the invention.

Figure 2 illustrates an exemplary cross-section of a groove for use in practicing the invention.

3 illustrates an exemplary stack of cells used to form a VMJ photovoltaic cell with a grooved surface in accordance with an aspect of the invention.

Figure 4 illustrates a particular cell that partially forms a VMJ photovoltaic cell according to one aspect of the invention.

Figure 5 illustrates a related method of producing VMJ photovoltaic cells with grooved surfaces to mitigate weight loss in accordance with an aspect of the present invention.

Figure 6 illustrates a schematic block diagram of the arrangement of buffer strips as part of a vertical multi-junction VMJ photovoltaic cell according to an aspect of the invention.

Figure 7 illustrates certain aspects of cells whose arrays may form VMJ photovoltaic cells according to a certain aspect of the invention.

8 illustrates an exemplary cross-section of a buffer strip in the form of an edge formation on the surface of a cell at either end of a VMJ photovoltaic cell.

Figure 9 illustrates a related method of employing a buffer strip at the terminal layer of a high voltage silicon vertical multi-junction VMJ photovoltaic cell to provide a barrier protecting its active layer.

Figure 10 illustrates a VMJ photovoltaic cell that can be used in the electrolysis of the present invention.

Figure 11 illustrates a single cell, a plurality of which forms a VMJ photovoltaic cell for electrolysis of the present invention.

Figure 12 illustrates a VMJ photovoltaic cell with a grooved surface to improve the efficiency of the electrolytic process.

Figure 13 illustrates an exemplary grooved surface of a VMJ photovoltaic cell for electrolysis according to an aspect of the invention.

14 presents a perspective view of an embodiment of a photovoltaic cell having a textured surface according to aspects described herein.

Detailed ways

The present invention is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It may be evident, however, that the invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the present invention.

In this specification, the appended claims, or the drawings, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or". That is, "X employs A or B" is intended to mean any of the stated naturally inclusive permutations, unless otherwise specified or apparent from the context. That is, if X employs A, X employs B, or X employs both A and B, then "X employs A or B" is satisfied under any of the above instances. In addition, the articles "a" and "an" used in this specification and drawings should generally be construed to mean "one or more" unless specified otherwise or obvious from the context to refer to the singular.

In addition, the terms "n-type" and "N-type", the terms "n+-type" and " The same goes for "N+ type". For doping acceptor impurities, the terms "p-type" and "P-type" are also used interchangeably, as are the terms "p+-type" and "P+-type". For clarity, doping types are also shown in abbreviated form, for example, n-type is denoted as N, p+-type is indicated as P+, etc. Multilayer photovoltaic elements or cells are labeled with a set of letters, each of which indicates the doping type of the layer; for example, a p-type/n-type junction is labeled PN, while p+-type/n-type/n+ Type knots are indicated by P+NN+; the notation of other knot combinations also obeys this annotation.

Figure 1 illustrates a schematic perspective view of the surface of a groove 100 as part of a vertical multi-junction VMJ photovoltaic cell 120 in accordance with an aspect of the present invention. This texturing 100 arrangement enables refracted light to be directed away from the p+ and n+ diffusely doped regions while generating the desired carriers. Accordingly, incident light may be refracted in a plane 110 having a normal vector n. Such a plane 110 is parallel to the PN junction plane of the VMJ photovoltaic cell 120 and may include the cross-sectional configuration of the groove 100 . Additionally, an anti-reflective coating may be applied to the textured 100 surface to increase incident light absorption in the photovoltaic cell. In other words, the orientation of the plane 110 is substantially perpendicular to the direction of stacking the battery cells 111 , 113 , 115 . It should be appreciated that other non-perpendicular orientations (eg, crystal planes exposed at various angles) are also contemplated and all such aspects are considered within the scope of the present invention.

2 illustrates an exemplary texture used to groove the surface of the VMJ photovoltaic cell on which the VMJ photovoltaic cell receives light. Such grooving may be in the form of cavity-shaped grooves, such as, for example, "V" shaped cross-sectional configurations, "U" shaped cross-sectional configurations with various angles (e.g., 0° << 180°), etc. , wherein the plane comprising the cross-sectional configuration is substantially perpendicular to the direction in which cells forming the VMJ photovoltaic cell are stacked and/or substantially parallel to the PN junction of the VMJ photovoltaic cell. It will be appreciated that the texturing 210, 220, 230 of the VMJ photovoltaic cells of the present invention differs from prior art techniques for conventional silicon photovoltaic cell texturing in the orientation of the PN junctions and/or interaction with incident light. For example, conventional silicon photovoltaic cells are usually textured to block the penetration of light so that more of the longer wavelengths are absorbed closer to the PN junction (horizontally positioned) for better carrier current collection and thereby lessen the impact on the sun. The differential spectral response at longer wavelengths in the spectrum. In contrast, this is not required in the VMJ photovoltaic cells of the present invention which include vertical junctions and already provide enhanced spectral response to longer wavelengths in the solar spectrum.

