Graphene-copper composite conductive paste and application thereof in efficient photovoltaic cell

Abstract

The invention discloses graphene-copper composite conductive paste and a preparation method and application thereof. The paste comprises graphene coated copper composite powder, a low-melting-point alloy bonding agent, functional glass powder and an organic carrier. Wherein the graphene coated copper composite powder is prepared by growing few layers of graphene in situ on the surface of copper powder through a chemical vapor deposition method, and a core-shell enhanced conductive unit is formed. According to the invention, the complete replacement of copper to silver (the silver content is 1t, 1%) in a photovoltaic electrode material is realized for the first time, meanwhile, the performance loss of a pure copper system is made up through the enhancement effect of graphene, and the photoelectric conversion efficiency reaches 97% or more of that of commercial silver paste on the basis that the material cost is reduced to 1 / 60 of that of the silver paste. The slurry is suitable for electrode preparation of various efficient photovoltaic cells such as HJT, TOPCon and perovskite, and has remarkable economic benefits and strategic significance.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic materials technology, specifically to a graphene-copper composite conductive paste for photovoltaic cell electrodes, its preparation method, and its application. Background Technology

[0002] Silver paste is currently the most critical non-silicon material in the production of crystalline silicon photovoltaic cells, undertaking the core functions of forming electrodes and collecting current. At present, photovoltaic silver paste accounts for 27% of the non-silicon cost of cells, making it one of the most expensive materials in photovoltaic modules. The continuous rise in silver prices and the increased silver paste consumption per unit of N-type cell technology have made cost reduction a particularly urgent need. The photovoltaic industry consumes a massive amount of silver; in 2024, solar photovoltaic manufacturing accounted for 32% of global industrial silver consumption. With the continued growth of global photovoltaic installed capacity, the scarcity and price volatility of silver resources have become bottlenecks restricting the sustainable development of the photovoltaic industry. The industry has been exploring alternatives to silver paste, and copper, with its conductivity second only to silver and costing only 1% of silver, has become the most promising alternative material. However, simply replacing silver with copper faces numerous technical challenges: copper is easily oxidized in air, diffuses rapidly in silicon leading to junction contamination, has inferior ohmic contact performance with silicon substrates compared to silver, and has a narrow sintering process window. While silver-plated copper technology is currently in use, it still contains approximately 30% silver; electroplating copper technology is complex and has a low yield rate in mass production. Therefore, developing an electrode paste that can completely eliminate dependence on silver, maintain high photoelectric conversion performance, and is suitable for large-scale production has become an urgent technical challenge for the photovoltaic industry. Summary of the Invention

[0003] The purpose of this invention is to provide a graphene-copper composite conductive paste and its preparation method, aiming to achieve a fundamental breakthrough in both cost reduction and performance enhancement of photovoltaic cell electrode materials. Technical solution: A graphene-copper composite conductive paste, comprising the following components by mass percentage: Graphene-coated copper composite powder: 80-90% The composite powder consists of a core of copper and a coating of 1-5 layers of graphene, with the graphene accounting for 0.5-5% of the total mass. Low melting point alloy bonding agent: 2-6% Selected from indium-based, bismuth-based, or tin-based alloy powders, these powders are used to bridge the composite powder and silicon matrix during sintering, forming excellent ohmic contacts. Functional glass powder: 1-4% The softening temperature is between 400-550℃, which helps the graphene-copper composite powder to make etch contact with the silicon wafer. Organic carrier: 7-12% It consists of organic solvents, thixotropic agents, and dispersants. Key preparation process: Preparation of composite powder: Graphene is directly grown on the surface of copper powder using chemical vapor deposition to form a dense and uniform coating layer. Slurry mixing and dispersion: The composite powder is mixed with alloy powder, glass powder and organic carrier under a protective atmosphere, ground to a fineness of ≤5μm, and then degassed under vacuum to obtain the final product. The most critical technical feature of this invention lies in the fact that graphene precisely adheres to the surface of copper powder to form a coating structure, achieving a revolutionary complementary advantage: Copper forms a low-cost, high-conductivity macroscopic three-dimensional network, which is the cornerstone for achieving "cheap substitution"; Graphene leverages its inherently high mobility to create an "electron highway" between copper particles, significantly improving overall conductivity; at the same time, its perfect barrier properties completely solve the technical problems of copper's easy oxidation and easy diffusion of pollution. The combination of the two allows the high performance of graphene to be realized through the practical application of copper as a carrier, while the stability and cost advantages of copper are maximized by the enhancement of graphene. Detailed Implementation

