Conductive silver paste, methods for fabricating back electrodes of solar cells, solar cells

Abstract

This application relates to the field of solar cells, and discloses conductive silver paste, a method for preparing a back electrode of a solar cell, and a solar cell. The conductive silver paste comprises: 50-90 parts by weight of conductive silver powder, 0.5-10 parts by weight of glass powder, 1-20 parts by weight of an organic carrier, 2-20 parts by weight of a solvent, and 0.5-10 parts by weight of an additive, wherein the specific surface area of ​​the conductive silver powder is 1.0 m². 2 / g-1.5m 2 / g. The conductive silver paste proposed in this application can be used as a paste for preparing the silver grid on the back electrode of a solar cell, which can improve the welding performance and conductivity of the back electrode of the solar cell, and is beneficial to improving the stability of the solar cell.

Description

Technical Field

[0001] This application relates to the field of solar cells, specifically to conductive silver paste, a method for preparing a back electrode for a solar cell, and a solar cell. Background Technology

[0002] Solar cells are one of the most commonly used power sources for low Earth orbit (LEO) spacecraft, widely applied in various types of satellites, space stations, and other space vehicles as their primary power source. For example, the International Space Station uses a large number of solar cells to meet its power needs. Solar cells used in LEO spacecraft offer high performance reliability and controllable manufacturing costs. However, the LEO space environment presents various environmental factors that can continuously damage solar cells, limiting their service life. These include the significant temperature variations between sun-facing and shaded states during orbital motion and the continuous radiation damage in space. Therefore, to further improve the performance of solar cells on LEO spacecraft, ongoing research into the materials and structures of solar cells is necessary. Summary of the Invention

[0003] In a first aspect, this application discloses a conductive silver paste comprising: 50-90 parts by weight of conductive silver powder, 0.5-10 parts by weight of glass powder, 1-20 parts by weight of an organic carrier, 2-20 parts by weight of a solvent, and 0.5-10 parts by weight of an additive, wherein the specific surface area of ​​the conductive silver powder is 1.0 m². 2 / g-1.5m 2 / g.

[0004] The conductive silver paste proposed in this application can be used as a paste for preparing the silver grid of the back electrode of a solar cell. This conductive silver paste has a high content of conductive silver powder, and by limiting the specific surface area of ​​the conductive silver powder, the sintering activity of the conductive silver powder and the synergistic relationship with other components are optimized. Therefore, this conductive silver paste can be used to prepare a highly reliable, low-resistivity back electrode for solar cells, improving the welding performance and conductivity of the back electrode, and thus contributing to the stability of the solar cell.

[0005] In some embodiments, the conductive silver paste comprises: 75-85 parts by weight of conductive silver powder, 1-5 parts by weight of glass powder, 1-10 parts by weight of organic carrier, 2-20 parts by weight of solvent, and 1-5 parts by weight of additives.

[0006] In some embodiments, the silver content in the conductive silver paste is 75%-85%. Therefore, the conductive silver paste has high conductivity.

[0007] In some embodiments, the conductive silver powder has a Dv50 particle size of 0.5 μm-1.5 μm and a tap density of 3 g / cm³. 3 -10g / cm 3 This results in a dense structure and high conductivity for the back electrode of the solar cell prepared with this conductive silver paste.

[0008] In some embodiments, the sintering temperature of the conductive silver powder is 200℃-300℃. Therefore, the conductive silver powder has high sintering activity, which is beneficial for improving the density of the silver gate prepared after sintering the conductive silver paste.

[0009] In some embodiments, the glass powder includes at least one of Te2O-Bi2O3-PbO glass, PbO-SiO2 glass powder, and lead-free glass powder, wherein the Dv50 particle size of the glass powder is 0.5μm-10μm. The aforementioned glass powder has a certain promoting effect on the sintering of conductive silver powder in conductive silver paste, thereby improving the sintering performance of the conductive silver paste.

[0010] In some embodiments, the organic carrier comprises at least one selected from ethyl hydroxyethyl cellulose, nitrocellulose, a mixture of ethyl cellulose and phenolic resin, alkyd resin, phenolic resin, acrylate resin, xylene resin, polybutene resin, polyester resin, urea resin, vinyl acetate resin, rosin, or polymethyl methacrylate of alcohol. Thus, the aforementioned organic carrier can impart viscosity and rheological properties to the conductive silver paste suitable for screen printing.

