Silver powder for back silver paste of N-type TOPCon solar cell and preparation method thereof

Abstract

The application provides silver powder for N-type TOPCon solar cell back silver paste and a preparation method thereof, and relates to the technical field of silver powder preparation.The method comprises the following steps: respectively preparing a silver salt solution, mixing a mixed reducing agent solution and a reaction base solution, wherein the mixed reducing agent solution comprises ferrous sulfate, ascorbic acid and a chelating agent, the mass ratio of the ferrous sulfate to the ascorbic acid is (4-10):1, and the reaction base solution comprises potassium sulfate and a dispersing agent; adding an acid solution into the silver salt solution to control the pH value of the silver salt solution to be 1-5; synchronously adding the silver salt solution and the mixed reducing agent solution controlled by the acid solution into the reaction base solution, and the dropping speed of the silver salt solution is 1.2 times to 2 times of the dropping speed of the mixed reducing agent solution; after the dropping is completed, stirring is carried out for a preset time, and then separation, washing, modification and drying are carried out to obtain the silver powder for the N-type TOPCon cell back electrode silver paste.

Description

Technical Field

[0001] This invention belongs to the field of silver powder preparation technology, and particularly relates to a silver powder for use in the back silver paste of N-type TOPCon solar cells and its preparation method. Background Technology

[0002] Photovoltaic silver paste is a type of electronic paste, primarily produced by screen printing grid lines onto both sides of a silicon wafer. After drying, it is sintered to serve as the electrodes for photovoltaic cells. The main raw material for photovoltaic silver paste preparation is silver powder. N-type TOPCon cells (solar cells with passivated contacts and tunnel oxide layers) use silver-aluminum paste as the front electrode and silver paste as the back electrode. Both electrodes can collect and extract photogenerated carriers, resulting in a significantly higher photoelectric conversion efficiency compared to PERC cells (passivated emitter and back electrode). Furthermore, N-type TOPCon cell equipment is compatible with PERC cell equipment, requiring lower retrofit costs, making it attractive to investors.

[0003] The morphology, particle size distribution, tap density, and dispersibility of silver powder affect its applicability. For solar cells, the fineness of the silver paste printed by high-resolution screen printing must be excellent, requiring the silver powder to have a narrow particle size distribution, high dispersibility, and high sphericity. Simultaneously, the prepared silver paste must possess suitable leveling properties, viscosity, and thixotropic properties, which places higher demands on the tap density and surface modification of the silver powder. The preparation of spherical silver powder is mainly carried out by chemical methods, with common chemical preparation methods including liquid-phase chemical reduction, spray pyrolysis, electrolysis, and microemulsion methods. Among these, the liquid-phase chemical reduction method is widely used due to its advantages of simple process, low energy consumption, easy parameter control, and suitability for large-scale production.

[0004] The invention, "Silver Powder for PERC Battery Front-End Silver Paste, its Preparation Method and Application," discloses a method in which a silver nitrate solution adjusted by pH adjustment is added at a predetermined rate to a reducing agent solution adjusted by pH adjustment. Immediately after the addition is complete, a surface modifier solution is added, and the mixture is stirred to obtain silver powder. In this preparation method, the nucleation, growth, and aggregation of crystal grains are controlled by the same reducing agent, which presents significant technical challenges. The method is easily affected by physicochemical factors such as ambient temperature, stirring method, and reagent purity. This manifests as uneven morphology, poor dispersibility, an excessively wide particle size distribution, and difficulty in controlling the stability of the preparation process. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a silver powder for the back silver paste of N-type TOPCon solar cells and its preparation method.

[0006] The first aspect of this invention discloses a method for preparing silver powder for the back silver paste of N-type TOPCon solar cells, the method comprising:

[0007] Step S1.1: Prepare silver salt solution, mixed reducing agent solution and reaction base solution respectively; the mixed reducing agent solution contains ferrous sulfate, ascorbic acid and chelating agent, the mass ratio of ferrous sulfate to ascorbic acid is (4~10):1, and the reaction base solution contains potassium sulfate and dispersant;

[0008] Step S1.2: Add an acid solution to the silver salt solution to adjust the pH value of the silver salt solution to 1-5;

[0009] Step S1.3: Simultaneously add the silver salt solution and the mixed reducing agent solution, which are controlled by the acid solution, to the reaction base liquid. After the addition is complete, stir the reaction for a preset time, and then separate, wash, modify and dry to obtain the silver powder for the silver paste of the back electrode of the N-type TOPCon battery.

