Welding method of solar cell

Abstract

The invention relates to a welding method of a solar battery, which comprises the following steps of: providing a battery piece, and arranging a grid line on the side surface of the battery piece; forming an organic solderability preservative film on the side surface of the battery piece, and enabling the organic solderability preservative film to cover the outer surface of the grid line; completely removing the organic solderability preservative film covering the part, needing to be welded with the welding wire, of the grid line, so that the part, needing to be welded with the welding wire, of the grid line is exposed; wherein in the process of removing the organic solderability preservative film at the position, where the welding wire needs to be welded, on the grid line, the temperature of the position, except for the welding wire, on the battery piece is made to be smaller than or equal to 200 DEG C; and the exposed parts on the grid lines are welded and connected with the welding wires. On one hand, the organic solderability preservative film covers the outer surface of the grid line, an anti-oxidation effect can be achieved, and compared with a tin plating process, the production cost is low; and on the other hand, the temperature of the parts except for the welding wire on the battery piece is controlled to be less than or equal to 200 DEG C, and the temperature is relatively low, so that the influence on the performance of an amorphous silicon layer, a silicon substrate and the like of the battery piece can be avoided.

Description

Technical Field

[0001] This application relates to the field of photovoltaic technology, and in particular to a method for welding solar cells. Background Technology

[0002] With the development of photovoltaic technology, solar cells are increasingly widely used in daily life. The methods for forming the grid electrodes of solar cells typically include copper electroplating and screen printing. The main difference between copper electroplating and screen printing lies in the metallization process after depositing the TCO (Transparent Conductive Oxides) conductive layer. Traditional screen printing involves printing conductive paste onto the TCO conductive layer and then curing it to form the grid electrodes. Copper electroplating, on the other hand, is a pressureless contact electrode metallization technology that deposits metallic copper on the surface of the TCO conductive layer through electrolytic reduction of copper ions to create copper grid electrodes. HJT cell grid electrodes obtained using copper electroplating technology can eliminate the dependence on the precious metal silver, achieving a complete replacement for the base metal copper. Furthermore, copper electroplating metallization technology can be completed at 200℃, meeting the low-temperature process requirements for HJT cell manufacturing. In addition, the electrode grid lines produced by copper electroplating are dense and uniform, with widths as low as 20μm or less. Narrower linewidths result in a larger aspect ratio, reducing shading loss and volume resistivity, thereby effectively improving cell conversion efficiency.

[0003] The copper electroplating process for preparing battery electrodes in related technologies mainly includes the following five steps:

[0004] 1. Depositing a Metal Seed Layer: Due to the poor adhesion between copper and TCO thin films, copper cannot be directly plated onto the TCO. Therefore, a metal seed layer (such as copper, nickel, silver, chromium, titanium, or alloys) with a thickness of 100 nm to 1 μm is first deposited on the TCO layer by physical vapor deposition or magnetron sputtering to enhance the adhesion and contact between the subsequent copper gate lines and the TCO. Among these, nickel seed layers are more commonly used due to their high cost-effectiveness, although silver seed layers have the lowest contact resistance and the best adhesion.

[0005] 2. Create a patterned mask: Create a mask with a specified grid electrode opening pattern on the metal seed layer.

[0006] 3. Copper electroplating: Copper electroplating is performed at the openings of the mask to form copper grid electrodes. This process mainly uses direct electroplating or photo-induced electroplating methods.

[0007] 4. Mask stripping: Removes the patterned mask.

[0008] 5. Etching the seed layer: Etching away excess metal seed layer not covered by copper grid lines.

[0009] To improve electrode performance, a protective layer of silver or tin, several hundred nanometers thick, is typically electroplated onto the surface of the formed copper grid lines. This protective layer primarily serves to prevent oxidation and failure of the copper grid lines, and also acts as a brazing layer for subsequent soldering. However, electroplating silver or tin increases the cost of solar cells.

[0010] Based on this, some related technologies have transplanted the OSP (Organic Solderability Preservatives) process from the PCB field to the oxidation protection of copper grid lines in solar cells. Compared to silver or tin protective layers (hundreds of nanometers thick), the thickness of the OSP film formed on the surface of the copper grid lines through the OSP process is, for example, 0.2μm~0.5μm. This means the OSP film is relatively thinner and the raw material cost is lower, which can significantly reduce electrode manufacturing costs. However, the OSP film increases contact resistance, leading to a decrease in the electrical performance and reliability of the solar cell. Summary of the Invention

[0011] Therefore, it is necessary to provide a solar cell welding method that addresses the shortcomings of existing technologies, reduces costs, does not increase contact resistance, and ensures the electrical performance and reliability of solar cells.

