Spherical silver-coated copper powder for silver paste of n-type hjt solar cell electrode and preparation method thereof

Abstract

The application provides a spherical silver-coated copper powder for N-type HJT solar cell electrode silver paste and a preparation method thereof, and relates to the technical field of metal powder preparation. The preparation method comprises the following steps: preparing an oxidizing agent solution and a double-reducing agent mixed solution; taking a spherical oxygen-free copper powder aqueous solution as a bottom liquid, adding a surfactant into the bottom liquid, and adjusting the pH of the bottom liquid to 6-12 by using ammonia water; adding a small amount of the oxidizing agent solution into the bottom liquid within 1 min, then adding a copper ion masking agent solution into the bottom liquid to continue the reaction for 4-6 min, and obtaining a first suspension; adding the remaining oxidizing agent solution and the double-reducing agent mixed solution into the first suspension, continuing to stir for a preset time after the addition is completed until the reaction is completed, and obtaining a second suspension; and performing centrifugation, washing and drying on the second suspension to obtain the silver-coated copper powder. The silver-coated copper powder prepared by using the method can realize complete coating of the silver layer on the surface of the copper powder.

Description

Technical Field

[0001] This invention belongs to the field of metal powder preparation technology, and in particular relates to a spherical silver-coated copper powder for silver paste used in N-type HJT solar cell electrodes and its preparation method. Background Technology

[0002] n-HJT cells can achieve a photoelectric conversion efficiency of up to 27%, and their low-temperature sintering process (<250℃) and simple four-step manufacturing process offer significant advantages over traditional crystalline silicon cells. However, the current production efficiency of HJT cells is not outstanding. One major reason is the high consumption of silver paste due to double-sided printing and wide grid lines. Silver powder, as the conductive component of silver paste, accounts for up to 90% of its content. As a precious metal, silver's high cost is a key factor restricting the penetration of n-HJT cell technology into the photovoltaic field. Therefore, how to reduce cell costs by substituting base metals for precious metals without significantly reducing cell efficiency is a pressing problem that needs to be solved in the photovoltaic industry.

[0003] Silver-coated copper powder, as an alternative to silver powder, involves depositing a thin layer of silver onto the surface of copper powder. At temperatures not exceeding 200°C, the nano-silver on the copper powder surface does not significantly aggregate, exposing the internal copper core and causing oxidation. Further research revealed that as the silver content on the copper powder surface increases, the temperature at which the internal copper is exposed also rises due to silver ion migration. Therefore, to use silver-coated copper powder as a substitute for silver powder, it is essential to achieve a dense and uniform silver plating layer on the copper powder surface with the lowest possible silver consumption.

[0004] Patent CN116967444A uses both alkaline nitrogen-containing reagents and carboxylate-containing reagents as complexing agents, and spherical oxygen-free copper powder and a reducing agent as the base solution. A nitric acid-acidified silver nitrate solution is added dropwise to the base solution, and finally, silver-coated copper powder is obtained through solid-liquid separation. However, the introduction of nitric acid causes some of the copper powder to convert into copper nitrate, and copper ions adsorb onto the surface of the copper powder, preventing silver particle deposition. Furthermore, this method does not include a copper ion masking agent, resulting in discontinuous silver plating on the copper powder surface and an unstable coating.

[0005] Therefore, existing technologies need to be improved. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a spherical silver-coated copper powder for N-type HJT solar cell electrode silver paste and its preparation method. First, a trace amount of silver nitrate is used to replace copper powder to generate silver target points on the copper powder surface. Then, a copper ion masking agent is added to eliminate the interference of free copper ions in the substrate on the silver plating process. Finally, a mixed reducing agent with different reducing abilities is used to achieve the growth of silver particles along the copper surface, thereby obtaining a dense spherical silver-coated copper powder.

