Preparation method of silver powder for solar cell back silver paste

Abstract

The present application relates to silver powder preparation technical field, specifically to a kind of solar cell back silver paste silver powder preparation method;The silver powder preparation method includes: preparation silver powder, preparation pretreatment silver powder and preparation solar cell back silver paste silver powder three processes;In the present application, glycerol is used as reducing agent, which plays the dual role of reducing agent and emulsifier, can effectively regulate the size of silver powder, reduce the amount of dispersing agent;In addition, silver nitrate solution and sodium hydroxide solution are used as raw materials in the present application, and silver oxide is used as intermediate, and the process design of in-situ reduction is used, so that the particle dispersion of silver powder is good in the reaction process, and the particle size distribution is uniform;In addition, the chemical bond formed by silver powder and the polymer grafted on its surface will be broken under heating conditions, that is, while improving the dispersion performance of silver powder, the conductivity of silver powder will not be affected, effectively ensuring the dispersion performance and conductivity of silver powder.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silver powder preparation, in particular to a preparation method of silver powder for solar cell back silver paste. BACKGROUND

[0002] A solar cell (solar chip, photovoltaic cell) is a kind of photovoltaic semiconductor wafer that directly generates electricity using sunlight. It can output voltage and generate current in a loop as long as it is illuminated by light that meets certain illumination conditions. In physics, it is called solar photovoltaic, simply photovoltaic. Solar cells are devices that convert light energy into electrical energy through the photoelectric effect or photochemical effect.

[0003] Solar cell back silver paste is a special coating material used in the manufacture of solar cells. It is usually composed of silver particles, organic solvents and organic polymers, etc. It has conductive and adhesive properties. Photovoltaic silver paste plays an important role in the manufacture of solar cells, used to make the positive electrode of the cell. On the front side of the solar cell, silver paste is coated or printed on the surface of the silicon wafer to form a metal electrode grid. These silver paste conductive grids help collect current and transfer it to the circuit of the cell, thereby improving the efficiency of the cell.

[0004] Currently, although the commercially available silver powder has excellent conductive properties, due to its own "small size" effect, its dispersion performance is relatively poor, which leads to its inability to disperse uniformly in the resin phase of the solar cell back silver paste, affecting the conductive performance and quality of the back silver paste. Therefore, the present application provides a preparation method of silver powder for solar cell back silver paste to solve the above technical problems. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of silver powder for solar cell back silver paste. In the present application, a polymer with a large molecular weight is introduced onto the surface of the silver powder, effectively reducing the phenomenon of "agglomeration" of silver powder, so that the silver powder can be dispersed in the resin system, effectively ensuring the dispersion performance and conductive performance of the silver powder for solar cell back silver paste, and also ensuring its quality.

[0006] To achieve the above purpose, the present application provides the following technical scheme:

[0007] A preparation method of silver powder for solar cell back silver paste, comprising the following steps:

[0008] Step one, preparing silver powder;

[0009] The silver micro-powder is prepared by adding a 0.2-0.3 g / mL sodium hydroxide aqueous solution at 55-65 ℃ dropwise into a 0.1-0.3 g / mL silver nitrate solution at 25-35 ℃ under stirring for 30-40 min, then adding a dispersant with a mass of 0.5-2% of the silver micro-powder into the mixture, and stopping heating when the temperature of the mixture reaches 60-70 ℃; adding a 45-55 wt% glycerol solution slowly, and filtering the product after stirring for 80-120 min; and washing and drying the filter cake, and storing the silver micro-powder for use.

[0010] Step two, preparing the pretreated silver micro-powder

[0011] The silver micro-powder is uniformly dispersed in 1, 4-epoxybutane at a solid-liquid ratio of 0.03-0.08 g / mL, and then 2-thiofurfuryl alcohol with a mass of 0.4-0.6 times of the silver micro-powder is added and stirred at 20-30 ℃ for 4-7 h; after the stirring, the product is subjected to high-speed centrifugal treatment, washed with 1, 4-epoxybutane for 2-3 times, and vacuum dried, and the pretreated silver micro-powder is obtained.

