Battery piece grid line preparation method and battery piece

Abstract

The invention relates to a method for preparing a grid line of a battery piece, which is characterized in that a layer of polymer solution capable of flowing and extending is coated on a mold, and the surface of the mold is provided with a convex structure completely corresponding to a pattern of the grid line of the battery piece. After the polymer solution is cured, a coating with a groove structure is formed, and the grooves are filled with conductive paste. And then, transferring the polymer coating coated with the conductive slurry to the upper surface and the lower surface of the battery piece by adopting a transfer printing technology, and realizing accurate transfer printing of the grid line by accurately regulating and controlling transfer printing parameters. A photocuring technology can be introduced in the transfer printing process, and the conductive slurry is rapidly cured through ultraviolet irradiation. A high-precision mold is adopted to ensure the precision of the size and the shape of the grid line, the functional requirements of different grid line areas are met through formula adjustment and a step-by-step coating technology, the traditional preparation process is simplified, the production efficiency is improved, the production cost is reduced, the electrode structure is optimized, and the production cost is reduced. And the current collection efficiency and the overall performance of the photovoltaic cell are improved.

Description

Technical Field

[0001] The present application relates to the technical field of solar cells, and in particular to a method for preparing grid lines of a solar cell and a solar cell. Background Art

[0002] As the core carrier for building a new power system, the photovoltaic industry has ushered in explosive growth. As the core component of the photovoltaic system, crystalline silicon solar cells currently occupy more than 90% of the global market share, and their performance improvement is of key significance to the development of the industry. Electrode grid lines serve as the key channels for battery charge transfer and directly affect the battery's photoelectric conversion efficiency and output performance. Among the current mainstream silver paste grid line preparation processes, screen printing technology occupies a dominant position due to its mature process system. It realizes grid line formation through four independent processes (back main / fine grid line printing, front main / fine grid line printing) combined with a drying-sintering process. However, this technical system faces multiple technical bottlenecks: First, due to the coupling effect of screen aperture and printing pressure parameters, the grid line width is generally greater than 35μm, and the aspect ratio is difficult to break through, resulting in shading loss and increased series resistance; second, multiple printing processes cause the equipment footprint to expand, the single-machine production capacity is less than 1200 pieces / hour, and the cost of screen consumables accounts for 15%-20%; third, the silver paste utilization rate during the printing process is less than 70%, and the printing accuracy is significantly affected by the attenuation of screen tension. When the screen is used more than 5000 times, the line width fluctuates by ±5μm; fourth, the energy consumption of the drying and curing process accounts for a high proportion of the total energy consumption of the production line, and multiple thermal shocks can easily cause hidden cracks in silicon wafers. Although the industry has attempted to introduce alternative technologies such as inkjet printing and flexographic printing, they all face new challenges, such as difficulty controlling the rheological properties of silver paste and increased electrode contact resistance. Therefore, developing high-precision, low-loss, and high-efficiency gate line forming technology, achieving line widths ≤ 20μm, reducing the number of process steps to less than two, and increasing silver paste utilization to over 85%, has become one of the paths to driving the development of photovoltaic cells. Summary of the Invention

[0003] The purpose of this application is to provide a method for preparing solar cell grid lines based on a coating, transfer, and water dissolution process. This process can simultaneously transfer the main grid and fine grid lines on the front and back sides, replacing traditional screen printing and achieving adjustable high-resolution grid line preparation. Depending on the requirements for the front and back grid lines, high-resolution conductive grid lines with an aspect ratio greater than 1 (up to 3) and a fine grid line width of 2-15μm can be prepared. Using polymer coatings such as PVA as transfer carriers and combining them with micro-nanofabrication technologies not only simplifies the preparation process and reduces costs, but also improves production efficiency and environmental friendliness.