Rather, one aspect of the grooves (e.g., V-grooves) used to practice the invention is to mitigate mass weight loss by reducing volume—(as opposed to using textured conventional solar The reflected or refracted light becomes closer to the knot). In particular, VMJ photovoltaic cells have demonstrated better carrier current collection for both short and long wavelengths, where the short wavelength response is due to the elimination of highly doped horizontal junctions at the top surface and the long wavelength response is due to the enhanced collection efficiency of the vertical junction. ) As another example, if instead of the cavity-shaped groove texture of the present invention, other textures (e.g., random, pyramidal, domed, and similar raised configurations) are implemented as part of a VMJ photovoltaic cell, then the incident light becomes direction, resulting in light absorption in the p+ and n+ diffused regions and thus reduced efficiency. It should be understood that such "U" and "V" shaped grooves are exemplary in nature and that other configurations are also within the scope of the present invention.

FIG. 3 illustrates an arrangement of battery cells 311 , 313 , 317 in which groove texture may be implemented on side 345 in accordance with an aspect of the invention. As previously explained, the VMJ photovoltaic cell 315 is itself formed from a plurality of integrally joined cells 311, 313, 317 (1 to k, where k is an integer), each cell itself being formed from stacked substrates or layers (not shown). )form. For example, each battery cell 311 may include a plurality of parallel semiconductor substrates stacked together, and is composed of an impurity-doped semiconductor material that forms a PN junction and enhances the PN junction toward such a PN junction. The minority carriers move in the "internal" electrostatic drift field. It is understood that various N+-type and P-type doped layer formations can be implemented as part of the battery cell and such arrangements are also within the scope of the present invention.

Correspondingly, the texture on the light receiving surface 345 facilitates the refracted light to be directed away from the p+ and n+ diffusely doped regions while generating the desired carriers. Accordingly, incident light may be refracted in a plane comprising the cross-sectional configuration and substantially perpendicular to the direction in which the battery cells are stacked (eg, perpendicular to vector n).

Figure 4 illustrates certain aspects of battery cells, an array of which can form a VMJ photovoltaic cell with the textured grooves of the present invention. The battery cell 400 includes layers 411 , 413 , 415 stacked together in a generally parallel arrangement. Such layers 411 , 413 , 415 may further comprise impurity-doped semiconductor material, where layer 413 is of one conductivity type and layer 411 is of the opposite conductivity type—to define a PN junction at intersection 412 . Likewise, layer 415 may be of the same conductivity type as layer 413 - additionally with a generally higher impurity concentration, thereby creating an internal electrostatic drift field that enhances minority carrier movement towards PN junction 412 . Such cells can be integrally bonded together to form VMJ photovoltaic cells and surfaces grooved according to various aspects of the invention.

According to yet another aspect, to fabricate the VMJ photovoltaic cell from multiple cells 400, initially the same PNN+ (or NPP+) junction may be formed to a high resistivity (eg, greater than 100 ohm-) to N-type (or P-type) silicon. cm) to a depth of about 3 to 10 μm in a flat wafer (having a thickness of about 0.008 inches). Subsequently, such PNN+ wafers are stacked together with thin aluminum sheets interposed between them, where the PNN+ junctions and crystallographic orientation of each wafer can be oriented in the same direction. Additionally, aluminum-silicon eutectic alloys may be used, or metals with a thermal coefficient approximately matching that of silicon, such as molybdenum or tungsten. Next, the silicon wafer and aluminum interface can be fused together so that the stacked assembly can be bonded together. Buffer strips with substantially low resistivity may also be provided in the form of a non-active layer arrangement stacked above and/or below the terminal layers of the VMJ photovoltaic cell in addition, thereby implementing protection of the active layer from harmful forms of stress and/or or strain (eg, thermal/mechanical stress, torsion, moment, shear, etc.) that may be induced in a VMJ photovoltaic cell during its fabrication and/or operation. The surface of such cells can then be grooved to mitigate weight loss, as described in detail above. It should be understood that other materials such as germanium and titanium may also be used. Likewise, aluminum-silicon eutectic alloys may also be used.

FIG. 5 illustrates a related method 500 of recessing the light-receiving surface of a VMJ photovoltaic cell. Although the exemplary method is illustrated and described herein as a series of blocks representing various events and/or actions, the disclosure is not limited by the illustrated order of such blocks. For example, some acts or events may occur in different orders and/or concurrently with other acts or events in accordance with the present invention than in the order illustrated herein. Moreover, not all illustrated blocks, events or acts may be required to implement a methodology in accordance with the invention. Furthermore, it should be appreciated that the exemplary and other methods according to the present invention may be implemented in conjunction with the methods illustrated and described herein, and may also be implemented in conjunction with other systems and devices not illustrated or described.