[0007] The first aspect of this invention discloses a method for preparing spherical silver-coated copper powder for silver paste used in N-type HJT solar cell electrodes. The preparation method includes:

[0008] Step S1: Dissolve silver nitrate in pure water to obtain an oxidizing agent solution with a silver nitrate concentration of 0.4-2.0 mol / L; dissolve reducing agent A and reducing agent B together in pure water to obtain a mixed solution of reducing agent A with a concentration of 0.1-0.8 mol / L and reducing agent B with a concentration of 0.1-0.5 mol / L.

[0009] Wherein, the reducing agent A has a greater reducing power than the reducing agent B;

[0010] Step S2: Disperse spherical oxygen-free copper powder in pure water to obtain a bottom solution with a concentration of 4-12 mol / L of spherical oxygen-free copper powder. At the same time, add Tween-80 as a surfactant to the bottom solution, start mechanical stirring, and then add ammonia water to the bottom solution to adjust the pH of the bottom solution to 6-12.

[0011] The volume ratio of the oxidant solution, the dual reducing agent mixed solution, and the bottom liquid is 1:2:1.

[0012] Step S3: At room temperature, the volume of the oxidant solution, which is one-sixtieth to one-hundred-fiftieth of the total volume of the oxidant solution, is added dropwise to the base liquid within 1 minute. The reaction is carried out for 1-2 minutes. Then, the copper ion masking agent solution is added to the base liquid, and the reaction is continued for 4-6 minutes to obtain the first suspension.

[0013] Step S4: Add the remaining oxidant solution and the dual reducing agent mixed solution dropwise into the first suspension. After the addition is complete, continue stirring for a preset time until the reaction is complete to obtain the second suspension.

[0014] The dripping time is not less than 30 minutes, and the dripping rate of the dual reducing agent mixed solution is at least twice the dripping rate of the oxidizing agent solution.

[0015] Step S5: After centrifuging the second suspension, a silver-coated copper precursor is obtained. The silver-coated copper precursor is washed multiple times with pure water and then dried to obtain the silver-coated copper powder.

[0016] According to the preparation method of the first aspect of the present invention, in step S1, both reducing agent A and reducing agent B are selected from one of ferrous ammonium sulfate, hydroxyl ammonium sulfate, hydroquinone, formaldehyde, and ascorbic acid.

[0017] According to the preparation method of the first aspect of the present invention, in step S2, the amount of Tween-80 used is 0.1 times the mass of the spherical oxygen-free copper powder.

[0018] According to the preparation method of the first aspect of the present invention, in step S3, 0.02 times the mass of α-amino acids of spherical oxygen-free copper powder are uniformly dissolved in anhydrous ethanol with a volume of 0.2 times the total volume of the oxidant solution to obtain the copper ion masking agent solution.

[0019] According to the preparation method of the first aspect of the present invention, the α-amino acid is at least one selected from glutamic acid, tryptophan, lysine, arginine, valine, histidine, proline, and glycine.

[0020] According to the preparation method of the first aspect of the present invention, in step S4, the oxidant solution and the dual reducing agent mixed solution are both added dropwise directly above the surface of the bottom liquid.

[0021] According to the preparation method of the first aspect of the present invention, in step S5, the drying temperature is 48-52°C and the drying time is 10-14h.

[0022] According to the preparation method of the first aspect of the present invention, the D of the spherical oxygen-free copper powder 50 Located in the 2.0-4.0 μm range, with a tap density > 4 g / cm³. 3 Specific surface area > 0.2m 2 / g.

[0023] According to the preparation method of the first aspect of the present invention, the mechanical stirring speed is 150-200 r / min.

[0024] The second aspect of this invention discloses a spherical silver-coated copper powder prepared using the aforementioned method for preparing spherical silver-coated copper powder for N-type HJT solar cell electrode silver paste.

[0025] In summary, the solution proposed in this invention has the following technical effects:

[0026] (1) The present invention uses a three-step method of displacement-masking-reduction to achieve complete silver coating on the surface of spherical copper powder. First, a small amount of silver nitrate is used to replace the spherical copper powder to generate silver target points on the surface of the spherical copper powder. Then, a copper ion masking agent is added to eliminate the interference of free copper ions in the base solution on the subsequent silver plating process. Finally, a mixed reducing agent with two different reducing abilities is used to achieve the growth of silver particles along the copper surface, resulting in a continuous and dense spherical silver-coated copper powder.

