Method for manufacturing a solar cell and screen printing device

Abstract

The application discloses a preparation method of a solar cell and a screen printing device, and belongs to the technical field of photovoltaics. The preparation method of the solar cell comprises the following steps: using a screen with a mesh number not lower than 200 to perform first coating on the surface of a metal seed layer of a cell base and to perform first drying, so as to obtain a first photoresist layer; and then using the screen with the mesh number not lower than 200 to perform second coating on the surface of the first photoresist layer and to perform second drying, so as to form a second photoresist layer on the surface of the first photoresist layer. The screen with the mesh number not lower than 200 is used to perform at least twice coating, so that the roughness of a coating surface can be reduced, and then the deviation of layer thicknesses at different positions of the photoresist layer can be reduced.

Description

Technical Field

[0001] This application relates to the field of photovoltaic technology, and more specifically, to a method for preparing a solar cell and a screen printing apparatus. Background Technology

[0002] Currently, silver paste screen printing technology is a common method for realizing the top grid electrode of silicon heterojunction solar cells. However, there are still some difficulties in realizing the top grid electrode of silicon heterojunction solar cells, such as reducing the resistance of silver paste screen printing and refining the metal lines, which makes it difficult to achieve the goal of high efficiency and low cost of solar cells.

[0003] Metallized electrodes, such as copper electrodes, offer advantages such as better plasticity, lower metal line resistance, less light-shielding loss, and lower cost, and are considered a breakthrough technology for fabricating solar cell electrodes using silver paste screen printing. However, directly electroplating metal electrodes onto transparent conductive films is non-selective, and the adhesion between directly electroplated metal and the transparent conductive film is poor, making it difficult to meet the requirements for solar cell module fabrication. Therefore, it is necessary to deposit a metal seed layer, such as a copper seed layer, onto the transparent conductive film, followed by patterning masking to achieve selective deposition and enhance the adhesion of the grid lines after electroplating.

[0004] However, solar cells obtained using existing copper interconnect technology are prone to various defects such as electrode plating defects, plating defects, grid line detachment, and poor ohmic contact between copper electrodes and the substrate at different locations. These defects result in grid line widening, increased shading area, and reduced photoelectric conversion efficiency. Summary of the Invention

[0005] The purpose of this application is to provide a method for fabricating solar cells and a screen printing apparatus to partially or completely improve the problem of poor photoelectric conversion efficiency of solar cells in related technologies.

[0006] In a first aspect, embodiments of this application provide a method for fabricating a solar cell, comprising: obtaining a cell substrate; the surface layer of the cell substrate being a metal seed layer; screen printing: coating a photoresist layer onto the surface of the metal seed layer; the photoresist layer comprising at least a first photoresist layer formed by a first coating and a first drying, and a second photoresist layer formed by a second coating and a second drying on the first photoresist layer; the mesh count of the screen used for the first coating and the second coating is not less than 200 mesh.

[0007] Using a screen printing stencil with a mesh size of at least 200, a first and second coating are applied to the surface of the metal seed layer. After each coating operation, the layer is dried to form a photoresist layer consisting of a first and a second photoresist layer stacked together. This facilitates subsequent patterning operations such as exposure and development, as well as electroplating to obtain grid lines, ultimately resulting in a solar cell. Compared to solar cells obtained by post-processing a photoresist layer formed in a single coating, the photoresist layer obtained in this example has a more uniform thickness. After subsequent exposure and development processes, more uniform grid lines can be obtained. Therefore, the grid lines electroplated within these uniform grid lines can have more uniform width and thickness, while reducing the proportion of broken grid lines, thereby improving the photoelectric conversion efficiency of the solar cell.

[0008] In conjunction with the first aspect, in an optional embodiment of this application, the mesh count of the screen used for the first and second coatings is 230-250 mesh, and the coating parameters include: screen spacing of 1-1.5 mm, printing pressure of 30-40 N, printing speed of 200-300 mm / s, and the viscosity of the photoresist paste of 900-1100 cps.

[0009] The mesh count of the screen used for the first and second coatings is 230-250 mesh. The coating parameters are: screen pitch 1-1.5mm, printing pressure 30-40N, printing speed 200-300mm / s, and the viscosity of the photoresist paste is 900-1100cps. By coating twice, a photoresist layer of the preset thickness can be obtained, while also improving the uniformity of the photoresist layer thickness.

[0010] In conjunction with the first aspect, in an optional embodiment of this application, the preparation method further includes exposure and development. The photoresist layer is exposed and developed to obtain gate grooves. The exposure energy is 70-90 mJ / cm². 2 The development time is 1.8-2.2 min, the developing solution is an 8-13 g / L sodium carbonate solution, and the thickness of the photoresist layer is 12-14 μm.

[0011] A photoresist layer with a thickness of 12-14μm is subjected to 70-90mJ / cm. 2 Exposure to high light intensity can cause a difference in properties between the exposed and unexposed areas of photoresist. Then, development with an 8-13 g / L sodium carbonate solution for 1.8-2.2 min can produce grid grooves with less residual photoresist, smaller deviation in the width of the upper and lower openings, and stable sidewalls that are less prone to collapse. This improves the quality of copper grid electrodes obtained by subsequent electroplating within the grid grooves.

