TW201409487A - Conductive compositions containing Li2RuO3 and ion-exchanged Li2RuO3 and their use in the manufacture of semiconductor devices - Google Patents

Abstract

The present invention is directed to an electrically conductive composition comprising (i) an electrically conductive metal, (ii) a component selected from the group consisting of Li2RuO3, ion-exchanged Li2RuO3 and mixtures thereof, and (iii) a glass frit all dispersed in an organic medium. The present invention is further directed to an electrode formed from the composition and a semiconductor device and, in particular, a solar cell comprising such an electrode. The electrodes provide good adhesion and good electrical performance.

Description

Conductive composition containing Li 2 RuO 3 and ion-exchanged Li 2 RuO 3 and use thereof in manufacturing a semiconductor device

The present invention relates generally to a conductive composition (e.g., a thick film paste or ink) and an electrode formed from the conductive composition. It further relates to a germanium semiconductor device, in particular, to the electrode for use in forming a solar cell.

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 facilitate the generation of electron-hole pairs 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. Typically, a thick film paste or ink (hereinafter sometimes simply referred to as "paste") is screen printed on a substrate and fired to form an electrode.

The front side or the sun side of the germanium wafer is often coated with an anti-reflective coating (ARC) to avoid reflection loss of incident sunlight, thereby increasing the efficiency of the solar cell. Typically, a two-dimensional electrode grid pattern (i.e., "front electrode") is attached to the n-side of the crucible, and an aluminum coating on the opposite side (back electrode) is attached to the p-side of the crucible. These contacts are electrical outlets from the p-n junction to the outside load.

The front electrode of a tantalum solar cell is usually formed by screen printing a paste. Typically, the paste contains conductive particles, glass frits, and Organic medium. After screen printing, the wafer and paste are fired in air, typically at a furnace set temperature of about 650 to 1000 ° C for a few seconds to form a conductive trace of dense solids. The organic component is also burned off in this firing step. Also during this firing step, the glass frit and any added flux react with the anti-reflective coating and etch through the anti-reflective coating to form a tight crucible-to-electrode contact. The glass frit and any added flux also provide adhesion to the substrate as well as adhesion to subsequent electrodes to the electrode. Good adhesion to the substrate and high solder adhesion to the leads are important for the performance of the solar cell and the manufacturability and reliability of the solar module.

There has been an ongoing effort to provide a paste composition that produces improved adhesion while maintaining electrical properties.

The present invention provides an electrically conductive composition comprising: (a) a conductive metal; (b) a component selected from the group consisting of Li ₂ RuO ₃ , ion exchanged Li ₂ RuO _{3 ,} and mixtures thereof (c) a glass frit; and (d) an organic medium; wherein the conductive metal, the component selected from the group consisting of Li ₂ RuO ₃ , ion exchanged Li ₂ RuO _{3 ,} and mixtures thereof, and The glass frit is dispersed in the organic medium.

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

The electrically conductive composition of the present invention simultaneously provides the ability to form an electrode wherein the electrode has good electrical properties and improved adhesion properties. Typically, the composition will be in the form of a thick film paste or ink that can be printed or coated into a desired pattern, such as by screen printing, stencil printing, electroplating, ink jet printing, and ejection. , molding or multiple printing or ribbon.

The conductive composition comprises a conductive metal, a component selected from the group consisting of Li ₂ RuO ₃ , ion exchanged Li ₂ RuO _{3 ,} and mixtures thereof, a glass frit, and an organic medium. In one embodiment, the composition comprises 75 to 90 weight percent of a conductive metal, 0.03 to 5 weight percent of a component selected from the group consisting of Li ₂ RuO ₃ , ion exchanged Li ₂ RuO _{3 ,} and mixtures thereof a 0.5 to 5 weight percent glass frit and 5 to 25 weight percent organic medium, wherein the conductive metal, the group selected from the group consisting of Li ₂ RuO ₃ , ion exchanged Li ₂ RuO _{3 ,} and mixtures thereof The composition and the glass frit are dispersed in the organic medium, and wherein the weight percentage is based on the total weight of the composition.

