Solar cell, preparation method thereof and photovoltaic module

Abstract

The invention discloses a solar cell, a preparation method thereof and a photovoltaic module, and relates to the photovoltaic field. The method comprises the steps of preparing an electrode on a substrate; the composite slurry for preparing the electrode comprises the following components: 60-85% of silver-coated copper powder, 3-12% of inorganic glass powder, 10-30% of an organic carrier, 0.05-1% of rare earth oxide and 1-3% of silicon carbide, totaling 100%. Wherein the inorganic glass powder is Bi2O3-B2O3-ZnO series lead-free glass powder, and the inorganic glass powder is B2O3-ZnO series lead-free glass powder The rare earth oxide is one or more of yttrium oxide, lanthanum oxide and cerium oxide. According to the electrode of the solar cell, the phenomenon that silver penetrates through the polycrystalline silicon layer to damage the tunneling oxide layer can be reduced, the contact resistance is reduced, the adhesive force is improved, an interface is effectively passivated, interface recombination is reduced, the conductivity of a sintering network is enhanced, and it is ensured that good electrode conductivity can be maintained and the cost is reduced under the condition that the silver content is low.

Description

Technical Field

[0001] This application relates to the field of photovoltaics, and in particular to a solar cell, a method for its fabrication, and a photovoltaic module. Background Technology

[0002] TOPCon solar cells are N-type silicon-based solar cells that employ tunneling oxide passivation contact technology. Compared to traditional PERC cells, TOPCon cells achieve more effective passivation and higher conversion efficiency by forming an ultra-thin tunneling oxide layer on their surface and then depositing a doped polycrystalline silicon layer. The advantages of TOPCon cells are mainly reflected in their excellent light absorption, better surface passivation, and lower interfacial recombination rate, which enables the cells to achieve higher theoretical conversion efficiencies.

[0003] Metallization is a crucial step in solar cell manufacturing, determining the performance of the cell electrodes, such as conductivity and adhesion. For TOPCon cells, the choice of metallization paste is particularly critical due to high-temperature sintering issues: the special structural requirements of TOPCon cells necessitate sintering at high temperatures during metallization to ensure good contact and conductivity between the electrodes and the silicon wafer. However, silver particles in traditional metallization pastes can easily penetrate the polycrystalline silicon layer at high temperatures, damaging the tunneling oxide layer and disrupting the passivation structure of the cell, thus increasing contact resistance and affecting the overall performance of the cell. The contradiction between contact resistance and adhesion: Contact resistance is a crucial indicator of the quality of electrical contact between the electrode and the silicon wafer, while adhesion is related to the reliability of the electrode. Current technologies often struggle to maintain low contact resistance while ensuring sufficient electrode adhesion, especially in the metallization of the front grid and back main grid of N-type silicon-based cells, where this contradiction is even more pronounced. Cost pressure: Silver is a key component of metallization paste, but due to its high price, the cost of silver paste accounts for a significant proportion of the overall cell manufacturing cost, typically around 25%-35%. Therefore, developing low-cost, high-performance metallization pastes has become an urgent problem for the industry. PID (Potential Induced Degradation) problem: Under certain conditions, batteries may suffer from the PID effect, meaning that battery performance gradually declines over time. While using aluminum-containing composite pastes can reduce costs, aluminum diffusion can exacerbate the PID problem, reducing battery life and stability. Summary of the Invention

[0004] This application provides a solar cell, its preparation method, and a photovoltaic module. The main purpose is to solve the problems that the electrodes of a solar cell are prone to damage during the sintering process, and that it is difficult to simultaneously achieve low contact resistivity and high adhesion.

[0005] According to one aspect of this application, a method for preparing a solar cell is provided, comprising preparing an electrode on a substrate; the composite paste for preparing the electrode comprises the following components: by weight percentage, 60-85% silver-coated copper powder, 3-12% inorganic glass powder, 10-30% organic carrier, 0.05-1% rare earth oxide, and 1-3% silicon carbide, totaling 100%; wherein the inorganic glass powder is Bi2O3-B2O3-ZnO series lead-free glass powder; and the rare earth oxide is one or more of yttrium oxide, lanthanum oxide, and cerium oxide.

[0006] Furthermore, by weight percentage, the composite slurry comprises the following components: 60-80% silver-coated copper powder, 5-10% inorganic glass powder, 10-30% organic carrier, 0.1-0.5% rare earth oxides, and 1-3% silicon carbide, totaling 100%.

[0007] Furthermore, by weight percentage, the composite slurry comprises the following components: 65-78% silver-coated copper powder, 5-9% inorganic glass powder, 12-28% organic carrier, 0.1-0.4% rare earth oxides, and 1-2.5% silicon carbide, totaling 100%.

[0008] Furthermore, by weight percentage, the composite slurry comprises the following components: 68-72% silver-coated copper powder, 6-8% inorganic glass powder, 15-25% organic carrier, 0.2-0.4% rare earth oxides, and 1.5-2.5% silicon carbide, totaling 100%.

[0009] Furthermore, the inorganic glass powder contains 40-70 wt% Bi2O3, 10-30 wt% B2O3, 5-25 wt% ZnO, and 0.1-0.5 wt% other oxide additives; wherein the other oxide additives are one or more of SiO2, Al2O3, and TiO2.

[0010] Furthermore, the softening point of inorganic glass powder is 580~650℃.

[0011] Furthermore, the median particle size D50 of the inorganic glass powder is 1.0~2.0μm.

[0012] Furthermore, the inorganic glass powder contains 55-65 wt% Bi2O3, 20-30 wt% B2O3, 10-25 wt% ZnO, and 0.1-0.4 wt% other oxide additives.

[0013] Furthermore, the softening point of inorganic glass powder is 590~630℃.

[0014] Furthermore, the median particle size D50 of the inorganic glass powder is 1.0~1.8μm.

