Photocuring silver paste, preparation method thereof and grid line manufacturing method

Abstract

The invention relates to photocuring silver paste, a preparation method thereof and a grid line manufacturing method, and belongs to the technical field of solar cell electrode materials. The silver paste comprises, by mass, 75%-88% of silver powder, 6%-10% of ultraviolet curing organic components, 2.5%-8% of glass powder and 1.0%-4.5% of auxiliaries. Wherein the ultraviolet curing organic component is composed of light-cured resin, a photoinitiator and a reactive diluent; the D50 particle size of the silver powder is 0.3-0.8 [mu] m, and more than 90% of particles are smaller than 1 [mu] m. The preparation method comprises the steps of step-by-step mixing and stirring, grinding and refining and vacuum defoaming. The manufacturing method of the grid line comprises the steps that after the silver paste is screen-printed to a battery piece, ultraviolet light preliminary curing is carried out, and then high-temperature sintering is carried out. According to the technical scheme, ultraviolet light rapid curing is used for replacing a traditional multi-channel drying process, the production efficiency is improved, the production line is shortened, and meanwhile high density and good electrical contact performance of the sintered grid line are ensured by controlling the content of organic components and optimizing the characteristics of silver powder.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, and in particular to a photocurable silver paste, its preparation method, and a grid line fabrication method. Background Technology

[0002] In the photovoltaic field, the performance of silver paste electrodes directly affects the conductivity, contact resistance, and even the final power generation efficiency of the battery. Therefore, optimizing the performance of the silver paste material and its electrode forming process is crucial. Currently, the mainstream process for producing battery grid line electrodes in the industry is as follows: First, silver paste is applied to the battery substrate via screen printing. Then, the printed battery cells are sequentially fed into a 3-5 gradient drying oven (temperature range 80-200℃) for 30-60 minutes to remove organic solvents from the paste. Finally, the paste is sintered in a high-temperature furnace at 700℃-800℃ for final curing. However, this traditional process has several shortcomings: First, the multiple drying steps increase the production line length (typically occupying 10-15 meters of space), increasing equipment investment costs and placing high demands on workshop layout. Second, the drying time limits the reduction of production cycle time, restricting further capacity increases. Third, during the gradient drying process, uneven evaporation of organic solvents can easily cause defects such as pinholes and cracks in the paste layer, which adversely affects the subsequent sintering quality and grid line performance.

[0003] Furthermore, existing silver paste preparation technologies also have bottlenecks affecting the performance of the final product. For example, in the mixing process, simple stirring methods are often used, failing to fully consider the differences in physical properties between the organic carrier and the inorganic powders (silver powder, glass powder), resulting in poor dispersion uniformity of the components and easy agglomeration of silver powder. At the same time, the silver powder particle size used in conventional silver pastes is usually 1-5μm. A wide particle size distribution and a large average particle size may affect the printability of the paste and the density and conductivity of the grid lines after sintering.

[0004] To meet the dual requirements of electrode performance and production efficiency in solar cells, it is necessary to develop a conductive silver paste with an organic component content that is suitable for high-temperature sintering, good mixing uniformity, and based on silver powder with optimized particle size. Summary of the Invention

[0005] This application aims to provide a method for preparing ultraviolet light-cured solar cell silver paste and its grid line fabrication, which resolves the contradiction between the content of cured organic components and the requirements of subsequent high-temperature sintering in traditional technologies. It simplifies the process while ensuring that the organic components can be fully decomposed during subsequent high-temperature sintering, avoiding the formation of voids in the grid lines, thereby obtaining electrodes with high density and low contact resistance.

[0006] The objective of this application is achieved through the following technical solution: the photocurable silver paste of this application is composed of the following components by mass percentage: Silver powder 75%-88% UV-curable organic components: 6%-10% Glass powder 2.5%-8% Additives 1.0%-4.5% The UV-curable organic component consists of a photocurable resin, a photoinitiator, and an active diluent. The D50 particle size of the silver powder particles is in the range of 0.3μm-0.8μm, and more than 90% of the particles have a particle size of less than 1μm.

[0007] In one embodiment, spherical silver powder accounts for 80%-95% of the total mass of silver powder.

[0008] In one embodiment, the UV-curable organic component comprises the following components by mass percentage: UV-cured resin 65%-75% Photoinitiator 12%-18% 10%-20% reactive diluent.

[0009] In one embodiment, the photocurable resin is selected from one or more of the following materials: 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, or polyethylene glycol diacrylate.

[0010] In one embodiment, the reactive diluent is isoborneol acrylate or cyclohexyl acrylate, and the photoinitiator is an α-hydroxy ketone photoinitiator.

[0011] In one embodiment, the glass powder is selected from one or more of the following materials: SiO2, B2O3, Bi2O3, ZnO, TiO2, MgO, Li2O or Al2O3.

[0012] In one embodiment, the additives include a dispersant, a defoamer, and a leveling agent, wherein the dispersant is a polycarboxylate, the defoamer is an organosilicon, and the leveling agent is an acrylate copolymer.