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

Conductive metal

The conductive metal is selected from the group consisting of silver, copper, nickel, aluminum, and palladium. The source of the conductive metal may be in the form of a sheet, a sphere, a granular form, a crystalline form, a powder or other irregular form, and a mixture thereof. The conductive metal can be provided in a colloidal suspension. In an embodiment the group The product contains from 75 to 90 weight percent of the conductive metal, wherein the weight percentage is based on the total weight of the composition.

In an embodiment, the conductive metal 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. Silver may also be in the form of silver oxide (Ag ₂ O), silver salts (eg, AgCl, AgNO ₃ , AgOOCCH ₃ (silver acetate), AgOOCF ₃ (silver trifluoroacetate), silver orthophosphate (Ag ₃ PO ₄ ). Or a mixture thereof). Other forms of silver that are compatible with the other components can also be used.

In an embodiment, the electrically conductive composition comprises coated electrically conductive silver particles. Suitable coatings include surfactants and phosphorus-containing compounds. 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 counterions can be ammonium, sodium, potassium, and mixtures thereof.

The particle size of silver is not subject to any particular restrictions. In one embodiment, the average particle size is less than 10 microns; in another embodiment, the average particle size is in the range of 1 to 6 microns.

In one embodiment, the conductive metal further comprises a metal selected from the group consisting of nickel, aluminum, and mixtures thereof.

The composition contains 50 to 90% by weight of the conductive metal based on the total weight of the composition.

Li ₂ RuO ₃ , ion exchanged Li ₂ RuO ₃ and mixtures thereof

The conductive composition contains a component selected from the group consisting of Li ₂ RuO ₃ , ion-exchanged Li ₂ RuO _{3 ,} and mixtures thereof. This component produces an improved adhesion of the electrode made of the composition. In one embodiment, the composition contains from 0.03 to 5 weight percent of the component, wherein the weight percentage is based on the total weight of the composition. In another embodiment, the composition contains from 0.06 to 3 weight percent of the ingredient. In yet another embodiment, the composition contains from 0.1 to 1 weight percent of the ingredient.

In one embodiment, the composition contains Li ₂ RuO ₃ . The structure of Li ₂ RuO ₃ , as discussed by James and Goodenough in Journal of Solid State Chemistry 74, pp. 287-294 (1988), is generally composed of two adjacent alternating layers, one layer containing only Li ions. The other layer contains both Ru and Li ions (ignoring oxygen atoms).

In another embodiment, the component contains ion exchanged Li ₂ RuO ₃ . "Ion-exchanged Li ₂ RuO ₃ " is used herein to describe Li ₂ RuO ₃ particles, wherein Li atoms have been at least partially associated with Al, Ga, K, Ca, Mn, Fe, Mg, H, Na, Cr, Co. , Ni, V, Cu, Zn, Ti or Zr atoms or a combination thereof. The ion-exchanged Li ₂ RuO ₃ system is described by the formula M ⁺¹ _x M ⁺² _y M ⁺³ _z Li _2-x-2y-3z RuO ₃ , where (x+2y+3z) 1.5, and wherein the M system is selected from one or more of the group consisting of Al, Ga, K, Ca, Mn, Fe, Mg, Na, H, Cr, Co, Ni, V, Cu, Zn, Ti, and Zr Group members. It is believed that the Li layer of the Li ₂ RuO ₃ structure contains about 75 mole % of aluminum in the structure, and the lithium ions can be immediately removed via ion exchange. Although lithium ions can move in the Li-only layer of Li ₂ RuO ₃ , they have a higher cation than Li (such as Mg ⁺² or Al ⁺³ ) due to their higher charge and accompanying stronger bonding. So it is not easy to move. It is therefore believed that the exchanged ions (e.g., magnesium) first replace the lithium ions on or near the surface of the particles and in the lithium-only layer, and are still substantially at that location. However, the more magnesium ions that can be exchanged with lithium ions, the deeper the magnesium ions move into the particles, and until all of the exchangeable lithium has been removed or the magnesium ions in the solution are depleted. When the Li ion in the Li-only layer is replaced by an exchange ion having an amount that is not significantly more than the Li ion in the Li-only layer, there is a tendency to produce a particle having a surface shell layer which is contained in the original Li-only layer. The exchanged ions and the remaining lithium ions of the inner core.