[0027] (2) This invention innovatively employs two reducing agents with different reducing properties as a mixed reducing agent to reduce silver nitrate to elemental silver. Based on the evolutionary law of particle nucleation-growth, the reducing agent with stronger reducing power in the mixed reducing agent formulation serves as a nucleating agent, causing silver atoms to deposit on the surface of spherical oxygen-free copper powder to form silver target sites; the reducing agent with weaker reducing power acts as a relay for "growth-aggregation," allowing the subsequently reduced silver atoms to preferentially deposit at locations with incomplete surface coating and high surface energy. Under the combined action of the two reducing agents, a smooth and dense silver thin layer is finally obtained on the surface of the spherical oxygen-free copper powder.

[0028] (3) The technical solution of the present invention can be completed at room temperature, with no special requirements for reaction equipment, and is suitable for industrial production. Attached Figure Description

[0029] 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.

[0030] Figure 1 The image shows the DSC test results of the spherical silver-coated copper powder prepared in Specific Embodiment 1 of the present invention.

[0031] Figure 2 This is an electron microscope image of oxygen-free copper powder in a specific embodiment 1 of the present invention.

[0032] Figure 3 Electron micrograph of spherical silver-coated copper powder prepared in specific embodiment 1 of the present invention. Detailed Implementation

[0033] 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.

[0034] The first aspect of this invention discloses a method for preparing spherical silver-coated copper powder for silver paste used in N-type HJT solar cell electrodes. The preparation method includes the following steps.

[0035] Step S1: Dissolve silver nitrate in pure water to obtain an oxidizing agent solution with a silver nitrate concentration of 0.4-2.0 mol / L. Dissolve reducing agent A and reducing agent B together in pure water to obtain a mixed solution of reducing agent A with a concentration of 0.1-0.8 mol / L and reducing agent B with a concentration of 0.1-0.5 mol / L.

[0036] The reducing agent A has a greater reducing power than the reducing agent B.

[0037] Step S2: Disperse spherical oxygen-free copper powder in pure water to obtain a base solution with a concentration of 4-12 mol / L of spherical oxygen-free copper powder. At the same time, add Tween-80 as a surfactant to the base solution, start mechanical stirring, and then add ammonia water to the base solution to adjust the pH of the base solution to 6-12.

[0038] The volume ratio of the oxidant solution, the mixed solution of the two reducing agents, and the bottom liquid is 1:2:1.

[0039] Step S3: At room temperature, the volume of the oxidant solution, which is one-sixtieth to one-hundred-fiftieth of the total volume of the oxidant solution, is added dropwise to the base liquid within 1 minute. The reaction is allowed to proceed for 1-2 minutes. Then, the copper ion masking agent solution is added to the base liquid, and the reaction continues for 4-6 minutes to obtain the first suspension.

[0040] Step S4: Add the remaining oxidant solution and the dual reducing agent mixed solution dropwise into the first suspension. After the addition is complete, continue stirring for a preset time until the reaction is complete to obtain the second suspension.

[0041] The dripping time is no less than 30 minutes, and the dripping rate of the dual reducing agent mixed solution is at least twice the dripping rate of the oxidizing agent solution.

[0042] Step S5: After centrifuging the second suspension, a silver-coated copper precursor is obtained. The silver-coated copper precursor is washed multiple times with pure water and then dried to obtain the silver-coated copper powder.

[0043] In step S1, silver nitrate is dissolved in pure water to obtain an oxidizing agent solution with a silver nitrate concentration of 0.4-2.0 mol / L, and reducing agent A and reducing agent B are dissolved together in pure water to obtain a mixed solution of reducing agent A with a concentration of 0.1-0.8 mol / L and reducing agent B with a concentration of 0.1-0.5 mol / L.