[0012] This application provides a method for welding solar cells, the welding method comprising the following steps:

[0013] A battery cell is provided, wherein grid lines are provided on the side of the battery cell;

[0014] An organic solder resist film is formed on the side of the battery cell, such that the organic solder resist film covers the outer surface of the grid line;

[0015] Remove the organic solder resist film covering the area on the grid line where welding wire needs to be welded, so that the area on the grid line where welding wire needs to be welded is exposed; wherein, during the process of removing the organic solder resist film at the area on the grid line where welding wire needs to be welded, the temperature of the part of the battery cell other than the area where welding wire is welded is ≤200℃.

[0016] The exposed portion of the grid line is welded to the welding wire.

[0017] In one embodiment, the step of completely removing the organic solder mask covering the portion of the gate line where welding wire needs to be welded includes:

[0018] The laser is focused on the area on the grid line where the welding wire needs to be welded, so that the organic solder resist film covering the area on the grid line where the welding wire needs to be welded is locally heated to ≥300°C, so that the organic solder resist film is ablated under the irradiation of the laser.

[0019] In one embodiment, the organic solder resist film covering the portion of the grid line where welding wire needs to be welded is locally heated to a temperature controlled to 300°C to 330°C; and / or, the time for which the organic solder resist film covering the portion of the grid line where welding wire needs to be welded is locally heated is controlled to 1 second to 5 seconds.

[0020] In one embodiment, prior to the step of focusing the laser on the portion of the grid line where the welding wire needs to be welded, the method further includes placing the battery cell in an environment with a protective gas that has an anti-oxidation effect.

[0021] And / or, the step of focusing the laser on the part of the grid line where the welding wire needs to be welded specifically includes: introducing a protective gas with anti-oxidation function into the part of the grid line where the welding wire needs to be welded.

[0022] In one embodiment, the step of completely removing the organic solder mask covering the portion of the gate line where welding wire needs to be welded includes:

[0023] At least one of the organic solder resist film covering the area on the grid line where welding wire needs to be welded and the surface of the welding wire is coated with flux.

[0024] In one embodiment, the flux comprises an acidic flux.

[0025] In one embodiment, the acidic flux includes a flux containing a moderately active or strongly acidic substance.

[0026] In one embodiment, the grid line includes a main grid wire; there are multiple main grid wires arranged in parallel with intervals; there are multiple welding wires, each welding wire being welded to each of the main grid wires accordingly;

[0027] The grid line also includes sub-grid wires, and each main grid wire is connected to a plurality of sub-grid wires. The plurality of sub-grid wires are arranged sequentially at intervals along the main grid wires to which they are connected. The extension direction of the main grid wire is set at an angle to the extension direction of the sub-grid wire. The outer surface of the sub-grid wire is covered by the organic solder mask.

[0028] In one embodiment, a plurality of grid lines are provided on both opposite sides of the battery cell;

[0029] The step of completely removing the organic solder resist film covering the parts of the grid lines that need to be welded includes: firstly, simultaneously removing the organic solder resist film covering the parts of the grid lines that need to be welded on one side of the battery cell, and then simultaneously removing the organic solder resist film covering the parts of the grid lines that need to be welded on the other side.

[0030] The step of welding the exposed parts of the grid lines to the welding wires includes: firstly, simultaneously welding each of the grid lines on one side of the battery cell to each of the welding wires, and then simultaneously welding each of the grid lines on the other side to each of the welding wires.

[0031] In one embodiment, the step of forming an organic solder resist film on the side of the battery cell, such that the organic solder resist film covers the outer surface of the grid line, includes:

[0032] The organic solder resist film is formed by spraying or wetting the surface of the grid lines of the battery cell; wherein the thickness of the organic solder resist film is 0.1μm~0.5μm.