[0012] Step three, preparing the silver powder for solar cell back silver paste

[0013] The pretreated silver micro-powder is uniformly dispersed in an organic solvent at a solid-liquid ratio of 0.05-0.08 g / mL, and then an equal amount of modifier is added, and the mixture is uniformly stirred and reacted at 50-60 ℃ for 6-10 h; after the reaction, the product is subjected to centrifugal separation, washed with the organic solvent for 3-4 times, and vacuum dried, and the silver powder for solar cell back silver paste is obtained.

[0014] Further, the dispersant in step one is any one of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

[0015] Further, the modifier in step three is prepared by adding methyl methacrylate into a 20-30% toluene aqueous solution at a dosage ratio of 0.5-0.6 g / mL, then adding a reaction intermediate with a mass of 3-5% of the methyl methacrylate and a reaction promoter with a mass of 2.0-3.0% of the methyl methacrylate into the mixture, stirring for 30-40 min under nitrogen atmosphere, then increasing the temperature of the mixture to 70-75 ℃, adding a persulfate with a mass of 20-30% of the reaction promoter, stirring and uniformly reacting for 5-8 h, then reacting at 80-85 ℃ for 30-40 min, and washing and drying the solid product in the product at room temperature after the reaction, and the modifier is obtained.

[0016] Further, the reaction promoter is selected from any one of azobisisobutyronitrile and azobisisoheptyl nitrile.

[0017] Further, the persulfate is selected from any one of ammonium persulfate and potassium persulfate.

[0018] Further, the organic solvent in the third step is selected from any one of N,N-dimethylformamide, toluene and dimethyl sulfoxide.

[0019] Further, the solute in the glycerol solution in the first step is distilled water, and the concentration of glycerol is 45-55 wt%.

[0020] Further, the preparation method of the reaction intermediate is as follows: 4-maleimide benzoyl chloride is uniformly dissolved in dichloromethane at a material ratio of 0.03-0.06 g / mL, then N,N-dimethyl-4-pyridine amine with a volume of 5-8% of dichloromethane is added, after uniform mixing and stirring, 2-hydroxyethyl methacrylate with a volume of 0.5-0.6 times of N,N-dimethyl-4-pyridine amine is added dropwise under the condition of ice water bath, and after natural warming to room temperature, the reaction is kept for 8-12 h; after the reaction is completed, the solid components in the product are washed with saturated sodium bicarbonate solution for 2-3 times; then washed with distilled water until neutral; after washing is completed, anhydrous magnesium sulfate is used for drying to remove dichloromethane therein; finally, the obtained viscous liquid is subjected to reduced pressure distillation to obtain the reaction intermediate.

[0021] Further, the mass ratio of silver nitrate to sodium hydroxide in the first step is 3-4:1.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] 1. In the present application, glycerol is used as a reducing agent, which plays a dual role of reducing agent and emulsifier, can effectively regulate the size of silver powder, and reduce the amount of dispersing agent. In addition, in the present application, silver nitrate solution and sodium hydroxide aqueous solution are used as raw materials, silver oxide is used as an intermediate, and an in-situ reduction process is designed, so that the silver powder has good particle dispersibility and uniform particle size distribution in the reaction process.

