Solar cell and preparation process thereof, laminated cell, photovoltaic module

Abstract

This invention provides a solar cell, its fabrication process, a tandem solar cell, and a photovoltaic module. The fabrication process of the solar cell includes: providing a cell substrate; printing a conductive material onto the cell substrate; and curing the conductive material to form initial grid lines. The conductive material includes bismuth-based lead-free glass; the conductive material also includes copper powder and nickel powder; the mass ratio of copper powder to nickel powder is 80~99.5:0.5~20, and the copper powder includes flake-shaped copper powder and spherical copper powder. In the fabrication process of this invention, the conductive material, through a ternary synergistic system of "copper-nickel-glass" and a dual-morphology copper powder composite design, achieves multiple effects such as suppressing copper diffusion and oxidation and improving adhesion under an air-sintering atmosphere, thereby improving the fill factor and photoelectric conversion efficiency of the solar cell.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, and more specifically, to a solar cell and its manufacturing process, a tandem cell, and a photovoltaic module. Background Technology

[0002] Currently, the formation of electrodes in solar cells relies on a standardized process of screen printing combined with high-temperature sintering. This process is mature, highly compatible, and applicable to various cell structures. Its core steps include: printing a conductive paste onto the silicon wafer surface, drying to remove organic components, and then performing high-temperature sintering. This allows the metal particles in the paste to melt and rearrange, forming ohmic contacts with the silicon substrate, and achieving a strong bond between the electrode and the silicon surface through a glass phase. This fabrication process requires low equipment investment, has a high production line reuse rate, and offers stable yields; therefore, it has been widely adopted.

[0003] However, in the fabrication process of solar cells, the screen printing-sintering process is extremely dependent on the performance of the conductive paste. To achieve a high-precision, fine grid (≤50μm), high aspect ratio, high adhesion, and low contact resistance electrode structure, the paste must possess excellent rheological stability, good screen passability, and morphology retention after drying during the printing process. During the sintering stage, at a high temperature of 750~800℃ in air, it must rapidly complete the volatilization of organic components, densification of metal particles, and the formation of stable ohmic contacts with the silicon substrate. This process window is extremely narrow: any slight deviation in paste composition or sintering behavior can easily lead to grid breakage, linewidth loss, oxidation and blackening, a surge in contact resistance, or a decrease in adhesion, directly causing cell efficiency degradation or module reliability failure. Summary of the Invention

[0004] The main objective of this invention is to provide a solar cell and its manufacturing process, a tandem cell, and a photovoltaic module, in order to solve the problems of atomic diffusion and oxidation, as well as high contact resistance, in base metal conductive materials in solar cells during high-temperature sintering in the prior art.

[0005] According to some embodiments of this application, one aspect of this application provides a process for fabricating a solar cell, which includes providing a cell substrate, printing conductive material on the cell substrate, and curing the conductive material to form initial grid lines; wherein the conductive material includes bismuth-based lead-free glass; the conductive material also includes copper powder and nickel powder; the mass ratio of copper powder to nickel powder is 80~99.5:0.5~20, and the copper powder includes flake copper powder and spherical copper powder.

[0006] In some embodiments, the diameter of the flake copper powder is 1~5 μm, the thickness of the flake copper powder is 0.1~0.5 μm, and the specific surface area of ​​the flake copper powder is 1.5~6 m². 2 / kg; the D50 particle size of spherical copper powder is 0.5~2μm; the D50 particle size of nickel powder is 0.1~1μm.

[0007] In some embodiments, the mass ratio of flake copper powder to spherical copper powder is 1~4:1~4.

[0008] In some embodiments, the copper powder is copper powder that has undergone antioxidant treatment; wherein, the flake copper powder is flake copper powder that has undergone a first antioxidant treatment, the conditions of which include treatment in an oxygen-containing atmosphere at 100~250°C for 30~120 min; the spherical copper powder is spherical copper powder that has undergone a second antioxidant treatment, the conditions of which include treatment in a hydrogen-nitrogen mixed atmosphere at 200~350°C for 60~180 min.

[0009] In some embodiments, the total mass content of copper powder and nickel powder in the conductive material is 40-70% based on the total mass of the conductive material.

[0010] In some embodiments, the mass content of bismuth-based lead-free glass in the conductive material is 1 to 10% based on the total mass of the conductive material.

[0011] In some embodiments, the bismuth-based lead-free glass comprises, by weight, 40-70 parts Bi2O3, 10-25 parts B2O3, 5-15 parts ZnO, 1-10 parts SiO2, and 0.5-10 parts of component A; component A is selected from any one or more of Al2O3, P2O5, and TeO2.

[0012] In some embodiments, the mass ratio of Bi2O3 to B2O3 in the bismuth-based lead-free glass is 2 to 5:1.

[0013] In some embodiments, the softening point of the bismuth-based lead-free glass is 400~550℃, and the D50 particle size of the bismuth-based lead-free glass is 0.5~3μm.

[0014] In some embodiments, conductive materials are printed on the battery substrate and then sintered. The sintering process includes pre-sintering and main sintering, with the pre-sintering temperature being lower than the main sintering temperature.

[0015] In some embodiments, the pre-sintering temperature is 300~450℃, the pre-sintering time is 2~5min, and the pre-sintering atmosphere is air.

[0016] In some embodiments, the main sintering temperature is 700~800℃, the main sintering time is 30~90s, and the main sintering atmosphere is nitrogen or argon.

[0017] According to some embodiments of this application, another aspect of this application provides a photovoltaic module, including a solar cell, which is prepared by the solar cell preparation process described above.

[0018] According to some embodiments of this application, another aspect of this application provides a stacked battery, which includes a top battery and a bottom battery, wherein the bottom battery is the aforementioned solar cell.

