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

Abstract

The embodiment of the present application relates to the photovoltaic field, and provides a solar cell and a preparation method thereof, printing a conductive paste on a cell substrate; the conductive paste is solidified to form an initial grid line; the initial grid line is sintered to obtain the solar cell; the conductive paste comprises composite conductive powder, glass powder, an organic carrier and an additive; the composite conductive powder has a core-shell structure, and comprises a copper core, a first coating layer and a second coating layer from inside to outside; the first coating layer is a Ni-M alloy layer, M is phosphorus and / or tungsten; the second coating layer is a modified silver layer, the modified silver layer comprises a silver matrix layer and a metal oxide layer attached to the side surface of the silver matrix layer away from the first coating layer, and the material of the metal oxide layer comprises an oxide of bismuth and / or an oxide of antimony. The solar cell provided by the embodiment of the present application can at least improve the photoelectric conversion efficiency of the solar cell.

Description

Technical Field

[0001] This application relates to the photovoltaic field, and in particular to a solar cell and its manufacturing process, a tandem cell, and a photovoltaic module. Background Technology

[0002] Traditional crystalline silicon solar cells typically use high-temperature sintered silver paste for the front-side grid lines. Silver powder, as a conductive filler, is expensive and accounts for a large portion of the cell's non-silicon cost. To reduce costs, the industry has attempted to replace silver with copper. However, copper is highly susceptible to oxidation during high-temperature sintering, and copper ions diffuse into silicon to form deep-level recombination centers, leading to a significant decrease in cell efficiency.

[0003] In recent years, silver-coated copper powder has become an important direction for cost reduction due to its core-shell structure, which retains the good conductivity of copper while achieving oxidation resistance through the silver layer. However, when conventional silver-coated copper powder is sintered at high temperatures (>600℃), cracks appear in the silver layer due to the mismatch in thermal expansion coefficients, and the diffusion of the copper core causes a surge in resistivity; the poor wettability between the organic carrier in the slurry and the silver-coated copper powder leads to poor aspect ratio of the printed grid lines, or even grid breakage; and the sintering process is mismatched, as traditional belt sintering furnaces have difficulty in accurately controlling the contact reaction between the silver-coated copper powder and the passivation layer, which easily leads to over-burning or poor contact. Summary of the Invention

[0004] This application provides a solar cell and its fabrication process, a tandem cell, and a photovoltaic module to solve the problems in the prior art, such as poor oxidation resistance, high contact resistance, poor grid line formation and electrode adhesion of silver-coated copper powder in solar cells, which lead to low photoelectric conversion efficiency and high production costs. It is at least beneficial to improve the photoelectric conversion efficiency of solar cells.

[0005] According to some embodiments of this application, one aspect of this application provides a process for fabricating a solar cell, which involves printing a conductive paste on a cell substrate; curing the conductive paste to form initial grid lines; and sintering the initial grid lines to obtain a solar cell. The conductive paste includes a composite conductive powder, glass powder, an organic carrier, and additives. The composite conductive powder has a core-shell structure, comprising a copper core, a first coating layer, and a second coating layer from the inside out. The first coating layer is a Ni-M alloy layer, where M is phosphorus and / or tungsten. The second coating layer is a modified silver layer, which includes a silver substrate layer and a metal oxide layer attached to the surface of the silver substrate layer away from the first coating layer. The material of the metal oxide layer includes bismuth oxide and / or antimony oxide.

[0006] According to some embodiments of this application, another aspect of this application provides a solar cell, which is prepared by the solar cell preparation process described above.

[0007] 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.

[0008] According to some embodiments of this application, another aspect of this application provides a photovoltaic module, including: a battery string, which is formed by connecting a plurality of solar cells as described above, or a stacked battery as described above; an encapsulating film for covering the surface of the battery string; and a cover plate for covering the surface of the encapsulating film facing away from the battery string.

[0009] The technical solution provided in this application has at least the following advantages: A nickel-phosphorus alloy layer and / or a nickel-tungsten alloy layer are coated onto the surface of the copper core to prevent the diffusion of copper atoms into the silver layer at high temperatures; further coating with a silver layer modified with bismuth and / or antimony oxides improves the wettability and sintering activity of the composite conductive powder and glass powder. This application, through core-shell structure design and interface modification, improves the oxidation resistance of silver-coated copper powder and reduces contact resistance, improves grid line formation, and is adaptable to high-temperature sintering or low-temperature curing processes, thereby improving the photoelectric conversion efficiency of solar cells while reducing production costs. Attached Figure Description

[0010] 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.

[0011] Figure 1 A schematic diagram of the structure of a solar cell according to an embodiment of this application is shown.

[0012] The above figures include the following reference numerals:

[0013] 101. Silicon substrate; 102. Front passivation layer; 103. Front main gate line; 104. Back passivation layer; 105. Back main gate line; 106. Tunneling oxide layer; 107. n+ polysilicon layer; 108. p+ emitter; 109. Front fine gate line; 110. Back fine gate line. Detailed Implementation

[0014] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0015] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0016] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0017] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0018] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0019] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0020] In the accompanying drawings corresponding to the embodiments of this application, the thickness and area of ​​the layers are enlarged for better understanding and ease of description. When describing a component (such as a layer, film, region, or substrate) on or on the surface of another component, the component may be "directly" located on the surface of the other component, or there may be a third component between the two components. Conversely, when describing a component on the surface of another component, or when another component is formed or disposed on the surface of a component, it indicates that there is no third component between the two components. Furthermore, when describing a component as being "generally" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a portion of the edge of the entire surface.

[0021] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included. Furthermore, when a component such as a layer, film, region, or plate is referred to as being "on / located" on another component, it can be "directly on" the other component (i.e., located on the surface of the other component with no other components between them), or another component may be present therein. Moreover, when a component such as a layer, film, region, or plate is "directly located" on another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it indicates that no other components are located therein.

[0022] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "part" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The embodiments of this application will now be described in detail with reference to the accompanying drawings. 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.

[0024] As described in the background section of this application, existing technologies suffer from poor oxidation resistance, high contact resistance, poor grid line formation, and poor electrode adhesion of silver-coated copper powder in solar cells, resulting in low photoelectric conversion efficiency and high production costs. To address these issues, this application provides a typical embodiment of a solar cell fabrication process: printing conductive paste onto a cell substrate; curing the conductive paste to form initial grid lines; and sintering the initial grid lines to obtain a solar cell. The conductive paste comprises composite conductive powder, glass powder, an organic carrier, and additives. The composite conductive powder has a core-shell structure, comprising, from the inside out, a copper core, a first coating layer, and a second coating layer. The first coating layer is a Ni-M alloy layer, where M is phosphorus and / or tungsten. The second coating layer is a modified silver layer, comprising a silver substrate layer and a metal oxide layer attached to the surface of the silver substrate layer away from the first coating layer. The metal oxide layer is made of bismuth oxide and / or antimony oxide.

[0025] In the solar cell of this application, the conductive paste is a silver-coated copper paste adaptable to high-temperature sintering processes (TOPCon, PERC) or low-temperature curing processes (HJT). Through the synergistic effect of core-shell structure design, interface modification, and laser-assisted sintering, the oxidation resistance and contact resistance issues of the silver-coated copper powder are addressed. By introducing an intermediate diffusion barrier layer and a surface modification layer, the conductive paste significantly improves the structural stability of the silver-coated copper powder at high temperatures. Combined with controlling the flow of the glass matrix and the precipitation of silver grains during the sintering process, low contact resistance and high adhesion are achieved. The process of this invention is compatible with existing production lines, requires no large-scale equipment modification, and has good economic benefits and industrialization prospects.