[0012] In conjunction with the first aspect, in an optional embodiment of this application, the thickness of the first photoresist layer is 6-7 μm.

[0013] In the above implementation process, the thickness of the first photoresist layer is set to 6-7 μm, so that the thickness difference between the first photoresist layer and the second photoresist layer is small, thereby making the difference between the uniformity of the thickness of the first photoresist layer and the uniformity of the thickness of the second photoresist layer smaller, which can further reduce the non-uniformity of the thickness of the photoresist layer.

[0014] In conjunction with the first aspect, in an optional embodiment of this application, the temperature of the first drying is 80-100°C and the time is 6-7 minutes;

[0015] And / or, the second drying temperature is 80-100℃, and the time is 6-7 minutes;

[0016] Optionally, the temperature for the first and / or second drying is 80-90°C.

[0017] In the above process, the battery substrate after the first coating is placed at a temperature of 80-100℃ and dried for 6-7 minutes. This avoids the photoresist in the photoresist reacting due to excessively high baking temperature or excessively long baking time, thus preventing a decrease in the sensitivity of the photoresist during subsequent exposure. Furthermore, the heat energy during drying also causes the resin within the photoresist to cross-link without dissolving, thereby avoiding affecting the quality of the grid lines obtained after subsequent development. If the drying temperature is too low or the drying time is too short, insufficient drying will lead to phenomena such as delamination and pattern distortion during subsequent development.

[0018] In conjunction with the first aspect, in an optional embodiment of this application, the temperature of the first drying is 80-90°C, and the ratio of the thickness of the first coating to the time of the first drying is 1:0.9-1.2μm / min;

[0019] And / or, the temperature for the second drying is 80-90℃, and the ratio of the thickness of the second coating to the time of the second drying is 1:0.9-1.2μm / min.

[0020] When drying at 80-90℃, the ratio between coating thickness and drying time is 1:0.9-1.2μm / min, which can further reduce the probability of over-drying or under-drying after the first or second coating.

[0021] In conjunction with the first aspect, in an optional embodiment of this application, the battery substrate has a front side and a back side, and the surface layer of both the front and back sides is a metal seed layer; screen printing includes the following sequential processes:

[0022] First coating on the front side, first drying on the front side, first coating on the back side, first drying on the back side, second coating on the front side, second drying on the front side, second coating on the back side, and second drying on the back side;

[0023] Alternatively, the process could be: first coating on the front side, first drying on the front side, first coating on the back side, first drying on the back side, second coating on the back side, second drying on the back side, second coating on the front side, and second drying on the front side.

[0024] After the first coating and drying of the front side of the battery substrate, the first coating and drying of the back side are performed. The first and second photoresist layers are prepared alternately on the front and back sides to avoid exposing the metal seed layer on the back side of the battery substrate to a high-temperature baking environment during the second baking of the front side of the battery substrate. This reduces the degree of oxidation of the metal seed layer on the back side of the battery substrate, thereby reducing the contact resistance between the subsequently obtained metal grid lines and the metal seed layer and improving the conversion efficiency of the solar cell.

[0025] Secondly, embodiments of this application provide a screen printing apparatus for implementing the solar cell fabrication method provided in the first aspect, comprising a printing mechanism and a drying mechanism. The printing mechanism includes a first screen and a second screen; the first screen is used for a first coating, and the second screen is used for a second coating; the mesh count of the first and second screens is not less than 200 mesh. The drying mechanism includes a first oven and a second oven; the first oven is disposed between the first and second screens and is used for a first drying of the first photoresist layer coated on the first screen; the second oven is disposed at the rear end of the second screen and is used for a second drying of the second photoresist layer coated on the second screen.

[0026] Using a first screen in a screen printing apparatus, a metal seed layer of the battery substrate can be coated for the first time, and then dried for the first time using a first oven to obtain a first photoresist layer; then using a second screen to coat the surface of the first photoresist layer for the second time, and then drying for the second time using a second oven, a second photoresist layer can be prepared on the first photoresist layer.

[0027] Using the above-mentioned screen printing apparatus to screen print photoresist on the battery substrate, since the mesh count of both the first and second screens is not less than 200 mesh, the thickness deviation of the first and second photoresist layers at different locations can be reduced, thereby improving the uniformity of the photoresist layer thickness obtained after screen printing.

[0028] In conjunction with the second aspect, in an optional embodiment of this application, the screen printing apparatus includes a conveying mechanism; the conveying mechanism is configured to convey the battery substrate to the area below the first screen, inside the first oven, below the second screen, and inside the second oven for first coating, first drying, second coating, and second drying of the battery substrate.

[0029] The battery substrate is transported to the bottom of the first screen for the first coating using a conveying mechanism. The battery substrate after the first coating is then transported to the first oven for the first drying to obtain the first photoresist layer. The battery substrate with the first photoresist layer is then transported to the second screen for the second coating. The battery substrate after the second coating is then transported to the second oven for the second drying to obtain the second photoresist layer on the surface of the first photoresist layer. This method can improve the preparation efficiency of the photoresist layer and avoid manual transfer of the battery substrate.

