TOPCon battery back slurry based on copper and copper alloy and preparation method of TOPCon battery back slurry

Abstract

The invention relates to the technical field of solar cells, in particular to copper and copper alloy-based TOPCon cell back paste and a preparation method thereof. The paste is composed of Cu-Sn alloy powder, electrolytic copper powder, vanadium-containing glass powder and an organic carrier, and the conductivity, the adhesive force and the long-term stability are remarkably improved through the synergistic effect of multiple components. The Cu-Sn alloy powder forms a liquid phase during sintering, a three-dimensional conductive network is constructed, and oxidation is inhibited; the vanadium-containing glass powder improves the interface bonding force through a nanometer enhancement effect and optimizes the thermal expansion matching property; the carbon-vanadium complex provides anti-corrosion protection in a humid and hot environment. The paste provided by the invention is superior to the prior art in the aspects of contact resistance, adhesive force, thermal expansion coefficient and damp-heat aging performance, and is suitable for industrial application of efficient TOPCon solar cells.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and particularly to a back paste for TOPCon cells based on copper and copper alloys and a preparation method thereof. Background Art

[0002] With the rapid development of the solar photovoltaic industry, TOPCon (Tunnel Oxide Passivated Contact) cells have become a research hotspot for the next generation of high-efficiency silicon-based solar cells due to their high conversion efficiency and excellent stability. In TOPCon cells, the performance of the back electrode paste has an important impact on the conductivity, interfacial bonding strength and long-term stability of the cells. However, the currently mainstream silver-based conductive pastes on the market are costly, which limits their application in large-scale production. Therefore, developing low-cost conductive pastes based on copper has become an important research direction.

[0003] Copper-based conductive pastes have become potential alternatives to silver-based pastes due to their excellent conductivity, rich resources and low cost. However, copper materials are relatively chemically active and prone to oxidation during sintering and use, resulting in an increase in interfacial contact resistance. In addition, the chemical compatibility and thermal expansion matching between copper and silicon-based materials are poor, and interfacial cracks or peeling are likely to occur due to thermal stress during sintering or long-term use, thus affecting the long-term reliability of the cells. In addition, copper-based conductive pastes are prone to performance degradation due to electrochemical corrosion in a humid and hot environment, further limiting their application in the photovoltaic field. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a back paste for TOPCon cells based on copper and copper alloys and a preparation method thereof, so as to solve the problems of high contact resistance, insufficient interfacial bonding strength, thermal expansion coefficient mismatch and serious performance degradation in a humid and hot environment existing in the existing copper-based conductive pastes.

[0005] Based on the above purpose, the present invention provides a back paste for TOPCon cells based on copper and copper alloys, which is prepared from the following raw materials by weight: 70-80 parts of Cu-Sn alloy powder, 8-12 parts of electrolytic copper powder, 3-8 parts of vanadium-containing glass powder and 8-12 parts of organic carrier;

[0006] Preferably, the particle size D50 of the Cu-Sn alloy powder is 1.1-1.3 μm.

[0007] Preferably, the particle size D50 of the electrolytic copper powder is 0.3-0.8 μm.

[0008] Furthermore, the preparation steps of the vanadium-containing glass powder are as follows:

[0009] S1: Add 5 g of ammonium metavanadate and 8 - 12 g of citric acid into 80 - 120 g of deionized water, heat up to 55 - 65 °C, stir for 20 - 40 min, then dropwise add a 5 wt% cetyltrimethylammonium bromide ethanol solution, stir at 55 - 65 °C for 10 - 14 h, centrifuge and transfer to a tubular furnace, and heat up to 380 - 420 °C at a rate of 3 - 10 °C / min under an Ar / H 2 atmosphere with a volume ratio of 95 / 5, hold for 1.5 - 2.5 h, and cool with the furnace to obtain a carbon - vanadium composite;

[0010] S2: Mix Bi 2 O 3 、B 2 O 3 、ZnO, SiO 2 and the carbon - vanadium composite, put them into a crucible, heat from room temperature to 850 - 950 °C at a rate of 4 - 6 °C / min, hold for 1.5 - 2.5 h, quench and then ball - mill to obtain vanadium - containing glass powder.