[0026] By introducing a Ni-M alloy layer as an intermediate barrier layer, the diffusion of the internal copper core to the silver substrate and battery interface is effectively blocked during subsequent sintering, thus avoiding the problems of increased electrode resistivity and decreased battery efficiency caused by copper impurity diffusion. Simultaneously, the metal oxide layer modifying the exterior of the silver layer improves the wetting performance of the conductive paste on the battery substrate or passivation layer surface, which is beneficial for promoting the regular formation of the grid lines after printing. The synergistic effect of the above multi-layer structure retains the cost-reducing advantage of the copper core while solving the technical problems of poor high-temperature sintering stability and poor paste wetting through the barrier layer and surface modification layer, achieving the fabrication of low-resistance, high-efficiency solar cells with well-formed grid lines. This application, through core-shell structure design and interface modification, improves the oxidation resistance of silver-coated copper powder and reduces contact resistance, improving grid line formation. It is adaptable to high-temperature sintering or low-temperature curing processes, improving the photoelectric conversion efficiency of solar cells while reducing production costs.

[0027] In one embodiment of this application, a conductive paste is screen-printed onto the surface of a battery substrate (such as a silicon wafer) to form a grid pattern, and then dried at 150~250°C to remove some of the solvent.

[0028] In one embodiment of this application, the copper core has a particle size Dv50 of 1.0~5.0 μm and a sphericity of 0.89~0.99; and / or a particle size variation coefficient CV of 10~25%. Under the above conditions, the core component in the composite conductive powder has suitable geometric dimensions, a highly regular spherical morphology, and a uniform particle size distribution. During the printing and curing process of the conductive paste, the copper cores with high sphericity and concentrated particle size distribution can be tightly stacked to form initial grid lines with low porosity and uniform structure, effectively reducing the uneven paste accumulation and rough grid line edges caused by irregular particle shapes or large differences in particle size. In the subsequent sintering stage, the uniform particle contact interface helps to reduce the inconsistency of contact resistance, increase the stability of the current transmission channel, thereby further reducing the fluctuation of electrode resistivity and improving the consistency of solar cell grid line formation and the uniformity of overall cell performance.

[0029] To achieve a more suitable geometric dimension and structural density in the Ni-M alloy layer, in one embodiment of this application, the thickness of the first coating layer is 20-100 nm; and / or the coverage of the first coating layer is 95-100%; and / or the weight ratio of M to Ni in the first coating layer is (0.02-0.2):1. The thinner thickness of the first coating layer combined with the high coverage allows the alloy layer to adhere tightly to the surface of the copper core, forming a continuous and pore-free physical barrier, effectively blocking the migration path of copper atoms during subsequent high-temperature sintering. A specific M to Ni weight ratio can further optimize the crystal structure and density of the alloy layer, enhancing its stability as a diffusion barrier layer. Under these conditions, the copper core is more effectively encapsulated, further suppressing the diffusion of copper into the silver layer and the silicon substrate, thereby improving the increase in electrode resistivity and the decrease in cell conversion efficiency caused by copper contamination, ultimately improving the conductivity of the solar cell grid and the overall cell efficiency.

[0030] The "coverage rate of the first coating layer" refers to the ratio of the area of ​​the first coating layer (i.e., the Ni-M alloy layer) covering the surface of the copper core to the total theoretically coverable surface area of ​​the copper core. This coverage rate characterizes the completeness of the first coating layer's coverage of the copper core surface. Specifically, the coverage rate is determined by: observing the cross-sections of at least 50 randomly selected composite conductive powder particles using a scanning electron microscope (SEM); statistically analyzing the percentage of continuous coverage length of the first coating layer on the circumferential direction of the copper core surface using image analysis software; and taking the average value as the coverage rate of the batch of powder; or performing elemental analysis on the powder surface using X-ray photoelectron spectroscopy (XPS) and indirectly estimating the coverage rate based on the copper element signal intensity.

[0031] When the coverage rate is 100%, it means that the first coating layer completely and continuously covers the copper core, with no exposed areas on the surface of the copper core. When the coverage rate is less than 100%, it means that there are exposed points or pinholes on the surface of the copper core that are not covered by the first coating layer. These areas will become preferential channels for the outward diffusion and oxidation of copper atoms during high-temperature sintering. In this application, the coverage rate of the first coating layer is preferably 95-100%. At this point, there are fewer exposed points on the surface of the copper core, and the first coating layer has a better blocking effect on the diffusion of copper atoms. The first coating layer plays an effective diffusion-blocking role, which is beneficial to ensuring the conductivity and reliability of the electrode after subsequent silver layer deposition and high-temperature sintering. It also helps to reduce the resistivity and contact resistance of the electrode body.

[0032] In one embodiment of this application, the bismuth oxide includes one or more of Bi₂O₃, Bi₂O₄, and Bi₂O₅; and / or the antimony oxide includes one or more of Sb₂O₃, Sb₂O₄, and Sb₂O₅. During sintering, these bismuth / antimony oxides with specific valence states adhering to the surface of the silver substrate can undergo interfacial reactions with the antireflection layer on the battery surface or the glass powder in the slurry. By utilizing the differences in melting points and reactivity of oxides with different valence states, the wetting and spreading behavior and reaction kinetics at the interface can be controlled, thereby improving the grid line forming quality and further reducing the electrode contact resistance, thus improving the conversion efficiency of the solar cell.

[0033] To further ensure that the modified silver layer retains sufficient effective conductive cross-section to maintain good bulk conductivity while reducing material waste and increased sintering shrinkage stress due to excessive silver layer thickness, in one embodiment of this application, the thickness of the second coating layer is 50-200 nm; and / or the thickness of the metal oxide layer is 0.5-10 nm; and / or the material of the metal oxide layer is granular with an average particle size of 1-15 nm. Controlling the size and morphology of the metal oxide layer attached to the surface of the silver substrate layer within the above range is beneficial for bismuth or antimony oxides to adhere to the surface of the silver layer in a uniform and dispersed state. During subsequent sintering, these nanoscale particulate oxides can more effectively undergo local creep reactions with the antireflection layer, promoting the interfacial bonding between the silver layer and the glass phase and silicon substrate. This significantly reduces the metal-silicon contact resistance while improving the wettability of the slurry and the quality of gate wire forming.

[0034] In one embodiment of this application, the conductive paste comprises, by weight, 70-90 parts of composite conductive powder, 1-5 parts of glass powder, 8-20 parts of organic carrier, and 0.1-3 parts of additives. The high content of composite conductive powder facilitates the formation of a dense and continuous conductive network within the electrode after sintering, thereby reducing contact resistance. A small amount of glass powder softens the flow during sintering to aid in wetting the silicon substrate and silver layer, without causing excessive electrode shrinkage or decreased adhesion due to excessive amount. An appropriate amount of organic carrier provides suitable viscosity and support, improving the aspect ratio and line integrity of the grid lines during printing. A small amount of additives further synergistically improves interfacial compatibility. Under these conditions, the components of the conductive paste can exert optimal synergistic effects during curing and high-temperature sintering, resulting in better grid line formation, higher conductivity, and higher electrode adhesion, which is beneficial for obtaining solar cells with low resistivity, high adhesion, and good formation.

