TW201308630A - Thick film paste containing bismuth-tellurium-oxide and its use in the manufacture of semiconductor devices - Google Patents

Abstract

The present invention is directed to an electroconductive thick film paste composition comprising electrically conductive Ag, a second electrically conductive metal selected from the group consisting of Ni, Al and mixtures thereof and a Pb-free bismuth-tellurium-oxide all dispersed in an organic medium. The present invention is further directed to an electrode formed from the thick film paste composition and a semiconductor device and, in particular, a solar cell comprising such an electrode.

Description

Thick film paste containing bismuth-tellurium-oxide and its use in the manufacture of semiconductor devices

The present invention is primarily directed to a thick film paste composition and a thick film electrode formed from the composition. It is further related to a semiconductor device, and more particularly to a conductive composition for forming a thick film electrode of a solar cell.

Although the present invention is particularly effective for light-receiving elements such as photodiodes and solar cells, the present invention is applicable to a wide-area semiconductor device. The background of the invention relating to a solar cell as a specific example of the prior art is described below.

A conventional solar cell structure having a p-type base has a negative electrode typically located on the front side or the sun side of the cell and a positive electrode on the back side. A radiation system that falls on the p-n junction of the semiconductor body and has a suitable wavelength serves as an external source of energy to create a hole-electron pair in the body. Due to the potential difference on the p-n junction, the holes and electrons move across the junction in opposite directions, thereby causing a current flow that can deliver power to an external circuit. Most solar cells are in the form of metallized, that is, tantalum wafers with conductive metal electrodes. A typical thick film paste is screen printed onto a substrate and fired to form an electrode.

An example of such a manufacturing method is described below with reference to Figures 1A through 1F.

FIG. 1A shows a single crystal or polycrystalline p-type tantalum substrate 10.

In FIG. 1B, the opposite conductivity type n-type diffusion layer 20 is formed using phosphorus oxychloride as a phosphorus source and thermally diffused by phosphorus. Formed over the entire surface of the p-type substrate 10 without any specific modification Diffusion layer 20. The depth of the diffusion layer can be varied by controlling the diffusion temperature and time, and typically forms a thickness range of about 0.3 to 0.5 microns. The n-type diffusion layer may have a sheet resistivity of from about 10 ohms per square to about 120 ohms per square.

As shown in FIG. 1C, after the front side of the diffusion layer is protected by a photoresist or the like, the diffusion layer 20 is removed from the remaining surface by etching so that the diffusion layer 20 remains only on the front surface. Next, the photoresist is removed using an organic solvent or the like.

Thereafter, as shown in FIG. 1D, an insulating layer 30 which also acts as an anti-reflection coating is formed on the n-type diffusion layer 20. The insulating layer is usually tantalum nitride, but may also be a SiN _x :H film (that is, the insulating film contains hydrogen for passivation during the subsequent firing process), a titanium oxide film, a hafnium oxide film or a hafnium oxide/titanium oxide. film. A tantalum nitride film having a thickness of about 700 to 900 Å is suitable for a refractive index of about 1.9 to 2.0. The deposition of the insulating layer 30 can be by sputtering, chemical vapor deposition, or other methods.

Next, an electrode is formed. As shown in FIG. 1E, the silver paste 500 for the front electrode is screen printed on the tantalum nitride film 30, followed by drying. Further, the back side silver or silver/aluminum paste 70 and the aluminum paste 60 are then screen-printed to the back side of the substrate, followed by drying. The firing from a few seconds to several tens of minutes is continuously carried out in an infrared oven at a temperature range of approximately 750 to 850 °C.

As a result, as shown in FIG. 1F, during firing, aluminum diffuses from the aluminum paste 60 onto the tantalum substrate 10 on the back side, thereby forming a p+ layer 40 containing a high concentration of aluminum dopant. This layer is often referred to as a back surface field (BSF) layer and it helps to improve the energy conversion efficiency of the solar cell.