In order to achieve exchange of Li ₂ RuO ₃ of lithium ions, preferably the Li ₂ RuO ₃ milled particle diameter in a range between about 0.5 and about 5 microns, for example, which is generally applicable to the subsequent screen printing The size range of the electrodes is formed. Any wet or dry milling technique can be used to achieve size reduction of Li ₂ RuO ₃ particles, such as vibratory milling, ball milling, hammer milling, media milling, bead milling, rod milling, jet milling or Plate grinding. This milling step can be carried out before or at the same time as the ion exchange step. The milling and ion exchange steps can be carried out in individual containers or in the same container.

In one embodiment, to maintain a substantially core-to-shell configuration, the milling of the particles should be completed or substantially completed prior to the ion exchange step. If milling is continued after the ion exchange process is completed, it is expected that the core that is not ion exchange will expose the untreated surface due to milling. This may or may not be important for subsequent chemical action of the microparticles.

During the ion exchange step, the particles in the solution are agitated by milling or milling or other suitable means, the solution containing Al, Ga, K, Ca, Mn, Fe, Na, H, Cr, Co, Ni, V, Ions of Cu, Zn, Ti, Zr or mixtures thereof. The plasma is obtained by dissolving a suitable salt of a desired element in a suitable solvent, preferably a mixture of water or water and a water-miscible solvent, such as a water-miscible solvent. An organic liquid such as methanol. After exposure to the salt solution, the lithium atoms in the Li ₂ RuO ₃ particles are replaced by cations from the solution. The ion exchanged Li ₂ RuO ₃ is further discussed in U.S. Patent No. 7,608,206 to VerNooy et al.

In yet another embodiment, the composition comprises a mixture of Li ₂ RuO ₃ and ion exchanged Li ₂ RuO ₃ .

Glass frit

There are many glass frits that are suitable for forming the present composition. In one embodiment, the composition contains from 0.5 to 5 weight percent glass frit, wherein the weight percentage is based on the total weight of the composition.

The glass compositions (also known as glass frits) described herein include specific percentages 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 methods known to those skilled in the art, including, but not limited to, sensing. Coupled plasma mass spectrometer (ICP-MS), inductively coupled plasma atomic emission spectrometer (ICP-AES) and the like. In addition, the following exemplary techniques can also be used: X-ray fluorescence spectroscopy (XRF), core magnetic resonance spectroscopy (NMR), electron paramagnetic resonance spectroscopy (EPR), Mössbauer spectroscopy, electron micro Probe energy dispersive spectroscopy (EDS), electron microprobe wavelength dispersive spectroscopy (WDS), and 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 be present in the range of hundreds to thousands of ppm. The presence of impurities will not alter the properties of the glass, composition, such as a thick film composition or a 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. As used herein, "lead-free" means that lead has not been intentionally added.

The various glass frits can be prepared by mixing the oxides (or other materials which decompose to the desired oxide upon heating) to be mixed therein using techniques well known to those skilled in the art. 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 frits may utilize alternative synthetic techniques (such as, but not limited to, water quenching, sol to 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 frit" includes all such products.

The glass frit can be lead or lead free.

Examples of typical lead-free glass frits for the composition include phthalates, barium borate, barium-strontium oxides, and mixtures thereof.