[0030] In conjunction with the second aspect, in an optional embodiment of this application, the screen printing apparatus includes two sets of one-to-one corresponding printing mechanisms and drying mechanisms, which are used to screen print on the front and back sides of the battery substrate, respectively.

[0031] The screen printing apparatus is equipped with two sets of one-to-one printing and drying mechanisms, which can perform the first coating and first drying on the back and front of the battery substrate, and the second coating and second drying on the back and front of the battery substrate, respectively, thereby reducing the unevenness of the photoresist layer thickness on the front and back of the battery substrate. Attached Figure Description

[0032] 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.

[0033] Figure 1 A schematic cross-sectional view of the battery substrate provided as an example in this application;

[0034] Figure 2 A flowchart illustrating the fabrication process of the photoresist layer is provided as an example in this application.

[0035] Figure 3 A plan view of the screen printing apparatus provided as an example in this application;

[0036] Figure 4 The microstructure of the grid groove provided in Example 2;

[0037] Figure 5 A first microscopic topographic image of the grid groove provided for Comparative Example 2;

[0038] Figure 6 The second microscopic topography of the grid groove provided for Comparative Example 2;

[0039] Figure 7 The third microscopic topography of the grid groove provided for Comparative Example 2.

[0040] icon:

[0041] 1-Solar cell; 10-Cell substrate; 11-Silicon substrate; 12-Transparent conductive thin film layer; 13-Metal seed layer; 14-Photoresist layer; 141-First photoresist layer; 142-Second photoresist layer; 15-Grid groove;

[0042] 2-Screen printing device; 21-Printing mechanism; 211-First screen; 212-Second screen; 22-Drying mechanism; 221-First drying oven; 222-Second drying oven; 23-Conveying mechanism. Detailed Implementation

[0043] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms “comprising” and “having”, and any variations thereof, in the specification and the foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0045] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0046] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0047] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), and similarly, "multiple segments" refers to two or more (including two segments).

[0048] In the description of the embodiments of this application, the technical terms "middle", "length", "width", "thickness", "upper", "lower", "left", "right", "bottom", "inner", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0049] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "connection" and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0050] Copper electrodes offer advantages such as better plasticity, lower metal line resistance, less light-shielding loss, and lower cost, and are considered a breakthrough technology for fabricating solar cell electrodes using silver paste screen printing. However, directly electroplating copper electrodes onto a transparent conductive film is non-selective, and the adhesion between directly electroplated copper and the transparent conductive film is poor, making it difficult to meet the requirements for solar cell module manufacturing. Therefore, it is necessary to deposit a copper seed layer on the transparent conductive film, and then prepare a mask through screen printing. The mask is then exposed and developed to create a pattern, enabling selective deposition to form electroplated copper grid lines.

[0051] However, solar cells obtained using existing copper interconnect technology have low photoelectric conversion efficiency. The inventors analyzed the reasons for this low efficiency and concluded that inhomogeneity in the width of the electroplated grid lines and the ohmic contact between the grid lines and the substrate affects both the current collection efficiency and the photoelectric conversion efficiency of the solar cell.

[0052] The inventors further analyzed the reasons for the uneven grid lines obtained by electroplating and found that during the electroplating of grid lines, different degrees of defects such as electrode plating defects, plating defects, grid line detachment, and poor ohmic contact between the metal electrode and the substrate are likely to occur at different locations of the solar cell. These defects cause the grid line width to widen, which increases the light-blocking area and affects the photoelectric conversion efficiency.

[0053] The inventors further analyzed the situation of poor copper grid lines in solar cells and believed that the uniformity of the thickness of the negative photoresist layer applied to the surface of the copper seed layer by screen printing directly affects the subsequent exposure, development and pattern metallization processes, and thus the quality of the copper electrode.

[0054] For example, the inventors discovered that if the photoresist is too thick, it will lead to insufficient subsequent exposure and too much photoresist residue at the bottom of the groove after development. This results in poor adhesion between the metal grid lines and the substrate after subsequent electroplating, which can easily lead to grid line detachment and poor ohmic contact between the metal grid line electrodes and the substrate, thereby affecting the photoelectric conversion efficiency.

[0055] For example, the inventors discovered that if the photoresist is too thin, it will lead to overexposure in the subsequent exposure, which can easily result in shallow grooves and collapse of the groove sidewalls after development. This can lead to defects such as plating defects and seepage of the metal grid lines after subsequent electroplating, causing the grid line width to widen, the light-blocking area to increase, and the conversion efficiency to decrease.

[0056] Therefore, if the thickness of the photoresist layer coated in the same solar cell is uneven, for example, thicker in some places and thinner in others, then during the exposure process, since the exposure process requires simultaneous exposure of the photoresist layer at different locations on the same cell substrate under the same exposure parameters, the uneven thickness of the photoresist layer will lead to overexposure in some areas and underexposure in others, affecting the uniformity of the grooves obtained after exposure and development. This will result in different degrees of plating defects, seepage, poor contact, and peeling between the copper electroplated grid lines of the same solar cell, thus affecting the conversion efficiency of the solar cell.

