Composite copper powder, method for preparing the same, copper paste, and solar cell

Abstract

The application provides a composite copper powder, a preparation method of the composite copper powder, copper paste and a solar cell. The composite copper powder comprises copper powder, a silver layer and an adsorption layer. The silver layer is coated on the outer surface of the copper powder, and the adsorption layer is attached to the surface of the silver layer away from the copper powder. The material of the adsorption layer is benzotriazole. The composite copper powder provided by the application has a double corrosion inhibition layer, and the synergistic effect of the double corrosion inhibition layer can solve the problem of copper powder oxidation.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, and in particular to a composite copper powder, a method for preparing the composite copper powder, copper paste, and a solar cell. Background Technology

[0002] As the global energy structure accelerates its transition to a green and low-carbon model, solar cells, with their advantages of being clean, renewable, and having diverse applications, have become the core carrier of the photovoltaic industry. Technological iterations continue to advance, with conversion efficiency and mass production economics constantly being optimized. Currently, the electrodes in solar cells are mostly made using silver paste. Although silver paste has excellent conductivity and contact properties, the high cost of silver paste raw materials significantly increases the mass production cost of solar cells, hindering the further advancement of grid parity in the photovoltaic industry.

[0003] To alleviate the cost pressure of silver paste, the industry is gradually trying to replace it with copper paste. Copper has the advantages of excellent conductivity and low raw material cost, which is suitable for the large-scale mass production needs of solar cell electrodes. However, the copper powder in copper paste is chemically active and is prone to oxidation to generate impurities such as copper oxide and cuprous oxide. This results in poor long-term oxidation resistance of the sintered electrodes, which restricts the application of copper paste in solar cells. Summary of the Invention

[0004] The purpose of this application is to provide a composite copper powder, a method for preparing the composite copper powder, a copper paste, and a solar cell. The composite copper powder has a double corrosion inhibition layer, and the problem of copper powder oxidation can be solved by utilizing the synergistic effect of the double corrosion inhibition layer.

[0005] This application provides a composite copper powder, which includes copper powder, a silver layer and an adsorption layer. The silver layer is coated on the outer surface of the copper powder, and the adsorption layer is attached to the surface of the silver layer away from the copper powder. The material of the adsorption layer is benzotriazole.

[0006] This application provides a composite copper powder. By coating the copper powder with a silver layer and then coating the silver layer with an adsorption layer, a double corrosion-inhibiting layer is formed on the outer side of the copper powder. The silver layer is dense and chemically stable. The inorganic silver layer physically isolates oxygen, effectively preventing oxygen from diffusing into the copper powder and avoiding oxidation of the inner copper powder, thus achieving a corrosion-inhibiting effect. The adsorption layer is made of benzotriazole (BTA), which can react with copper ions (Cu²⁺). +A stable complex (Cu-BTA) is formed to inhibit the migration of copper ions to the material surface, preventing the formation of verdigris (Cu2(OH)2CO3), thus achieving a corrosion inhibition effect. Simultaneously, the adsorption layer coats the outside of the silver layer, forming a molecular-level protection, further increasing the difficulty of oxygen intrusion into the copper powder, thereby further enhancing the corrosion inhibition effect of the adsorption layer. Furthermore, BTA is adsorbed onto the surface of the silver layer through π-π conjugation, forming strong chemical bonds between BTA and the silver layer, making BTA less prone to volatilization during long-term storage or at high temperatures, thus improving the protective effect of the adsorption layer. In the composite copper powder provided in this application, the silver layer and the adsorption layer work synergistically to achieve a dual effect of mitigating copper powder oxidation corrosion, while simultaneously solving the problem of copper powder oxidation caused by oxidation diffusion and copper ion migration. This improves the long-term oxidation resistance of the composite copper powder sintered electrode, meeting the requirement of TOPCon batteries for electrode materials to have "stable service life of more than 25 years".

[0007] In one possible implementation, the copper powder has a particle size of 2μm to 5μm.

[0008] In one possible implementation, the thickness of the silver layer is 5 nm to 10 nm.

[0009] In one possible implementation, the thickness of the adsorption layer is 5 nm to 8 nm.

[0010] This application also provides a copper paste, which includes composite copper powder, glass powder and an organic carrier, wherein the composite copper powder is the aforementioned composite copper powder.

[0011] In one possible implementation, the glass powder comprises ZnO, P2O5, and B2O3, wherein the molar ratio of ZnO:P2O5:B2O3 in the glass powder is (3.5~4.5):(2.5~3.5):(2.5~3.5).

[0012] In one possible implementation, the copper paste comprises 80% to 85% composite copper powder, 2% to 3% glass powder, and 12% to 18% organic carrier by weight.

[0013] In one possible implementation, the organic carrier comprises, by weight, 40%–50% terpineol, 20%–45% co-solvent, 2%–6% ethyl cellulose and auxiliaries, wherein the co-solvent is butyl carbitol or butyl carbitol acetate.