The dry aluminum paste 60 is converted into an aluminum back electrode 61 by firing. The back side silver or silver/aluminum paste 70 is simultaneously fired to become a silver or silver/aluminum back electrode 71. During firing, the boundary between the backside aluminum and the backside silver or silver/aluminum exhibits an alloyed state, thereby achieving electrical connection. Most of the area of the back electrode is occupied by the aluminum electrode 61, in part because of the formation of the p+ layer 40. Since it is impossible to solder to an aluminum electrode, silver or silver/aluminum back electrode 71 is formed over the back side of the portion as an electrode for interconnecting solar cells via a copper strip or the like. In addition, the front side silver paste 500 is sintered and penetrates the tantalum nitride film 30 during firing to achieve electrical contact with the n-type layer 20. This type of program is often referred to as "burn through." The fired electrode 501 of Figure 1F clearly shows the result of burn through.

Efforts continue to provide thick film paste compositions with reduced silver and lead-free, while still retaining the electrical properties and other related properties of the resulting electrodes and devices. The present invention provides a silver paste composition while providing a lead-free system with a relatively small amount of silver while still retaining electrical and mechanical properties.

The present invention provides a thick film paste composition comprising: (a) 25 to 55 weight percent of conductive silver; (b) 5 to 35 weight percent of a second conductive metal selected from the group consisting of nickel, aluminum, and mixtures thereof a group formed; (c) 0.5 to 5 weight percent of lead-free bismuth-tellurium-oxide; and (d) an organic medium; wherein the conductive silver, the second conductive metal, and the bismuth-tellurium-oxide system Dispersed in the organic medium, and wherein the weight percentage is based on the total weight of the paste composition; the bismuth-tellurium-oxide comprises 22 to 42 weights based on the total weight of the bismuth-tellurium-oxide Percentage of Bi ₂ O ₃ and 58 to 78 weight percent of TeO ₂ .

The present invention also provides a semiconductor device, particularly a solar cell, comprising an electrode formed from the composition of the paste, wherein the paste composition has been fired to remove the organic medium and form the electrode.

The conductive thick film paste composition of the present invention contains a reduced amount of conductive silver, but at the same time provides the ability to form an electrode from the paste, wherein the electrode has good electrical and bonding properties.

The conductive thick film paste composition comprises conductive silver; a second conductive metal selected from the group consisting of nickel, aluminum and mixtures thereof; a lead-free bismuth-tellurium-oxide; and an organic vehicle. It is used to form a screen printing electrode. In various embodiments, it is used to form electrodes on semiconductor devices, particularly on solar cells. In this type of embodiment, it is used to form the marker electrode on the back side of the tantalum substrate of the solar cell. The paste composition comprises 25 to 55 weight percent of conductive silver; 5 to 35 weight percent of a second conductive metal selected from the group consisting of nickel, aluminum, and mixtures thereof; 0.5 to 5 weight percent of bismuth - a cerium-oxide; and an organic medium, wherein the silver, the second conductive metal, and the cerium-lanthanum-oxide are all dispersed in the organic medium, and wherein the weight percentage is based on the total weight of the paste composition basis.

Each component of the thick film paste composition of the present invention is explained in detail below.

silver

In the present invention, one of the conductive phases of the paste is silver (Ag). The silver may be in the form of a silver metal, a silver alloy or a mixture thereof. Typically, in silver powder, the silver particles are in the form of flakes, spheres, granules, crystals, other irregularities, and mixtures thereof. Silver can be provided in a colloidal suspension. The silver may also be in the form of silver oxide (Ag ₂ O), a silver salt such as AgCl, AgNO ₃ , AgOOCCH ₃ (silver acetate), AgOOCF ₃ (silver trifluoroacetate), silver orthophosphate (Ag ₃ PO ₄ ) or Its mixture. Other forms of silver that are compatible with other thick film paste ingredients can also be used.

In one embodiment, the thick film paste composition comprises coated conductive silver particles. Suitable coatings include phosphorus and surfactants. Suitable surfactants include polyethylene oxide, polyethylene glycol, benzotriazole, poly(ethylene glycol) acetic acid, lauric acid, oleic acid, citric acid, myristic acid, linoleic acid, hard Fatty acid, palmitic acid, stearate, palmitate and mixtures thereof. The salt relative ions can be ammonium, sodium, potassium, and mixtures thereof.

The particle size of silver is not subject to any particular restrictions. In one embodiment, an average particle size is less than 10 microns; in another embodiment, the average particle size is less than 5 microns.