[0015] Furthermore, the weight ratio of Bi2O3, B2O3 and ZnO in the inorganic glass powder is 1:(0.3~0.5):(0.1~0.3).

[0016] Furthermore, the copper core particle size D50 of the silver-coated copper powder is 0.1~1.0μm.

[0017] Furthermore, the silver shell of the silver-coated copper powder completely covers the copper core, and the thickness of the silver shell is 10% to 30% of the radius of the copper core.

[0018] Furthermore, organic carriers include organic solvents, resins, and dispersants.

[0019] Furthermore, the organic solvent is selected from one or more of terpineol, butyl carbitol, and diethylene glycol butyl ether acetate.

[0020] Furthermore, the resin is selected from one or more of ethyl cellulose and acrylic resin.

[0021] Furthermore, the dispersant is a phosphate ester dispersant.

[0022] Furthermore, the phosphate ester dispersant is at least one of dodecyl phosphate, polyoxyethylene ether phosphate, and nonylphenol polyoxyethylene ether phosphate.

[0023] Furthermore, the weight ratio of organic solvent, resin and dispersant is 1:(0.08~0.12):(0.02~0.05).

[0024] Furthermore, the rare earth oxides are Y2O3 and La2O3; the weight ratio of Y2O3 to La2O3 is 1:(0.25~4).

[0025] Furthermore, the average particle size of the rare earth oxides is 0.1~1.0 μm.

[0026] Furthermore, the silicon carbide is β-silicon carbide.

[0027] Furthermore, the average particle size of silicon carbide is 50~500nm.

[0028] Furthermore, the preparation method of the composite slurry includes the following steps:

[0029] Step S1: Obtain silver-coated copper core powder, Bi2O3-B2O3-ZnO lead-free glass powder, organic carrier, silicon carbide and rare earth oxides according to the proportions of each component in the slurry; wherein, the rare earth oxides are one or more of yttrium oxide, lanthanum oxide and cerium oxide;

[0030] Step S2: Dry mix silver-coated copper core powder, Bi2O3-B2O3-ZnO lead-free glass powder, silicon carbide and rare earth oxides to obtain dry mixed powder;

[0031] Step S3: Wet mix the dry powder and the organic carrier to obtain a premix;

[0032] Step S4: Roll and disperse the premix to obtain a composite slurry.

[0033] Furthermore, in step S4, the rolling dispersion treatment is carried out using a three-roll mill with a rolling gap of 5~15μm and a rolling temperature of 35~45℃.

[0034] Furthermore, after the composite paste is sintered at 780~820℃, the electrode contact resistance formed on the N-type TOPCon silicon wafer is less than 0.6mΩ·cm², and the welding pull force is greater than 2.5N / mm.

[0035] According to a second aspect of this application, a solar cell is provided, which is prepared using the above-described solar cell preparation method.

[0036] According to a third aspect of this application, a photovoltaic module is provided, comprising a plurality of solar cells, wherein the solar cells are as described above, and the plurality of solar cells are electrically connected by interconnecting strips.

[0037] The technical solution provided in this application has at least the following advantages:

[0038] (1) The electrode paste in the solar cell preparation method of this application uses silver-coated copper core-shell structure particles as the metal phase, which can effectively reduce the phenomenon of silver particles in traditional silver paste penetrating the polycrystalline silicon layer and damaging the tunnel oxide layer during the sintering process; it can significantly reduce the contact resistance between the silicon substrate and the metal electrode, thereby improving the photoelectric conversion efficiency of TOPCon solar cells; at the same time, the electrode after sintering of the composite paste has high adhesion and is not easy to fall off, which helps the stability of the cell structure.

[0039] (2) The composite slurry formulation of this application uses Bi2O3-B2O3-ZnO series lead-free glass powder as the key component. The softening point of this glass powder is 580~650℃, which allows the temperature window of the slurry during the sintering process to be widened to 780~820℃ (±15℃), which can adapt to different equipment conditions and process flow, and reduce the yield loss caused by improper temperature control.

[0040] (3) The addition of rare earth oxides such as Y2O3 and La2O3 as functional additives to the composite slurry of this application can effectively passivate the interface between the electrode and the silicon substrate, reduce interfacial recombination, and improve the electrical performance and stability of the battery. At the same time, the addition of nano-silicon carbide enhances the conductivity of the sintered network, ensuring that good electrode conductivity can be maintained even at a low silver content.

[0041] (4) The use of silver-coated copper particles in this application can maintain high battery efficiency and significantly reduce production costs even with a significant reduction in silver content. Detailed Implementation

[0042] As is known from the background technology, the silver paste of traditional TOPCon solar cells is prone to penetrating the polycrystalline silicon layer during the electrode sintering process, damaging the tunneling oxide layer, destroying the cell passivation structure, and thus increasing the contact resistance. Furthermore, the metal electrode is difficult to maintain sufficient adhesion while keeping the silicon substrate and the electrode at a low contact resistance. In addition, aluminum-containing composite pastes are prone to exacerbating PID problems due to aluminum diffusion, reducing cell life and stability.

[0043] According to one aspect of this application, a method for preparing a solar cell is provided, the method comprising preparing an electrode on a substrate, wherein the composite paste for preparing the electrode comprises the following components: by weight percentage, 60-85% silver-coated copper powder, 3-12% inorganic glass powder, 10-30% organic carrier, 0.05-1% rare earth oxide, and 1-3% silicon carbide, totaling 100%; wherein the inorganic glass powder is Bi2O3-B2O3-ZnO series lead-free glass powder; and the rare earth oxide is one or more of yttrium oxide, lanthanum oxide, and cerium oxide.

[0044] The silver-coated copper powder content in the composite slurry of this application is any value or a range between any two of 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, and 85%; the inorganic glass powder content is any value or a range between any two of 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, and 12%; the organic carrier content is any value or a range between any two of 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, and 30%; the rare earth oxide content is any value or a range between any two of 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1%; and the silicon carbide content is any value or a range between any two of 1%, 1.5%, 2%, 2.5%, and 3%.

