Lead-free glass-coated copper powder and conductive copper paste for HJT photovoltaic cell and preparation method of lead-free glass-coated copper powder and conductive copper paste

Abstract

The invention relates to lead-free glass-coated copper powder for an HJT photovoltaic cell, conductive copper paste and a preparation method of the lead-free glass-coated copper powder and the conductive copper paste, the glass-coated copper powder comprises nano-copper powder and a coating layer on the surface of the nano-copper powder, and the coating layer is composed of bismuthate glass. According to the preparation method, a sol-gel method is adopted, the bismuthate glass is coated on the nano copper powder, the glass and the copper powder form a core-shell structure, the glass can be molten into a liquid phase during sintering, the contact between the glass and the copper powder is more uniform, and the oxidation resistance of the copper powder is enhanced. The prepared glass-coated copper powder can effectively isolate the copper powder from being in contact with an external oxidizing agent, excellent anti-oxidation protection is provided, the rapid oxidation point of the copper powder is increased by 100-150 DEG C compared with the rapid oxidation point of the copper powder before coating, and the service life of the copper powder is prolonged; meanwhile, the conductive copper paste has high stability, high reliability, low cost and high conductivity, and meets the environmental protection requirement.

Description

Technical Field

[0001] This invention belongs to the field of electronic materials technology, and specifically relates to a lead-free glass-coated copper powder, conductive copper paste and its preparation method for HJT photovoltaic cells. Background Technology

[0002] Currently, the photovoltaic industry is accelerating its upgrade towards high-efficiency N-type cell technology. Heterojunction (HJT) photovoltaic cells, with their significant advantages such as high conversion efficiency, low temperature coefficient, and high bifaciality, have become a highly promising development direction. However, because HJTs employ a bifacial power generation structure, low-temperature silver paste needs to be coated on both sides of the cell, resulting in a much higher silver powder consumption than single-sided PERC photovoltaic cells. The high cost of silver powder has become a key bottleneck restricting its large-scale commercialization and further cost reduction. Driven by the photovoltaic industry's continuous pursuit of the core goal of "cost reduction and efficiency improvement," finding a "cost-effective alternative" to silver powder is urgently needed.

[0003] Copper is considered a promising alternative material due to its similar conductivity to silver (its volume conductivity is about 97% of silver's), abundant reserves, and significant cost advantages. However, the biggest inherent disadvantage of copper powder is its susceptibility to oxidation. In electrode preparation and usage environments, its conductivity drops sharply due to oxidation, making it difficult to meet the requirements for long-term reliable operation of photovoltaic cells. Therefore, copper powder surface modification technology, which combines cost advantages with potential performance guarantees, has emerged as an important research direction for reducing the cost of bifacial solar cells such as HJT.

[0004] Traditional conductive pastes for solar cells mostly still use lead-containing low-melting-point glass. Due to the toxicity of lead, a key development direction for solar cells is environmental friendliness, primarily manifested in lead-free technology. The key to lead-free technology lies in developing lead-free low-melting-point glass. Currently, bismuthate systems are an important research direction for lead-free glass in solar cell conductive pastes. At present, there is a lack of relevant products on the market for lead-free glass used in conductive copper paste for HJT solar cells. Using traditional conductive silver paste glass powder presents problems such as excessively high melting point of the glass powder, easy oxidation of copper, and poor adhesion between the paste and the silicon wafer, thus affecting the photoelectric conversion efficiency of the solar cell. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method for preparing lead-free glass-coated copper powder, conductive copper paste, and their preparation for HJT photovoltaic cells. The specific technical solution is as follows: This invention provides a lead-free glass-coated copper powder for HJT photovoltaic cells. The lead-free glass-coated copper powder is a bismuthate glass-coated copper powder, which includes nano-copper powder and a bismuthate glass coating layer densely wrapped around the surface of the nano-copper powder.

[0006] As a preferred embodiment of the present invention, the bismuthate glass is prepared by the sol-gel method, and its molar percentage composition is: 30-60% bismuth precursor, 15-30% boron precursor, 15-30% inorganic zinc salt, and 10-20% inorganic barium salt.

[0007] As a preferred embodiment of the present invention, the solvent of the glass sol in the sol-gel method is one or more of ethanol, ethylene glycol, glacial acetic acid, and acetylacetone; the bismuth-containing precursor is any one of bismuth nitrate, bismuth acetate, and bismuth alkoxide; the boron-containing precursor is any one of tributyl borate, boron trioxide, and boric acid; the inorganic zinc salt is any one of zinc nitrate or zinc acetate; and the inorganic barium salt is any one of barium nitrate or barium acetate.