Because of the cost, it is advantageous to reduce the amount of silver in the paste while retaining the properties required for the paste and the electrodes formed from the paste. In addition, the present thick film paste enables the formation of electrodes having reduced thickness and leads to further savings.

Second conductive metal

One of the second conductive phases of the paste is a metal selected from the group consisting of nickel (Ni), aluminum (Al), and mixtures thereof. The mixture can be in the form of an alloy.

Nickel and aluminum powders contain particles of various shapes, for example, sheet form, spherical form, granular form, crystalline form, other irregular forms, and mixtures thereof. The particle sizes of nickel and aluminum are not subject to any particular limitation. In one embodiment, an average particle size is less than 10 microns; in another embodiment, the average particle size is less than 5 microns.

In one embodiment, the thick film paste composition comprises coated conductive nickel and/or aluminum particles. Suitable coatings include phosphorus and surfactants. Suitable surfactants include polyethylene oxide, polyethylene glycol, benzotriazole, poly(ethylene glycol) acetic acid, lauric acid, oleic acid, citric acid, myristic acid, linoleic acid, hard Fatty acid, palmitic acid, stearate, palmitate and mixtures thereof. The salt relative ions can be ammonium, sodium, potassium, and mixtures thereof.

铋-碲-oxide

One component of the paste composition is lead-free bismuth-tellurium-oxide (Bi-Te-O). In one embodiment, the oxide can be a glass composition, such as a glass. In another embodiment, the oxide can be crystalline, partially crystalline, amorphous, partially amorphous, or a combination thereof. In an embodiment, Bi-Te-O may comprise more than one glass composition. In one embodiment, the Bi-Te-O composition can include a glass composition and an additional composition (eg, a crystalline composition).

Bi-Te-O may be Bi ₂ O ₃ , TeO ₂ and other oxides to be incorporated therein by using techniques known to those skilled in the art (or when heated) Prepared by mixing with other materials that will decompose into the desired oxide. Such preparation techniques can include heating the mixture in air or an oxygen-containing atmosphere to form a melt; quenching the melt; and grinding, honing, and/or screening the quenched material to provide a A powder of required particle size. The mixture of ruthenium, osmium and other oxides to be incorporated therein is typically subjected to a peak temperature of from 800 to 1200 °C. The molten mixture can be quenched, for example, on a stainless steel platen or a stainless steel roll rotating in the opposite direction to form a thin plate. The resulting sheet can be milled to form a powder. Typically, the milled powder having a d ₅₀ of 0.1 to 3.0 microns. One skilled in the art of making glass can utilize alternative synthetic techniques (such as, but not limited to, water quenching, sol-gel, spray pyrolysis, or other techniques suitable for making glass in powder form).

The oxide product of the above procedure is typically substantially an amorphous (no crystalline) solid material, i.e., glass. However, in some embodiments, the resulting oxide can be amorphous, partially amorphous, partially crystalline, crystalline, or a combination thereof. As used herein, "glass" includes all such products.

The starting mixture used to make Bi-Te-O comprises 22 to 42 weight percent Bi ₂ O ₃ and 58 to 78 weight percent TeO ₂ based on the total weight of the starting mixture of Bi-Te-O.

In another embodiment, in addition to Bi ₂ O ₃ and TeO ₂ , the starting mixture used to make Bi-Te-O comprises 0.1 to 7 based on the total weight of the starting mixture of Bi-Te-O. Percent by weight of Li ₂ O and 0.1 to 4 weight percent of TiO ₂ . In a still further embodiment, the starting mixture comprises from 0.1 to 8 weight percent B ₂ O ₃ , from 0.1 to 3 weight percent ZnO and 0.3 based on the total weight of the initial mixture of Bi-Te-O. Up to 2% by weight of P ₂ O ₅ .

In another embodiment, the starting mixture used to make the Bi-Te-O comprises 0.9 to 5, based on the total weight of the starting mixture of Bi-Te-O, in addition to Bi ₂ O ₃ and TeO ₂ . Li ₂ O by weight and 0.3 to 2 weight percent of TiO ₂ . In yet another embodiment, the starting mixture comprises 0.9 to 6 weight percent B ₂ O ₃ , 0.1 to 2 weight percent ZnO, and 0.3, based on the total weight of the starting mixture of Bi-Te-O. Up to 1% by weight of P ₂ O ₅ .

