A highly reliable back electrode silver paste for PERC solar cells and its preparation method

Abstract

The present invention relates to the technical field of H01L31 / 0224. More specifically, the present invention relates to a high-reliability PERC cell back electrode silver paste and a preparation method thereof. The high-reliability PERC cell back electrode silver paste, by weight, comprises 56-65 parts of spherical silver powder, 1-2 parts of glass powder, 0.05-0.3 parts of inorganic auxiliary agent, and the organic binder is supplemented to 100 parts. By adding a certain amount of inorganic auxiliary agent and ensuring a certain weight ratio between the inorganic auxiliary agent and the glass powder, under the condition of not damaging the cell protective film equally, the aging tensile force is significantly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of H01L31 / 0224, and more specifically, the present invention relates to a high-reliability PERC cell back electrode silver paste and a preparation method thereof. Background Art

[0002] In the PERC solar cell back electrode silver paste, the glass frit acts as an inorganic binder, and the bonding performance is commonly characterized by tensile strength, while the durability (reliability) of the bonding is characterized by the aged tensile strength. The stronger the corrosion of the inorganic binder, the denser the combination of the back electrode and the substrate during the sintering process of the cell, and the higher its tensile strength and aged tensile strength. At the same time, the damage to the cell protective film is also stronger, resulting in a decrease in the cell efficiency. Therefore, the current back electrode silver paste cannot simultaneously meet the problems of tensile strength value and cell efficiency. Chinese Patent CN201310208529 discloses a back electrode silver paste for solar cells, including silver powder, an inorganic bonding phase, and an organic bonding phase. However, due to the small content of the inorganic bonding phase, it cannot be evenly dispersed in the silver paste, affecting the corrosion and sintering properties. Summary of the Invention

[0003] In view of some problems existing in the prior art, the first aspect of the present invention provides a high-reliability PERC cell back electrode silver paste, which, by weight, includes 56 - 65 parts of spherical silver powder, 1 - 2 parts of glass powder, 0.05 - 0.3 parts of inorganic additives, and the organic binder is supplemented to 100 parts.

[0004] In one embodiment, by weight, the high-reliability PERC cell back electrode silver paste includes 60 parts of spherical silver powder, 1.5 parts of glass powder, 0.1 part of inorganic additives, and the organic binder is supplemented to 100 parts.

[0005] In one embodiment, the spherical silver powder satisfies at least one of the following conditions:

[0006] (1) The D10 particle size is 0.5 - 1.5 μm;

[0007] (2) The D50 particle size is 1 - 2 μm;

[0008] (3) The D90 particle size is 2 - 3 μm;

[0009] (4) The tapped density is 3.5 - 5.5 g / cm 3 ;

[0010] (5) The specific surface area is 1 - 2 m 2 / g.

[0011] In this application, the particle sizes are all measured by a laser particle size distribution analyzer.

[0012] The morphology of the silver powder has a great influence on the efficiency of the battery cell. In this application, spherical silver powder is used, especially with a D10 particle size of 0.5 - 1.5 μm, a D50 particle size of 1 - 2 μm, a D90 particle size of 2 - 3 μm, and a tapped density of 3.5 - 5.5 g / cm 3 , and a specific surface area of 1 - 2 m 2 / g. At this time, the printed pattern lines are uniform, smooth, and there are no problems such as broken lines. It may be that the spherical silver powder with this specific particle size distribution and tapped density has good uniformity when passing through the screen, improving the printing performance. Combining with the spherical silver powder with a specific surface area of 1 - 2 m 2 / g in this application, it avoids excessive shrinkage during sintering, avoids pore defects, and improves the densification and uniformity of the film layer.

[0013] In one embodiment, the glass powder comprises at least one of the following components in the form of elemental substances and / or oxides; Pb, Bi, Si, Ti, Cu, Mn, Mg, Ca; the softening point of the glass powder is 450 - 600 °C. In this application, the glass powder with a softening point of 450 - 600 °C can well wet the spherical silver powder, making it have good bonding properties, while avoiding the problem of sintering shrinkage and improving the controllability of sintering.