[0057] Therefore, this application provides a method for fabricating a solar cell. Using a screen with a mesh size of at least 200, a first coating is applied to the surface of the metal seed layer 13 of the cell substrate 10 and then dried to obtain a first photoresist layer 141. Then, using the same screen with a mesh size of at least 200, a second coating is applied to the surface of the first photoresist layer 141 and dried to obtain a second photoresist layer 142. The first photoresist layer 141 and the second photoresist layer 142 together form a photoresist layer 14.

[0058] Since the mesh count of the screen used in both coating operations is not less than 200 mesh, the mesh openings of the screen are small, the passability of the photoresist paste is poor, the film thickness is reduced, and the roughness of the coated surface is also reduced. This can reduce the thickness deviation of the first photoresist layer 141 and the second photoresist layer 142 at different locations, thereby reducing the thickness deviation of the photoresist layer 14 at different locations and improving the uniformity of the thickness of the photoresist layer 14.

[0059] The method for fabricating solar cells provided in this embodiment will be described in further detail below.

[0060] Methods for manufacturing solar cells include:

[0061] S1. Obtain a battery substrate 10, the surface of which is a metal seed layer 13.

[0062] Please see Figure 1 For example, the battery substrate 10 includes a silicon base layer 11, a transparent conductive thin film layer 12, and a metal seed layer 13 stacked together.

[0063] Among them, silicon substrate 11 refers to the intrinsic amorphous silicon and P-type amorphous silicon thin films on the front side of the N-type silicon wafer, and the intrinsic amorphous silicon and N-type amorphous silicon thin films on the back side of the silicon wafer.

[0064] Alternatively, silicon substrate 11 refers to intrinsic amorphous silicon and N-type amorphous silicon thin films on the front side of a P-type silicon wafer, and intrinsic amorphous silicon and P-type amorphous silicon thin films on the back side of the silicon wafer.

[0065] like Figure 1 As shown, the battery substrate 10 has a front side and a back side, and the surface layer of both the front and back sides is a metal seed layer 13. That is, a transparent conductive thin film layer 12 and a metal seed layer 13 are stacked on the front side of the silicon substrate 11, and a transparent conductive thin film layer 12 and a metal seed layer 13 are stacked on the back side of the silicon substrate 11.

[0066] This application does not limit how the battery substrate 10 is obtained. In one possible embodiment, the battery substrate 10 can be obtained by the following method:

[0067] (1) Cleaning and flocking

[0068] Textured surfaces are fabricated on the front and back sides of an N-type monocrystalline silicon wafer to reduce light reflectivity and increase incident light absorption.

[0069] When preparing the textured surface, the N-type single crystal silicon wafer can be immersed in an alkaline solution such as NaOH to form several parallel and sequentially connected pyramid-shaped textured surfaces on both sides of the N-type single crystal silicon wafer.

[0070] (2) Deposition of amorphous silicon thin film

[0071] Intrinsic amorphous silicon films are deposited on the front and back sides of a silicon wafer after cleaning and texturing. For example, boron doping is performed on the intrinsic amorphous silicon film on the front side, and phosphorus doping is performed on the intrinsic amorphous silicon film on the back side.

[0072] (3) Deposit a transparent conductive thin film layer 12

[0073] Depositing a transparent conductive thin film layer 12 on an amorphous silicon thin film can not only protect the amorphous silicon thin film, but also increase the collection efficiency of charge carriers and reduce light reflection.

[0074] (4) Deposited metal seed layer 13

[0075] A metal seed layer 13 is deposited on the surface of the front transparent conductive film layer 12 and the back transparent conductive film layer 12 respectively to obtain the battery substrate 10.

[0076] For example, copper seed layers are deposited on the surfaces of the transparent conductive thin film layers 12 on the front and back sides using methods such as PVD or magnetron sputtering, so that copper grid lines can be formed by electroplating on the copper seed layers in the future.

[0077] S2, screen printing

[0078] A photoresist layer 14 is formed by coating the surface of the metal seed layer 13; the photoresist layer 14 includes at least a first photoresist layer 141 formed by a first coating and a first drying, and a second photoresist layer 142 formed by a second coating and a second drying on the first photoresist layer 141; the mesh count of the screen during the first coating and the second coating is not less than 200 mesh.

[0079] The mesh count of the screen used in both coating operations is not less than 200 mesh. The smaller the mesh size of the screen, the poorer the permeability of the photoresist paste, the smaller the film thickness, and the smaller the surface roughness of the coating. This can reduce the thickness deviation at different positions of the first photoresist layer 141 and the second photoresist layer 142, thereby reducing the thickness deviation at different positions of the photoresist layer 14 and improving the uniformity of the photoresist layer 14 thickness.

[0080] Furthermore, a 230-250 mesh screen can be used to perform the first coating and the second coating, respectively.