[0011] Preferably, in step S1, the weight ratio of ammonium metavanadate, citric acid, deionized water and cetyltrimethylammonium bromide ethanol solution is 5:8 - 12:80 - 120:10 - 30.

[0012] Further, in step S2, the weight ratio of Bi 2 O 3 、B 2 O 3 、ZnO, SiO 2 and the carbon - vanadium composite is 4 - 6:1.5 - 2.5:1 - 2:0.5 - 1.5:0.2 - 0.8.

[0013] Preferably, the Cu - Sn alloy powder is prepared from copper ingots and tin ingots according to a weight ratio of 97 - 92:3 - 8.

[0014] Preferably, the preparation steps of the Cu - Sn alloy powder are as follows: Put copper ingots and tin ingots in, heat to 1150 - 1250 °C under argon protection to form a molten alloy, atomize through an air - atomizing nozzle at a pressure of 0.5 - 0.7 MPa, and then perform hydrogen reduction treatment to obtain a Cu - Sn alloy powder with an oxygen content lower than 800 ppm.

[0015] Preferably, the preparation method of the organic carrier is as follows: Add ethyl cellulose and benzotriazole carboxylate into a pine oil alcohol / butyl carbitol mixed solvent, heat up to 50 - 70 °C, and stir for 20 - 40 min to obtain the organic carrier.

[0016] Preferably, the weight ratio of ethyl cellulose, benzotriazole carboxylate and pine oil alcohol / butyl carbitol mixed solvent is 3 - 5:0.1 - 1:80 - 120.

[0017] Preferably, the volume ratio of the terpineol / butyl carbitol mixed solvent is 6:4.

[0018] Furthermore, the present invention also provides a preparation method of a TOPCon cell back paste based on copper and copper alloys, comprising the following steps: adding Cu-Sn alloy powder, electrolytic copper powder and vanadium-containing glass powder into an organic carrier, premixing at a rotation speed of 150-250 rpm for 20-30 min, and then transferring it into a ball mill tank and ball milling for 3-5 h to obtain a TOPCon cell back paste based on copper and copper alloys.

[0019] Advantages of the present invention:

[0020] The copper-based conductive paste provided by the present invention significantly improves the comprehensive performance through the synergistic effect of multiple components. In terms of electrical conductivity, copper alloy powder and electrolytic copper powder with a specific ratio form a bimodal particle size distribution, and a three-dimensional interpenetrating conductive network is constructed through the dual mechanisms of solid-state diffusion and liquid-phase sintering, effectively reducing the interfacial contact resistance. Alloying elements preferentially diffuse to the grain boundaries at high temperatures to form a low-resistance interfacial layer, while suppressing the oxidation tendency of the copper matrix, ensuring the long-term stability of the conductive path.

[0021] In terms of interfacial bonding strength, the specially modified glass phase forms a dual bonding mechanism of chemical bonding and mechanical interlocking with metal particles through the nano-enhancement effect. The composite additive regulates the viscosity and wettability of the glass phase during the sintering process, promotes the interfacial reaction to generate a transition layer, and significantly enhances the adhesion between the electrode and the substrate. This transition layer also has excellent thermal shock resistance, effectively alleviating the interfacial peeling caused by thermal stress.

[0022] In terms of thermal expansion matching, by adjusting the ratio of the metal phase to the glass phase and the negative thermal expansion characteristics of the composite additive, the overall thermal expansion coefficient of the paste is kept in good match with the silicon substrate. This thermodynamic compatibility effectively inhibits the generation of interfacial microcracks during the temperature cycle, ensuring the integrity of the electrode structure under wide temperature range working conditions. Detailed implementation manners

[0023] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further elaborates on the present invention with reference to specific embodiments.