[0014] This application also provides a solar cell, which includes a substrate and an electrode, wherein the electrode forms an ohmic contact with the substrate, and the electrode is made by sintering the aforementioned copper paste.

[0015] This application also provides a method for preparing composite copper powder, comprising: Preparation of copper powder; Copper powder is mixed with a silver ion source to react and obtain an intermediate, which includes copper powder and a silver layer, with the silver layer coating the outer surface of the copper powder. The intermediate and the adsorption layer material are mixed to prepare composite copper powder. The adsorption layer is attached to the surface of the silver layer away from the copper powder. The material of the adsorption layer is benzotriazole.

[0016] In one possible implementation, the steps for preparing copper powder include: mixing raw materials including a copper ion source, citrate and glucose with a solvent, and reacting to obtain copper powder. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a solar cell provided in an embodiment of this application; Figure 2 for Figure 1 The diagram shows the structure of the composite copper powder in the copper paste used for the electrodes in the solar cell. Figure 3 for Figure 2 The diagram shows the preparation process of the composite copper powder.

[0019] Reference numerals: 1, solar cell; 100, substrate; 101, first surface; 103, second surface; 210, passivation layer; 230, front electrode; 310, tunneling oxide layer; 330, doped polycrystalline silicon layer; 350, back electrode; 400, electrode; 10, copper powder; 30, silver layer; 50, adsorption layer. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of the solar cell 1 provided in an embodiment of this application.

[0022] This application provides a solar cell 1, which is a tunnel oxide passivated contact (TOPCon) cell. Exemplarily, the solar cell 1 includes a substrate 100, a passivation layer 210, a tunnel oxide layer 310, a doped polycrystalline silicon layer 330, and an electrode 400. The electrode 400 forms an ohmic contact with the substrate 100.

[0023] Specifically, the substrate 100 includes a first surface 101 and a second surface 103, which are disposed opposite to each other along the thickness direction of the substrate 100. In this embodiment, the substrate 100 is a silicon wafer, the first surface 101 is the front side of the silicon wafer, and the second surface 103 is the back side of the silicon wafer.

[0024] A passivation layer 210 is applied to the first surface 101 of the substrate 100 to achieve passivation layer 210 disposed on the substrate 100. The passivation layer 210 covers the front side of the substrate 100 to reduce surface recombination losses and improve the open-circuit voltage (Voc) of the solar cell 1. For example, the material of the passivation layer 210 can be alumina (Al2O3) or silicon nitride (SiNx), etc.

[0025] A tunneling oxide layer 310 is disposed on the second surface 103, so that the tunneling oxide layer 310 is disposed on the side of the substrate 100 opposite to the passivation layer 210. The tunneling oxide layer 310 is located on the back side of the substrate 100, and plays a tunneling role, allowing charge carriers to pass through, and reducing recombination by isolating the back electrode 350 from the substrate 100. In this embodiment, the tunneling oxide layer 310 is an ultrathin silicon oxide (SiO2) layer with a thickness of 1nm~2nm.

[0026] A doped polysilicon layer 330 is disposed on the side of the tunneling oxide layer 310 facing away from the second surface 103 of the substrate 100. The doped polysilicon layer 330 is used to form a passivation contact structure, further reducing surface recombination and improving carrier collection efficiency. In this embodiment, the doped polysilicon layer 330 is formed by depositing a layer of phosphorus-doped polysilicon on the tunneling oxide layer 310.

[0027] In this embodiment, electrode 400 includes a front electrode 230 and a back electrode 350. The front electrode 230 penetrates the passivation layer 210 and forms an ohmic contact with the substrate 100. The front electrode 230 is used to collect and transmit the current generated by the first surface 101. The front electrode 230 is a metal grid line, including fine grid lines and main grid lines. The fine grid lines and main grid lines can be formed on the passivation layer 210 using conductive paste through screen printing and then sintered to form the front electrode 230. For example, the conductive paste used in the front electrode 230 can be silver paste or copper paste.

[0028] The back electrode 350 is disposed on the side of the doped polysilicon layer 330 away from the tunneling oxide layer 310 and forms an ohmic contact with the substrate 100. The back electrode 350 serves as the main conductive path on the back side of the substrate 100, undertaking the function of current transmission. The back electrode 350 is a metallization layer, which can be formed on the doped polysilicon layer 330 using conductive paste through screen printing or electroplating processes, and then sintered to form the back electrode 350. In some embodiments, an ultrathin silver layer can be printed first as a "seed layer," followed by a copper paste layer to improve the ohmic junction and prevent copper diffusion.

[0029] In this embodiment, electrode 400 is made by sintering copper paste. The copper powder used in existing copper pastes is easily corroded by oxygen and oxidized, leading to increased resistance of electrode 400 and consequently reducing the performance of solar cell 1. To solve the above problem, this application provides a copper paste comprising composite copper powder. The composite copper powder has a dual corrosion inhibition layer, utilizing the synergistic effect of the dual corrosion inhibition layers to solve the problem of copper powder oxidation. The copper paste provided in this application embodiment will be specifically described below with reference to the structure of the composite copper powder.

