Silver powder and its preparation method and application

Abstract

The present invention discloses a silver powder, a preparation method and an application thereof, and belongs to the technical field of silver powder. The preparation method of the silver powder comprises: mixing a silver ion solution, a reducing solution and a dispersant solution to react and obtain a reaction liquid; separating the reaction liquid into solid and liquid, mixing the solid with a coating agent solution, and drying; the coating agent solution comprises at least one of lauric acid, sodium laurate, a silane coupling agent, oleic acid, lauric acid, stearic acid, palmitic acid and benzotriazole, and at least one of acrylic resin, rosin resin and polyvinyl butyral. By introducing a resin with high adhesion in the process of preparing the silver powder and using the resin as a coating agent component, the adhesion of the TOPCon back-side fine grid slurry after printing on the silicon wafer can be improved, thereby avoiding the phenomenon of grid line falling off of the back-side slurry. At the same time, it can ensure that the slurry viscosity is low, improve printing smoothness, and avoid the problem of a large number of broken grids during the printing process.

Description

Technical Field

[0001] The present invention relates to the technical field of silver powder, and in particular to silver powder and a preparation method and application thereof. Background Art

[0002] TOPCon cells are also known as tunnel oxide passivated contacts. A 1nm to 2nm tunnel oxide layer is prepared on the back of the cell, and then a layer of doped polysilicon is deposited. Together, these two layers form a passivated contact structure. Conductive silver paste is printed on the silicon wafer surface via screen printing on both the front and back of the TOPCon cell. The entire printing process is divided into four steps: one step prints the back main grid, followed by drying; the second step prints the back fine grid, followed by drying; the third step prints the front main grid, followed by drying; and the fourth step prints the front fine grid, followed by sintering. Between the second and third steps, the TOPCon back fine grid is in direct contact with the printing machine, making it easy for the grid lines to fall off, so the back conductive silver paste needs to have good adhesion.

[0003] Existing TOPCon backside fine grid pastes primarily use resins combined with solvents and leveling agents to create an organic carrier. This organic carrier is then mixed with glass powder and silver powder to create a silver paste to improve the paste's adhesion and printability. However, this solution often struggles to balance adhesion and printability. Good adhesion requires the addition of a large amount of resin, but excessive resin can lead to excessive paste viscosity and poor printing.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a silver powder and a preparation method and application thereof, so as to solve or improve the above-mentioned technical problems.

[0006] The present invention can be implemented like this:

[0007] In a first aspect, the present invention provides a method for preparing silver powder, comprising the following steps:

[0008] mixing the silver ion solution, the reducing solution and the dispersant solution to react and obtain a reaction solution; separating the reaction solution into a solid and a liquid and collecting a solid;

[0009] mixing the solid with the coating agent solution and drying;

[0010] The coating agent solution includes a first solute and a second solute, wherein the first solute includes at least one of lauric acid, sodium laurate, silane coupling agent, oleic acid, lauric acid, stearic acid, palmitic acid and benzotriazole; and the second solute includes at least one of acrylic resin, rosin resin and polyvinyl butyral resin.

[0011] In an optional embodiment, the second solute is at least one of thermoplastic acrylate, hydrogenated rosin resin and polyvinyl butyral resin.

[0012] In an optional embodiment, in the coating agent solution, the content of the first solute is 0.01 g / mL to 0.05 g / mL, and the content of the second solute is 0.01 g / mL to 0.05 g / mL.

[0013] In an optional embodiment, in the coating agent solution, the solvent includes at least one of ethanol, isopropanol and acetone.

[0014] In an optional embodiment, the concentration of silver ions in the silver ion solution is 0.1 mol / L to 5 mol / L;

[0015] In an optional embodiment, the concentration of silver ions in the silver ion solution is 0.5 mol / L to 3 mol / L;

[0016] In an alternative embodiment, the silver ion solution is obtained by mixing silver nitrate with water.

[0017] In an optional embodiment, the concentration of the reducing agent in the reducing solution is 0.2 mol / L to 2 mol / L;

[0018] In an optional embodiment, the concentration of the reducing agent in the reducing solution is 0.4 mol / L to 1.5 mol / L.

[0019] In an alternative embodiment, the reducing agent comprises at least one of glucose, hydrazine hydrate, sodium borohydride, potassium borohydride, ascorbic acid, urea, formaldehyde and isoascorbic acid.

[0020] In an optional embodiment, the content of the dispersant in the dispersant solution is 0.01 g / mL to 1 g / mL.

[0021] In an optional embodiment, the content of the dispersant in the dispersant solution is 0.05 g / mL to 0.5 g / mL.

[0022] In an alternative embodiment, the dispersant in the dispersant solution comprises at least one of polyvinyl pyrrolidone, maleic acid, cyclodextrin, fumaric acid, gelatin, malic acid, gum arabic, polyacrylamide, and oleic acid.