[0044] The reducing agent A has a greater reducing power than the reducing agent B.

[0045] In some embodiments, in step S1, both reducing agent A and reducing agent B are selected from ferrous ammonium sulfate, hydroxyl ammonium sulfate, hydroquinone, formaldehyde, and ascorbic acid.

[0046] This invention innovatively employs two reducing agents with different reducing properties as a mixed reducing agent to reduce silver nitrate to elemental silver. Based on the particle nucleation-growth evolution law, the reducing agent with stronger reducing power in the mixed reducing agent formulation acts as a nucleating agent, causing silver atoms to deposit on the surface of spherical oxygen-free copper powder to form silver target sites; the reducing agent with weaker reducing power acts as a relay for the "growth-aggregation" process, allowing the subsequently reduced silver atoms to preferentially deposit on sites with incomplete surface coating and high surface energy. Under the combined action of the two reducing agents, a smooth and dense silver thin layer is finally obtained on the surface of the spherical oxygen-free copper powder.

[0047] In step S2, spherical oxygen-free copper powder is dispersed in pure water to obtain a base solution with a concentration of 4-12 mol / L of spherical oxygen-free copper powder. At the same time, Tween-80 as a surfactant is added to the base solution, mechanical stirring is started, and then ammonia water is added to the base solution to adjust the pH of the base solution to 6-12.

[0048] The volume ratio of the oxidant solution, the mixed solution of the two reducing agents, and the bottom liquid is 1:2:1.

[0049] The reducing agents used in this invention are all alkaline reagents. When the pH of the substrate solution is less than 6, the reducing ability of the reducing agent decreases, and it fails to achieve the desired reduction effect. When the pH of the substrate solution is greater than 12, the redox reaction rate is too fast, making it impossible to control the nucleation and growth process. In addition, when the pH of the substrate solution is greater than 12, ascorbic acid, one of the reducing agents in this invention, is deactivated and converted into uronic acid.

[0050] In some embodiments, the D of the spherical oxygen-free copper powder 50 Located in the 2.0-4.0 μm range, with a tap density > 4 g / cm³. 3 Specific surface area > 0.2m 2 / g.

[0051] In some embodiments, in step S2, the amount of Tween-80 used is 0.1 times the mass of the spherical oxygen-free copper powder, so as to increase the activation energy of the surface of the spherical oxygen-free copper powder and promote the nucleation of silver atoms on the surface of the copper powder.

[0052] Tween-80 has a good emulsifying effect, which enables copper powder to be uniformly dispersed in the solution in this invention.

[0053] In some embodiments, the mechanical stirring speed is 150-200 r / min. This is to ensure the homogeneity of the solution throughout the reaction process and to avoid excessive stirring that would result in excessively small silver-coated copper powder particle size.

[0054] In step S3, at room temperature, an amount of the oxidant solution, ranging from one-sixtieth to one-hundredth of the total volume of the oxidant solution, is added dropwise to the base solution within 1 minute. The reaction is allowed to proceed for 1-2 minutes. Then, a copper ion masking agent solution is added to the base solution, and the reaction continues for 4-6 minutes to obtain the first suspension.

[0055] In this invention, a small amount of silver nitrate (one-sixtieth to one-hundred-fiftieth of the total amount of silver nitrate) is first used to replace spherical copper powder to generate relatively uniformly distributed silver target points on the surface of the spherical copper powder. Then, a copper ion masking agent is added to eliminate the interference of free copper ions in the base solution on the subsequent silver plating process.

[0056] Meanwhile, it should be noted that the displacement reduction time in step S3 should not exceed 2 minutes to avoid the complete oxidation of the spherical oxygen-free copper powder in the bottom solution, thus failing to obtain spherical silver-coated copper powder.

[0057] In some embodiments, in step S3, 0.02 times the mass of α-amino acids of spherical oxygen-free copper powder are uniformly dissolved in anhydrous ethanol with a volume of 0.2 times the total volume of the oxidant solution to obtain the copper ion masking agent solution.