[0030] See Figure 2 , Figure 2 for Figure 1 A schematic diagram of the composite copper powder structure in the copper paste used in the electrode 400 of the solar cell 1 shown.

[0031] The copper paste comprises composite copper powder, glass powder, and an organic carrier. In this embodiment, the copper paste comprises 80%–85% composite copper powder, 2%–3% glass powder, and 12%–18% organic carrier by weight. For example, in this embodiment, the viscosity of the copper paste at 25°C is 150 Pa·s–200 Pa·s.

[0032] The composite copper powder comprises copper powder 10, a silver layer 30, and an adsorption layer 50. The silver layer 30 coats the outer surface of the copper powder 10, and the adsorption layer 50 is attached to the surface of the silver layer 30 facing away from the copper powder 10. In this embodiment, the particle size of the copper powder 10 is 2μm to 5μm. Exemplarily, the particle size of the copper powder 10 can be 2μm, 3μm, 4μm, 5μm, or any value between these values.

[0033] The thickness of the silver layer 30 is 5nm to 10nm. For example, the thickness of the silver layer 30 is 5nm, 7nm, 10nm, or any value between these values. The silver layer 30 is dense and chemically stable, effectively preventing oxygen from diffusing into the copper powder 10.

[0034] The thickness of the adsorption layer 50 is 5nm to 8nm. For example, the thickness of the adsorption layer 50 can be 5nm, 6nm, 7nm, 8nm, or any value between these values. The material of the adsorption layer 50 is benzotriazole (BTA). Benzotriazole molecules are adsorbed onto the silver layer 30 on the surface of the copper powder 10 through π-π conjugation, forming a molecular-level protective film. The silver layer 30 is formed by the deposition of nano-silver particles. At the microscale, the nano-silver particle stack may contain grain boundaries, pores, or extremely small defects, making the silver layer 30 not completely dense and potentially becoming a pathway for copper ions to diffuse outward. BTA mainly targets and chemically captures and inhibits the microscopic defects, potential damage, and trace amounts of copper ions that may be generated under long-term extreme environments in the silver layer 30, preventing them from developing into corrosion products (such as verdigris) that significantly increase the resistance of the composite copper powder. Specifically, benzotriazole (BTA) can react with copper ions (Cu²⁺). + A stable complex (Cu-BTA) is formed, thereby inhibiting the migration of copper ions to the surface of electrode 400, thus avoiding the oxidation of copper powder 10 to form verdigris (Cu2(OH)2CO3).

[0035] The glass powder serves two purposes: firstly, it lowers the sintering temperature of the copper paste to below 700°C to suit the low-temperature sintering process of solar cell 1; secondly, it ensures good wettability with the composite copper powder surface, thereby reducing interfacial resistance. In this embodiment, the softening point of the glass powder is 600°C to 640°C. The coefficient of thermal expansion of the glass powder is 7.0 × 10⁻⁶. -6 / ℃~8.0×10 -6 / ℃, the coefficient of thermal expansion of glass powder is 6.5×10. -6 / ℃ matching can prevent stress cracks from forming during sintering.

[0036] In this embodiment, the glass powder is phosphate glass powder. Exemplarily, copper paste is first screen-printed onto the passivation layer 210 of the solar cell 1. Then, through a sintering process, the phosphate glass powder in the copper paste etches through the passivation layer 210, thereby achieving ohmic contact between the conductive copper powder and the silicon substrate, forming the front electrode 230. The glass powder includes ZnO, P2O5, and B2O3, with a molar ratio of ZnO:P2O5:B2O3 of (3.5~4.5):(2.5~3.5):(2.5~3.5). In this embodiment, the glass powder comprises 3.5 mol%~4.5 mol% ZnO, 2.5 mol%~3.5 mol% P2O5, and 2.5 mol%~3.5 mol% B2O3. For example, phosphate glass powder is prepared by using components including ZnO, P2O5 and B2O3 as raw materials, melting at 1000℃ for 2 hours by high-temperature melting method, water quenching and ball milling to a particle size of 1μm~3μm.

[0037] The phosphate glass powder selected for its P2O5 (phosphorus pentoxide) as the main network forging is based on the unique advantages of P2O5 in low-temperature sintering and thermal expansion: 1. P2O5 can form a low-melting-point glass network with a low softening point. 2. By combining P2O5 with ZnO and B2O3, the coefficient of thermal expansion of the phosphate glass can be finely controlled, achieving adjustable thermal expansion. 3. The phosphate glass formed by sintering the phosphate glass powder exhibits good wettability on silicon wafers and metal (copper / silver) surfaces, facilitating the formation of low-resistance ohmic contacts.