[0024] 2、The silver micro powder prepared in the present application is uniformly dispersed in 1,4-epoxy butane, and 2-thiofurfuryl alcohol is added to pretreat the silver micro powder, so as to prepare for subsequent chemical reaction. In addition, 4-maleimide benzoyl chloride, N,N-dimethyl-4-pyridine amine, and methyl methacrylate-2-hydroxyethyl ester are used as raw materials to prepare a reaction intermediate through chemical reaction. Then, the reaction intermediate, methyl methacrylate, azobis isobutyronitrile, and persulfate are used as raw materials to prepare a modifier. Then, the pretreated silver micro powder is uniformly dispersed in N,N-dimethyl formamide, and an equal amount of modifier is added. Chemical reaction occurs between the modifier and the pretreated silver micro powder, and finally a polymer with a large molecular weight is introduced onto the surface of the silver powder, effectively reducing the phenomenon of "agglomeration" of the silver micro powder, so that the silver powder can be dispersed in the resin system. In addition, the chemical bond formed by the silver powder and the polymer grafted on the surface of the silver powder will be broken under heating conditions, that is, the dispersibility of the silver powder is improved without affecting the conductivity of the silver powder, effectively ensuring the dispersibility and conductivity of the silver powder. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] Embodiment 1

[0027] A preparation method of a silver powder for a solar cell back silver paste, comprising the following steps:

[0028] Step one, preparing silver micro powder;

[0029] A sodium hydroxide aqueous solution with a concentration of 0.2 g / mL and a temperature of 55℃ is added dropwise to a silver nitrate solution with a concentration of 0.1 g / mL and a temperature of 25℃ under stirring within 30 min, then a fatty alcohol polyoxyethylene ether with a mass of 0.5% of the sodium hydroxide aqueous solution is added to the obtained mixture, and the heating is stopped when the temperature of the mixture rises to 60℃; a glycerol solution with a concentration of 45wt% is slowly added, and the obtained product is filtered after stirring for 80 min. The filter cake is washed with water and dried, and the obtained silver micro powder is stored for use.

[0030] The solute in the glycerol solution is glycerol, the solvent is distilled water, and the concentration of glycerol is 45wt%; and the mass ratio of silver nitrate to sodium hydroxide is 3:1.

[0031] Step two, preparing pretreated silver micro powder;

[0032] The silver micro-powder is uniformly dispersed in 1, 4-epoxy butane at a solid-liquid ratio of 0.03 g / mL, then 2-thio furan methanol with a mass of 0.4 times of the silver micro-powder is added, and stirring treatment is carried out at a temperature of 20℃ for 4h; after the stirring treatment is completed, high-speed centrifugal treatment is carried out, then 1, 4-epoxy butane is used for washing twice, and vacuum drying treatment is carried out, and the obtained is the pretreated silver micro-powder;

[0033] Step three, preparing silver powder for solar cell back silver paste;

[0034] The pretreated silver micro-powder is uniformly dispersed in N, N-dimethyl formamide at a solid-liquid ratio of 0.05 g / mL, then the modifier with an amount equal to that of the pretreated silver micro-powder is added, after uniform mixing and stirring, heat preservation reaction is carried out at a temperature of 50℃ for 6h; after the reaction is completed, the obtained product components are sequentially subjected to centrifugal separation, N, N-dimethyl formamide washing for 3 times, and vacuum drying treatment, and finally obtained is the silver powder for solar cell back silver paste.

[0035] The preparation method of the modifier in step three is as follows: 0.5 g / mL of methyl methacrylate is added to a toluene aqueous solution with a volume concentration of 20%, then 3% of the reaction intermediate of the mass of the methyl methacrylate, 2.0% of azobisisobutyronitrile are sequentially added, mixing and stirring are carried out for 30 min under the protection of nitrogen atmosphere, then the temperature of the obtained mixed phase is raised to 70℃, 20% of ammonium persulfate of the mass of the azobisisobutyronitrile is added, after uniform mixing and stirring, heat preservation reaction is carried out for 5h; then heat preservation reaction is carried out at a temperature of 80℃ for 30 min; after the reaction is completed, the solid product in the obtained product components is washed with 1, 4-epoxy butane and methanol respectively, and room temperature drying treatment is carried out, and finally obtained is the modifier.