In one embodiment, Bi-Te-O can be a homogeneous powder. In another embodiment, Bi-Te-O can be a combination of more than one powder, wherein each powder can be a homogeneous population, respectively. The composition of the overall combination of the two powders is within the above range. For example, Bi-Te-O may comprise a combination of two or more different powders; these powders may each have different compositions and may or may not be within the above ranges; however, combinations of these powders may be within the above ranges.

In one embodiment, the Bi-Te-O composition can include a powder comprising a homogeneous powder comprising some but not all of the desired elements of the Bi-Te-O composition; and a second powder comprising the other One or more of the required elements. For example, the Bi-Te-O composition further comprising Li and Ti may include a first powder including Bi, Te, Li, and O; and a second powder including TiO ₂ . In one embodiment of this embodiment, the powders may be co-melted to form a uniform composition. In a further embodiment of this embodiment, the powders can be separately added to a thick film composition.

In one embodiment, some or all of any Li ₂ O may be substituted with Na ₂ O, K ₂ O, Cs ₂ O, or Rb ₂ O, resulting in a glass composition having properties similar to those listed above. .

The glass composition (also known as glass) described herein includes a specific percentage of ingredients. In particular, the percentage is the percentage of the ingredients used in the starting materials used to form a glass composition as described herein. Such nomenclature has long been known to those skilled in the art. In other words, the composition contains some ingredients, and the percentage of those ingredients is expressed as a percentage of the corresponding oxide form. As is known to those of ordinary skill in the art of glass chemistry, a certain portion of the volatile species may be released during the glass manufacturing process. An example of a volatile species is oxygen. It is also important to understand that although glass behaves like an amorphous material, it may contain traces of crystalline material.

If starting with fired glass, one of ordinary skill in the art can calculate the percentage of the starting ingredients described herein using a method known to those skilled in the art, including, but not limited to: Inductively Coupled Plasma Emission Spectrometer (ICPES), Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) and the like. In addition, the following exemplary techniques can be used: X-ray fluorescence spectroscopy (XRF); nuclear magnetic resonance spectroscopy (NMR); electron paramagnetic resonance spectroscopy (EPR); Mössbauer spectroscopy; Probe Energy Dispersion Spectroscopy (EDS); Electron Microprobe Wavelength Dispersion Spectroscopy (WDS); Cathodoluminescence (CL).

Those of ordinary skill in the art will appreciate that the choice of materials can unintentionally include impurities that can be incorporated into the glass during processing. For example, impurities may exist in the range of hundreds to thousands of ppm.

The presence of impurities will not alter the properties of the glass, thick film composition or firing device. For example, even if the thick film composition includes impurities, a solar cell containing the thick film composition can still have the efficiencies described herein.

The content of Bi-Te-O in the present thick film paste composition is typically from 0.5 to 5 weight percent based on the total weight of the thick film paste composition. In one embodiment, the amount is from 1 to 3.5 weight percent. Bi-Te-O is an essential component of the cream composition, but can also play an important role as one of the other thick film formulations.

Organic medium

The inorganic component of the thick film paste composition is mixed with an organic medium to form a viscous paste having a suitable consistency and rheology for printing. A variety of inert viscous materials can be used as organic media. The organic medium can be one in which the inorganic component can be suitably stabilized during manufacture, transport and storage of the paste and during the screen printing process on the printing screen.

Suitable organic media are provided with rheological properties which provide stable solid dispersion, viscosity and texturization suitable for screen printing, proper substrate and paste solid wettability, an excellent drying rate, and excellent firing properties. The organic medium can include thickeners, stabilizers, surfactants, and/or other common additives. This type of shake densifying thickener is an organic shake aid (thixatrol). The organic medium can be a solution in which a polymer is dissolved in a solvent. Suitable polymers include ethyl cellulose, ethyl hydroxyethyl cellulose, wood rosin, mixtures of ethyl cellulose and phenolic resins, polymethacrylates of lower alcohols, and mono-glycols of ethylene glycol monoacetate. ether. Suitable solvents include terpenes, for example, alpha- or beta-rosinol or other solvents (eg, kerosene, dibutyl phthalate, butyl carbitol, butyl) A mixture of carbitol acetate, hexanediol and an alcohol having a boiling point above 150 ° C and an alcohol ester. Other suitable organic media components include: bis(2-(2-butoxyethoxy)adipate ethyl ester, dibasic esters (eg DBE, DBE-2, DBE-3, DBE-4, DBE-5) , DBE-6, DBE-9 and DBE 1B), octyl epoxy tallate, isotetradecanol and hydrogenated rosin pentaerythritol ester. The organic medium may also contain volatile liquids to The thick film paste composition is applied to the substrate to promote rapid hardening.