[0024] Example 1:

[0025] (1) Put 97 g of copper ingot and 3 g of tin ingot, heat to 1150 °C under argon protection to form a molten alloy, atomize it through an air atomization nozzle at a pressure of 0.5 MPa, and then perform hydrogen reduction treatment to obtain Cu-Sn alloy powder with an oxygen content of 775 ppm and a particle size D50 of 1.1 μm;

[0026] (2) Add 5 g of ammonium metavanadate and 8 g of citric acid to 80 g of deionized water, heat up to 55 °C, stir for 20 min, then dropwise add 10 g of cetyltrimethylammonium bromide ethanol solution (concentration 5 wt%), stir at 55 °C for 10 h, centrifuge and transfer to a tube furnace, and heat up to 380 °C at a rate of 3 °C / min under an Ar / H 2 (95 / 5) atmosphere, hold for 1.5 h, and cool with the furnace to obtain a carbon-vanadium composite;

[0027] (3) Mix 4 g of Bi 2 O 3 , 1.5 g of B 2 O 3 , 1 g of ZnO, 0.5 g of SiO 2 and 0.2 g of the carbon-vanadium composite, put them into a crucible, heat from room temperature to 850 °C at a rate of 4 °C / min, hold for 1.5 h, quench and then ball mill to obtain vanadium-containing glass powder with a D50 particle size of 1.1 μm;

[0028] (4) Add 3 g of ethyl cellulose and 0.1 g of benzotriazole carboxylate to 80 g of a pine oil alcohol / butyl carbitol mixed solvent (volume ratio 6:4), heat up to 50 °C, stir for 20 min to obtain an organic carrier;

[0029] (5) Add 70 g of Cu-Sn alloy powder, 8 g of electrolytic copper powder (D50 particle size 0.3 μm) and 3 g of vanadium-containing glass powder to 8 g of the organic carrier, premix at a speed of 150 rpm for 20 min, then transfer to a ball mill jar and ball mill for 3 h to obtain a TOPCon cell back paste based on copper and copper alloys.

[0030] Example 2:

[0031] (1) Put 95 g of copper ingot and 5 g of tin ingot, heat to 1200 °C under argon protection to form a molten alloy, atomize through an air atomization nozzle at a pressure of 0.6 MPa, and then perform hydrogen reduction treatment to obtain Cu-Sn alloy powder with an oxygen content of 750 ppm and a D50 particle size of 1.2 μm;

[0032] (2) Add 5 g of ammonium metavanadate and 10 g of citric acid to 100 g of deionized water, heat up to 60 °C, stir for 30 min, then dropwise add 20 g of cetyltrimethylammonium bromide ethanol solution (concentration 5 wt%), stir at 60 °C for 12 h, centrifuge and transfer to a tube furnace, and heat up to 400 °C at a rate of 5 °C / min under an Ar / H 2 (95 / 5) atmosphere, hold for 2 h, and cool with the furnace to obtain a carbon-vanadium composite;

[0033] (3) Mix 5 g of Bi 2 O 3 , 2 g of B 2 O3 and 1 g of SiO are mixed with 1.5 g of ZnO and 0.5 g of carbon-vanadium composite, put into a crucible, heated from room temperature to 900 °C at a rate of 5 °C / min, held for 2 h, quenched and then ball-milled to obtain vanadium-containing glass powder with a D50 particle size of 1.2 μm; 2

[0034] (4) 4 g of ethyl cellulose and 0.5 g of benzotriazole carboxylate are added to 100 g of a mixed solvent of terpineol / butyl carbitol (volume ratio 6:4), heated to 60 °C, and stirred for 30 min to obtain an organic carrier;

[0035] (5) 75 g of Cu-Sn alloy powder, 10 g of electrolytic copper powder (D50 particle size of 0.5 μm), and 5 g of vanadium-containing glass powder are added to 10 g of the organic carrier, premixed at a speed of 200 rpm for 30 min, then transferred to a ball mill and ball-milled for 4 h to obtain a back paste for TOPCon cells based on copper and copper alloys.

