Method for improving welding tension of electrode

Abstract

The invention discloses a method for improving electrode welding tension, and relates to the technical field of photovoltaics. The method for improving the welding tension of the electrode comprises the following steps: depositing an edge passivation layer on the side surface of a battery piece; the set areas of the front face and / or the back face of the battery piece are / is attached to the hydrogel containing the acidic substance so as to etch and remove the passivation layer material plated on the electrode in a winding mode, and the passivation layer material comprises the material plated in a winding mode when the edge passivation layer is deposited. According to the invention, the passivation layer material which is plated on the electrode in the winding manner is removed, so that the adverse effect of the passivation layer material which is plated in the winding manner on the subsequent welding of the welding strip can be avoided, and the binding force between the welding strip and the electrode of the battery piece is improved. The hydrogel is attached to the battery piece after absorbing the acidic material, and the acidic material can be prevented from flowing randomly, so that the set area can be accurately etched, and other areas are not affected.

Description

Technical Field

[0001] This application relates to the field of photovoltaic technology, and more specifically, to a method for improving electrode welding pull strength. Background Technology

[0002] Photovoltaic modules in related technologies are packaged in the form of half-cells. Therefore, after depositing functional layers on a whole silicon wafer, half-cells need to be obtained through laser cutting. Cutting the cell creates a new surface, namely the edge side of one side. This new surface often contains numerous recombination centers such as dangling bonds, impurities, and lattice defects, leading to efficiency loss. Therefore, edge passivation is performed on the side of the cell. Edge passivation involves depositing a passivation layer on the fresh surface of the half-cell to reduce carrier recombination and improve cell efficiency. Research has found that using edge passivation technology can potentially improve cell conversion efficiency by 0.2%; or improve module efficiency by 5W. With continuous iteration and optimization of equipment, the final efficiency improvement is expected to reach over 0.2%.

[0003] However, while edge passivation improves efficiency, some of the deposited passivation material is also deposited around the electrodes on the front and / or back of the solar cell, especially the main busbar and pads. When the electrodes on the solar cell are soldered to the solder ribbon, the deposited material can negatively affect the welding pull, leading to a decrease in welding pull and affecting the reliability of the photovoltaic module.

[0004] Therefore, this application is hereby submitted. Summary of the Invention

[0005] The purpose of this application is to provide a method for improving electrode welding pull strength, which can increase the welding pull strength between the electrode and the solder strip of the solar cell.

[0006] This application is implemented as follows: This application provides a method for improving the tensile strength of electrode welding, comprising: An edge passivation layer is deposited on the side of the solar cell; A designated area on the front and / or back of the battery cell is attached to a hydrogel containing an acidic substance to etch away the passivation layer material deposited around the electrode, wherein at least a portion of the electrode is located within the designated area, and the passivation layer material includes the material deposited around the electrode during the deposition of the edge passivation layer.

[0007] In an optional embodiment, the acidic substance includes hydrofluoric acid.

[0008] In an optional implementation, the electrodes of the solar cell include main grid lines, and the defined region includes the area containing the portion of the main grid lines near the edge of the solar cell.

[0009] In an optional embodiment, the content of acidic substances in the hydrogel is 3 wt.% to 10 wt.%.

[0010] In an optional implementation, the duration of hydrogel application to the set area is 4 to 10 minutes.

[0011] In an optional embodiment, the step of etching away the passivation layer material deposited around the electrode is performed at a temperature of 1°C to 50°C.

[0012] In an optional embodiment, the hydrogel is a polyvinyl alcohol hydrogel.

[0013] In an optional implementation, the material of the edge passivation layer is AlO. x .

[0014] In an optional implementation, the edge passivation layer is deposited using an atomic layer deposition process.

[0015] In an optional embodiment, after the step of etching away the passivation layer material plated around the electrode, the method for improving electrode welding pull strength further includes: Clean the battery cells and dry them.

