Method for preparing silver-plated copper powder of conductive paste for heterojunction solar cells

Abstract

The invention discloses a method for preparing silver-plated copper powder of conductive paste for heterojunction solar cells, belonging to the field of preparation of silver-plated copper powder materials. The copper powder is pretreated and then dispersed, a dispersant is a chloride salt, activated and dispersed copper powder is added into deionized water, and then a reducing agent and a silver ammonia solution are added in sequence, so that the generated silver is directly coated on the surface of the copper. The prepared silver-plated copper powder has a complete silver layer coating, and the silver-plated copper powder particles have good dispersibility. Compared with the silver-plated copper powder conductive paste currently available on the market, the method has better conductivity and lower resistivity.

Description

Technical Field

[0001] The invention belongs to the field of silver-plated copper powder material preparation, and specifically relates to a method for preparing silver-plated copper powder for conductive paste for heterojunction solar cells. The silver-plated copper powder is mixed with flaky silver powder, modified epoxy resin, curing agent and solvent in proportion to prepare low-temperature paste for heterojunction solar cells. Background Art

[0002] Heterojunction solar cells are a new type of high-efficiency solar cells. Their high conversion efficiency, low temperature coefficient, and thin-film production have become a new technology trend in the solar industry. However, heterojunction solar cells also face problems such as huge initial equipment investment, high target material and slurry costs, and reducing the cost of low-temperature slurry for heterojunction solar cells has become an urgent problem that the industry needs to solve. Therefore, the use of silver-coated copper powder instead of pure silver powder to prepare low-temperature slurry for heterojunction solar cells has become a research hotspot in the industry in recent years. However, in the process of preparing silver-plated copper powder, it is difficult to disperse copper powder particles, especially copper powder for submicron silver-plated copper powder used for screen printing. The dispersants currently used are mostly dispersed in the form of organic-coated copper powder (such as PVP), but the disadvantage of this dispersion method is that the dispersion effect is not good, and the organic coating layer is difficult to remove, which will eventually affect the conductivity of the silver-plated copper powder. Summary of the invention

[0003] The present invention is to overcome the above-mentioned shortcomings and provide a method for preparing silver-plated copper powder for conductive paste for heterojunction solar cells, which solves the problem that conventional dispersants have poor effect in dispersing copper powder, resulting in copper powder agglomeration and ineffective silver plating, and the currently commonly used organic dispersants (such as PVP, etc.) are difficult to remove. The prepared silver-plated copper powder material has good copper powder dispersibility, good silver plating effect, and good conductivity. The present invention is based on silver nitrate as the silver source, chloride salt as the dispersant, and sodium hypophosphite as the reducing agent. The innovation is to use chloride salt as the dispersant instead of the existing organic dispersant, which solves the problem that the organic coating layer dispersant is difficult to remove and affects the conductivity of the silver-plated copper powder.

[0004] Specifically, the method is implemented as follows: A method for preparing silver-plated copper powder for conductive paste for heterojunction solar cells, characterized in that the preparation steps are as follows:

[0005] Step 1: pretreatment of copper powder by removing impurities using alkali washing and acid washing;

[0006] Step 2, dispersion treatment of copper powder, take the active copper powder of step 1, add deionized water, add a small amount of sodium hydroxide to adjust the pH to 8-8.5, keep warm at 60°C, add chloride salt and continue stirring for 5 minutes, pour out the supernatant, repeatedly wash 2-3 times to prepare for silver plating, the amount of chloride salt added is 0.025-0.05g per 100g of copper powder;

[0007] Step 3, adding deionized water and reducing agent sodium hypophosphite to the copper powder dispersed in step 2, and fully stirring and dispersing the reducing agent sodium hypophosphite, wherein the amount of the reducing agent sodium hypophosphite added is 15% of the mass of the copper powder;

[0008] Step 4, slowly drop the silver ammonia solution into the beaker containing copper powder, maintain the stirring speed at 200 r / min, heat to 40°C, and keep warm for 20 minutes. After the reaction is completed, add polyvinyl pyrrolidone (PVP) to the beaker, heat to 60°C and continue stirring;

[0009] Step 5, remove the supernatant from the solution after the reaction in step 4, wash with deionized water and anhydrous ethanol for 3-4 times respectively, centrifuge and dry.

[0010] Furthermore, the copper powder used in step 1 has a particle size of 2 μm to 3 μm.

[0011] Furthermore, since there is a coating agent on the surface of the copper powder to prevent oxidation, and there may be a small amount of copper oxide, pretreatment is required to remove the coating agent and oxide before silver plating. Specifically, sodium hydroxide is first added and stirred for 10 minutes, and then dilute sulfuric acid is added and stirred for 10 minutes under heating conditions at 60°C, the supernatant is poured off, and the copper powder solution is repeatedly washed until the pH is 7.