In one embodiment of the lead-free glass frit, the composition of the oxide component ranges from 55 to 90 weight percent Bi ₂ O ₃ , 0.5 to 35 weight percent SiO ₂ , 0 to 0 based on the total weight of the glass composition. 5 wt% B ₂ O ₃ , 0 to 5 wt% Al ₂ O ₃ and 0 to 15 wt% ZnO. In another embodiment, the composition of the oxide component ranges from 28 to 85 weight percent Bi ₂ O ₃ , 0.1 to 18 weight percent SiO ₂ , 1 to 25 weight percent B ₂ O ₃ , 0 to 6 Weight percent Al ₂ O ₃ , 0 to 1 weight percent CaO, 0 to 42 weight percent ZnO, 0 to 4 weight percent Na ₂ O, 0 to 3.5 weight percent Li ₂ O, 0 to 3 weight percent Ag ₂ O, 0 to 4.5 weight percent of CeO ₂ , 0 to 3.5 weight percent of SnO _{2 ,} and 0 to 15 weight percent of BiF ₃ .

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

Examples of typical lead-containing glass frits for the composition include lead citrate, lead borosilicate, and lead-antimony oxide.

In one embodiment of the leaded glass frit, the composition of the oxide component ranges from 20 to 83 weight percent PbO, from 1 to 35 weight percent SiO ₂ , from 01.5 to 19 weight, based on the total weight of the glass composition. Percent B ₂ O ₃ , 0 to 35 weight percent Bi ₂ O ₃ , 0 to 7 weight percent Al ₂ O ₃ , 0 to 12 weight percent ZnO, 0 to 4 weight percent CuO, 0 to 7 weight percent TiO ₂ , 0 to 5 weight percent CdO, and 0 to 30 PbF ₂ .

The starting mixture used to make the Pb-Te-O glass frit includes 25 to 65 weight percent PbO and 35 to 75 weight percent TeO ₂ based on the total weight of the starting mixture of Pb-Te-O. In a further embodiment, the starting mixture for making Pb-Te-O, in addition to PbO and TeO ₂ , comprises 0.1 to 5 weight percent Li ₂ O and 0.1 to 5 weight percent TiO ₂ based on The total weight of the starting mixture of Pb-Te-O. This Pb-Te-O can be expressed as Pb-Te-Li-Ti-O. In still further embodiments, the starting mixture used to make Pb-Te-O and Pb-Te-Li-Ti-O comprises 0.1 to 3 weight percent B ₂ O ₃ and 0.5 to 5 weight percent Bi ₂ O ₃ .

Organic medium

The inorganic component of the composition is mixed with an organic medium to form a thick thick film paste or a less viscous ink 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 on the printing screen during the manufacture, transportation and storage of the paste or ink and during the screen printing process.

Suitable organic media have rheological properties that provide stable dispersion of the solid, suitable viscosity and texturation for printing, proper wettability of the substrate and paste solids, good drying rate, and good firing properties. The organic medium can include thickeners, stabilizers, surfactants, and/or other common additives. One such shaker thickener is Thixatrol® (Elementis plc, London, UK). 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 carbitol acetate, hexa A mixture of an alcohol and an alcohol having a boiling point above 150 ° C and an alcohol ester. Other suitable organic media components include: bis(2-(2-butoxyethoxy)ethyl adipate, dibasic esters such as 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. Media can also A volatile liquid is included to promote rapid hardening after application of the paste composition on a substrate.

The optimum amount of organic medium in the composition depends on the method of applying the composition and the particular organic medium employed. The composition contains 5 to 50% by weight of the organic medium based on the total weight of the composition.

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

Preparation of composition

In one embodiment, the composition may be melted by mixing the conductive metal, the group selected from the group consisting of Li ₂ RuO ₃ , ion-exchanged Li ₂ RuO _{3 ,} and mixtures thereof in any order. The block and the organic medium are prepared. In certain embodiments, the inorganic materials are first mixed and then added to the organic medium. In other embodiments, the conductive metal, which is a major portion of the inorganic material, is slowly added to the organic medium. The viscosity can be adjusted by adding a solvent as needed. A high shear mixing method is beneficial for dispersing particles in the medium.