[0011] In some embodiments, the solvent includes at least one selected from diethylene glycol diethyl ether, butyl carbitol (diethylene glycol monobutyl ether), diethylene glycol butyl ether acetate, carbitol butyl ether acetate, diacetone alcohol, terpineol, benzyl alcohol, cyclohexanone, methyl ethyl ketone, divalent esters, 2,2,4-trimethyl-1,3-pentanediol monoisobutyl ester, and 2,2,4-trimethyl-1,3-pentanediol diisobutyl ester. Therefore, the aforementioned solvent can improve the fluidity of the conductive silver paste for preparing the back electrode of a solar cell.

[0012] In some embodiments, the additive includes a dispersant, which comprises at least one selected from sorbitan trioleate, dimethylacetamide, TDO, BYK-110, and BYK-111. The aforementioned dispersant can reduce the agglomeration of conductive silver powder, allowing the conductive silver paste to pass through the screen more smoothly for printing. This, in turn, helps improve the quality of screen printing.

[0013] In a second aspect of this application, a method for preparing a back electrode of a solar cell using the conductive silver paste proposed in this application is characterized by comprising: performing a first screen printing process on the surface of a solar cell backsheet using conductive silver paste to obtain a solar cell backsheet with a silver paste main grid; sequentially drying and sintering the solar cell backsheet with the silver paste main grid to obtain a solar cell backsheet with a silver main grid; performing a second screen printing process and drying process on the solar cell backsheet with the silver main grid using aluminum paste to obtain a solar cell backsheet with an aluminum secondary grid; covering the aluminum secondary grid with a glass paste, and sequentially drying and sintering the paste to prepare the back electrode of the solar cell.

[0014] This method first prints a silver main grid, then prints an aluminum secondary grid, and finally prints a glass paste onto the aluminum secondary grid, followed by sintering to create an outer protective layer covering the aluminum secondary grid. This method reduces the formation of mixed crystals between silver and aluminum. The glass paste printed at the junction of the silver and aluminum secondary grids also protects this junction, reducing accelerated aging during service caused by differences in the thermal expansion coefficients and crystal structures of silver and aluminum. Protecting the junction between the aluminum secondary grid and the silver-aluminum grid helps reduce aging and powder shedding at the junction of the silver and aluminum electrodes. Therefore, the back electrode of the solar cell prepared by the method proposed in this application has better stability and a longer service life.

[0015] In some embodiments, the mesh count of the screen used for the first screen printing process is 200-300 mesh. This allows for the printing of silver grid lines with consistent width and neat edges, contributing to improved performance and appearance quality of the solar cell's back electrode.

[0016] In some embodiments, the mesh count of the screen used for the second screen printing process is 300-400 mesh. This facilitates the fabrication of aluminum sub-grids with clear edge lines, thereby improving current collection performance.

[0017] In a third aspect of this application, this application proposes a solar cell that uses the conductive silver paste proposed in this application to prepare a silver grid, or includes a solar cell back electrode prepared by the method proposed herein.

[0018] The solar cell proposed in this application has high stability of the back cell, which is beneficial to improving the conductivity and service life of the solar cell. Attached Figure Description

[0019] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0020] Figure 1This is a cell design pattern for the silver grid on the back electrode of a solar cell in one embodiment of this application;

[0021] Figure 2 This is a cell design pattern for the aluminum sub-grid of the back electrode of a solar cell in one embodiment of this application. Detailed Implementation

[0022] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0023] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0024] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0025] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0026] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0027] Solar cells convert solar energy into electrical energy, serving as the power source for low-Earth orbit (LEO) spacecraft. Solar cells suitable for LEO spacecraft include p-type passivated emitter solar cells and back-contact solar cells (p-PERC cells). Conductive pastes can be screen-printed onto the back surface of p-PERC cells to fabricate the back electrode, a method that significantly reduces manufacturing costs. However, the LEO environment is subject to space radiation, and the bombardment of high-energy particles by these particles can cause defects in the back electrode material, leading to drastic changes in environmental stability as the spacecraft's trajectory shifts. During use, the back electrode can detach or peel due to decreased adhesion, affecting the long-term stability and reliability of the cell.