[0012] Furthermore, the chloride salt in step 2 is sodium chloride or potassium chloride.

[0013] Furthermore, the preparation method of the silver ammonia solution in step 4 is to place 30% silver nitrate of the weight of the copper powder in deionized water, stir evenly and then slowly add ammonia water. When the color of the solution becomes turbid first and then clear, stop adding ammonia water.

[0014] Furthermore, in step 4, the amount of polyvinyl pyrrolidone added is 5% of the mass of the copper powder.

[0015] The beneficial effects of the present invention are:

[0016] 1. The present invention uses chloride salt as a dispersant, the obtained copper powder has good dispersibility, the prepared silver-plated copper powder has a complete silver layer, and the silver-plated copper powder particles have good dispersibility;

[0017] 2. Using the chemical reduction method, add the activated and dispersed copper powder into deionized water, then add the reducing agent and silver ammonia solution in sequence, so that the generated silver is directly coated on the surface of the copper, and the surface of the copper powder is evenly coated with a layer of silver plating;

[0018] 3. The low-temperature conductive paste finally obtained for heterojunction solar cells has better conductivity and lower resistivity than the silver-plated copper powder conductive paste currently available on the market. DETAILED DESCRIPTION

[0019] Example 1

[0020] A method for preparing silver-plated copper powder of conductive paste for heterojunction solar cells, the preparation steps are as follows:

[0021] Step 1, pretreatment of copper powder, first add sodium hydroxide to copper powder with a particle size of 2μm~3μm and stir for 10min, then add dilute sulfuric acid and stir for 10min under heating conditions of 60℃, pour off the supernatant, and repeatedly wash the copper powder solution until the pH is 7;

[0022] Step 2, dispersion treatment of copper powder, take 10g of active copper powder in step 1, add it to 100g of deionized water, add a small amount of sodium hydroxide to adjust the pH to 8, keep warm at 60°C, add 0.0025g of sodium chloride and continue stirring for 5min, pour off the supernatant, and wash repeatedly 2-3 times to prepare for silver plating;

[0023] Step 3, add 200g of deionized water and 1.5g of sodium hypophosphite to the dispersed copper powder in step 2, stir and disperse them thoroughly for later use. Take another beaker, add 50g of deionized water and 3g of silver nitrate, stir until the solution is clear, and then slowly add ammonia water. When the solution is observed to be turbid first and then clear, stop adding ammonia water to obtain a silver ammonia solution;

[0024] Step 4, slowly drop the silver ammonia solution prepared in step 3 into the beaker containing copper powder in step 3, keep the stirring speed at 200r / min, the heating temperature at 40°C, and keep warm for 20min. After the reaction is completed, add 0.5g PVP to the beaker, raise the temperature to 60°C and continue stirring;

[0025] Step 5, the supernatant of the solution after the reaction in step 4 is removed, and the solution is washed with deionized water and anhydrous ethanol for 3-4 times respectively, and finally a silver-plated copper powder with a silver content of 30% is obtained, which is dried after centrifugation.

[0026] 0.16 g of acrylic acid-modified epoxy resin, 0.24 g of butene-modified epoxy resin, 0.5 g of butyl carbitol acetate, 4.5 g of flaky silver powder, and 4.5 g of the above-prepared silver-plated copper powder were accurately weighed, fully mixed, and dispersed seven times in a three-roll mill to obtain a conductive paste for heterojunction solar cells prepared with silver-plated copper powder. The specific properties are as follows:

[0027]

[0028] Example 2

[0029] A method for preparing silver-plated copper powder of conductive paste for heterojunction solar cells, the preparation steps are the same as those in Example 1, wherein in step 2, the pH is adjusted to 8.5 and the amount of sodium chloride added is 0.005 g.

[0030] 0.16 g of acrylic acid-modified epoxy resin, 0.24 g of butene-modified epoxy resin, 0.5 g of butyl carbitol acetate, 4.5 g of flaky silver powder, and 4.5 g of the above-prepared silver-plated copper powder were accurately weighed, fully mixed, and dispersed seven times in a three-roll mill to obtain a conductive paste for heterojunction solar cells prepared with silver-plated copper powder. The specific properties are as follows:

[0031]

[0032] Example 3

[0033] A method for preparing silver-plated copper powder of conductive paste for heterojunction solar cells, the preparation steps are the same as those in Example 1, wherein in step 2, the pH is adjusted to 8.5 and the amount of sodium chloride added is 0.0075 g.