[0023] In an optional embodiment, the reaction temperature of the silver ion solution, the reducing solution and the dispersant solution is 15° C. to 50° C., and the reaction time is 5 min to 20 min;

[0024] In an optional embodiment, the molar ratio of the reducing agent in the reducing solution to the silver ions in the silver ion solution is 0.5:1 to 4:1, and the mass of the dispersant in the dispersant solution is 1% to 40% of the mass of the silver source providing silver ions in the silver ion solution.

[0025] In an optional embodiment, the molar ratio of the reducing agent in the reducing solution to the silver ions in the silver ion solution is 0.5:1 to 2:1, and the mass of the dispersant in the dispersant solution is 10% to 30% of the mass of the silver source providing silver ions in the silver ion solution.

[0026] In an optional embodiment, the silver ion solution and the reducing solution are both introduced into the dispersant solution at a flow rate of 5 mL / min to 50 mL / min.

[0027] In an optional embodiment, the reaction is carried out at a stirring speed of 200 rpm to 250 rpm.

[0028] In an optional embodiment, the mass ratio of solid to coating agent solution is 1:1 to 1:2.

[0029] In an optional embodiment, the solid and the coating agent solution are mixed at a stirring speed of 100 rpm to 800 rpm for 5 min to 60 min.

[0030] In an optional embodiment, the drying temperature after the solid and the coating agent solution are mixed is 35° C. to 60° C., and the drying time is 1 hour to 5 hours.

[0031] In an optional embodiment, the solid is further washed before being mixed with the coating agent solution.

[0032] In an optional embodiment, the solid is washed with deionized water and ethanol in sequence until the conductivity of the washing liquid is ≤20 μs / cm.

[0033] In a second aspect, the present invention provides a silver powder prepared by the preparation method of any one of the aforementioned embodiments.

[0034] In an optional embodiment, the silver powder D 50 It is 1.2μm~1.8μm.

[0035] In an optional embodiment, the tap density of the silver powder is 5.5 g / cm 3 ~6.3g / cm 3 .

[0036] In an optional embodiment, the specific surface area of ​​the silver powder is 0.35 m 2 / g~0.75m 2 / g.

[0037] In an optional embodiment, the burnout of the silver powder is 0.5 wt % to 1 wt %.

[0038] In a third aspect, the present invention provides a silver paste, wherein raw materials for preparing the silver paste include an organic carrier, glass powder, and the silver powder of the aforementioned embodiment.

[0039] In an optional embodiment, the raw materials for preparing the silver paste include, by weight, 86 to 90 parts of silver powder, 8 to 12 parts of organic vehicle, and 2 to 3 parts of glass powder.

[0040] In a fourth aspect, the present invention provides a TOPCon battery, wherein the silver paste on the back side of the TOPCon battery is the silver paste of the aforementioned embodiment.

[0041] The beneficial effects of the present invention include:

[0042] By introducing a highly adhesive resin during the preparation of silver powder and using this resin as a coating agent, the adhesion of the TOPCon back-side fine grid paste after printing on the silicon wafer can be improved, preventing the grid lines from falling off on the back side of the paste. At the same time, it can ensure that the paste viscosity is low, improve printing smoothness, and avoid the problem of a large number of broken grids during the printing process.

[0043] Among them, thermoplastic acrylates, hydrogenated rosin resins, and polyvinyl butyral resins contain a large number of polar groups, carboxyl groups, or hydroxyl groups, which can firmly adsorb to the surface of the silver powder. When the silver powder coated with these resins is prepared into a slurry, the silver powder particles can be connected together through the long chain action of the resin. At the same time, the polar groups can also firmly adsorb to the surface of the cell, ensuring the adhesion of the fine grid. When silver powder that has not been coated with these resins is prepared into a slurry, the silver powder particles are not effectively connected, so the fine grid can be damaged by even the slightest external force. DETAILED DESCRIPTION

[0044] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0045] The silver powder provided by the present invention and its preparation method and application are described in detail below.

[0046] The present invention provides a method for preparing silver powder, comprising the following steps:

[0047] mixing the silver ion solution, the reducing solution and the dispersant solution to react and obtain a reaction solution; separating the reaction solution into a solid and a liquid and collecting a solid;

[0048] mixing the solid with the coating agent solution and drying;

[0049] The coating agent solution includes a first solute and a second solute, wherein the first solute includes at least one of lauric acid, sodium laurate, silane coupling agent, oleic acid, lauric acid, stearic acid, palmitic acid and benzotriazole; and the second solute includes at least one of acrylic resin, rosin resin and polyvinyl butyral resin.

[0050] In some preferred embodiments, the second solute is at least one of thermoplastic acrylate, hydrogenated rosin resin, and polyvinyl butyral resin.