Electrode formation

The composition can be deposited by, for example, screen printing, stencil printing, electroplating, injection, ink jet printing, molding or multiple printing or ribbon.

In this electrode formation process, the composition is first dried and then heated to remove the organic medium and to sinter the inorganic material. Heating 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 so that the organic binder material can be destroyed from the dried paste composition as well as any other organic materials present. material. In one embodiment, the firing temperature is from 700 to 950 °C. The firing can be carried out in a belt furnace using a high conveying rate (e.g., 100 to 500 cm/min), and the resulting residence time is 0.03 to 5 minutes. Multiple temperature zones (eg, 3 to 11 zones) can be used to control the desired thermal profile.

In one embodiment, a semiconductor device is fabricated from an article comprising a semiconductor substrate with a junction and a tantalum nitride insulating film formed on a major surface of the substrate. The composition is applied (for example, coated or screen printed) on the insulating film in a predetermined shape and thickness and at a predetermined position. The composition has the ability to partially or completely pass through the insulating layer. Thereafter, firing is performed, and the composition reacts with the insulating film and passes through the insulating film, thereby generating electrical contact with the ruthenium substrate, thereby forming an electrode.

An example of this method of forming an electrode will be described below with reference to Figs. 1A to 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. The diffusion layer 20 is formed over the entire surface of the 矽p-type substrate 10 without any specific modification. 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 protecting the front side of the diffusion layer with a photoresist or the like, the diffusion layer 20 is removed from the remaining surface by etching to The diffusion-promoting layer 20 remains only on the front side. The photoresist is then removed using an organic solvent or the like.

Thereafter, as shown in FIG. 1D, an insulating layer 30 which also acts as an anti-reflective coating (ARC) 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 composition 500 of the present invention is screen printed to produce a front electrode on the insulating film 30 and then dried. Further, the back side silver or silver/aluminum paste 70 and the aluminum paste 60 are subsequently screen-printed to the back side of the substrate, followed by drying. The firing from a few seconds to several tens of minutes is continued in an infrared belt furnace at a temperature range of approximately 750 to 950 °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 contributes to improving 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. Because it is impossible to solder to an aluminum electrode, silver or silver/aluminum back electrode 71 Above the back side of the portion, as an electrode for interconnecting solar cells via copper strips or the like. Further, the front side composition 500 of the present invention is sintered and passes through the insulating film 30 during firing, thereby achieving 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.

Instance

Solar cell power measurement

A commercial current-voltage (JV) tester ST-1000 (Telecom-STV Ltd., Moscow, Russia) was used to perform the efficiency and fill factor measurement of the polycrystalline germanium photovoltaic cell. Two electrical connections (one for voltage and one for current) are connected to the top and bottom of each photovoltaic cell. Instantaneous light excitation was used to avoid heating the tantalum photovoltaic cell and the JV curve was obtained under standard temperature conditions (25 °C). A flash lamp having a spectral output similar to the solar spectrum illuminates the photovoltaic cell from a vertical distance of 1 m. The power of the flash is maintained constant for 14 microseconds. During this period, the strength at the surface of the sample (corrected for external solar cells) was 1000 W/m ² (or 1 Sun). During this 14 microsecond period, the JV tester changed the artificial electrical load on the sample from a short circuit to an open circuit. The JV tester records the current induced by the light through the photovoltaic cell and the voltage of the photovoltaic cell while the load varies between the load ranges. By multiplying the current by the voltage at each voltage level, a curve of power versus voltage is obtained from this data. The maximum value of the power versus voltage curve is used as the characteristic output power of the solar cell to calculate the solar cell efficiency. This maximum power is divided by the sample area to obtain the maximum power density at 1 Sun intensity. This value is then divided by the input intensity of 1000 W/m ² to obtain efficiency, and this efficiency is then multiplied by 100 to present the result as a percentage efficiency. Other relevant parameters are also obtained from this same current-voltage curve. One such parameter is a fill factor (FF), which can be obtained by calculating the ratio of the maximum power of the solar cell to the product of the open circuit voltage and the short circuit current. The FF is defined as the ratio of the maximum power of the solar cell to the product of V _oc and I _sc multiplied by 100.