[0008] The present invention also provides a conductive copper paste prepared by coating copper powder with lead-free glass for HJT photovoltaic cells as described above, wherein the mass percentages of each component of the conductive copper paste are as follows: 75-90% copper powder coated with bismuthate glass and 10-25% organic carrier.

[0009] As a preferred embodiment of the present invention, the organic carrier includes a mixed solvent, a thickener, a reducing agent, a thixotropic agent, a coupling agent, and an antifoaming agent.

[0010] As a preferred embodiment of the present invention, the mixed solvent is two or more of terpineol, diethylene glycol butyl ether, butyl carbitol acetate, and dibutyl phthalate; the thickener is one or more of ethyl cellulose, hydroxypropyl methyl cellulose, epoxy resin, and polyester resin; the reducing agent is one or more of C6-C22 aliphatic compounds containing reducing groups such as thiol and amine, citric acid, glycerol, and ascorbic acid; the thixotropic agent is one or more of hydrogenated castor oil, polyamide wax, and fumed silica; the coupling agent is one or more of silane coupling agents, fluorosiloxanes, and titanate coupling agents; and the defoamer is one or more of n-butanol, sodium dodecyl sulfonate 1,4-dihydroxysulfonate amine, and modified siloxanes.

[0011] The present invention also provides a method for preparing lead-free glass-coated copper powder for HJT photovoltaic cells as described above, the method comprising the following steps: Step S1: Using the sol-gel method, the bismuth-containing precursor is added to a solvent of ethanol and glacial acetic acid and dissolved, with the pH controlled in the range of 1.5 to 2.5. The mixture is stirred at 60 to 70 °C until completely dissolved to obtain a bismuth solution. In another container, the boron-containing precursor is dissolved in ethylene glycol, heated and stirred until completely dissolved. After complete dissolution, inorganic zinc salt and inorganic barium salt are added to obtain a boron / zinc / barium solution. Step S2: Under vigorous stirring, the boron / zinc / barium solution is slowly added dropwise to the bismuth solution. After mixing, the reaction vessel is placed in a water bath at 70~80 ℃ and stirred continuously for 2~4 hours to obtain a bismuth boron zinc barium glass sol solution. Step S3: Disperse the nano copper powder in ethanol by ultrasonication, then add bismuth boron zinc barium glass sol solution, and add a composite coupling system of silane coupling agent and titanate coupling agent. Stir and heat continuously to remove the solvent to obtain bismuth boron zinc barium glass sol coated copper powder. Step S4: Under an inert gas atmosphere, the temperature is increased to 350-450 ℃ at a rate of 1-2 ℃ / min, and calcined at this temperature for 1-2 hours. After cooling, bismuth boron zinc barium glass-coated copper powder is obtained.

[0012] As a preferred embodiment of the present invention, the nano-copper powder includes flakes and spheres, with a weight ratio of flakes to spheres of 7:3 to 3:7.

[0013] As a preferred embodiment of the present invention, the flaky copper powder D50 has a particle size of 1~10 μm and a median thickness of 100~500 nm; the spherical copper powder D50 has a particle size of 100~800 nm.

[0014] As a preferred embodiment of the present invention, the mass of the bismuth boron zinc barium glass accounts for 0.5 to 10 wt% of the copper powder coated with the calcined bismuth boron zinc barium glass.