Initially, and at 510, a plurality of battery cells having PN junctions are formed as previously described in detail. As previously explained, each battery cell itself may comprise a plurality of parallel semiconductor substrates stacked together. Each layer may consist of an impurity-doped semiconductor material forming a PN junction, and further includes an "internal" electrostatic drift field that enhances minority carrier movement towards such a PN junction. Subsequently, and at 520, a plurality of such cells are integrated to form a VMJ photovoltaic cell, where buffer strips may also be implemented as protection for such cells (eg, stress/strain induced thereon during fabrication). Next and at 530, on the light-receiving surface of the VMJ photovoltaic cell, a cavity-shaped groove can be formed (e.g., via a dicing saw), wherein the plane comprising the cross-sectional configuration is approximately perpendicular to the stack forming the VMJ The orientation of the cells of the photovoltaic cell. Then and at 540, incident light may be refracted in a plane including the cross-sectional configuration (and/or parallel to the PN junction) and substantially perpendicular to a direction in which the battery cells are stacked.

Figure 6 illustrates a schematic block diagram of the arrangement of buffer strips as part of a vertical multi-junction VMJ photovoltaic cell according to an aspect of the invention. The VMJ photovoltaic cell 615 is itself formed from a plurality of integrally bonded cells 611 , 617 (1 to n, where n is an integer), each cell itself formed from a stacked substrate or layer (not shown). For example, each battery cell 611, 617 may include a plurality of parallel semiconductor substrates stacked together, and is composed of an impurity-doped semiconductor material that forms a PN junction and enhances the orientation toward such The "internal" electrostatic drift field for minority carrier movement of the PN junction. Accordingly, the various active layers (e.g., nn+ and/or p+n junctions, or pp+ and/or pn+ junctions) positioned at any end of the VMJ photovoltaic cell 615 (and as part of its cell) can be protected from Subjecting to detrimental forms of stress and/or strain (eg, thermal/mechanical stress, torque, moment, shear, etc. that may be induced in a VMJ photovoltaic cell during its fabrication and/or operation).

Furthermore, each of the buffer strips 610, 612 may be formed via a material having a substantially low resistivity ohmic contact (eg, any range with an upper limit of less than about 0.5 ohm-cm), while mitigating and/or eliminating Undesired auto doping. For example, the buffer strips 610, 612 can be formed by using p-type doped low-resistivity wafers using other p-type dopants (eg, aluminum alloys) to mitigate the risk of auto-doping (as opposed to using expect pn junctions compared to n-type wafers - when it is desired to create substantially low-resistivity ohmic contacts).

Figure 7 illustrates certain aspects of battery cells, an array of which may form a VMJ photovoltaic cell. Battery cell 700 includes layers 711 , 713 , 715 stacked together in a generally parallel arrangement. Such layers 711 , 713 , 715 may further comprise impurity-doped semiconductor material, where layer 713 is of one conductivity type and layer 711 is of the opposite conductivity type—to define a PN junction at intersection 712 . Likewise, layer 715 may be of the same conductivity type as layer 713 - additionally with a generally higher impurity concentration, thereby creating an internal electrostatic drift field that enhances minority carrier movement towards PN junction 712 . Such cells can be integrally bonded together to form a VMJ photovoltaic cell, wherein the buffer strips of the present invention can be positioned to protect the VMJ photovoltaic cell and the associated cells and/or layers forming it.

According to yet another aspect, to fabricate the VMJ photovoltaic cell from multiple cells 700, initially the same PNN+ (or NPP+) junction may be formed to a high resistivity (e.g., greater than 100 ohm) to N-type (or P-type) silicon -cm) to a depth of about 3 to 10 μm in a flat wafer (having a thickness of about 0.008 inches). Subsequently, such PNN+ wafers are stacked together with a thin aluminum layer inserted between each wafer, where the PNN+ junctions and crystallographic orientation of each wafer can be oriented in the same direction. Additionally, aluminum-silicon eutectic alloys may be used, or metals with a thermal coefficient approximately matching that of silicon, such as molybdenum or tungsten. Next, the silicon wafer and aluminum interface can be fused together so that the stacked assembly can be bonded together. In addition, aluminum-silicon eutectic alloys may also be used. It is understood that various N+-type and P-type doped layers may be implemented as part of the battery cell and such arrangements are also within the scope of the present invention.

Buffer strips with substantially low resistivity may also be provided in the form of a non-active layer arrangement stacked above and/or below the terminal layers of the VMJ photovoltaic cell in addition, thereby implementing protection of the active layer from harmful forms of stress and/or or strain (eg, thermal/mechanical stress, torsion, moment, shear, etc.) that may be induced in a VMJ photovoltaic cell during its fabrication and/or operation.