[0058] This invention uses inexpensive α-amino acids as copper ion masking agents, which can reduce production costs; in addition, α-amino acids have a small molecular weight, and their residual amount has little impact on the electrical properties of the product.

[0059] In some embodiments, the α-amino acid is at least one selected from glutamic acid, tryptophan, lysine, arginine, valine, histidine, proline, and glycine.

[0060] In step S4, the remaining oxidant solution and the dual reducing agent mixed solution are added dropwise to the first suspension. After the addition is completed, stirring is continued for a preset time until the reaction is completed, and a second suspension is obtained.

[0061] The dripping time is no less than 30 minutes, and the dripping rate of the dual reducing agent mixed solution is at least twice the dripping rate of the oxidizing agent solution.

[0062] In this invention, a thin and dense silver film is obtained by depositing silver atoms at the target site using a redox method. To avoid adhesion between copper particles and individual nucleation of silver atoms in the solution, the dropping time is controlled to be 30 minutes or more. Furthermore, the dropping rate of the dual reducing agent mixture must be greater than the dropping rate of the oxidizing agent solution to ensure in-situ reduction growth of silver at the silver deposition target site on the copper powder surface.

[0063] Specifically, the preset time is 8-12 minutes, preferably 10 minutes.

[0064] In some embodiments, in step S4, both the oxidant solution and the dual reducing agent mixed solution are added by dropping them directly above the surface of the bottom liquid.

[0065] Specifically, in steps S3 and S4, a peristaltic pump is used to add the solution dropwise.

[0066] In step S5, the second suspension is centrifuged to obtain a silver-coated copper precursor. The silver-coated copper precursor is washed multiple times with pure water and then dried to obtain the silver-coated copper powder.

[0067] In some embodiments, in step S5, the drying temperature is 48-52°C, preferably 50°C; the drying time is 10-14 hours, preferably 12 hours.

[0068] The second aspect of this invention discloses a spherical silver-coated copper powder for use in silver paste for N-type HJT solar cell electrodes.

[0069] Example 1

[0070] The first step involves dissolving 0.5 mol of silver nitrate in 500 mL of pure water as an oxidizing agent solution, dissolving 0.2 mol of ascorbic acid and 0.1 mol of hydroquinone together in 1000 mL of pure water as a dual reducing agent mixed solution, and completely dissolving 7.68 g of arginine in 100 mL of anhydrous ethanol as a copper ion masking agent solution.

[0071] The second step is to add 5 mol of spherical oxygen-free copper powder (D 50 =3.6μm) dispersed in 500mL of pure water as the base solution, and 38.4g of Tween-80 was added to the base solution. Mechanical stirring was turned on (speed of 150-200r / min). Then, ammonia water was added to the base solution to adjust the pH of the base solution to 8.

[0072] The third step involves adding 5 mL of silver nitrate solution to the base solution obtained in the previous step within 1 minute using a peristaltic pump at room temperature, reacting for 1 minute, and then adding all of the copper ion masking agent solution to the base solution and continuing the reaction for 5 minutes to obtain the first suspension.

[0073] Fourth step: Using a peristaltic pump, the remaining silver nitrate solution and the mixed solution of the two reducing agents are dripped into the first suspension from above the surface of the bottom liquid. After the dripping is completed, continue stirring for 10 minutes until the reaction is complete to obtain the second suspension. The dripping rate of the silver nitrate solution is 9 ml / min, and the dripping rate of the mixed solution of the two reducing agents is 20 ml / min.

[0074] The fifth step involves centrifuging the second suspension to obtain the silver-coated copper precursor. The silver-coated copper precursor is then washed multiple times with pure water and dried to obtain spherical silver-coated copper powder. The drying temperature is 50°C and the drying time is 12 hours.

[0075] EDS analysis showed that the silver-coated copper powder prepared in Example 1 contained 15 wt% silver and had a tap density of 4.8 g / cm³. 3 The specific surface area is 0.26 μm. 2 / g.