The optimum amount of organic medium in the thick film paste composition is related to the method of applying the paste and the particular organic medium used. The thick film paste composition contains more than 30 and less than 60 weight percent of the organic medium based on the total weight of the paste composition.

If the organic medium comprises a polymer, the polymer typically comprises from 8 to 15 weight percent of the organic composition.

Inorganic additive

The Bi-Ti-O used in the composition of the present invention provides adhesion. However, an inorganic adhesion promoter can be added to increase the adhesion characteristics. The inorganic additive may be selected from the group consisting of Bi ₂ O ₃ , TiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , SnO ₂ , Sb ₂ O ₅ , Cr ₂ O ₃ , Fe ₂ O ₃ , ZnO. , CuO, Cu ₂ O, MnO ₂ , Co ₂ O ₃ , NiO, RuO ₂ , a metal which produces the listed metal oxide during firing, and which produces the listed metal oxide during firing Metal compounds and mixtures thereof. Additives help increase adhesion without affecting electrical properties and tortuosity.

The inorganic additive has an average diameter in the range of 0.5 to 10.0 μm, or, when the additive is in the form of an organometallic compound, the average diameter thereof is dispersed to the molecular level. Based on the total weight of the paste composition The amount of the additive to be added to the paste composition is 0.5 to 5 weight percent.

Preparation of thick film paste composition

In one embodiment, the thick film paste composition can be prepared by mixing conductive silver powder, second conductive metal powder, Bi-Te-O powder, and an organic medium with any inorganic additive in any order. In certain embodiments, the inorganic materials are first mixed and then added to the organic medium. In other embodiments, the silver powder and the second conductive metal powder, which are a major portion of the inorganic material, are slowly added to the organic medium. The viscosity can be adjusted by adding a solvent as needed. A mixing method that provides high shear force can be used.

The thick film paste composition comprises 25 to 55 weight percent of conductive silver and 5 to 35 weight percent of the second conductive metal based on the total weight of the paste composition. In one embodiment, the thick film paste composition comprises 36 to 48 weight percent conductive silver and 12 to 24 weight percent second conductive metal. In still another embodiment, the thick film paste composition comprises 36 to 42 weight percent conductive silver and 18 to 24 weight percent second conductive metal. The thick film paste contains less than 70% by weight of inorganic components, that is, conductive silver powder, second conductive metal powder, Bi-Te-O powder, and any inorganic additive, based on the total weight of the paste composition.

The thick film paste composition can be deposited by screen printing, electroplating, extrusion molding, ink jet, shaping or multiple printing or color ribbons.

In this electrode forming process, the thick film paste composition is first dried. The dried paste typically has a thickness of about 10 to 14 μm. The dried paste is then heated to remove the organic medium and the sintered inorganic material. This heated The process can be carried out in air or an oxygen-containing atmosphere. This step is often referred to as "burning." The firing temperature profile is typically set to enable the organic binder material to be destroyed from the dried thick film paste composition and any other organic materials contained therein. In one embodiment, the firing temperature is 750 to 950 °C. The firing process can be carried out in a belt furnace using a high delivery rate (e.g., 100-500 cm/min), and the resulting residence time is 0.05 to 5 minutes. Multiple temperature zones (eg, 3 to 11 zones) can be used to control the desired thermal profile.

An example of preparing a solar cell using the paste composition of the present invention is explained with reference to Figs. 2A to 2D.