8 illustrates an exemplary cross-section of a buffer strip in the form of an edge formation 810 ( 812 ) on the surface of a terminal layer 831 ( 841 ) of a battery cell 830 ( 840 ), which partially forms the VMJ photovoltaic cell 800 . Such edge formations 810, 812 act as protective boundaries for the active layers of the cell, and further partially form the frame of the VMJ photovoltaic cell 800 for handling and transportation (e.g., a low-resistivity buffer strip of the VMJ photovoltaic cell and edge or end contacts). Also, by enabling a firm grip on the VMJ photovoltaic cell 800, the edge formation also facilitates handling associated with anti-reflective coatings (e.g., when the cell is held securely during operation (e.g., by Coating can be applied evenly while mechanically clamped). Furthermore, such edge formations can be physically located adjacent to other edge formations during the deposition process, where they can be easily removed without damaging the battery cells 830, 840 inadvertently penetrating down onto the contact surface. of any undesired dielectric coating material. Edge formations 810 ( 812 ) representing buffer strips can be formed from substantially low resistivity and highly doped silicon (eg, about 0.008" thick), wherein the edge formations can then contact the VMJ photovoltaic cells from the photovoltaic cell array. Conductive leads of another VMJ photovoltaic cell segment in . Furthermore, due to the generally low resistivity of the buffer strip, the conductive leads are not required to have full electrical contact with the buffer strip. Therefore, it may be a partial contact, Such as a point contact or a series of point contacts while providing good electrical contact. It should be appreciated that Figure 8 is exemplary in nature and that other variations (such as buffer strips 810 formed at the time of manufacture to the surface of 800, It is also within the scope of the invention that 810 is bonded to active layer 841. For example, the shape of 810 may represent a partial wire contact to a metallization layer on a buffer strip as previously described.

The conductive leads may be in the form of electrode layers formed by depositing a first conductive material on a substrate - and may comprise tungsten, silver, copper, titanium, chromium, cobalt, tantalum, germanium, gold, aluminum, magnesium, Manganese, indium, iron, nickel, palladium, platinum, zinc, their alloys, indium tin oxide, other conductive and semiconductive metal oxides, nitrides and silicon dioxide, polysilicon, doped amorphous silicon and various metals composition alloy. In addition, other doped or undoped conductive or semiconductive polymers, oligomers or monoliths can be used as electrodes, such as PEDOT/PSS, polyaniline, polythiophene, polypyrrole, its derivatives, and the like. In addition, non-metallic materials (eg, amorphous carbon) can also be used for electrode formation since some metals can have oxide layers formed thereon that can deleteriously affect the performance of VMJ photovoltaic cells. It should be appreciated that the edge formation of FIG. 8 is exemplary in nature and that other buffer strip configurations (e.g., rectangular, circular, cross-sectional) having extents of surface contact with the active layer are also within the scope of the present invention. .

Furthermore, various aspects of the present invention can be implemented as part of a wafer having a Miller index (111) for the orientation of the associated crystal planes of the buffer zone, which is considered to be more efficient than is typically used to fabricate functional VMJ photovoltaics. The (100) crystalline oriented silicon of the battery cell is mechanically stronger and etches slower. Accordingly, the low-resistivity silicon layer may have a different crystallographic orientation than that of the active cell, wherein by employing such an alternate orientation, a device with improved mechanical strength/terminal contacts is provided. In other words, the edges of a (100) oriented cell etch faster and substantially trim the corners of an active cell with this crystallographic orientation compared to a non-active (111) oriented end layer, resulting in an More stable device construction with higher mechanical strength for soldering or otherwise connecting end contacts.

Figure 9 illustrates a related method 900 of employing buffer strips at the terminal layers of a high voltage silicon vertical multi-junction VMJ photovoltaic cell to provide barriers protecting its active layers. Although the exemplary method is illustrated and described herein as a series of blocks representing various events and/or actions, the disclosure is not limited by the illustrated order of such blocks. For example, some acts or events may occur in different orders and/or concurrently with other acts or events in accordance with the present invention than in the order illustrated herein. Moreover, not all illustrated blocks, events or acts may be required to implement a methodology in accordance with the invention. Furthermore, it should be appreciated that the exemplary and other methods according to the present invention may be implemented in conjunction with the methods illustrated and described herein, and may also be implemented in conjunction with other systems and devices not illustrated or described. Initially, and at 910, a plurality of battery cells having PN junctions are formed as previously described in detail. As previously explained, each battery cell itself may comprise a plurality of parallel semiconductor substrates stacked together. Each layer may consist of an impurity-doped semiconductor material forming a PN junction, and further includes an "internal" electrostatic drift field that enhances minority carrier movement towards such a PN junction. Subsequently and at 920, a plurality of such cells are integrated to form a VMJ photovoltaic cell. Next and at 930, a buffer strip contacting the terminal layer of the VMJ photovoltaic cell can be implemented to provide a barrier protecting its active layer. Such buffer strips may be in the form of an arrangement of inactive layers that are additionally stacked above and/or below the terminal layers of the VMJ photovoltaic cell. The VMJ photovoltaic cell can then be implemented at 940 as part of a photovoltaic cell.