[0033] The aforementioned solar cell welding method has two advantages. First, the organic solder resist film covering the outer surface of the grid lines provides oxidation protection, resulting in lower production costs compared to tin plating. Second, removing only a portion of the organic solder resist film from the grid lines, compared to removing all portions, minimizes the impact on the temperature of areas on the cell other than the solder wires. This allows the temperature of areas on the cell other than the solder wires to be controlled, for example, ≤200℃. Completely removing the organic solder resist film from the grid lines prevents incomplete soldering between the grid lines and the solder wires. Furthermore, since the temperature of areas on the cell other than the solder wires is controlled at ≤200℃, the relatively low temperature avoids impacting the performance of the amorphous silicon layer and silicon substrate of the cell. Attached Figure Description

[0034] Figure 1 This is a structural diagram of an organic solder resist film covering the grid lines of a battery cell according to an embodiment of this application.

[0035] Figure 2 for Figure 1 The diagram shows the structure of the battery cell after welding wires onto its grid lines.

[0036] Figure 3 This is a structural diagram of a battery cell with an organic solder resist film covering the grid lines, according to another embodiment of this application.

[0037] Figure 4 for Figure 3 The diagram shows the structure of the battery cell after welding wires onto its grid lines.

[0038] Explanation of reference numerals in the attached figures:

[0039] 10. Solar cell; 11. Busbar; 111. Main busbar; 112. Sub-busbar; 12. Silicon substrate; 13. Amorphous silicon layer; 14. TCO layer; 20. Organic solder mask; 30. Solder wire. Detailed Implementation

[0040] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0041] In related technologies, in order to reduce the cost of anti-oxidation of copper grid lines, thinner OSP film with lower material cost is used. Based on the excellent heat resistance of OSP film, its decomposition temperature usually needs to reach above 300℃, which enables it to effectively protect the copper surface at high welding temperatures and play a good role in preventing oxidation.

[0042] However, as mentioned in the background section, the use of OSP film in solar cells in related technologies increases the contact resistance. This problem arises because the OSP film itself is an insulator. If it is not completely decomposed during the welding process of the copper grid wire and the welding wire, it may increase the contact resistance between the welding wire and the copper grid wire, thereby affecting the performance of the solar cell and reducing the light utilization rate of the solar cell.

[0043] Research has found that the complete decomposition of OSP membranes requires the simultaneous fulfillment of the following conditions:

[0044] Temperature: ≥ 300℃ (decomposition threshold of alkylbenzimidazoles);

[0045] Time: 30 to 120 seconds (adjusted according to film thickness);

[0046] Atmosphere: Inert (N2) or reducing (formic acid vapor) environment to prevent copper oxidation.

[0047] However, for solar cells, especially heterojunction cells or perovskite cells, when the OSP film is removed by decomposing it at a high temperature above 300°C, the temperature drop of the amorphous silicon layer (a-Si:H) is greater than 200°C. When the temperature of the amorphous silicon layer is greater than 200°C, hydrogen may escape, resulting in thermal degradation defects and reducing the performance of the solar cell.

[0048] For the reasons mentioned above, this application provides a welding method for solar cells that can reduce costs, without increasing contact resistance, and ensure the electrical performance and reliability of solar cells.

[0049] It should be noted that the solar cells in this embodiment include, but are not limited to, heterojunction cells, perovskite cells, back contact cells, or passivated contact cells. The specific type can be flexibly adjusted and set according to actual needs, and is not limited here.

[0050] See Figure 1 and Figure 2 or Figure 3 and Figure 4 This application provides a method for welding solar cells according to one embodiment. The welding method includes the following steps:

[0051] Step S100: Provide a battery cell 10, the side of which is provided with grid lines 11.

[0052] Optionally, the material of the grid line 11 may include, but is not limited to, various metals such as copper, aluminum, or gold.

[0053] In this embodiment, copper is preferably used as the material for the grid lines 11, as it has a lower cost. The grid lines 11 are formed on the side of the battery cell 10 by electroplating.

[0054] The number of gate lines 11 is not limited to one, but can be, for example, multiple. The more gate lines 11 there are, the stronger the ability to collect charge carriers will be, which can help improve optical efficiency.

[0055] The solar cell 10 may have grid lines 11 arranged on only one side and no grid lines 11 arranged on the other side, or it may have grid lines 11 arranged on both opposite sides. In order to improve light efficiency, grid lines 11 are arranged on both opposite sides of the solar cell 10 (that is, the front and back sides of the solar cell 10).