[0051] By introducing a resin with high adhesion during the preparation of silver powder and using the resin as a coating agent component, the present invention can improve the adhesion of the TOPCon back-side fine grid slurry after printing on the silicon wafer, thereby avoiding the phenomenon of grid line shedding in the back-side slurry. At the same time, it can ensure that the slurry viscosity is low, improve printing smoothness, and avoid the problem of a large number of broken grids during the printing process.

[0052] Among them, thermoplastic acrylates, hydrogenated rosin resins, and polyvinyl butyral resins contain a large number of polar groups, carboxyl groups, or hydroxyl groups, which can firmly adsorb to the surface of the silver powder. When the silver powder coated with these resins is prepared into a slurry, the silver powder particles can be connected together through the long chain action of the resin. At the same time, the polar groups can also firmly adsorb to the surface of the cell, ensuring the adhesion of the fine grid. When silver powder that has not been coated with these resins is prepared into a slurry, the silver powder particles are not effectively connected, so the fine grid can be damaged by even the slightest external force.

[0053] It should be noted that if the above resin components are directly added during the reaction process, the resin will not be dissolved and normal production and preparation cannot be carried out.

[0054] In some optional embodiments, the concentration of silver ions in the silver ion solution can be 0.1mol / L to 5mol / L, such as 0.1mol / L, 0.5mol / L, 1mol / L, 1.5mol / L, 2mol / L, 2.5mol / L, 3mol / L, 3.5mol / L, 4mol / L, 4.5mol / L or 5mol / L, or other values ​​within the range of 0.1mol / L to 5mol / L. In some more typical embodiments, the concentration of silver ions in the silver ion solution is 0.5mol / L to 3mol / L.

[0055] The silver ion solution can be obtained by mixing a silver source (such as silver nitrate) with water. In addition, the silver source can also be at least one of silver sulfate, silver carbonate, silver acetate, silver lactate, silver bromide, silver iodide, silver phosphate and silver stearate.

[0056] In some optional embodiments, the concentration of the reducing agent in the reducing solution can be 0.2 mol / L to 2 mol / L, such as 0.2 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, or 2 mol / L, or other values ​​within the range of 0.2 mol / L to 2 mol / L. In some typical embodiments, the concentration of the reducing agent in the reducing solution is 0.4 mol / L to 1.5 mol / L.

[0057] By way of example, the reducing agent may include at least one of glucose, hydrazine hydrate, sodium borohydride, potassium borohydride, ascorbic acid, urea, formaldehyde, and isoascorbic acid.

[0058] In some optional embodiments, the content of the dispersant in the dispersant solution is 0.01 g / mL to 1 g / mL, and can be 0.01 g / mL, 0.05 g / mL, 0.1 g / mL, 0.2 g / mL, 0.5 g / mL, 0.8 g / mL or 1 g / mL, etc., or other values ​​within the range of 0.01 g / mL to 1 g / mL. In some more typical embodiments, the content of the dispersant in the dispersant solution is 0.05 g / mL to 0.5 g / mL, and further 0.06 g / mL to 0.1 mg / mL.

[0059] By way of example, the dispersant in the dispersant solution may include at least one of polyvinyl pyrrolidone, maleic acid, cyclodextrin, fumaric acid, gelatin, malic acid, gum arabic, polyacrylamide, and oleic acid.

[0060] In some optional embodiments, the reaction temperature of the silver ion solution, the reducing solution and the dispersant solution can be 15°C to 50°C, such as 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, or other values ​​within the range of 15°C to 50°C.

[0061] The reaction time of the silver ion solution, the reducing solution and the dispersant solution can be 5 min to 20 min, such as 5 min, 10 min, 15 min or 20 min, or other values ​​within the range of 5 min to 20 min.

[0062] In some optional embodiments, the molar ratio of the reducing agent in the reducing solution to the silver ions in the silver ion solution is 0.5:1 to 4:1, such as 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, or other values ​​within the range of 0.5:1 to 4:1. In some more typical embodiments, the molar ratio of the reducing agent in the reducing solution to the silver ions in the silver ion solution is 0.5:1 to 2:1, further 0.8:1 to 1.5:1.

[0063] The mass of the dispersant in the dispersant solution is 1% to 40% of the mass of the silver source providing silver ions in the silver ion solution, such as 1%, 2%, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35% or 40%, and may also be other values ​​within the range of 1% to 40%. In some typical embodiments, the mass of the dispersant in the dispersant solution is 10% to 30% of the mass of the silver source providing silver ions in the silver ion solution, and further 19.6% to 29.4%.

[0064] The solvent in the silver ion solution, reducing solution and dispersant solution is water.

[0065] In some embodiments, the silver ion solution and the reducing solution are both introduced into the dispersant solution at a flow rate of 5 mL / min to 50 mL / min (e.g., 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min, 40 mL / min, 45 mL / min, or 50 mL / min, etc.).

[0066] Preferably, the reaction of the silver ion solution, the reducing solution and the dispersant solution is carried out under stirring. The stirring speed can be 200 rpm to 250 rpm, such as 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm or 250 rpm.