[0036] The preparation method of the reaction intermediate is as follows: 4-maleimide benzoyl chloride is uniformly dissolved in dichloromethane at a material ratio of 0.03 g / mL, then 5% of N, N-dimethyl-4-pyridine amine of the volume of the dichloromethane is added, after uniform mixing and stirring, 0.5 times of the methyl methacrylate-2-hydroxyethyl of the volume of the N, N-dimethyl-4-pyridine amine is added dropwise under the condition of ice water bath, after natural temperature rise to room temperature, heat preservation reaction is carried out for 8h; after the reaction is completed, the solid components in the product are washed with saturated sodium bicarbonate solution for 2 times; then distilled water is used for washing until neutral; after the washing is completed, anhydrous magnesium sulfate is used for drying to remove the dichloromethane in it; finally, the obtained viscous liquid is subjected to reduced pressure distillation to obtain the reaction intermediate.

[0037] Example 2

[0038] A preparation method of silver powder for solar cell back silver paste, comprising the following steps:

[0039] Step one, preparing silver micro-powder;

[0040] A 0.25 g / mL concentration, 60°C temperature sodium hydroxide aqueous solution is added dropwise to a 0.2 g / mL concentration, 30°C temperature silver nitrate solution while stirring for 35 minutes, then 1.5% by mass alkylphenol polyoxyethylene ether is added to the resulting mixture, and heating is stopped when the temperature rises to 65°C; a 50 wt% concentration glycerol solution is slowly added, and the resulting product components are filtered after stirring for 100 minutes, the filter cake is washed with water and dried, and the resulting silver micropowder is stored and used as needed;

[0041] The solute in the glycerol solution is glycerol, the solvent is distilled water, and the concentration of glycerol is 50 wt%; the mass ratio of silver nitrate to sodium hydroxide is 3.5:1.

[0042] Step two, preparation of pretreated silver micropowder

[0043] The silver micropowder is uniformly dispersed in 1,4-dioxane at a solid-liquid ratio of 0.05 g / mL, then 2-thiofurfuryl alcohol is added in an amount of 0.5 times the mass of the silver micropowder, and stirring is performed at a temperature of 25°C for 6 hours; after stirring is complete, high-speed centrifugal treatment is performed, and then 1,4-dioxane is used to wash the resulting product three times, and vacuum drying treatment is performed, and the resulting product is the pretreated silver micropowder.

[0044] Step three, preparation of silver powder for solar cell back silver paste

[0045] The pretreated silver micropowder is uniformly dispersed in toluene at a solid-liquid ratio of 0.06 g / mL, then an equal amount of modifier is added to the pretreated silver micropowder, and after uniform mixing and stirring, the resulting mixture is incubated at a temperature of 55°C for 8 hours; after the reaction is complete, the resulting product components are sequentially subjected to centrifugal separation, toluene washing four times, and vacuum drying treatment, and the final resulting product is the silver powder for solar cell back silver paste.

[0046] The preparation method of the modifier in step three is as follows: 0.55 g / mL of methyl methacrylate is added to a 25% volume concentration toluene aqueous solution, then 4% of a reaction intermediate and 2.5% of azobisisheptyl nitrile, which are 4% and 2.5% by mass of the methyl methacrylate, are sequentially added, and the resulting mixture is mixed and stirred for 35 minutes under the protection of a nitrogen atmosphere, then the temperature of the resulting mixture is raised to 70°C, and 25% by mass of potassium persulfate, which is 25% by mass of the azobisisheptyl nitrile, is added, the resulting mixture is mixed and stirred uniformly, and then incubated at a temperature of 70°C for 6 hours; then incubation is performed at a temperature of 80°C for 35 minutes; after the reaction is complete, the solid product in the resulting product components is washed with 1,4-dioxane and methanol, and then dried at room temperature, and the final resulting product is the modifier.