[0016] This application has the following beneficial effects: A method for improving electrode welding pull strength includes: depositing an edge passivation layer on the side of a solar cell; attaching a designated area on the front and / or back of the solar cell to a hydrogel containing an acidic substance to etch away the passivation layer material coated around the electrode, wherein at least a portion of the electrode is located within the designated area, and the passivation layer material includes the material coated around the electrode during the deposition of the edge passivation layer. In this application, by removing the passivation layer material coated around the electrode with an acidic substance after depositing the edge passivation layer, the coated passivation layer material can be prevented from adversely affecting subsequent welding of the solder ribbon, improving the adhesion between the solder ribbon and the electrode of the solar cell, thereby preventing separation of the solder ribbon from the electrode of the solar cell and improving the reliability of the photovoltaic module. After absorbing the acidic substance, the hydrogel adheres to the solar cell, preventing the acidic substance from flowing freely and corroding other parts of the solar cell (such as the edge passivation layer). Therefore, using hydrogel to confine the acidic substance allows for precise etching of the designated area without affecting other areas. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of a method for improving electrode welding pull force in one embodiment of this application; Figure 2 This is a schematic diagram of the structure of the battery cell in one embodiment of this application; Figure 3 This is a schematic diagram of a hydrogel being attached to a designated area of ​​a battery cell in one embodiment of this application.

[0019] Key component symbols: 100 - Solar cell; 101 - Plating area; 102 - Designated area; 110 - Silicon substrate; 120 - P-type emitter; 130 - Front passivation layer; 140 - Front antireflection layer; 150 - Tunneling oxide layer; 160 - N-type doped silicon layer; 170 - Back antireflection layer; 181 - Front electrode; 182 - Back electrode; 190 - Edge passivation layer. Detailed Implementation

[0020] Photovoltaic modules in related technologies are packaged in the form of half-cell cells. Taking the fabrication of TOPCon cells as an example, the steps include: texturing, boron diffusion, alkaline polishing, deposition of n-type polycrystalline silicon, annealing, cleaning, deposition of a front passivation layer, deposition of front / back anti-reflection layers, fabrication of grid lines, slicing (i.e., forming a half-cell cell), edge passivation, and testing and sorting. Slicing creates a fresh surface, and edge passivation deposits an edge passivation layer on this fresh surface to reduce carrier recombination and improve cell efficiency. In traditional edge passivation processes, cells are stacked to shield the front and back sides as much as possible, exposing only the sides. However, during edge passivation deposition, cells cannot be completely bonded together, inevitably leaving gaps. The high path of freedom of deposited atoms makes it easy for plating to occur, resulting in a passivation layer material being deposited on the front and back edges near the edges as well. When these passivation layer materials can reach 20nm, when they cover electrodes (such as grid lines and pads), it can lead to poor bonding between the electrodes and solder ribbons during subsequent welding, resulting in low pull strength. This will significantly affect the performance and reliability of photovoltaic modules.

[0021] Therefore, this application provides a method to improve electrode welding pull force. After edge passivation, the passivation layer material coated around the cell is etched using a hydrogel containing acidic substances to eliminate the negative impact of the coated passivation layer material on the welding, thereby improving the performance and reliability of the photovoltaic module.

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0024] Figure 1 This is a flowchart illustrating a method for improving electrode welding pull force in one embodiment of this application. Figure 1 As shown, the method for improving electrode welding pull force provided in this application embodiment includes the following steps: Step S100: Deposit an edge passivation layer on the side of the solar cell.