Figure 10 illustrates a VMJ photovoltaic cell that may be used in accordance with one aspect of the invention. The VMJ photovoltaic cell 1515 is itself formed from a plurality of integrally bonded cells 1511, 1517 (1 to n, where n is an integer), each cell itself formed from a stacked substrate or layer (not shown). For example, each battery cell 1511, 1517 may include a plurality of parallel semiconductor substrates stacked together, and is composed of an impurity-doped semiconductor material that forms a PN junction and enhances the orientation towards such The "internal" electrostatic drift field for minority carrier movement of the PN junction. Furthermore, by implementing one or more buffer strips 1510, 1512, various active layers (e.g., nn+ and/or p+n junctions) located at any end of the VMJ photovoltaic cell 1515 (and as part of its cell) can be protected. ) from detrimental forms of stress and/or strain (eg, thermal/mechanical stresses, torques, moments, shear forces, etc. that may be induced in a VMJ photovoltaic cell during its fabrication and/or operation). Each of such buffer strips 1510, 1512 may be formed from a material having a substantially low resistivity ohmic contact (eg, any range with an upper limit of less than about 0.5 ohm-cm), while mitigating and/or eliminating Desired auto-doping. For example, the buffer strips 1510, 1512 can be formed by using p-type doped low-resistivity wafers with other p-type dopants (eg, aluminum alloys) to mitigate the risk of autodoping (as opposed to using expect pn junctions compared to n-type wafers - when it is desired to create substantially low-resistivity ohmic contacts). For example, catalyst materials (eg, platinum, titanium, etc.) may also be employed at the terminal contacts of the VMJ photovoltaic cells to facilitate electrolytic operation. )

Figure 11 illustrates certain aspects of battery cells 1600, an array of which may form a VMJ photovoltaic cell for use in the present invention. Battery cell 1600 includes layers 1611 , 1613 , 1615 stacked together in a generally parallel arrangement. Such layers 1611 , 1613 , 1615 may further comprise impurity-doped semiconductor material, where layer 1613 is of one conductivity type and layer 1611 is of the opposite conductivity type—to define a PN junction at intersection 1612 . Likewise, layer 1615 may be of the same conductivity type as layer 1613 - additionally with a generally higher impurity concentration, thereby creating an internal electrostatic drift field that enhances minority carrier movement towards PN junction 1612 . Such cells can be monolithically joined together to form a VMJ photovoltaic cell.

According to yet another aspect, to fabricate a VMJ photovoltaic cell from multiple cells 1600, initially the same PNN+ (or NPP+) junction can be formed to a high resistivity (e.g., greater than 100 ohm-cm) to N-type (or P-type) silicon ) to a depth of about 3 to 10 μm inches in a flat wafer (having a thickness of about 0.008 inches). Subsequently, such PNN+ wafers are stacked together with a thin aluminum layer inserted between each wafer, where the PNN+ junctions and crystallographic orientation of each wafer can be oriented in the same direction. In addition, aluminum-silicon eutectic alloys may be used, or metals such as germanium and titanium, or metals such as molybdenum or tungsten, which have thermal coefficients approximately matched to silicon, may also be used. Next, the silicon wafer and aluminum alloy interfaces can be fused together so that the stacked assembly (eg, further including catalyst material) can be bonded together. It should be understood that other materials such as germanium and titanium may also be used. Likewise, aluminum-silicon eutectic alloys may also be used. It should be further appreciated that the electrolyte should be selected such that it does not deleteriously affect the operation of the VMJ photovoltaic cell, and/or cause chemical reactions that are deleterious to the VMJ photovoltaic cell. It is understood that various N+-type and P-type doped layer formations can be implemented as part of the battery cell and such arrangements are also within the scope of the present invention.

Figure 12 illustrates yet another aspect of the invention including use in VMJ photovoltaic cells with textured surfaces. Depicted is a schematic perspective view of a grooved surface 1700 as part of a vertical multi-junction VMJ photovoltaic cell 1720 in accordance with an aspect of the present invention. This texturing 1700 arrangement enables refracted light to be directed away from the p+ and n+ diffusely doped regions while generating the desired carriers. Accordingly, incident light may be refracted in a plane 1710 having a normal vector n. Such a plane 1710 is parallel to the PN junction plane of the VMJ photovoltaic cell 1720 and may include the cross-sectional configuration of the groove 1700 . In other words, the orientation of plane 1710 is substantially perpendicular to the direction of stacking battery cells 1711 , 1713 , 1715 .

