A high specific surface area, high activity silver powder and its preparation method and application

Abstract

The present invention discloses a high specific surface area, high activity silver powder and its preparation method and application, wherein the silver powder has an irregular mesoporous structure on the surface, and the specific surface area of ​​the high specific surface area, high activity silver powder is 1.19-1.29m 2 / g, the sintering softening temperature of the high specific surface area and high activity silver powder is 580-637°C, and the preparation method comprises the following steps: S1. adding a silver source solution and a reducing agent solution dropwise to a dispersant solution to carry out a reduction reaction to obtain a silver powder suspension; S2. adjusting the pH value of the silver powder suspension to 3-5, adding a precipitant and stirring the reaction, and then adding a reducing agent solution to carry out a reduction reaction to obtain a mixture; S3. adding a flocculant to the mixture, flocculating and stratifying, filtering, washing, and drying to obtain a surface-loaded nanolayer silver powder. The prepared silver powder has high sintering activity and high specific surface area, and the silver electrode has high density after sintering.

Description

Technical Field

[0001] The present invention relates to the technical field of front silver paste, and in particular to a high-specific surface area, high-activity silver powder, and a preparation method and application thereof. Background Art

[0002] Front silver paste is a key material in the production of crystalline silicon solar cells. It is screen-printed onto a silicon substrate and then sintered at high temperatures to form electrodes. The conductive phase in the front silver paste is silver powder, which contains 80-90% silver. During high-temperature sintering, the silver powder partially dissolves in the molten glass powder, forming a good ohmic contact between the silver electrode and the silicon substrate. Parameters such as the silver powder's surface morphology, particle size and particle size distribution, and specific surface area directly affect the conductivity and density of the electrode after sintering the front silver paste, which in turn affects the photovoltaic conversion efficiency of the solar cell. Therefore, improving the silver powder's surface morphology and sintering performance will facilitate the sintering of dense silver electrodes and enhance the photovoltaic conversion efficiency of solar cells.

[0003] In the related art, Chinese patent publication number CN106041123A discloses a highly active hollow silver powder for front-side silver in solar cells and a preparation method thereof. The prepared silver powder is hollow inside, which reduces the sintering temperature to a certain extent. However, it uses nanobubbles as a carrier, which is difficult to achieve in large-scale production, limiting its mass production application, and its sintering activity still needs to be improved. Summary of the Invention

[0004] In view of this, the present application provides a high specific surface area, high activity silver powder and its preparation method and application, which has high sintering activity, high specific surface area, and high density of silver electrode after sintering.

[0005] In order to achieve the above technical objectives, this application adopts the following technical solutions:

[0006] In the first aspect, the present application provides a high specific surface area, high activity silver powder, which is a silver powder with an irregular mesoporous structure on the surface, and the specific surface area of ​​the high specific surface area, high activity silver powder is 1.19-1.29m 2 / g, the sintering softening temperature of high specific surface area and high activity silver powder is 580-637℃.

[0007] In a second aspect, the present application provides a method for preparing high specific surface area and high activity silver powder, comprising the following steps:

[0008] S1. The silver source solution and the reducing agent solution are added dropwise to the dispersant solution to carry out a reduction reaction to obtain a silver powder suspension;

[0009] S2. Adjust the pH value of the silver powder suspension to 3-5, add a precipitant and stir the reaction, then add a reducing agent solution to carry out a reduction reaction to obtain a mixture;

[0010] S3. Add a flocculant to the mixture, flocculate and separate, filter, wash, and dry to obtain surface-loaded nano-layer silver powder.

[0011] Preferably, in step S1, the dropping method is a double dropping method.

[0012] Preferably, in step S1, the molar ratio of the silver source to the reducing agent is 1:0.3-0.4.

[0013] Preferably, the precipitant is one or more of sodium carbonate, potassium carbonate, and potassium oxalate.

[0014] Preferably, in step S2, the molar ratio of the precipitant to the silver source is 0.1-0.2:1.