[0028] To improve the stability of the back electrode of a solar cell, this application proposes a conductive silver paste and a method for preparing the back electrode of a solar cell. By adjusting the composition of the conductive silver paste to increase its silver content, the structure and performance of the back electrode of the solar cell prepared using this conductive silver paste are improved. Furthermore, a method for preparing the back electrode of a solar cell using this conductive silver paste is also proposed, thereby improving the stability of the prepared back electrode of the solar cell.

[0029] In a first aspect, this application discloses a conductive silver paste comprising: 50-90 parts by weight of conductive silver powder, 0.5-10 parts by weight of glass powder, 1-20 parts by weight of an organic carrier, 2-20 parts by weight of a solvent, and 0.5-10 parts by weight of an additive, wherein the specific surface area of ​​the conductive silver powder is 1.0 m². 2 / g-1.5m 2 / g.

[0030] The conductive silver paste proposed in this application can be used as a paste for preparing the silver grid of the back electrode of a solar cell. This conductive silver paste has a high content of conductive silver powder. By limiting the specific surface area of ​​the conductive silver powder, the conductive silver paste maintains high fluidity despite its high silver content. By optimizing the sintering activity of the conductive silver powder and its synergistic relationship with other components, the film-forming temperature of the conductive silver powder is matched with the decomposition temperature of the organic carrier and solvent in the conductive silver paste. This allows the conductive silver paste to be used to prepare solar cell back electrodes with high electrode density through screen printing and sintering, reducing problems such as electrode blistering and electrode detachment. Therefore, the silver grid of the back electrode of the solar cell prepared with this conductive silver paste has a dense microstructure and high surface smoothness, which is beneficial for forming ohmic contacts with the solar cell backsheet. Thus, this conductive silver paste can be used to prepare high-reliability, low-resistivity solar cell back electrodes, improving the welding performance and conductivity of the solar cell back electrode, and contributing to the stability of the solar cell.

[0031] In some embodiments, the conductive silver paste comprises: 75-85 parts by weight of conductive silver powder, 1-5 parts by weight of glass powder, 1-10 parts by weight of organic carrier, 2-20 parts by weight of solvent, and 1-5 parts by weight of additives.

[0032] In some embodiments, the silver content in the conductive silver paste is 75%-85%. Therefore, the conductive silver paste has high conductivity.

[0033] In some embodiments, the conductive silver powder has a Dv50 particle size of 0.5 μm-1.5 μm and a tap density of 3 g / cm³. 3 -10g / cm 3 The conductive silver powder can be spherical or irregularly shaped. The Dv50 particle size and tap density of the conductive silver powder are within the aforementioned range. During the silver paste sintering process for preparing the back electrode of a solar cell, this facilitates the mixing and sintering of the conductive silver powder with glass powder to form a glass phase with a relatively continuous and uniform silver content. Therefore, the back electrode of the solar cell prepared from this conductive silver paste has good structural density and high conductivity.

[0034] In some embodiments, the sintering temperature of the conductive silver powder is 200℃-300℃. Therefore, the conductive silver powder has high sintering activity, which is beneficial for improving the density of the silver gate prepared after sintering the conductive silver paste.

[0035] In some embodiments, the glass powder includes at least one of Te2O-Bi2O3-PbO glass, PbO-SiO2 glass powder, and lead-free glass powder, wherein the Dv50 particle size of the glass powder is 0.5μm-10μm. The aforementioned glass powder sintering promotes the sintering of conductive silver powder in the conductive silver paste, causing the conductive silver powder to undergo sintering changes while the glass powder softens and further mixes and sinters with the conductive silver powder, which is beneficial for improving the adhesion of the conductive silver paste to the surface of the solar panel. Its Dv50 particle size within the aforementioned range is conducive to mixing and dispersing with the conductive silver powder. Therefore, it is beneficial for improving the sintering performance of the conductive silver paste.