[0076] Figure 1 The figure shows the DSC test results of the spherical silver-coated copper powder prepared in Example 1. As can be seen from the figure, the initial oxidation temperature of the spherical silver-coated copper powder is 244℃, which proves that the antioxidant capacity of the silver-coated copper powder prepared in this invention is fully applicable to HJT slurry.

[0077] Figure 2 This is an electron microscope image of oxygen-free copper powder in specific embodiment 1 of the present invention. Figure 3 Electron micrograph of spherical silver-coated copper powder prepared in specific embodiment 1 of the present invention. (Comparison) Figure 2 and Figure 3 It can be seen that the silver layer on the surface of the copper powder is dense and continuous.

[0078] Example 1: Application Test of Spherical Silver-Coated Copper Powder

[0079] This embodiment provides an N-type HJT solar cell electrode silver paste, which, based on 100% of its total mass, comprises the following components:

[0080] 71% flake silver powder (company: Ningxia Zhongse New Materials; product name: AgF-8C), 18% silver-coated copper powder prepared in Example 1, 5% bisphenol A type epoxy resin, 2% modified graphene, 0.2% dimethylacetamide, 0.4% hydrogenated castor oil, 1% butyl carbitol, and 2.4% terpineol.

[0081] Comparative Application Test of Ordinary Spherical Silver Powder

[0082] A comparative example provides an N-type HJT solar cell electrode silver paste, which, based on 100% of its total mass, comprises the following components:

[0083] Flake silver powder 71% (Company: Ningxia Zhongse New Materials; Product name: AgF-8C), spherical silver powder 18% (Company: Ningxia Zhongse New Materials; Product name: AgRC-02), bisphenol A type epoxy resin 5%, modified graphene 2%, dimethylacetamide 0.2%, hydrogenated castor oil 0.4%, butyl carbitol 1%, terpineol 2.4%.

[0084] The two types of silver paste were rolled using a three-roll mill and printed onto the front surface of N-type PERC solar cells for testing. The commonly used TLM (Transmission Line Model) was used to test the contact resistance and photoelectric conversion efficiency of the two types of cells prepared above. The results are shown in Table 1.

[0085] Table 1

[0086]

[0087]

[0088] As can be seen from Table 1, the contact resistance and photoelectric conversion efficiency of the battery made by the spherical silver-coated copper powder prepared by the method of the present invention are comparable to those of ordinary spherical silver powder.

[0089] Example 2

[0090] The first step involves dissolving 0.4 mol of silver nitrate in 500 mL of pure water as an oxidizing agent solution, dissolving 0.3 mol of formaldehyde and 0.3 mol of hydroxyl ammonium sulfate together in 1000 mL of pure water as a dual reducing agent mixed solution, and completely dissolving 5.12 g of tryptophan in 100 mL of anhydrous ethanol as a copper ion masking agent solution.

[0091] The second step is to add 4 mol of spherical oxygen-free copper powder (D 50 =2.6μm) dispersed in 500mL of pure water as the base solution, and 25.6g of Tween-80 was added to the base solution. Mechanical stirring was turned on (speed of 150-200r / min). Then, ammonia water was added to the base solution to adjust the pH of the base solution to 10.

[0092] Third, at room temperature, 8 mL of silver nitrate solution is added dropwise to the base solution obtained in the previous step within 1 minute using a peristaltic pump, and the reaction is allowed to proceed for 1.5 minutes. Then, the copper ion masking agent solution is added to the base solution, and the reaction continues for 4 minutes.

[0093] Fourth step: Use a peristaltic pump to drop the remaining silver nitrate solution and the mixed solution of the two reducing agents into the first suspension from above the bottom liquid surface. After the addition is completed, continue stirring for 8 minutes until the reaction is complete. The dropping rate of the silver nitrate solution is 7 ml / min and the dropping rate of the mixed solution of the two reducing agents is 16 ml / min.

[0094] The fifth step involves centrifuging the second suspension to obtain a silver-coated copper precursor. The silver-coated copper precursor is then washed multiple times with pure water and dried to obtain spherical silver-coated copper powder. The drying temperature is 48℃ and the drying time is 14h.