First, a tantalum substrate 102 having a diffusion layer and an anti-reflective coating is prepared. As shown in Fig. 2A, an electrode 104 mainly composed of silver is mounted on the light-receiving front side (surface) of the ruthenium substrate. As shown in Figure 2B, an aluminum paste (e.g., PV333, PV322 (commercially available from DuPont Co., Wilmington, DE)) is applied by screen printing on the back side of the substrate followed by drying 106. As shown in Fig. 2C, the paste composition of the present invention is then coated with the dried aluminum paste in a partially overlapping state, followed by drying 108. The drying temperature of each paste is preferably 150 ° C or lower. Likewise, the overlap of the aluminum paste and the paste of the present invention is preferably from about 0.5 to 2.5 mm.

Next, as shown in Fig. 2D, the substrate is continuously fired at a temperature of 700 to 950 ° C for 1 to 15 minutes to obtain a desired solar cell. The electrode 112 is formed from the paste composition of the present invention, wherein the composition has been fired to remove the organic medium and the sintered inorganic material. The resulting solar cell has an electrode 104 on the light-receiving front side of the substrate 102, and has an aluminum electrode 110 mainly composed of aluminum on the back surface and a fired one. An electrode 112 composed of the inventive paste composition. The electrode 112 acts as a marker electrode on the back side of the solar cell.

Instance Example 1

Preparation of bismuth-tellurium-oxide

A bismuth-tellurium-oxide (Bi-Te-O) composition is prepared by mixing and blending Bi ₂ O ₃ , TeO ₂ , Li ₂ CO ₃ , TiO ₂ , B ₂ O ₃ , BPO ₄ (or LiPO ₃ ) and ZnO powder to obtain a Bi-Te-O composition comprising 26.64% by weight of Bi ₂ O ₃ , 67.22% by weight of TeO ₂ , 2.16% by weight of LiO ₂ , 0.48% by weight of TiO ₂ , and 2.09 by weight Percentage of B ₂ O ₃ , 0.98 weight percent ZnO, and 0.43 weight percent P ₂ O ₅ . The blended powder batch was loaded into a platinum alloy crucible, then inserted into a furnace and continuously heated at 900 ° C in air or O ₂ for one hour to melt the mixture. The liquid melt was quenched from 900 ° C by removing the platinum crucible from the furnace and rotating the melt through a stainless steel roll having a gap of 0.010 to 0.020" in the opposite direction. The resulting material was coarsely crushed in a stainless steel vessel. The ground material is then ball milled in a zirconia medium and water in an alumina-silicate ceramic ball mill until the d ₅₀ is 0.5 to 0.7 microns. The ball milled material is then separated from the mill balls, wet sieved and hot air The oven was allowed to dry. The dried powder was passed through a 200 mesh screen to provide a Bi-Te-O powder for use in the preparation of the thick film paste described below. X-ray analysis of the powder revealed amorphous material Characterization. The material was characterized by thermomechanical analysis (TMA) and showed particle sintering started at 320 ° C and converted to a complete viscous flow at 353 ° C. The liquidus used for the composition appeared close to 511 °C (between 320 °C and 511 °C, some of the crystalline phase can be formed briefly and re-dissolved in the region between the start of sintering and the liquidus temperature).

Preparation of thick film paste composition

The thick film paste was prepared by mixing silver, nickel, Bi-Te-O powder prepared in Example 1 above, an organic medium, an organic shaking aid, and an adhesion promoter. Adding Ag, Ni, Bi-Te- O , and adhesion promoting agent to the organic medium and ^{Thixatrol ® (Elementis Specialities, Inc.,} Hightstown, NJ), accompanied by continuous stirring. Since silver and nickel are the major components of the solid, they must be added slowly to ensure better wetting. The paste was then passed through a three-roll mill several times with a 1 mil gap. The dispersion is measured by abrasive fineness (FOG) to ensure that the FOG is less than or equal to 20/10.

The proportion of the ingredients used in this example was 54 weight percent silver, 6 weight percent nickel, 2 weight percent Bi-Te-O, 35.25 weight percent organic media, 0.75 weight percent organic rocking aid, and 2.0. A weight percent inorganic adhesion promoter consisting of 1.0 weight percent ZnO, 0.6 weight percent Bi ₂ O _{3 ,} and 0.4 weight percent copper.

Test electrode

In order to determine the adhesive properties of the electrode formed from the paste composition, the paste composition is screen printed onto the surface of the tantalum wafer in the form of an electrode. The paste is then dried and fired in an oven.