[0038] Based on the mass of the organic carrier, it comprises 40%–50% terpineol, 20%–45% co-solvent, 2%–6% ethyl cellulose, and additives. The co-solvent is butyl carbitol (BC) or butyl carbitol acetate (BCA). Terpineol, as the main solvent in the organic carrier, provides basic fluidity to the copper paste, regulates its drying speed, and ensures uniform coating. The combination of butyl carbitol (BC) or butyl carbitol acetate (BCA) with terpineol optimizes the solvent evaporation profile, preventing "screen drying" in copper paste printing and reducing its leveling properties. Ethyl cellulose (EC), as a thickener or film-forming agent, controls the viscosity, thixotropy, or film-forming properties of the copper paste, ensuring the three-dimensional shape (aspect ratio) of the printed lines and thus guaranteeing line integrity during printing.

[0039] The additives include at least one of leveling agents, thixotropic agents, plasticizers, coupling agents, and defoamers. For example, the leveling agent is BYK-163, which can also be called a dispersant. It is used to wet and disperse silver powder and modified glass powder, preventing agglomeration, reducing the surface tension of the copper paste, and preventing "orange peel" texture during copper paste printing. For example, the thixotropic agent is fumed SiO2, providing shear-thinning properties to prevent copper paste from settling during storage, ensuring that the copper paste "flows freely and stays put" during printing, and ensuring uniform dispersion of the ground glass powder and composite copper powder in the organic carrier, guaranteeing the uniformity of the copper paste during long-term storage. For example, the plasticizer is di-n-butyl phthalate (DBP), used to increase the flexibility of the copper paste film and improve the adhesion between the copper paste and the substrate. Dibutyl phthalate (DBP), as a plasticizer, is used to prevent the copper paste from hardening during storage. The organic carrier is plasticized with DBP, which prevents the copper paste from settling or yellowing during long-term storage, and ensures good weather resistance, suitable for the 25-year lifespan requirement of solar cell 1. For example, a silane coupling agent is used to enhance the compatibility between the inorganic powder and the organic carrier in the copper paste. For example, BYK-066N is used to eliminate air bubbles introduced during stirring and grinding, preventing pinholes in the electrodes formed after the copper paste sintering.

[0040] Furthermore, by optimizing the organic carrier, including ethyl cellulose, terpineol, leveling agents, and fumed SiO2, and by controlling the content of each component, the prepared copper paste exhibits better printing performance and stability. Table 1 shows the composition of the organic carrier in a typical embodiment.

[0041] Table 1. Composition of the organic carrier in the typical embodiments

[0042] This application provides a composite copper powder. A silver layer 30 is coated on the outer surface of the copper powder 10, and an adsorption layer 50 is coated on the outer surface of the silver layer 30, thus forming a double corrosion-inhibiting layer on the outer side of the copper powder 10. The silver layer 30 is dense and chemically stable. The inorganic silver layer 30 can physically isolate oxygen, effectively preventing oxygen from diffusing into the interior of the copper powder 10 and avoiding oxidation of the inner copper powder 10, thereby achieving a corrosion-inhibiting effect. The adsorption layer 50 is made of benzotriazole (BTA), which can react with copper ions (Cu²⁺). +A stable complex (Cu-BTA) is formed to inhibit the migration of copper ions to the material surface, preventing the formation of verdigris (Cu2(OH)2CO3), thus achieving a corrosion inhibition effect. Simultaneously, the adsorption layer 50 coats the outside of the silver layer 30, forming a molecular-level protection that further increases the difficulty of oxygen intrusion into the copper powder 10, thereby further enhancing the corrosion inhibition effect of the adsorption layer 50. Furthermore, BTA is adsorbed onto the surface of the silver layer 30 through π-π conjugation, forming strong chemical bonds between BTA and the silver layer 30, making BTA less prone to volatilization during long-term storage or at high temperatures, thus improving the protective effect of the adsorption layer 50. In the composite copper powder provided in this application embodiment, the silver layer 30 and the adsorption layer 50 work synergistically to achieve a dual effect of mitigating the oxidation corrosion of the copper powder 10, while simultaneously solving the problem of copper powder 10 oxidation caused by oxidation diffusion and copper ion migration. This improves the long-term oxidation resistance of the composite copper powder sintered electrode, meeting the requirement of TOPCon batteries for electrode materials to have "stable service life of more than 25 years". Among them, the industry standard of "stable service for more than 25 years" requires that the resistance increase of electrode materials be ≤25% after 1000 hours of aging.

[0043] Furthermore, the organic carrier used in the copper paste provided in this application embodiment plays a role before copper paste printing and sintering, providing suitable rheological properties to ensure that the copper paste can be uniformly printed into the desired shape (such as grid line shape). During the sintering process, the organic carrier decomposes and volatilizes under heat, and the glass powder can melt and take over the "bonding" work, transitioning from the "shape maintenance" provided by the organic carrier to the "structural solidification" provided by the glass powder, ensuring that the copper paste forms a solidified electrode after sintering.

[0044] See Figure 3 , Figure 3 for Figure 2 The diagram shows the preparation process of the composite copper powder.