Figure 13 illustrates an exemplary texture used to groove the surface of the VMJ photovoltaic cell on which it receives light for electrolysis of electrolyte. Such grooving may be in the form of cavity-shaped grooves, such as "V" shaped cross-sectional configurations, "U" shaped cross-sectional configuration, etc., wherein the plane comprising said cross-sectional configuration is substantially perpendicular to the direction in which the cells forming said VMJ photovoltaic cell are stacked, and/or substantially parallel to a PN junction of said VMJ photovoltaic cell. It will be appreciated that the texturing 1810, 1820, 1830 of the VMJ photovoltaic cells of the present invention differs from prior art techniques for conventional silicon photovoltaic cell texturing in the orientation of the PN junctions and/or interaction with incident light. For example, conventional silicon photovoltaic cells are usually textured to block the penetration of light so that more of the longer wavelengths are absorbed closer to the PN junction (horizontally positioned) for better carrier current collection and thereby lessen the impact on the sun. The differential spectral response at longer wavelengths in the spectrum. In contrast, this is not required in the VMJ photovoltaic cells of the present invention which include vertical junctions and already provide enhanced spectral response to longer wavelengths in the solar spectrum.

Rather, one aspect of the grooves (e.g., V-grooves) used to implement Figure 7 is to mitigate mass weight loss by reducing volume—(as opposed to using textured conventional solar The reflected or refracted light becomes closer to the knot). In particular, VMJ photovoltaic cells have demonstrated better carrier current collection for both short and long wavelengths, where the short wavelength response is due to the elimination of highly doped horizontal junctions at the top surface and the long wavelength response is due to the enhanced collection efficiency of the vertical junction. ) As another example, if instead of the cavity-shaped groove texture of the present invention, other textures (e.g., random, pyramidal, domed, and similar raised configurations) are implemented as part of a VMJ photovoltaic cell, then the incident light becomes direction, resulting in light absorption in the p+ and n+ diffused regions and thus reduced efficiency. In addition, a reflective coating can be applied to the backside of the VMJ photovoltaic cell to further enhance light absorption.

In another aspect, the invention relates to improving the performance of photovoltaic cells (eg, solar cells), especially high intensity solar cells (eg, edge-illuminated or vertical junction structures) that can produce substantially high power outputs at high-intensity radiation levels. Listed herein are various designs of PV elements forming cells for making VMJ photovoltaic cells to reduce recombination losses of photogenerated carriers via patterned contacts.

The VMJ photovoltaic cell has an inherent theoretical upper limit efficiency of more than 30% at 1000 suns concentration, so further performance improvements are possible using experimental understanding and insights from computer simulations and modeling analysis. While it is easy to model conventional one solar concentrator solar cells with good results using analytical equations, this is not the case for edge-illuminated VMJ photovoltaic cells operating at high intensities, where even second-order effects can affect the cell Operational efficiency has a real impact. Although aspects or features of the invention are illustrated in connection with solar cells, such aspects or features and associated advantages can be utilized in other photovoltaic cells (e.g., thermal photovoltaic cells or cells excited by a laser source of photons) (e.g., Carrier recombination loss reduction). Furthermore, aspects of the invention may also be implemented in other types of energy conversion cells (eg, beta voltaic cells).

The physics of electron-hole carrier pairs generated in solar cells at high intensities is quite complex, as many physical parameters come into play, including but not limited to: surface recombination velocity, carrier mobility and concentration, emitter (e.g. , diffusion) reverse saturation current, minority carrier lifetime, bandgap narrowing, built-in electrostatic field and various recombination mechanisms. Mobility decreases rapidly with increasing carrier density, and Auger recombination rapidly increases with intensity as the cube of carrier density. To incorporate such aspects into the modeling of VMJ solar cell performance, computer simulations (e.g., two-dimensional numerical calculation analysis of photogenerated carrier transport in semiconductors) can provide insights into operating at or at high intensities. Insights on the physical parameters of vertical junction cells or PV elements. Such simulations provide analysis and design tools to understand possible sources of performance efficiency and improve the performance of VMJ photovoltaic cells at high intensities. It should be appreciated that while it is easy to model conventional one solar concentrator solar cells with good results using simple analytical equations, this is not the case for edge-illuminated VMJ photovoltaic cells operating at high irradiance intensities, since at high intensities even Second order effects can also have a strong impact on cell operating efficiency.