Test procedure - adhesion

After firing, the solder strip is soldered to the fired paste. Since the present invention contains only lead-free Bi-Te-O, 无 uses lead-free solder. The lead-free solder used was 96.5 tin/3.5 silver. The soldering temperature for lead-free solder is in the range of 345 to 375 ° C and the soldering time is 5 to 7 seconds. The flux used was MF200.

The welding area is close to 2 mm × 2 mm. The bond strength is obtained by pulling the solder ribbon to the surface of the battery at an angle of 90°. The evaluation of the bond strength is specified on the assumption that the bond strength of 2.5 N or higher is good.

The adhesion was measured for the sample of Example 1, and the average of the 18 measurements was 5.35 N.

Example 2

Except that 48 weight percent silver, 12 weight percent nickel, 2 percent by weight of the Bi-Te-O, 35.25 weight percent organic medium, 0.75 weight percent of Thixatrol ^® and 2.0 weight percent of an inorganic adhesion-promoting agent is used for preparing the In addition to the paste, Example 2 was carried out as described in Example 1, which consisted of 1.0% by weight of ZnO, 0.6% by weight of Bi ₂ O ₃ and 0.4% by weight of copper.

The adhesion was determined for the sample of Example 2 as described in Example 1. The average adhesion is 4.94 N.

Example 3

This was prepared except that 42 weight percent silver, 18 weight percent nickel, 2.0 weight percent Bi-Te-O, 35.25 weight percent organic media, 0.75 weight percent Thixatrol ^{® ,} and 2.0 weight percent inorganic adhesion promoter were used. In addition to the paste, Example 3 was carried out as described in Example 1, which consisted of 1.0% by weight of ZnO, 0.6% by weight of Bi ₂ O ₃ and 0.4% by weight of copper.

The adhesion was determined for the sample of Example 3 as described in Example 1. The average adhesion is 4.14 N.

Example 4

Except that 36 weight percent silver, 24 weight percent nickel, 2.0 weight percent Bi-Te-O, 35.25 weight percent organic medium, 0.75 weight percent of Thixatrol ^® and 2.0 weight percent of an inorganic adhesion-promoting agent is used for preparing the In addition to the paste, Example 4 was carried out as described in Example 1, which consisted of 1.0 weight percent ZnO, 0.6 weight percent Bi ₂ O ₃ and 0.4 weight percent copper.

The adhesion was determined for the sample of Example 4 as described in Example 1. The average adhesion is 5.15 N.

Example 5

Except that 54 weight percent silver, 6 weight percent nickel, 4.5 weight percent of Bi-Te-O, 32.75 weight percent organic medium, 0.75 weight percent of Thixatrol ^® and 2.0 weight percent of an inorganic adhesion-promoting agent is used for preparing the In addition to the paste, Example 5 was carried out as described in Example 1, which consisted of 1.0% by weight of ZnO, 0.6% by weight of Bi ₂ O ₃ and 0.4% by weight of copper.

The adhesion was determined for the sample of Example 5 as described in Example 1. The average adhesion is 3.00 N.

Example 6

Except that 48 weight percent silver, 12 weight percent nickel, 4.5 weight percent of Bi-Te-O, 32.75 weight percent organic medium, 0.75 weight percent of Thixatrol ^® and 2.0 weight percent of an inorganic adhesion-promoting agent is used for preparing the In addition to the paste, Example 6 was carried out as described in Example 1, which consisted of 1.0 weight percent ZnO, 0.6 weight percent Bi ₂ O ₃ and 0.4 weight percent copper.

The adhesion was determined for the sample of Example 6 as described in Example 1. The average adhesion is 4.43 N.

10‧‧‧p-type substrate

20‧‧‧n type diffusion layer

30‧‧‧Nitride film, titanium oxide film or hafnium oxide film

40‧‧‧p+ layer (back surface electric field, BSF)

60‧‧‧Aluminum paste formed on the back side

61‧‧‧Aluminum backside electrode

70‧‧‧Silver/aluminum paste formed on the back side

71‧‧‧Silver/aluminum backside electrode

500‧‧‧ Silver paste formed on the front side

501‧‧‧ Silver front electrode

102‧‧‧矽 substrate

104‧‧‧Light-receiving surface side electrode

106‧‧‧Paste composition for aluminum electrodes

108‧‧‧The paste composition of the present invention for marking electrodes

110‧‧‧Aluminum electrode

112‧‧‧mark electrode

1A to 1F illustrate the fabrication of a semiconductor device. The reference numerals shown in Figs. 1A to 1F are explained below.