[0035] To achieve a better thermodynamic match between the softening behavior of the glass powder during sintering and the metal oxides and antireflection layer on the surface of the silver layer, in one embodiment of this application, the glass powder, with a molar percentage of 100%, comprises: 40-60% Bi2O3, 10-20% B2O3, 5-15% SiO2, 5-20% ZnO, and 1-5% additives; the additives include one or more of TeO2, Sb2O3, and WO3; and / or, with a weight percentage of 100% organic carrier, the organic carrier comprises 5-15% resin, 80-90% solvent, and 1-5% thixotropic agent; and / or, with a weight percentage of 100% additives, the additives comprise 20-50% dispersant, 10-50% antioxidant, and 0-40% leveling agent.

[0036] The aforementioned glass powder composition facilitates the full softening of the glass matrix at high temperatures and wets the silicon substrate interface, thereby enhancing the adhesion between the electrode and the silicon wafer and reducing contact resistance. When the organic carrier composition is within the aforementioned range, the slurry exhibits more suitable rheological properties, resulting in more stable aspect ratios and contour integrity of the grid lines after printing and curing, reducing collapse or deformation. Specific types of additives are used to synergistically protect the copper core from oxidation in the early stages of sintering, maintain the uniform dispersion of the composite conductive powder in the slurry, reduce powder agglomeration, and further improve the resistivity, adhesion, and grid line formation properties of the solar cell.

[0037] Conductive slurry can be prepared by the following method: Resin, solvent, and thixotropic agent are heated and stirred in a water bath at 60~80℃ until completely dissolved, and filtered to obtain an organic carrier for later use; composite conductive powder, glass powder, and additives are premixed and added to the organic carrier, and mixed evenly in a planetary mixer; the mixture is then transferred to a three-roll mill for rolling, controlling the rolling pressure and number of rolling cycles until the slurry fineness is ≤5μm; vacuum defoaming and filtration are performed to obtain the conductive slurry.

[0038] For similar reasons, in one embodiment of this application, the resin includes ethyl cellulose and acrylic resin, with a mass ratio of ethyl cellulose to acrylic resin of (3~5):1; and / or the solvent includes diethylene glycol monobutyl ether acetate and / or terpineol; and / or the thixotropic agent includes hydrogenated castor oil and / or polyamide wax; and / or the dispersant includes polyester-type superdispersant and / or polyether-type dispersant; and / or the antioxidant includes organophosphorus antioxidants and / or benzotriazole compounds; and / or the leveling agent includes polyacrylate leveling agents and / or silicone leveling agents.

[0039] In one embodiment of this application, the preparation method of the composite conductive powder includes the following steps: Step S1, depositing a Ni-M alloy layer on the surface of a copper core using a nickel source and a deposition raw material via chemical plating or displacement method to obtain a first intermediate; the deposition raw material includes a phosphorus source and / or a tungsten source; Step S2, mixing the first intermediate with a silver ammonia solution and a reducing agent, and performing reduction deposition to deposit a silver substrate layer on the surface of the first intermediate to obtain a second intermediate; Step S3, mixing the second intermediate with a solution of a metal salt and heating it to form a metal oxide layer on the surface of the silver substrate layer to obtain the composite conductive powder; the metal salt includes a bismuth salt and / or an antimony salt.

[0040] First, using a nickel source and deposition materials containing phosphorus and / or tungsten sources, a Ni-M alloy layer is deposited on the surface of a copper core using chemical plating or displacement methods, forming a dense first intermediate. Then, the first intermediate is mixed with a silver ammonia solution and a reducing agent, and a silver substrate layer is grown on the surface of the Ni-M alloy layer through a reduction deposition process, yielding a second intermediate. Finally, the second intermediate is mixed with a metal salt solution containing bismuth and / or antimony salts and heated, then ultrasonically dispersed for 10–30 min. This causes the metal salts to decompose and form a nano-oxide layer, promoting the in-situ generation and attachment of bismuth or antimony oxides on the surface of the silver substrate layer, thus obtaining a surface-modified composite conductive powder. This preparation process utilizes a wet chemical reaction pathway to achieve a strong bond between the metal oxide layer and the silver substrate layer. This not only optimizes the surface state of the powder but also effectively inhibits the diffusion of the copper core to the silver layer during high-temperature sintering, reducing electrode resistivity. Simultaneously, it improves the wettability of the slurry, contributing to better grid line formation and ultimately enhancing the photoelectric conversion efficiency of the solar cell.

[0041] In one embodiment of this application, in step S1, the nickel source includes nickel sulfate and / or nickel nitrate; and / or the phosphorus source includes sodium hypophosphite (NaH2PO2·H2O), phosphorous acid, and one or more of hypophosphite; and / or the tungsten source includes sodium tungstate (Na2WO4·2H2O), ammonium metatungstate, and tungstic acid, and / or the electroless plating method includes: mixing a copper core with a nickel source and a deposition material, and performing electroless plating to obtain a first intermediate; wherein the electroless plating temperature is 75~85℃, the time is 10~40min, and the pH value of the plating solution is 4.5~6.5 (if adjustment is required, hydrochloric acid or sodium hydroxide can be used for adjustment); and / or the displacement method includes: mixing a copper core with a nickel source, a deposition material, and a solvent, and performing displacement to obtain a first intermediate; wherein the solvent includes water, the displacement temperature is 25~60℃, and the time is 5~20min. Optionally, the phosphorus source is sodium hypophosphite; and / or the tungsten source is sodium tungstate.

[0042] By limiting the specific types of phosphorus or tungsten sources used in the electroless plating or replacement method, and further controlling parameters such as reaction temperature, time, and pH, the deposition rate and crystallinity of the Ni-M alloy layer can be effectively regulated. This results in a more uniform and dense anti-diffusion layer, which more effectively blocks the diffusion of copper atoms into the silver layer and silicon substrate during subsequent high-temperature sintering, thus reducing contact resistivity. Simultaneously, by limiting the temperature and time of the electroless plating or replacement method within the aforementioned range, it is possible to reduce powder agglomeration or abnormal particle size while promoting complete coverage of the copper core surface by the nickel-tungsten alloy layer. This is beneficial for improving the dispersion stability of the composite conductive powder in the organic carrier and the printing adaptability of the final paste.

[0043] To further improve the preparation quality and structural stability of the composite conductive powder, in one embodiment of this application, in step S2, the reducing agent includes one or more of glucose, potassium sodium tartrate, formaldehyde, hydrazine hydrate, ascorbic acid, and ethylene glycol; and / or the mass ratio of the reducing agent to the first intermediate is (0.1~0.5):1; and / or the reduction deposition temperature is 40~60℃, and the time is 20~60min; and / or the first intermediate is mixed with silver ammonia solution and replaced at 25~60℃ for 5~20min to form a layer containing silver seeds with a thickness of 20~30nm on the surface of the first intermediate, thus obtaining a pretreated intermediate; then the pretreated intermediate is mixed with silver ammonia solution and reducing agent, and reduction deposition is performed until the thickness of the silver substrate layer is 50~200 nm, thus obtaining a second intermediate.