[0025] In the embodiments of this application, the solar cell 100 can be a tunneling oxide passivated contact cell (TOPCon) or other types of cells such as heterojunction cells. Electrodes are provided on the front and / or back sides of the solar cell 100; at least one side of the solar cell 100 has a fresh surface formed by cutting. Figure 2 This is a schematic diagram of the structure after the edge passivation layer 190 is deposited on the side of the battery cell 100 in one embodiment of this application. Figure 2 As shown, taking a TOPCon battery as an example, the battery cell 100 includes a silicon substrate 110, a p-type emitter 120, a front passivation layer 130, a tunneling oxide layer 150, an n-type doped silicon layer 160, a front electrode 181, and a back electrode 182. The silicon substrate 110 can be n-type silicon. The p-type emitter 120 is disposed on the front side of the silicon substrate 110 and can be obtained through boron diffusion. The front passivation layer 130 is disposed on the side of the p-type emitter 120 away from the silicon substrate 110, and the material of the front passivation layer 130 can be aluminum oxide. The front electrode 181 passes through the front passivation layer 130 and connects to the p-type emitter 120. The tunneling oxide layer 150 is disposed on the back side of the silicon substrate 110, and the tunneling oxide layer 150 is silicon oxide with a thickness of 0.5 nm to 3 nm. The n-type doped silicon layer 160 is disposed on the side of the tunneling oxide layer 150 away from the silicon substrate 110, and the n-type doped silicon layer 160 can be phosphorus-doped polycrystalline silicon. The back electrode 182 is connected to the n-type doped silicon layer 160.

[0026] Furthermore, the solar cell 100 may also include a front antireflection layer 140 and a back antireflection layer 170 to improve light utilization and increase the photoelectric efficiency of the solar cell 100. The materials of the front antireflection layer 140 and the back antireflection layer 170 may be SiN. x Alternatively, a composite layer structure can be adopted.

[0027] In this embodiment, the electrodes of the solar cell 100 can be in the form of grid lines, including main grid lines, fine grid lines, and pads located on the main grid lines. The pads can be used to solder with solder ribbons to connect multiple solar cells 100 together to form a cell string. The multiple cell strings can be arranged and laminated to form a photovoltaic module.

[0028] In this embodiment, the solar cell 100 is cut after the electrodes are formed. For the cut solar cell 100, an edge passivation layer 190 is deposited on the fresh side after cutting, or the edge passivation layer 190 can be deposited on the entire side of the solar cell 100. The purpose of this step is to reduce carrier recombination and improve cell efficiency.

[0029] Optionally, in order to improve the efficiency of depositing the edge passivation layer 190, the individual solar cells 100 can be stacked first, and the edges of multiple solar cells 100 can be passivated at one time, which can reduce the amount of plating around the front and back of the solar cells 100.

[0030] Optionally, the edge passivation layer 190 is made of AlO2. x In other embodiments, the edge passivation layer 190 may also be made of other materials with passivation properties. Optionally, the edge passivation layer 190 is deposited using atomic layer deposition (ALD). ALD can precisely control the composition and thickness of the edge passivation layer 190, and can ensure the film is dense and has a uniform thickness. Optionally, the thickness of the edge passivation layer 190 is 10 nm to 30 nm, for example, any value among 10 nm, 15 nm, 20 nm, 25 nm, and 30 nm, or a value between any two values.

[0031] Step S200: A designated area on the front and / or back of the battery cell is attached to a hydrogel containing an acidic substance to etch away the passivation layer material deposited around the electrode, wherein at least a portion of the electrode is located within the designated area, and the passivation layer material includes the material deposited around the electrode during the deposition of the edge passivation layer.

[0032] Due to the high free path of atomic layer deposition (ALD), and the unavoidable gaps between the solar cells 100, some atoms may enter these gaps and deposit on the front and / or back sides of the solar cells 100, forming a passivation layer. This passivation layer material adheres to the electrodes, affecting subsequent welding. Therefore, this step utilizes an acidic substance to remove the passivation layer material from the electrodes, effectively improving the subsequent welding quality and increasing the welding pull strength of the electrodes.

[0033] Optionally, the acidic substance includes weak acids; using strong acids could potentially damage the gate lines. Optionally, the acidic substance includes hydrofluoric acid. Hydrofluoric acid can effectively remove passivation layer materials (such as AlO₂). x In other embodiments, the acidic substance may include hydrofluoric acid and ammonium fluoride (NH4F), or other acidic substances capable of removing the passivation layer material, or a combination of multiple acidic substances. Optionally, the pH value of the acidic substance is less than 5.