[0013] This application also provides a method for preparing a photocurable silver paste, comprising: Silver powder pretreatment includes feeding high-purity spherical silver powder into an air jet mill and grinding it under a pressure of 0.6MPa-0.8MPa to obtain primary ground silver powder. The primary ground silver powder is then added to an ultrasonic mill for ultrasonic grinding, and subsequently collected by passing it through 5μm, 2μm, and 1μm sieves. Preparation of UV-curable organic components: Weigh out the photocurable resin, photoinitiator, and reactive diluent according to the proportion, and mix them evenly to obtain a transparent and uniform UV-curable organic component; Add the ingredients in the following order and mix them together: a) First add 50-60% of the total silver powder, then add all the UV-curable organic components, and stir to initially wet and disperse the silver powder; b) Add the remaining silver powder and continue stirring for 10-15 minutes; c) Add glass powder, dispersant, defoamer, and leveling agent in sequence, and stir until each component is evenly dispersed to obtain the initial silver paste; The initial silver paste is ground and refined to a fineness of ≤5μm, and then vacuum degassing is performed to obtain photocurable silver paste.

[0014] In one embodiment, the mixing step is carried out using a planetary mixer with a stirring speed in the range of 1500 r / min to 2500 r / min and a revolution speed in the range of 300 r / min to 500 r / min.

[0015] This application further provides a method for fabricating grid lines, which uses the aforementioned photocurable silver paste and includes the following steps: Photocurable silver paste is printed onto the front or back electrode area of ​​the solar cell using screen printing, transfer printing, inkjet printing, tracing, or stencil printing processes. Preliminary curing is performed using ultraviolet light irradiation; After initial solidification, sintering is performed to obtain grid lines.

[0016] Compared with the prior art, this application has the following beneficial effects: This application limits the total content of UV-curable organic components in the silver paste to a specific range of 6%-10% (by mass), and uses photocurable resins with high double bond content (such as HDDA, TPGDA, PEGDA, etc.) and α-hydroxyketone photoinitiators. This allows the silver paste to achieve sufficient initial curing after printing through short-term (e.g., 3-5 seconds) UV irradiation, effectively avoiding problems such as sagging and deformation. Simultaneously, this content of organic components can be completely combusted and decomposed during the subsequent high-temperature sintering process at 720℃-780℃, without generating excessive gas, thus preventing the formation of voids or loose structures within the grid lines. Combined with glass powder of specific components, the final electrode grid line density is improved, and the contact resistance with the battery substrate is reduced.

[0017] In terms of preparation method, a multi-stage grinding process combining air jet milling and ultrasonic milling is employed, followed by sequential sieving for classification. This results in fine-particle-size, narrowly distributed silver powder, which helps improve the bulk density and sintering activity of the silver powder. Furthermore, a step-by-step planetary mixing process is used in the preparation method. First, a portion of the silver powder is mixed with all organic components to achieve good wetting. Then, the remaining silver powder is added to increase the bulk density. Finally, glass powder and additives are added, effectively promoting the uniform dispersion of all components, especially the high proportion of silver powder, and reducing agglomeration. These measures collectively result in a silver paste with suitable viscosity and good printability, ensuring the clarity and uniformity of screen-printed lines.

[0018] The UV-curable silver paste and grid line fabrication method described in this application replaces the traditional solvent removal process, which requires multiple (3-5) gradient drying ovens and takes 30-60 minutes, with UV irradiation (3-5 seconds). This shortens the electrode fabrication production line and reduces equipment footprint and investment. Simultaneously, the extremely short initial curing time significantly reduces production cycle time and increases output per unit time. Furthermore, eliminating the energy consumption of multiple drying ovens also reduces energy consumption during the production process. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart of a method for preparing photocurable silver paste according to an embodiment of this application; Figure 2 This is a flowchart illustrating a grid line fabrication method in one embodiment of this application. Detailed Implementation

[0020] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0021] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0022] 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.

[0023] To overcome the efficiency and quality issues caused by the drying process, this application introduces ultraviolet (UV) light curing technology into the silver paste system. This replaces the traditional thermal drying process with rapid photopolymerization, achieving second-level curing, significantly shortening the production line and improving production efficiency. The following detailed embodiments will elaborate on the UV-curable silver paste proposed in this application, its preparation method, and the method for fabricating grid lines using this silver paste. Specifically, the selection and proportioning of each component, key preparation steps and process parameters, and its application to the formation of solar cell electrodes will be explained to demonstrate how the aforementioned technical problems are solved and the corresponding technical effects are achieved.

[0024] In a preferred embodiment of this application, the photocurable silver paste comprises the following components by weight percentage: Silver powder 75%-88% UV-curable organic components: 6%-10% Glass powder 2.5%-8% Additives 1.0%-4.5% The UV-curable organic component consists of a photocurable resin, a photoinitiator, and an active diluent. The D50 particle size of the silver powder particles is in the range of 0.3μm-0.8μm, and more than 90% of the particles have a particle size of less than 1μm.