[0036] In some embodiments, the organic carrier comprises at least one selected from ethyl hydroxyethyl cellulose, nitrocellulose, a mixture of ethyl cellulose and phenolic resin, alkyd resin, phenolic resin, acrylate resin, xylene resin, polybutene resin, polyester resin, urea resin, vinyl acetate resin, rosin, or polymethyl methacrylate of alcohol. Thus, the aforementioned organic carrier can impart viscosity and rheological properties to the conductive silver paste suitable for screen printing.

[0037] In some embodiments, the solvent includes at least one selected from diethylene glycol diethyl ether, butyl carbitol (diethylene glycol monobutyl ether), diethylene glycol butyl ether acetate, carbitol butyl ether acetate, diacetone alcohol, terpineol, benzyl alcohol, cyclohexanone, methyl ethyl ketone, divalent esters, 2,2,4-trimethyl-1,3-pentanediol monoisobutyl ester, and 2,2,4-trimethyl-1,3-pentanediol diisobutyl ester. Therefore, the aforementioned solvent can improve the fluidity of the conductive silver paste for preparing the back electrode of a solar cell.

[0038] In some embodiments, the additives include dispersants, which include at least one of sorbitan trioleate, dimethylacetamide (DMA), TDO, BYK-110, and BYK-111. TDO is Nouryon Duomeen TDO dispersant, and BYK-110 and BYK-111 are dispersants manufactured by BYK (Germany). The aforementioned dispersants can reduce the agglomeration of conductive silver powder, allowing the conductive silver paste to pass through the screen more smoothly for printing. This, in turn, improves the quality of screen printing.

[0039] In a second aspect of this application, a method for preparing a back electrode of a solar cell using the conductive silver paste proposed in this application is characterized by comprising: performing a first screen printing process on the surface of a solar cell backsheet using conductive silver paste to obtain a solar cell backsheet with a silver paste main grid; sequentially drying and sintering the solar cell backsheet with the silver paste main grid to obtain a solar cell backsheet with a silver main grid; performing a second screen printing process and drying process on the solar cell backsheet with the silver main grid using aluminum paste to obtain a solar cell backsheet with an aluminum secondary grid; covering the aluminum secondary grid with a glass paste, and sequentially drying and sintering the paste to prepare the back electrode of the solar cell.

[0040] The method for fabricating the back electrode of a solar cell proposed in this application is referenced. Figure 1 The first screen printing process includes screen printing conductive silver paste onto a solar cell backsheet using a stencil, allowing control over the printed pattern and the width of the printed silver paste grid. Through a sintering process, the conductive silver paste printed on the solar cell backsheet forms the silver grid. (Reference) Figure 2 The second screen printing process includes printing aluminum paste onto the backsheet of a solar cell using a screen printing plate. The pattern printed with the aluminum paste overlaps with the silver main grid, and part of the aluminum paste is printed onto the surface of the silver main grid, forming overlapping layers. After drying, the aluminum paste printed on the solar backsheet forms an aluminum sub-grid. The glass paste covering the printed aluminum sub-grid is then sintered to encapsulate the aluminum sub-grid within the glass paste layer, becoming the outer protective layer of the aluminum sub-grid. This method first prints and prepares the silver main grid, then prints and prepares the aluminum sub-grid, and finally prints glass paste on the aluminum sub-grid to prepare an outer protective layer covering the aluminum sub-grid.

[0041] This method first prints a silver main grid, then prints an aluminum secondary grid, and finally prints a glass paste onto the aluminum secondary grid, followed by sintering to create an outer protective layer covering the aluminum secondary grid. This method reduces the formation of mixed crystals between silver and aluminum. The glass paste printed at the junction of the silver and aluminum secondary grids also protects this junction, reducing accelerated aging during service caused by differences in the thermal expansion coefficients and crystal structures of silver and aluminum. Protecting the junction between the aluminum secondary grid and the silver-aluminum grid helps reduce aging and powder shedding at the junction of the silver and aluminum electrodes. Therefore, the back electrode of the solar cell prepared by the method proposed in this application has better stability and a longer service life.

[0042] In some embodiments, the sintering temperature is 500℃-900℃.