[0015] Preferably, the molar ratio of the reducing agent in step S2 to the silver source in step S1 is 1-2:10.

[0016] Preferably, in step S1, the temperature of the reduction reaction is 30-40°C.

[0017] Preferably, the reducing agent in step S1 and step S2 is of the same type.

[0018] In a third aspect, the present application provides a front silver paste containing high specific surface area and high activity silver powder.

[0019] The beneficial effects of the present application are as follows: the high specific surface area and high activity silver powder of the present solution has a large number of micro-mesoporous structures, a high specific surface area, a low sintering softening temperature, and a high sintering activity. Compared with spherical silver powder with a smooth surface, the tap density is comparable, and the dispersion performance is good; the positive silver paste prepared using the high specific surface area and high activity silver powder of the present solution has good printing performance, and the electrode obtained after sintering has a high degree of density; the method for preparing high specific surface area and high activity silver powder of the present solution is simple in process, high in yield, and the raw materials are environmentally friendly and non-irritating, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the SEM analysis diagram of Example 1;

[0021] Figure 2 This is the SEM analysis diagram of Example 2;

[0022] Figure 3 This is the SEM analysis diagram of Comparative Example 1;

[0023] Figure 4 This is the SEM analysis diagram of Comparative Example 2;

[0024] Figure 5 1-2 and the TMA curve of Comparative Example 1.

[0025] Figure 6These are pictures of the silver grid lines after sintering of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] The present application provides a high specific surface area, high activity silver powder, which is a silver powder with an irregular mesoporous structure on the surface. The specific surface area of ​​the high specific surface area, high activity silver powder is 1.19-1.29m 2 / g, the sintering softening temperature of high specific surface area and high activity silver powder is 580-637℃. Compared with silver powder with smooth surface, silver powder with rough surface has larger specific surface area and higher Gibbs surface energy. At the same temperature, silver powder is easy to melt, thus having higher sintering activity.

[0028] The present application provides a method for preparing high specific surface area and high activity silver powder, comprising the following steps:

[0029] S1. The silver source solution and the reducing agent solution are added dropwise to the dispersant solution to carry out a reduction reaction to obtain a silver powder suspension;

[0030] S2. Adjust the pH value of the silver powder suspension to 3-5, add a precipitant and stir the reaction, then add a reducing agent solution to carry out a reduction reaction to obtain a mixture;

[0031] S3. Add a flocculant to the mixture, flocculate and separate, filter, wash, and dry to obtain surface-loaded nano-layer silver powder.

[0032] In this solution, step S1 is to obtain silver powder by wet reduction, and step S2 is to first adjust the pH, then use a precipitant to precipitate excess silver ions, and then add a newly configured reducing agent to continue the reduction reaction, adjust the surface morphology of the silver powder, so that an irregular mesoporous structure is formed on the surface of the silver powder, and the silver powder obtained by this method has a higher tap density and better dispersion performance; in step S2, if the pH is too acidic, the silver ions cannot be precipitated, and if it is too alkaline, small silver particles will be generated, and neither can form the structure of the high specific surface area and high activity silver powder of this solution.

[0033] In step S1 , the dropping method is a double dropping method. Compared with forward dropping or reverse dropping, the double dropping method can improve the dispersion performance of the product and make the particle size more uniform.

[0034] In step S1, the molar ratio of the silver source to the reducing agent is 1:0.3-0.4. After the reaction is completed within this range, there is little residual silver source or reducing agent. In some embodiments, the reducing agent can be one or more of ascorbic acid, formaldehyde, and hydrazine hydrate, and the silver source can be silver nitrate or other reducible silver salts.

[0035] The precipitating agent is one or more of sodium carbonate, potassium carbonate, and potassium oxalate, and is used to precipitate excess silver ions. In step S2, the molar ratio of the precipitating agent to the silver source is 0.1-0.2:1. A smaller amount results in incomplete precipitation, while a larger amount may change the pH of the solution. The ratio of the sum of the molar amounts of the reducing agent used in steps S1 and S2 to the molar amount of the silver source is 0.5:1.