[0067] Under the above conditions, the silver ion solution and the reducing solution can be reacted uniformly and sufficiently.

[0068] After the reaction is completed, the reaction solution obtained by the reaction is subjected to solid-liquid separation, and the separated solid is collected and washed.

[0069] In some optional embodiments, the solid may be washed with deionized water and ethanol in sequence until the conductivity of the washing liquid is ≤20 μs / cm.

[0070] Furthermore, the washed solid is mixed with a coating agent solution.

[0071] In some optional embodiments, the mass ratio of the solid to the coating agent solution may be 1:1 to 1:2, such as 1:1, 1:1.5 or 1:2.

[0072] In the coating agent solution, the content of the first solute is 0.01 g / mL to 0.05 g / mL, such as 0.01 g / mL, 0.02 g / mL, 0.03 g / mL, 0.04 g / mL or 0.05 g / mL, or any other value within the range of 0.01 g / mL to 0.05 g / mL.

[0073] The content of the second solute is 0.01 g / mL to 0.05 g / mL, such as 0.01 g / mL, 0.02 g / mL, 0.03 g / mL, 0.04 g / mL or 0.05 g / mL, and can also be any other value within the range of 0.01 g / mL to 0.05 g / mL.

[0074] For example, the solvent in the coating agent solution may include at least one of ethanol, isopropyl alcohol, acetone, and the like.

[0075] In the second solute, if the amount of resin used is too small compared to the solid, it is not conducive to the dispersion of silver powder; if the amount of resin used is too large compared to the solid, it is easy to cause the silver powder to be too sticky, affecting the printability of the slurry.

[0076] The solid and the coating agent solution are mixed at a stirring speed of 100 rpm to 800 rpm (such as 100 rpm, 200 rpm, 400 rpm, 600 rpm or 800 rpm, etc.) for 5 min to 60 min (such as 5 min, 10 min, 20 min, 30 min, 40 min, 50 min or 60 min, etc.).

[0077] Mixing under the above conditions can make the coating more uniform.

[0078] In some optional embodiments, the drying temperature after the solid and the coating agent solution are mixed is 35°C to 60°C (such as 35°C, 40°C, 45°C, 50°C, 55°C or 60°C, etc.), and the drying time is 1h to 5h (such as 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, etc.).

[0079] As mentioned above, the preparation method of the silver powder provided by the present invention is simple in process, easy to operate, and saves time and labor.

[0080] The energy consumption is low, the silver powder yield is high and the spherical morphology of the silver powder can be effectively maintained.

[0081] Correspondingly, the present invention also provides a silver powder, which is prepared by the above preparation method.

[0082] In some optional embodiments, the D of the silver powder 50 It is 1.2μm~1.8μm.

[0083] In some optional embodiments, the tap density of the silver powder is 5.5 g / cm 3 ~6.3g / cm 3 .

[0084] In some optional embodiments, the specific surface area of ​​the silver powder is 0.35 m 2 / g~0.75m 2 / g.

[0085] In some optional embodiments, the burnout of the silver powder is 0.5 wt % to 1 wt %.

[0086] The silver powder particles provided by the present invention have good morphology and high specific surface area, which are beneficial to improving sintering activity and sintering shrinkage.

[0087] In addition, the present invention also provides a silver paste, the raw materials for preparing the silver paste include an organic carrier, glass powder and the above-mentioned silver powder.

[0088] In some optional embodiments, the raw materials for preparing the silver paste include, by weight, 86 to 90 parts of silver powder, 8 to 12 parts of organic vehicle, and 2 to 3 parts of glass powder.

[0089] The amount of silver powder may be 86 parts, 86.5 parts, 87 parts, 87.5 parts, 88 parts, 88.5 parts, 89 parts, 89.5 parts or 90 parts, or other values ​​within the range of 86 to 90 parts.

[0090] The amount of the organic carrier can be 8 parts, 8.5 parts, 9 parts, 9.5 parts, 10 parts, 10.5 parts, 11 parts, 11.5 parts or 12 parts, etc., and can also be other values ​​within the range of 8 to 12 parts.

[0091] The amount of glass powder used can be 2 parts, 2.5 parts, 3 parts, etc., or other values ​​within the range of 2 to 3 parts.

[0092] The viscosity of the silver paste is about 100 Pa·s to 180 Pa·s (measurement conditions: Brookfield DV2T viscometer, rotation speed 10 rpm), which has good printing smoothness and avoids or improves the risk of a large number of broken grids during the printing process; at the same time, the paste also has good adhesion and can improve the phenomenon of grid line falling off.

[0093] As mentioned above, after the silver powder provided by the present invention is prepared into a slurry, it can be smoothly printed on a screen below 10μm. The printed grid lines have excellent adhesion after drying, without falling off (3M tape after drying the grid lines, 0 falling off) and smooth printing without broken grids.