[0043] Sintering within the aforementioned temperature range removes organic components such as solvents from the conductive silver paste, allowing the conductive silver powder particles to melt and fuse, forming a complete silver grid structure. This results in a more dense microstructure and a smoother surface for the silver grid. Furthermore, during sintering, a chemical bond forms between the silver grid and the solar cell backsheet, ensuring the grid adheres firmly. This improves the grid structure, enhances the bond between the grid and the backsheet, and reduces the likelihood of grid detachment or peeling.

[0044] Sintering the glass slurry within the aforementioned temperature range softens the glass particles, reduces their viscosity, and induces flow, forming a dense, layered structure. In this application, the glass slurry covers the printed aluminum sub-grid. During sintering, the glass slurry forms a glass film that fills the pores on the surface of the aluminum sub-grid and covers the overlap between the aluminum sub-grid and the silver main grid. This improves the stability of the aluminum sub-grid structure, reduces the formation of silver-aluminum mixed crystals, enhances the adhesion stability between the aluminum sub-grid and the solar cell backsheet, and reduces aging phenomena such as powder shedding.

[0045] In some embodiments, the sintering process includes a gradient sintering process.

[0046] In some embodiments, the drying temperature is 150°C-250°C.

[0047] In some embodiments, the method for preparing glass paste includes: premixing 25 parts by weight of lead-free glass powder, 15 parts by weight of ethyl cellulose resin, and 60 parts by weight of solvent diethylene glycol butyl ether acetate using a planetary stirrer for degassing, and then rolling the mixture using a three-roll mill until the fineness reaches below 10 μm to obtain glass paste.

[0048] In some embodiments, the mesh count of the screen used for the first screen printing process is 200-300 mesh. The first screen printing process includes printing conductive silver paste onto the backsheet of the solar cell. With the mesh count within the aforementioned range, the conductive silver paste can pass through the mesh openings of the screen relatively easily, and the screen printing precision is high. This allows for the printing of silver grid lines with consistent width and neat edges, contributing to improved performance and appearance quality of the solar cell's back electrode.

[0049] In some embodiments, the mesh count of the screen used for the second screen printing process is 300-400 mesh. The second screen printing process includes printing aluminum paste onto the backsheet of the solar cell. A mesh count within the aforementioned range reduces issues such as blurry printing, broken lines, or uneven thickness. This facilitates the fabrication of aluminum sub-grids with clear edge lines, improving current collection performance.

[0050] In a third aspect of this application, this application proposes a solar cell that uses the conductive silver paste proposed in this application to prepare a silver grid, or includes a solar cell back electrode prepared by the method proposed herein.

[0051] The solar cell proposed in this application includes a p-type passivated emitter and a back-contact solar cell (p-PERC cell). The silver grid in the back electrode of the solar cell, prepared using the conductive silver paste proposed herein, improves the electrode density and surface smoothness of the silver grid, thereby enhancing the electrode welding performance and conductivity of the p-PERC cell. Using the method proposed in this application to prepare the back electrode of the solar cell, the glass paste forms an outer protective layer, reducing phenomena such as aging and powder shedding, improving the stability of the back cell, and contributing to improved conductivity and service life of the solar cell.

[0052] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0053] Example 1

[0054] S1: 80 parts by weight of conductive silver powder in the form of spherical silver powder (average particle size 1μm, tap density 5g / cm³). 3 -6g / cm 3The following ingredients were used to prepare a conductive silver paste with a silver content of 80%: 2 parts by mass of PbO-SiO2 glass powder, 3 parts by mass of ethyl cellulose resin, 14 parts by mass of solvent diethylene glycol butyl ether acetate, and 1 part by mass of additive BYK-111 (sintering temperature 200℃-300℃). After premixing with a planetary stirrer, the paste was rolled with a three-roll mill until the fineness reached below 10μm.

[0055] S2: Using a screen printing machine at a squeegee pressure of 0.18MPa, conductive silver paste and aluminum paste are printed on the back sheet of a TCO / Si solar cell according to the unit design pattern of the solar cell back electrode: the conductive silver paste is printed on the solar cell back sheet, and after drying and sintering, aluminum paste is printed on top, and after drying, glass paste is printed on top of the aluminum paste, and after drying and sintering, the back electrode of the solar cell is prepared.