[0004] The object of the present application is achieved through the following technical solution: the method for preparing the grid lines of a cell of the present application comprises: coating a polymer solution on a mold, wherein the mold comprises protrusions corresponding to the grid line pattern of the cell; curing the polymer solution to obtain a polymer coating having grooves; filling the grooves of the polymer coating with a conductive paste; With the side coated with the conductive paste facing the battery cell, the upper and lower surfaces of the battery cell are respectively covered with the polymer coating after the conductive paste is filled; Transfer the conductive paste in the groove to the upper and lower surfaces of the battery cell.

[0005] In one embodiment, during the hot pressing transfer process, the applied pressure is in the range of 1-15 MPa, the temperature is in the range of 80-180° C., and the duration is in the range of 0.1-10 min.

[0006] In one embodiment, light irradiation is performed during the transfer process, and the conductive paste is cured by light curing while being transferred.

[0007] In one embodiment, the protrusion includes a first protrusion corresponding to the main grid line and a second protrusion corresponding to the fine grid line, the first protrusion is used to form a first groove in the polymer coating, and the second protrusion is used to form a second groove in the polymer coating, the width of the first protrusion is in the range of 20-300μm, the height of the first protrusion is in the range of 10-50μm, the width of the second protrusion is in the range of 2-40μm, and the height of the second protrusion is in the range of 5-20μm.

[0008] In one embodiment, during the process of filling the groove of the polymer coating with the conductive paste, the first groove and the second groove are filled with different conductive pastes, and the second groove is filled after the first groove is filled with the conductive paste.

[0009] In one embodiment, a roller pressing method is used to simultaneously perform micro-nano transfer printing on the upper and lower surfaces of the battery cell.

[0010] In one embodiment, the method further comprises the step of removing the polymer coating.

[0011] In one embodiment, the polymer includes one or more of PVA, PVP, PEO, and PEG, and the polymer coating is removed by dissolving in an aqueous solution.

[0012] In one embodiment, the conductive paste is one of silver paste, aluminum paste, copper paste, silver-coated copper paste, chromium paste, tin paste, indium paste, nickel paste, titanium paste or tantalum paste, silver-coated copper, silver-coated aluminum, and silver-coated nickel.

[0013] In one embodiment, the method further includes a step of sintering the transferred conductive paste.

[0014] In one embodiment, the grid line shape is one or more combinations of an isosceles triangle, an isosceles trapezoid, an ellipse, a hexagon, a right-angled trapezoid, or a rectangle.

[0015] In one embodiment, the groove has an aspect ratio greater than 1, and a bottom width in the range of 2-40 μm.

[0016] In one embodiment, the step of forming the mold is further included, specifically comprising: On a hard substrate, a hard mold having protrusions corresponding to the grid line pattern of the cell is formed by removing material; Alternatively, a soft mold having protrusions corresponding to the grid line pattern of the cell is formed by embossing, removing or template curing; Alternatively, a soft mold is first made, and then a metal mold with protrusions corresponding to the grid line pattern of the cell is made by electroplating.

[0017] In addition, the present application also provides a battery cell, including grid lines on the front and back sides, and the grid lines on the front and back sides are prepared by the aforementioned battery cell grid line preparation method.

[0018] Compared with the prior art, this application has the following beneficial effects: This application achieves micron-level precision control of electrode patterns through coating and transfer technology. The width of fine grid lines can be as low as 15μm or less, preferably controlled within the range of 2-15μm, with an aspect ratio greater than 1, exceeding the limit of traditional screen printing technology. The introduction of polymer solutions such as PVA as transfer media, combined with precision molds and micro-nano embossing / transfer technology, greatly simplifies the preparation steps, reduces intermediate links, and makes the entire preparation process smoother and more efficient. Materials such as PVA are not only low-cost and easy to obtain, but their solubility also reduces waste generation in the production process, effectively reducing material waste. PVA film can be dissolved under mild conditions, is easy to recycle and process, reduces the emission of harmful substances, conforms to the concept of green manufacturing, and contributes to sustainable development.