[0019] According to some embodiments of this application, another aspect of this application provides a photovoltaic module, including: a battery string, an encapsulating film, and a cover plate. The battery string is formed by connecting multiple solar cells as described above, or stacked cells as described above. The encapsulating film is used to cover the surface of the battery string. The cover plate is used to cover the surface of the encapsulating film facing away from the battery string.

[0020] The technical solution provided in this application has at least the following advantages: The conductive material in the solar cell fabrication process of this application, through a ternary synergistic system of "copper-nickel-glass" and a dual-morphology copper powder composite design, achieves multiple effects such as suppressing copper diffusion and oxidation and improving adhesion under an air sintering atmosphere. Simultaneously, the conductive material does not rely on the precious metal silver, significantly reducing costs. Specifically, 1) This application innovatively introduces a ternary synergistic system of "copper-nickel-glass." During the sintering process, the bismuth-based lead-free glass softens first, thereby wetting the surface of the silicon wafer and the metal particles. The nickel powder preferentially reacts with silicon, forming a thin and continuous nickel-silicon compound (such as NiSi, NiSi2) transition layer at the silicon / electrode interface. By controlling the mass ratio of copper powder to nickel powder within the above range, this transition layer can not only form excellent ohmic contact with silicon, reducing the interface barrier, but also serve as an effective diffusion barrier layer, preventing copper atoms from diffusing into the silicon mass, and as a stress buffer layer, matching the difference in thermal expansion coefficients between silicon and copper. Meanwhile, adding metallic nickel powder can lower the overall sintering temperature, thereby further reducing the oxidation tendency of copper at high temperatures. 2) This application combines flake copper powder with spherical copper powder. The flake copper powder is conducive to forming a densely layered conductive film, thereby providing high in-plane conductivity; the spherical copper powder can fill the gaps between the flake copper powder, constructing a three-dimensional conductive path. The combination of the two can further improve the conductivity of the conductive material at a lower metal content. 3) The conductive material used in this application is bismuth-based lead-free glass, which can achieve good fluidity at a lower temperature (matching the nickel-silicon reaction temperature), thereby effectively encapsulating the copper powder, isolating the copper powder from oxygen, and providing a "liquid protective layer" for the copper powder at the peak sintering temperature, thereby further inhibiting copper oxidation. At the same time, the thermal expansion coefficient of bismuth-based lead-free glass is adjustable, and it has good compatibility with the silicon substrate, thereby further enhancing the adhesion of the conductive material to the silicon surface. Furthermore, the conductive material of this application can be directly applied to existing screen printing equipment and sintered in existing chain sintering furnaces and air atmospheres, eliminating the need for complex protective gas systems and thus significantly reducing process modification and production costs. In summary, the solar cell fabrication process of this application can suppress copper diffusion and oxidation while enabling the conductive material to achieve low contact resistance, high conductivity, and excellent adhesion, thereby improving the fill factor and photoelectric conversion efficiency of the solar cell. Attached Figure Description

[0021] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the drawings in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional art, the drawings used in the embodiments 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.

[0022] Figure 1 A schematic diagram of the structure of the solar cell in Embodiment 1 of this application is shown.

[0023] The above figures include the following reference numerals:

[0024] 1. Silicon substrate; 2. Tunneling oxide layer; 3. Doped polycrystalline silicon layer; 4. Passivation and antireflection layer; 5. First electrode; 6. Second electrode; 7. Nickel-silicon compound transition layer; 8. Copper electrode. Detailed Implementation

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] Based on the background technology analysis, the problems in the fabrication process of solar cells can be optimized by focusing on the conductive paste. Currently, the price of silver in silver paste has severely constrained the manufacturing cost of cells. Therefore, some studies have proposed replacing silver with copper. However, existing copper-based pastes still face the following technical bottlenecks in practical applications: 1) Copper atoms easily diffuse into the silicon lattice during high-temperature sintering, forming deep-level recombination centers, which severely impairs the minority carrier lifetime and photoelectric conversion efficiency of the cell; 2) Copper is easily oxidized during high-temperature sintering in air, generating high-resistivity copper oxide, which leads to a sharp decrease in electrode conductivity; 3) The thermal expansion coefficients of copper and silicon differ significantly, and it is difficult to form a good alloy contact layer, resulting in poor electrode adhesion and easy detachment; 4) Copper is difficult to form low-resistivity ohmic contacts on the silicon surface.

[0027] To address these issues, some studies have proposed using copper-silver mixed slurries. However, the introduction of silver has not fundamentally solved the cost problem, and the risk of silver migration remains. Furthermore, while sintering with pure copper slurry in a formic acid reducing atmosphere or a high-purity nitrogen-hydrogen mixture can suppress copper oxidation and diffusion to some extent, it requires expensive specialized sintering equipment, has a narrow process window, is difficult to adapt to existing large-scale production lines, and increases energy consumption and operating costs.

[0028] As analyzed above in this application, the base metal conductive materials in the prior art solar cells suffer from problems such as atomic diffusion and oxidation, as well as high contact resistance during high-temperature sintering. In order to solve the above problems, this application provides a solar cell and its manufacturing process, a tandem cell, and a photovoltaic module.

[0029] In a typical embodiment of this application, a process for fabricating a solar cell is provided. The process includes: providing a cell substrate; printing a conductive material on the cell substrate; and curing the conductive material to form initial grid lines. The conductive material includes bismuth-based lead-free glass. The conductive material also includes copper powder and nickel powder. The mass ratio of copper powder to nickel powder is 80~99.5:0.5~20. The copper powder includes flake copper powder and spherical copper powder.