[0056] Step S200: An organic solder resist film 20 (i.e., an OSP film) is formed on the side of the battery cell 10, such that the organic solder resist film 20 covers the outer surface of the grid lines 11, as shown below. Figure 1 or Figure 3 As shown;

[0057] Step S300: Completely remove the organic solder mask 20 covering the areas of the grid line 11 where the welding wire 30 needs to be welded, exposing these areas. That is, only a portion of the grid line 11 is exposed, not all of it. The exposed areas of the grid line 11 are the areas where the welding wire 30 needs to be welded, and are used for welding to the wire 30. Areas of the grid line 11 where the welding wire 30 does not need to be welded remain unexposed, retaining the original organic solder mask 20. Because the unexposed areas of the grid line 11 are protected by the organic solder mask 20, it provides oxidation protection.

[0058] During the process of removing the organic solder resist film 20 at the location where the welding wire 30 needs to be welded on the grid line 11, the temperature of the part of the battery cell 10 other than the welding wire 30 is ≤200℃.

[0059] Specifically, the temperature of the parts of the solar cell 10 other than the welding wire 30 is, but is not limited to, 200℃, 180℃, 170℃, 150℃, 100℃, 80℃, or 50℃, which can be flexibly adjusted and set according to actual needs. The lower the temperature of the parts of the solar cell 10 other than the welding wire 30, the less impact it has on the performance of the amorphous silicon layer 13 and silicon substrate 12 of the solar cell 10.

[0060] It should be noted that, in this embodiment, the parts of the battery cell 10 other than the welding wire 30 include, but are not limited to, the amorphous silicon layer 13, the silicon substrate 12, and the TCO layer 14.

[0061] Please see Figures 1 to 4 In any given embodiment, the solar cell 10 is exemplified as a heterojunction solar cell 10. However, it should be noted that this is not a limitation, and other types of solar cells 10 are also possible. The solar cell 10 further includes a silicon substrate 12, an amorphous silicon layer 13, and a TCO layer 14. The amorphous silicon layer 13 and the TCO layer 14 are stacked on the front side of the silicon substrate 12, and the amorphous silicon layer 13 and the TCO layer 14 are also stacked on the back side of the silicon substrate 12. Gate lines 11 are disposed on the side of the TCO layer 14 opposite to the amorphous silicon layer 13.

[0062] Step S400: Weld the exposed portion of the grid line 11 to the welding wire 30, forming an alloy structure at the welded joint between the grid line 11 and the welding wire 30, such as... Figure 2 or Figure 4 As shown.

[0063] In this process, after the welding wire 30 is connected to the grid line 11, the grid line 11 will transfer the collected charge carriers to the welding wire 30, which will then converge and transmit them outward.

[0064] The aforementioned solar cell welding method has two advantages. First, the organic solder resist film 20 covering the outer surface of the grid lines 11 provides oxidation protection, resulting in lower production costs compared to tin plating. Second, by removing only a portion of the organic solder resist film 20 from the grid lines 11, compared to removing all portions, it is advantageous to minimize the temperature impact on the areas of the cell 10 other than the welding wires 30, while still ensuring the temperature of these areas is controlled, for example, ≤200°C. Complete removal of the organic solder resist film 20 from the grid lines 11 prevents incomplete soldering between the grid lines 11 and the welding wires 30. Furthermore, since the temperature of the areas of the cell 10 other than the welding wires 30 is controlled at ≤200°C, the relatively low temperature avoids performance impacts on the amorphous silicon layer 13 and the silicon substrate 12 of the cell 10.

[0065] It should be noted that Organic Solder Protector 20 (OSP) is a final treatment technology applied to clean bare copper surfaces. It self-assembles to form an organic thin film on the copper surface, primarily composed of imidazole compounds (such as alkylbenzimidazole). Its protective principle lies in the fact that copper atoms (3d¹...) 0 Electrons coordinate with the imidazole ring of the alkylbenzimidazole molecule, forming a coordinate bond. Multiple copper atoms continuously coordinate with the molecule, eventually forming an organic copper coordination polymer film (OSP film) on the copper surface. Intermolecular van der Waals forces cause this film thickness to increase to approximately 0.2 to 0.5 micrometers. The most crucial characteristic of the OSP film is its excellent heat resistance; its decomposition temperature typically needs to reach above 300°C, which allows it to effectively protect the copper surface and prevent oxidation at the high temperatures of soldering.