[0019] In addition, the application of the roller pressing method realizes the synchronous transfer of the upper and lower surfaces of the battery cell, further shortening the production cycle, thereby improving the overall production efficiency. At the same time, this application allows the selection of conductive pastes with different formulations for the main grid and fine grid according to demand, while ensuring excellent conductive performance, providing greater cost control space, and reducing the overall production cost of the battery cell. The transfer carrier and the conductive paste have good compatibility and moderate adhesion, ensuring the precise positioning of the conductive paste during the transfer process and close fit with the silicon wafer substrate, avoiding the problem of falling off or poor contact, and enhancing the stability and durability of the battery cell.

[0020] Furthermore, the high transparency of the PVA film can be utilized to introduce a photocuring step, using ultraviolet light irradiation to complete the rapid curing of the conductive paste. Combined with the transfer process, the process time can be shortened. The technical solution of this application is not only suitable for the production of standard-sized battery cells, but its high flexibility and scalability also means that the grid line pattern, size and material can be easily adjusted according to market demand to meet diversified and customized product needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of a method for preparing a grid line of a cell in one embodiment of the present application; Figure 2 This is a structural diagram of a method for preparing a grid line of a cell in one embodiment of the present application; Figure 3 It is a structural diagram of a method for preparing a cell grid line in another embodiment of the present application.

[0022] Explanation of reference numerals: 100, polymer coating; 200, conductive paste; 300, battery cell. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are described in detail below in conjunction with the accompanying drawings. It will be understood that the specific embodiments described herein are only used to explain the present application, rather than to limit the present application. It should also be noted that, for ease of description, only some, rather than all, structures related to the present application are shown in the accompanying drawings. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0024] As used herein, the terms "comprise," "comprising," and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0025] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0026] In the field of solar cell preparation that pursues high efficiency, environmental protection and cost control, traditional screen printing technology has inherent problems such as resolution limitations, material waste and environmental impact, which prompts the industry to continuously explore more advanced preparation processes. In this context, the present application intends to provide a new method for preparing grid lines of solar cells, which integrates coating, transfer and other technologies to achieve high-precision replication of grid line patterns and low-cost production. By using polymer solutions, especially polyvinyl alcohol (PVA) as a transfer carrier, combined with precision mold design and micro-nano transfer technology, not only can the front and back grid lines of the solar cell be transferred up and down at the same time, but the resolution of the grid lines can also be improved, and the width of the fine grid lines can be achieved to a level of less than 15μm and an aspect ratio greater than 1. The following will specifically introduce the steps, technical features and beneficial effects of this method for preparing grid lines of solar cells. The specific process of the solar cell is not limited, and it is applicable to different specific types of solar cells, including but not limited to HJT (heterojunction), TOPCon, BC, and perovskite / silicon stacked solar cells, which can improve the overall conversion efficiency and meet the needs of the photovoltaic market. Please refer to Figure 1 A method for preparing a cell grid line in a preferred embodiment of the present application includes: first, applying a layer of a flowable and extensible polymer solution on a mold, the surface of the mold having a protruding structure that completely corresponds to the cell grid line pattern. In this step, a polymer material such as PVA (polyvinyl alcohol), PVP (polyvinyl pyrrolidone), PEO (polyethylene oxide) or PEG (polyethylene glycol) can be selected as the main component of the polymer solution. These polymer materials not only have good film-forming properties and solubility, ensuring that the conductive paste 200 can closely adhere to the silicon wafer surface during the transfer process, but can also be easily dissolved after the transfer is completed, thereby realizing the transfer of the conductive paste 200 from the polymer coating 100 to the silicon wafer, achieving the purpose of preparing multiple grid lines at one time.