[0030] The conductive material in the solar cell fabrication process of this application achieves multiple effects, including suppressing copper diffusion and oxidation and improving adhesion, through a ternary synergistic system of "copper-nickel-glass" and a composite design of dual-morphology copper powder, under an air sintering atmosphere. Simultaneously, the conductive material does not rely on the precious metal silver, significantly reducing costs. Specifically, 1) This application innovatively introduces a "copper-nickel-glass" ternary synergistic system. During sintering, the bismuth-based lead-free glass softens first, thereby wetting the surface of the silicon wafer and metal particles. The nickel powder preferentially reacts with silicon, forming a thin and continuous nickel-silicon compound (such as NiSi, NiSi2) transition layer at the silicon / electrode interface. By controlling the mass ratio of copper powder to nickel powder within the aforementioned range, this transition layer can form excellent ohmic contact with silicon, reducing the interfacial barrier, and also serve as an effective diffusion barrier layer to prevent copper atoms from diffusing into the silicon mass. Furthermore, it can act as a stress buffer layer to match the difference in thermal expansion coefficients between silicon and copper. At the same time, the addition of nickel powder can lower the overall sintering temperature, thereby further reducing the tendency of copper to oxidize at high temperatures. 2) This application combines flake-shaped copper powder with spherical copper powder. The flake-shaped copper powder facilitates the formation of a densely layered conductive film, thereby providing high in-plane conductivity; the spherical copper powder can fill the gaps between the flake-shaped copper powder, constructing a three-dimensional conductive path. The combination of the two can further improve the conductivity of the conductive material with a lower metal content. 3) The conductive material of this application uses bismuth-based lead-free glass, which can achieve good fluidity at a lower temperature (matching the reaction temperature of nickel and silicon), thereby effectively encapsulating the copper powder, isolating the copper powder from oxygen, and providing a "liquid protective layer" for the copper powder at the peak sintering temperature, thereby further inhibiting copper oxidation. At the same time, the thermal expansion coefficient of bismuth-based lead-free glass is adjustable, and it has good compatibility with the silicon substrate, thereby further enhancing the adhesion of the conductive material to the silicon surface. In addition, the conductive material of this application can be directly applied to existing screen printing equipment, and can be sintered in existing chain sintering furnaces and air atmospheres without the need for a complex protective gas system, thereby greatly reducing process modification costs and production costs. In summary, the solar cell fabrication process of this application can suppress copper diffusion and oxidation while enabling conductive materials to achieve low contact resistance, high conductivity, and excellent adhesion, thereby improving the fill factor and photoelectric conversion efficiency of solar cells.

[0031] In one embodiment of this application, the diameter of the flake copper powder is 1~5μm, the thickness of the flake copper powder is 0.1~0.5μm, and the specific surface area of ​​the flake copper powder is 1.5~6m². 2 / kg; the D50 particle size of spherical copper powder is 0.5~2μm; the D50 particle size of nickel powder is 0.1~1μm.

[0032] Controlling the diameter, thickness, and specific surface area of ​​the flake copper powder within the aforementioned ranges is beneficial for improving the density of the conductive film, thereby further enhancing the in-plane conductivity of the electrode. Optionally, the aspect ratio (diameter / thickness) of the flake copper powder is 15:1 to 30:1. A high aspect ratio helps it to orient itself along the printing direction during printing, reducing line resistance. Controlling the D50 particle size of the spherical copper powder within the aforementioned range helps to better fill the voids in the flake copper powder, thereby better constructing a three-dimensional conductive path. Controlling the D50 particle size of the nickel powder within the aforementioned range facilitates better wetting by the softened glass, thereby promoting its reaction with silicon and forming a thin and continuous nickel-silicon compound transition layer at the silicon / electrode interface.

[0033] Flake diameter is the maximum planar diameter of the plate-like particles. D50 particle size is defined as the particle diameter corresponding to the cumulative volume accounting for 50% of the particle size distribution. D50 particle size is determined using a laser diffraction particle size analyzer. Specific surface area is determined using the BET nitrogen adsorption method.

[0034] In one embodiment of this application, the mass ratio of flake copper powder to spherical copper powder is 1~4:1~4.

[0035] Controlling the mass ratio of flake copper powder to spheroidal copper powder within the above range helps to further enhance their synergistic effect. While the flake copper powder forms a conductive framework structure, the spheroidal copper powder can more fully fill the gaps between the framework, constructing a dense and uniform three-dimensional conductive network, thereby further improving the conductivity of the conductive material.

[0036] In one embodiment of this application, the copper powder is copper powder that has undergone antioxidant treatment; wherein, the flake copper powder is flake copper powder that has undergone a first antioxidant treatment, the conditions of which include: treatment in an oxygen-containing atmosphere at 100~250℃ for 30~120min; the spherical copper powder is spherical copper powder that has undergone a second antioxidant treatment, the conditions of which include: treatment in a hydrogen-nitrogen mixed atmosphere at 200~350℃ for 60~180min.

[0037] Flake copper powder has a relatively large specific surface area. After the first antioxidant treatment, the Cu2O layer formed on its surface reacts with the glass during sintering to generate a liquid-phase encapsulation layer, which helps to further inhibit oxidation. Spherical copper powder has a relatively small specific surface area. After the second antioxidant treatment, the natural oxide layer is removed, resulting in a highly active surface. During sintering, it preferentially alloys with nickel powder or is rapidly sintered, thereby better filling the gaps between the flake copper powders and constructing a three-dimensional conductive network. Treating copper powders of different morphologies with the above-mentioned antioxidant treatments under different conditions helps to improve synergy. The oxide layer of the flake copper powder provides protection, while the spherical copper powder provides driving force. The two work synergistically during sintering, with the spherical copper powder initiating sintering first, and then the oxide layer of the flake copper powder controlling the rate of shrinkage, thereby reducing electrode cracking caused by excessive shrinkage. At the same time, the flake copper powder dominates the bulk phase conductivity, while the spherical copper powder is enriched at the interface, forming a gradient transition layer in synergy with nickel powder, thus solving the problems of diffusion barrier and ohmic contact.