[0036] Example 3:

[0037] (1) 92 g of copper ingot and 8 g of tin ingot are put in, heated to 1250 °C under argon protection to form a molten alloy, atomized through an air atomization nozzle at a pressure of 0.7 MPa, and then subjected to hydrogen reduction treatment to obtain Cu-Sn alloy powder with an oxygen content of 720 ppm and a D50 particle size of 1.3 μm;

[0038] (2) 5 g of ammonium metavanadate and 12 g of citric acid are added to 120 g of deionized water, heated to 65 °C, stirred for 40 min, then 30 g of cetyltrimethylammonium bromide ethanol solution (concentration 5 wt%) is added dropwise, stirred at 65 °C for 14 h, centrifuged and then transferred to a tube furnace, heated to 420 °C at a rate of 10 °C / min under an Ar / H 2 (95 / 5) atmosphere, held for 2.5 h, and cooled with the furnace to obtain a carbon-vanadium composite;

[0039] (3) 6 g of Bi 2 O 3 、2.5 g of B 2 O 3 、2 g of ZnO, 1.5 g of SiO 2 and 0.8 g of carbon-vanadium composite are mixed, put into a crucible, heated from room temperature to 950 °C at a rate of 6 °C / min, held for 2.5 h, quenched and then ball-milled to obtain vanadium-containing glass powder with a D50 particle size of 1.4 μm;

[0040] (4) 5 g of ethyl cellulose and 1 g of benzotriazole carboxylate are added to 120 g of a mixed solvent of terpineol / butyl carbitol (volume ratio 6:4), heated to 70 °C, and stirred for 40 min to obtain an organic carrier;

[0041] ​(5) Add 80 g of Cu-Sn alloy powder, 12 g of electrolytic copper powder (particle size D50 is 0.8 μm), and 8 g of vanadium-containing glass powder to 12 g of organic carrier, premix at a speed of 250 rpm for 30 min, then transfer to a ball mill and ball mill for 5 h to obtain the back paste of TOPCon battery based on copper and copper alloy.

[0042] Comparative Example 1:

[0043] The difference between Comparative Example 1 and Example 2 is that the carbon-vanadium complex in step (2) is replaced by V 2 O 5 ; Specific implementation method:

[0045] (1) Put 95 g of copper ingot and 5 g of tin ingot, heat to 1200 °C under argon protection to form a molten alloy, atomize through an air atomization nozzle at a pressure of 0.6 MPa, and then perform hydrogen reduction treatment to obtain Cu-Sn alloy powder with an oxygen content of 750 ppm and a particle size D50 of 1.2 μm;

[0046] (2) Mix 5 g of Bi 2 O 3 , 2 g of B 2 O 3 , 1.5 g of ZnO, 1 g of SiO 2 and 0.5 g of V 2 O 5 Mix, put into a crucible, heat from room temperature to 900 °C at a rate of 5 °C / min, keep warm for 2 h, quench and then ball mill to obtain vanadium-containing glass powder with a particle size D50 of 1.2 μm;

[0047] (3) Add 4 g of ethyl cellulose and 0.5 g of benzotriazole carboxylate to 100 g of a mixed solvent of terpineol / butyl carbitol (volume ratio 6:4), heat to 60 °C, and stir for 30 min to obtain an organic carrier;

[0048] (4) Add 75 g of Cu-Sn alloy powder, 10 g of electrolytic copper powder (particle size D50 is 0.5 μm), and 5 g of vanadium-containing glass powder to 10 g of organic carrier, premix at a speed of 200 rpm for 30 min, then transfer to a ball mill and ball mill for 4 h to obtain the back paste of the battery.