[0014] In one embodiment, the glass powder comprises at least the following components in the form of elemental substances and / or oxides; Pb 30 - 55%, Bi 10 - 20%, Si 10 - 25%, Ti 5 - 10%, Cu 3 - 10%, Mn 5 - 20%, Mg 0 - 5%, Ca 0 - 10%.

[0015] Preferably, the average particle size of the glass powder is 1 - 2.5 μm.

[0016] In one embodiment, the preparation method of the glass powder includes: mixing the various components of the glass powder evenly, melting them at 900 - 1100 °C until they are clear and transparent, then quenching, and drying after ball milling.

[0017] In one embodiment, the inorganic auxiliary agent is elemental tellurium and / or tellurium compound. Preferably, the average particle size of the inorganic auxiliary agent is less than one-tenth of that of the glass powder. In the present application, the average particle size of the glass powder > 1 μm, and its content is only 1-2 wt%, so that the glass powder cannot be uniformly dispersed in the back electrode silver paste microscopically. The applicant unexpectedly found in experiments that adding the specific content of elemental tellurium and / or tellurium compound in the present application will not affect the corrosiveness of the glass powder. Especially when the particle size of the inorganic auxiliary agent is less than one-tenth of the particle size of the glass powder, the area affected by the inorganic auxiliary agent during the sintering process becomes smaller, greatly accelerating the sintering aid effect of the glass powder on the spherical silver powder, promoting the sintering of the nearby spherical silver powder and the glass powder, but it cannot sink to the surface of the silicon wafer or penetrate the silicon nitride protective film more than 80 nm, thereby making the back electrode silver layer denser, the combination with the substrate closer, and greatly improving the aging tensile strength of the back electrode.

[0018] Preferably, the particle size of the inorganic auxiliary agent is 100 nm.

[0019] Examples of the elemental tellurium and tellurium compounds in the present application include tellurium powder, tellurium oxide, telluric acid, bismuth telluride, zinc telluride, lead telluride, cadmium telluride, copper telluride, hafnium telluride, chromium telluride, nickel telluride, arsenic telluride, tungsten telluride, indium telluride, samarium telluride, germanium telluride, gallium telluride, tin telluride, neodymium telluride, zirconium telluride, francium telluride, di-tert-butyl tellurium, diethyl tellurium, tellurium isopropoxide, etc.

[0020] In the present application, the inorganic auxiliary agent can be added alone, or the inorganic auxiliary agent can be made into an inorganic auxiliary agent pre-paste for addition.

[0021] In one embodiment, the inorganic auxiliary agent is made into an inorganic auxiliary agent pre-paste for addition. In the inorganic auxiliary agent pre-paste, the inorganic auxiliary agent accounts for 5-50 wt%, preferably 15 wt%.

[0022] Preferably, the fineness of the inorganic auxiliary agent pre-paste is less than 1 μm.

[0023] For the preparation method of the inorganic auxiliary agent pre-paste in the present application, those skilled in the art can make a conventional selection according to needs. For example: mix the inorganic auxiliary agent and the carrier, and perform high-speed dispersion and three-roll rolling to a suitable fineness.

[0024] In one embodiment, the weight ratio of the glass powder to the inorganic auxiliary agent is (5:1)-(80:1). The applicant unexpectedly found that when the weight ratio of the glass powder to the inorganic auxiliary agent is (5:1)-(80:1), the aging tensile strength can be further improved, and the influence on the silicon nitride film layer on the back of the silicon wafer is small. The smaller the ratio, the stronger the improvement effect on the aging tensile strength, and the higher the ratio, the weaker the improvement effect on the aging tensile strength.

[0025] The specific proportion of inorganic additives and glass powder in the present application, and the softening point of the glass powder is 450-600°C, so that the spherical silver powders in the present application achieve surface contact. At the same time, in the silver paste in the present application, there is good overlap between the spherical silver powders, and there may be different degrees of overlap. At the same time, the agglomeration problem of the spherical silver powders can be avoided, a certain fluidity is ensured, the resistance value is reduced, and the efficiency of the battery cell is improved.