Adhesion measurement

The adhesion of the electrodes was measured by the following procedure. The copper strip coated with Sn/Pb solder (Ulbrich Stainless Steels & Special Metals, Inc.) was immersed in a soft solder (Kester-952s from Kester) and then dried in air. Seconds. A half of the solder-coated copper strip was placed on the electrode and soldered by a soldering system (SEMBK Corporation (SEMBK Corporation Co., Ltd.) SCB-160). The soldering iron is set at a temperature of 220 to 240 ° C, and the actual temperature of the soldering iron at the tip is 195 ° C to 215 ° C, as measured by a K-type thermocouple.

The copper strip portion which was not adhered to the electrode was horizontally bent and pulled by a machine (Peel Force 606 of MOGRL Technology Co., MOGRL Technology Co., Ltd.) at 120 mm/min. The force that forces the copper strip away (Newton, N) is recorded as solder adhesion.

Synthesis and milling of Li ₂ RuO ₃

Example 1

18.85 g of Li ₂ CO _{3 was} thoroughly mixed with 33.33 g of RuO ₂ powder and calcined in air at 1000 ° C for 12 hours. The X-ray powder diffraction pattern of the resulting material showed only Li ₂ RuO ₃ with no impurity phase.

This material was milled in isopropanol to a d ₉₀ of 0.87 microns. The powder was separated from the slurry, dried and sieved to -230 mesh.

Preparation of thick film paste

Example 2

The main batch of thick film paste was prepared by mixing the displayed ingredients in the amount indicated in Table I in a Thinky Mixer (Thinky Corp., Laguna Hills, Calif.). The resulting roll was milled in three rolls and subjected to multiple passes at increasing pressure and finally at 2 rounds at 250 psi.

Preparation was carried out by dissolving 7 weight percent of N200 Aqualon ethylcellulose (Ashland, Inc., Covington, KY) of Cawinton, Kentucky, in a film forming aid (Texanol). quality. A glass frit was prepared by melting and quenching the amount of oxide shown in Table II, followed by milling the glass into a fine powder.

The composition of the present invention was prepared using 5.4692 g of a master batch thick film paste, and the composition of the present invention was mixed with 0.0439 g of Li ₂ RuO ₃ (from Example 1) in a Thinky mixer. Also add 0.0361 g of extra Texanol to adjust the viscosity. The amount of Li ₂ RuO ₃ in the paste composition of the present invention was 0.8% by weight based on the total weight of the composition.

The mixture was crushed on a Hoover M-5 automatic flat bottom mortar (Hiwassee, Va.) to completely mix Li ₂ RuO ₃ . The paste composition of the present invention was screen printed on a 1" x 1" wafer (cut from a 6" x 6" 65 ohm polysilicon wafer by a wafer cutter with a SiNx resistance of about 70 nm on the front side. Reflective coating). The graphic consists of 11 fingers (100 microns wide) and 1 bus bar (1.25 mm wide). A fully grounded plane made of commercially available aluminum paste is printed on the back side of each wafer. After drying at 150 ° C for 10 minutes, wafers (5 wafers per temperature) were fired in a PV-614 6 zone belt furnace of Radiant Technology at a series of peak temperatures, and the belt speed was 457 cm per minute. Report the final zone set temperature (value peak set temperature). The average peak efficiency was 13.99% at 865 °C, while the average peak FF was 75.14 at 865 °C. By comparison, the main batch paste without any addition of Li ₂ RuO ₃ was very inefficient (<4%).