[0036] In some embodiments, the dispersant may be one or more of gum arabic, polyethylene glycol, polyvinyl alcohol, and polyvinyl pyrrolidone.

[0037] The molar ratio of the reducing agent in step S2 to the silver source in step S1 is 1-2:10. If the amount is too small, the reduction is incomplete, and if the amount is too large, it is wasted. The type of reducing agent in step S1 and step S2 is the same.

[0038] In step S1, the temperature of the reduction reaction is 30-40°C. If the reaction temperature is too high, the particle size of the obtained silver powder will be too small.

[0039] The present application provides a front silver paste containing high specific surface area and high activity silver powder, which has good printing performance and a high density of electrodes obtained after sintering.

[0040] The present invention is further described below through specific examples.

[0041] Example 1

[0042] A method for preparing high specific surface area and high activity silver powder comprises the following steps:

[0043] S1. 1 L of a 2 mol / L silver nitrate aqueous solution and 1 L of a 0.8 mol / L ascorbic acid aqueous solution were added dropwise to 1 L of a 0.1 mol / L gum arabic aqueous solution with stirring at a rate of 50 ml / min, a stirring speed of 350 rpm, and a reaction temperature of 30 ° C to obtain a silver powder suspension;

[0044] S2. After the addition step in step S1, sodium hydroxide solution was added to adjust the pH of the reaction system to 3, and then 100 ml of a 2 mol / L sodium carbonate solution was added to precipitate excess silver ions in the reaction system. After stirring for 10 minutes, 1 L of a 0.2 mol / L ascorbic acid aqueous solution was added at a dropping rate of 10 ml / min, and the reduction reaction was continued to obtain a mixture;

[0045] S3. Add 5 ml of 1% polyacrylamide solution to the mixture for flocculation and stratification. Filter and wash the mixture five times and then dry it to obtain surface-loaded nano-layer silver powder.

[0046] Characterization analysis was performed by SEM, such as Figure 1 As shown in the figure, there are a lot of pores on the surface of the silver powder. The tap density is 6.39g / cm 3 , with a specific surface area of ​​1.29m 2 / g, laser particle size results: D10 is 0.79um; D50 is 1.21um; D90 is 1.99um, through TMA analysis, it can be seen that Figure 5 As shown, its sintering softening temperature is 580℃.

[0047] Example 2

[0048] A method for preparing high-specific surface area and high-activity silver powder, wherein the other steps are the same as those in Example 1, except that in step S2, the pH is 5 and the amount of sodium carbonate added is 200 ml.

[0049] Characterization analysis was performed by SEM, such as Figure 2 As shown, there are a lot of pores on the surface of the silver powder. Tap density 6.40g / cm 3 , with a specific surface area of ​​1.19m 2 / g, laser particle size results: D10 is 0.80um; D50 is 1.24um; D90 is 1.91um. Through TMA analysis, it can be seen that Figure 5 As shown, its sintering softening temperature is 637℃.

[0050] Example 3

[0051] A method for preparing high-specific surface area and high-activity silver powder. The other steps are the same as those in Example 1, except that in step S1, the concentration of ascorbic acid is 0.6 mol / L, and in step S2, the concentration of ascorbic acid is 0.4 mol / L. SEM characterization analysis shows that there are a large number of pores on the surface of the silver powder. The tap density is 6.20 g / cm 3 , with a specific surface area of ​​1.29m 2 / g, laser particle size results: D10 is 0.78um; D50 is 1.26um; D90 is 1.97um. TMA analysis shows that its sintering softening temperature is 627℃.

[0052] Example 4

[0053] A method for preparing high-specific surface area and high-activity silver powder, wherein the other steps are the same as those in Example 1, except that the pH is 5.