Computational simulations based on a model of a contact-to-contact VMJ photovoltaic cell incorporating an array of semiconductor physical elements revealed several specific regions in the VMJ photovoltaic cell where recombination loss of photogenerated carriers occurs at high intensities. At least some of such regions exhibit complex loss mechanisms that depend on intensity. Computational simulations revealed several regions in a PV element or VMJ photovoltaic cell that could be improved to reduce recombination loss and improve the performance of the VMJ photovoltaic cell. Aspects of the invention provide such improvements.

Series resistance has been recognized as an important source of design problems for conventional concentrator solar cells. The VMJ photovoltaic cell design proved more than adequate in this regard, showing that series resistance was not a problem even at a concentration of 2500 suns. In some cases, however, it may be advantageous to trade an increase in series resistance for a minor design simplicity to improve the efficiency of the VMJ photovoltaic cells of the photovoltaic concentrator operating at close to 1000 suns concentration.

It will be appreciated that designing for operation at substantially higher intensities (e.g., 2500 suns concentrating at which VMJ photovoltaic cells can still operate efficiently) may require substantially more demanding and expensive Aggregator systems are engineered without the potential to contribute any better overall performance or economics. Thus, aspects or features of solar cells recited in this disclosure and associated processes for their production can improve the efficiency performance of high intensity VMJ photovoltaic cells operating in the 1000 sun concentration range or higher. Efficiency improvements may make VMJ solar cells or other solar cells utilizing aspects of the present invention more cost efficient and feasible, even though their intensity for greater than 1000 sun concentration may involve additional fabrication and a potential increase in series resistance. Aspects or features described herein may provide sufficient engineering design trade-offs to make photovoltaic concentrator systems using solar cells, VMJ photovoltaic cells, or otherwise utilizing aspects of the invention more feasible and cost-effective while providing lower $/watt performance .

In silico for conventional VMJ photovoltaic cell designs (e.g. P+NN+ sheets with deep junctions) using realistic parameters for good silicon processing (minority-carrier lifetime, surface recombination velocity, etc.) at intensities greater than 500 suns Modeling analysis revealed the following percentage recombination losses for some specific regions:

Thus, this analysis shows that the heavily doped P+ and N+ diffused emitter regions whose metal contacts account for more than half of all recombination losses in cells forming VMJ solar cells, and that optimized diffused N+ emitters can differ in design from Optimal diffused P+ emitter (partially due to differences in mobility). The relative magnitude of recombination losses from the N+ and P+ regions can be switched for N+PP+ cells or P+NN+ cells (with shallow P+N junctions). In one aspect, the present invention is directed to reducing recombination losses in the aforementioned diffusion regions to improve the performance of VMJ photovoltaic cells.

High minority-carrier lifetime and low surface recombination velocity have been successfully achieved in conventional VMJ photovoltaic cell development with open circuit voltage V _oc =0.8 volts per cell junction at high strength. V _oc is determined by the current generated by sunlight and the diffuse emitter reverse saturation current (J _o ), where both P+N and NN+ junctions present in the cell of a VMJ solar cell contribute to the open circuit voltage. The best junction from the TV point is the lowest J _o ; using J _o =1x10 ^–13 Acm ^–2 , which represents a high quality low reverse saturation current in a diffused junction, analysis shows that a diffusion depth of about 3 to 10 μm is optimal for P+ and N+ diffusion, even when considering the infinite recombination velocity at the ohmic metal contacts.

It should be noted that computer simulations reveal NN+ junction enhancement at high becomes less effective at lower intensities, which can lead to higher recombination in the N+ region as shown above.

14 presents a perspective view of an example embodiment of a textured vertical multi-junction VMJ photovoltaic cell 2405 having a textured surface and formed by stacking the cells 2410 ₁ through 2410 ₁₀ in a direction normal to the plane of the cells; A battery cell 2410κ (where κ = 1, 2, . . . 10) is constructed of PV elements with patterned dielectric coatings and metal contacts, as described herein. Although a group of 10 cells is illustrated in the example textured PV cell 2405, note that a textured VMJ photovoltaic cell may contain M cells, where M is a positive integer. Cells in a textured VMJ photovoltaic cell (eg, 2410 _κ ) can be embodied in cells 2070λ, 2180λ, or 2350, or any other cell produced as described herein. In photovoltaic cell 2405, textured surface 2412 is a V-groove surface; however, other various shapes of grooves or cavities may be formed, such as U-grooves. The textured surface is formed onto a plane (qrs) exposed or substantially exposed to electromagnetic radiation from processing a monolithic stack of battery cells or PV elements having patterned metal contacts as described herein; see, for example, FIG. 20D. Incident light may be refracted in a plane 2430 having a normal vector n2432. Such a plane 2430 is parallel to the surface of the battery cells _2410K on which the patterned dielectric material is coated, and may include the cross-sectional configuration of the grooves 2415—the plane 2430 is generally perpendicular to the direction of stacking the battery cells 2410K. The texturing of the surface of the monolithic stack of cells 2410κ (which results in the textured surface 2412) enables refracted light to be directed away from the P+ and N+ diffusely doped regions without impeding the photogeneration of carriers, effectively making the composition textured photovoltaic The battery cells of battery 2405 are made thinner and reduce recombination losses as indicated previously. Additionally, an anti-reflective coating can be applied to the textured surface 2410 to increase the absorption of incident light in the cell.