[0027] Specifically, a flat coating method can be used to evenly coat PVA or other materials directly on the mold. By drying or other curing methods, the polymer solution is formed into a whole, and a film with a thickness of 10-50 μm is stably prepared. In addition, the film can be flexible, so that the film has a certain mechanical strength while maintaining good flexibility and plasticity, forming a polymer coating 100 with a groove structure corresponding to the protrusions of the mold. Please refer to further Figure 2 and Figure 3Then, these grooves are filled with a conductive paste 200. For example, a highly conductive silver paste, silver-coated copper paste, aluminum paste, etc. can be selected to ensure the excellent performance of the electrode. Specifically, the conductive paste is one of silver paste, aluminum paste, copper paste, silver-coated copper paste, chromium paste, tin paste, indium paste, nickel paste, titanium paste or tantalum paste, silver-coated copper, silver-coated aluminum, and silver-coated nickel. Next, the polymer coating 100 coated with the conductive paste 200 is placed with the conductive paste 200 facing the battery cell 300, and is covered on the upper and lower surfaces of the battery cell 300 respectively. A roller transfer method can be used to achieve precise transfer of the PVA coating by precisely controlling key parameters such as pressure, temperature, and time. Transfer can be performed simultaneously on the upper and lower parts of the battery cell 300, thereby reducing the multiple steps required for traditional screen printing. In a specific embodiment, through transfer technology, the PVA grooves coated with silver paste can fit tightly with the silicon wafer. Under the action of heating or light curing, the conductive paste 200 quickly solidifies and forms electrode grid lines with a specific pattern. This process not only realizes the efficient preparation of multiple grid lines at one time, but also through precise control of transfer parameters, it can also effectively adjust the size, shape and distribution of the grid lines, thereby further optimizing the electrode structure, reducing ohmic loss, and improving the current collection efficiency and overall performance of the photovoltaic cell.

[0028] By simultaneously performing the transfer process on the top and bottom sides of the silicon wafer, combining polymer carrier-assisted transfer with photocuring technology, the goal of producing multiple gate lines in a single step was achieved. During this process, water-soluble polymer materials such as PVA, with their excellent solubility properties, serve as transfer carriers to achieve the gate line transfer process, enabling the conductive paste to be accurately and securely transferred to the silicon wafer surface and easily removed. The simultaneous transfer of the top and bottom sides of the silicon wafer allows the production of the main fine gate lines on both the front and back sides to be completed in a single step, greatly simplifying the traditional preparation process and improving production efficiency.

[0029] During the hot-press transfer process, a series of key process parameters were carefully controlled to ensure optimal transfer results. Experiments revealed that the applied pressure was kept within a range of 1 to 15 megapascals (MPa). This pressure range ensures close contact between the polymer carrier and the silicon wafer while avoiding material damage caused by excessive pressure. The transfer temperature was set between 80 and 180 degrees Celsius (°C), a temperature range sufficient to soften the polymer carrier and facilitate effective transfer of the conductive paste 200 while preventing performance degradation of the silicon wafer due to excessive temperatures. Furthermore, the transfer duration was strictly controlled between 0.1 and 10 minutes (min), ensuring a sufficient transfer process while improving production efficiency and avoiding unnecessary energy consumption. This series of meticulous parameter adjustments ensures the efficiency, stability, and controllability of the hot-press transfer process.

[0030] In order to further ensure the transfer effect and improve the stability, a light irradiation step can be introduced during the transfer process to cure the conductive paste 200 by light curing while transferring (specifically, attaching Figure 3 ). A special photocurable conductive paste 200 is selected, and some photocurable components are added to the conductive paste 200 so that after being exposed to light, specifically, the paste can quickly undergo a chemical reaction under the irradiation of ultraviolet light, and the fluidity of the paste is greatly reduced, thereby achieving rapid curing at room temperature, so that it can be more stably retained in the designed position in subsequent steps. This method can fully utilize the high transparency of the polymer coating formed by materials such as PVA, PVP, PEO, PEG, etc., so that the ultraviolet light can penetrate the polymer coating and directly act on the conductive paste 200 underneath. In actual operation, an ultraviolet lamp is used to irradiate the conductive paste 200 in the polymer coating, and the irradiation time is controlled between 5 and 30 seconds. In this process, not only is the curing of the conductive paste 200 completed, but the overall process time is shortened, further improving production efficiency. Compared with the thermal curing method, the photocuring technology does not require a long heating process, which can further reduce energy consumption and time waste.