[0038] In one embodiment of this application, the total mass content of copper powder and nickel powder in the conductive material is 40-70% based on the total mass of the conductive material.

[0039] Controlling the total mass content of copper and nickel powder in conductive materials within the above-mentioned range helps to improve the conductivity of conductive materials while reducing costs.

[0040] In one embodiment of this application, the mass content of bismuth-based lead-free glass in the conductive material is 1-10% based on the total mass of the conductive material.

[0041] Controlling the mass content of bismuth-based lead-free glass in conductive materials within the above-mentioned range not only helps to form a protective layer on the surface of copper powder, isolating oxygen and thus further mitigating copper oxidation, but also helps to further improve the adhesion of conductive materials on silicon surfaces.

[0042] In one embodiment of this application, the bismuth-based lead-free glass comprises, by weight, 40-70 parts Bi2O3, 10-25 parts B2O3, 5-15 parts ZnO, 1-10 parts SiO2, and 0.5-10 parts of component A; component A is selected from any one or more of Al2O3, P2O5, and TeO2.

[0043] Bismuth-based lead-free glass containing the above-mentioned components helps to improve its fluidity at lower temperatures (matching the reaction temperature of nickel and silicon) through the synergistic interaction of the components. This allows for better encapsulation of copper powder, isolating the copper powder from oxygen, and providing a "liquid protective layer" for the copper powder at the peak sintering temperature, thereby further mitigating copper oxidation. Furthermore, the coefficient of thermal expansion of bismuth-based lead-free glass can be flexibly adjusted, exhibiting good compatibility with silicon, which helps to further enhance its adhesion to silicon.

[0044] In one embodiment of this application, the mass ratio of Bi2O3 to B2O3 in the bismuth-based lead-free glass is 2~5:1.

[0045] The presence of Bi2O3 and B2O3 within the aforementioned range in the preparation of bismuth-based lead-free glass helps to better regulate the softening point and melt viscosity of the glass powder, thereby facilitating the formation of ohmic contacts during sintering and also helping to fully coat the surface of the copper powder, thus inhibiting copper oxidation.

[0046] In one embodiment of this application, the softening point of the bismuth-based lead-free glass is 400~550℃; the D50 particle size of the bismuth-based lead-free glass is 0.5~3μm.

[0047] Controlling the softening point and D50 particle size of bismuth-based lead-free glass within the above range helps it soften and melt in time during sintering, forming a uniform, continuous and moderately fluid liquid protective layer on the surface of copper powder, thereby reducing the oxidation of copper in the air atmosphere.

[0048] Optionally, the mass ratio of the total mass of copper powder and nickel powder, the mass of bismuth-based lead-free glass, and the mass of the organic carrier is 40~70:1~10:25~55, or more preferably 55~65:3~7:28~42, which helps to further enhance the synergistic effect of the three components, thereby improving the performance of the conductive material.

[0049] Optionally, the mass ratio of nickel powder to bismuth-based lead-free glass is 0.3 to 3:1.

[0050] Controlling the mass ratio of nickel powder to bismuth-based lead-free glass within the above range helps the softened bismuth-based lead-free glass wet the surface of the nickel powder, which is beneficial for the subsequent reaction of nickel powder with silicon. This results in the formation of a thin and continuous nickel-silicon compound transition layer at the silicon / electrode interface, thereby creating a low-resistance contact and mitigating the diffusion of copper atoms into the silicon mass.

[0051] In one embodiment of this application, the battery substrate further includes an organic carrier; wherein, by weight, the organic carrier includes: 70-95 parts of organic solvent, 5-25 parts of organic binder, 0.1-3 parts of surfactant, and 0.1-2 parts of thixotropic agent.

[0052] Organic carriers containing the above-mentioned components help optimize the rheological properties and printability of conductive pastes. At the same time, they can decompose smoothly and volatilize completely during the sintering stage, reducing carbonization residue and porosity tendency, promoting the formation of a tight, low-resistance interface structure between the metal components and the silicon substrate, and slowing down the oxidation and migration behavior of metals in high-temperature environments, thereby improving the consistency of electrode forming and the stability of battery performance.

[0053] To further improve the overall performance of the organic carrier, in one embodiment of this application, the organic solvent is selected from any one or more of terpineol, diethylene glycol butyl ether acetate, tributyl citrate, and butyl carbitol; the organic binder is selected from any one or more of ethyl cellulose, nitrocellulose, and acrylic resin; the surfactant is selected from any one or more of lecithin, hydrogenated castor oil, and fatty acid polyethylene glycol esters; and the thixotropic agent is selected from any one or more of polyamide wax and hydrogenated castor oil derivatives.

[0054] In one embodiment of this application, the mass content of the organic carrier in the conductive material is 25-55%.

[0055] Controlling the mass content of organic carriers in conductive materials within the above-mentioned range helps to optimize the rheological properties and printability of conductive pastes, enabling them to exhibit good thixotropic behavior during screen printing. This means that the paste maintains a high viscosity in a static state to reduce material flow, and rapidly reduces viscosity when subjected to shearing to allow it to pass smoothly through the screen, thereby effectively reducing defects such as screen clogging, uneven diffusion at the edge of the pattern, and film thickness dispersion.