[0081] Furthermore, a 240-mesh screen can be used for the first coating and the second coating, which can not only obtain the photoresist layer 14 of the preset thickness through two coatings, but also further improve the uniformity of the photoresist layer 14 thickness.

[0082] The battery substrate 10 has a front side and a back side. Both the front side and the back side of the battery substrate 10 need to be coated with a photoresist layer 14 so that the corresponding front gate electrode and back gate electrode can be fabricated on the front side and the back side of the battery substrate 10 in the future.

[0083] The definition of the front and back sides of the battery substrate 10 does not restrict whether the N-side or the P-side of the battery substrate 10 is the front or the back side. The front and back sides of the battery substrate 10 refer to the two opposite surfaces of the battery substrate 10.

[0084] This application does not limit how the photoresist layer 14 is prepared on the front and back sides of the battery substrate 10. Those skilled in the art can make appropriate adjustments as needed, provided that the photoresist layer 14 on both the front and back sides of the battery is obtained through the first coating and the first drying and the second coating and the second drying.

[0085] In one possible embodiment, a first coating is performed on the metal seed layer 13 on the front side of the battery substrate 10, followed by a first drying process, to obtain a battery substrate 10 with a first photoresist layer 141 formed on the front side. Then, a second coating is performed on the first photoresist layer 141 on the front side of the battery substrate 10, followed by a second drying process, to form a second photoresist layer 142 on the first photoresist layer 141 on the front side, thus completing the fabrication of the photoresist layer 14 on the front side of the battery substrate 10.

[0086] Then, a first coating is applied to the metal seed layer 13 on the back side of the battery substrate 10, followed by a first drying process, to obtain a battery substrate 10 with a first photoresist layer 141 formed on the back side. A second coating is then applied to the first photoresist layer 141 on the back side of the battery substrate 10, followed by a second drying process, to form a second photoresist layer 142 on the first photoresist layer 141 on the back side, thus completing the fabrication of the photoresist layer 14 on the back side of the battery substrate 10.

[0087] That is, the photoresist layer 14 on the front side of the battery substrate 10 can be prepared by screen printing first, and then the photoresist layer 14 on the back side of the battery substrate 10 can be prepared by screen printing.

[0088] However, the inventors believe that after the front photoresist layer 14 is prepared on the front side of the battery substrate 10, the back photoresist layer 14 is prepared on the back side of the battery substrate 10. This will increase the degree of oxidation of the metal seed layer 13 on the back side of the battery substrate 10, which will in turn increase the contact resistance between the subsequently obtained electroplated metal grid lines and the metal seed layer 13, thereby reducing the conversion efficiency of the solar cell 1.

[0089] Specifically, when preparing the front photoresist layer 14, the battery substrate 10 needs to be placed in an oven for a first drying and a second drying. However, the metal seed layer 13 on the back of the battery substrate 10 also undergoes two drying processes in the oven. Since the surface of the metal seed layer 13 on the back of the battery substrate 10 is not coated with photoresist, the metal seed layer 13 on the back will oxidize during the two drying processes, and the degree of oxidation will increase.

[0090] Based on this, please refer to Figure 2 This application embodiment also provides a method for preparing a photoresist layer 14 on the front and back sides of a battery substrate 10, comprising:

[0091] In sequence:

[0092] First coating on the front side, first drying on the front side, first coating on the back side, first drying on the back side, second coating on the front side, second drying on the front side, second coating on the back side, and second drying on the back side.

[0093] Alternatively, the process could be: first coating on the front side, first drying on the front side, first coating on the back side, first drying on the back side, second coating on the back side, second drying on the back side, second coating on the front side, and second drying on the front side.

[0094] Between the first drying operation on the front side and the second drying operation on the front side, at least the first coating and the first drying operation on the back side of the battery substrate 10 are performed first. This avoids the metal seed layer 13 on the back side of the battery substrate 10 being exposed to the oven for two drying operations, thereby reducing the degree of oxidation of the metal seed layer 13 on the back side.

[0095] Furthermore, this application does not limit the thickness of the photoresist layer 14, and relevant personnel can make corresponding adjustments as needed.

[0096] In one possible embodiment, the method for fabricating the solar cell provided in this example further includes:

[0097] S3, Exposure and Development

[0098] Exposure of the photoresist layer 14 can create a difference in properties between the exposed and unexposed areas of the photoresist. Then, development is performed using a developer to obtain the gate grooves 15. Since the photoresist is prepared by coating in two or more layers, more uniform gate grooves can be obtained after the exposure and development process.

[0099] For example, the photoresist layer 14 is exposed and developed to obtain the gate groove 15; wherein the exposure energy is 85 mJ / mm. 2 The development time is 2 minutes, and the developing solution is an 8-13 g / L sodium carbonate solution.

[0100] Furthermore, in order to improve the quality of the grid groove 15, reduce the probability of residual adhesive and sidewall collapse of the grid groove 15 after exposure and development, and reduce the opening deviation of the grid groove 15, in some possible embodiments, a photoresist layer 14 with a thickness of 12-14 μm can be prepared by screen printing.