[0015] The beneficial effects of this invention are: 1. The copper powder coating preparation method of the present invention adopts the sol-gel method to obtain a core-shell structure powder, which makes the contact between the glass melted into liquid phase and the copper powder more uniform during the sintering process. At the same time, the glass coating layer acts as a protective layer to enhance the oxidation resistance of the copper powder. The copper slurry prepared further has a lower sintering temperature and better oxidation resistance. 2. The glass system of this invention adopts a bismuthate system, which reduces the sintering temperature, lowers the preparation cost, simplifies the process, and is non-toxic and environmentally friendly; 3. The bismuthate glass-coated copper powder for HJT photovoltaic cells prepared by this invention has a dense coating layer that can isolate the copper powder from external oxidants, providing good oxidation resistance to the copper powder and effectively preventing the oxidation of copper paste to form copper oxides that are difficult to conduct electricity, thus affecting the performance of photovoltaic devices. In addition, during the sintering process with the HJT photovoltaic substrate, the glass melts into a liquid phase and has more uniform contact with the copper powder, promoting the sintering of the copper powder. 4. The raw materials of this invention contain different proportions of flake and spherical nano-copper powder. The flake copper powder can overlap with each other to form a two-dimensional conductive main network, ensuring basic conductivity. The spherical copper powder can effectively fill the gaps between the flake powders, constructing a denser three-dimensional conductive structure, thereby significantly reducing resistance. The two work together to optimize the conductive path, while also improving the printing rheology of the paste and the density of the sintered film, achieving a "1+1>2" effect. 5. In this invention, the reducing agent in the organic carrier used for the conductive copper paste is a C6~C group containing reducing groups such as thiol and amine groups. 22 One or more of aliphatic compounds, citric acid, glycerol, and ascorbic acid can not only isolate oxygen and resist oxidation, but also allow copper powder to react preferentially with oxygen during sintering, thus avoiding oxidation and providing extra protection for the pre-sintering stage. This can ensure the conductivity of conductive copper paste, reduce resistivity changes, and extend its service life. 6. The lead-free glass-coated copper powder prepared by this invention can effectively isolate the copper powder from external oxidants, providing excellent antioxidant protection. Compared with copper powder without glass coating, the temperature at which oxidation begins is increased by 100-150 ℃, and the temperature at which oxidation is complete is increased by 150-200 ℃, thus extending its service life. At the same time, the conductive copper paste has high stability, high reliability, low cost, and high conductivity, meeting environmental protection requirements. 7. This invention uses a mixed solvent system of ethanol and glacial acetic acid and strictly controls the pH value within the range of 1.5 to 2.5, which solves the problem of easy hydrolysis and precipitation of bismuth precursor; 8. The present invention employs a coupling system in which a composite of silane coupling agent and titanate coupling agent is added to the sol, which can achieve effective wetting and coating of copper powder while obtaining a stable sol. 9. The present invention establishes a heat treatment mechanism for raising the temperature to 350-450°C at a specific heating rate of 1-2°C / min under an inert atmosphere. This heat treatment mechanism can ensure the complete decomposition of organic matter and densification of the glass layer, while also effectively suppressing the oxidation of copper and the reduction of bismuth. Attached Figure Description

[0016] Figure 1 The image shown is a scanning electron microscope image of the bismuthate glass-coated copper nanoparticles prepared in Example 1 of the present invention; Figure 2 A scanning electron microscope image of the bismuthate glass-coated copper nanoparticles prepared in Example 2 of the present invention is shown. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] The technical solution in this invention embodiment is to solve the technical problems in the background art, and provides the following: a lead-free glass-coated copper powder, conductive copper paste for HJT photovoltaic cells, and their preparation method, the main working principle of which is as follows: The lead-free glass-coated copper powder prepared in this invention is a core-shell structured powder, and its coating layer is composed of bismuthate glass. A dense coating layer is formed through a sol-gel method and heat treatment. During sintering, the glass coating layer softens to form a liquid phase, wetting the copper powder and the substrate, resulting in good adhesion between the sintered copper film and the HJT photovoltaic substrate.

[0019] Furthermore, the glass layer acts as an insulator to prevent copper powder from contacting the oxidant, thus enhancing the oxidation resistance of the copper powder. The low-temperature sintering antioxidant copper powder of this invention uses lead-free, low-melting-point bismuthate glass, which lowers the sintering temperature of the conductive copper paste. The copper paste prepared in this invention can be co-fired with the HJT photovoltaic substrate to form a dense conductive pattern, resulting in strong adhesion to the substrate.

[0020] To better understand the above technical solutions, the following will provide a detailed description of the technical solutions in conjunction with the accompanying drawings, specific embodiments, and comparative examples.

[0021] Example 1 As a preferred technical solution, a method for preparing lead-free glass-coated copper powder and conductive copper paste for HJT photovoltaic cells includes the following specific steps: Step S1: Dissolve 60 g of bismuth nitrate in a mixture of ethanol and glacial acetic acid, keeping the pH between 1.5 and 2.5, and stir at 65 °C until completely dissolved to obtain a bismuth solution. In another container, dissolve 18 g of tri-n-butyl borate in an appropriate amount of ethylene glycol, heat gently and stir until completely dissolved. After complete dissolution, add 15 g of zinc nitrate and 7 g of barium acetate to obtain a boron / zinc / barium solution.

[0022] Step S2: Under vigorous stirring, the boron / zinc / barium solution is slowly added dropwise to the bismuth solution. After mixing, the reaction vessel is placed in a water bath at 70 °C and stirred continuously for 3 hours to obtain a bismuth-boron-zinc-barium glass sol solution.

[0023] Step S3: Disperse 500 g of nano copper powder in ethanol by ultrasonication, then add dropwise a glass sol containing 35 g of bismuth boron zinc barium glass after calcination, and add a composite coupling system of 5 g of silane coupling agent and titanate coupling agent. Stir and heat continuously to remove the solvent to obtain copper powder coated with bismuth boron zinc barium glass sol.