[0047] The preparation method of the reaction intermediate is as follows: 4-maleimide benzoyl chloride is uniformly dissolved in dichloromethane at a material ratio of 0.05 g / mL, then N,N-dimethyl-4-pyridine amine with a volume of 6% of dichloromethane is added, after uniform mixing and stirring, 2-hydroxyethyl methacrylate with a volume of 0.55 times of N,N-dimethyl-4-pyridine amine is added dropwise in an ice water bath, and then the reaction is carried out at room temperature for 10 h after natural temperature rise; after the reaction is completed, the solid components in the product are washed with saturated sodium bicarbonate solution for 3 times; then washed with distilled water until neutral; after washing, dry with anhydrous magnesium sulfate to remove dichloromethane; finally, the obtained viscous liquid is subjected to vacuum distillation to obtain the reaction intermediate.

[0048] Example 3

[0049] A preparation method of silver powder for solar cell back silver paste, comprising the following steps:

[0050] Step one, preparation of silver micro powder;

[0051] A sodium hydroxide aqueous solution with a concentration of 0.3 g / mL and a temperature of 65°C is added dropwise to a silver nitrate solution with a concentration of 0.3 g / mL and a temperature of 35°C for 40 min while stirring, then a fatty alcohol polyoxyethylene ether with a mass of 2% of the obtained mixture is added, and the heating is stopped when the temperature rises to 70°C; a glycerol solution with a concentration of 55 wt% is slowly added, and the obtained product components are filtered after stirring for 120 min, and the obtained filter cake is washed with water and dried in sequence, and the obtained silver micro powder is stored for use;

[0052] The solute in the glycerol solution is glycerol, the solvent is distilled water, and the concentration of glycerol is 5 wt%; and the mass ratio of silver nitrate to sodium hydroxide is 4:1.

[0053] Step two, preparation of pretreated silver micro powder;

[0054] The silver micro powder is uniformly dispersed in 1,4-butanediol at a solid-liquid ratio of 0.08 g / mL, then 2-thiofurfuryl alcohol with a mass of 0.6 times of the silver micro powder is added, and stirring treatment is carried out at a temperature of 30°C for 7 h; after the stirring treatment is completed, high-speed centrifugal treatment is carried out, and then vacuum drying treatment is carried out after washing with 1,4-butanediol for 3 times, and the obtained is the pretreated silver micro powder;

[0055] Step three, preparation of silver powder for solar cell back silver paste;

[0056] The pretreated silver micropowder was uniformly dispersed in dimethyl sulfoxide at a solid-liquid ratio of 0.08 g / mL, and then an equal amount of the modifier was added. After uniform mixing and stirring, the mixture was incubated at 60°C for 10 h. After the reaction was completed, the obtained product components were sequentially subjected to centrifugal separation, dimethyl sulfoxide washing 4 times, and vacuum drying treatment. Finally, the obtained product was the silver powder for solar cell back silver paste.

[0057] The preparation method of the modifier in step three is as follows: 0.6 g / mL of methyl methacrylate was added to a 30% toluene aqueous solution, and then 5% of the reaction intermediate and 3.0% of azobisisobutyronitrile were sequentially added. After mixing and stirring for 40 min under the protection of nitrogen atmosphere, the temperature of the obtained mixed phase was raised to 75°C, and 30% of ammonium persulfate was added. After uniform mixing and stirring, the mixture was incubated at 85°C for 40 min. After the reaction was completed, the solid product was washed with 1,4-epoxybutane and methanol, and then dried at room temperature. Finally, the obtained product was the modifier.

[0058] The preparation method of the reaction intermediate is as follows: 0.06 g / mL of 4-maleimide benzoyl chloride was uniformly dissolved in dichloromethane, and then 8% of N,N-dimethyl-4-pyridine amine was added. After uniform mixing and stirring, 0.6 times of methyl methacrylate-2-hydroxyethyl ester was added dropwise under the condition of ice water bath. After natural temperature rise to room temperature, the mixture was incubated at room temperature for 12 h. After the reaction was completed, the solid components were washed with saturated sodium bicarbonate solution for 3 times. Then, the mixture was washed with distilled water until neutral. After washing, the mixture was dried with anhydrous magnesium sulfate to remove dichloromethane. Finally, the obtained viscous liquid was subjected to vacuum distillation to obtain the reaction intermediate.