[0045] This application also provides a method for preparing the above-mentioned composite copper powder, comprising: S10, Preparation of copper powder 10.

[0046] In this embodiment, the steps for preparing copper powder 10 include: mixing raw materials including a copper ion source, citrate, and glucose with a solvent, and reacting to obtain copper powder 10. For example, copper sulfate, trisodium citrate, and glucose are added to deionized water and stirred to obtain spherical copper powder 10 (particle size 2-5 μm, purity 99.95%). In this embodiment, the basic copper powder 10 is prepared using a citrate-glucose reduction method, wherein citrate complexes with copper ions. This complexation reaction controls the subsequent reduction rate of copper ions, resulting in copper powder 10 with uniform particle size and no oxide layer on the surface, suitable for subsequent uniform attachment of a corrosion-inhibiting layer onto the copper powder 10.

[0047] S20. Copper powder 10 is mixed with a silver ion source to obtain an intermediate. The intermediate includes copper powder 10 and a silver layer 30, with the silver layer 30 coating the outer surface of copper powder 10.

[0048] The reaction principle of step S20 is as follows: copper atoms (Cu) on the surface of copper powder 10 0 ) to silver ions (Ag) in the silver ion source + ) reduced to elemental silver (Ag) 0 A 5-10 nm silver layer 30 is deposited on the surface of the copper powder 10. In this embodiment, scanning electron microscopy (SEM) shows that the silver layer 30 uniformly covers the surface of the copper powder 10, without agglomeration or cracking. Compared to bare copper powder 10, the intermediate obtained in step S20 has the copper powder 10 densely coated with the silver layer 30, reducing oxygen permeability by more than 90% and effectively preventing oxygen from diffusing into the copper powder 10.

[0049] For example, the silver ion source is silver nitrate. In this embodiment, basic copper powder 10 is added to deionized water to obtain a dispersion of copper powder 10. After stirring evenly, silver nitrate solution is added, stirred at room temperature, centrifuged, and washed with deionized water to obtain an intermediate.

[0050] S30. The intermediate and the material of the adsorption layer 50 are mixed to prepare composite copper powder. The adsorption layer 50 is attached to the surface of the silver layer 30 away from the copper powder 10. The material of the adsorption layer 50 is benzotriazole.

[0051] In this embodiment, the intermediate was added to a 1 g / L benzotriazole (BTA) ethanol solution and ultrasonically treated at 200 W for 1 hour to prepare composite copper powder. In this embodiment, X-ray photoelectron spectroscopy (XPS) detected characteristic peaks of B and N elements on the surface of silver layer 30, proving that BTA was successfully adsorbed on the surface of silver layer 30.

[0052] This application provides a method for preparing composite copper powder. Copper powder 10 is mixed with a silver ion source to form a silver layer 30 through an in-situ reaction. The silver layer 30 coats the unreacted copper powder 10 and is tightly bonded to it, effectively preventing oxygen from penetrating the interior of the copper powder 10 and avoiding oxidation. Then, benzotriazole (BTA) is adsorbed onto the surface of the silver layer 30 through π-π conjugation to form a molecular-level protective layer, further increasing the difficulty of oxygen penetration into the copper powder 10. Simultaneously, BTA can also react with copper ions (Cu²⁺). +A stable complex (Cu-BTA) is formed to inhibit the migration of copper ions to the material surface, thus avoiding the formation of verdigris (Cu2(OH)2CO3) and improving the long-term antioxidant properties of the prepared composite copper powder.

[0053] This application also provides a method for preparing the above-mentioned copper paste, comprising: P10. Place the composite copper powder and glass powder in a solvent and mix them evenly to obtain a suspension.

[0054] For example, in this embodiment, the glass powder is phosphate glass powder. The composite copper powder and phosphate glass powder are added to anhydrous ethanol and ultrasonically dispersed to obtain a uniform suspension.

[0055] P20. Add an organic carrier to the suspension and mix to obtain a slurry.

[0056] In this embodiment, an organic carrier is obtained by mixing raw materials including ethyl cellulose, terpineol, dibutyl phthalate, and fumed SiO2. The organic carrier is then added to the suspension obtained in step P10 and thoroughly mixed to obtain a slurry.

[0057] P30. Grind the slurry to obtain copper paste.

[0058] The purpose of grinding is to break up the agglomeration of composite copper powder to ensure the printability of the copper paste. For example, a three-roll mill is used to grind the paste, with the gap of the three-roll mill set to 30μm, and grinding is performed 4 times to obtain copper paste.

[0059] The copper paste preparation method provided in this application is simple and does not require complex processes such as electroplating or chemical plating. It can be mass-produced based on existing copper paste production lines.

[0060] The following describes the performance of the copper paste provided in the embodiments of this application and the electrode 400 made using the copper paste, in conjunction with experiments.