[0045] The composite paste for solar cells provided in this application has the following synergistic effects in its components:

[0046] (1) Silver-clad copper core-shell structure as conductive phase: This structure is supported by a copper core, which reduces the amount of precious metal silver used. During the sintering process, the copper core can effectively suppress the excessive aggregation and excessive penetration of silver particles, thereby preventing silver from penetrating the polycrystalline silicon layer and damaging the ultrathin tunneling oxide layer (usually 1-2 nm) underneath. At the same time, the outer silver shell provides an excellent conductive path, ensuring that a low-resistance ohmic contact can be formed between the electrode and the silicon substrate.

[0047] (2) Bi2O3-B2O3-ZnO lead-free glass powder as binder: The softening point (580~650℃) and chemical activity of the glass powder are specifically designed to match the sintering process window of the TOPCon battery and the thermal stability and thickness of the tunneling oxide layer on its surface; during sintering, the molten glass phase can moderately corrode the extremely thin oxide layer on the silicon wafer surface, promoting the electrical contact between the metal phase and the silicon substrate, which is also the core and professional role of the slurry glass phase; the glass powder acts as a binder to encapsulate and bridge the silver-coated copper particles, fill the pores, form a dense and solid electrode body, and significantly improve the adhesion of the electrode; the fluidity of the glass powder helps to smooth the microstructure of the electrode.

[0048] (3) Rare earth oxides (Y2O3 / La2O3) as interface modifiers: Rare earth oxides react at the sintering interface, which can passivate silicon surface defects and reduce the interface state density, thereby reducing the interface recombination loss of charge carriers; they can adjust the interface reaction kinetics between the glass phase and silicon, making it more mild and uniform, avoiding local over-corrosion, thereby obtaining low contact resistance while protecting the integrity of the tunneling oxide layer; this forms a double guarantee with the anti-permeation effect of silver-coated copper particles.

[0049] (4) Nano-silicon carbide as a conductive reinforcing phase: Nano-silicon carbide particles have high hardness and certain conductivity. In the sintering network, they can play a mechanical support and bridging role between silver-coated copper particles, prevent excessive sintering shrinkage, and enhance the mechanical stability of the electrode structure. Its own conductivity and contact with metal particles help to build a more multi-dimensional conductive network. Especially when the silver content is reduced, it plays a key compensating role in maintaining the overall conductivity of the electrode.

[0050] The components in the slurry have the following synergistic effects: the above four types of components complement each other to achieve a comprehensive effect of low damage, low resistance, high adhesion and high conductivity; the silver-coated copper structure and rare earth oxides jointly protect the passivation structure; while achieving electrical contact and high adhesion, the reaction process of the glass powder is optimized by the rare earth oxides; and silicon carbide enhances the mechanical and electrical properties of the conductive network bonded by the glass powder.

[0051] To achieve optimal synergistic effects, the proportions of the various components in the slurry were progressively optimized. In some specific embodiments, the composite slurry, by weight percentage, comprises the following components: 60-80% silver-coated copper powder, 5-10% inorganic glass powder, 10-30% organic carrier, 0.1-0.5% rare earth oxides, and 1-3% silicon carbide, totaling 100%. Further, the silver-coated copper powder content is 65-78%, the inorganic glass powder content is 5-9%, the organic carrier content is 12-28%, the rare earth oxide content is 0.1-0.4%, and the silicon carbide content is 1-2.5%, totaling 100%. Furthermore, the content of silver-coated copper powder is 65-72%, the content of inorganic glass powder is 6-8%, the content of organic carrier is 15-25%, the content of rare earth oxides is 0.2-0.4%, and the content of silicon carbide is 1.5-2.5%; even further, the content of silver-coated copper powder is 68-72%, the content of inorganic glass powder is 6-8%, the content of organic carrier is 15-23%, the content of rare earth oxides is 0.2-0.4%, and the content of silicon carbide is 1.5-2.5%, totaling 100%. The solid content of the slurry is 70-90%. By adopting the above preferred ranges, the comprehensive effects of low damage, low resistance, high adhesion, and high conductivity can be fully achieved.

[0052] To lower the sintering temperature and enhance the adhesion of the electrodes after sintering, the inorganic glass composition is optimized. In some specific embodiments, the inorganic glass powder contains 40-70 wt% Bi₂O₃, 10-30 wt% B₂O₃, 5-25 wt% ZnO, and 0.1-0.5 wt% other oxide additives, totaling 100 wt%. The other oxide additives are one or more of SiO₂, Al₂O₃, and TiO₂. Furthermore, the inorganic glass powder contains 55-65 wt% Bi₂O₃, 20-30 wt% B₂O₃, 10-25 wt% ZnO, and 0.1-0.4 wt% other oxide additives; even further, the weight ratio of Bi₂O₃, B₂O₃, and ZnO is 1:(0.3-0.5):(0.1-0.3), or for example, 1:0.4:0.2. The softening point of the inorganic glass powder is 580-650℃, for example 590-630℃, or even 600-630℃. The median particle size D50 of the inorganic glass powder is 1.0-2.0 μm, for example 1.0-1.8 μm, or even 1.2-1.6 μm, and further 1.4-1.6 μm. Using the above-mentioned Bi2O3-B2O3-ZnO series lead-free glass powder formulation, softening point, particle size, etc., this glass powder is matched with the sintering process window of TOPCon cells and the thermal stability and thickness of the tunneling oxide layer on its surface; during sintering, the molten glass phase can moderately corrode the extremely thin oxide layer on the silicon wafer surface, which can promote the electrical contact between the metal phase and the silicon substrate; it acts as a binder to encapsulate and bridge silver-coated copper particles, fill pores, form a dense and robust electrode body, and significantly improve the adhesion of the electrode; its fluidity helps to smooth the electrode microstructure.