[0010] The dropping rate of the silver salt solution is 1.2 to 2 times that of the dropping rate of the mixed reducing agent solution.

[0011] According to the method of the first aspect of the present invention, in step S1.1, the chelating agent in the mixed reducing agent solution is one or more of histidine, tryptophan, arginine or valine.

[0012] According to the method of the first aspect of the present invention, in step S1.2, the acid solution is hydrochloric acid, sulfuric acid or nitric acid.

[0013] According to the method of the first aspect of the present invention, in step S1.1, the dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol, Tween 80, and gum arabic.

[0014] According to the method of the first aspect of the present invention, in step S1.1, the silver salt solution is a silver nitrate solution.

[0015] A second aspect of this invention discloses a method for preparing silver powder for the back silver paste of N-type TOPCon solar cells, the method comprising:

[0016] Step S2.1: Prepare silver salt solution, ferrous sulfate solution, ascorbic acid solution and reaction base solution respectively. The ferrous sulfate solution includes a chelating agent, and the reaction base solution includes potassium sulfate and a dispersant.

[0017] Step S2.2: Add an acid solution to the silver salt solution to adjust the pH value of the silver salt solution to 1-5;

[0018] In step S2.3, the silver salt solution, the ferrous sulfate solution, and the ascorbic acid solution, which are controlled by the acid solution, are simultaneously added dropwise to the reaction substrate at a molar ratio of ferrous sulfate to silver salt of (1-3):1 and a molar ratio of ascorbic acid to silver salt of (0.05-0.3):1. After the addition is complete, the reaction is stirred for a preset time, and then separated, washed, modified, and dried to obtain the silver powder for the silver paste of the back electrode of the N-type TOPCon battery.

[0019] According to the method of the second aspect of the present invention, in step S2.1, the chelating agent in the mixed reducing agent solution is one or more of histidine, tryptophan, arginine or valine.

[0020] According to the method of the second aspect of the present invention, in step S2.2, the acid solution is hydrochloric acid, sulfuric acid or nitric acid.

[0021] According to the method of the second aspect of the present invention, in step S2.1, the dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol, Tween 80, and gum arabic.

[0022] The third aspect of the present invention discloses a silver powder for the back silver paste of N-type TOPCon solar cells, which is prepared by any of the preparation methods described above.

[0023] In summary, the solution proposed in this invention has the following technical effects:

[0024] 1. Adjusting the silver salt solution to a stronger acidity can passivate the reducing power of ascorbic acid, allowing the redox reaction between two reducing agents with different reducing abilities to proceed smoothly. This is more conducive to the weak reducing agent ferrous sulfate participating in the growth-aggregation process, rather than the nucleation process.

[0025] 2. Using a weakly acidic chelating agent and ascorbic acid together to dissolve ferrous sulfate can effectively prevent the hydrolysis of ferrous ions and ensure the reduction kinetics. Furthermore, the ferrous ion chelate formed reduces the reduction potential of ferric ions, ensuring that ferrous ions cannot participate in the nucleation of crystals, but instead participate in the growth and aggregation of crystal nuclei as a relatively weak reducing agent.

[0026] 3. Chelating agents containing both carboxyl and amino groups will remain in the silver powder. During the high-temperature sintering process of the slurry, they can generate nitrogen-doped quantum dots and carbon quantum dots with better conductivity, which can improve battery efficiency.

[0027] 4. The method of simultaneously adding two reducing agents has several advantages over the method of first adding a very small amount of medium-strong reducing agent as a nucleating agent and then adding a weak reducing agent as a growth agent. On the one hand, it can increase the reaction concentration and eliminate the disadvantage of ferrous sulfate heptahydrate having a large molecular weight, low solubility, and inability to prepare silver powder at high concentration and high efficiency. On the other hand, the nanocrystal nuclei have a large specific surface energy and are easy to aggregate and grow. This places strict requirements on the timing and method of adding the weak reducing agent. If the time interval between additions is too long, it is easy to cause particle agglomeration, which is not conducive to industrial production. The method of simultaneously adding two reducing agents can effectively eliminate the possibility of crystal nuclei colliding and agglomerating, and can make the growth process faster. Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a flowchart illustrating a method for preparing silver powder for the back side silver paste of an N-type TOPCon solar cell according to an embodiment of the present invention;

[0030] Figure 2 This is a scanning electron microscope image of the silver powder prepared in Example 1 of this application.