[0044] Using a mild reducing agent and a low-temperature reaction environment can slow down the reduction rate of silver ions, promoting more uniform and dense deposition of silver atoms on the surface of the nickel-phosphorus / nickel-tungsten alloy layer, further reducing porosity or defects in the silver layer. Optionally, a silver seed layer with a thickness of 20-30 nm can be formed on the surface of the alloy layer through a substitution reaction, and then the subsequent silver substrate layer can be deposited based on this. Using the silver seed as a growth nucleus significantly improves the interfacial bonding between the silver layer and the underlying alloy, and makes the crystal integrity and continuity of the final silver substrate layer more complete. The dense and well-bonded silver substrate layer coating can further enhance the oxidation resistance of the copper nucleus during high-temperature sintering, reduce the diffusion of copper to the surface, thereby improving the low resistivity and high adhesion of the electrode after laser sintering and high-temperature heat treatment, and improving the overall photoelectric conversion efficiency of the solar cell.

[0045] In one embodiment of this application, in step S3, the bismuth salt includes one or more of bismuth acetate (Bi(CH3COO)3), bismuth nitrate (Bi(NO3)3·5H2O), and bismuth citrate; and / or the antimony salt includes antimony acetate (Sb(CH3COO)3), antimony trichloride (SbCl3), and potassium antimony tartrate (C8H4K2O). 12 One or more of Sb2·3H2O; and / or a solution of a metal salt, wherein the solvent includes ethanol and / or isopropanol; and / or the heating atmosphere is a nitrogen atmosphere or an argon atmosphere, the temperature is 150~300℃, and the time is 30~60min.

[0046] Using the aforementioned bismuth and antimony salts as precursors, and mixing them with the aforementioned organic solvents, the excellent solubility and permeability of the organic solvents allow the metal salts to uniformly coat the surface of the silver substrate layer. Subsequent heat treatment under an inert protective atmosphere provides a gentle and controlled process that not only promotes the decomposition of the metal salts and the formation of a dense nanoscale bismuth or antimony oxide layer, but also effectively reduces high-temperature-induced grain coarsening or copper core oxidation in the silver substrate layer, thereby improving the interfacial bonding stability between the modified layer and the silver substrate layer. The stable metal oxide modified layer continues to improve the wettability of the slurry and antireflection layer during subsequent laser pre-sintering and high-temperature main sintering processes, promoting the softening and flow of glass powder and forming good ohmic contact. This reduces electrode contact resistance, resulting in solar cell electrodes with lower contact resistivity and higher adhesion, which is beneficial for improving the photoelectric conversion efficiency of the cell and reducing manufacturing costs.

[0047] In one embodiment of this application, sintering includes: step B1, performing laser pre-sintering on the initial grid line to obtain a first grid line; step B2, performing heating main sintering on the first grid line to obtain a second grid line; and step B3, applying a reverse bias voltage to the intersection of the main grid and the fine grid in the second grid line and performing laser supplementary sintering to form an electrode on the surface of the cell substrate to obtain a solar cell.

[0048] This application significantly improves the structural stability of silver-coated copper powder at high temperatures by introducing an intermediate diffusion barrier layer and a surface modification layer. After the conductive paste solidifies to form the initial grid lines, laser pre-sintering, heating main sintering, and laser supplementary sintering at the intersection of the main grid and the fine grid are performed in sequence. By combining this multi-step synergistic process, the flow of the glass body and the precipitation of silver grains can be controlled to achieve low contact resistance and high adhesion.

[0049] Laser pre-sintering uses a continuous or quasi-continuous laser to scan the initial grid lines after drying. The high-energy-density laser beam softens the glass powder in the slurry and induces localized creep reactions between the metal oxides on the silver layer surface and the anti-reflection layer (SiNx), effectively improving the wettability between the slurry and the silicon substrate and laying a good interfacial foundation for subsequent high-temperature main sintering. The laser-pre-sintered cells are then fed into a chain sintering furnace for heating and main sintering, promoting the melting and interconnection of silver particles and further reducing resistivity. Finally, a reverse bias is applied to the sintered grid lines, and a pulsed laser is used to perform a secondary scan on specific areas of the grid lines (such as the intersection of the main grid and the fine grid), forming a localized remelting zone. This further reduces contact resistance, eliminates microscopic contact gaps at the intersection, and significantly reduces the contact resistance in this area. This improves the overall photoelectric conversion efficiency and production yield of the solar cell while maintaining high electrode adhesion and low resistance characteristics.

[0050] A laser pre-sintering step is introduced before sintering. By controlling the laser power density and scanning speed, the glass powder in the slurry is softened, and a local reaction is induced between the metal oxide layer on the modified silver layer surface and the antireflection film on the battery surface to form a better ohmic contact. In one embodiment of this application, the laser power density of the laser pre-sintering is 1×10⁻⁶. 4 ~5×10 4 The laser wavelength for laser pre-sintering is 808–1064 nm, with a spot size of 50–200 μm, matching the grid line width. The laser's strength is W / cm², and the scanning speed is 1–5 m / s. The laser wavelength for pre-sintering is 808–1064 nm, and the spot size is 50–200 μm, matching the grid line width. The temperature for main sintering is 700–850 °C, and the time is 30–90 s. This specific thermal process promotes the softening of the glass powder to fill the gaps between the electrode and the silicon substrate. Furthermore, the Ni-M alloy layer effectively inhibits the diffusion of copper nuclei into the silicon substrate. This results in electrodes with high adhesion and low contact resistance, while reducing the increase in electrode resistivity and the decrease in cell conversion efficiency caused by copper diffusion, significantly improving the overall electrical performance of the solar cell.

[0051] In one embodiment of this application, the laser power density for laser-assisted sintering is 1×10⁻⁶. 4 ~5×10 4The laser-assisted sintering wavelength is 500-550 nm, and the pulse width is 1-100 ns; the reverse bias voltage for laser-assisted sintering is 5-15 V, and the pulsed laser energy density is 1-10 J / cm². During the sintering process, a reverse bias voltage within the above range is applied to the heated and sintered gate lines, and a pulsed laser with a specific energy density is used to perform a secondary scanning process on a specific area. This reverse bias voltage helps to establish an electric field environment conducive to carrier transport at the interface between the electrode and the silicon substrate, while the local thermal energy provided by the pulsed laser can locally remelt the gate lines, promoting atomic-level diffusion and bonding between the electrode metal and the semiconductor surface, thereby significantly reducing the contact resistance.

[0052] This application utilizes the high conductivity of the silver-modified layer in the composite conductive powder to effectively reduce Joule heat loss during current transmission within the electrode body, thereby improving the overall conductivity efficiency of the electrode. In one embodiment of this application, the bulk resistivity of the electrode is ≤5×10⁻⁶. -6 Ω cm; and / or the contact resistance between the electrode and the battery substrate ≤2 mΩ cm²; and / or the cell substrate includes a silicon substrate. Conductive paste can be printed on the boron-diffracted emitter side (front) or the phosphorus-doped polycrystalline silicon layer side (back) of the TOPCon cell to form contact electrodes.

[0053] In another typical embodiment of this application, a solar cell is provided, which is prepared by the above-described solar cell preparation process.

[0054] In some embodiments, a solar cell includes: a cell substrate having a front side and a back side; and electrodes located on the front side and / or the back side of a silicon substrate.