[0094] Furthermore, the present invention also provides a TOPCon battery, the back silver paste of the TOPCon battery is the above-mentioned silver paste.

[0095] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0096] Example 1

[0097] This embodiment provides a method for preparing silver powder, comprising the following steps:

[0098] S1: Use a peristaltic pump to evenly add 300 mL of silver ion solution and 400 mL of reducing solution to 300 mL of dispersant solution at a rate of 10 mL / min, stirring at 200 rpm, controlling the process temperature at 40°C, and react for 10 minutes.

[0099] The silver ion solution was prepared by mixing silver nitrate with deionized water, with a silver ion concentration of 2 mol / L. The reducing solution was prepared by mixing glucose with deionized water, with a glucose concentration of 1.2 mol / L. The dispersant solution was prepared by mixing 25 g of polyvinylpyrrolidone K30 with 300 mL of deionized water.

[0100] That is, the molar ratio of the reducing agent in the reducing solution to the silver ions in the silver ion solution is 0.8:1, and the mass of the dispersant in the dispersant solution is 24.5% of the mass of the silver source providing silver ions in the silver ion solution.

[0101] S2: After the reaction is completed, the obtained reaction solution is filtered to collect the solid; and the solid is washed with deionized water and ethanol respectively until the conductivity of the washing solution is ≤20 μS / cm to obtain a wet powder.

[0102] S3: The cleaned wet powder and the coating agent solution were stirred at a mass ratio of 1:1 (stirring speed of 450 rpm) for 10 minutes, then dried (temperature of 40°C, time of 2 hours), and sieved to obtain silver powder recorded as A1.

[0103] The coating agent solution was prepared by dissolving 2 g of lauric acid and 2 g of acrylic resin (Mitsubishi BR115) in 100 mL of ethanol.

[0104] The mass yield of the silver powder obtained in this embodiment is 93.02%.

[0105] Example 2

[0106] This embodiment provides a method for preparing silver powder, comprising the following steps:

[0107] S1: Use a peristaltic pump to evenly add 300 mL of silver ion solution and 500 mL of reducing solution to 300 mL of dispersant solution at a rate of 15 mL / min, stirring at 220 rpm, controlling the process temperature at 35°C, and react for 10 minutes.

[0108] The silver ion solution was prepared by mixing silver nitrate with deionized water, with a silver ion concentration of 2 mol / L. The reducing solution was prepared by mixing ascorbic acid with deionized water, with a ascorbic acid concentration of 1.5 mol / L. The dispersant solution was prepared by mixing 30 g of polyacrylamide with 300 mL of deionized water.

[0109] That is, the molar ratio of the reducing agent in the reducing solution to the silver ions in the silver ion solution is 1.25:1, and the mass of the dispersant in the dispersant solution is 29.4% of the mass of the silver source providing silver ions in the silver ion solution.

[0110] S2: After the reaction is completed, the obtained reaction solution is filtered to collect the solid; and the solid is washed with deionized water and ethanol respectively until the conductivity of the washing solution is ≤20 μS / cm to obtain a wet powder.

[0111] S3: The cleaned wet powder and the coating agent solution were stirred at a mass ratio of 1:1.5 (stirring speed of 550 rpm) for 10 minutes, then dried (temperature of 45 ° C, time of 1.5 hours), sieved, and the obtained silver powder was recorded as A2.

[0112] The coating agent solution is composed of 2g stearic acid and 2g hydrogenated rosin resin (Eastman 105) was dissolved in 100 mL of ethanol.

[0113] The yield of the silver powder obtained in this example is 92.40%.

[0114] Example 3

[0115] This embodiment provides a method for preparing silver powder, comprising the following steps:

[0116] S1: Use a peristaltic pump to evenly add 300 mL of silver ion solution and 600 mL of reducing solution to 300 mL of dispersant solution at a rate of 10 mL / min, stirring at 210 rpm, controlling the process temperature at 25°C, and react for 15 minutes.

[0117] The silver ion solution was prepared by mixing silver nitrate with deionized water, with a silver ion concentration of 2 mol / L. The reducing solution was prepared by mixing formaldehyde with deionized water, with a formaldehyde concentration of 1.5 mol / L. The dispersant solution was prepared by mixing 20 g of polyacrylamide with 300 mL of deionized water.

[0118] That is, the molar ratio of the reducing agent in the reducing solution to the silver ions in the silver ion solution is 1.5:1, and the mass of the dispersant in the dispersant solution is 19.6% of the mass of the silver source providing silver ions in the silver ion solution.

[0119] S2: After the reaction is completed, the obtained reaction solution is filtered to collect the solid; and the solid is washed with deionized water and ethanol respectively until the conductivity of the washing solution is ≤20 μS / cm to obtain a wet powder.