[0056] The above-mentioned conductive material can be prepared by the following methods:

[0057] Preparation of the organic carrier: The organic solvent was heated to 70-90℃, and the organic binder was slowly added while stirring until completely dissolved. After cooling to room temperature, the surfactant and thixotropic agent were added and stirred until homogeneous to obtain a uniform organic carrier.

[0058] Premixing: Copper powder, nickel powder and bismuth-based lead-free glass are mixed in a three-dimensional mixer for 1-3 hours to obtain a uniform composite functional powder.

[0059] Mixing and kneading: The composite functional powder and a portion of the organic carrier (approximately 1 / 2 to 2 / 3 of the total mass) are initially mixed in a planetary mixer to form a mixture (paste).

[0060] Three-roll milling: The mixture is dispersed by rolling through a three-roll mill, with the roll gap gradually reduced to below 5 μm, for a total of 5 to 10 passes, until the fineness of the slurry meets the requirements (≤10 μm by a scraper fineness gauge). During this process, the remaining organic carrier is gradually added to adjust the viscosity.

[0061] Degassing and filtration: The rolled slurry is vacuum degassed and filtered through a 200-400 mesh sieve to obtain conductive material.

[0062] In one embodiment of this application, conductive material is printed on a battery substrate and then sintered. The sintering process includes pre-sintering and main sintering, and the temperature of pre-sintering is lower than that of main sintering.

[0063] The preferred sintering process helps to achieve a synergistic effect between pre-sintering and the antioxidant treatment of sheet copper powder, promoting the reaction of Cu2O layer with Bi2O3 in glass to form a protective layer. At the same time, the main sintering helps to promote the reaction of nickel powder with silicon, thereby promoting the formation of diffusion barrier layer, and thus reducing copper oxidation at high temperature and copper diffusion into silicon.

[0064] In one embodiment of this application, the pre-sintering temperature is 300~450℃, the pre-sintering time is 2~5min, and the pre-sintering atmosphere is air.

[0065] Controlling the pre-sintering temperature, time, and atmosphere within the above range helps to promote the reaction between the Cu2O layer formed by the anti-oxidation treatment of the sheet copper powder and the Bi2O3 in the glass to form a protective layer, thereby further inhibiting oxidation.

[0066] In one embodiment of this application, the main sintering temperature is 700~800℃, the main sintering time is 30~90s, and the main sintering atmosphere is nitrogen or argon.

[0067] Controlling the temperature, time, and atmosphere of the main sintering within the above range helps to improve the density of the diffusion barrier layer, thereby better reducing the diffusion of copper atoms into the silicon mass and reducing the tendency of copper to oxidize.

[0068] In another typical embodiment of this application, a solar cell is provided, which is prepared by the above-described solar cell preparation process.

[0069] The conductive material in the solar cell prepared by the above-described solar cell fabrication process of this application achieves low contact resistance (<5 mΩ·cm). 2 High conductivity (volume resistivity < 5 × 10⁻⁶) -6 Excellent adhesion (greater than 2N, according to ASTM D3359) results in high fill factor and photoelectric conversion efficiency in solar cells.

[0070] A solar cell includes a copper electrode, a first electrode, a silicon substrate, a tunneling oxide layer (SiO2, 1-2 nm thick), a doped polycrystalline silicon layer (50-200 nm thick), a passivation antireflection layer, a nickel-silicon compound transition layer (10-30 nm thick), and a second electrode.

[0071] In another typical embodiment of this application, a stacked battery is provided, which includes a top battery and a bottom battery, wherein the bottom battery is the solar cell described above.

[0072] Stacked cells, including the aforementioned solar cells, have high photoelectric conversion efficiency and controllable cost.

[0073] In another typical embodiment of this application, a photovoltaic module is provided, including: a battery string, an encapsulating film, and a cover plate. The battery string is formed by connecting multiple solar cells as described above, or stacked cells as described above. The encapsulating film is used to cover the surface of the battery string, and the cover plate is used to cover the surface of the encapsulating film facing away from the battery string.

[0074] Using solar cells based on copper-nickel-bismuth-based glass composite conductive materials as cell string units not only achieves an electrode structure with low contact resistance and high adhesion, ensuring that the cell has a photoelectric conversion efficiency close to that of silver paste, but also maintains the long-term stability of the electrodes through encapsulation films and cover plates, improving the overall mechanical strength and environmental tolerance of the module, so that the module has significant cost advantages while maintaining high reliability.

[0075] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0076] Example 1

[0077] Preparation of the organic carrier: 80g of terpineol and 15g of diethylene glycol butyl ether acetate were mixed as an organic solvent and heated to 85℃. 10g of ethyl cellulose, an organic binder, was added while stirring. After complete dissolution, the mixture was cooled. 1.5g of lecithin, a surfactant, and 0.5g of polyamide wax, a thixotropic agent, were added, and the mixture was stirred for 2 hours to obtain the organic carrier.

[0078] Preparation of conductive material: Take 35g of flake copper powder (2μm diameter, 0.1μm thickness, specific surface area 3m²). 2 15g of spherical copper powder (D50 particle size 1μm) and 5g of nickel powder (D50 particle size 0.5μm) were prepared. Separately, 5g of bismuth-based lead-free glass (softening point 480℃) was prepared, comprising, by weight, 60 parts Bi₂O₃, 18 parts B₂O₃, 10 parts ZnO, 5 parts SiO₂, and 2 parts Al₂O₃. The powders were premixed for 2 hours, then initially kneaded with 40g of organic carrier, and rolled 8 times using a three-roll mill until the required fineness was achieved (≤10μm by scraper fineness gauge), with 15g of organic carrier added during the process. The rolled slurry was then vacuum degassed and passed through a 300-mesh sieve to obtain the conductive material.