[0061] Example 1: Example 1 provides a copper paste, prepared according to the following steps: (1) Preparation of composite copper powder: Take 0.1 mol copper sulfate, 0.2 mol trisodium citrate and 0.1 mol glucose and add them to 1L deionized water. Stir at 80℃ for 1 hour to obtain 10 spherical copper powders.

[0062] 10g of basic copper powder 10 was added to 1L of deionized water to obtain a copper powder 10 dispersion with a mass concentration of 10mg / mL. After stirring evenly, 10mL of 0.01mol / L silver nitrate solution was added, and the mixture was stirred at room temperature for 30 minutes. After centrifugation and washing three times with deionized water, an intermediate was obtained.

[0063] The intermediate was added to a 1 g / L benzotriazole (BTA) ethanol solution and ultrasonically treated at 200 W for 1 hour to prepare composite copper powder. The composite copper powder consists of copper powder 10, a silver layer 30, and an adsorption layer 50. The particle size of copper powder 10 is 3 μm, the thickness of silver layer 30 is 8 nm, and the thickness of adsorption layer 50 (BTA layer) is 6 nm.

[0064] (2) Preparation of phosphate glass powder: Phosphate glass powder was prepared using ZnO (4mol%), P2O5 (3mol%), and B2O3 (3mol%) as raw materials by high-temperature melting method (melting at 1000℃ for 2 hours, followed by water quenching and ball milling to a particle size of 1-3μm). The softening point of the phosphate glass powder is 620℃.

[0065] (3) Take 6.8g of composite copper powder and 2.5g of phosphate glass powder and add 50mL of anhydrous ethanol. Disperse the mixture by ultrasonication at 300W for 20 minutes to obtain a uniform suspension.

[0066] (4) Take 2.4% ethyl cellulose, 43.2% terpineol, 45% butyl carbitol, 0.96% BYK-163, 0.24% fumed SiO2, 5% dibutyl phthalate, 3% silane coupling agent and 0.2% defoamer and mix them to obtain an organic carrier. Add 12% organic carrier to the suspension obtained in step (2) and stir magnetically at 300 rpm for 1 hour to fully mix and obtain a slurry.

[0067] (5) The slurry was ground using a three-roll mill with a gap of 30 μm. The mill was ground 4 times to obtain a copper slurry with a solid content of 80% and a viscosity of 180 Pa·s at 25°C.

[0068] Example 2: Example 2 provides a copper paste. The preparation process differs from that of Example 1 in that, in step (1) of Example 2, the concentration of silver nitrate was increased, the stirring time was extended, the concentration of benzotriazole (BTA) ethanol solution was increased, and the ultrasonic time was extended during the preparation of the composite copper powder. Specifically, step (1) of Example 2 is as follows: Take 0.1 mol copper sulfate, 0.2 mol trisodium citrate and 0.1 mol glucose and add them to 1 L of deionized water. Stir at 80 °C for 1 hour to obtain 10 spherical copper powders.

[0069] 10g of basic copper powder 10 was added to 1L of deionized water to obtain a copper powder 10 dispersion with a mass concentration of 10mg / mL. After stirring evenly, 10mL of 0.015mol / L silver nitrate solution was added, and the mixture was stirred at room temperature for 40 minutes. After centrifugation and washing three times with deionized water, an intermediate was obtained.

[0070] The intermediate was added to a 1.5 g / L benzotriazole (BTA) ethanol solution and ultrasonically treated at 200 W for 1.5 hours to prepare composite copper powder. The composite copper powder comprises copper powder 10, a silver layer 30, and an adsorption layer 50. The copper powder 10 has a particle size of 3 μm, the silver layer 30 has a thickness of 10 nm, and the adsorption layer 50 (BTA layer) has a thickness of 8 nm.

[0071] Comparative Example 1: Comparative Example 1 provides a copper paste, the preparation process of which differs from that of Example 2 in that the composite copper powder prepared in step (1) of Comparative Example 1 does not contain the adsorption layer 50. Specifically, step (1) of Comparative Example 1 is as follows: Preparation of composite copper powder: 0.1 mol copper sulfate, 0.2 mol trisodium citrate and 0.1 mol glucose were added to 1 L of deionized water and stirred at 80 °C for 1 hour to obtain 10 spherical copper powders.

[0072] 10g of basic copper powder 10 was added to 1L of deionized water to obtain a copper powder 10 dispersion with a mass concentration of 10mg / mL. After stirring evenly, 10mL of 0.015mol / L silver nitrate solution was added, and the mixture was stirred at room temperature for 40 minutes. After centrifugation and washing three times with deionized water, composite copper powder was obtained. The composite copper powder consists of copper powder 10 and a silver layer 30. The particle size of copper powder 10 is 2μm~5μm, and the thickness of silver layer 30 is 10nm.

[0073] Comparative Example 2: Comparative Example 2 provides a copper paste, the preparation process of which is the same as that of Example 1, except that the composite copper powder prepared in step (1) of Comparative Example 2 does not contain the silver layer 30. Specifically, step (1) of Comparative Example 2 is as follows: Preparation of composite copper powder: 0.1 mol copper sulfate, 0.2 mol trisodium citrate and 0.1 mol glucose were added to 1 L of deionized water and stirred at 80 °C for 1 hour to obtain 10 spherical copper powders.