[0095] EDS analysis showed that the silver-coated copper powder prepared in Example 2 contained 14 wt% silver and had a tap density of 4.1 g / cm³. 3 Specific surface area 0.36m 2 / g.

[0096] Example 3

[0097] The first step involves dissolving 0.8 mol of silver nitrate in 500 mL of pure water as an oxidizing agent solution, dissolving 0.7 mol of hydroxyammonium sulfate and 0.1 mol of hydroquinone together in 1000 mL of pure water as a dual reducing agent mixed solution, and completely dissolving 5.76 g of proline in 100 mL of anhydrous ethanol as a copper ion masking agent solution.

[0098] The second step involves adding 4.5 mol of spherical oxygen-free copper powder (D... 50 =3.5μm) dispersed in 500mL of pure water as the base solution, and 28.8g of Tween-80 was added to the base solution. Mechanical stirring was turned on (speed of 150-200r / min). Then, ammonia water was added to the base solution to adjust the pH of the base solution to 8.

[0099] Third, at room temperature, 7 mL of silver nitrate solution is added dropwise to the base solution obtained in the previous step within 1 minute using a peristaltic pump, and the reaction is allowed to proceed for 2 minutes. Then, the copper ion masking agent solution is added to the base solution, and the reaction continues for 6 minutes.

[0100] Fourth step: Use a peristaltic pump to drop the remaining silver nitrate solution and the mixed solution of the two reducing agents into the first suspension from above the surface of the bottom liquid. After the addition is completed, continue stirring for 12 minutes until the reaction is complete. The dropping rate of the silver nitrate solution is 12 ml / min and the dropping rate of the mixed solution of the two reducing agents is 25 ml / min.

[0101] The fifth step involves centrifuging the second suspension to obtain a silver-coated copper precursor. The silver-coated copper precursor is then washed multiple times with pure water and dried to obtain spherical silver-coated copper powder. The drying temperature is 52℃ and the drying time is 10 hours.

[0102] EDS analysis showed that the silver-coated copper powder prepared in Example 3 contained 22 wt% silver and had a tap density of 4.6 g / cm³. 3 Specific surface area 0.28m 2 / g.

[0103] In summary, the solution proposed in this invention has the following technical effects:

[0104] (1) The present invention uses a three-step method of displacement-masking-reduction to achieve complete silver coating on the surface of spherical copper powder. First, a small amount of silver nitrate is used to replace the spherical copper powder to generate silver target points on the surface of the spherical copper powder. Then, a copper ion masking agent is added to eliminate the interference of free copper ions in the base solution on the subsequent silver plating process. Finally, a mixed reducing agent with two different reducing abilities is used to achieve the growth of silver particles along the copper surface, resulting in a continuous and dense spherical silver-coated copper powder.

[0105] (2) This invention innovatively employs two reducing agents with different reducing properties as a mixed reducing agent to reduce silver nitrate to elemental silver. Based on the evolutionary law of particle nucleation-growth, the reducing agent with stronger reducing power in the mixed reducing agent formulation serves as a nucleating agent, causing silver atoms to deposit on the surface of spherical oxygen-free copper powder to form silver target sites; the reducing agent with weaker reducing power acts as a relay for "growth-aggregation," allowing the subsequently reduced silver atoms to preferentially deposit at locations with incomplete surface coating and high surface energy. Under the combined action of the two reducing agents, a smooth and dense silver thin layer is finally obtained on the surface of the spherical oxygen-free copper powder.

[0106] (3) The technical solution of the present invention can be completed at room temperature, with no special requirements for reaction equipment, and is suitable for industrial production.