[0066] OSP film is commonly used in PCB surface treatment processes. OSP technology has broad development prospects and has the following significant advantages:

[0067] 1. Effective protection and solderability: Prevents copper surface oxidation and ensures good solderability of the copper surface.

[0068] 2. Strong compatibility: It is highly compatible with various fluxes and solder pastes.

[0069] 3. Simple and stable process: The processing technology is simple, the operation is stable, the tank solution is easy to maintain, and the operation is easy.

[0070] 4. High cost-effectiveness: The process cost is low and the economic benefits are significant.

[0071] 5. Good environmental performance: The solution does not contain difficult-to-treat organic solvents, making it green and environmentally friendly, and the waste liquid treatment is simple.

[0072] In order to ensure that the temperature of the parts of the solar cell 10 other than the welding wire 30 is ≤200℃, the following will elaborate on the methods of removing the organic solder resist 20 at the locations where the welding wire 30 needs to be welded on the grid lines 11, mainly using laser removal of the organic solder resist 20 and applying flux to at least one of the organic solder resist 20 and the welding wire 30. Compared with the related technology of heating the organic solder resist 20 to raise its temperature to greater than 300℃ to decompose it, both the laser removal of the organic solder resist 20 and the application of flux to at least one of the organic solder resist 20 and the welding wire 30 can ensure that the temperature of the parts of the solar cell 10 other than the welding wire 30 is ≤200℃, thereby avoiding performance impact on the amorphous silicon layer 13 and silicon substrate 12 of the solar cell 10.

[0073] For example, in step S300, the step of completely removing the organic solder resist film 20 covering the area on the gate line 11 where the solder wire 30 needs to be welded includes: focusing a laser on the area on the gate line 11 where the solder wire 30 needs to be welded, so that the organic solder resist film 20 covering the area on the gate line 11 where the solder wire 30 needs to be welded is locally heated to ≥300°C, so that the organic solder resist film 20 is completely ablated under the irradiation of the laser, thereby exposing the gate line 11, and proceeding to step S400.

[0074] Thus, by using a laser to act on the area on the grid line 11 where the welding wire 30 needs to be welded, the organic solder resist film 20 covering this area can be locally heated to ≥300°C, which is higher than the decomposition temperature of the organic solder resist film 20. This completely ablates the organic solder resist film 20, preventing any residue of the organic solder resist film 20 on the area on the grid line 11 where the welding wire 30 needs to be welded, thereby avoiding the problem of incomplete soldering between the grid line 11 and the welding wire 30. Furthermore, since the laser energy is mainly focused on the organic solder resist film 20 on the grid line 11 where the welding wire 30 needs to be welded, while other parts of the solar cell 10 are not irradiated by the laser, the temperature of these parts is not significantly affected by the laser. The temperature can be controlled, for example, ≤200°C, thus avoiding damage to the amorphous silicon layer 13 and silicon substrate 12 of the solar cell 10 during the welding process, and preventing any impact on the performance of the solar cell 10.

[0075] Based on the aforementioned embodiments, the temperature to which the organic solder resist film 20 covering the portion of the grid line 11 where the welding wire 30 needs to be welded is locally heated is controlled to include, but is not limited to, 300°C to 330°C, specifically, 300°C, 302°C, 304°C, 308°C, 310°C, 315°C, 320°C, or 330°C. Thus, on the one hand, the higher temperature allows the organic solder resist film 20 covering the portion of the grid line 11 where the welding wire 30 needs to be welded to be completely removed; on the other hand, when the temperature is below 330°C, the temperature is not excessively high, preventing the temperature of the portion of the cell 10 other than the welding wire 30 from exceeding 200°C and affecting the performance of the cell 10.

[0076] Based on the aforementioned embodiments, the time for local heating of the organic solder resist film 20 covering the portion of the grid line 11 where the welding wire 30 needs to be welded is controlled to include, but is not limited to, 1 second to 5 seconds, specifically, 1 second, 2 seconds, 3 seconds, 4 seconds, or 5 seconds. Thus, when the heating time is less than 1 second, the heating time is too short, and the organic solder resist film 20 covering the portion of the grid line 11 where the welding wire 30 needs to be welded cannot be completely removed; when the heating time is greater than 5 seconds, the heating time is too long, which will cause the temperature of the portion of the battery cell 10 other than the welding wire 30 to exceed 200°C, thus affecting the performance of the battery cell 10.