[0034] 0.16 g of acrylic acid-modified epoxy resin, 0.24 g of butene-modified epoxy resin, 0.5 g of butyl carbitol acetate, 4.5 g of flaky silver powder, and 4.5 g of the above-prepared silver-plated copper powder were accurately weighed, fully mixed, and dispersed seven times in a three-roll mill to obtain a conductive paste for heterojunction solar cells prepared with silver-plated copper powder. The specific properties are as follows:

[0035]

[0036] Example 4

[0037] A method for preparing silver-plated copper powder of conductive paste for heterojunction solar cells, the preparation steps are the same as those in Example 1, wherein the chloride salt added in step 2 is potassium chloride.

[0038] 0.16 g of acrylic acid-modified epoxy resin, 0.24 g of butene-modified epoxy resin, 0.5 g of butyl carbitol acetate, 4.5 g of flaky silver powder, and 4.5 g of the above-prepared silver-plated copper powder were accurately weighed, fully mixed, and dispersed seven times in a three-roll mill to obtain a conductive paste for heterojunction solar cells prepared with silver-plated copper powder. The specific properties are as follows:

[0039] Viscosity (Pas) Volume resistivity (Ωcm) Contact resistivity (Ω / cm2) 162 <![CDATA[6.37x10 -6 ]]> <![CDATA[2.82x10 -2 ]]>

[0040] Comparative Example

[0041] The silver-plated copper powder sold by Guangxin Import and Export Co., Ltd., model GB3501, was selected, 0.16g of acrylic acid-modified epoxy resin, 0.24g of butene-modified epoxy resin, 0.5g of butyl carbitol acetate, and 4.5g of flaky silver powder were accurately weighed, and 4.5g of the silver-plated copper powder prepared above was fully mixed and dispersed seven times in a three-roll mill to obtain a conductive paste for heterojunction solar cells prepared with the silver-plated copper powder. The specific characteristics are as follows:

[0042]

[0043] It can be seen from the results of the embodiments and comparative examples that the silver-plated copper powder conductive paste prepared by the present invention has better conductive properties, lower resistivity and better conductive performance than the currently existing silver-plated copper powder paste.

Claims

1. A method for preparing silver-plated copper powder for conductive paste for heterojunction solar cells, characterized in that The preparation steps are as follows: Step 1: pretreatment of copper powder by removing impurities using alkali washing and acid washing; Step 2, dispersion treatment of copper powder, take the active copper powder of step 1, add deionized water, add a small amount of sodium hydroxide to adjust the pH to 8-8.5, keep warm at 60°C, add chloride salt and continue stirring for 5 minutes, pour out the supernatant, repeatedly wash 2-3 times to prepare for silver plating, the amount of chloride salt added is 0.025-0.05g per 100g of copper powder; Step 3, adding deionized water and reducing agent sodium hypophosphite to the copper powder dispersed in step 2, and fully stirring and dispersing the reducing agent sodium hypophosphite, wherein the amount of the reducing agent sodium hypophosphite added is 15% of the mass of the copper powder; Step 4, slowly add the silver ammonia solution dropwise to the beaker containing copper powder, maintain the stirring speed at 200 r / min, heat to 40°C, and keep warm for 20 minutes. After the reaction is completed, add polyvinyl pyrrolidone to the beaker, heat to 60°C and continue stirring; Step 5, remove the supernatant from the solution after the reaction in step 4, wash with deionized water and anhydrous ethanol for 3-4 times, centrifuge and dry; The chloride salt in step 2 is sodium chloride or potassium chloride; In step 4, the amount of polyvinyl pyrrolidone added is 5% of the mass of the copper powder.

2. The method for preparing silver-plated copper powder of a conductive paste for heterojunction solar cells according to claim 1, characterized in that The copper powder used in step 1 has a particle size of 2 μm to 3 μm.

3. The method for preparing silver-plated copper powder of conductive paste for heterojunction solar cells according to claim 1, characterized in that The pretreatment of the copper powder in step 1 is specifically to first add sodium hydroxide and stir for 10 minutes, then add dilute sulfuric acid and stir for 10 minutes under heating conditions of 60° C., pour off the supernatant, and repeatedly wash the copper powder solution until the pH is 7.

4. The method for preparing silver-plated copper powder of conductive paste for heterojunction solar cells according to claim 1, characterized in that The preparation method of the silver ammonia solution in step 4 is to place 30% silver nitrate of the weight of the copper powder in deionized water, stir evenly and then slowly add ammonia water. When the color of the solution becomes turbid first and then clear, stop adding ammonia water.

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