[0079] After the conductive material battery is screen-printed onto the first side (front) of the TOPCON solar cell and dried and cured, it is sintered in a chain sintering furnace. The sintering process involves pre-sintering at 400°C in an air atmosphere for 3 minutes, followed by main sintering at 780°C in a nitrogen atmosphere for 60 seconds. The belt speed of the chain sintering furnace is 4.5 m / min. This forms the first and second electrodes, resulting in a solar cell with the structure shown below. Figure 1As shown, the solar cell includes a copper electrode 8, a first surface electrode 5, a silicon substrate 1 (N-type monocrystalline silicon), a tunneling oxide layer 2 (SiO2, 1 nm thick), and a doped polycrystalline silicon layer 3 (N... + The structure consists of a 100nm thick layer, a passivation antireflection layer 4 (SiNx / AlOx), a nickel-silicon compound transition layer 7 (20nm thick), and a second electrode 6.

[0080] Example 2

[0081] The difference from Example 1 is that the mass of nickel powder was adjusted to 5.5g, the D50 particle size of the nickel powder was 0.1μm, and the mass of bismuth-based lead-free glass was 7g, and a solar cell was finally obtained.

[0082] Example 3

[0083] The difference from Example 1 is that the bismuth-based lead-free glass comprises: 50 parts Bi2O3, 12 parts B2O3, 10 parts ZnO, 10 parts SiO2 and 8 parts Al2O3. The softening point of the bismuth-based lead-free glass is 520°C and the peak sintering temperature is 800°C, ultimately yielding a solar cell.

[0084] Example 4

[0085] Preparation of the organic carrier: 65g of terpineol and 5g of tributyl citrate were mixed as an organic solvent and heated to 70℃. 5g of nitrocellulose, an organic binder, was added while stirring. After complete dissolution, the mixture was cooled. 0.1g of hydrogenated castor oil, a surfactant, and 0.1g of polyamide wax, a thixotropic agent, were added and stirred for 2 hours to obtain the organic carrier.

[0086] Preparation of conductive material: Take 25.6g of flake copper powder (flake diameter 5μm, thickness 0.5μm, specific surface area 6m²). 26.4 g of spherical copper powder (D50 particle size of 2 μm) and 8 g of nickel powder (D50 particle size of 1 μm) were prepared. Separately, 10 g of bismuth-based lead-free glass (softening point of 400℃) was prepared, comprising 70 parts by weight of Bi₂O₃, 10 parts by weight of B₂O₃, 15 parts by weight of ZnO, 1 part by weight of SiO₂, and 10 parts by weight of TeO₂. The powders were premixed for 2 hours, then initially kneaded with 38 g of organic carrier, and rolled 10 times using a three-roll mill until the required fineness was achieved (≤10 μm by scraper fineness gauge), with 12 g of organic carrier added during the process. The rolled slurry was then vacuum degassed and passed through a 300-mesh sieve to obtain the conductive material. The flake copper powder was a flake copper powder that had undergone a first antioxidant treatment, which was performed in oxygen at 100℃ for 120 minutes. The spherical copper powder is a type of spherical copper powder that has undergone a second antioxidant treatment. The conditions for the second antioxidant treatment are to treat it in a hydrogen-nitrogen mixed atmosphere (volume ratio of hydrogen to nitrogen is 2:1) at 200°C for 180 minutes, and finally obtain the solar cell.

[0087] Example 5

[0088] The difference from Example 1 is that the total mass of copper powder and nickel powder is 55g, and the mass ratio of copper powder to nickel powder is 99.5:0.5, ultimately resulting in a solar cell.

[0089] Example 6

[0090] The difference from Example 1 is that the total mass of the flake copper powder and the spherical copper powder is 50g, and the mass ratio of the flake copper powder to the spherical copper powder is 4:1; wherein, the flake copper powder has a diameter of 3μm, a thickness of 0.2μm, and a specific surface area of ​​4m². 2 / kg; the D50 particle size of the spherical copper powder is 0.5μm, and finally a solar cell is obtained.

[0091] Example 7

[0092] The difference from Example 1 is that the total mass of the flake copper powder and the spherical copper powder is 50g, and the mass ratio of the flake copper powder to the spherical copper powder is 5:1; wherein, the flake copper powder has a diameter of 6μm, a thickness of 0.6μm, and a specific surface area of ​​7m². 2 / kg; the D50 particle size of the spherical copper powder is 2.5μm, and finally a solar cell is obtained.

[0093] Example 8

[0094] The difference from Example 1 is that, by weight, the bismuth-based lead-free glass comprises: 40 parts Bi2O3, 25 parts B2O3, 5 parts ZnO, 10 parts SiO2, and 0.5 parts P2O5. The bismuth-based lead-free glass has a D50 particle size of 0.5 μm and a softening point of 550°C, ultimately yielding a solar cell.

[0095] Example 9

[0096] The difference from Example 1 is that, by weight, it includes: 75 parts Bi2O3, 5 parts B2O3, 3 parts ZnO, 15 parts SiO2 and 12 parts P2O5. The bismuth-based lead-free glass has a D50 particle size of 3.5 μm and a softening point of 380°C, and finally a solar cell is obtained.

[0097] Example 10

[0098] The difference from Example 1 is that the total weight of Bi2O3 and B2O3 in the bismuth-based lead-free glass is 78 parts, and the mass ratio of Bi2O3 to B2O3 is 5:1, ultimately resulting in a solar cell.

[0099] Example 11

[0100] The difference from Example 1 is that the total weight of Bi2O3 and B2O3 in the bismuth-based lead-free glass is 78 parts, and the mass ratio of Bi2O3 to B2O3 is 7:1, which ultimately yields a solar cell.