[0034] In this embodiment, since the acidic substance mainly targets the passivation layer material coated on the electrode, in order to prevent the acidic substance from flowing freely and corroding other parts of the battery cell 100 (such as the edge passivation layer 190 on the side of the battery cell 100 obtained in step S100), a hydrogel is used in this embodiment to constrain the acidic substance within the hydrogel. Then, the hydrogel is used to adhere to the designated area 102 on the battery cell 100 that needs to be etched, which can achieve precise etching and removal of the passivation layer material on the electrode in the designated area 102 without affecting other areas.

[0035] Figure 3 This is a schematic diagram showing the attachment of hydrogel to a designated area 102 of the battery cell 100 in one embodiment of this application. Figure 3 As shown, in this embodiment, the designated area 102 is adjacent to the edge of the battery cell 100, and at least a portion of it is located within the plating area 101. It is understood that plating often occurs at the edge of the battery cell 100, therefore the plating area 101 is adjacent to the edge of the battery cell 100.

[0036] In this embodiment, the electrodes of the solar cell 100 include main grid lines, and the defined region 102 includes the region containing the portion of the main grid lines near the edge of the solar cell 100. Because the edge of the solar cell 100 (e.g., Figure 3 The plating risk in the winding plating area 101 is relatively high. Therefore, the designated area 102 is for the portion of the main grid line near the edge of the cell 100. This can save the use of hydrogel and acidic materials, and also avoid damage to other parts of the cell 100 due to excessive etching. Optionally, the electrodes of the cell 100 include main grid lines, fine grid lines, and pads. The designated area 102 includes the location of the main grid lines and pads near the edge of the cell 100; or, the designated area 102 includes the parts of the electrodes that need to be soldered later.

[0037] like Figure 3 As shown, the setting area 102 is multi-point configured. For example, the setting area 102 just covers one end of each main grid line near the edge of the cell 100. This allows only the passivation layer material around the electrodes to be etched away, while ignoring the material around other parts. In other optional embodiments, the entire plating area 101 of the cell 100 can be bonded to the hydrogel, which allows etching of the plating material around the entire edge of the cell 100; even the entire surface of the cell 100 can be bonded to the hydrogel to remove the plating material on the entire front and / or back sides. In some embodiments, the pads of the cell 100 are located within a range of 5mm to 50mm from the edge, so the setting area 102 can be set as the area from the edge of the cell 100 to 10mm to 70mm inside the edge. The area from the edge of the cell 100 to 10mm to 70mm inside the edge can also be considered as the plating area 101.

[0038] In actual operation, the hydrogel can be placed on a substrate corresponding to the designated area 102 on the battery cell 100, and then the battery cell 100 can be placed on the substrate so that the designated area 102 of the battery cell 100 is exactly in contact with the hydrogel. Alternatively, the hydrogel can be placed on the designated area 102 on the battery cell 100.

[0039] Optionally, the content of acidic substances in the hydrogel is 3 wt.% to 10 wt.%, for example, the content of acidic substances is any value among 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, and 10 wt.%, or any value between any two points.

[0040] Optionally, the duration for attaching hydrogel to region 102 can be set to 4 min to 10 min. For example, the attachment duration can be any value among 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, and 10 min, or any value between any two points.

[0041] Furthermore, the step of removing the passivation layer material coated on the electrode using an acidic substance is carried out at a temperature of 1°C to 50°C, for example, at 25°C.

[0042] Optionally, the hydrogel is polyvinyl alcohol hydrogel (PVA). Optionally, both the front and back sides of the solar cell 100 are etched using a hydrogel containing an acidic substance to remove the coating material; furthermore, the etched areas on the front and back sides of the solar cell 100 are symmetrical.

[0043] Furthermore, after the step of removing the passivation layer material coated on the electrode using an acidic substance, the method for improving electrode welding pull also includes cleaning the battery cell 100 and drying the battery cell 100.

[0044] Optionally, the method for cleaning the battery cell 100 includes: rinsing in a water bath with deionized water for 1 to 3 minutes, for example, rinsing for 2 minutes. The drying temperature is 80°C to 100°C, for example, 95°C.