[0031] A specific implementation involves irradiating the conductive paste 200 with a UV light source while the roller press performs the transfer. This simultaneous transfer and photocuring process not only simplifies the process flow but also improves production continuity and stability. After photocuring, the conductive paste 200 has formed a preliminary electrode structure. Sintering (heating to a certain temperature) is then performed to further enhance the electrode's conductivity and adhesion, ensuring the quality and reliability of the cell grid lines.

[0032] Specifically, the protrusion structure is divided into two categories: one is the first protrusion corresponding to the main grid line, and the other is the second protrusion matching the fine grid line. After the polymer coating 100 is cured and peeled off, corresponding first grooves and second grooves are formed on the coating surface respectively. The width of the first protrusion is precisely controlled within the range of 20 to 300 microns, and the height is between 10 and 50 microns, adapting to the size and distribution of the main grid line and the fine grid line, ensuring effective conduction of current while reducing resistance loss. In contrast, the width of the second protrusion is narrower, ranging from 2 to 40 microns, and the height is between 5 to 20 microns, which helps the fine grid line to distribute the photocurrent more evenly and improve the light capture efficiency of the battery. In order to ensure the accurate replication of the conductive grid line during the transfer process, the mold manufactured using high-precision processing technology can ensure that the size and shape of the protrusion structure are transferred during the transfer, which has a direct impact on maintaining the geometric accuracy of the grid line, reducing error accumulation and ultimately reducing the ohmic loss of the electrode grid line. The high precision of the mold also means that a high degree of consistency can be maintained in mass production, which is crucial to improving the overall quality and reliability of photovoltaic cells.

[0033] Since the method of first forming a groove and then filling it with a conductive paste for transfer printing is adopted, and the shape of the protrusion can be selected as needed, the shape of the grid line is one or more combinations of an isosceles triangle, an isosceles trapezoid, an ellipse, a hexagon, a right-angled trapezoid or a rectangle. When the grid line has a beveled edge, more light irradiated on the grid line will be reflected toward the cell, thereby improving light utilization. Therefore, the grid line preparation method of the present application can more easily achieve the preparation of grid lines with improved light utilization. In addition, compared with the screen printing method, the aspect ratio of the groove of the present application is greater than 1, and the bottom width is in the range of 2-40μm, which can achieve low-cost high aspect ratio grid line preparation.

[0034] Furthermore, by adjusting the conductive paste 200 formula and combining it with advanced coating technology to meet the specific requirements of different busbar characteristics, a more flexible manufacturing strategy is achieved. By utilizing a barrier for step-by-step coating, conductive paste 200 with varying performance characteristics can be used for busbars of varying sizes. For example, for busbars requiring higher conductivity, a paste with a higher silver content can be used; whereas for finer busbars, greater emphasis may be placed on the paste's fluidity and adhesion to ensure good coverage and connectivity. Targeted formulation adjustments and optimized coating processes optimize conductivity and enhance the photovoltaic cell's photoelectric conversion efficiency.

[0035] During the preparation of the polymer coating 100, a refined filling strategy can be adopted for the first and second grooves preset on its surface. Instead of simply using the same conductive paste 200 to fill all grooves, different conductive pastes 200 are selected and filled according to the specific needs of the main fine grid lines and the auxiliary grid lines or the grid lines in different regions. Specifically, a specific conductive paste 200 is first filled into the first groove. The paste formula is optimized to meet the special requirements of the conductive performance, adhesion, etc. of the grid lines corresponding to the first groove. After the conductive paste 200 in the first groove reaches the preset processing state, it turns to the second groove and fills it with another conductive paste 200 designed for its specific needs. The practice of filling different conductive pastes 200 in steps can be based on a comprehensive consideration of the current transmission characteristics, lighting conditions and mechanical stress distribution of different grid line areas in the photovoltaic module. By specifically adjusting the conductive paste 200 formula for the main fine grid lines, that is, using different conductive paste 200 formulas, it is possible to more accurately match the functional requirements of each grid line area, thereby effectively improving the overall conductive performance and photoelectric conversion efficiency of the photovoltaic module. By customizing the conductive paste 200 formula, the conductivity requirements of different grid line areas can be met in a targeted manner, resistance loss can be reduced, current transmission efficiency can be improved, and precise matching of grid line requirements with the characteristics of the conductive paste 200 can help maximize light capture and conversion efficiency, thereby improving the power generation capacity of the entire photovoltaic module. The step-by-step coating technology allows for flexible adjustment of the conductive paste 200 formula in different areas on the production line to adapt to diverse product needs while maintaining high production efficiency.