[0053] To balance conductivity, sintering characteristics and electrode adhesion, the ratio of silver-coated copper powder and inorganic glass powder is optimized. In some specific embodiments, the weight ratio of silver-coated copper powder to inorganic glass powder is 1:(0.08~0.12).

[0054] In order to control costs while ensuring interface passivation, the ratio of silver-coated copper powder and rare earth oxides is optimized. In some specific embodiments, the weight ratio of silver-coated copper powder and rare earth oxides is 1:(0.003~0.006).

[0055] To optimize the construction and mechanical strength of the conductive network, the ratio of silver-coated copper powder and silicon carbide is optimized. In some specific embodiments, the weight ratio of silver-coated copper powder to silicon carbide is 1:(0.02~0.04).

[0056] To improve the high conductivity and low contact resistance of the slurry after sintering, the particle size and silver shell thickness of the silver-coated copper are optimized. In some specific embodiments, the copper core particle size D50 of the silver-coated copper powder is 0.1~1.0μm, preferably 0.15~0.5μm. For example, the copper core diameter of the silver-coated copper powder is 150~180nm. The silver shell of the silver-coated copper powder completely covers the copper core, and the thickness of the silver shell is 10%~30% of the radius of the copper core; for example, the thickness of the silver shell is 55~65nm. The above-mentioned silver-coated copper powder can reduce the amount of precious metal silver used. During the sintering process, the copper core can effectively inhibit the excessive aggregation and excessive penetration of silver particles, thereby preventing silver from penetrating the polycrystalline silicon layer and damaging the ultrathin tunneling oxide layer underneath. At the same time, the outer silver shell provides an excellent conductive path, ensuring that a low-resistance ohmic contact can be formed between the electrode and the silicon substrate.

[0057] Considering the rheological properties, adhesiveness, and dispersibility of the composite slurry, the proportions of each component in the organic carrier are adjusted. In some specific embodiments, the organic carrier includes an organic solvent, a resin, and a dispersant. The organic solvent is selected from one or more of terpineol, butyl carbitol, and diethylene glycol butyl ether acetate; the resin is selected from one or more of ethyl cellulose and acrylic resin; and the dispersant is a phosphate ester dispersant, specifically at least one of dodecyl phosphate, polyoxyethylene ether phosphate, and nonylphenol polyoxyethylene ether phosphate. The weight ratio of the organic solvent, resin, and dispersant is 1:(0.08~0.12):(0.02~0.05); particularly, the weight ratio of terpineol, ethyl cellulose, and phosphate ester dispersant is 1:(0.08~0.12):(0.02~0.05), for example, 1:0.1:0.03. The organic carrier with the above proportions exhibits good rheological properties, contributing to the flowability and stability during screen printing, and improving adhesion after electrode sintering.

[0058] To ensure that rare earth oxides form a high-quality oxide interface protective layer on the silicon wafer surface after sintering, thereby reducing interfacial recombination and lowering contact resistance, the composition of the rare earth oxides is optimized. In some specific embodiments, the rare earth oxides are Y₂O₃ and La₂O₃, with a weight ratio of Y₂O₃ to La₂O₃ of 1:(0.25~4), for example, 1:1. The median particle size of the rare earth oxides is 0.1~1.5 μm, preferably 0.5~1.5 μm. The selected rare earth oxides (Y₂O₃ / La₂O₃) react at the sintering interface, passivating silicon surface defects, reducing interfacial state density, and minimizing carrier recombination losses. The interfacial reaction kinetics between the glass phase and silicon can be adjusted to be more moderate and uniform, avoiding localized over-corrosion, and protecting the integrity of the tunneling oxide layer while achieving low contact resistance.

[0059] To further improve the conductivity of the electrode after sintering, silicon carbide is added to the slurry, and its particle size is optimized. In some specific embodiments, the silicon carbide is β-silicon carbide; the average particle size of the silicon carbide is 50~500nm, for example 50~150nm. This type of nano-silicon carbide particles possesses high hardness and certain conductivity, and in the sintered network, it can provide mechanical support and bridging between the silver-coated copper particles, preventing excessive sintering shrinkage and enhancing the mechanical stability of the electrode structure. Its own conductivity and contact with metal particles help to construct a more multi-dimensional conductive network, especially when the silver content is reduced, playing a key compensatory role in maintaining the overall conductivity of the electrode.

[0060] In some specific embodiments, the preparation method of the above-mentioned composite slurry includes:

[0061] Step S1: Obtain silver-coated copper core powder, Bi2O3-B2O3-ZnO lead-free glass powder, organic carrier, nano-silicon carbide and rare earth oxides according to the proportions of each component in the slurry; wherein, the rare earth oxides are one or more of yttrium oxide, lanthanum oxide and cerium oxide;

[0062] Step S2: Dry mix silver-coated copper core powder, lead-free glass powder, nano silicon carbide and rare earth oxides to obtain dry-mixed powder;

[0063] Step S3: Wet mix the dry powder and the organic carrier to obtain a premix;

[0064] Step S4: Roll and disperse the premix to obtain a composite slurry.

[0065] In some specific embodiments, in step S4, the rolling dispersion is carried out using a three-roll mill with a rolling gap of 5~15μm and a rolling temperature of 35~45℃.

[0066] In some specific embodiments, after the composite slurry is sintered at 780~820℃, the electrode contact resistance formed on the N-type TOPCon silicon wafer is less than 0.6mΩ·cm², and the welding pull force is greater than 2.5N / mm.