[0031] Figure 3 This is a scanning electron microscope image of the silver powder prepared in Example 2 of this application.

[0032] Figure 4 This is a scanning electron microscope image of the silver powder prepared in Example 3 of this application.

[0033] Figure 5 This is a scanning electron microscope image of the silver powder prepared in Example 4 of this application. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Please see Figure 1The first aspect of the present invention discloses a method for preparing silver powder for silver paste on the back side of N-type TOPCon solar cells, the method being implemented through steps S1.1-S1.3.

[0036] Step S1.1: Prepare silver salt solution, mixed reducing agent solution and reaction base solution respectively; the mixed reducing agent solution contains ferrous sulfate, ascorbic acid and chelating agent, the mass ratio of ferrous sulfate to ascorbic acid is (4~10):1, and the reaction base solution contains potassium sulfate and dispersant;

[0037] In step S1.1, the chelating agent in the mixed reducing agent solution is one or more of histidine, tryptophan, arginine or valine.

[0038] In step S1.1, the dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol, Tween 80, and gum arabic.

[0039] In step S1.1, the silver salt solution is a silver nitrate solution.

[0040] Step S1.2: Add an acid solution to the silver salt solution to adjust the pH value of the silver salt solution to 1-5;

[0041] In step S1.2, the acid solution is hydrochloric acid, sulfuric acid, or nitric acid.

[0042] Step S1.3: Simultaneously add the silver salt solution and the mixed reducing agent solution, which are controlled by the acid solution, to the reaction base liquid. After the addition is complete, stir the reaction for a preset time, and then separate, wash, modify and dry to obtain the silver powder for the silver paste of the back electrode of the N-type TOPCon battery.

[0043] The dropping rate of the silver salt solution is 1.2 to 2 times that of the dropping rate of the mixed reducing agent solution, so as to achieve a molar ratio of ferrous sulfate to silver salt of (1 to 3):1 and a molar ratio of ascorbic acid to silver salt of (0.05 to 0.3):1.

[0044] A second aspect of this invention discloses a method for preparing silver powder for the back silver paste of N-type TOPCon solar cells, the method comprising:

[0045] Step S2.1: Prepare silver salt solution, ferrous sulfate solution, ascorbic acid solution and reaction base solution respectively. The ferrous sulfate solution includes a chelating agent, and the reaction base solution includes potassium sulfate and a dispersant.

[0046] Step S2.2: Add an acid solution to the silver salt solution to adjust the pH value of the silver salt solution to 1-5;

[0047] In step S2.3, the silver salt solution, the ferrous sulfate solution, and the ascorbic acid solution, which are controlled by the acid solution, are simultaneously added dropwise to the reaction substrate at a molar ratio of ferrous sulfate to silver salt of (1-3):1 and a molar ratio of ascorbic acid to silver salt of (0.05-0.3):1. After the addition is complete, the reaction is stirred for a preset time, and then separated, washed, modified, and dried to obtain the silver powder for the silver paste of the back electrode of the N-type TOPCon battery.

[0048] In step S2.1, the chelating agent in the mixed reducing agent solution is one or more of histidine, tryptophan, arginine or valine.

[0049] In step S2.2, the acid solution is hydrochloric acid, sulfuric acid, or nitric acid.

[0050] The second aspect of this invention discloses a method for preparing silver powder for the back silver paste of N-type TOPCon solar cells. The difference between this method and the first aspect of this invention is that the two reducing agent solutions are prepared separately or as a mixture.

[0051] The silver powder preparation method will be described in detail below through four examples.

[0052] Example 1

[0053] A method for preparing silver powder for silver paste on the back electrode of an N-type TOPCon battery includes the following steps:

[0054] S1. Prepare 200 g / L silver nitrate solution, 275 g / L ferrous sulfate solution, 40 g / L ascorbic acid solution, 60 g / L histidine solution, 10 g / L potassium sulfate solution, and 6 g / L gum arabic solution respectively.

[0055] S2. Add an acid solution to the silver salt solution to adjust the pH value of the silver salt solution to 3;

[0056] S3. Add the silver salt solution and reducing agent solution dropwise simultaneously to the reaction substrate prepared in step S1, with a molar ratio of ferrous sulfate to silver salt of 1.5:1 and a molar ratio of ascorbic acid to silver salt of 0.2:1. The dropping rate of silver nitrate is 1.4 times that of the reducing agent solution. After the addition is complete, stir for 10 minutes, then separate, wash, modify with 0.3% oleic acid, and dry to obtain the silver powder for the back electrode silver paste of the N-type TOPCon battery. The scanning electron microscope image of the prepared silver powder is shown below. Figure 2 As shown.