[0036] A roller pressing method is adopted to perform synchronous micro-nano transfer processing on the upper and lower surfaces of the battery cell 300 at the same time. Through roller transfer technology, the precise transfer of patterns or functional layers on the upper and lower surfaces of the silicon wafer can be completed simultaneously in a single operation, that is, in a continuous process flow, replacing the previous cumbersome and time-consuming four-step screen printing process. The traditional four-step screen printing process requires multiple printing, drying and curing steps for the front and back of the battery cell 300 respectively, which not only has low production efficiency, but also increases material waste and production costs. In contrast, the integrated transfer method using roller transfer technology has achieved an improvement in production efficiency, reduced process steps, and shortened the overall production cycle. In addition, roller transfer technology can also ensure the consistency and high precision of the patterns or functional layers on the upper and lower surfaces, which is crucial to improving the photoelectric conversion efficiency and long-term stability of photovoltaic cells.

[0037] The technical solution of this application uses a room-temperature water-soluble transparent polymer film material, such as polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), or polyethylene oxide (PEO). These polymer film materials not only provide necessary protection or auxiliary functions during processing, but also can be easily dissolved in water at room temperature. The use of room-temperature water-soluble transparent polymer film materials simplifies the removal process of the polymer coating 100, avoiding the use of high-cost and environmentally unfriendly demolding methods such as high temperature or chemical solvents, thereby significantly reducing the demolding cost. Furthermore, the formula of the conductive paste 200 for the main fine grid lines is optimized. As a key material in the manufacture of photovoltaic cells 300, the performance of the conductive paste 200 directly affects the photoelectric conversion efficiency and production cost of the cell. By adjusting the formula of the conductive paste 200, the utilization rate of the silver paste can be improved, effectively reducing material waste in process steps such as printing and curing, helping to reduce overall production costs and also helping to improve the conductive performance and stability of the cell 300. The simplified demolding steps and the optimized silver paste formula jointly promote the smoothness of the overall production process. The optimized conductive paste 200 formula not only reduces material waste, but also helps to improve the conductivity and stability of the battery cell 300.

[0038] Specifically, the polymer can be preferably polyvinyl alcohol (PVA), whose coating can be effectively removed by dissolving in an aqueous solution. Based on a novel mechanism of hydrogen bonding between components in the metal paste and the PVA material, the non-reactivity and weak adhesion between PVA and the conductive paste 200 binder and solvent are revealed, thus establishing PVA as an ideal carrier material for conductive paste 200 transfer. As a biodegradable and environmentally friendly material, PVA exhibits a low environmental impact, highly consistent with the concept of contemporary green manufacturing. PVA has a glass transition temperature between 75°C and 85°C. When heated above 100°C in air, it gradually discolors and becomes brittle. This physical property ensures that the PVA maintains a stable form after transfer, with no rebound and excellent shape retention. With sophisticated hot pressing equipment, the molding accuracy of the PVA transfer coating can be precisely controlled, allowing for the careful design of the grid line size and shape. Notably, PVA exhibits excellent insolubility in a variety of organic solvents, including gasoline, kerosene, vegetable oil, benzene, toluene, ethylene dichloride, carbon tetrachloride, acetone, ethyl acetate, methanol, and ethylene glycol. Furthermore, PVA is incompatible with the binder in conductive paste 200 and does not chemically react with it. By adjusting the alcoholysis degree of PVA or adopting a blending modification strategy, its water solubility can be flexibly controlled, achieving rapid dissolution at room temperature and facilitating subsequent processing.