[0059] Comparative Example 1: commercially available silver powder with a specific surface area of 1.5-2.0 (m 2 / g);

[0060] Comparative Example 2: silver micropowder prepared by step one;

[0061] Performance test: the silver powders provided by Examples 1-3 and Comparative Examples 1-2 were respectively marked as Examples 1-3 and Comparative Examples 1-2. The related properties of the silver powder samples provided by Examples 1-3 and Comparative Examples 1-2 were respectively detected, and the conductive properties were measured. The obtained detection results are recorded in the following table:

[0062] The test method of the conductive performance is as follows: 50 parts of each group of silver powder sample, 22 parts of adhesive and 4 parts of lead-free glass powder are weighed by weight; then the silver powder, organic adhesive and lead-free glass powder are mixed uniformly and then are treated by three-roll grinding machine, and the period viscosity is adjusted to 70 Pa.s. The obtained silver paste is printed on an alumina substrate by 280 mesh silk screen printing, and is sintered at a peak of 800 DEG C for 2 min, and then the sheet resistance is measured after it is naturally cooled to room temperature, and the obtained test results are recorded in the following table:

[0063] The preparation method of the adhesive is as follows: the following raw materials are weighed by weight: 45 parts of terpineol, 7 parts of butyl carbitol, 6 parts of butyl carbitol acetate, 6 parts of ethyl cellulose, 8 parts of diethyl phthalate and 2 parts of sorbitan stearate; the weighed raw materials are transferred into a reaction kettle, heated to 90 DEG C, and stirred while heating, until a uniform and transparent adhesive finished product is obtained.

[0064] The preparation method of the lead-free glass powder is as follows: 36 parts of Bi2O3, 7 parts of B2O3, 1.2 parts of NaF, 13 parts of SiO2, 7 parts of ZnO, 2.5 parts of TiO2, 11 parts of Al2O3 and 2 parts of P2O5 are weighed by weight; the weighed raw materials are mixed uniformly by a mixer, then are loaded into a quartz crucible, dried in an oven at 150 DEG C for 1.5 h, then the quartz crucible is taken out and placed in a muffle furnace, and is melted at a temperature of 1200 DEG C for 0.8 h; after the melting is completed, the deionized water is quenched, and then is ball milled for 18 h, and then is dried to obtain the lead-free glass powder.

[0065]

[0066] By comparing and analyzing the related data in the table, it can be known that the polymer with large molecular weight is introduced on the surface of the silver powder in the application, which effectively reduces the phenomenon of "agglomeration" of the silver powder, so that the silver powder can be dispersed in the resin system, and the dispersion performance and the conductive performance of the silver powder for the silver paste on the back of the solar cell are effectively ensured, and the quality is also ensured. Therefore, it is shown that the prepared silver powder product has a broader market prospect, and is more suitable for promotion.

[0067] In the description of the present specification, the description of the terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0068] The preferred embodiments of the application disclosed above are only to facilitate the elucidation of the application. The preferred embodiments do not describe all the details of the application and limit the application to the specific embodiments described. Obviously, many modifications and variations can be made in light of the teachings above. The description is chosen and described in order to best explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the application and get the best results from the application. The application is only limited by the claims and their full scope and equivalents.