[0101] Example 12

[0102] The difference from Example 1 is that the total mass content of copper powder and nickel powder in the conductive material, the mass ratio of bismuth-based lead-free glass to the mass of organic carrier is 70:1:29, and a solar cell is finally obtained.

[0103] Example 13

[0104] The difference from Example 1 is that the total mass content of copper powder and nickel powder in the conductive material, the mass ratio of bismuth-based lead-free glass to the mass of organic carrier is 75:0.5:24.5, and a solar cell is finally obtained.

[0105] Example 14

[0106] The difference from Example 1 is that the mass of nickel powder is 3g, the mass of bismuth-based lead-free glass is 10g, and the mass ratio of nickel powder to bismuth-based lead-free glass is 0.3:1, ultimately resulting in a solar cell.

[0107] Example 15

[0108] The difference from Example 1 is that the mass of nickel powder is 1g, the mass of bismuth-based lead-free glass is 10g, and the mass ratio of nickel powder to bismuth-based lead-free glass is 0.1:1, ultimately resulting in a solar cell.

[0109] Example 16

[0110] The difference from Example 1 is that the flake copper powder is flake copper powder that has undergone a first antioxidant treatment, which is performed in oxygen at 100°C for 120 minutes. The spherical copper powder is near-spherical copper powder that has undergone a second antioxidant treatment, which is performed in a hydrogen-nitrogen mixed atmosphere (volume ratio of hydrogen to nitrogen is 1:1) at 200°C for 180 minutes, ultimately yielding a solar cell.

[0111] Example 17

[0112] The difference from Example 1 is that the flake copper powder is flake copper powder that has undergone a first antioxidant treatment, which is performed in oxygen at 250°C for 30 minutes. The spherical copper powder is near-spherical copper powder that has undergone a second antioxidant treatment, which is performed in a hydrogen-nitrogen mixed atmosphere (volume ratio of hydrogen to nitrogen is 1:1) at 350°C for 60 minutes, ultimately yielding a solar cell.

[0113] Example 18

[0114] The difference from Example 1 is that the flake copper powder is flake copper powder that has undergone a first antioxidant treatment, which is to be treated in oxygen at 280°C for 20 minutes. The spherical copper powder is near-spherical copper powder that has undergone a second antioxidant treatment, which is to be treated in a hydrogen-nitrogen mixed atmosphere (volume ratio of hydrogen to nitrogen is 1:1) at 20°C for 200 minutes, and finally a solar cell is obtained.

[0115] Example 19

[0116] The difference from Example 1 is that the sintering process is to perform pre-sintering at 300°C for 5 minutes in an air atmosphere, followed by main sintering at 700°C for 30 seconds in a nitrogen atmosphere, and finally obtain a solar cell.

[0117] Example 20

[0118] The difference from Example 1 is that the sintering process is to perform pre-sintering at 500°C for 1 minute in an air atmosphere, followed by main sintering at 650°C for 100 seconds in a nitrogen atmosphere, and finally obtain a solar cell.

[0119] Comparative Example 1

[0120] The difference from Example 1 is that pure copper powder is used instead of nickel powder, and the copper powder is spherical. The glass is lead borosilicate glass, and a solar cell is finally obtained.

[0121] Comparative Example 2

[0122] The difference from Example 1 is that the conductive material used is front-side silver paste (DuPont). TM Solamet® PV76x series), ultimately resulting in solar cells.

[0123] Test method:

[0124] Contact resistance: Tested according to T / CPIA 0051-2023 "Test method for contact resistivity of metal electrodes of crystalline silicon photovoltaic cells - transmission line model method (TLM)".

[0125] Electrode adhesion: Tested according to Clause 5.2.2 of GB / T 29195-2012 "General Specification for Crystalline Silicon Solar Cells for Ground Use".

[0126] Battery conversion efficiency: Tested in accordance with GB / T 34160-2017 "Test Method for Photovoltaic Conversion Efficiency of Ground-mounted Photovoltaic Modules" and IEC 60904 series standards.

[0127] The electrodes and solar cells of the above embodiments and comparative examples were tested for performance. Twenty cells were used for each example, and the average value was calculated. The test results are shown in Table 1.

[0128] Table 1

[0129]

[0130] As can be seen from the above, the electrode in Comparative Example 1 was severely oxidized and blackened after sintering, with significantly higher contact resistance and poor electrode adhesion, resulting in a significant reduction in battery efficiency. Although the electrode in Comparative Example 2 has excellent performance, its cost is high.

[0131] The conductive material of this application adopts a "copper-nickel-glass" ternary synergistic system, which achieves electrode adhesion and battery conversion efficiency comparable to the silver paste in Comparative Example 2, and is far superior to the pure copper conductive material that is simply replaced in Comparative Example 1.

[0132] The solar cell of this application can also be used as a base cell to form a tandem cell with a perovskite cell, and the tandem cell can be applied to a photovoltaic module to improve the photoelectric conversion efficiency of the photovoltaic module.