[0039] Specifically, it also includes the step of sintering the transferred conductive paste 200, that is, heating it to a certain temperature. Sintering can effectively promote the fusion of metal particles (such as silver, copper, etc.) in the conductive paste 200 to form a continuous and dense conductor, thereby improving the conductivity of the circuit and reducing resistance and signal loss. Through high-temperature treatment, the organic matter in the conductive paste 200 is removed, reducing deformation and stress concentration caused by mismatch of thermal expansion coefficients, which helps to improve the dimensional stability and thermal stability of the entire electronic component.

[0040] In order to improve the accuracy of the grid line pattern during the transfer process, the present application further optimizes the mold forming steps. The steps of forming the mold specifically include forming a hard mold with protrusions corresponding to the grid line pattern of the cell on a hard substrate by removing material; or forming a soft mold with protrusions corresponding to the grid line pattern of the cell by embossing, removal or template curing; or first making a soft mold and then making a metal mold with protrusions corresponding to the grid line pattern of the cell by electroplating.

[0041] The first type of mold is a hard mold, and the manufacturing method used includes a method of photolithography combined with electroforming replication. First, electron beam lithography (EBL) or laser direct writing is used to make a groove master including a protrusion with a width of 2-40μm on a silicon / glass substrate. The master structure is then copied to a nickel or copper mold through an electroforming process. The accuracy of this method can be controlled within ±0.1μm, which is suitable for mass production. For hard molds, electric spark wire cutting can also be used to directly process the conductive hard mold, and the accuracy can be controlled within ±1 μm. Attention should be paid to the effect of electrode loss on the groove depth. In addition, super-hard alloy milling cutters can be used to process nickel / copper molds. Polishing allowance must be reserved in this method. Hard molds are preferably made using a method of photolithography combined with electroforming replication, followed by milling.

[0042] The second type of module is a soft mold, which is manufactured using an imprinting method. First, a hard master (such as a nickel mold) is made. The master is then pressed into a PET substrate coated with UV glue and demolded after UV curing. This method is efficient, low-cost, and suitable for large-area replication of flexible devices. Laser direct writing combined with UV curing can also be used. Specifically, a groove structure is formed on the PET substrate before curing (the groove structure corresponds to the area where the grid lines are not formed). The depth is precisely controlled by the laser energy and the number of scans, with a resolution of up to 1 μm. UV curing is then performed to form a soft mold. This method does not require a mask and is highly flexible.

[0043] In the third type of method, the mold is a hard-soft combination mold with a metal part and a flexible part. The flexible part is first formed by embossing, removal or template curing, and then the metal layer is electroplated. The mold formed in this way has more precise grid line size during embossing, and in actual operation, the window of process parameters is large, which can reduce the difficulty of production control. This method is the optimal mold formation method.

[0044] In addition, the present application also provides a battery cell 300, including grid lines on the front and back sides, and the grid lines on the front and back sides are prepared by the aforementioned battery cell grid line preparation method.

[0045] The method of the present application, by precisely controlling the rolling parameters (including pressure, time, etc.) and high-precision molds, can accurately control the size and shape of the composite conductive grid lines obtained by transferring polymers such as polyvinyl alcohol (PVA), thereby effectively reducing the ohmic loss of the electrode grid lines. As an eco-friendly and biodegradable material, PVA reduces the negative impact on the environment, and its coating is water-soluble at room temperature, which greatly reduces the cost of the demolding process. By transferring on the upper and lower surfaces of the silicon wafer at the same time, this method completes the four-step process required for traditional screen printing in one step, improving production efficiency and reducing production costs. In addition, the solution of the present application also has the ability to flexibly adjust the formula of the conductive paste 200 for the main grid and fine grid, allowing different conductive paste 200 formulas to be selected according to grid line requirements, and achieved through step-by-step coating technology. This feature helps to further improve the photoelectric conversion efficiency of photovoltaic cells. Thanks to the high transparency of the PVA film, it is possible to use the photocurable conductive paste 200, which only requires 5 to 30 seconds of ultraviolet light exposure to complete the curing, further shortening the process flow and improving the overall production efficiency. The method of the present application is not only simple in process, but also the materials used comply with economic and environmental protection principles, and the overall process cost is relatively low.