[0074] Copper powder 10 was added to a 1 g / L benzotriazole (BTA) ethanol solution and ultrasonically treated at 200 W for 1 hour to prepare composite copper powder. The composite copper powder consists of copper powder 10 and an adsorption layer 50. The particle size of copper powder 10 is 3 μm, and the thickness of adsorption layer 50 (BTA layer) is 6 nm.

[0075] Test samples were prepared using copper pastes from Examples 1-2 and Comparative Examples 1-2. The preparation process involved screen printing copper paste onto a TOPCon solar cell silicon wafer to create a specific grid pattern. The silicon wafer with the printed copper paste was then placed in a sintering furnace and sintered at a temperature not exceeding 700°C to form the test sample. The copper paste sintering formed conductive electrodes.

[0076] The parameters of the electrodes formed by copper paste sintering in the test samples and the aging performance of the test samples were determined using the four-probe method. The results are shown in Table 2. In Table 2, the initial sheet resistance (denoted as R_initial) of the electrodes was determined using the four-probe method, and the linear resistivity of the electrodes was calculated using the Transmission Line Model (TLM) method. The specific test procedure for determining the initial sheet resistance of the electrodes using the four-probe method is as follows: (1) Samples and equipment: Prepare test samples using a four-probe tester with the tips of the four metal probes arranged at equal intervals on the same straight line.

[0077] (2) Place the probes: Press the four probes of the four-probe tester vertically and lightly onto the surface of the test sample to ensure good contact between the probes and the electrodes.

[0078] (3) Apply current: Apply a constant DC current (I) between the two outer probes (probes 1 and 4).

[0079] (4) Measure voltage: Measure the voltage drop (V) between the two inner probes (probes 2 and 3).

[0080] (5) Calculation of sheet resistance: For conductive electrode (thin film) dimensions that are much larger than the probe spacing, the sheet resistance (Rs) is calculated using the formula: Rs = k * (V / I). Here, k is the probe coefficient, which is related to the probe spacing. For an infinitely large thin film with a constant probe spacing of s, k = π / ln2 ≈ 4.5324. The final result is usually expressed in Ω / sq.

[0081] The aging performance test procedure for the test samples is as follows: (1) Place the test sample in a constant temperature and humidity test chamber. The test chamber conditions are set as follows: the temperature is constant at 85℃ and the relative humidity is constant at 85%RH.

[0082] (2) Start the aging test, take out the test sample after 1000 hours of continuous placement, and restore it for 24 hours in a standard laboratory environment (such as 25℃ / 50%RH) to stabilize the electrical performance.

[0083] (3) The sheet resistance of the electrodes in the aged test sample was determined by the above four-probe method (denoted as R_aging).

[0084] (4) Calculate the resistance increase according to the formula: (R_aging-R_initial) / R_initial×100%.

[0085] The testing procedure for the antioxidant lifetime of the test samples is as follows: (1) Place the test sample in a constant temperature and humidity test chamber. The test chamber conditions are set as follows: the temperature is constant at 85℃ and the relative humidity is constant at 85%RH.

[0086] (2) Start the aging test, take out some test samples at predetermined time points (e.g., 250h, 500h, 750h, 1000h, 1250h, 1500h...), and restore them for 24 hours in a standard laboratory environment (e.g., 25℃ / 50%RH) to stabilize electrical performance.

[0087] (3) After each recovery, the current sheet resistance (R0) of the sample is measured using the four-probe method. t ).

[0088] (4) Calculate the resistance increase at each time point: (R) t -R0) / R0×100%.

[0089] (5) By fitting or interpolating the data, the exact time when the resistance increase reaches the critical value is estimated, which is the oxidation resistance life of the copper paste. In the embodiments of this application, the time corresponding to when the resistance increase reaches the critical value of 30% is identified as the oxidation resistance life of the test sample.

[0090] Table 2. Parameters and aging performance of electrodes formed by copper paste sintering in Examples 1-2 and Comparative Examples 1-2.

[0091] As can be seen from Table 2, the linear resistivity of the electrodes formed by sintering copper paste provided in Examples 1 and 2 is close to the linear resistivity of silver paste, which is 3 × 10⁻⁶. -5 With a resistance of Ω·cm, copper paste exhibits excellent conductivity. Furthermore, since the cost of copper is approximately 1 / 100th that of silver, the cost of copper paste is reduced by 60% compared to silver paste, offering a cost advantage. In addition, the electrodes formed by sintering the copper pastes of Examples 1 and 2 show a resistance increase of ≤25% after 1000 hours of aging, demonstrating long-term oxidation resistance and meeting the electrode material requirements of TOPCon batteries. Experimental results show that the copper paste provided in this application, by adjusting its composition, can combine good conductivity, low cost, and long-term oxidation resistance.