[0024] Step S4: Under a nitrogen atmosphere, the temperature is increased to 410 ℃ at a rate of 2 ℃ / min and held at this temperature for 2 hours to remove residual solvent and precursor decomposition products from the gel, and to completely densify the bismuth boron zinc barium glass gel to form a glassy substance. After cooling, bismuth boron zinc barium glass coated copper powder is obtained.

[0025] Step S5: Weigh 85 g of bismuthate glass-coated copper powder and 15 g of organic carrier. The organic carrier comprises 11 g of a mixed solvent of terpineol and diethylene glycol butyl ether, 0.5 g of 1-dodecyl mercaptan, 1.5 g of ethyl cellulose, 1 g of hydrogenated castor oil, 0.6 g of KH570, and 0.4 g of n-butanol. Mix the bismuthate glass-coated copper powder and organic carrier evenly to obtain the lead-free glass-coated conductive copper paste for HJT photovoltaic cells.

[0026] Example 2 This embodiment provides a lead-free glass-coated copper powder and conductive copper paste for HJT photovoltaic cells, and their preparation method. The specific preparation method is the same as in Example 1, except that the content of the organic carrier in step S5 of Example 1 is changed to include 11.3 g of a mixed solvent of terpineol and diethylene glycol butyl ether, 0.5 g of 1-dodecyl mercaptan, 1.2 g of ethyl cellulose, 1 g of hydrogenated castor oil, 0.6 g of KH570, and 0.4 g of n-butanol.

[0027] Example 3 This embodiment provides a lead-free glass-coated copper powder and conductive copper paste for HJT photovoltaic cells, and their preparation method. The specific preparation method is the same as in Example 1, except that the content of the organic carrier in step S5 of Example 1 is changed to include 11.6 g of a mixed solvent of terpineol and diethylene glycol butyl ether, 0.5 g of 1-dodecyl mercaptan, 1 g of ethyl cellulose, 1 g of hydrogenated castor oil, 0.5 g of KH570, and 0.4 g of n-butanol.

[0028] Example 4 This embodiment provides a lead-free glass-coated copper powder and conductive copper paste for HJT photovoltaic cells, and their preparation method. The specific preparation method is the same as in Example 1, except that the content of the organic carrier in step S5 of Example 1 is changed to include 10.5 g of a mixed solvent of terpineol and diethylene glycol butyl ether, 0.5 g of 1-dodecyl mercaptan, 1.3 g of ethyl cellulose, 1.2 g of hydrogenated castor oil, 0.6 g of KH570, and 0.4 g of n-butanol.

[0029] Comparative Example 1 Weigh 79.4 g of nano copper powder, then weigh 5.6 g of bismuth boron zinc barium glass powder, and mix them with 11 g of terpineol and diethylene glycol butyl ether mixed solvent, 0.5 g of 1-dodecyl mercaptan, 1.5 g of ethyl cellulose, 1 g of hydrogenated castor oil, 0.6 g of KH570 and 0.4 g of n-butanol to prepare conductive copper paste.

[0030] Comparative Example 2 Weigh 79.4 g of nano copper powder, then weigh 5.6 g of borosilicate glass powder, and mix them with 11 g of a mixed solvent of terpineol and diethylene glycol butyl ether, 0.5 g of 1-dodecyl mercaptan, 1.5 g of ethyl cellulose, 1 g of hydrogenated castor oil, 0.6 g of KH570, and 0.4 g of n-butanol to prepare a conductive copper paste.

[0031] Based on the above experimental steps and by controlling the amount of raw materials, Examples 1-4 and Comparative Example 1 were obtained, and their formulations and properties are shown in Table 1: Table 1. Components and properties of Examples 1-4 and Comparative Example 1 As can be seen from Table 1, the overall performance of the conductive copper paste prepared by this invention is significantly better than that of conductive copper paste prepared by borosilicate glass powder or by the traditional method of adding copper powder to low-melting-point glass powder. In particular, the sintering temperature is much lower than that of the conductive copper paste prepared by borosilicate glass powder in Comparative Example 2; the rapid oxidation temperature is much higher than that of the conductive copper paste prepared by the traditional method of adding copper powder to low-melting-point glass powder in Comparative Example 1; and the electrode sheet resistance is also significantly better than that of the conductive copper paste prepared by the traditional method of adding copper powder to low-melting-point glass powder in Comparative Example 1.

[0032] from Figure 1 and Figure 2 It can be seen that the bismuthate glass prepared by the method of the present invention can coat the nano copper powder to form a core-shell structure, thereby preventing the oxidation of the copper powder.