Example 3

The compositions of the present invention were prepared and tested as described in Example 2 except that 0.0908 g of Li ₂ RuO _{3 was} crushed into 5.4816 g of the master batch paste and 0.0611 g of additional Texanol was added to adjust the viscosity. The amount of Li ₂ RuO ₃ in the paste composition of the present invention was 1.6% by weight based on the total weight of the composition. The average peak value efficiency was 14.41% at 890 ° C, while the value peak average FF was 75.90 at 890 ° C. By comparison, the main batch paste without any addition of Li ₂ RuO ₃ was very inefficient (<4%).

Example 4

The compositions of the present invention were prepared and tested as described in Example 2 except that 0.1793 g of Li ₂ RuO _{3 was} crushed into 5.6127 g of the master batch paste and 0.0386 g of additional Texanol was added to adjust the viscosity. The amount of Li ₂ RuO ₃ in the paste composition of the present invention was 3.2% by weight based on the total weight of the composition. The average peak value efficiency was 14.53% at 890 °C, while the value peak average FF was 76.68 at 890 °C. By comparison, the main batch paste without any addition of Li ₂ RuO ₃ was very inefficient (<4%).

Example 5

The compositions of the present invention were prepared and tested as described in Example 2 except that 0.2437 g of Li ₂ RuO _{3 was} broken up into 5.0770 g of the master batch paste and 0.0399 g of additional Texanol was added to adjust the viscosity. The amount of Li ₂ RuO ₃ in the paste composition of the present invention was 4.8 weight percent based on the total weight of the composition. The average peak value efficiency was 13.99% at 940 °C, while the value peak average FF was 74.44 at 940 °C. By comparison, the main batch paste without any addition of Li ₂ RuO ₃ was very inefficient (<4%).

Example 6

0.0757 g of Li ₂ RuO ₃ (from Example 1) and 28.5446 g of PV16A paste (DuPont Microcircuit Materials, Wilmington DE) were mixed in a Thinky mixer to prepare a composition. . 0.1751 g of Texanol was added to adjust the viscosity. The amount of Li ₂ RuO ₃ in the paste composition of the present invention was 0.263% by weight based on the total weight of the composition.

The inventive paste composition produced by three-roll milling (3 rounds at 0 psi and 3 rounds at 100 psi). The test wafer was printed in a manner similar to that described in Example 2. The wafer was fired in a BTU International IR belt furnace in Zone 4 with a belt speed of 221 cm per minute. The average peak value efficiency was 15.41% at 910 ° C, while the value peak average FF was 79.08 at 910 ° C.

Example 7

The composition was prepared and tested as described in Example 6, except that 0.1133 g of Li ₂ RuO _{3 was} mixed with 28.1699 g of PV16A paste and 0.1455 g of Texanol was added to adjust the viscosity. The amount of Li ₂ RuO ₃ in the paste composition of the present invention was 0.398% by weight based on the total weight of the composition. The average peak value efficiency was 15.17% at 920 ° C, while the value peak average FF was 77.86 at 920 ° C.

Example 8

The composition was prepared and tested as described in Example 6, except that 0.1373 g of Li ₂ RuO _{3 was} mixed with 25.9434 g of PV16A paste and 0.2372 g of Texanol was added to adjust the viscosity. The amount of Li ₂ RuO ₃ in the paste composition of the present invention was 0.522% by weight based on the total weight of the composition. The average peak value efficiency was 15.26% at 910 ° C, while the value peak average FF was 78.42 at 910 ° C.

Control experiment A

For comparison with Examples 6 to 8, a PV16A paste to which Li ₂ RuO _{3 was} not added was printed and fired as described in Example 6. The average peak value efficiency was 15.16% at 910 ° C, while the value peak average FF was 78.00 at 910 ° C.

Example 9

Glass frits were prepared from the compositions shown in Table III:

Two pastes were prepared using this glass frit. Paste A has a 1.60 weight percent frit, no lithium niobate, 88.83% silver powder, and an organic medium consisting of a solvent, a binder, a shaker, and a surfactant. Paste B is similar to Paste A, the only difference between which is that paste B contains 0.13 weight percent lithium niobate. After printing and firing, the batteries made from the two pastes have similar efficiencies and fill factors. However, paste A has a median adhesion of 1.28 N and a bus bar thickness of 11.5 microns. The paste has a median adhesion of 3.16 N and a bus bar thickness of 10.35 μm, which increases adhesion by 247%.