[0101] For example, the thickness of the photoresist layer 14 is 12 μm.

[0102] Furthermore, a first photoresist layer 141 with a thickness of 6-7 μm can be obtained through the first coating and the first drying.

[0103] The thickness of the first photoresist layer 141 is set to 6-7 μm, so that the thickness difference between the first photoresist layer 141 and the second photoresist layer 142 is small, thereby reducing the difference between the thickness deviation of the first photoresist layer 141 and the thickness deviation of the second photoresist layer 142, which can further reduce the thickness non-uniformity of the photoresist layer 14.

[0104] Furthermore, to avoid over-drying or under-drying during the first and second drying processes, in some possible implementations, the temperature of the first drying is 80-100°C, and the time is 6-7 minutes.

[0105] The second drying temperature is 80-100℃, and the time is 6-7 minutes;

[0106] For example, the temperature for the first and second drying processes is 90°C, and the drying time is 6 minutes.

[0107] Furthermore, to facilitate the adjustment of the drying time according to the coating thickness by relevant personnel, in one possible embodiment, the temperature of the first drying is 80-90°C, and the ratio of the thickness of the first coating to the drying time of the first drying is 1:0.9-1.2μm / min.

[0108] The temperature for the second drying is 80-90℃, and the ratio of the thickness of the second coating to the drying time for the second drying is 1:0.9-1.2μm / min.

[0109] For example, if the thickness of the first coating is 6 μm and the thickness of the second coating is 7 μm, then the drying time for the first coating is 6 min and the drying time for the second coating is 7 min.

[0110] Furthermore, this application embodiment also provides a screen printing apparatus 2 for screen printing a photoresist layer 14 onto a battery substrate 10.

[0111] Please see Figure 3The screen printing apparatus 2 includes a printing mechanism 21 and a drying mechanism 22. The printing mechanism 21 includes a first screen 211 and a second screen 212. The first screen 211 is used for the first coating, and the second screen 212 is used for the second coating. The mesh count of both the first and second screens is not less than 200 mesh. The drying mechanism 22 includes a first oven 221 and a second oven 222. The first oven 221 is located between the first and second screens 211 and is used to perform a first drying of the first photoresist layer 141 coated on the first screen 211. The second oven 222 is located at the rear end of the second screen 212 and is used to perform a second drying of the second photoresist layer 142 coated on the second screen 212.

[0112] This application does not limit the specific configuration of the printing mechanism 21. In one possible embodiment, the printing mechanism 21 further includes a first printing table opposite to the first screen 211 and a second printing table opposite to the second screen 212, for placing the battery substrate 10 for corresponding printing.

[0113] Furthermore, a scraper is provided above the first screen printing plate 211 and the second screen printing plate 212 to apply photoresist from the first screen printing plate 211 and the second screen printing plate 212 to the surface of the battery substrate 10.

[0114] Furthermore, this application does not limit the specific configuration of the drying mechanism 22, and relevant personnel can make corresponding adjustments as needed.

[0115] In one possible embodiment, the first oven 221 and the second oven 222 are open-type, with interconnected inlets and outlets, so that the battery substrate 10 is sent from the inlet to the oven for drying and then sent out of the oven from the outlet.

[0116] Furthermore, in order to improve the printing efficiency of the screen printing apparatus 2, the screen printing apparatus 2 also includes a conveying mechanism 23.

[0117] The conveying mechanism 23 is configured to convey the battery substrate 10 to the area below the first screen 211, inside the first oven 221, below the second screen 212, and inside the second oven 222 for first coating, first drying, second coating, and second drying of the battery substrate 10.

[0118] This application does not limit the specific configuration of the conveying mechanism 23. In one possible embodiment, the conveying mechanism 23 includes multiple conveyor belts. Conveyor belts are provided between the first screen 211 and the first oven 221, and between the second screen 212 and the second oven 222, for transferring the battery substrate 10 after the corresponding process.

[0119] Furthermore, to facilitate the preparation of photoresist layers 14 on the front and back sides of the battery substrate 10, the screen printing apparatus 2 provided in this example includes two sets of corresponding printing mechanisms 21 and drying mechanisms 22. The conveying mechanism 23 is also used to transfer the battery substrate 10 after corresponding operations between the two sets of printing mechanisms 21 and drying mechanisms 22.

[0120] For example, the two sets of printing mechanisms 21 and drying mechanisms 22 are arranged in series. For easy distinction, the two sets of printing mechanisms 21 are named front printing mechanism 21 and back printing mechanism 21; the two sets of drying mechanisms 22 are named front drying mechanism 22 and back drying mechanism 22.

[0121] The system is configured in series, that is, the following components are arranged sequentially: front first screen 211, first conveyor belt, front first oven 221, first turning machine, back first screen 211, second conveyor belt, back first oven 221, third conveyor belt, back second screen 212, fourth conveyor belt, back second oven 222, second turning machine, front second screen 212, fifth conveyor belt, and front second oven 222, to sequentially perform front first coating, front first drying, back first coating, back first drying, back second coating, back second drying, front second coating, and front second drying.