[0057] Example 2

[0058] A method for preparing silver powder for silver paste on the back electrode of an N-type TOPCon battery includes the following steps:

[0059] S1. Prepare 200 g / L silver nitrate solution, 310 g / L ferrous sulfate solution, 20 g / L ascorbic acid solution, 40 g / L arginine solution, 10 g / L potassium sulfate solution, and 10 g / L polyethylene glycol solution respectively.

[0060] S2. Add an acid solution to the silver salt solution to adjust the pH value of the silver salt solution to 2.5;

[0061] S3. With a molar ratio of ferrous sulfate to silver salt of 1.7:1 and a molar ratio of ascorbic acid to silver salt of 0.1:1, silver salt solution and reducing agent solution are simultaneously added dropwise to the reaction substrate prepared in step S1. The dropping rate of silver nitrate is 1.2 times that of the reducing agent solution. After the addition is complete, the mixture is stirred for 10 minutes, then separated, washed, modified with 0.3% oleic acid, and dried to obtain the silver powder for the back electrode silver paste of the N-type TOPCon battery. A scanning electron microscope image of the prepared silver powder is shown below. Figure 3 As shown.

[0062] Example 3

[0063] A method for preparing silver powder for silver paste on the back electrode of an N-type TOPCon battery includes the following steps:

[0064] S1. Prepare 100 g / L silver nitrate solution, 180 g / L ferrous sulfate solution, 30 g / L ascorbic acid solution, 6 g / L valine solution, 10 g / L potassium sulfate solution, and 6 g / L polyvinylpyrrolidone solution respectively.

[0065] S2. Add an acid solution to the silver salt solution to adjust the pH value of the silver salt solution to 4;

[0066] S3. Add silver salt solution and reducing agent solution dropwise simultaneously to the reaction substrate prepared in step S1, with a molar ratio of ferrous sulfate to silver salt of 2:1 and a molar ratio of ascorbic acid to silver salt of 0.3:1. The dropping rate of silver nitrate is 1.8 times that of the reducing agent solution. After the addition is complete, stir for 10 minutes, then separate, wash, modify with 0.3% oleic acid, and dry to obtain silver powder for the back electrode silver paste of the N-type TOPCon battery. The scanning electron microscope image of the prepared silver powder is shown below. Figure 4 As shown.

[0067] Example 4

[0068] A method for preparing silver powder for silver paste on the back electrode of an N-type TOPCon battery includes the following steps:

[0069] S1. Prepare 250 g / L silver nitrate solution, 530 g / L ferrous sulfate solution, 20 g / L ascorbic acid solution, 4 g / L valine solution, 30 g / L tryptophan solution, 10 g / L potassium sulfate solution, and 15 g / L polyvinylpyrrolidone solution respectively.

[0070] S2. Add an acid solution to the silver salt solution to adjust the pH value of the silver salt solution to 1.5;

[0071] S3. With a molar ratio of ferrous sulfate to silver salt of 2.4:1 and a molar ratio of ascorbic acid to silver salt of 0.08:1, silver salt solution and reducing agent solution were simultaneously added dropwise to the reaction substrate prepared in step S1. The dropping rate of silver nitrate was 1.4 times that of the reducing agent solution. After the addition was complete, the mixture was stirred for 10 minutes, then separated, washed, modified with 0.3% oleic acid, and dried to obtain the silver powder for the back electrode silver paste of the N-type TOPCon battery. A scanning electron microscope image of the prepared silver powder is shown below. Figure 5 As shown.

[0072] The physical parameters of the silver powder obtained in Examples 1-4 are shown in Table 1.

[0073] Table 1 Physical Parameters of Silver Powder

[0074]

[0075] The third aspect of the present invention discloses a silver powder for the back silver paste of N-type TOPCon solar cells, which is prepared by any of the preparation methods described above.

[0076] In summary, the solution proposed in this invention has the following technical effects:

[0077] 1. Adjusting the silver salt solution to a stronger acidity can passivate the reducing power of ascorbic acid, allowing the redox reaction between two reducing agents with different reducing abilities to proceed smoothly. This is more conducive to the weak reducing agent ferrous sulfate participating in the growth-aggregation process, rather than the nucleation process.