[0025] A key aspect of this embodiment lies in limiting the total content of the UV-curable organic component. This component's total mass percentage is controlled between 6% and 10% to balance the compatibility between rapid photocuring and high-temperature sintering. Too low a content leads to insufficient strength of the photopolymer crosslinking network, failing to provide sufficient initial curing strength immediately after printing to resist sagging or pattern deformation. Too high a content (e.g., exceeding 10%) may result in excessive gas production due to excessive decomposition of organic matter during the subsequent high-temperature sintering stage. When gas escape is obstructed, it can easily leave pores inside the grid lines, impairing their density and conductivity. Through the synergy of the photocurable resin, photoinitiator, and reactive diluent, it is ensured that the silver paste can complete the transformation from a liquid state to a solid state with a certain mechanical strength within seconds under UV irradiation of a specific wavelength and intensity, thus replacing the traditional thermal drying process.

[0026] Another key aspect lies in the precise control of the physical properties of the silver powder. Specifically, the D50 particle size of the silver powder used is limited to the range of 0.3 μm to 0.8 μm, and more than 90% of the particles are required to be smaller than 1 μm. This particle size and narrow distribution are beneficial for increasing the packing density of the silver powder particles, providing a physical basis for the subsequent sintering to form a dense metallic conductive network. This helps reduce the bulk resistance of the grid lines. Fine-particle silver powder has a higher specific surface area and sintering activity, promoting inter-particle fusion at the same sintering temperature and time, thereby improving the mechanical strength and density of the sintered grid lines. Furthermore, uniform and fine silver powder particles are more likely to achieve good dispersion stability in organic carriers, reducing printing defects caused by particle agglomeration, such as broken lines or uneven linewidth, thus improving the printability of the silver paste. To achieve this particle size characteristic, multi-stage grinding processes, including air jet milling and ultrasonic milling, can be used, combined with graded sieving to ensure the concentration of the particle size distribution. By comprehensively designing and controlling the particle size of silver powder, the total amount and composition of UV-curable organic components, and the dosage of glass powder and additives, a conductive silver paste for solar cells was obtained that can be rapidly pre-cured under UV light, adapt to subsequent high-temperature sintering processes, and has good printability and electrode performance.

[0027] With the D50 particle size of silver powder controlled between 0.3μm and 0.8μm and more than 90% of it being less than 1μm, and the proportion of spherical silver powder in the total mass of silver powder ranging from 80% to 95%, spherical particles have a smaller specific surface area and a more regular geometric shape compared to flake or irregularly shaped silver powder. When subjected to shear force (such as stirring or the action of a printing squeegee), spherical particles will not interlock with each other, which helps to reduce the viscosity of the paste at high shear rates, thereby improving the smoothness of the printing process. This allows the silver paste to pass through the screen mesh more smoothly, which is conducive to forming fine grid lines with clear edges and high resolution. Furthermore, it enables the silver powder particles to achieve a higher filling density in the paste and in the preliminary cured layer before subsequent sintering.

[0028] Specifically, the UV-curable organic component comprises the following components by mass percentage: 65%-75% UV-curable resin, 12%-18% photoinitiator, and 10%-20% reactive diluent. This ratio range is used to regulate the reaction kinetics of the photopolymerization system, the properties of the cured film, and its compatibility with inorganic fillers. First, the UV-curable resin, as the main component forming the three-dimensional cross-linked network, constitutes the majority (65%-75%) of the organic component, providing the necessary initial mechanical strength and cohesive force to effectively resist sagging and maintain pattern accuracy. The photoinitiator content is controlled at 12%-18%, which helps generate a sufficient concentration of active free radicals in the gaps between silver powder particles and on the surface of the slurry, initiating rapid and sufficient surface and near-surface curing under short-term UV irradiation, meeting the rapid curing cycle requirements of the production line. The reactive diluent is used to adjust the overall viscosity of the organic phase, enabling it to fully wet and disperse a high proportion of silver and glass powder, ensuring the uniformity of the paste and a suitable printing viscosity. The above-mentioned ratio range ensures that while providing sufficient dilution and wetting capabilities, the resin phase will not be over-diluted, thereby compromising the strength of the cured film.

[0029] In a specific embodiment, the photocurable resin is selected from one or more of the following materials: 1,6-hexanediol diacrylate (HDDA), tripropylene glycol diacrylate (TPGDA), or polyethylene glycol diacrylate (PEGDA, for example, with a molecular weight of 200-400). HDDA and TPGDA are typical bifunctional acrylates. HDDA has a straight-chain hexane structure, and the polymer network formed after curing has a high crosslinking density, which can provide high hardness and rigidity to the initially cured silver paste film layer, helping to maintain the stability of the pattern size and prevent deformation during subsequent handling or pre-treatment before sintering. PEGDA (polyethylene glycol diacrylate) helps to improve the wettability of the resin system to inorganic powders (silver powder, glass powder), promotes the interfacial bonding between the organic and inorganic phases, and its flexible segments can give the cured film a certain degree of elasticity. By selecting one or more of HDDA, TPGDA, or PEGDA for compounding, the hardness, flexibility, adhesion, and wettability of the pre-cured film can be finely adjusted according to actual needs, ensuring that the photocurable resin components not only meet the process requirements of rapid curing but also take into account compatibility with high-temperature sintering processes.