[0107] 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 spherical silver-coated copper powder for silver paste in N-type HJT solar cell electrodes, characterized in that, The preparation method includes: Step S1: Dissolve silver nitrate in pure water to obtain an oxidizing agent solution with a silver nitrate concentration of 0.4-2.0 mol / L; dissolve reducing agent A and reducing agent B together in pure water to obtain a mixed solution of reducing agent A with a concentration of 0.1-0.8 mol / L and reducing agent B with a concentration of 0.1-0.5 mol / L. Wherein, the reducing agent A has a greater reducing power than the reducing agent B; Step S2: Disperse spherical oxygen-free copper powder in pure water to obtain a bottom solution with a concentration of 4-12 mol / L of spherical oxygen-free copper powder. At the same time, add Tween-80 as a surfactant to the bottom solution, start mechanical stirring, and then add ammonia water to the bottom solution to adjust the pH of the bottom solution to 6-12. The volume ratio of the oxidant solution, the dual reducing agent mixed solution, and the bottom liquid is 1:2:

1. Step S3: At room temperature, the volume of the oxidant solution, which is one-sixtieth to one-hundred-fiftieth of the total volume of the oxidant solution, is added dropwise to the base liquid within 1 minute. The reaction is carried out for 1-2 minutes. Then, the copper ion masking agent solution is added to the base liquid, and the reaction is continued for 4-6 minutes to obtain the first suspension. Step S4: Add the remaining oxidant solution and the dual reducing agent mixed solution dropwise into the first suspension. After the addition is complete, continue stirring for a preset time until the reaction is complete to obtain the second suspension. The dripping time is not less than 30 minutes, and the dripping rate of the dual reducing agent mixed solution is at least twice the dripping rate of the oxidizing agent solution. Step S5: After centrifuging the second suspension, a silver-coated copper precursor is obtained. The silver-coated copper precursor is washed multiple times with pure water and then dried to obtain the silver-coated copper powder.

2. The method for preparing spherical silver-coated copper powder for silver paste in N-type HJT solar cell electrodes according to claim 1, characterized in that, In step S1, both reducing agent A and reducing agent B are selected from one of ferrous ammonium sulfate, hydroxyl ammonium sulfate, hydroquinone, formaldehyde, and ascorbic acid.

3. The method for preparing spherical silver-coated copper powder for silver paste in N-type HJT solar cell electrodes according to claim 1, characterized in that, In step S2, the amount of Tween-80 used is 0.1 times the mass of the spherical oxygen-free copper powder.

4. The method for preparing spherical silver-coated copper powder for silver paste in N-type HJT solar cell electrodes according to claim 1, characterized in that, In step S3, 0.02 times the mass of α-amino acids in spherical oxygen-free copper powder are uniformly dissolved in anhydrous ethanol with a volume of 0.2 times the total volume of the oxidant solution to obtain the copper ion masking agent solution.

5. The method for preparing spherical silver-coated copper powder for silver paste in N-type HJT solar cell electrodes according to claim 4, characterized in that, The α-amino acid is at least one selected from glutamic acid, tryptophan, lysine, arginine, valine, histidine, proline, and glycine.

6. The method for preparing spherical silver-coated copper powder for silver paste in N-type HJT solar cell electrodes according to claim 1, characterized in that, In step S4, both the oxidant solution and the dual reducing agent mixed solution are added by dropping them directly above the surface of the bottom liquid.

7. The method for preparing spherical silver-coated copper powder for silver paste in N-type HJT solar cell electrodes according to claim 1, characterized in that, In step S5, the drying temperature is 48-52℃ and the drying time is 10-14h.

8. The method for preparing spherical silver-coated copper powder for silver paste in N-type HJT solar cell electrodes according to claim 1, characterized in that, The spherical oxygen-free copper powder D 50 Located in the 2.0-4.0 μm range, with a tap density > 4 g / cm³. 3 Specific surface area > 0.2m 2 / g.

9. The method for preparing spherical silver-coated copper powder for silver paste in N-type HJT solar cell electrodes according to claim 1, characterized in that, The mechanical stirring speed is 150-200 r / min.

10. A spherical silver-coated copper powder prepared by the method for preparing spherical silver-coated copper powder for N-type HJT solar cell electrode silver paste according to any one of claims 1-9.

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