[0077] For example, before the step of focusing the laser on the part of the grid line 11 where the welding wire 30 needs to be welded, the method further includes placing the cell 10 in an environment with a protective gas that has an anti-oxidation effect.

[0078] Alternatively, the step of focusing the laser on the part of the grid line 11 where the welding wire 30 needs to be welded specifically includes: introducing a protective gas with anti-oxidation function into the part of the grid line 11 where the welding wire 30 needs to be welded.

[0079] Thus, the protective gas with anti-oxidation function can prevent the organic solder mask 20 on the part of the grid line 11 that needs to be welded with the welding wire 30 from being removed and coming into contact with air, thereby ensuring the welding quality between the grid line 11 and the welding wire 30.

[0080] Optionally, the protective gas with anti-oxidation function includes, but is not limited to, inert gases and other gases that do not participate in chemical reactions, such as nitrogen and helium. The specific gas can be flexibly selected according to actual needs and is not limited here.

[0081] In another embodiment, instead of using the laser as described in the above embodiments to remove the organic solder mask 20, step S300, the step of completely removing the organic solder mask 20 covering the portion of the gate line 11 where the solder wire 30 needs to be soldered, includes applying flux to at least one of the organic solder mask 20 covering the portion of the gate line 11 where the solder wire 30 needs to be soldered and the surface of the solder wire 30. That is, flux can be applied to the organic solder mask 20 covering the portion of the gate line 11 where the solder wire 30 needs to be soldered, flux can be applied to the surface of the solder wire 30, or flux can be applied to both.

[0082] Thus, during the welding process between the welding wire 30 and the grid line 11, the flux helps to completely remove the organic solder resist film 20 covering the area of ​​the grid line 11 where the welding wire 30 needs to be welded. Furthermore, after the organic solder resist film 20 covering the area of ​​the grid line 11 where the welding wire 30 needs to be welded is completely removed, the area of ​​the grid line 11 where the welding wire 30 needs to be welded is exposed, allowing for a stable weld connection with the welding wire 30 and preventing incomplete welds. Moreover, the process temperature for removing the organic solder resist film 20 using flux is ≤200℃, thus preventing the cell 10 from overheating and damaging it, and thus avoiding any impact on its performance.

[0083] Based on the aforementioned embodiments, the flux includes an acidic flux. Thus, before the welding wire 30 is welded to the grid line 11, the acidic flux can effectively and completely etch away the organic solder resist film 20 covering the area on the grid line 11 where the welding wire 30 needs to be welded, thereby avoiding the problem of incomplete soldering. Furthermore, the process temperature for removing the organic solder resist film 20 using the acidic flux is ≤200℃, thereby preventing the cell 10 from overheating and damaging the cell 10, and affecting its performance.

[0084] For example, an acidic flux can be either a flux containing moderately active acidic substances or a flux containing strongly acidic substances, without limitation.

[0085] When the acidic flux includes a flux containing moderately active acidic substances, on the one hand, it has a greater corrosive ability and can effectively remove the organic solder resist film 20 on the grid line 11 when it contacts the grid line 11. On the other hand, the corrosive ability is not too great and will not cause corrosion to the battery cell 10.

[0086] Among them, moderately active acidic substances include, but are not limited to, succinic acid, glutaric acid, adipic acid, diethylamine hydrochloride, cyclohexylamine hydrochloride, etc. The specific substances can be flexibly adjusted and set according to actual needs, and are not limited here.

[0087] When acidic flux includes flux containing strongly acidic substances, it has a greater corrosive ability and can effectively remove the organic solder resist film 20 on the grid lines 11. To avoid damage to the battery cell 10 caused by the acidic flux, the concentration of the strongly acidic substances can be appropriately controlled to reduce the intensity of acidic corrosion and prevent damage to the battery cell 10.

[0088] Optionally, the strongly acidic substances include, but are not limited to, hydrochloric acid, sulfuric acid, or nitric acid, and can be flexibly adjusted and set according to actual needs.