[0030] In a specific embodiment, the reactive diluent is selected as isobornyl acrylate (IBOA) or cyclohexyl acrylate (CHA), and the photoinitiator is selected as an α-hydroxy ketone photoinitiator. Both IBOA and CHA are monofunctional acrylate monomers. When participating in the curing reaction, the monofunctional IBOA and CHA mainly play a role in extending polymer chain segments and adjusting crosslinking density, helping to avoid excessive brittleness of the initially cured film due to excessive crosslinking, and improving the flexibility and adhesion of the cured layer to the substrate. α-hydroxy ketone photoinitiators are selected; for example, 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP) or 1-hydroxycyclohexylphenyl ketone (HCPK) can be selected. These photolysis methods generate free radicals efficiently, which is crucial for initiating sufficient surface and shallow curing reactions within a very short exposure time in systems containing a large amount of opaque silver powder. This ensures that a rapid and uniform photocuring reaction can be achieved while meeting the rheological properties requirements of the slurry.

[0031] Glass powder serves as the inorganic binder phase in silver paste, achieving electrical bonding and mechanical anchoring. In specific embodiments, the glass powder material is selected from one or more of the following oxides: SiO2, B2O3, Bi2O3, ZnO, TiO2, MgO, Li2O, or Al2O3. Specifically, SiO2 and B2O3 are common glass network forgings, constituting the skeletal structure of the glass and influencing its softening point, chemical stability, and mechanical strength. ZnO and TiO2 can act as network intermediates or modifiers, adjusting the glass's coefficient of thermal expansion to more closely resemble a silicon substrate and reducing thermal stress during sintering and cooling. Alkaline earth metals or alkali metal oxides such as MgO and Li2O, as network modifiers, can further reduce glass viscosity and improve its high-temperature fluidity, while Al2O3 helps improve the glass's chemical durability and mechanical strength. A combination of one or more of the listed oxides can be used to create a glass system with specific softening points, coefficients of thermal expansion, and chemical activities. For example, by designing a SiO2-B2O3-Bi2O3-ZnO system, the resulting glass powder exhibits suitable melting and flow characteristics within a preset sintering temperature range, such as 720℃-780℃, achieving low-resistance contact between the gate electrode and the silicon substrate, while minimizing the influence of the glass phase itself on the conductive path.

[0032] In a specific embodiment, the additives include a dispersant, a defoamer, and a leveling agent, wherein the dispersant is a polycarboxylate, the defoamer is an organosilicon, and the leveling agent is an acrylate copolymer. The dispersant, a polycarboxylate, typically possesses the structural characteristics of anchoring groups and solvated segments. The anchoring groups (such as carboxyl groups) can firmly adhere to the surface of silver powder and glass powder particles through physical adsorption or chemical action, while the solvated segments extending towards the organic carrier (i.e., the UV-curable organic component) form steric hindrance, effectively preventing particle aggregation and sedimentation caused by van der Waals forces. The defoamer, an organosilicon, avoids the formation of air bubbles during high-speed mixing of the silver paste (such as planetary mixing) and subsequent three-roll milling, effectively eliminating these bubbles to prevent the formation of voids in the slurry. The leveling agent, an acrylate copolymer, reduces surface tension and homogenizes the film surface by forming a monolayer at the gas-liquid interface.

[0033] This application also provides a method for preparing a photocurable silver paste, comprising: Silver powder pretreatment includes feeding high-purity spherical silver powder into an air jet mill and grinding it under a pressure of 0.6MPa-0.8MPa to obtain primary ground silver powder. The primary ground silver powder is then added to an ultrasonic mill for ultrasonic grinding, and subsequently collected by passing it through 5μm, 2μm, and 1μm sieves. Preparation of UV-curable organic components: Weigh out the photocurable resin, photoinitiator, and reactive diluent according to the proportion, and mix them evenly to obtain a transparent and uniform UV-curable organic component; Add the ingredients in the following order and mix them together: a) First add 50-60% of the total silver powder, then add all the UV-curable organic components, and stir to initially wet and disperse the silver powder; b) Add the remaining silver powder and continue stirring for 10-15 minutes; c) Add glass powder, dispersant, defoamer, and leveling agent in sequence, and stir until each component is evenly dispersed to obtain the initial silver paste; The initial silver paste is ground and refined to a fineness of ≤5μm, and then vacuum degassing is performed to obtain photocurable silver paste.

[0034] The photocurable silver paste preparation method provided in this application, through specific process steps and parameter control, transforms the aforementioned component scheme into a uniform and stable paste with the expected performance. First, the silver powder pretreatment includes primary grinding of high-purity spherical silver powder using an air jet mill at a pressure of 0.6MPa-0.8MPa. The high-speed airflow carries the energy generated by particle collisions, initially breaking down and spherizing the silver powder to reduce particle size and control morphology. Subsequently, the primary grinding product is fed into an ultrasonic mill for further processing. The high-frequency impact and microjets generated by ultrasonic cavitation can more effectively break down fine agglomerates and activate the particle surface. Finally, the powder is sequentially graded and sieved through 5μm, 2μm, and 1μm screens to ensure that the collected silver powder meets the particle size distribution characteristic of over 90% of the particles having a diameter less than 1μm, as required by this application.