[0049] Comparative Example 2:

[0050] The difference between Comparative Example 2 and Example 2 is that the carbon-vanadium complex is not added in step (3); Specific implementation method:

[0052] (1) Put 95 g of copper ingot and 5 g of tin ingot, heat to 1200 °C under argon protection to form a molten alloy, atomize through an air atomization nozzle at a pressure of 0.6 MPa, and then perform hydrogen reduction treatment to obtain Cu-Sn alloy powder with an oxygen content of 750 ppm and a particle size D50 of 1.2 μm;

[0053] (2) Mix 5 g of Bi 2 O 3 , 2 g of B 2 O 3 , 1.5 g of ZnO and 1 g of SiO 2 , put them into a crucible, heat from room temperature to 900 °C at a rate of 5 °C / min, hold for 2 h, and then perform quenching and ball milling to obtain glass powder with a particle size D50 of 1.2 μm;

[0054] (3) Add 4 g of ethyl cellulose and 0.5 g of benzotriazole carboxylate to 100 g of a mixed solvent of terpineol / butyl carbitol (volume ratio 6:4), heat to 60 °C, and stir for 30 min to obtain an organic carrier;

[0055] (4) Add 75 g of Cu-Sn alloy powder, 10 g of electrolytic copper powder (particle size D50 is 0.5 μm) and 5 g of glass powder to 10 g of the organic carrier, premix at a speed of 200 rpm for 30 min, and then transfer to a ball mill jar and ball mill for 4 h to obtain the back paste of the battery.

[0056] Comparative Example 3:

[0057] The difference between Comparative Example 3 and Example 2 is that: Cu-Sn alloy powder was not added in step (5); Specific implementation method:

[0059] (1) Put 95 g of copper ingot and 5 g of tin ingot, heat to 1200 °C under argon protection to form a molten alloy, atomize through an air atomization nozzle at a pressure of 0.6 MPa, and then perform hydrogen reduction treatment to obtain Cu-Sn alloy powder with an oxygen content of 750 ppm and a particle size D50 of 1.2 μm;

[0060] (2) Add 5 g of ammonium metavanadate and 10 g of citric acid to 100 g of deionized water, heat to 60 °C, stir for 30 min, and then dropwise add 20 g of cetyltrimethylammonium bromide ethanol solution (concentration 5 wt%), stir at 60 °C for 12 h, centrifuge and transfer to a tube furnace, and heat to 400 °C at a rate of 5 °C / min in an Ar / H 2 (95 / 5) atmosphere, hold for 2 h, and cool with the furnace to obtain a carbon vanadium complex;

[0061] (3) Mix 5 g of Bi 2 O 3 , 2 g of B 2 O3 and 1.5 g of ZnO, 1 g of SiO 2 are mixed and put into a crucible. It is heated from room temperature to 900 °C at a rate of 5 °C / min, held for 2 h, quenched and then ball-milled to obtain vanadium-containing glass powder with a D50 particle size of 1.2 μm;

[0062] (4) 4 g of ethyl cellulose and 0.5 g of benzotriazole carboxylate are added to 100 g of a mixed solvent of terpineol / butyl carbitol (volume ratio 6:4), heated to 60 °C, and stirred for 30 min to obtain an organic carrier;

[0063] (5) 85 g of electrolytic copper powder (with a D50 particle size of 0.5 μm) and 5 g of vanadium-containing glass powder are added to 10 g of the organic carrier, premixed at a speed of 200 rpm for 30 min, and then transferred to a ball-milling tank and ball-milled for 4 h to obtain the back paste of the battery.

[0064] Comparative Example 4:

[0065] The difference between Comparative Example 4 and Example 2 is that: electrolytic copper powder is not added in step (5); Specific implementation method:

[0067] (1) 95 g of copper ingot and 5 g of tin ingot are put in, heated to 1200 °C under argon protection to form a molten alloy, atomized through an air atomizing nozzle at a pressure of 0.6 MPa, and then subjected to hydrogen reduction treatment to obtain Cu-Sn alloy powder with an oxygen content of 750 ppm and a D50 particle size of 1.2 μm;

[0068] (2) 5 g of ammonium metavanadate and 10 g of citric acid are added to 100 g of deionized water, heated to 60 °C, stirred for 30 min, and then 20 g of cetyltrimethylammonium bromide ethanol solution (concentration 5 wt%) is added dropwise, stirred at 60 °C for 12 h, centrifuged and then transferred to a tubular furnace, and heated to 400 °C at a rate of 5 °C / min under an Ar / H 2 (95 / 5) atmosphere, held for 2 h, and cooled with the furnace to obtain a carbon-vanadium composite;