[0089] Please see Figure 3 and Figure 4 For example, the grid line 11 includes a main grid line 111. There are multiple main grid lines 111, which are arranged side by side with intervals. There are multiple welding wires 30, and each welding wire 30 is welded to each corresponding main grid line 111.

[0090] Please see Figure 3 and Figure 4 For example, the gate line 11 also includes sub-gate lines 112. Each main gate line 111 is connected to multiple sub-gate lines 112, and the multiple sub-gate lines 112 are arranged sequentially at intervals along the main gate lines 111 to which they are connected. The extension direction of the main gate line 111 is set at an angle to the extension direction of the sub-gate line 112. Since the sub-gate lines 112 do not need to be soldered to the solder wire 30, their outer surfaces are covered by an organic solder mask 20, which prevents the sub-gate lines 112 from being exposed and thus oxidized.

[0091] Please see Figures 1 to 4 Taking any one of the battery cells 10 as an example, which has multiple grid lines 11 on both opposite sides, the grid lines 11 on both opposite sides of the battery cell 10 need to be welded with welding wire 30.

[0092] For example, the step of completely removing the organic solder mask 20 covering the area on the gate line 11 where the solder wire 30 needs to be soldered includes:

[0093] Step S310: Simultaneously remove the organic solder resist film 20 covering the parts of each grid line 11 on one side of the battery cell 10 that need to be welded with welding wire 30.

[0094] Step S320: Simultaneously remove the organic solder mask 20 covering the parts of each grid line 11 on the other side that need to be soldered with welding wire 30.

[0095] For example, the step of welding the exposed portion of the grid line 11 to the welding wire 30 includes:

[0096] Step S410: Simultaneously weld each grid line 11 on one side of the battery cell 10 to each welding wire 30;

[0097] Step S420: Simultaneously weld each grid line 11 on the other side to each welding wire 30.

[0098] Thus, on the one hand, the removal and welding of the organic solder resist film 20 are carried out simultaneously on all sides of the battery cell 10, resulting in high welding efficiency; on the other hand, the removal and welding of the organic solder resist film 20 are carried out sequentially on the two opposite sides of the battery cell 10, which can prevent the temperature of the battery cell 10 from becoming too high when the removal or welding of the organic solder resist film 20 is carried out simultaneously on the two opposite sides of the battery cell 10.

[0099] It should be noted that the order of steps S310 and S320 in the above embodiments can be arbitrarily set according to requirements and is not limited here. The order of steps S410 and S420 can also be arbitrarily set according to requirements and is not limited here.

[0100] For example, step S410 may be located after either step S310 or step S320, and this is not limited here. Step S420 may be located after either step S310 or step S320, and this is not limited here.

[0101] For example, the step of forming an organic solder resist film 20 on the side of the battery cell 10, such that the organic solder resist film 20 covers the outer surface of the grid line 11, includes: attaching the organic solder resist film 20 to the surface of the grid line 11 of the battery cell 10 by spraying or wetting; wherein the thickness of the organic solder resist film 20 is 0.1μm~0.5μm.

[0102] Specifically, the thickness of the organic solder mask 20 includes, but is not limited to, 0.1μm, 0.2μm, 0.3μm or 0.5μm, etc., which can be flexibly selected and set according to actual needs, and are not limited here.

[0103] Thus, when the thickness of the organic solder mask 20 is less than 0.1 μm, it cannot effectively prevent oxidation; when the thickness of the organic solder mask 20 is greater than 0.5 μm, incomplete decomposition during later soldering leads to cold solder joints. That is, when the thickness of the organic solder mask 20 is 0.1 μm to 0.5 μm, it can not only effectively prevent the gate line 11 from being oxidized, but also avoid cold solder joint problems during later soldering processes.

[0104] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, the term "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0105] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0106] In this application, unless otherwise expressly specified and limited, the use of descriptions such as "above" or "below" the second feature indicates that the first and second features are in direct contact or indirect contact via an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0107] It should be noted that if an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. If an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. If so, the terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application are for illustrative purposes only and do not represent the only possible implementation.