[0067] In some specific embodiments, the silver-coated copper powder is obtained by chemical plating; for example, the plating solution includes: 1-5% silver salt, 3-8% copper, 5-15% reducing agent, 1-5% complexing agent, and the balance being solvent, totaling 100 wt%; wherein, the silver salt is selected from at least one of silver nitrate and silver acetate; the reducing agent is selected from at least one of glucose, formaldehyde, and hydrazine hydrate; the solvent is selected from at least one of deionized water and alcohol solvents; and the complexing agent is selected from at least one of ammonia, ethylenediaminetetraacetic acid (EDTA), and potassium sodium tartrate.

[0068] Rare earth oxides are obtained by ball milling; inorganic glass powder is obtained by ball milling; organic carrier is obtained by three-roll mill dispersion; the mixing temperature is 35~50℃. The ball milling method described above uses a rotation speed of 200~400 rpm, a milling time of 5~15 h, and a ball-to-material ratio of 3:1~8:1; the three-roll mill dispersion method includes a rotation speed of 100~300 rpm.

[0069] Inorganic glass powder (Bi2O3-B2O3-ZnO system): Bi2O3, B2O3, ZnO and other oxide raw materials are mixed in a certain proportion and then prepared by melting-quenching-ball milling process.

[0070] According to a third aspect of this application, a TOPCon solar cell is provided, including an electrode; the electrode is made of the composite paste described above or the composite paste obtained by the preparation method described above.

[0071] In some specific embodiments, the structure of a TOPCon solar cell comprises a device structure consisting of various thin films and semiconductor layers, from the light-incident side to the back-light side. These layers (such as antireflective coatings, emitters, tunneling oxide layers, etc.) are deposited or grown on the cell production line using semiconductor processes such as PECVD, LPCVD, diffusion, and oxidation.

[0072] In some specific embodiments, the structure of the above-mentioned TOPCon solar cell, from the light-incident side to the back-light side, includes: an anti-reflection film (such as a SiNx layer), a front n+ emitter, an n-type silicon substrate, a back tunneling oxide layer (SiO2), a phosphorus-doped polycrystalline silicon layer (n+ poly-Si), and a back passivation film; the electrodes include a front fine grid electrode and a back main grid electrode formed by screen printing composite paste and sintering, wherein the front electrode forms an ohmic contact with the n+ emitter, and the back electrode forms an ohmic contact with the n+ poly-Si layer.

[0073] In some specific embodiments, when in use, the composite paste is applied to the front fine grid and / or the back main grid pattern of the battery by screen printing. After drying, it is sintered in a nitrogen or nitrogen-hydrogen mixed atmosphere at a peak temperature of 780~820°C and held for 1~3 minutes to form a metallized electrode.

[0074] According to a fourth aspect of this application, a photovoltaic module is provided, comprising a plurality of solar cells; the solar cells are the aforementioned solar cells, and the plurality of solar cells are electrically connected by interconnecting strips.

[0075] According to a fifth aspect of this application, a photovoltaic system is provided, comprising one or more photovoltaic modules; the photovoltaic modules are those described above.

[0076] The embodiments of this application will now be described in detail. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0077] The sources of the raw materials used in the following embodiments of this application are as follows:

[0078] Silver-coated copper core-shell structure powder: prepared by chemical plating; wherein the plating solution comprises: 3% silver salt, 6% copper, 10% reducing agent, 3% complexing agent, and the balance being solvent, totaling 100wt%; wherein the silver salt is selected from at least one of silver nitrate and silver acetate; the reducing agent is selected from at least one of glucose, formaldehyde, and hydrazine hydrate; the solvent is selected from at least one of deionized water and alcohol solvents; and the complexing agent is selected from at least one of ammonia, ethylenediaminetetraacetic acid (EDTA), and potassium sodium tartrate.

[0079] Silver salts (silver nitrate, silver acetate), copper salts (copper sulfate): Sinopharm Chemical Reagent Co., Ltd., analytical grade (AR) or electronic grade.

[0080] Reducing agents, complexing agents, solvents: Sinopharm, Aladdin brand.

[0081] Ethyl cellulose: Dow's ETHOCEL™ series, or Shin-Etsu products.

[0082] Phosphate ester dispersants: BYK's DISPERBYK™ series and BASF's EFKA™ series.

[0083] Inorganic glass powder (Bi2O3-B2O3-ZnO system): The raw materials are mixed in a weight ratio of Bi2O3, B2O3 and ZnO of 1:0.4:0.2, and then prepared by melting-quenching-ball milling.

[0084] Rare earth oxides (Y2O3, La2O3): High-purity products (99.9% or 99.99%) from Sinopharm Group or China Rare Earth Group Co., Ltd.

[0085] Silicon carbide (nanoscale): German company SGL Carbon, Japanese company Ube Industries (UBE), or domestic company such as Donghai JA Solar.

[0086] Example 1

[0087] A method for fabricating a top-mount solar cell includes sintering composite paste into electrodes on a fine grid pattern designed on the front side and a main grid and fine grid pattern designed on the back side of the top-mount solar cell, respectively; wherein, the electrode fabrication method includes:

[0088] (1) Preparation of electrode composite paste:

[0089] Step S1: Obtain the following raw materials according to the formula: 70% silver-coated copper powder (copper core diameter 200nm, silver shell thickness 70nm), 8% Bi2O3-B2O3-ZnO inorganic glass powder (median particle size 1.3μm, softening point 600℃), 20% organic carrier, 0.3% rare earth oxides, 1.7% silicon carbide (particle size 100nm), totaling 100wt%; wherein, Bi2O3:B2O3:ZnO=1:0.4:0.2; the organic carrier is terpineol, ethyl cellulose and dodecyl phosphate (weight ratio 1:0.1:0.03); the rare earth oxides are Y2O3 and La2O3 (weight ratio 1:1); the solid content is 80%.

[0090] Step S2: Dry-mix silver-coated copper core powder, lead-free glass powder, nano-silicon carbide and rare earth oxides to obtain dry-mixed powder; then wet-mix the dry-mixed powder and organic carrier to obtain premix; finally, use a three-roll mill to roll and disperse the premix, with a rolling gap of 10μm and a rolling temperature of 35℃ to obtain composite slurry.