[0035] During the mixing stage, the order of addition is as follows: First, add about half to six-tenths (50-60%) of the silver powder and mix it with all the UV-curable organic components. After initial wetting and dispersion, add the remaining silver powder. First, mix a portion of the silver powder with the entire organic phase to ensure sufficient organic components to coat and wet this portion of silver powder, forming a premixed slurry. Then, add the remaining silver powder. This newly added silver powder is more easily wetted and dispersed by the already uniformly distributed organic phase, thus gradually establishing a more uniform powder dispersion state throughout the mixing process, improving mixing efficiency and uniformity. Subsequently, add the glass powder and various additives (dispersant, defoamer, leveling agent) in sequence, allowing these trace components to further disperse in the already pre-homogenized system.

[0036] Finally, a three-roll mill and other equipment are used for grinding and refining. This process uses high shear force to further break down any small agglomerates that may remain from the previous mixing, and to more evenly disperse all solid particles (silver powder, glass powder) within the organic carrier, ensuring the fineness of the slurry. The fineness after grinding is controlled to ≤5μm. Subsequently, a vacuum degassing process is used to remove air that may have been trapped inside the slurry during mixing and grinding. The manufacturing method employs a process chain design that controls raw material characteristics through pretreatment, optimizes mixing through stepwise feeding, and ensures homogeneity through grinding and degassing. This process is adapted to the specific formulation proposed in this application (especially the high-solids-content, fine-particle-size silver powder and the specific UV-curing system).

[0037] In this specific embodiment, a planetary mixing tank is used in the mixing and stirring step. The rotational speed of the stirring paddle is in the range of 1500 r / min to 2500 r / min, and the revolution speed is in the range of 300 r / min to 500 r / min. By simultaneously rotating at high speed around its own axis and revolving around the central axis of the mixing tank, a three-dimensional flow field is generated within the tank. The high-speed rotation provides radial shear force and circumferential flow force, breaking up soft agglomerates between silver powder particles to achieve uniform dispersion at the microscale. The revolution speed ensures that the trajectory of the stirring paddle covers almost the entire area within the tank, providing a controllable mechanical environment for the mixing process of this specific silver paste formulation that combines efficient shear dispersion and comprehensive mixing capabilities.

[0038] This application further provides a method for manufacturing grid lines, which uses the aforementioned photocurable silver paste and includes the following steps: printing the photocurable silver paste onto the front or back electrode area of ​​the solar cell using screen printing, transfer printing, inkjet printing, tracing, or stencil printing; performing preliminary curing using ultraviolet light irradiation; and sintering to obtain grid lines after preliminary curing.

[0039] Based on the UV-curable silver paste prepared using the specific formulation and process provided in this application, this application further provides a matching grid line fabrication method. Utilizing the properties of the silver paste, a simplified process flow replaces the traditional multi-step drying path. The initial step of this method is to screen print the UV-curable silver paste onto the front or back electrode area of ​​a solar cell (such as a TOPCon cell). This step utilizes the suitable rheological properties (such as viscosity and thixotropy) and fineness (≤5μm) of the paste after optimization by the aforementioned preparation process to precisely transfer the paste to the surface of the cell substrate, forming a wet film with a predetermined pattern, such as main grid lines and fine grid lines. Transfer methods include screen printing, transfer printing, inkjet printing, stencil printing, or stencil printing.

[0040] Screen printing utilizes a screen with a preset pattern. Silver paste is transferred to the surface of the battery cell by squeezing through the mesh using a squeegee. The rheological properties of the silver paste in this application (such as the viscosity range measured in the embodiments, and the thixotropy and leveling properties obtained by adjusting the additive system) and the fineness of the silk powder (≤5μm) enable it to pass smoothly through the mesh of the screen, forming a wet film with clear edges. The subsequent ultraviolet curing step can quickly fix the pattern and prevent sagging. Alternatively, transfer printing, inkjet printing, embossing, or stencil printing can be selected. In transfer printing, silver paste is printed onto an intermediate carrier (such as a flexible mold) to form a precise pattern, which is then transferred to the surface of the solar cell. In inkjet printing uses a printhead to precisely spray silver paste in droplet form onto designated locations on the solar cell. This process requires the silver paste to have low viscosity and specific rheological properties to prevent printhead clogging and ensure accurate droplet formation and positioning. The silver paste in this application can further reduce viscosity within the total organic component range (6%-10%) by adjusting the type and proportion of the reactive diluent to meet the fluid requirements of inkjet printing. Embossing or stencil printing uses a printing plate with raised or recessed patterns, transferring the paste onto the substrate through contact imprinting. The high proportion and fine-particle-size spherical silver powder in the silver paste of this application contribute to achieving good transfer efficiency and film uniformity. After printing, the pattern can be initially cured in seconds by ultraviolet light irradiation.

[0041] Subsequently, preliminary curing is performed using ultraviolet light irradiation. This step directly utilizes the photochemical reaction characteristics of the ultraviolet-curing organic components in the silver paste (containing 6%-10% of specific photoinitiators and resins). When the printed wet film is exposed to ultraviolet light of a specific wavelength (e.g., 365-395nm) and sufficient intensity (e.g., corresponding to 800-1500W light power), the photoinitiator rapidly decomposes to generate free radicals, initiating a rapid polymerization and cross-linking reaction of the acrylate resin. This transforms the wet film from a liquid state to a solid state with a certain mechanical strength within a very short time (e.g., 3-5 seconds), thus "locking in" the printed pattern. This replaces the traditional solvent drying process, which requires multiple gradient heating steps and takes tens of minutes, achieving instantaneous pattern fixation, effectively preventing deformation problems such as sagging and diffusion, shortening the production cycle, and simplifying the production line layout.