[0069] (3) 5 g of Bi 2 O 3 、2 g of B 2 O 3 、1.5 g of ZnO, 1 g of SiO 2 and 0.5 g of carbon-vanadium composite are mixed, put into a crucible, heated from room temperature to 900 °C at a rate of 5 °C / min, held for 2 h, quenched and then ball-milled to obtain vanadium-containing glass powder with a D50 particle size of 1.2 μm;

[0070] (4) Add 4 g of ethyl cellulose and 0.5 g of benzotriazole carboxylate to 100 g of a mixture solvent of terpineol / butyl carbitol (volume ratio 6:4), heat up to 60 °C, and stir for 30 min to obtain an organic carrier;

[0071] (5) Add 85 g of Cu-Sn alloy powder and 5 g of vanadium-containing glass powder to 10 g of the organic carrier, premix at a rotation speed of 200 rpm for 30 min, then transfer to a ball mill jar and ball mill for 4 h to obtain the back paste of the battery.

[0072] Performance test:

[0073] Preparation of solar cell wafers: Select N-type TOPCon cell silicon wafers (size 182 mm × 182 mm, with an 80-nm polysilicon layer deposited on the back), use a 500-mesh nickel screen to print the pastes prepared in the examples and comparative examples on the back of the silicon wafers, and control the wet weight at 30 ± 1 mg / cm 2 , then heat at 160 °C for 2 h, and then sinter at 750 °C for 2 min to obtain the corresponding solar cell wafers.

[0074] Contact resistance: Test according to standard GB / T 1551-2021, measure using a four-probe tester under the condition of constant temperature at 25 °C, set the probe pressure to 0.5 N, and the spacing calibration error < ±0.5%, and the results are shown in Table 1.

[0075] Adhesion: Test according to standard GB / T 2792-2014, use a universal material testing machine to vertically peel at a speed of 50 mm / min, and the results are shown in Table 1.

[0076] Coefficient of thermal expansion (CTE): Test according to standard GB / T 4339-2008, use a thermomechanical analyzer, temperature range: 25 - 500 °C (heating rate 5 °C / min), and the results are shown in Table 1.

[0077] Damp heat aging test: Test according to standard GB / T 2423.3-2016, temperature: 85 °C ± 2 °C, humidity: 85% RH ± 3%, duration: 1000 h, then test the contact resistance after standing at room temperature for 24 h, calculate the growth rate, and the results are shown in Table 1.

[0078] Table 1 Performance test results

[0079]

[0080] Data analysis:

[0081] From the data of Examples 1 - 3 in Table 1, it can be seen that the back paste for TOPCon cells based on copper and copper alloys provided by the present invention has a low contact resistance, high adhesion, appropriate thermal expansion coefficient, and excellent damp heat resistance. This indicates that the synergistic effect of Cu - Sn alloy powder and carbon - vanadium composite significantly improves the comprehensive performance of the paste. The Cu - Sn alloy powder may form a liquid phase during the sintering process through its low melting point characteristic (the melting point of Sn is 232 °C), promoting the metallurgical bonding between conductive particles, thereby reducing the contact resistance. At the same time, the oxidation inhibition characteristic of Sn reduces the interfacial oxide layer, further optimizing the conductivity. The carbon skeleton in the carbon - vanadium composite may provide a three - dimensional conductive network, while the vanadium species act as a sintering aid in the glass phase, reducing the glass softening point and promoting the interfacial bonding between the paste and the silicon wafer, thereby improving the adhesion. In addition, the high thermal stability of the carbon - vanadium composite may inhibit the excessive flow of the glass phase during the sintering process, making the thermal expansion coefficient closer to that of the silicon wafer (about 3 - 4 ppm / °C) and reducing the microcracks caused by thermal stress. The improvement in the damp heat aging performance may stem from the hydrophobic carbon layer of the carbon - vanadium composite blocking the penetration of water vapor, while the dense structure of the Cu - Sn alloy reduces the electrochemical corrosion path.