[0091] (2) Electrode preparation: The composite paste is precisely printed on the fine grid pattern designed on the front side of the TOPCon cell and the main grid and fine grid pattern designed on the back side through screen printing process. The printed wet film is dried in a tunnel furnace to remove most of the organic solvent. Then, it is rapidly sintered at high temperature in a nitrogen or nitrogen-hydrogen mixed protective atmosphere, with a peak temperature of about 800°C and a holding time of 2 minutes. During this process, the glass powder in the paste melts and achieves ohmic contact with the silicon substrate. The metal particles are sintered into a dense conductive grid, and finally, a firmly attached front electrode and a back electrode with low contact resistance are formed.

[0092] The structure of the prepared TOP cell solar cell, from the light-incident side to the back-light side, includes: the front electrode prepared in step (2), the anti-reflection film (SiNx layer), the front n+ emitter, the n-type silicon substrate, the back tunneling oxide layer (SiO2), the phosphorus-doped polycrystalline silicon layer (n+ poly-Si), the back passivation film, and the back electrode prepared in step (2).

[0093] Example 2

[0094] Example 2 differs from Example 1 in that the slurry formulation in step S1 is replaced with: 60% silver-coated copper powder (copper core diameter 200nm, silver shell thickness 50nm), 8% inorganic glass powder (particle size 1.2μm, softening point 600℃), 29.75% organic carrier, 0.25% rare earth oxides, and 2% silicon carbide (particle size 120nm), totaling 100%; wherein, the inorganic glass powder is Bi2O3-B2O3-ZnO lead-free glass (Bi2O3:B2O3:ZnO=1:0.35:0.15); the organic carrier is terpineol, ethyl cellulose, and polyoxyethylene ether phosphate (weight ratio 1:0.12:0.04); the rare earth oxides are Y2O3 and La2O3 (weight ratio 2:1); the solid content is 70.25%;

[0095] Replace the electrode preparation conditions in (2) with: sintering in a nitrogen atmosphere and holding at a peak temperature of 780℃ for 3 min to obtain the TOPCon battery electrode. The other steps are the same.

[0096] Example 3

[0097] Example 3 differs from Example 1 in that the slurry formulation in step S1 is replaced with: 80% silver-coated copper powder (copper core diameter 200nm, silver shell thickness 80nm), 6% inorganic glass powder (particle size 1.5μm, softening point 600℃), 12.15% organic carrier, 0.35% rare earth oxides, and 1.5% silicon carbide (particle size 120nm), totaling 100%; wherein, the inorganic glass powder is Bi2O3-B2O3-ZnO lead-free glass (Bi2O3:B2O3:ZnO=1:0.45:0.25); the organic carrier is terpineol, ethyl cellulose, and phosphate ester dispersant (weight ratio 1:0.08:0.02); the rare earth oxides are Y2O3 and La2O3 (weight ratio 1:1); the solid content is 88%;

[0098] Replace the electrode preparation conditions in (2) with: sintering in a nitrogen atmosphere and holding at a peak temperature of 820℃ for 1.5 min to obtain the TOPCon battery electrode. The other steps are the same.

[0099] Example 4

[0100] Example 4 differs from Example 1 in that the slurry formulation in step S1 is replaced with: 65% silver-coated copper powder (copper core diameter 200nm, silver shell thickness 80nm), 9% inorganic glass powder (particle size 1.5μm, softening point 600℃), 23.92% organic carrier, 0.28% rare earth oxides, and 1.8% silicon carbide (particle size 120nm), totaling 100%. The inorganic glass powder is Bi2O3-B2O3-ZnO lead-free glass (Bi2O3:B2O3:ZnO=1:0.3:0.1); the organic carrier is terpineol, ethyl cellulose, and phosphate ester dispersant (weight ratio 1:0.1:0.03); the rare earth oxides are Y2O3 and La2O3 (weight ratio 1:4); the solid content is 76%; the TOPCon battery electrode is obtained by screen printing the electrode and then sintering it, with the other steps remaining the same.

[0101] Example 5

[0102] Example 5 differs from Example 1 in that the slurry formulation in step S1 is replaced with: 76% silver-coated copper powder (copper core diameter 200nm, silver shell thickness 80nm), 6% inorganic glass powder (particle size 1.5μm, softening point 600℃), 16% organic carrier, 0.5% rare earth oxides, and 1.5% silicon carbide (particle size 120nm), totaling 100%. The inorganic glass powder is Bi2O3-B2O3-ZnO lead-free glass (Bi2O3:B2O3:ZnO=1:0.5:0.3); the organic carrier is terpineol, ethyl cellulose, and phosphate ester dispersants (weight ratio 1:0.09:0.035); the rare earth oxides are Y2O3 and La2O3 (weight ratio 4:1); the solid content is 76%; the TOPCon battery electrode is obtained by screen printing the electrode and then sintering it, with the other steps remaining the same.

[0103] Example 6

[0104] The difference between Example 6 and Example 1 is that the weight ratio of the inorganic glass components Bi2O3, B2O3 and ZnO in step S1 is replaced with 1:0.25:0.05, while the other steps are the same.

[0105] Example 7

[0106] The difference between Example 7 and Example 1 is that the weight ratio of the rare earth oxide components Y2O3 and La2O3 in step S1 is replaced with 1:1.5, while the other steps are the same.

[0107] Comparative Example 1

[0108] The difference between Comparative Example 1 and Example 1 is that the composite slurry in step S1 does not contain 0.3% rare earth oxides, and the reduced amount is made up by the organic carrier to make up the total amount of the formulation 100%. The other steps are the same.