[0004] Example 1: Low-temperature composite slurry for HJT batteries This embodiment provides a graphene-copper composite conductive paste, which, by mass percentage, comprises: 85% graphene-coated copper composite powder, 5% indium bismuth alloy powder (In70Bi30), 2% functional glass powder (softening point 420℃), and 8% organic carrier. The preparation steps of the graphene-coated copper composite powder are as follows: Copper powder pretreatment: Spherical copper powder with an average particle size of 5μm was placed in a tube furnace and reduced at 500℃ for 30 minutes under a hydrogen-argon mixed atmosphere (H2:Ar volume ratio 1:10) to remove oxides from the surface of the copper powder. CVD Growth: The treated copper powder was evenly spread in a quartz boat and pushed into the central temperature zone of the CVD reaction chamber. The vacuum was evacuated to below 5 × 10⁻³ Pa, and argon gas (flow rate 200 sccm) was introduced to restore the furnace pressure to atmospheric pressure. The temperature was then increased to 950℃ at a rate of 10℃ / min. After the temperature stabilized, methane (flow rate 20 sccm) and hydrogen gas (flow rate 10 sccm) were introduced, and the reaction was maintained for 30 minutes to grow few-layer graphene in situ on the surface of the copper powder. Cooling and passivation: The methane flow was stopped, and the mixture was cooled to room temperature at a rate of 5℃ / min under argon protection to obtain copper composite powder uniformly coated with graphene. Raman spectroscopy characterization showed that the obtained graphene consisted of 2-5 layers, with continuous and uniform coating and no obvious defects. Then, the above-mentioned graphene-coated copper composite powder is mixed with indium bismuth alloy powder, functional glass powder and organic carrier under argon protection, and ground to a fineness of ≤5μm by a three-roll mill, and vacuum degassing is performed to obtain the slurry. The paste was applied to the surface of the HJT battery silicon substrate by screen printing, dried at 180°C, and then sintered by light pulse at a temperature below 200°C to form an electrode. Test results: On HJT cells, the conversion efficiency reached 25.2%, which is comparable to commercial silver paste (25.4%), with a cost reduction of 85%. Moreover, the efficiency degradation rate after damp heat aging test (85℃ / 85%RH, 1000h) was less than 2%, which is better than silver paste. Example 2: Composite slurry for TOPCon batteries The mixture consists of 88% graphene-coated copper composite powder, 3% tin-bismuth alloy powder (Sn42Bi58), 3% functional glass powder (softening point 580℃), and 6% organic carrier. The preparation method is the same as in Example 1, and the sintering temperature is 780℃. Test results: On TOPCon batteries, the conversion efficiency reached 24.8%, the electrode adhesion was improved by 15%, and the potential risk of induced degradation was significantly reduced. Beneficial effects

[0005] Compared with the prior art, the present invention has the following beneficial effects: Completely eliminate dependence on silver: Using copper as the main conductive material, the silver content is reduced to less than 1%, thus solving the problem of the photovoltaic industry's resource dependence on the precious metal silver from the source. This leads to a dramatic drop in costs: the material cost is only about 1 / 60 of that of traditional silver paste, clearing away the biggest material cost obstacle to grid parity for photovoltaics. Performance rivals that of silver paste: Through the enhancement effect of graphene, the photoelectric conversion efficiency reaches more than 97% of that of commercial silver paste, and the HJT cell efficiency reaches 25.2%, which is comparable to that of silver paste. High reliability: The graphene coating perfectly solves the problems of copper oxidation and diffusion contamination, significantly improving the long-term stability of the battery. Good process compatibility: Existing screen printing equipment can be used without large-scale equipment modification. Strategic contribution to the new energy industry: The dual breakthroughs of this invention—cost reduction and efficiency improvement—have jointly accelerated the competitiveness of photovoltaics as a major new energy source, and have positive strategic significance for promoting the transformation of the global energy structure towards a cleaner and more sustainable direction.

Claims

1. A graphene-copper composite conductive paste, characterized in that, By mass percentage, it includes the following components: 80-90% graphene-coated copper composite powder, 2-6% low-melting-point alloy bonding agent, 1-4% functional glass powder, and 7-12% organic carrier.

2. The graphene-copper composite conductive paste according to claim 1, characterized in that, In the graphene-coated copper composite powder, the surface of the copper powder particles is coated with 1-5 layers of few-layer graphene, and the graphene accounts for 0.5-5% of the composite powder by mass.

3. The graphene-copper composite conductive paste according to claim 1, characterized in that, The low-melting-point alloy bonding agent is selected from one or more of indium-based alloys, bismuth-based alloys, or tin-based alloys.

4. The graphene-copper composite conductive paste according to claim 1, characterized in that, The functional glass powder is bismuth-based lead-free glass powder or tellurate glass powder, and its softening temperature is between 400-550℃.

5. The graphene-copper composite conductive paste according to claim 1, characterized in that, The organic carrier is composed of an organic solvent, a thixotropic agent, and a dispersant; the organic solvent is selected from terpineol, butylcarbitol, or mixtures thereof; the thixotropic agent is selected from one or two of ethyl cellulose and hydrogenated castor oil; and the dispersant is selected from one or more of polyvinylpyrrolidone and phosphate esters.

6. A method for preparing the graphene-copper composite conductive paste according to any one of claims 1-5, characterized in that, Includes the following steps: Preparation of graphene-coated copper composite powder; The graphene-coated copper composite powder was mixed with a low-melting-point alloy bonding agent, functional glass powder and organic carrier under a protective atmosphere and ground to a fineness of ≤5μm to obtain a mixed slurry. The mixed slurry was placed in a vacuum degassing machine to remove air bubbles at a vacuum level below -0.08 MPa, resulting in the final slurry.

7. The preparation method according to claim 6, characterized in that, The graphene-coated copper composite powder was prepared by chemical vapor deposition, including the following steps: Copper powder is pretreated at 300-500℃ for 30-60 minutes in a reducing atmosphere; Place it in the CVD reaction chamber, evacuate it, introduce protective gas, and heat it to 800-1050℃. Carbon source gas and hydrogen are introduced, and the reaction is carried out for 10-60 minutes to grow graphene in situ on the surface of copper powder. Cool down to room temperature under a protective atmosphere.

8. The application of the graphene-copper composite conductive paste according to any one of claims 1-5 in the preparation of photovoltaic cell electrodes.

9. The application according to claim 8, characterized in that, Includes the following steps: The paste is applied to the surface of a silicon substrate by screen printing, dried at 150-200°C, and then sintered at 600-850°C under inert gas protection, or sintered by light pulse at a temperature below 200°C in a low-temperature battery.