[0042] The UV-curable silver paste of this application, through its specific rheological properties, fine powder characteristics, and rapid photocuring capability obtained by formulation design, is not only suitable for traditional screen printing, but also compatible with various patterning processes such as transfer printing, inkjet printing, tracing, or stencil printing. This provides flexible process options for the manufacture of solar cell electrodes. Regardless of the printing method used, the subsequent UV irradiation step can replace the time-consuming multiple heat drying steps, thereby simplifying the production process and improving efficiency.

[0043] The next step after preliminary curing is sintering to obtain the grid lines. The solar cells, after preliminary UV curing, are fed into a high-temperature sintering furnace (e.g., at 720-780°C). The organic polymer network formed by preliminary curing undergoes thermal decomposition and complete combustion at high temperatures. Next, silver powder particles melt on their surfaces, interconnect, and densify at high temperatures, forming a continuous metallic conductive network. Simultaneously, glass powder softens and flows, reacting with the surface of the solar cell (such as silicon and passivation layers) to form strong ohmic contacts and act as a bond. This step depends on the integrity of the film layer after preliminary curing and the compatibility of the organic component content in the silver paste formulation with the sintering process. The silver paste provided in this application, due to its precisely controlled organic component content and the selection of materials that are easily decomposed at high temperatures, ensures that organic matter is thoroughly removed during sintering, avoiding the formation of harmful voids in the conductive grid lines due to gas generation from residual decomposition, thereby ultimately obtaining grid line electrodes with high density and low contact resistance. The grid line fabrication method of this application involves three steps: "screen printing - rapid preliminary curing with ultraviolet light - high-temperature sintering". By introducing the ultraviolet curing step as an efficient and clean means of fixing the pattern, the lengthy and energy-consuming drying process in traditional processes is avoided while ensuring the final electrode performance. Specific Implementation The following will further describe some specific implementation methods and provide a more detailed explanation of the technical solution of this application. The prepared gate lines were tested, including: UV curing condition, gate line density, contact resistance, and EL conversion efficiency. The test results are shown in Table 1. The gate line density was determined using microscopic image analysis, and the specific detection steps are as follows: By cutting the cross-section of the grid line, taking cross-sectional images using a scanning electron microscope (SEM) or metallographic microscope, and using image analysis software to calculate the "area ratio of dense region", the density is approximately replaced (because the holes inside the grid line are mostly open / closed holes, the cross-sectional image can reflect the overall density).

[0045] Specific steps: (1) Sample preparation Cut a 1cm x 1cm section from the solar cell containing the grid lines and embed it with resin (such as epoxy resin) to ensure that the grid lines are fixed in place and do not fall off. Grinding and polishing: Use metallographic sandpaper (400#→800#→1500#→3000#) to gradually grind the inlaid sample until the cross-section of the grid lines is exposed; finally, polish with diamond polishing paste (0.5μm grit) to ensure that the cross-section is flat and free of scratches; Etching treatment: Immerse the cross-section in diluted nitric acid (5% volume concentration) for 10-15 seconds to remove the oxide layer produced by polishing, making the dense area and the pores more clearly contrasted.

[0046] (2) Image acquisition Use a SEM (500-2000x magnification) or a metallurgical microscope (200-500x magnification) to capture cross-sectional images of the grid lines; Take three cross-sections at three different locations for each grid line (both ends + the middle), and take two images at each location to ensure that the entire grid line thickness (typically 10-20 μm) is covered.

[0047] (3) Image analysis Open the image with ImageJ or Photoshop and use the "thresholding" function to distinguish between "dense areas" (silver phase, high grayscale value) and "holes / voids" (low grayscale value). The density is calculated as the ratio of the area of ​​the dense region (S1) to the total area of ​​the raster lines in the image (Stotal): ρ = S1 / Stotal × 100%.

[0048] Regarding the selection of magnification, when the fine grid line width is <50μm, a magnification of 500x can clearly observe holes larger than 1μm; if it is necessary to detect tiny holes (<0.5μm), a magnification of 2000x is required. To avoid a polishing illusion, excessive polishing can cause metal flow on the grid surface, masking the actual holes. Therefore, the polishing intensity must be controlled. For statistical representativeness, at least 5 grid lines should be analyzed for each batch of samples, and 3 cross sections should be analyzed for each grid line to avoid bias in results caused by local holes.

[0049] Example 1 This embodiment provides a UV-curable silver paste, the composition of which is: 85% silver powder (mass percentage, the same below), 10% UV-curable organic component (of which 6% is photocurable resin, 1% is photoinitiator, and 3% is reactive diluent), 3% glass powder, and 2% additives. Figure 1 The process flow shown is as follows: Silver powder is pretreated to achieve a D50 particle size of approximately 0.5 μm; organic components are mixed uniformly; using a planetary mixer, 50% of the silver powder is first added and mixed with all organic components, then the remaining silver powder is added, and finally glass powder and additives are added, stirring and dispersing evenly; then, it is refined to a fineness ≤5 μm using a three-roll mill, and after vacuum degassing, the finished silver paste is obtained. The viscosity of this silver paste is 15134 Pa·s. For application, follow... Figure 2 The process involves sequentially screen printing the front main grid, fine grid, and back main grid, fine grid, onto the TOPCon solar cell. After each screen printing step, the cell is irradiated under specific ultraviolet light for 3-5 seconds for preliminary curing. Finally, the grid lines are sintered at approximately 750°C. Test results show that the obtained grid line density is 95%, the contact resistance is 4.8 mΩ, the cell's EL image is bright, and the conversion efficiency reaches 26.41%.