[0078] 2. Using a weakly acidic chelating agent and ascorbic acid together to dissolve ferrous sulfate can effectively prevent the hydrolysis of ferrous ions and ensure the reduction kinetics. Furthermore, the ferrous ion chelate formed reduces the reduction potential of ferric ions, ensuring that ferrous ions cannot participate in the nucleation of crystals, but instead participate in the growth and aggregation of crystal nuclei as a relatively weak reducing agent.

[0079] 3. Chelating agents containing both carboxyl and amino groups will remain in the silver powder. During the high-temperature sintering process of the slurry, they can generate nitrogen-doped quantum dots and carbon quantum dots with better conductivity, which can improve battery efficiency.

[0080] 4. The method of simultaneously adding two reducing agents has several advantages over the method of first adding a very small amount of medium-strong acid as a reducing agent for nucleation and then adding a weak reducing agent for growth. On the one hand, it can increase the reaction concentration and eliminate the disadvantage of ferrous sulfate heptahydrate having a large molecular weight, low solubility, and inability to prepare silver powder at high concentration and high efficiency. On the other hand, the nanocrystal nuclei have a large specific surface energy and are easy to aggregate and grow. This places strict requirements on the timing and method of adding the weak reducing agent. If the time interval between additions is too long, it is easy to cause particle agglomeration, which is not conducive to industrial production. The method of simultaneously adding two reducing agents can effectively eliminate the possibility of crystal nuclei colliding and agglomerating, and can make the growth process faster.

[0081] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing silver powder for the back silver paste of N-type TOPCon solar cells, characterized in that, The method includes: Step S1.1: Prepare a silver salt solution, a mixed reducing agent solution, and a reaction base solution. The mixed reducing agent solution contains ferrous sulfate, ascorbic acid, and a chelating agent, wherein the mass ratio of ferrous sulfate to ascorbic acid is (4-10):

1. The reaction base solution contains potassium sulfate and a dispersant. In step S1.1, the dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol, Tween 80, and gum arabic. In step S1.1, the silver salt solution is a silver nitrate solution. Step S1.2: Add an acid solution to the silver salt solution to adjust the pH value of the silver salt solution to 1-4; Step S1.3: Simultaneously add the silver salt solution and the mixed reducing agent solution, which are controlled by the acid solution, to the reaction base liquid. After the addition is complete, stir the reaction for a preset time, and then separate, wash, modify and dry to obtain silver powder for silver paste for the back electrode of N-type TOPCon battery. The dropping rate of the silver salt solution is 1.2 to 2 times that of the dropping rate of the mixed reducing agent solution.

2. The method for preparing silver powder according to claim 1, characterized in that, In step S1.1, the chelating agent in the mixed reducing agent solution is one or more of histidine, tryptophan, arginine or valine.

3. The method for preparing silver powder according to claim 1, characterized in that, In step S1.2, the acid solution is hydrochloric acid, sulfuric acid, or nitric acid.

4. A method for preparing silver powder for the back silver paste of N-type TOPCon solar cells, characterized in that, The method includes: Step S2.1: Prepare silver salt solution, ferrous sulfate solution, ascorbic acid solution and reaction base solution respectively. The ferrous sulfate solution includes a chelating agent, and the reaction base solution includes potassium sulfate and a dispersant. The dispersant is one or more of polyvinylpyrrolidone, polyethylene glycol, Tween 80, and gum arabic. The silver salt solution is silver nitrate solution. Step S2.2: Add an acid solution to the silver salt solution to adjust the pH value of the silver salt solution to 1-4; In step S2.3, the silver salt solution, the ferrous sulfate solution, and the ascorbic acid solution, which are controlled by the acid solution, are simultaneously added dropwise to the reaction substrate at a molar ratio of ferrous sulfate to silver salt of (1-3):1 and a molar ratio of ascorbic acid to silver salt of (0.05-0.3):

1. After the addition is complete, the reaction is stirred for a preset time, and then separated, washed, modified, and dried to obtain silver powder for silver paste for the back electrode of N-type TOPCon battery.

5. The method for preparing silver powder according to claim 4, characterized in that, In step S2.1, the chelating agent in the ferrous sulfate solution is one or more of histidine, tryptophan, arginine, or valine.

6. The method for preparing silver powder according to claim 4, characterized in that, In step S2.2, the acid solution is hydrochloric acid, sulfuric acid, or nitric acid.

7. A silver powder for use in the back silver paste of N-type TOPCon solar cells, characterized in that, It is prepared by any one of the preparation methods described in claims 1-6.

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