What has been described above includes examples of systems and methods that provide the advantages of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one skilled in the art can recognize that claimed subject matter is possible in many other combinations and permutations. Furthermore, to the extent that the terms "includes", "has", "possesses" and the like are used in this detailed description, claims, appendices, and drawings, such terms are intended to be included in a manner similar to The term "comprising" is to be construed when it is used as a transition word in the claims.

Claims (20)

1. photovoltaic cell is characterized in that comprising:

Vertical many knot VMJ photovoltaic cells, it comprises a plurality of whole battery unit that engages that piles up along stacking direction; And

The texturizing surfaces that is used for light-receiving of described VMJ photovoltaic cell, described texturizing surfaces are used for alleviating the body weight group loss of described VMJ photovoltaic cell.

2. photovoltaic cell according to claim 1 is characterized in that described stacking direction is approximately perpendicular to transversal described texturizing surfaces to produce the plane of the cross sectional pattern that roughly repeats.

3. photovoltaic cell according to claim 2, it is characterized in that the described cross sectional pattern that roughly repeats the plane its formed by the chamber connected in star.

4. photovoltaic cell according to claim 3 is characterized in that described chamber connected in star comprises V-arrangement cross-sectional configuration or U-shaped cross-section configuration at least.

5. photovoltaic cell according to claim 3 is characterized in that described each photovoltaic cell itself comprises a plurality of parallel Semiconductor substrate or the layer that is stacked.

6. photovoltaic cell according to claim 5 is characterized in that described each substrate or layer are made of the impurity doped semiconductor material that forms PN junction.

7. photovoltaic cell according to claim 6 is characterized in that described substrate comprises that further promotion is towards " Inner portion " electrostatic dispersion field that the minority carrier of described PN junction moves.

8. photovoltaic cell according to claim 7 is characterized in that described substrate has various rear surfaces and the side surface of reflectance coating.

9. photovoltaic cell according to claim 4 is characterized in that described V-arrangement cross-sectional configuration roughly is confined in the tagma of p+nn+ battery unit to increase the optical absorption path of longer wavelength in the solar spectrum.

10. photovoltaic cell according to claim 9; it is characterized in that the form supply that the non-active layer of the described terminal layer top that is stacked in described VMJ photovoltaic cell and/or below is arranged has the roughly buffer strip of low-resistivity, thereby implement stress and/or strain that the protective effect layer is avoided harmful form.

11. a photovoltaic cell manufacture method is characterized in that comprising:

Integrally engage a plurality of active layers to form the VMJ photovoltaic cell; And

Alleviate bulk diffusion in the described VMJ photovoltaic cell via the texturizing surfaces of the reception incident light of described VMJ photovoltaic cell.

12. photovoltaic cell manufacture method according to claim 11 is characterized in that further comprising described incident light is reflected in the plane of the PN junction that is parallel to described VMJ photovoltaic cell.

13. photovoltaic cell manufacture method according to claim 11 is characterized in that further promoting refract light is guided p+ and the n+ diffusing, doping district of leaving the VMJ photovoltaic cell.

14. photovoltaic cell manufacture method according to claim 11 is characterized in that further comprising described incident light is reflected in the plane of the PN junction that is parallel to described VMJ photovoltaic cell.

15. photovoltaic cell manufacture method according to claim 11 is characterized in that integrally engaging a plurality of active layers and further comprises the photovoltaic cell unit that is stacked.

16. photovoltaic cell manufacture method according to claim 15 is characterized in that silicon wafer and aluminium interface are fused together to form the VMJ photovoltaic cell.

17. photovoltaic cell manufacture method according to claim 15 is characterized in that further comprising that each active layer can be made of the impurity doped semiconductor material that forms PN junction.

18. photovoltaic cell manufacture method according to claim 15 is characterized in that further comprising chamber connected in star Zuo Wei Pattern physics and chemistry surface.

19. photovoltaic cell manufacture method according to claim 15 is characterized in that further comprising above the terminal layer that is stacked in described VMJ photovoltaic cell and/or the form supply of the non-active layer layout of below has the roughly buffer strip of low-resistivity.

20. a photovoltaic cell is characterized in that comprising:

Be used for to strengthen the member to the spectral response of wavelength of photovoltaic cell; And

Member for the body weight group loss that alleviates described photovoltaic cell.

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