[0120] S3: The cleaned wet powder and the coating agent solution were stirred at a mass ratio of 1:1.2 (stirring speed of 600 rpm) for 10 minutes, then dried (temperature of 45 ° C, time of 3 hours), sieved, and the obtained silver powder was recorded as A3.

[0121] The coating agent solution was prepared by dissolving 2 g of stearic acid and 1.5 g of polyvinyl butyral resin (Kuraray B60HH) in 100 mL of ethanol.

[0122] The yield of the silver powder obtained in this example is 92.25%.

[0123] Example 4

[0124] This embodiment provides a method for preparing silver powder, comprising the following steps:

[0125] S1: Use a peristaltic pump to evenly add 300 mL of silver ion solution and 500 mL of reducing solution to 300 mL of dispersant solution at a rate of 5 mL / min, stirring at 230 rpm, controlling the process temperature at 15°C, and react for 20 minutes.

[0126] The silver ion solution was prepared by mixing silver nitrate with deionized water, with a silver ion concentration of 0.5 mol / L. The reducing solution was prepared by mixing hydrazine hydrate with deionized water, with a hydrazine hydrate concentration of 0.4 mol / L. The dispersant solution was prepared by mixing 5 g of maleic acid with 300 mL of deionized water.

[0127] That is, the molar ratio of the reducing agent in the reducing solution to the silver ions in the silver ion solution is 1.33:1, and the mass of the dispersant in the dispersant solution is 19.6% of the mass of the silver source providing silver ions in the silver ion solution.

[0128] S2: After the reaction is completed, the obtained reaction solution is filtered to collect the solid; and the solid is washed with deionized water and ethanol respectively until the conductivity of the washing solution is ≤20 μS / cm to obtain a wet powder.

[0129] S3: The cleaned wet powder and the coating agent solution were stirred at a mass ratio of 1:2 (stirring speed of 100 rpm) for 60 minutes, then dried (temperature of 35 ° C, time of 6 hours), sieved, and the obtained silver powder was recorded as A4.

[0130] The coating agent solution is composed of 2g sodium laurate, 1.0g polyvinyl butyral resin (Kuraray B30HH) and 1g hydrogenated rosin resin ( 3085) was dissolved in 100 mL of ethanol.

[0131] The yield of the silver powder obtained in this example is 91.20%.

[0132] Example 5

[0133] This embodiment provides a method for preparing silver powder, comprising the following steps:

[0134] S1: Use a peristaltic pump to evenly add 300 mL of silver ion solution and 500 mL of reducing solution to 300 mL of dispersant solution at a rate of 50 mL / min, stirring at a speed of 250 rpm, controlling the process temperature at 50°C, and react for 5 minutes.

[0135] The silver ion solution was prepared by mixing silver nitrate with deionized water, with a silver ion concentration of 3 mol / L. The reducing solution was prepared by mixing sodium borohydride with deionized water, with a sodium borohydride concentration of 2 mol / L. The dispersant solution was prepared by mixing 30 g of cyclodextrin with 300 mL of deionized water.

[0136] That is, the molar ratio of the reducing agent in the reducing solution to the silver ions in the silver ion solution is 1.11:1, and the mass of the dispersant in the dispersant solution is 19.6% of the mass of the silver source providing silver ions in the silver ion solution.

[0137] S2: After the reaction is completed, the obtained reaction solution is filtered to collect the solid; and the solid is washed with deionized water and ethanol respectively until the conductivity of the washing solution is ≤20 μS / cm to obtain a wet powder.

[0138] S3: The cleaned wet powder and the coating agent solution were stirred at a mass ratio of 1:1 (stirring speed of 800 rpm) for 5 minutes, then dried (temperature of 60°C, time of 1 hour), and sieved to obtain silver powder recorded as A5.

[0139] The coating agent solution was prepared by dissolving 2 g of palmitic acid, 1.5 g of acrylic resin (HIPLAAD ER 2602, Japan) and 1 g of polyvinyl butyral resin (Kuraray B20H) in 100 mL of ethanol.

[0140] The yield of the silver powder obtained in this example is 92.10%.

[0141] Comparative Example 1

[0142] The difference between this comparative example and Example 1 is that the coating agent solution is obtained by dissolving 2 g of lauric acid and 0.5 g of acrylic resin (Mitsubishi BR115) in 100 mL of ethanol. The obtained product is recorded as B1, with a yield of 93.48% and a loss on ignition of 0.88 wt%.

[0143] Comparative Example 2

[0144] The difference between this comparative example and Example 1 is that the coating agent solution is obtained by dissolving 2 g of lauric acid and 10 g of acrylic resin (Mitsubishi BR115) in 100 mL of ethanol. The obtained product is recorded as B2, with a yield of 92.87% and a loss on ignition of 0.89 wt%.

[0145] Comparative Example 3

[0146] The difference between this comparative example and Example 1 is that the coating agent solution is obtained by dissolving 2 g of lauric acid in 100 mL of ethanol. The obtained product is recorded as B3, with a yield of 92.87% and a loss on ignition of 0.72 wt%.