10: p type germanium substrate

20: n type diffusion layer

30: tantalum nitride film, titanium oxide film or hafnium oxide film

40: p+ layer (back surface electric field, BSF)

60: aluminum paste formed on the back side

61: Aluminum back side electrode (obtained by firing the back side aluminum paste)

70: Silver/aluminum paste formed on the back side

71: Silver/aluminum backside electrode (obtained by firing the backside silver/aluminum paste)

500: silver paste formed on the front side

501: silver front electrode (formed by firing the front side silver paste)

2A to 2D explain a manufacturing procedure for an embodiment of manufacturing a solar cell using the conductive paste of the present invention. The reference numerals shown in Figs. 2A to 2D are explained below.

102 矽 substrate with a diffusion layer and an anti-reflective coating

104 light-receiving surface side electrode

106 Paste composition for aluminum electrodes

108 paste composition of the present invention for marking electrodes

110 aluminum electrode

112 mark electrode

102‧‧‧矽 substrate

104‧‧‧Light-receiving surface side electrode

110‧‧‧Aluminum electrode

112‧‧‧mark electrode

Claims (9)

A thick film paste composition comprising: (a) 25 to 55 weight percent of conductive silver; (b) 5 to 35 weight percent of a second conductive metal selected from the group consisting of nickel, aluminum, and mixtures thereof a group; (c) 0.5 to 5 weight percent of lead-free bismuth-tellurium-oxide; and (d) an organic medium; wherein the conductive silver, the second conductive metal, and the cerium-lanthanum-oxide are dispersed therein In an organic medium, and wherein the weight percentage is based on the total weight of the paste composition; based on the total weight of the bismuth-tellurium-oxide, the bismuth-tellurium-oxide comprises 22 to 42 weight percent of Bi ₂ O ₃ and 58 to 78 weight percent of TeO ₂ . The thick film paste composition of claim 1, comprising 36 to 48 weight percent of the conductive silver and 12 to 24 weight percent of the second conductive metal, wherein the weight percentage is the total weight of the paste composition Based on. The thick film paste composition according to claim 1, which further comprises 0.1 to 7 weight percent of Li ₂ O and 0.1 to 4 by weight based on the total weight of the cerium-lanthanum oxide. Percentage of TiO ₂ . The thick film paste composition according to claim 3, which further comprises 0.1 to 8 weight percent of B ₂ O ₃ , 0.1 to 3 based on the total weight of the cerium-lanthanum oxide ZnO by weight and 0.3 to 2 weight percent of P ₂ O ₅ . The thick film paste composition of claim 1, the thick film paste composition comprising less than 70% by weight of an inorganic component. The thick film paste composition according to claim 1, wherein the thick film paste composition further comprises 0.5 to 5 weight percent of an inorganic additive selected from the group consisting of Bi ₂ O ₃ , TiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , SnO ₂ , Sb ₂ O ₅ , Cr ₂ O ₃ , Fe ₂ O ₃ , ZnO, CuO, Cu ₂ O, MnO ₂ , Co ₂ O ₃ , NiO, RuO ₂ , A metal of a listed metal oxide, a metal compound which produces a listed metal oxide during firing, and mixtures thereof may be produced during firing, wherein the weight percentage is based on the total weight of the paste composition Based on. The thick film paste composition of claim 6, the thick film paste composition comprising less than 70% by weight of an inorganic component comprising the conductive silver powder, the second conductive metal powder, and the Bi-Te-O powder And any such inorganic additive, wherein the weight percentage is based on the total weight of the paste composition. A solar cell comprising an electrode formed from the thick film paste composition of any one of claims 1 to 7, wherein the thick film paste composition has been fired to remove the organic medium and form The electrode. The solar cell of claim 8, wherein the electrode is a marker electrode located on a back side of the solar cell.