[0026] The organic binder is not particularly limited in the present application and can be routinely selected by those skilled in the art.

[0027] In one embodiment, the organic binder includes, by weight percentage, 5-20% polymer resin, 70-90% solvent, 0-8% dispersant, and 0-8% thixotropic agent.

[0028] Examples of the polymer resin in the present application include acrylic resin, polyurethane, epoxy resin, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, rosin, hydrogenated rosin, hydrogenated rosin tetrapentanol ester, polyamide, and the like.

[0029] Examples of the solvent in the present application include DBE, alcohol ester 12, butyl carbitol, butyl carbitol acetate, terpineol, aliphatic hydrocarbons, and the like.

[0030] Preferably, the dispersant is an aliphatic amide dispersant.

[0031] The organic adhesive in the present application can be purchased or prepared by oneself, and the preparation method can be conventionally selected by those skilled in the art.

[0032] In one embodiment, the preparation method of the organic binder comprises: mixing the components of the organic binder, heating and stirring at 60-80° C. for 1-4 hours until the components are miscible.

[0033] In one embodiment, the fineness of the high-reliability PERC cell back electrode silver paste is less than 12 microns.

[0034] The second aspect of the present invention provides a method for preparing a high-reliability PERC cell back electrode silver paste, comprising: uniformly mixing spherical silver powder, glass powder, inorganic additives and organic adhesives, and then grinding them to a fineness of less than 12 microns.

[0035] In the preparation method of the back electrode silver paste of the present application, the silver paste may be filtered through a 200-500 mesh filter cloth, or may not be filtered. Those skilled in the art may make the selection according to their needs.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention provides a highly reliable PERC back electrode silver paste and a preparation method thereof. By adding a certain amount of inorganic additives and ensuring a certain weight ratio of the inorganic additives and glass powder, under the condition of not damaging the battery cell protective film, the aging tensile strength is significantly improved. Detailed Embodiments

[0038] The present invention is illustrated below by way of detailed embodiments, but is not limited to the specific examples given below.

[0039] Embodiment

[0040] Example 1

[0041] Embodiment 1 of the present invention provides a highly reliable PERC battery cell back electrode silver paste. By weight, specifically, it is 60 parts of spherical silver powder, 1.5 parts of glass powder, 0.667 parts of inorganic additive pre-paste, and the organic binder is supplemented to 100 parts.

[0042] The particle size D10 of the spherical silver powder is 0.5 - 1.5 μm; the particle size D50 is 1 - 2 μm; the particle size D90 is 2 - 3 μm; the tapped density is 3.5 - 5.5 g / cm 3 ; the specific surface area is 1 - 2 m 2 / g.

[0043] By weight percentage, the glass powder is composed of the following components: Pb 50%, Bi 15%, Si 15%, Ti 6%, Cu 3%, Mn 5%, Mg 3%, Ca 3%, and the average particle size is 1 μm.

[0044] The preparation method of the glass powder is as follows: After mixing each component evenly, it is melted at 1000 °C until it is clear and transparent, then quenched, and dried after ball milling.

[0045] The inorganic additive pre-paste, with a fineness less than 1 μm, includes 15 wt% of inorganic additives and 85 wt% of a carrier. The inorganic additive is tellurium powder with a particle size of 100 nm. The carrier is ethyl cellulose STD100.

[0046] Among them, the components of the organic binder, by weight percentage, are as follows: 10% of ethyl cellulose STD100, 5% of dispersant Dumeen TDO, 10% of DBE, 10% of Texanol Ester Alcohol, 30% of butyl carbitol, and 35% of butyl carbitol acetate.

[0047] The preparation method of the highly reliable PERC battery cell back electrode silver paste is as follows:

[0048] (1) mixing the components of the organic binder, heating them in an oil bath at 80° C., and then stirring and dissolving them for 2 hours until the materials are completely miscible, thereby obtaining an organic binder;

[0049] (2) Spherical silver powder, glass powder, inorganic additive pre-slurry, and organic binder are mixed and stirred for 30 minutes to make each material evenly wetted. Then, the slurry is ground with a three-roll mill to obtain a slurry with good dispersion and a fineness of <7 μm as measured by a FOG scraper fineness meter. The slurry is then filtered using a 400-mesh filter cloth.