[0109] Comparative Example 2

[0110] The difference between Comparative Example 2 and Example 1 is that the content of rare earth oxides in step S1 is replaced with 2%, and the amount of increase is adjusted by reducing the content of organic carrier to make the total amount of the formula 100%, while the other steps are the same.

[0111] Comparative Example 3

[0112] The difference between Comparative Example 3 and Example 1 is that the composite slurry in step S1 does not contain 1.7% silicon carbide, and the reduced amount is made up by the organic carrier to make up the total amount of the formulation 100%. The other steps are the same.

[0113] Comparative Example 4

[0114] The difference between Comparative Example 4 and Example 1 is that the silver-coated copper powder in the composite slurry of step S1 is replaced with pure silver powder, while the other steps are the same.

[0115] Comparative Example 5

[0116] The difference between Comparative Example 5 and Example 1 is that the content of silicon carbide in step S1 is replaced with 5%, and the amount of increase is adjusted by reducing the content of organic carrier to make the total amount of the formulation 100%, while the other steps are the same.

[0117] Comparative Example 6

[0118] The difference between Comparative Example 6 and Example 1 is that the content of inorganic glass powder in step S1 is replaced with 15%, and the amount of increase is adjusted by reducing the content of organic carrier to make the total amount of the formula 100%. The other steps are the same.

[0119] Comparative Example 7

[0120] The difference between Comparative Example 7 and Example 1 is that the content of inorganic glass powder in step S1 is replaced with 1%, and the reduced amount is made up by the organic carrier to make up the total amount of the formula 100%. The other steps are the same.

[0121] Comparative Example 8

[0122] The difference between Comparative Example 8 and Example 1 is that the content of silver-coated copper powder in step S1 is replaced with 50%, and the reduced amount is made up by the organic carrier to make up the total amount of the formula 100%. The other steps are the same.

[0123] Comparative Example 9

[0124] The difference between Comparative Example 9 and Example 1 is that the content of silver-coated copper powder in step S1 is replaced with 90%, and the amount of increase is adjusted by reducing the content of organic carrier to make the total amount of the formula 100%. The other steps are the same.

[0125] Performance testing:

[0126] The performance of each embodiment and each comparative example was tested using the following testing methods, and the results are shown in Table 1.

[0127] (1) Core electrical performance: Contact resistance (ρc) - directly reflects the ability of the slurry to form ohmic contact; the contact resistance (ρc) is measured by transmission line measurement (TLM) method, referring to the photovoltaic industry standard method of GB / T 1551-2021 / four-point probe tester (KyenceR-CHEK), and the contact resistance per unit area (mΩ·cm²) is measured.

[0128] (2) Mechanical reliability: Electrode adhesion (welding pull) - assesses the firmness of the bond between the electrode and the silicon wafer; electrode adhesion is tested by welding pull test. The solder strip is welded to the grid line with reference to GB / T 20560-2006 / Tension testing machine (Instron3343), and peeled off in the vertical direction to test the tensile strength (N / mm).

[0129] (3) Ultimate performance indicators: Photovoltaic conversion efficiency (η) of the battery - the final manifestation of comprehensive performance; Photovoltaic conversion efficiency IV characteristic test (AM1.5G), the battery efficiency is measured under the standard test conditions (STC) of GB / T6495.1-2022 / Solar Simulator (Newport Oriel Sol3A).

[0130] Table 1

[0131]

[0132]

[0133] As shown in Table 1, the electrode pastes of the TOP solar cells prepared in the various embodiments of this application exhibit high conductivity, adhesion, and photoelectric conversion efficiency. Using the TOPCon electrode composite paste provided in the embodiments of this application, an excellent balance of low contact resistance, high electrode adhesion, and high photoelectric conversion efficiency can be achieved simultaneously while significantly reducing silver content (thus reducing costs). In contrast, the comparative examples, due to the absence of key components or imbalanced proportions, all exhibit significant defects in one or more key performance aspects.

[0134] Comparative Example 1 (without rare earth oxides): Interface passivation failure led to a significant increase in contact resistance and a severe decrease in electrode adhesion.

[0135] Comparative Example 2 (excessive rare earth oxide content): The formation of an excessively thick enriched layer at the interface hinders carrier transport, leading to increased contact resistance and reduced photoelectric conversion efficiency.

[0136] Comparative Example 3 (without silicon carbide): The incomplete conductive network structure leads to increased contact resistance and reduced photoelectric conversion efficiency.

[0137] Comparative Example 4 (pure silver powder): The cost is extremely high, and silver is prone to excessive penetration during sintering, which seriously damages the electrode adhesion and passivation structure.

[0138] Comparative Example 5 (Excess Silicon Carbide): Excessive semiconductor / insulating phase hinders conductivity, resulting in increased contact resistance and decreased efficiency.

[0139] Comparative Example 6 (Excessive Glass Powder): Excessive erosion of the silicon interface damages the passivation layer, leading to a sharp increase in contact resistance and efficiency loss.

[0140] Comparative Example 7 (insufficient glass powder): Insufficient sintering liquid phase leads to poor interfacial contact, significantly increased contact resistance, and reduced photoelectric conversion efficiency.

[0141] Comparative Example 8 (insufficient silver-coated copper powder): Insufficient conductive phase leads to a lack of conductive pathways, resulting in significant deterioration of contact resistance and efficiency.

[0142] Comparative Example 9 (excessive silver-coated copper powder): The binder phase (glass powder) was relatively insufficient, resulting in poor electrode adhesion and loss of cost advantage.

[0143] This application provides an electrode composite paste in the TOPCon solar cell fabrication method, which can effectively reduce the phenomenon of silver particles in traditional silver paste penetrating the polycrystalline silicon layer and damaging the tunneling oxide layer during sintering; it can significantly reduce the contact resistance between the silicon substrate and the metal electrode, thereby improving the photoelectric conversion efficiency of the TOPCon solar cell; at the same time, the electrode after sintering of the composite paste has high adhesion, which can broaden the temperature window of the paste during sintering to 780-820℃ (±15℃); it can effectively passivate the interface between the electrode and the silicon substrate, reduce interface recombination, enhance the conductivity of the sintered network, ensure good electrode conductivity even at low silver content, and significantly reduce production costs.