[0122] Alternatively, the following can be arranged sequentially: front first screen 211, first conveyor belt, front first oven 221, first turning machine, back first screen 211, second conveyor belt, back first oven 221, second turning machine, front second screen 212, third conveyor belt, front second oven 222, third turning machine, back second screen 212, fourth conveyor belt, back second oven 222, to sequentially perform front first coating, front first drying, back first coating, back first drying, front second coating, front second drying, back second coating and back second drying.

[0123] Furthermore, the fabrication method of solar cell 1 also includes:

[0124] S4, Post-processing

[0125] Post-processing includes electroplating operations on the metal grid lines in the grid line groove 15.

[0126] Excess photoresist layer 14 and metal seed layer 13 are removed from the battery substrate 10 obtained after electroplating. Because the grid lines are more uniform, the grid lines formed by electroplating in the uniform grid lines can have more uniform width and thickness, and reduce the proportion of broken grids, thereby improving the photoelectric conversion efficiency of the solar cell.

[0127] 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.

[0128] Example 1

[0129] Example 1 provides a solar cell 1, including a cell substrate 10 and photoresist layers 14 formed on both sides of the cell substrate 10, which are prepared by the following method:

[0130] The battery substrate 10 is subjected to the following processes in sequence: first coating on the front side, first drying on the front side, first coating on the back side, first drying on the back side, second coating on the back side, second drying on the back side, second coating on the front side, and second drying on the front side.

[0131] The photoresist used in the first and second coatings was a negative photoresist, with a screen mesh count of 240. The printing parameters were set as follows: squeegee angle 45°, squeegee depth 2.0 mm, screen spacing 1.1 mm, printing pressure 30 N, printing speed 260 mm / s, ink return blade depth 0.2 mm, ink return speed 400 mm / s, photoresist slurry viscosity 1000 cps, drying temperature 90℃, and drying time 6 min.

[0132] The thickness values ​​of the photoresist layer 14 on the front side of the solar cell 1 were measured at 25 points, as shown in Table 1. The 25-point thickness values ​​were obtained by selecting 5 test points at even intervals along the width and length directions of the rectangular cell substrate 10 after coating.

[0133] Example 2

[0134] Example 2 provides a solar cell 1, which differs from Example 1 in that:

[0135] The solar cell 1 provided in Example 1 is exposed and developed to obtain the grid groove 15.

[0136] The energy of the exposure was 85 mJ / cm. 2 The development time is 2 minutes, and the developing solution is an 8-13 g / L sodium carbonate solution.

[0137] The microstructure of the grid groove 15 in a region with a thickness of 12 μm was observed, such as... Figure 4 As shown.

[0138] from Figure 4 It can be seen that when the photoresist film thickness is 12µm, the upper opening of the groove is 27.58µm and the lower opening is 25.21µm. The difference between the upper and lower openings of the groove is small, and the groove shape is close to an ideal rectangle.

[0139] Comparative Example 1

[0140] Comparative Example 1 provides a solar cell 1, which differs from Example 1 in that: a 120-mesh screen is used to perform a single coating on the front side, a single drying on the front side, a single coating on the back side, and a single drying on the back side.

[0141] The printing parameters were set as follows: squeegee angle 30°, squeegee pressing depth 2.6mm, screen spacing 1.5mm, printing pressure 35N, printing speed 300mm / s, ink return blade pressing depth 0.2mm, ink return speed 400mm / s, drying temperature 90℃, drying time 12min; the temperature for the first drying of the front side and the first drying of the back side was 90℃, and the drying time was 12min.

[0142] The thickness values ​​of the photoresist layer 14 on the front side of the solar cell 1 were measured at 25 points, as shown in Table 1.

[0143] Table 1

[0144]

[0145]

[0146] As can be seen from Table 1, the coating thickness uniformity of Example 1 is 7.69%, while that of Comparative Example 1 is 29.63%. Film thickness uniformity is defined as: (maximum value - minimum value) / (maximum value + minimum value).

[0147] This application utilizes a 240-mesh screen to apply the coating twice and perform corresponding drying operations, resulting in a more uniform film thickness and a smaller difference in film thickness for the photoresist layer 14 formed by the first photoresist layer 141 and the second photoresist layer 142.

[0148] Comparative Example 2

[0149] The difference between Comparative Example 2 and Example 2 is that the solar cell 1 provided in Comparative Example 1 is exposed and developed to obtain the grid groove 15. The exposure and development conditions are the same as those in Example 2.

[0150] The morphology of the gate groove 15 with a thickness of 9 μm was observed, and the results are as follows: Figure 5 As shown. The morphology of the gate groove 15 with a thickness of 17 μm was observed, and the results are as follows. Figure 6 and Figure 7 As shown.

[0151] from Figure 5 It can be seen that after the 9μm thick photoresist layer 14 is exposed and developed, the developing solution excessively corrodes the sidewalls of the bottom part of the tank, and the width of the tank opening at different heights varies greatly, which will lead to an increase in the light-shielding area of ​​the grid lines formed after electroplating.