Claims

1. A method for preparing a grid line of a battery cell, characterized in that: include: Applying a polymer solution on a mold, wherein the mold includes protrusions corresponding to a grid line pattern of a cell; curing the polymer solution to obtain a polymer coating having grooves; filling the grooves of the polymer coating with a conductive paste; With the side coated with the conductive paste facing the battery cell, the upper and lower surfaces of the battery cell are respectively covered with the polymer coating after the conductive paste is filled; Transfer the conductive paste in the groove to the upper and lower surfaces of the battery cell.

2. The method for preparing a battery grid line according to claim 1, wherein: During the transfer process, the applied pressure is in the range of 1-15 MPa, the temperature is in the range of 80-180° C., and the duration is in the range of 0.1-10 min.

3. The method for preparing a battery grid line according to claim 1, wherein: During the transfer process, light irradiation is performed, and the conductive paste is cured by light curing while being transferred.

4. The method for preparing a cell grid line according to claim 1, wherein: The protrusions include a first protrusion corresponding to the main grid line and a second protrusion corresponding to the fine grid line, the first protrusion is used to form a first groove in the polymer coating, and the second protrusion is used to form a second groove in the polymer coating, the width of the first protrusion is in the range of 20-300μm, the height of the first protrusion is in the range of 10-50μm, the width of the second protrusion is in the range of 2-40μm, and the height of the second protrusion is in the range of 5-20μm.

5. The method for preparing a grid line of a battery cell according to claim 4, characterized in that: In the process of filling the groove of the polymer coating with the conductive paste, the first groove and the second groove are filled with different conductive pastes, and the second groove is filled after the first groove is filled with the conductive paste.

6. The method for preparing a battery grid line according to claim 1, wherein: The roller pressing method is used to simultaneously perform micro-nano transfer on the upper and lower surfaces of the battery cell.

7. The method for preparing a battery grid line according to claim 1, wherein: Also included is the step of removing the polymer coating.

8. The method for preparing a battery grid line according to claim 7, characterized in that: The polymer includes one or more of PVA, PVP, PEO, and PEG, and the polymer coating is removed by dissolving in an aqueous solution.

9. The method for preparing a grid line of a battery cell according to claim 1, characterized in that: The conductive paste is one of silver paste, aluminum paste, copper paste, silver-coated copper paste, chromium paste, tin paste, indium paste, nickel paste, titanium paste or tantalum paste, silver-coated copper, silver-coated aluminum, and silver-coated nickel.

10. The method for preparing a battery grid line according to claim 1, wherein: The method also includes a step of sintering the transferred conductive paste.

11. The method for preparing a grid line of a battery cell according to claim 1, characterized in that: The grid line shape is one or more combinations of an isosceles triangle, an isosceles trapezoid, an ellipse, a hexagon, a right-angled trapezoid or a rectangle.

12. The method for preparing a battery grid line according to claim 1, wherein: The groove aspect ratio is greater than 1, and the bottom side width is in the range of 2-40 μm.

13. The method for preparing a grid line of a battery cell according to claim 1, wherein: The step of forming the mold further comprises: On a hard substrate, a hard mold having protrusions corresponding to the grid line pattern of the cell is formed by removing material; Alternatively, a soft mold having protrusions corresponding to the grid line pattern of the cell is formed by embossing, removal or template curing; Alternatively, a soft mold is first made, and then a metal mold with protrusions corresponding to the grid line pattern of the cell is made by electroplating.

14. A solar cell comprising grid lines on the front and back sides, characterized in that: The grid lines on the front and back are prepared by the method for preparing grid lines of a cell according to any one of claims 1 to 12.

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