Example 10

Two pastes were prepared using the glass frit of Example 9. Paste C has 1.69% frit, no lithium niobate, 88.73% silver powder, and an organic medium composed of a solvent, a binder, a shaker, and a surfactant. Paste D had 1.69% frit, 0.100 weight percent lithium niobate, 88.63% silver powder, and the same organic medium as paste C. Three additional pastes were prepared by blending paste C with paste D to complete a paste having an amount of intermediate lithium niobate of 0.010 weight percent, 0.025 weight percent, and 0.050 weight percent, respectively. After printing and firing the five pastes, the adhesion and the thickness of the bus bar were measured. The results of these measurements are shown in Table IV.

10‧‧‧p-type substrate

20‧‧‧n type diffusion layer

30‧‧‧ARC

40‧‧‧p+ layer

60‧‧‧Aluminum paste

61‧‧‧Aluminum backside electrode

70‧‧‧Silver/Aluminum Cream

71‧‧‧Silver/aluminum backside electrode

500‧‧‧The paste of the invention

501‧‧‧ front electrode

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

10: p type germanium substrate

20: n type diffusion layer

30: ARC (such as tantalum nitride film, titanium oxide film or hafnium oxide film)

40: p+ layer (back field, BSF)

60: aluminum paste deposited on the back side

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

70: Silver/aluminum paste deposited on the back side

71: Silver/aluminum backside electrode (fired back silver/aluminum paste)

500: a paste of the invention deposited on the front side

501: front electrode (formed by firing the front side paste 500)

Claims (10)

A conductive composition comprising: (a) a conductive metal; (b) a component selected from the group consisting of Li ₂ RuO ₃ , ion exchanged Li ₂ RuO _{3 ,} and mixtures thereof; (c) a glass melting And (d) an organic medium; wherein the conductive metal, the component selected from the group consisting of Li ₂ RuO ₃ , ion exchanged Li ₂ RuO _{3 ,} and mixtures thereof, and the glass frit system are dispersed therein In organic media. The composition of claim 1, the composition comprising 50 to 90 weight percent of a conductive metal, 0.03 to 5 weight percent of a composition selected from the group consisting of Li ₂ RuO ₃ , ion exchanged Li ₂ RuO _{3 ,} and mixtures thereof The composition of the group, 0.5 to 5 weight percent of the glass frit, and 5 to 50 weight percent of the organic medium, wherein the weight percentage is based on the total weight of the composition. The composition of claim 1, wherein the component is Li ₂ RuO ₃ . The composition of claim 1, wherein the component is ion-exchanged Li ₂ RuO ₃ , wherein the Li atom has been at least partially passed through Al, Ga, K, Ca, Mn, Fe, Mg, H, Na, Cr, Co, Ni, V, Cu, Zn, Ti or Zr atoms or a combination thereof are exchanged. The composition of claim 1, the conductive metal comprising a metal selected from the group consisting of silver, copper, palladium, and mixtures thereof. The composition of claim 5, the conductive metal further comprising a metal selected from the group consisting of nickel, aluminum, and mixtures thereof. The composition of claim 1, wherein the glass frit comprises a lead-containing glass frit selected from the group consisting of lead citrate, lead borosilicate, lead-antimony oxide, and mixtures thereof. The composition of claim 1, wherein the glass frit comprises a lead-free glass frit selected from the group consisting of citrate, barium borate, barium-strontium oxide, and mixtures thereof. A semiconductor device comprising an electrode formed from the composition of claim 1 wherein the composition has been fired to remove the organic medium and form the electrode. A solar cell comprising an electrode formed from the composition of any one of claims 1 to 8, wherein the composition has been fired to remove the organic medium and form the electrode.