[0055] In some embodiments, the electrode includes a fine gate line and a main gate line, wherein the width of the fine gate line is 20~50μm and the aspect ratio is 0.3~0.6.

[0056] In some embodiments, the solar cell is a TOPCon cell, a PERC cell, or an HJT cell.

[0057] The solar cells prepared by the above-described solar cell preparation process of this application achieve high oxidation resistance, low bulk resistivity, low contact resistance, and good grid line forming and electrode adhesion, thereby enabling the solar cells to have high photoelectric conversion efficiency and low production cost.

[0058] In some embodiments, the structure of a solar cell is as follows: Figure 1As shown, the solar cell includes a silicon substrate 101, a p+ emitter 108 and a front passivation layer 102 located on the front side of the silicon substrate, a tunneling oxide layer 106 and an n+ polycrystalline silicon layer 107 located on the back side of the silicon substrate, and electrodes (including main grid lines and fine grid lines, front main grid line 103, front fine grid line 109, back fine grid line 110, and back main grid line 105) located on the surfaces of the front passivation layer 102 and the n+ polycrystalline silicon layer 107, respectively. The electrodes are prepared from the conductive paste provided in this embodiment using the laser sintering process provided in this embodiment.

[0059] In another typical embodiment of this application, a tandem solar cell is provided, comprising a top cell and a bottom cell, wherein the bottom cell is the aforementioned solar cell. The tandem solar cell comprising the aforementioned solar cell has high photoelectric conversion efficiency and controllable cost.

[0060] 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.

[0061] In some embodiments, the encapsulating film is an ethylene-vinyl acetate copolymer (EVA) film or a polyolefin elastomer (POE) film; the cover plate is tempered glass or a transparent polymer plate.

[0062] Photovoltaic modules, by integrating the aforementioned solar cells or tandem cells, effectively utilize the low contact resistance, low bulk resistivity, and strong adhesion of the electrode characteristics on the cell surface. This reduces series resistance losses within the module, improves the collection efficiency of photogenerated carriers, and ultimately enhances the overall photoelectric conversion efficiency of the module. Simultaneously, due to the excellent oxidation resistance and structural stability of the cell electrodes, electrode performance degradation is slow during long-term outdoor operation, helping to maintain the long-term stability of the module's output power. Furthermore, by encapsulating the cell strings in an encapsulating film and covering them with a cover plate, not only is physical protection provided for the cells, isolating them from the potential environmental impacts of moisture and oxygen on the silver-clad copper electrodes, but the lamination structure also enhances the overall mechanical strength of the module, improving its reliability and lifespan under complex operating conditions.

[0063] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0064] Example 1

[0065] A solar cell includes a silver-clad copper conductive paste suitable for the front grid lines of a TOPCon cell.

[0066] 1. Preparation of conductive paste

[0067] 1.1 Composite conductive powder

[0068] In step S1, copper powder (Dv50 of 2.0 μm, sphericity of 0.98, CV of 12%) is dispersed in a plating solution containing nickel sulfate and sodium hypophosphite. The pH of the plating solution is 5.5. Chemical plating is performed at 75°C for 20 min to deposit a Ni-P alloy layer with a thickness of about 50 nm on the surface of the copper core, thus obtaining the first intermediate.

[0069] In step S2, the first intermediate is transferred to a silver ammonia solution, and glucose reducing agent is added dropwise (the mass ratio of reducing agent to the first intermediate is 0.3:1) to carry out reduction deposition. The reaction temperature is controlled at 50°C and the time is 40 min. A silver substrate layer with a thickness of about 120 nm is deposited on the surface of the first intermediate to obtain the second intermediate.

[0070] Step S3: The second intermediate is dispersed in an ethanol solution containing bismuth acetate, stirred and evaporated to dryness, and then heated at 200°C under a nitrogen atmosphere for 30 minutes to uniformly modify the surface of the silver substrate layer in the form of Bi element in oxide form, forming a metal oxide layer with a thickness of about 5 nm, thus obtaining a composite conductive powder.

[0071] 1.2 Glass powder

[0072] Based on a 100% molar percentage of glass powder, including 50% Bi2O3, 15% B2O3, 10% SiO2, 20% ZnO, and 5% TeO2, the mixture is melt-quenched and then ball-milled to a D50 of 1.0 μm.

[0073] 1.3 Organic carrier

[0074] Ethyl cellulose (STD4) and acrylic resin (BR-113) were dissolved in a mixed solvent (diethylene glycol monobutyl ether acetate and terpineol, volume ratio 1:1) at a mass ratio of 4:1, with hydrogenated castor oil added as a thixotropic agent. The mixture was heated and stirred in a 70°C water bath until completely dissolved, and then filtered to obtain the organic carrier. Based on a 100% weight percentage of organic carrier, the organic carrier comprised 10% resin, 87% solvent, and 3% thixotropic agent.

[0075] 1.4 Preparation of conductive paste

[0076] Take 85 parts of composite conductive powder, 3 parts of glass powder, and additives (0.5 parts of triphenylphosphine and 0.5 parts of BYK-103 dispersant) and premix them. Add 11 parts of organic carrier and mix them evenly in a planetary mixer. Transfer the mixture to a three-roll mill for rolling. Roll the mixture 6 times until the fineness of the slurry is ≤5μm. After the fineness is qualified, perform vacuum defoaming and filtration to obtain conductive slurry.

[0077] 2. Fabrication of solar cells

[0078] The conductive paste is printed on the front side of the TOPCon cell and dried and cured at 200°C to form the initial grid lines.

[0079] Step B1, Laser Pre-Sintering: A continuous laser with a wavelength of 1064 nm and a power density of 3 × 10⁻⁶ nm is used. 4 W / cm², spot width 80μm, scanning along the initial grid line at a speed of 3m / s;

[0080] Step B2, heating the main sintering (chain sintering): enter the sintering furnace, peak temperature 800℃, time 50s, belt speed 4000mm / min;

[0081] Step B3, laser-assisted sintering: After sintering, the solar cell is subjected to a 10V reverse bias voltage, and a pulsed laser (wavelength 532nm, pulse width in the nanosecond range, energy density 5J / cm²) is used to scan the intersection of the main grid and the fine grid to assemble the solar cell.

[0082] Example 2

[0083] The difference from Example 1 is that in the preparation method of the composite conductive powder, in step S1, copper powder (Dv50 is 2.0 μm, sphericity is 0.98, CV is 12%) is dispersed in a plating solution containing nickel sulfate and sodium tungstate. The pH value of the plating solution is 5.5. Chemical plating is performed at 75°C for 20 min to deposit a Ni-W alloy layer with a thickness of about 50 nm on the surface of the copper core, thus obtaining the first intermediate.

[0084] Example 3

[0085] The difference from Example 1 is that in the preparation method of the composite conductive powder, in step S3, the second intermediate is dispersed in an ethanol solution containing antimony acetate, stirred and evaporated to dryness, and then heated at 200°C under a nitrogen atmosphere for 30 minutes to uniformly modify the surface of the silver substrate layer in the form of oxide, forming a metal oxide layer with a thickness of about 5 nm, thus obtaining the composite conductive powder.

[0086] Example 4

[0087] The difference from Example 1 is that the preparation method of the composite conductive powder includes the following steps:

[0088] In step S1, copper powder (Dv50 of 1.0 μm, sphericity of 0.95, CV of 10%) is dispersed in a plating solution containing nickel sulfate and phosphorous acid. The pH of the plating solution is 4.5. Chemical plating is performed at 75°C for 40 min to deposit a Ni-P alloy layer with a thickness of about 20 nm on the surface of the copper core, thus obtaining the first intermediate.