[0147] Comparative Example 4

[0148] The difference between this comparative example and Example 4 is that the coating agent solution does not contain polyvinyl butyral resin. The obtained product is recorded as B4, with a yield of 90.2% and a loss on burn of 0.76 wt%.

[0149] Comparative Example 5

[0150] The difference between this comparative example and Example 1 is that the coating agent solution does not contain acrylic resin. The obtained product is recorded as B5, with a yield of 92.2% and a loss on burn of 0.81 wt%.

[0151] ①. The performance of the silver powder obtained in Examples 1 to 5 was tested, and the results are shown in Table 1.

[0152] Table 1 Comparison results of silver powder

[0153] <![CDATA[D 50 (μm)]]> <![CDATA[Tap density (g / cm 3 )]]> <![CDATA[Specific surface area (m 2 / g)]]> Burning loss (wt%) Yield (%) Example 1 1.55 6.23 0.62 0.68 93.02 Example 2 1.66 6.20 0.64 0.59 92.40 Example 3 1.45 5.95 0.45 0.50 92.25 Example 4 1.51 5.50 0.51 0.52 91.20 Example 5 1.58 5.89 0.60 0.56 92.10

[0154] ②. The silver powder obtained in each embodiment and comparative example was respectively prepared into a slurry with glass powder and an organic carrier. The specific operation was as follows: 528g of silver powder, 13.2g of glass powder and 58.8g of organic carrier were weighed and mixed evenly. After stirring evenly with a homogenizer, the mixture was rolled using a 60E Eckart three-roll mill to produce a TOPCon backside fine grid slurry, wherein the organic carrier was composed of ethyl cellulose STD-4, SEBS and diethylene glycol butyl ether acetate in a mass ratio of 5:5:90.

[0155] At the same time, a control example was set up: 528g of silver powder (silver powder in comparative example 1), 13.2g of glass powder and 58.8g of organic carrier were weighed and mixed evenly. After stirring evenly with a homogenizer, they were rolled using a 60E Aikar three-roller mill to make TOPCon back-side fine grid slurry, wherein the organic carrier was composed of acrylic resin BR115, ethyl cellulose STD-4, SEBS and diethylene glycol butyl ether acetate in a mass ratio of 5:5:5:85.

[0156] 3M Test: The prepared slurry was screen-printed on a Maxwell printer. The printed TOPCon silicon wafer was then dried in a drying oven (300°C to 350°C for 30 seconds). 3M tape was then applied to the dried silicon wafer. Gently press with your fingers until no bubbles are visible under the tape. The tape was then quickly removed from the silicon wafer by hand. The gate lines were observed to detach from the wafer. The results are shown in Table 2.

[0157] EL testing: After drying, each TOPCon wafer was subjected to subsequent processes, including front-side busbar and fine grid printing and sintering (sintering furnace temperature ranged from 350°C to 780°C, with a peak temperature of 780°C and a sintering time of 60 seconds). The sintered wafers were tested for grid breakage using EL testing equipment. The results are shown in Table 3.

[0158] Table 2 Comparison results

[0159] 3M fine grid shedding ratio Example 1 0％ Example 2 0％ Example 3 0％ Example 4 0％ Example 5 0％ Comparative Example 1 8％ Comparative Example 2 0％ Comparative Example 3 35％ Comparative Example 4 30％ Comparative Example 5 45％ Control Example 5％

[0160] As can be seen from Table 2, by introducing the resin into the coating agent solution to coat the wet silver powder, the fine grid can be effectively prevented from falling off. From Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, if the acrylic resin content is too low (as in Comparative Example 1), 8% of the fine grid will fall off. Only when the acrylic resin content reaches a certain level can the fine grid be prevented from falling off.

[0161] Table 3 Comparison results

[0162] EL gate breaking number (roots) Example 1 0 Example 2 0 Example 3 0 Example 4 0 Example 5 0 Comparative Example 1 15 Comparative Example 2 80 Comparative Example 3 75 Comparative Example 4 72 Comparative Example 5 76 Control Example 100

[0163] It can be seen from Table 3 that the grid breaking phenomenon can be effectively avoided by introducing the resin into the coating agent solution to coat the silver wet powder.

[0164] Comparative Examples 1, 2, and 3 show that while breakage in Comparative Example 1 decreased, it still did not meet the requirements, indicating that the resin content was too low. While the resin content in Comparative Example 2 was sufficient, the excessive addition resulted in excessive viscosity and poor printing, which also increased breakage. The comparative example added acrylic resin during the slurry preparation process. While this method reduced 3M shedding, breakage was exacerbated. Acrylic resin can improve adhesion, but adding it during the slurry preparation process worsened the slurry's printability.