[0082] From the data of Example 2 and Comparative Example 1 in Table 1, it can be seen that the contact resistance of Example 2 is significantly lower than that of Comparative Example 1, and the adhesion and thermal expansion coefficient are also better, indicating that the carbon - vanadium composite has multiple advantages compared to V 2 O 5 . V 2 O 5 may form a high - resistance vanadate glass phase (such as BiVO 4 ) during high - temperature sintering, while the carbon matrix in the carbon - vanadium composite physically isolates and inhibits the excessive oxidation of vanadium, retaining some vanadium in a low - valence state, which can enhance the carrier mobility. In addition, the carbon - vanadium composite prepared by the CTAB template method has a mesoporous structure and acts as a nano - reinforcing phase in the paste, improving the interfacial bonding force through the mechanical interlocking effect. The difference in the thermal expansion coefficient may be due to the negative thermal expansion characteristic of carbon partially offsetting the positive thermal expansion of the glass phase, while the higher CTE of V 2 O 5 causes the CTE of Comparative Example 1 to rise to 6.2 ppm / °C. The improvement in the growth rate of the contact resistance after damp heat aging is related to the antioxidant property of the carbon layer. Carbon can react with oxygen preferentially to form CO / CO 2 , protecting the vanadium and copper components from oxidation corrosion.

[0083] From the data of Example 2 and Comparative Example 2 in Table 1, it can be seen that in Comparative Example 2, due to the absence of the carbon - vanadium composite, the contact resistance increases, the adhesion decreases, the thermal expansion coefficient reaches 6.8 ppm / °C, and the resistance increases by 1.8% after damp heat aging, which is significantly inferior to Example 2. This indicates that the carbon - vanadium composite plays a key modification role in the glass powder.

[0084] From the data of Example 2 and Comparative Example 3 in Table 1, it can be seen that when the Cu-Sn alloy powder was not used in Comparative Example 3, the contact resistance increased to 0.78 mΩ·cm 2 , and the adhesion was only 4.0 N / mm, indicating that the Cu-Sn alloy powder is crucial for conductivity and adhesion. The Cu-Sn alloy powder (melting point about 800-900 °C) partially melts during sintering at 750 °C and fills the gaps between copper powders through capillary action to form a continuous conductive path. While the pure electrolytic copper powder (melting point 1085 °C) does not reach the melting point and is only connected by solid-state diffusion, with a higher porosity. The addition of Sn also optimizes the conductivity by forming intermetallic compounds, and its hardness is higher than that of pure copper, which can enhance the mechanical anchoring effect of the paste and improve the adhesion. The difference in the coefficient of thermal expansion may be related to the slightly lower CTE of the Cu-Sn alloy than that of pure copper, which is closer to the CTE of the silicon wafer. The 2.5% increase in resistance after damp heat aging (compared with 0.8%) is due to the preferential oxidation of Sn to form SnO 2 , while in Example 2, Sn exists in the form of an alloy, and the oxidation kinetics is inhibited.

[0085] From the data of Example 2 and Comparative Example 4 in Table 1, it can be seen that when the electrolytic copper powder was not added in Comparative Example 4, the contact resistance increased, indicating that there is a synergistic conductive mechanism between the electrolytic copper powder and the Cu-Sn alloy powder. The electrolytic copper powder can fill the gaps between the Cu-Sn alloy powders to form a bimodal particle size distribution, increasing the sintering density. In addition, the surface activity of the electrolytic copper powder is relatively high, and a fresh copper surface is generated through an oxidation-reduction reaction during sintering, promoting diffusion welding between particles. The decrease in adhesion may be due to the lack of the nanoscale rough surface of the electrolytic copper powder, weakening the mechanical interlocking with the glass phase. The increase in the coefficient of thermal expansion reflects that the decrease in copper content leads to the overall CTE of the paste being closer to that of the glass phase, exacerbating the mismatch with the silicon wafer. The deterioration of the damp heat aging performance is due to the lack of electrolytic copper powder, which simplifies the conductive network and increases the local current density, accelerating the electrochemical corrosion of the Cu-Sn alloy.