[0054] Example 5

[0055] A method for preparing high specific surface area and high activity silver powder. The other steps are the same as those in Example 1, except that the amount of sodium carbonate added is 200 ml. SEM characterization analysis shows that there are a large number of pores on the surface of the silver powder. The tap density is 6.15 g / cm 3 , with a specific surface area of ​​1.34m 2 / g, laser particle size results: D10 is 0.74um; D50 is 1.33um; D90 is 2.07um. TMA analysis shows that its sintering softening temperature is 634℃.

[0056] Comparative Example 1

[0057] A method for preparing silver powder, wherein the other steps are the same as those in Example 1, except that step S2 is not included.

[0058] Characterization analysis was performed by SEM, such as Figure 3 As shown, the silver powder has a smooth surface, a tap density of 6.43 g / cm3, and a specific surface area of ​​0.51 m 2 / g, laser particle size results: D10 is 0.8um; D50 is 1.25um; D90 is 1.92um. TMA analysis shows that its sintering softening temperature is 660℃.

[0059] Comparative Example 2

[0060] A method for preparing silver powder, wherein the other steps are the same as those in Example 1, except that the pH value is 2.

[0061] Characterization analysis was performed by SEM, such as Figure 5 As shown, the silver powder has a smooth surface, a tap density of 6.39 g / cm3, and a specific surface area of ​​0.52 m 2 / g, laser particle size results: D10 is 0.77um; D50 is 1.22um; D90 is 1.89um.

[0062] From the above results, it can be seen that in Comparative Example 1, the silver powder with irregular mesoporous structure on the surface as in the present solution was not obtained without pH adjustment, precipitation with a precipitant, and reduction with a reducing agent, and the specific surface area and sintering activity were low. In Comparative Example 2, the pH range was not within the scope of the present application, and the silver powder obtained did not have an irregular mesoporous structure on the surface, and the specific surface area and sintering activity were low. Figure 6 As shown, there are pictures of the silver grid lines after sintering of Example 1 and Comparative Example 1. The silver powder prepared in this application has a high specific surface area and high sintering activity. The positive silver paste prepared using the high specific surface area and high activity silver powder of this solution has good printing performance, and the electrode obtained after sintering has a high degree of density.

[0063] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing high specific surface area and high activity silver powder, characterized in that: The steps include: S1. The silver source solution and the reducing agent solution are added dropwise to the dispersant solution to carry out a reduction reaction to obtain a silver powder suspension; S2. Adjust the pH value of the silver powder suspension to 3-5, add a precipitant and stir the reaction, then add a reducing agent solution to carry out a reduction reaction to obtain a mixture; S3. A flocculant is added to the mixture, and after flocculation and delamination, the mixture is filtered, washed, and dried to obtain the high specific surface area, high activity silver powder; the high specific surface area, high activity silver powder is a silver powder having an irregular mesoporous structure on the surface, and the specific surface area of ​​the high specific surface area, high activity silver powder is 1.19-1.29m 2 / g, the sintering softening temperature of the high-specific surface area and high-activity silver powder is 580-637°C; the reducing agent includes one or more of ascorbic acid, formaldehyde, and hydrazine hydrate, and the silver source includes silver nitrate; the precipitating agent is one or more of sodium carbonate, potassium carbonate, and potassium oxalate; in step S1, the molar ratio of the silver source to the reducing agent is 1:0.3-0.4; the molar ratio of the reducing agent in step S2 to the silver source in step S1 is 1-2:10, and in step S2, the molar ratio of the precipitating agent to the silver source is 0.1-0.2:

1.

2. The method for preparing high specific surface area and high activity silver powder according to claim 1, characterized in that: In step S1 , the dropping method is a double dropping method.

3. The method for preparing high specific surface area and high activity silver powder according to claim 1, characterized in that: In step S1, the temperature of the reduction reaction is 30-40°C.

4. The method for preparing high specific surface area and high activity silver powder according to claim 1, characterized in that: The reducing agent in step S1 and step S2 is of the same type.

5. A front silver paste containing high specific surface area and high activity silver powder obtained by the preparation method according to any one of claims 2 to 4.

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