[0165] In summary, by introducing a resin with high adhesion during the preparation of silver powder and using this resin as a coating agent component, the adhesion of the TOPCon back-side fine grid paste after printing on the silicon wafer can be improved, avoiding the phenomenon of grid lines falling off in the back-side paste. At the same time, it can ensure that the paste viscosity is low, improve printing smoothness, and avoid the problem of a large number of broken grids during the printing process.

[0166] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing silver powder, characterized in that: The following steps are involved: mixing a silver ion solution, a reducing solution and a dispersant solution to react to obtain a reaction solution; separating the reaction solution into a solid and a liquid, and collecting a solid; mixing the solid with a coating agent solution and drying; The coating agent solution includes a first solute and a second solute, wherein the first solute includes at least one of lauric acid, sodium laurate, a silane coupling agent, oleic acid, stearic acid, palmitic acid and benzotriazole; and the second solute includes at least one of acrylic resin, rosin resin and polyvinyl butyral resin. In the coating agent solution, the content of the first solute is 0.01 g / mL to 0.05 g / mL, and the content of the second solute is 0.01 g / mL to 0.05 g / mL.

2. The preparation method according to claim 1, characterized in that In the coating agent solution, the solvent includes at least one of ethanol, isopropanol and acetone.

3. The preparation method according to claim 1, characterized in that The concentration of silver ions in the silver ion solution is 0.1 mol / L to 5 mol / L; The silver ion solution is obtained by mixing silver nitrate and water.

4. The preparation method according to claim 3, characterized in that The concentration of silver ions in the silver ion solution is 0.5 mol / L to 3 mol / L.

5. The preparation method according to claim 1, characterized in that The concentration of the reducing agent in the reducing solution is 0.2 mol / L to 2 mol / L; The reducing agent includes at least one of glucose, hydrazine hydrate, sodium borohydride, potassium borohydride, ascorbic acid, urea, formaldehyde and isoascorbic acid.

6. The preparation method according to claim 5, characterized in that The concentration of the reducing agent in the reducing solution is 0.4 mol / L to 1.5 mol / L.

7. The preparation method according to claim 1, characterized in that The content of the dispersant in the dispersant solution is 0.01 g / mL to 1 g / mL; the dispersant in the dispersant solution includes at least one of polyvinyl pyrrolidone, maleic acid, cyclodextrin, fumaric acid, gelatin, malic acid, gum arabic, polyacrylamide and oleic acid.

8. The preparation method according to claim 7, characterized in that The content of the dispersant in the dispersant solution is 0.05 g / mL to 0.5 g / mL.

9. The preparation method according to any one of claims 1 to 8, characterized in that The reaction temperature of the silver ion solution, the reducing solution and the dispersant solution is 15° C. to 50° C., and the reaction time is 5 min to 20 min. The molar ratio of the reducing agent in the reducing solution to the silver ions in the silver ion solution is 0.5:1 to 4:1, and the mass of the dispersant in the dispersant solution is 1% to 40% of the mass of the silver source providing silver ions in the silver ion solution; The silver ion solution and the reducing solution are both introduced into the dispersant solution at a flow rate of 5 mL / min to 50 mL / min; The reaction was carried out at a stirring speed of 200 rpm to 250 rpm.

10. The preparation method according to claim 9, characterized in that The molar ratio of the reducing agent in the reducing solution to the silver ions in the silver ion solution is 0.5:1 to 2:1, and the mass of the dispersant in the dispersant solution is 10% to 30% of the mass of the silver source providing silver ions in the silver ion solution.

11. The preparation method according to claim 1, characterized in that The mass ratio of the solid to the coating agent solution is 1:1 to 1:2; The solid and the coating agent solution are mixed at a stirring speed of 100 rpm to 800 rpm for 5 min to 60 min; The drying temperature after the solid and the coating agent solution are mixed is 35° C. to 60° C., and the drying time is 1 hour to 5 hours.

12. The preparation method according to claim 11, characterized in that Before mixing with the coating agent solution, the solid is washed with deionized water and ethanol in sequence until the conductivity of the washing liquid is ≤20μs / cm.

13. A silver powder, characterized in that: Prepared by the preparation method according to any one of claims 1 to 12; The silver powder D 50 1.2μm~1.8μm; The tap density of the silver powder is 5.5 g / cm 3 ~6.3g / cm 3 ; The specific surface area of ​​the silver powder is 0.35m 2 / g~0.75m 2 / g; The burnout of the silver powder is 0.5 wt % to 1 wt %.

14. A silver paste, characterized in that: The raw materials for preparing the silver paste include an organic carrier, glass powder and the silver powder according to claim 13; In parts by weight, the raw materials for preparing the silver paste include 86 to 90 parts of the silver powder, 8 to 12 parts of the organic vehicle, and 2 to 3 parts of the glass powder.

15. A TOPCon battery, characterized in that: The silver paste on the back side of the TOPCon battery is the silver paste according to claim 14.