[0086] Those of ordinary skill in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A TOPCon battery back paste based on copper and copper alloys, characterized in that: The method is prepared from the following raw materials by weight: 70-80 parts of Cu-Sn alloy powder, 8-12 parts of electrolytic copper powder, 3-8 parts of vanadium-containing glass powder and 8-12 parts of organic carrier; The particle size D50 of the Cu-Sn alloy powder is 1.1-1.3 μm; The particle size D50 of the electrolytic copper powder is 0.3-0.8 μm; The preparation steps of the vanadium-containing glass powder are as follows: S1: Add 5g of ammonium metavanadate and 8-12g of citric acid to 80-120g of deionized water, heat to 55-65°C, stir for 20-40min, then add 5wt% hexadecyltrimethylammonium bromide ethanol solution dropwise, stir at 55-65°C for 10-14h, transfer to a tube furnace after centrifugation, heat to 380-420°C at 3-10°C / min in an Ar / H2 atmosphere with a volume ratio of 95 / 5, keep warm for 1.5-2.5h, and cool with the furnace to obtain a carbon-vanadium complex; S2: Mix Bi2O3, B2O3, ZnO, SiO2 and carbon-vanadium complex, put into a crucible, heat from room temperature to 850-950°C at 4-6°C / min, keep warm for 1.5-2.5h, quench and then ball mill to obtain vanadium-containing glass powder; In the step S1, the weight ratio of ammonium metavanadate, citric acid, deionized water and hexadecyltrimethylammonium bromide ethanol solution is 5:8-12:80-120:10-30; In the step S2, the weight ratio of Bi2O3, B2O3, ZnO, SiO2 and the carbon-vanadium complex is 4-6:1.5-2.5:1-2:0.5-1.5:0.2-0.

8.

2. The TOPCon battery back paste based on copper and copper alloy according to claim 1, characterized in that: The Cu-Sn alloy powder is prepared from copper ingots and tin ingots in a weight ratio of 97-92:3-8.

3. The TOPCon battery back paste based on copper and copper alloy according to claim 1, characterized in that: The preparation steps of the Cu-Sn alloy powder are as follows: copper ingots and tin ingots are put in, heated to 1150-1250° C. under argon protection to form a molten alloy, atomized through an atomization nozzle at a pressure of 0.5-0.7 MPa, and then subjected to hydrogen reduction treatment to obtain a Cu-Sn alloy powder with an oxygen content of less than 800 ppm.

4. The TOPCon battery back paste based on copper and copper alloy according to claim 1, characterized in that: The preparation method of the organic carrier is as follows: ethyl cellulose and benzotriazole carboxylate are added into a terpineol / butyl carbitol mixed solvent, the temperature is raised to 50-70° C., and stirred for 20-40 minutes to obtain the organic carrier.

5. The TOPCon battery back paste based on copper and copper alloy according to claim 4, characterized in that: The weight ratio of the ethyl cellulose, benzotriazole carboxylate and terpineol / butyl carbitol mixed solvent is 3-5:0.1-1:80-120.

6. The TOPCon battery back paste based on copper and copper alloy according to claim 4, characterized in that: The volume ratio of the terpineol / butyl carbitol mixed solvent is 6:

4.

7. A method for preparing a TOPCon battery backside slurry based on copper and copper alloy according to any one of claims 1 to 6, characterized in that: The following steps are involved: Cu-Sn alloy powder, electrolytic copper powder and vanadium-containing glass powder are added to an organic carrier, premixed at a rotation speed of 150-250 rpm for 20-30 minutes, and then transferred to a ball mill and ball milled for 3-5 hours to obtain a TOPCon battery back slurry based on copper and copper alloys.

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