[0152] from Figure 6 It can be seen that after exposure and development of the 17μm photoresist layer 14, the upper opening is 16.11µm and the lower opening is 22.39µm, indicating insufficient development. The measurement points for the widths of the upper and lower openings are shown below. Figure 6 The scale lines are shown in the image. And through... Figure 7 It can be seen that there is a lot of photoresist residue at the bottom of the gate groove 15, indicating that the thickness of the photoresist layer 14 is uneven. After exposure and development, it will affect the uniformity of the shape and size of the gate groove 15.

[0153] Test case

[0154] Copper grid lines were prepared by electroplating the solar cells 1 provided in Example 2 and Comparative Example 2. The proportions of uneven thickness and broken grid lines in the copper grid lines of Example 2 and Comparative Example 2 were statistically analyzed, and the conversion efficiency of the solar cells with grid lines was tested. The statistical and test results are shown in Table 2.

[0155] Table 2

[0156] Uneven thickness ratio 10.57％ 35.23％ Broken grid ratio 12％ 26％ Conversion efficiency 23.8％ 23.92％

[0157] As shown in Table 2, the preparation method provided in this application example can form a photoresist layer 14 with a more uniform film thickness, thereby forming grid grooves 15 with more uniform shape and size after exposure and development operations. This facilitates the formation of copper grid lines with more uniform thickness and lower grid breakage rate after electroplating operations, thereby improving the conversion efficiency of the solar cell 1.

[0158] 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 fabricating a solar cell, characterized in that, include: A battery substrate is obtained; the surface layer of the battery substrate is a metal seed layer. Screen printing: A photoresist layer is formed by coating the surface of the metal seed layer; the photoresist layer includes at least a first photoresist layer formed by a first coating and a first drying, and a second photoresist layer formed by a second coating and a second drying on the first photoresist layer. The mesh count of the screen used for the first coating and the second coating is not less than 200 mesh.

2. The method for preparing a solar cell according to claim 1, characterized in that, The mesh count of the screen used for the first and second coatings is 230-250 mesh, and the coating parameters include: screen spacing 1-1.5mm, printing pressure 30-40N, printing speed 200-300mm / s, and photoresist viscosity 900-1100cps.

3. The method for preparing a solar cell according to claim 2, characterized in that, The preparation method further includes: Exposure and development: The photoresist layer is exposed and developed to obtain gate grooves; The energy of the exposure is 70-90 mJ / cm. 2 The development time is 1.8-2.2 min, and the developing solution is an 8-13 g / L sodium carbonate solution; the thickness of the photoresist layer is 12-14 μm.

4. The method for preparing a solar cell according to claim 1, characterized in that, The thickness of the first photoresist layer is 6-7 μm.

5. The method for preparing a solar cell according to claim 4, characterized in that, The temperature for the first drying step is 80-100℃, and the time is 6-7 minutes. And / or, the second drying temperature is 80-100℃ and the time is 6-7 minutes.

6. The method for preparing a solar cell according to claim 5, characterized in that, The temperature for the first drying and / or the second drying is 80-90℃.

7. The method for preparing a solar cell according to claim 5, characterized in that, The temperature of the first drying is 80-90℃, and the ratio of the thickness of the first coating to the time of the first drying is 1:0.9-1.2μm / min; And / or, the temperature of the second drying is 80-90℃, and the ratio of the thickness of the second coating to the time of the second drying is 1:0.9-1.2μm / min.

8. The method for preparing a solar cell according to claim 1, characterized in that, The battery substrate has a front side and a back side, and the surface layer of both the front side and the back side is the metal seed layer; the screen printing includes the following sequential processes: First coating on the front side, first drying on the front side, first coating on the back side, first drying on the back side, second coating on the front side, second drying on the front side, second coating on the back side, and second drying on the back side; Alternatively, the process could be: first coating on the front side, first drying on the front side, first coating on the back side, first drying on the back side, second coating on the back side, second drying on the back side, second coating on the front side, and second drying on the front side.

9. A screen printing apparatus for implementing the method for preparing a solar cell according to any one of claims 1-8, characterized in that, include: A printing mechanism, comprising a first screen and a second screen; The first screen is used for the first coating, and the second screen is used for the second coating; the mesh count of the first screen and the second screen is not less than 200 mesh. A drying mechanism, comprising a first drying oven and a second drying oven; the first drying oven is disposed between the first screen and the second screen and is used to perform the first drying of the first photoresist layer coated on the first screen; the second drying oven is disposed at the rear end of the second screen and is used to perform the second drying of the second photoresist layer coated on the second screen.

10. The screen printing apparatus according to claim 9, characterized in that, The screen printing apparatus includes a conveying mechanism; the conveying mechanism is configured to convey the battery substrate to the area below the first screen, inside the first oven, below the second screen, and inside the second oven to perform the first coating, the first drying, the second coating, and the second drying on the battery substrate.

11. The screen printing apparatus according to claim 9, characterized in that, The screen printing apparatus includes two sets of one-to-one printing mechanisms and drying mechanisms, which are used to screen print on the front and back sides of the battery substrate, respectively.

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