[0089] In step S2, the first intermediate is transferred to a silver ammonia solution, and potassium sodium tartrate reducing agent is added dropwise (the mass ratio of reducing agent to the first intermediate is 0.1:1) to carry out reduction deposition. The reaction temperature is controlled at 40°C and the time is 20 min. A silver substrate layer with a thickness of about 50 nm is deposited on the surface of the first intermediate to obtain the second intermediate.

[0090] Step S3: The second intermediate is dispersed in an isopropanol solution containing bismuth nitrate, stirred and evaporated to dryness, and then heated at 150°C under a nitrogen atmosphere for 60 minutes to uniformly modify the surface of the silver substrate layer in the form of Bi element in oxide form, forming a metal oxide layer with a thickness of about 0.5 nm, thus obtaining a composite conductive powder.

[0091] Example 5

[0092] The difference from Example 1 is that the preparation method of the composite conductive powder includes the following steps:

[0093] In step S1, copper powder (Dv50 of 5.0 μm, sphericity of 0.90, CV of 25%) is dispersed in a plating solution containing nickel nitrate and hypophosphoric acid. The pH of the plating solution is 6.5. Chemical plating is performed at 85°C for 10 min to deposit a Ni-P alloy layer with a thickness of about 100 nm on the surface of the copper core, thus obtaining the first intermediate.

[0094] In step S2, the first intermediate is transferred to a silver ammonia solution, and hydrazine hydrate reducing agent (the mass ratio of reducing agent to the first intermediate is 0.5:1) is added dropwise to carry out reduction deposition. The reaction temperature is controlled at 60°C and the time is 60 min. A silver substrate layer with a thickness of about 200 nm is deposited on the surface of the first intermediate to obtain the second intermediate.

[0095] Step S3: The second intermediate is dispersed in an ethanol solution containing bismuth citrate, stirred and evaporated to dryness, and then heated at 300°C under a nitrogen atmosphere for 30 minutes to uniformly modify the surface of the silver substrate layer in the form of Bi element in oxide form, forming a metal oxide layer with a thickness of about 10 nm, thus obtaining a composite conductive powder.

[0096] Example 6

[0097] The difference from Example 1 is that the method for preparing the solar cell includes the following steps:

[0098] The conductive paste is printed on the front side of the TOPCon cell and dried and cured at 200°C to form the initial grid lines.

[0099] Step B1, Laser Pre-Sintering: Using a continuous laser with a wavelength of 808 nm and a power density of 1 × 10⁻⁶. 4 W / cm², spot width 50μm, scanning along the initial grating line at a speed of 1 m / s;

[0100] Step B2, heating the main sintering (chain sintering): enter the sintering furnace, peak temperature 700℃, time 90s, belt speed 4000mm / min;

[0101] Step B3, laser-assisted sintering: After sintering, a 5V reverse bias voltage is applied to the solar cell, and a pulsed laser (wavelength 532nm, pulse width in the nanosecond range, energy density 1J / cm²) is used to scan the intersection of the main grid and the fine grid to obtain the solar cell.

[0102] Example 7

[0103] The difference from Example 1 is that the method for preparing the solar cell includes the following steps:

[0104] The conductive paste is printed on the front side of the TOPCon cell and dried and cured at 200°C to form the initial grid lines.

[0105] Step B1, Laser Pre-Sintering: Using a continuous laser with a wavelength of 915nm and a power density of 5×10⁻⁶. 4 W / cm², spot width 200μm, scanning along the initial grating line at a speed of 5 m / s;

[0106] Step B2, heating the main sintering (chain sintering): enter the sintering furnace, peak temperature 850℃, time 30s, belt speed 4000mm / min;

[0107] Step B3, laser-assisted sintering: After sintering, a 15V reverse bias voltage is applied to the solar cell, and a pulsed laser (wavelength 532nm, pulse width in the nanosecond range, energy density 10J / cm²) is used to scan the intersection of the main grid and the fine grid to obtain the solar cell.

[0108] Example 8

[0109] The difference from Example 1 is that the preparation method of the conductive paste includes the following steps:

[0110] 1.1 Composite conductive powder

[0111] Same as Example 1.

[0112] 1.2 Glass powder

[0113] Based on a 100% molar percentage of glass powder, including 40% Bi2O3, 20% B2O3, 15% SiO2, 20% ZnO, and 5% additives, the mixture is melt-quenched and then ball-milled to a D50 of 1.0 μm.

[0114] 1.3 Organic carrier

[0115] Ethyl cellulose (STD4) and acrylic resin (BR-113) were dissolved in a mixed solvent (diethylene glycol monobutyl ether acetate and terpineol, volume ratio 1:1) at a mass ratio of 3:1, with hydrogenated castor oil added as a thixotropic agent. The mixture was heated and stirred in a 70°C water bath until completely dissolved, and then filtered to obtain the organic carrier. Based on a 100% weight percentage of organic carrier, the organic carrier comprises 5% resin, 90% solvent, and 5% thixotropic agent.

[0116] 1.4 Preparation of conductive paste

[0117] Take 70 parts of composite conductive powder, 5 parts of glass powder, and additives (0.05 parts of triphenylphosphine and 0.05 parts of BYK-103 dispersant) and premix them. Add 8 parts of organic carrier and mix them evenly in a planetary mixer. Transfer the mixture to a three-roll mill for rolling. Roll the mixture 6 times until the fineness of the slurry is ≤5μm. After the fineness is qualified, perform vacuum defoaming and filtration to obtain conductive slurry.

[0118] Example 9

[0119] The difference from Example 1 is that the preparation method of the conductive paste includes the following steps:

[0120] 1.1 Composite conductive powder

[0121] Same as Example 1.

[0122] 1.2 Glass powder

[0123] Based on a 100% molar percentage of glass powder, including 60% Bi2O3, 15% B2O3, 10% SiO2, 10% ZnO, and 5% additives, the mixture is melt-quenched and then ball-milled to a D50 of 1.0 μm.

[0124] 1.3 Organic carrier

[0125] Ethyl cellulose (STD4) and acrylic resin (BR-113) were dissolved in a mixed solvent (diethylene glycol monobutyl ether acetate and terpineol, volume ratio 1:1) at a mass ratio of 5:1, and polyamide wax was added as a thixotropic agent. The mixture was heated and stirred in a 70°C water bath until completely dissolved, and then filtered to obtain the organic carrier. Based on a 100% weight percentage of organic carrier, the organic carrier comprised 15% resin, 80% solvent, and 5% thixotropic agent.

[0126] 1.4 Preparation of conductive paste

[0127] Take 90 parts of composite conductive powder, 1 part of glass powder, and additives (0.15 parts of triphenylphosphine and 0.15 parts of BYK-103 dispersant) and premix them. Add 20 parts of organic carrier and mix them evenly in a planetary mixer. Transfer the mixture to a three-roll mill for rolling. Roll the mixture 6 times until the fineness of the slurry is ≤5μm. After the fineness is qualified, perform vacuum defoaming and filtration to obtain conductive slurry.