[0045] The table below shows the test results of electrode welding pull force of the battery cell 100 prepared in Example 1 of this application and the battery cell 100 prepared using the conventional process (Comparative Example 1). Both Example 1 and Comparative Example 1 use battery cells 100 with the same structural design; the only difference is in the manufacturing process. In Example 1, after depositing the edge passivation layer 190, an acidic step is added to remove the passivation layer (i.e., step S200 in the above examples). Eight points are selected for testing on each battery cell 100, and the test points are arranged sequentially from the edge to the center of the battery cell 100 according to the numbers 1-8.

[0046]

[0047] As can be seen from the table above, in Comparative Example 1, the weld pull is lower closer to the edge. This means that the closer to the edge, the more passivation layer material is coated, and the greater the negative impact on the weld pull. In Example 1, by using acidic etching to remove the passivation layer material coated on the electrode, the weld pull at each test point is relatively uniform, and a high weld pull can still be maintained even near the edge of the cell 100. Therefore, it can be concluded that the method for improving electrode weld pull provided in the embodiments of this application can effectively improve the welding effect between the electrode and the solder strip, reduce the risk of solder strip detachment from the electrode, and improve the reliability of photovoltaic modules.

[0048] In summary, this application provides a method for improving electrode welding pull strength, comprising: depositing an edge passivation layer 190 on the side of a solar cell 100; attaching a designated area on the front and / or back of the solar cell to a hydrogel containing an acidic substance to etch away the passivation layer material coated around the electrode, wherein at least a portion of the electrode is located within the designated area, and the passivation layer material includes the material coated around the electrode during the deposition of the edge passivation layer 190. In this application, by removing the passivation layer material coated around the electrode with an acidic substance after depositing the edge passivation layer 190, the adverse effects of the coated passivation layer material on subsequent welding of the solder ribbon can be avoided, improving the bonding strength between the solder ribbon and the electrode of the solar cell 100, thereby preventing the solder ribbon from separating from the electrode of the solar cell 100 and improving the reliability of the photovoltaic module. After absorbing acidic substances, the hydrogel adheres to the battery cell 100, preventing the acidic substances from flowing freely and corroding other parts of the battery cell 100 (such as the edge passivation layer 190). Therefore, using hydrogel to confine acidic substances allows for precise etching of a designated area without affecting other areas.

[0049] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for improving the tensile strength of electrode welding, characterized in that, include: An edge passivation layer is deposited on the side of the solar cell; A predetermined area on the front and / or back of the battery cell is attached to a hydrogel containing an acidic substance to etch away the passivation layer material deposited around the electrode, wherein at least a portion of the electrode is located within the predetermined area, and the passivation layer material includes the material deposited around the electrode during the deposition of the edge passivation layer.

2. The method for improving electrode welding tensile strength according to claim 1, characterized in that, The acidic substance includes hydrofluoric acid.

3. The method for improving electrode welding tensile strength according to claim 1, characterized in that, The electrodes of the solar cell include main grid lines, and the defined region includes the area containing the portion of the main grid lines near the edge of the solar cell.

4. The method for improving electrode welding tensile strength according to claim 1, characterized in that, The content of the acidic substance in the hydrogel is 3 wt.% to 10 wt.%.

5. The method for improving electrode welding tensile strength according to claim 1, characterized in that, The hydrogel is attached to the designated area for 4 to 10 minutes.

6. The method for improving electrode welding tensile strength according to claim 1, characterized in that, The etching process to remove the passivation layer material coated on the electrode is performed at a temperature of 1°C to 50°C.

7. The method for improving electrode welding tensile strength according to claim 1, characterized in that, The hydrogel is a polyvinyl alcohol hydrogel.

8. The method for improving electrode welding tensile strength according to any one of claims 1-7, characterized in that, The material of the edge passivation layer is AlO. x .

9. The method for improving electrode welding tensile strength according to any one of claims 1-7, characterized in that, The edge passivation layer is deposited using an atomic layer deposition process.

10. The method for improving electrode welding tensile strength according to any one of claims 1-7, characterized in that, After the step of etching away the passivation layer material plated around the electrode, the method for improving electrode welding pull strength further includes: Clean the battery cells and dry them.

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