[0050] Example 2 The silver paste composition of this embodiment is: 82.5% silver powder, 10% UV-curable organic components (6% UV-curable resin, 1% photoinitiator, 3% reactive diluent), 5.5% glass powder, and 2% additives. The preparation and application processes are the same as in Example 1. The viscosity of the obtained silver paste is 15568 Pa·s. After fabricating the grid lines using the same process, the grid line density was measured to be 94%, the contact resistance was 4.2 mΩ, and the cell conversion efficiency was 26.33%.

[0051] Example 3 The silver paste composition of this embodiment is: 80% silver powder, 10% UV-curable organic components (6% UV-curable resin, 1% photoinitiator, 3% reactive diluent), 8% glass powder, and 2% additives. The preparation and application processes are the same as in Example 1. The viscosity of the obtained silver paste is 16195 Pa·s. After fabricating the grid lines using the same process, the grid line density was measured to be 97%, the contact resistance was 3.9 mΩ, and the cell conversion efficiency was 26.25%.

[0052] Example 4 The silver paste composition of this embodiment is: 87% silver powder, 7% UV-curable organic components (4% UV-curable resin, 1% photoinitiator, 2% reactive diluent), 5% glass powder, and 1% additives. The preparation and application processes are the same as in Example 1. The viscosity of the obtained silver paste is 23187 Pa·s. After fabricating the grid lines using the same process, the grid line density was measured to be 97%, the contact resistance was 4.3 mΩ, and the cell conversion efficiency was 26.74%.

[0053] Example 5 The silver paste composition of this embodiment is: 87% silver powder, 8% UV-curable organic components (5.5% UV-curable resin, 0.5% photoinitiator, 2% reactive diluent), 4% glass powder, and 1% additives. The preparation and application processes are the same as in Example 1. The viscosity of the obtained silver paste is 21761 Pa·s. After fabricating the grid lines using the same process, the grid line density was measured to be 96%, the contact resistance was 4.7 mΩ, and the cell conversion efficiency was 26.59%.

[0054] Example 6 The silver paste composition of this embodiment is: 88% silver powder, 7.5% UV-curable organic components (5% UV-curable resin, 0.5% photoinitiator, 2% reactive diluent), 5% glass powder, and 1.5% additives. The preparation and application processes are the same as in Example 1. The viscosity of the obtained silver paste is 22598 Pa·s. After fabricating the grid lines using the same process, the grid line density was measured to be 98%, the contact resistance was 4.3 mΩ, and the cell conversion efficiency was 26.91%.

[0055] Comparative Example 1 The silver paste composition of this comparative example is: 85% silver powder, 10% UV-curable organic components (8% UV-curable resin, 2% photoinitiator, 0% reactive diluent), 3% glass powder, and 2% additives. The preparation process is the same as in Example 1, but because the reactive diluent content in the organic components is 0%, the system viscosity is higher. The viscosity of the obtained silver paste is 28769 Pa·s. The application process is the same as in Example 1, with surface drying after UV curing. After high-temperature sintering, although the grid line density (95%) and contact resistance (4.8 mΩ) are acceptable, the battery conversion efficiency is 25.92%, lower than that of the example.

[0056] Comparative Example 2 The silver paste composition of this comparative example is: 80% silver powder, 15% UV-curable organic components (8% UV-curable resin, 2% photoinitiator, 5% reactive diluent), 3% glass powder, and 2% additives. The preparation and application process are the same as in Example 1. The resulting silver paste has a viscosity of 12680 Pa·s and is surface-dry after UV curing. After high-temperature sintering, the grid line density is 91%, the contact resistance is 5.0 mΩ, and the cell conversion efficiency is 25.73%, all of which are inferior to those of the example.

[0057] As can be seen from the foregoing, this application provides an ultraviolet light curable silver paste, its preparation method, and a grid line fabrication method, which solves the problems of long production lines, low efficiency, and grid line quality defects caused by the need for multiple drying processes in existing TOPCon solar cell silver pastes.

[0058] The core of this application lies in providing a UV-curable silver paste with specific components. This silver paste comprises 75%-88% silver powder, 6%-10% UV-curable organic components, 2.5%-8% glass powder, and 1.0%-4.5% additives by weight. The UV-curable organic components consist of a photocurable resin (65%-75%), a photoinitiator (12%-18%), and a reactive diluent (10%-20%), with this ratio balancing the compatibility of rapid photocuring and high-temperature sintering. The D50 particle size of the silver powder is controlled between 0.3μm and 0.8μm, with over 90% of the particles being smaller than 1μm. This particle size characteristic, combined with a high proportion (80%-95%) of spherical morphology, helps improve the printability of the paste and the density of the grid lines after sintering. The photocurable resin can be an acrylate such as HDDA, TPGDA or PEGDA, the reactive diluent can be IBOA or CHA, the photoinitiator can be an α-hydroxy ketone, the glass powder can be one or more oxides such as SiO2 and B2O3, and the additives include polycarboxylate dispersants, silicone defoamers and acrylate copolymer leveling agents.