[0128] Example 10

[0129] The difference from Example 1 is that in the preparation method of the composite conductive powder, in step S1, copper powder (Dv50 is 2.0 μm, sphericity is 0.98, CV is 12%) is mixed with nickel sulfate, sodium hypophosphite and deionized water, and replaced at 40°C for 12 min to deposit a Ni-P alloy layer with a thickness of about 50 nm on the surface of the copper core to obtain the first intermediate.

[0130] Example 11

[0131] The difference from Example 1 is that in the preparation method of the composite conductive powder, in step S2, the first intermediate is mixed with silver ammonia solution and replaced at 40°C for 12 min to form a layer containing silver seeds with a thickness of 25 nm on the surface of the first intermediate, thus obtaining a pretreated intermediate; then the pretreated intermediate is transferred to silver ammonia solution, and potassium sodium tartrate / hydrazine hydrate reducing agent (the mass ratio of reducing agent to the first intermediate is 0.3:1) is added dropwise to carry out reduction deposition. The reaction temperature is controlled at 50°C and the time is 40 min to deposit a silver substrate layer with a total thickness of about 120 nm on the surface of the first intermediate, thus obtaining the second intermediate.

[0132] Comparative Example 1

[0133] The difference from Example 1 is that the composite conductive powder does not have a Ni-P alloy layer (step S1 is not performed), and only simple silver-coated copper powder is used.

[0134] Comparative Example 2

[0135] The difference from Example 1 is that the composite conductive powder does not have a metal oxide layer (step S3 is not performed).

[0136] The composite conductive powder and solar cells of the above embodiments and comparative examples were tested as follows, and the results are shown in Tables 1 and 2.

[0137] 1. Composite conductive powder

[0138] The particle size Dv50 and coefficient of variation (CV) of the copper core were determined according to GB / T 19077-2016 "Particle Size Analysis by Laser Diffraction". A laser particle size analyzer (such as Malvern Mastersizer 3000) was used for measurement. The particle size corresponding to a cumulative volume distribution of 50% was defined as Dv50, and CV was automatically calculated by the instrument.

[0139] The sphericity of the copper core was determined according to GB / T 29526-2013 "Determination of Sphericity of Powder Particles - Dynamic Image Analysis Method". A dynamic image analyzer (such as FRITSCH Particle Sizer) was used to scan no fewer than 1000 particles, and the average value was calculated as the ratio of the circumference of the equivalent circle of the particle's projected area to the actual projected circumference of the particle.

[0140] The composition of the first coating layer and the weight ratio of M to Ni were determined using X-ray photoelectron spectroscopy (XPS) combined with inductively coupled plasma atomic emission spectrometry (ICP-OES). XPS was used to confirm the chemical states of the elements, and ICP-OES (referring to GB / T 30903-2014 "Inductively Coupled Plasma Mass Spectrometry") was used to determine the mass ratio of M to Ni.

[0141] The thickness of the first coating layer and the total thickness of the second coating layer were determined according to GB / T 30558-2014 "Geometric Specifications for Products (GPS) - Measurement Method by Scanning Electron Microscopy (SEM)". The cross-section of the powder (no less than 50 particles) was observed using SEM, and at least 8 measurement points were evenly selected around the circumference of each particle. The thickness was taken as the average value of each point.

[0142] Coverage of the first coating layer: determined according to GB / T 30558-2014, using SEM combined with energy dispersive spectroscopy (EDS). At least 50 cross-sections of the composite powder particles were randomly selected, and the percentage of continuous coverage length of the first coating layer on the circumferential direction of the copper core surface was statistically analyzed, with the average value taken.

[0143] Composition of the metal oxide layer: X-ray photoelectron spectroscopy (XPS) was used.

[0144] Thickness of the metal oxide layer: determined according to GB / T 30558-2014, and the cross-section of the powder was observed using a transmission electron microscope (TEM, such as FEI Talos F200X).

[0145] Average particle size of the metal oxide layer: SEM or TEM were used to observe and measure the maximum size of no less than 50 oxide particles randomly selected, and the arithmetic mean was taken.

[0146] 2. Solar cells

[0147] Electrode adhesion: Determined according to Clause 5.2.2 of GB / T 29195-2012 "General Specification for Crystalline Silicon Solar Cells for Terrestrial Use" or GB / T 17473.4-2008 "Test Method for Adhesion Determination of Noble Metal Pastes for Microelectronics Technology".

[0148] Volume resistivity: Measured according to GB / T 17473.3-2008 "Test Methods for Noble Metal Pastes for Microelectronics Technology - Determination of Sheet Resistance", using the four-probe method.

[0149] Contact resistance: Measured according to T / CPIA 0051-2023 "Test Method for Contact Resistivity of Metal Electrodes in Crystalline Silicon Photovoltaic Cells - Transmission Line Model (TLM)".

[0150] Battery efficiency: Measured according to IEC 60904-1:2020 "Photovoltaic devices - Part 1: Measurement of photovoltaic current-voltage characteristics" and GB / T 6495.1, calculated after measuring the IV curve under standard test conditions (AM1.5G, 1000 W / m², 25℃).

[0151] Table 1

[0152]

[0153] Table 2

[0154]

[0155] As can be seen, in Comparative Example 1, the absence of a Ni-P alloy diffusion barrier layer led to a significant diffusion of copper atoms into the silver layer and silicon substrate during high-temperature sintering. Copper ions formed deep-level recombination centers in the silicon, resulting in increased bulk resistivity, increased contact resistance, decreased electrode adhesion, and noticeable oxidation and discoloration at the grid line edges, leading to a lower battery efficiency compared to pure silver paste. In Comparative Example 2, the lack of a metal oxide layer resulted in poor wettability between the silver layer and glass powder. The glass powder eroded the silver layer unevenly during sintering, increasing contact resistance, decreasing adhesion, and exhibiting significant contact defects, resulting in a lower battery efficiency compared to pure silver paste. Example 1 showed an average electrode line resistance of 0.8 Ω / cm, reducing the cost per watt by 15%.

[0156] In summary, this application effectively suppresses the high-temperature diffusion of copper atoms by setting a Ni-M alloy diffusion barrier layer, improves the wettability and sintering activity of the silver layer and glass powder by using a metal oxide layer, and optimizes the metal-semiconductor interface contact by using a synergistic process of laser pre-sintering and laser supplementary sintering. The bulk resistivity and contact resistance of each embodiment are low, the electrode adhesion is close to or better than that of pure silver paste, and the battery efficiency reaches 99.90~100.08% of that of pure silver paste.

[0157] As shown above, this application constructs a multi-layered core-shell structured composite conductive powder by sequentially depositing a Ni-M alloy diffusion barrier layer and a silver substrate layer on the surface of the copper core, and forming a metal oxide modification layer on the surface of the silver substrate layer. This effectively suppresses the outward diffusion of copper atoms during high-temperature sintering, while simultaneously improving the wettability and sintering activity between the silver layer and the glass powder. Furthermore, through a multi-step synergistic process of laser pre-sintering, heating main sintering, and laser supplementary sintering, controllable flow of the glass body and preferential precipitation of silver grains are achieved, forming a good ohmic contact between the electrode and the silicon substrate.