[0092] The composite copper powders provided in Examples 1 and 2 were characterized by scanning electron microscopy (SEM). The silver layer 30 uniformly covered the copper powder 10 without cracking. X-ray photoelectron spectroscopy (XPS) confirmed the detection of B and N elements, demonstrating the successful adsorption of the BAT (benzotriazole) layer. Comparing Examples 1-2 and Comparative Examples 1-2, the composite copper powder used in the copper paste of Comparative Example 1 had only a silver layer 30 coating on the outside of the copper powder 10, while the composite copper powder in the copper paste of Comparative Example 2 had only a BAT layer adsorbed on the outside of the copper powder 10. After sintering, the electrodes formed from the copper pastes of Comparative Examples 1 and 2 showed a resistance increase of more than 25% after aging for 1000 hours.

[0093] Scanning electron microscopy (SEM) revealed obvious cracks in the silver layer 30 of the electrode in Comparative Example 1, with a crack width of approximately 100 nm. The significant increase in resistance after aging of the electrode in Comparative Example 1 is due to the presence of silver layer 30 (silver has a thermal expansion coefficient of 19 × 10⁻⁶). -6 / ℃) and copper powder 10 (the coefficient of thermal expansion of copper is 17×10) -6 The large difference in thermal expansion coefficients between the two is significant. During sintering (700℃) and long-term service (outdoor temperature difference -40℃ to 85℃), the silver layer 30 is prone to cracking due to thermal stress, resulting in microcracks. These microcracks provide diffusion channels for oxygen, which then penetrates into the copper powder 10. This causes the copper powder 10 to be gradually oxidized into Cu2O (red) and CuO (black), leading to a sharp increase in resistance. As a result, the resistance of the electrode increases by more than 80% after 1000 hours of aging.

[0094] XPS analysis of the electrode in Comparative Example 2 revealed the presence of CuO characteristic peaks (Cu 2p3 / 2 binding energy 934 eV) on the surface of copper powder 10. The significant increase in resistance after aging of the electrode in Comparative Example 2 was attributed to the fact that the BAT (benzotriazole) layer failed to physically isolate oxygen, allowing oxygen to react with the surface of copper powder 10 to generate CuO, resulting in a resistance increase of >70%.

[0095] Experimental results show that in the composite copper powder provided in this application embodiment, by coating the outside of the copper powder 10 with a silver layer 30 and an adsorption layer 50, the two work together to achieve a dual effect of mitigating the oxidation and corrosion of the copper powder 10, thereby improving the long-term oxidation resistance of the copper paste sintered electrode.

[0096] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A composite copper powder, characterized in that, The composite copper powder includes copper powder, a silver layer, and an adsorption layer. The silver layer coats the outer surface of the copper powder, and the adsorption layer is attached to the surface of the silver layer away from the copper powder. The material of the adsorption layer is benzotriazole.

2. The composite copper powder according to claim 1, characterized in that, The thickness of the silver layer is 5nm~10nm.

3. The composite copper powder according to claim 1, characterized in that, The thickness of the adsorption layer is 5nm~8nm.

4. A copper paste, characterized in that, The copper paste comprises composite copper powder, glass powder and organic carrier, wherein the composite copper powder is the composite copper powder according to any one of claims 1 to 3.

5. The copper paste according to claim 4, characterized in that, The glass powder comprises ZnO, P2O5 and B2O3, wherein the molar ratio of ZnO:P2O5:B2O3 in the glass powder is (3.5~4.5):(2.5~3.5):(2.5~3.5).

6. The copper paste according to claim 4, characterized in that, The copper paste comprises 80% to 85% of the composite copper powder, 2% to 3% of the glass powder, and 12% to 18% of the organic carrier, based on the mass of the copper paste.

7. The copper paste according to any one of claims 4 to 6, characterized in that, Based on the mass of the organic carrier, the organic carrier comprises 40% to 50% terpineol, 20% to 45% co-solvent, 2% to 6% ethyl cellulose and auxiliaries, wherein the co-solvent is butyl carbitol or butyl carbitol acetate.

8. A solar cell, characterized in that, The solar cell includes a substrate and an electrode, the electrode forming an ohmic contact with the substrate, and the electrode being made by sintering the copper paste according to any one of claims 4 to 7.

9. A method for preparing composite copper powder, characterized in that, include: Preparation of copper powder; The copper powder is mixed with a silver ion source to react and obtain an intermediate, the intermediate comprising the copper powder and a silver layer, the silver layer coating the outer surface of the copper powder; The intermediate and the material of the adsorption layer are mixed to prepare composite copper powder. The adsorption layer is attached to the surface of the silver layer away from the copper powder. The material of the adsorption layer is benzotriazole.

10. The method for preparing composite copper powder according to claim 9, characterized in that, The steps for preparing copper powder include: mixing raw materials including a copper ion source, citrate and glucose with a solvent, and reacting to obtain the copper powder.

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