[0050] Example 2

[0051] A PERC cell back electrode silver paste, which is the same as Example 1, except that the weight portion of the inorganic auxiliary agent pre-slurry is 0.167 parts.

[0052] The silver paste for the back electrode of the PERC cell is the same as that in Example 1.

[0053] Example 3

[0054] A PERC cell back electrode silver paste, which is the same as Example 1, except that the weight portion of the inorganic auxiliary agent pre-slurry is 0.333 parts.

[0055] The silver paste for the back electrode of the PERC cell is the same as that in Example 1.

[0056] Example 4

[0057] A PERC cell back electrode silver paste, which is the same as Example 1, except that the weight portion of the inorganic auxiliary agent pre-slurry is 2 parts.

[0058] The silver paste for the back electrode of the PERC cell is the same as that in Example 1.

[0059] Example 5

[0060] A PERC cell back electrode silver paste, which is the same as Example 1, except that the weight parts of the inorganic auxiliary agent pre-slurry is 3 parts.

[0061] The silver paste for the back electrode of the PERC cell is the same as that in Example 1.

[0062] Example 6

[0063] A PERC cell back electrode silver paste, which is the same as Example 1, except that the weight portion of the inorganic auxiliary agent pre-slurry is 0 part.

[0064] The silver paste for the back electrode of the PERC cell is the same as that in Example 1.

[0065] Performance Evaluation

[0066] Print the back electrode silver paste of Examples 1-5 on a PERC single-crystal 166-size silicon wafer, and use the BACCINI solar cell printing system for the printer. The back electrode uses a 9BB customized graphic screen, and a CT sintering furnace is used for sintering, with a peak temperature of 780 °C. During the aging tensile test, the treatment conditions are 150 °C for 30 minutes, and then the peeling strength tester KJ1065D-B is used to test the pull-off force. And evaluate the PL brightness value, with a total score of 10 points.

[0067] Table 1

[0068]

Claims

1. A highly reliable PERC cell back electrode silver paste, characterized in that, By weight, 60 parts of spherical silver powder, 1.5 parts of glass powder, 0.333 part of inorganic additive pre-paste, and the organic binder is supplemented to 100 parts; The spherical silver powder has a particle size D10 of 0.5 - 1.5 μm, a particle size D50 of 1 - 2 μm, a particle size D90 of 2 - 3 μm, a tapped density of 3.5 - 5.5 g / cm 3 ; and a specific surface area of 1 - 2 m 2 / g; By weight percentage, the glass powder is composed of the following components: Pb 50%, Bi 15%, Si 15%, Ti 6%, Cu 3%, Mn 5%, Mg 3%, Ca 3%, and the average particle size is 1 μm; The preparation method of the glass powder is as follows: After mixing each component evenly, melt it at 1000 °C until it is clear and transparent, then quench it, and dry it after ball milling; The inorganic additive pre-paste, with a fineness less than 1 μm, includes 15 wt% of inorganic additive and 85 wt% of carrier, where the inorganic additive is tellurium powder with a particle size of 100 nm; the carrier is ethyl cellulose STD100; Among them, the components of the organic binder, by weight percentage, are as follows: 10% of ethyl cellulose STD100, 5% of dispersant Dumeen TDO, 10% of DBE, 10% of Texanol Ester Alcohol, 30% of butyl carbitol, and 35% of butyl carbitol acetate; The preparation method of the high-reliability PERC cell back electrode silver paste is as follows: (1) Mix each component of the organic binder, heat it in an oil bath at 80 °C, and then stir and dissolve for 2 hours until the materials are completely miscible to obtain the organic binder; (2) Mix the spherical silver powder, glass powder, inorganic additive pre-paste, and organic binder, stir for 30 min to uniformly wet each material, and then grind it with a three-roll mill to a slurry with good dispersibility and a fineness tested by a FOG blade fineness gauge <7 μm, and then filter the slurry with a 400-mesh filter cloth.

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