[0144] 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 method for preparing a solar cell, characterized in that, The method includes fabricating electrodes on a substrate; the composite slurry for fabricating the electrodes comprises the following components by weight percentage: 60-85% silver-coated copper powder, 3-12% inorganic glass powder, 10-30% organic carrier, 0.05-1% rare earth oxides, and 1-3% silicon carbide, totaling 100%; wherein the inorganic glass powder is Bi2O3-B2O3-ZnO series lead-free glass powder; and the rare earth oxides are one or more of yttrium oxide, lanthanum oxide, and cerium oxide.

2. The method for preparing a solar cell according to claim 1, characterized in that, The composite slurry comprises the following components by weight percentage: 60-80% silver-coated copper powder, 5-10% inorganic glass powder, 10-30% organic carrier, 0.1-0.5% rare earth oxide, and 1-3% silicon carbide, totaling 100%.

3. The method for preparing a solar cell according to claim 1, characterized in that, The composite slurry comprises the following components by weight percentage: 65-78% silver-coated copper powder, 5-9% inorganic glass powder, 12-28% organic carrier, 0.1-0.4% rare earth oxide, and 1-2.5% silicon carbide, totaling 100%.

4. The method for preparing a solar cell according to claim 1, characterized in that, The composite slurry comprises the following components by weight percentage: 68-72% silver-coated copper powder, 6-8% inorganic glass powder, 15-25% organic carrier, 0.2-0.4% rare earth oxide, and 1.5-2.5% silicon carbide, totaling 100%.

5. The method for preparing a solar cell according to any one of claims 1 to 4, characterized in that, The Bi2O3-B2O3-ZnO series lead-free glass powder contains 40-70 wt% Bi2O3, 10-30 wt% B2O3, 5-25 wt% ZnO, and 0.1-0.5 wt% other oxide additives; wherein the other oxide additives are one or more of SiO2, Al2O3, and TiO2. And / or, the softening point of the inorganic glass powder is 580~650℃; And / or, the median particle size D50 of the inorganic glass powder is 1.0~2.0μm.

6. The method for preparing a solar cell according to claim 5, characterized in that, The content of Bi2O3 is 55-65 wt%, the content of B2O3 is 20-30 wt%, the content of ZnO is 10%-25 wt%, and the content of other oxide additives is 0.1-0.4 wt%. And / or, the softening point of the inorganic glass powder is 590~630℃; And / or, the median particle size D50 of the inorganic glass powder is 1.0~1.8μm.

7. The method for preparing a solar cell according to any one of claims 1 to 4, characterized in that, The weight ratio of Bi2O3, B2O3, and ZnO in the Bi2O3-B2O3-ZnO series lead-free glass powder is 1:(0.3~0.5):(0.1~0.3). And / or, the copper core particle size D50 of the silver-coated copper powder is 0.1~1.0μm; And / or, the silver shell of the silver-coated copper powder completely covers the copper core; the thickness of the silver shell is 10% to 30% of the radius of the copper core.

8. The method for preparing a solar cell according to any one of claims 1 to 4, characterized in that, The organic carrier includes an organic solvent, a resin, and a dispersant; And / or, the rare earth oxides are Y2O3 and La2O3; the weight ratio of Y2O3 to La2O3 is 1:(0.25~4). And / or, the median particle size of the rare earth oxide is 0.1~1.5 μm; And / or, the silicon carbide is β-silicon carbide; And / or, the average particle size of the silicon carbide is 50~500nm.

9. The method for preparing a solar cell according to claim 8, characterized in that, The organic solvent is selected from one or more of terpineol, butyl carbitol and diethylene glycol butyl ether acetate; And / or, the resin is selected from one or more of ethyl cellulose and acrylic resin; And / or, the dispersant is a phosphate ester dispersant; the phosphate ester dispersant is at least one of dodecyl phosphate, polyoxyethylene ether phosphate, and nonylphenol polyoxyethylene ether phosphate; And / or, the weight ratio of the organic solvent, the resin and the dispersant is 1:(0.08~0.12):(0.02~0.05).

10. The method for preparing a solar cell according to any one of claims 1 to 4, characterized in that, The preparation method of the composite slurry includes the following steps: Step S1: Obtain silver-coated copper core powder, Bi2O3-B2O3-ZnO lead-free glass powder, organic carrier, silicon carbide and rare earth oxides according to the proportions of each component in the slurry; wherein, the rare earth oxides are one or more of yttrium oxide, lanthanum oxide and cerium oxide; Step S2: Dry mix the silver-coated copper core powder, the Bi2O3-B2O3-ZnO lead-free glass powder, the silicon carbide and the rare earth oxide to obtain a dry-mixed powder. Step S3: Wet mix the dry powder and the organic carrier to obtain a premix; Step S4: The premixed material is rolled and dispersed to obtain the composite slurry.

11. The method for preparing a solar cell according to claim 10, characterized in that, The rolling dispersion treatment is performed using a three-roll mill with a rolling gap of 5~15μm and a rolling temperature of 35~45℃; And / or, after the composite slurry is sintered at 780~820℃, the electrode contact resistance formed on the N-type TOPCon silicon wafer is less than 0.6mΩ·cm², and the welding pull force is greater than 2.5N / mm.

12. A solar cell, characterized in that, The solar cell is the solar cell prepared by the method described in any one of claims 1 to 11.

13. A photovoltaic module, characterized in that, It includes multiple solar cells, the solar cells being the solar cells of claim 12, the multiple solar cells being electrically connected via interconnecting strips.

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