[0133] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0134] The conductive material in the solar cell fabrication process of this application achieves multiple effects, including suppressing copper diffusion and oxidation and improving adhesion, through a ternary synergistic system of "copper-nickel-glass" and a composite design of dual-morphology copper powder, under an air sintering atmosphere. Simultaneously, the conductive material does not rely on the precious metal silver, significantly reducing costs. Specifically, 1) This application innovatively introduces a "copper-nickel-glass" ternary synergistic system. During sintering, the bismuth-based lead-free glass softens first, thereby wetting the surface of the silicon wafer and metal particles. The nickel powder preferentially reacts with silicon, forming a thin and continuous nickel-silicon compound (such as NiSi, NiSi2) transition layer at the silicon / electrode interface. By controlling the mass ratio of copper powder to nickel powder within the aforementioned range, this transition layer can form excellent ohmic contact with silicon, reducing the interfacial barrier, and also serve as an effective diffusion barrier layer to prevent copper atoms from diffusing into the silicon mass. Furthermore, it can act as a stress buffer layer to match the difference in thermal expansion coefficients between silicon and copper. At the same time, the addition of nickel powder can lower the overall sintering temperature, thereby further reducing the tendency of copper to oxidize at high temperatures. 2) This application combines flake-shaped copper powder with spherical copper powder. The flake-shaped copper powder facilitates the formation of a densely layered conductive film, thereby providing high in-plane conductivity; the spherical copper powder can fill the gaps between the flake-shaped copper powder, constructing a three-dimensional conductive path. The combination of the two can further improve the conductivity of the conductive material with a lower metal content. 3) The conductive material of this application uses bismuth-based lead-free glass, which can achieve good fluidity at a lower temperature (matching the reaction temperature of nickel and silicon), thereby effectively encapsulating the copper powder, isolating the copper powder from oxygen, and providing a "liquid protective layer" for the copper powder at the peak sintering temperature, thereby further inhibiting copper oxidation. At the same time, the thermal expansion coefficient of bismuth-based lead-free glass is adjustable, and it has good compatibility with the silicon substrate, thereby further enhancing the adhesion of the conductive material to the silicon surface. In addition, the conductive material of this application can be directly applied to existing screen printing equipment, and can be sintered in existing chain sintering furnaces and air atmospheres without the need for a complex protective gas system, thereby greatly reducing process modification costs and production costs. In summary, the solar cell fabrication process of this application can suppress copper diffusion and oxidation while enabling conductive materials to achieve low contact resistance, high conductivity, and excellent adhesion, thereby improving the fill factor and photoelectric conversion efficiency of solar cells.

[0135] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A process for fabricating a solar cell, characterized in that, A battery substrate is provided, on which conductive material is printed; The conductive material is cured to form the initial gate lines; The conductive material includes bismuth-based lead-free glass; The conductive material also includes copper powder and nickel powder; The mass ratio of copper powder to nickel powder is 80~99.5:0.5~20, and the copper powder includes flake copper powder and spherical copper powder. The copper powder is copper powder that has undergone antioxidant treatment; wherein, the flake copper powder is flake copper powder that has undergone a first antioxidant treatment, the conditions of which include: treatment in an oxygen-containing atmosphere at 100~250℃ for 30~120min; the spherical copper powder is spherical copper powder that has undergone a second antioxidant treatment, the conditions of which include: treatment in a hydrogen-nitrogen mixed atmosphere at 200~350℃ for 60~180min; After the conductive material is printed on the battery substrate, it is sintered. The sintering process includes pre-sintering and main sintering, and the temperature of the pre-sintering is lower than the temperature of the main sintering.

2. The fabrication process of the solar cell according to claim 1, characterized in that, The flake-shaped copper powder has a diameter of 1~5μm, a thickness of 0.1~0.5μm, and a specific surface area of ​​1.5~6m². 2 / kg; the D50 particle size of the spherical copper powder is 0.5~2μm; the D50 particle size of the nickel powder is 0.1~1μm.

3. The fabrication process of the solar cell according to claim 1, characterized in that, The mass ratio of the flake-shaped copper powder to the spherical copper powder is 1~4:1~4.

4. The fabrication process of the solar cell according to any one of claims 1 to 3, characterized in that, Based on the total mass of the conductive material, the total mass content of the copper powder and the nickel powder in the conductive material is 40-70%.

5. The fabrication process of the solar cell according to any one of claims 1 to 3, characterized in that, Based on the total mass of the conductive material, the mass content of the bismuth-based lead-free glass in the conductive material is 1-10%.

6. The fabrication process of a solar cell according to any one of claims 1 to 3, characterized in that, By weight, the bismuth-based lead-free glass comprises: 40-70 parts Bi2O3, 10-25 parts B2O3, 5-15 parts ZnO, 1-10 parts SiO2, and 0.5-10 parts component A; component A is selected from any one or more of Al2O3, P2O5, and TeO2.

7. The fabrication process of the solar cell according to claim 6, characterized in that, The mass ratio of Bi₂O₃ to B₂O₃ in the bismuth-based lead-free glass is 2~5:

1.

8. The fabrication process of the solar cell according to any one of claims 1 to 3, characterized in that, The softening point of the bismuth-based lead-free glass is 400~550℃, and the D50 particle size of the bismuth-based lead-free glass is 0.5~3μm.

9. The fabrication process of the solar cell according to claim 1, characterized in that, The pre-sintering temperature is 300~450℃, the pre-sintering time is 2~5min, and the pre-sintering atmosphere is air.

10. The fabrication process of the solar cell according to claim 1, characterized in that, The main sintering temperature is 700~800℃, the main sintering time is 30~90s, and the main sintering atmosphere is nitrogen or argon.

11. A solar cell, characterized in that, The solar cell is prepared by the solar cell preparation process according to any one of claims 1 to 10.

12. A stacked battery, the stacked battery comprising a top battery and a bottom battery, characterized in that, The bottom cell is the solar cell described in claim 11.

13. A photovoltaic module, characterized in that, include: A battery string is formed by connecting multiple solar cells as described in claim 11, or stacked cells as described in claim 12; An encapsulating film is used to cover the surface of the battery string; as well as A cover plate is used to cover the surface of the encapsulating film that faces away from the battery string.

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