[0108] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0109] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for welding solar cells, characterized in that, The welding method includes the following steps: A battery cell (10) is provided, wherein grid lines (11) are provided on the side of the battery cell (10); An organic solder resist film (20) is formed on the side of the battery cell (10) so that the organic solder resist film (20) covers the outer surface of the grid line (11); Remove the organic solder resist film (20) covering the area on the grid line (11) where the welding wire (30) needs to be welded, so that the area on the grid line (11) where the welding wire (30) needs to be welded is exposed; wherein, during the process of removing the organic solder resist film (20) at the area on the grid line (11) where the welding wire (30) needs to be welded, the temperature of the area on the battery cell (10) other than the area where the welding wire (30) is welded is ≤200℃; The exposed portion of the grid line (11) is welded to the welding wire (30).

2. The welding method according to claim 1, characterized in that, The step of completely removing the organic solder mask (20) covering the portion of the grid line (11) where the welding wire (30) needs to be welded includes: The laser is focused on the part of the grid line (11) where the welding wire (30) needs to be welded, so that the organic solder resist film (20) covering the part of the grid line (11) where the welding wire (30) needs to be welded is locally heated to ≥300°C, so that the organic solder resist film (20) is ablated under the irradiation of the laser.

3. The welding method according to claim 2, characterized in that, The temperature of the organic solder resist film (20) covering the portion of the grid line (11) where the welding wire (30) needs to be welded is controlled to be 300°C to 330°C; and / or the time of the organic solder resist film (20) covering the portion of the grid line (11) where the welding wire (30) needs to be welded is controlled to be 1S to 5S.

4. The welding method according to claim 2, characterized in that, Before the step of focusing the laser on the area on the grid line (11) where the welding wire (30) needs to be welded, the method further includes: placing the battery cell (10) in an environment with a protective gas that has an anti-oxidation effect; And / or, the step of focusing the laser on the part of the grid line (11) where the welding wire (30) needs to be welded specifically includes: introducing a protective gas with anti-oxidation function into the part of the grid line (11) where the welding wire (30) needs to be welded.

5. The welding method according to claim 1, characterized in that, The step of completely removing the organic solder mask (20) covering the portion of the grid line (11) where the welding wire (30) needs to be welded includes: At least one of the organic solder mask (20) covering the portion of the grid line (11) where the welding wire (30) needs to be welded and the surface of the welding wire (30) is coated with flux.

6. The welding method according to claim 5, characterized in that, The flux includes acidic flux.

7. The welding method according to claim 6, characterized in that, The acidic flux includes fluxes containing acidic substances with moderate or strong acidity.

8. The welding method according to claim 1, characterized in that, The grid line (11) includes a main grid line (111); there are multiple main grid lines (111), and the multiple main grid lines (111) are arranged in parallel with intervals; there are multiple welding wires (30), and each welding wire (30) is welded to each of the main grid lines (111); The gate line (11) also includes a sub-gate line (112), each of the main gate lines (111) is connected to a plurality of the sub-gate lines (112), and the plurality of sub-gate lines (112) are arranged sequentially at intervals along the main gate lines (111) to which they are connected; the extension direction of the main gate line (111) is set at an angle to the extension direction of the sub-gate line (112); the outer surface of the sub-gate line (112) is covered by the organic solder mask (20).

9. The welding method according to claim 1, characterized in that, The battery cell (10) has multiple grid lines (11) on its two opposite sides; The step of completely removing the organic solder resist film (20) covering the parts of the grid lines (11) that need to be welded with welding wires (30) includes: firstly, simultaneously removing the organic solder resist film (20) covering the parts of the grid lines (11) that need to be welded with welding wires (30) on one side of the battery cell (10), and then simultaneously removing the organic solder resist film (20) covering the parts of the grid lines (11) that need to be welded with welding wires (30) on the other side; The step of welding the exposed parts of the grid lines (11) to the welding wires (30) includes: firstly, welding each of the grid lines (11) on one side of the battery cell (10) to each of the welding wires (30) simultaneously, and then welding each of the grid lines (11) on the other side to each of the welding wires (30) simultaneously.

10. The welding method according to any one of claims 1 to 9, characterized in that, The step of forming an organic solder resist film (20) on the side of the battery cell (10) such that the organic solder resist film (20) covers the outer surface of the grid line (11) includes: The organic solder resist film (20) is formed on the surface of the grid lines (11) of the battery cell (10) by spraying or rinsing; wherein the thickness of the organic solder resist film (20) is 0.1μm~0.5μm.

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