[0033] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A copper powder coated with lead-free glass for HJT photovoltaic cells, characterized in that: The lead-free glass-coated copper powder is bismuthate glass-coated copper powder, which includes nano-copper powder and a bismuthate glass coating layer densely wrapped around the surface of the nano-copper powder.

2. The copper powder coated with lead-free glass for HJT photovoltaic cells according to claim 1, characterized in that: The bismuthate glass is prepared by the sol-gel method, and its molar percentage composition is as follows: 30-60% bismuth precursor, 15-30% boron precursor, 15-30% inorganic zinc salt, and 10-20% inorganic barium salt.

3. The copper powder coated with lead-free glass for HJT photovoltaic cells according to claim 2, characterized in that: In this sol-gel method, the solvent for the glass sol is one or more of ethanol, ethylene glycol, glacial acetic acid, and acetylacetone; the bismuth-containing precursor is any one of bismuth nitrate, bismuth acetate, and bismuth alkoxide; the boron-containing precursor is any one of tributyl borate, boron trioxide, and boric acid; the inorganic zinc salt is any one of zinc nitrate or zinc acetate; and the inorganic barium salt is any one of barium nitrate or barium acetate.

4. A conductive copper paste prepared by coating copper powder with lead-free glass for HJT photovoltaic cells as described in claim 1, characterized in that, The mass percentages of the components in the conductive copper paste are as follows: 75-90% bismuthate glass-coated copper powder and 10-25% organic carrier.

5. The conductive copper paste according to claim 4, characterized in that: The organic carrier includes a mixed solvent, thickener, reducing agent, thixotropic agent, coupling agent, and defoamer.

6. The conductive copper paste according to claim 5, characterized in that: The mixed solvent is two or more of terpineol, diethylene glycol butyl ether, butyl carbitol acetate, and dibutyl phthalate; the thickener is one or more of ethyl cellulose, hydroxypropyl methyl cellulose, epoxy resin, and polyester resin; the reducing agent is one or more of C6-C22 aliphatic compounds containing reducing groups such as thiol and amine, citric acid, glycerol, and ascorbic acid; the thixotropic agent is one or more of hydrogenated castor oil, polyamide wax, and fumed silica; the coupling agent is one or more of silane coupling agents, fluorosiloxanes, and titanate coupling agents; and the defoamer is one or more of n-butanol, sodium dodecyl sulfonate 1,4-dihydroxysulfonate amine, and modified siloxanes.

7. A method for preparing lead-free glass-coated copper powder for HJT photovoltaic cells as described in claim 2, characterized in that, The method includes the following steps: Step S1: Using the sol-gel method, the bismuth-containing precursor is added to a solvent of ethanol and glacial acetic acid and dissolved, with the pH controlled in the range of 1.5 to 2.

5. The mixture is stirred at 60 to 70 °C until completely dissolved to obtain a bismuth solution. In another container, the boron-containing precursor is dissolved in ethylene glycol, heated and stirred until completely dissolved. After complete dissolution, inorganic zinc salt and inorganic barium salt are added to obtain a boron / zinc / barium solution. Step S2: Under vigorous stirring, the boron / zinc / barium solution is slowly added dropwise to the bismuth solution. After mixing, the reaction vessel is placed in a water bath at 70-80 ℃ and stirred continuously for 2-4 hours to obtain a bismuth boron zinc barium glass sol solution. Step S3: Disperse the nano copper powder in ethanol by ultrasonication, then add bismuth boron zinc barium glass sol solution, and add a composite coupling system of silane coupling agent and titanate coupling agent. Stir and heat continuously to remove the solvent to obtain bismuth boron zinc barium glass sol coated copper powder. Step S4: Under an inert gas atmosphere, the temperature is increased to 350-450 ℃ at a rate of 1-2 ℃ / min, and calcined at this temperature for 1-2 hours. After cooling, bismuth boron zinc barium glass-coated copper powder is obtained.

8. The preparation method according to claim 7, characterized in that: The nano-copper powder includes flakes and spheres, with a weight ratio of flakes to spheres of 7:3 to 3:

7.

9. The preparation method according to claim 8, characterized in that: The flake-shaped copper powder has a D50 particle size of 1~10 μm and a median thickness of 100~500 nm; the spherical copper powder has a D50 particle size of 100~800 nm.

10. The preparation method according to claim 7, characterized in that: The mass of the bismuth boron zinc barium glass accounts for 0.5 to 10 wt% of the copper powder coated with bismuth boron zinc barium glass after calcination.

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