Claims

1. A method for producing a silver powder for a silver paste for a back surface of a solar cell, characterized by, The method comprises the following steps: Step 1, preparation of silver micro-powder; A sodium hydroxide aqueous solution with a concentration of 0.2-0.3 g / mL and a temperature of 55-65 ℃ is added dropwise into a silver nitrate solution with a concentration of 0.1-0.3 g / mL and a temperature of 25-35 ℃ under stirring for 30-40 min, then a dispersant with a mass of 0.5-2% of the silver micro-powder is added into the obtained mixture, and the heating is stopped when the temperature of the mixture is increased to 60-70 ℃; a glycerol solution with a concentration of 45-55 wt% is slowly added, and the obtained product is filtered after stirring for 80-120 min, and the obtained filter cake is washed with water and dried, and the obtained silver micro-powder is stored and used; Step 2, preparation of pretreated silver micro-powder; The silver micro-powder is uniformly dispersed in 1,4-dioxane at a solid-liquid ratio of 0.03-0.08 g / mL, then 2-thiofurfuryl alcohol with a mass of 0.4-0.6 times of the silver micro-powder is added, and stirring is performed at a temperature of 20-30 ℃ for 4-7 h; after the stirring, high-speed centrifugal treatment is performed, and the obtained product is washed with 1,4-dioxane for 2-3 times and then vacuum dried, and the obtained product is the pretreated silver micro-powder; Step 3, preparation of silver powder for solar cell back silver paste; The pretreated silver micro-powder is uniformly dispersed in an organic solvent at a solid-liquid ratio of 0.05-0.08 g / mL, then an equal amount of modifier is added, and the mixture is uniformly stirred and reacted at a temperature of 50-60 ℃ for 6-10 h; after the reaction, the obtained product is subjected to centrifugal separation, washed with organic solvent for 3-4 times, and vacuum dried, and the obtained product is the silver powder for solar cell back silver paste; The preparation method of the modifier in step 3 is as follows: methyl methacrylate is added to a toluene aqueous solution with a volume concentration of 20-30% at a dosage ratio of 0.5-0.6 g / mL, then a reaction intermediate with a mass of 3-5% of the methyl methacrylate and a reaction promoter with a mass of 2.0-3.0% of the methyl methacrylate are sequentially added, the mixture is stirred for 30-40 min under the protection of nitrogen atmosphere, then the temperature of the obtained mixture is increased to 70-75 ℃, and a persulfate salt with a mass of 20-30% of the reaction promoter is added, the mixture is uniformly stirred and reacted at a temperature of 70-75 ℃ for 5-8 h, and then reacted at a temperature of 80-85 ℃ for 30-40 min; after the reaction, the solid product in the obtained product is washed with 1,4-dioxane and methanol and dried at room temperature, and the obtained product is the modifier; The reaction promoter is selected from any one of azobis isobutyronitrile and azobis isoheptyl nitrile. The preparation method of the reaction intermediate is: uniformly dissolving 4-maleimide benzoyl chloride in dichloromethane at a material ratio of 0.03-0.06 g / mL, then adding N, N-dimethyl-4-pyridine amine with a volume of 5-8% of dichloromethane, mixing and stirring uniformly, then adding 2-hydroxyethyl methacrylate with a volume of 0.5-0.6 times of N, N-dimethyl-4-pyridine amine under the condition of ice water bath, naturally warming to room temperature, then keeping reaction for 8-12 h; after the reaction is completed, washing the solid components in the product with saturated sodium bicarbonate solution for 2-3 times; then washing with distilled water until neutral; after washing, drying with anhydrous magnesium sulfate to remove dichloromethane; finally, performing vacuum distillation on the obtained viscous liquid to obtain the reaction intermediate.

2. The method for preparing silver powder for silver paste of solar cell back surface according to claim 1, characterized in that: The dispersant in step one is selected from any one of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

3. The method for preparing silver powder for silver paste of solar cell back surface according to claim 1, characterized in that: The persulfate salt is selected from any one of ammonium persulfate and potassium persulfate.

4. The method for preparing silver powder for silver paste of solar cell back surface according to claim 1, characterized in that: The organic solvent in step three is selected from any one of N, N-dimethylformamide, toluene and dimethyl sulfoxide.

5. The method for preparing silver powder for silver paste of solar cell back surface according to claim 1, characterized in that: In step one, the solute in the glycerol solution is glycerol, the solvent is distilled water, and the concentration of glycerol is 45-55 wt%.

6. The method for preparing silver powder for silver paste of solar cell back surface according to claim 1, characterized in that: The mass ratio of silver nitrate to sodium hydroxide in step one is 3-4:1.

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