[0059] This application also provides a method for preparing the aforementioned silver paste, comprising: pretreatment of silver powder by air jet milling and ultrasonic milling, followed by classification and sieving; preparation of organic components by mixing photocurable resin, photoinitiator, and reactive diluent; stepwise mixing in a planetary mixer in the following order: first adding a portion of the silver powder and all the organic components, then adding the remaining silver powder, and finally adding glass powder and additives; and finally grinding the initial mixture to refine it (fineness ≤ 5 μm) and degassing it under vacuum. The rotation and revolution speeds of the planetary mixer are controlled at 1500-2500 r / min and 300-500 r / min, respectively.

[0060] Based on the silver paste, this application further provides a method for fabricating grid lines, comprising: screen printing the silver paste onto the electrode area of ​​the battery cell; using ultraviolet light irradiation for 3-5 seconds for preliminary curing instead of traditional drying; and finally performing high-temperature sintering to form the final grid lines.

[0061] Through the above technical solution, this application realizes the replacement of minute-level multi-stage thermal drying with second-level ultraviolet curing. While shortening the production line and improving production efficiency, it ensures high density and low contact resistance of the grid lines after sintering by controlling the content of organic components and optimizing the characteristics of silver powder, thus providing an efficient electrode preparation solution for TOPCon solar cells.

[0062] The above is only one specific implementation of this application, and any other improvements made based on the concept of this application shall be considered within the scope of protection of this application.

Claims

1. A light-curable silver paste, characterized in that, It consists of the following components by mass percentage: Silver powder 75%-88% UV-curable organic components: 6%-10% Glass powder 2.5%-8% Additives 1.0%-4.5% The UV-curable organic component consists of a photocurable resin, a photoinitiator, and an active diluent. The D50 particle size of the silver powder particles is in the range of 0.3μm-0.8μm, and more than 90% of the particles have a particle size of less than 1μm.

2. The photocurable silver paste according to claim 1, characterized in that, Spherical silver powder accounts for 80%-95% of the total mass of silver powder.

3. The photocurable silver paste according to claim 1, characterized in that, The UV-curable organic component consists of the following components by mass percentage: UV-cured resin 65%-75% Photoinitiator 12%-18% 10%-20% reactive diluent.

4. The photocurable silver paste according to claim 3, characterized in that, The photocurable resin is selected from one or more of the following materials: 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, or polyethylene glycol diacrylate.

5. The photocurable silver paste according to claim 4, characterized in that, The reactive diluent is isoborneol acrylate or cyclohexyl acrylate, and the photoinitiator is an α-hydroxy ketone photoinitiator.

6. The photocurable silver paste according to claim 1, characterized in that, The glass powder is selected from one or more of the following materials: SiO2, B2O3, Bi2O3, ZnO, TiO2, MgO, Li2O or Al2O3.

7. The photocurable silver paste according to claim 1, characterized in that, The additives include dispersants, defoamers, and leveling agents. The dispersant is a polycarboxylate, the defoamer is an organosilicon, and the leveling agent is an acrylate copolymer.

8. A method for preparing a photocurable silver paste, characterized in that, include: Silver powder pretreatment includes feeding high-purity spherical silver powder into an air jet mill and grinding it under a pressure of 0.6MPa-0.8MPa to obtain primary ground silver powder. The primary ground silver powder is then added to an ultrasonic mill for ultrasonic grinding, and subsequently collected by passing it through 5μm, 2μm, and 1μm sieves. Preparation of UV-curable organic components: Weigh out the photocurable resin, photoinitiator, and reactive diluent according to the proportion, and mix them evenly to obtain a transparent and uniform UV-curable organic component; Add the ingredients in the following order and mix them together: a) First add 50-60% of the total silver powder, then add all the UV-curable organic components, and stir to initially wet and disperse the silver powder; b) Add the remaining silver powder and continue stirring for 10-15 minutes; c) Add glass powder, dispersant, defoamer, and leveling agent in sequence, and stir until each component is evenly dispersed to obtain the initial silver paste; The initial silver paste is ground and refined to a fineness of ≤5μm, and then vacuum degassing is performed to obtain photocurable silver paste.

9. The method for preparing photocurable silver paste according to claim 8, characterized in that, In the mixing step, a planetary mixer is used, with the impeller speed ranging from 1500 r / min to 2500 r / min and the revolution speed ranging from 300 r / min to 500 r / min.

10. A method for fabricating grid lines, comprising using the photocurable silver paste as described in any one of claims 1-7, characterized in that, Includes the following steps: Photocurable silver paste is printed onto the front or back electrode area of ​​the solar cell using screen printing, transfer printing, inkjet printing, tracing, or stencil printing processes. Preliminary curing is performed using ultraviolet light irradiation; After initial solidification, sintering is performed to obtain grid lines.

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