[0158] 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 conductive paste is printed on a battery substrate; the conductive paste is cured to form initial grid lines; the initial grid lines are sintered to obtain the solar cell; The conductive paste includes composite conductive powder, glass powder, organic carrier and additives; The composite conductive powder has a core-shell structure, which includes a copper core, a first coating layer and a second coating layer from the inside out. The first coating layer is a Ni-M alloy layer, where M is phosphorus and / or tungsten; The second coating layer is a modified silver layer, which includes a silver substrate layer and a metal oxide layer attached to the surface of the silver substrate layer away from the first coating layer. The material of the metal oxide layer includes bismuth oxide and / or antimony oxide.

2. The fabrication process of the solar cell according to claim 1, characterized in that, The copper cores have a particle size Dv50 of 1.0~5.0 μm and a sphericity of 0.89~0.99; and / or The coefficient of variation (CV) of the copper core is 10-25%; and / or The thickness of the first coating layer is 20~100nm; and / or The coverage of the first coating layer is 95-100%; and / or In the first coating layer, the weight ratio of M to Ni is (0.02~0.2):

1.

3. The fabrication process of the solar cell according to claim 1 or 2, characterized in that, The bismuth oxide includes one or more of Bi₂O₃, Bi₂O₄, and Bi₂O₅; and / or The antimony oxide includes one or more of Sb₂O₃, Sb₂O₄, and Sb₂O₅; and / or The thickness of the second coating layer is 50~200 nm; and / or The thickness of the metal oxide layer is 0.5~10 nm; and / or The metal oxide layer is made of particulate material with an average particle size of 1~15 nm.

4. The fabrication process of the solar cell according to claim 1 or 2, characterized in that, By weight, the conductive paste comprises 70-90 parts of the composite conductive powder, 1-5 parts of the glass powder, 8-20 parts of the organic carrier, and 0.1-3 parts of the additives. and / or Based on a molar percentage content of 100% for the glass powder, the glass powder comprises: 40-60% Bi₂O₃, 10-20% B₂O₃, 5-15% SiO₂, 5-20% ZnO, and 1-5% additives; the additives include one or more of TeO₂, Sb₂O₃, and WO₃; and / or Based on a weight percentage of 100%, the organic carrier comprises 5-15% resin, 80-90% solvent, and 1-5% thixotropic agent; and / or Based on a weight percentage of 100%, the additive includes 20-50% dispersant, 10-50% antioxidant and 0-40% leveling agent.

5. The fabrication process of the solar cell according to claim 4, characterized in that, The resin comprises ethyl cellulose and acrylic resin, wherein the mass ratio of ethyl cellulose to acrylic resin is (3~5):1; and / or The solvent includes diethylene glycol monobutyl ether acetate and / or terpineol; and / or The thixotropic agent comprises hydrogenated castor oil and / or polyamide wax; and / or The dispersant includes polyester-type superdispersants and / or polyether-type dispersants; and / or The antioxidants include organophosphorus antioxidants and / or benzotriazole compounds; and / or The leveling agent includes polyacrylate leveling agents and / or silicone leveling agents.

6. The fabrication process of the solar cell according to claim 1 or 2, characterized in that, The preparation method of the composite conductive powder includes the following steps: Step S1: The Ni-M alloy layer is deposited on the surface of the copper core using a chemical plating method or a displacement method with a nickel source and deposition raw materials to obtain a first intermediate; the deposition raw materials include a phosphorus source and / or a tungsten source; Step S2: The first intermediate is mixed with silver ammonia solution and reducing agent, and reduction deposition is performed to deposit a silver substrate layer on the surface of the first intermediate to obtain the second intermediate; Step S3: The second intermediate is mixed with a solution of a metal salt and heated to form a metal oxide layer on the surface of the silver substrate layer, thereby obtaining the composite conductive powder; the metal salt includes bismuth salt and / or antimony salt.

7. The fabrication process of the solar cell according to claim 6, characterized in that, In step S1 The nickel source includes nickel sulfate and / or nickel nitrate; and / or The phosphorus source includes one or more of sodium hypophosphite, phosphorous acid, and hypophosphite; and / or The tungsten source includes one or more of sodium tungstate, ammonium metatungstate, and tungstic acid; and / or The electroless plating method includes: mixing the copper core with the nickel source and the deposition raw material, and performing electroless plating to obtain the first intermediate; wherein the electroless plating temperature is 75~85℃, the time is 10~40min, and the pH value of the plating solution is 4.5~6.5; and / or The displacement method includes: mixing the copper core with the nickel source, the deposition raw material, and the solvent, and performing displacement to obtain the first intermediate; wherein the displacement temperature is 25~60℃ and the time is 5~20min.

8. The fabrication process of the solar cell according to claim 6, characterized in that, In step S2 The reducing agent includes one or more of glucose, potassium sodium tartrate, formaldehyde, hydrazine hydrate, ascorbic acid, and ethylene glycol; and / or The mass ratio of the reducing agent to the first intermediate is (0.1~0.5):1; and / or The reduction deposition temperature is 40~60℃, and the time is 20~60 min; and / or The first intermediate is mixed with the silver ammonia solution and subjected to displacement at 25-60°C for 5-20 minutes to form a layer containing silver seeds with a thickness of 20-30 nm on the surface of the first intermediate, thus obtaining a pretreated intermediate; then the pretreated intermediate is mixed with the silver ammonia solution and the reducing agent to perform the reduction deposition until the thickness of the silver substrate layer is 50-200 nm, thus obtaining the second intermediate.

9. The fabrication process of the solar cell according to claim 6, characterized in that, In step S3 The bismuth salt includes one or more of bismuth acetate, bismuth nitrate, and bismuth citrate; and / or The antimony salt includes one or more of antimony acetate, antimony trichloride, and potassium antimony tartrate; and / or The solvent in the solution of the metal salt includes ethanol and / or isopropanol; and / or The heating atmosphere is a nitrogen atmosphere or an argon atmosphere, the temperature is 150~300℃, and the time is 30~60min.

10. The fabrication process of the solar cell according to claim 1 or 2, characterized in that, The sintering includes: Step B1: Perform laser pre-sintering on the initial gate line to obtain the first gate line; Step B2: The first gate line is heated and sintered to obtain the second gate line; Step B3: Apply a reverse bias voltage to the intersection of the main grid and the fine grid in the second grid line, and perform laser-assisted sintering to form an electrode on the surface of the battery substrate, thereby obtaining the solar cell.

11. The fabrication process of the solar cell according to claim 10, characterized in that, The laser power density of the laser pre-sintering is 1×10⁻⁶. 4 ~5×10 4 W / cm², scanning speed of 1~5 m / s; and / or The laser wavelength for laser pre-sintering is 808~1064nm, and the spot size is 50~200μm; and / or The heating temperature for the main sintering is 700~850℃, and the time is 30~90s; and / or The wavelength of the laser-assisted sintering is 500~550nm, and the pulse width is 1~100ns; and / or The reverse bias voltage for laser-assisted sintering is 5~15V, and the pulsed laser energy density is 1~10 J / cm².

12. The fabrication process of the solar cell according to claim 10, characterized in that, The volume resistivity of the electrode is ≤5×10⁻⁶. -6 Ω·cm; and / or The contact resistance between the electrode and the battery substrate is ≤2 mΩ·cm²; and / or The battery substrate includes a silicon substrate.

13. 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 12.

14. 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 13.

15. A photovoltaic module, characterized in that, include: A battery string is formed by connecting multiple solar cells as described in claim 13, or stacked cells as described in claim 14. 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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