[0056] Comparative Example 1

[0057] S1: 80 parts by weight of conductive silver powder in the form of spherical silver powder (average particle size 1μm, tap density 5g / cm³). 3 -6g / cm 3 The following ingredients were used to prepare a conductive silver paste with a silver content of 80%: 2 parts by mass of PbO-SiO2 glass powder, 3 parts by mass of ethyl cellulose resin, 14 parts by mass of solvent diethylene glycol butyl ether acetate, and 1 part by mass of additive BYK-111 (sintering temperature 200℃-300℃). After premixing with a planetary stirrer, the paste was rolled with a three-roll mill until the fineness reached below 10μm.

[0058] S2: Using a screen printing machine at a squeegee pressure of 0.18MPa, traditional silver paste and aluminum paste are printed on the back sheet of a TCO / Si solar cell according to the unit design pattern of the solar cell back electrode: After printing the traditional silver paste on the solar cell back sheet, it is dried and sintered, and then aluminum paste is printed on top, dried and sintered to prepare the back electrode of the solar cell.

[0059] Comparative Example 2

[0060] S1: Uses traditional silver paste with a silver content of 65%.

[0061] S2: Using a screen printing machine at a squeegee pressure of 0.18MPa, conductive silver paste and aluminum paste are printed on the back sheet of a TCO / Si solar cell according to the unit design pattern of the solar cell back electrode: the conductive silver paste is printed on the solar cell back sheet, and after drying and sintering, aluminum paste is printed on top, and after drying, glass paste is printed on top of the aluminum paste, and after drying and sintering, the back electrode of the solar cell is prepared.

[0062] Test method:

[0063] 1. Welding tensile test

[0064] A desktop welding machine (FJL2023001) was used, with a pressure setting of 8N and a voltage setting of 0.7V. The battery with the welded tensile test piece or interconnect piece was fixed to the testing machine. The tensile test piece should be bent upwards at 45° and clamped tightly with clamps. The direction of force was at a 135° angle to the solar cell. The tensile strength of the weld joint was determined using the following two methods. The rate of force applied to the tensile test piece should not exceed 1N / s. The indicated tensile force reading was recorded at the instant the tensile piece was pulled off the battery.

[0065] 2. Steady-state damp heat test

[0066] Perform steady-state damp heat tests in the following order:

[0067] a) Measure electrical performance before testing;

[0068] b) Place the battery in the sample holder, then place the sample holder in a humidity test chamber. The temperature of the humidity test chamber should be 60℃±2℃, and the relative humidity should not be less than 90%, for 96 hours. The sample holder and the humidity test chamber should meet the following requirements:

[0069] 1) The battery sample and sample holder materials do not undergo chemical reactions under humid heat conditions; 2) Condensation on the walls and top of the humid heat test chamber should not fall onto the battery; 3) The water used as the moisture source in the humid heat test chamber is deionized water; 4) The sample holder and humid heat test chamber should not introduce corrosive contaminants into the battery.

[0070] c) After the test, first check the battery for appearance and mechanical defects;

[0071] d) Conduct an electrode firmness test and inspect for electrode defects. Cover the upper and lower surfaces of the solar cell with tape that has a peel strength of not less than 3.4 N / cm between the tape and a clean steel surface. Rub the tape until there are no hazy gaps and it firmly adheres to the solar cell. Then peel the tape off at an angle of 0° to 90° to the solar cell surface. The antireflective coating of the cell should not have gaps larger than 1.8 mm in diameter; gaps between 0.6 mm and 1.8 mm in diameter should not exceed 5 per square centimeter; gaps smaller than 0.6 mm in diameter are negligible. Gaps caused by coating fixtures are permissible, but the area of ​​these gaps should not exceed 1% of the total cell area.

[0072] Test results: See Table 1.

[0073] Table 1

[0074]

[0075] As shown in Table 1, the conductive silver paste proposed in this application can improve the welding pull force of the back electrode of the solar cell and reduce the resistance, making the printed back electrode of the solar cell adhere more firmly and improving the electrical performance of the back electrode of the solar cell. The method for preparing the back electrode of the solar cell proposed in this application can improve the stability of the back electrode of the solar cell and reduce aging and powder shedding.

[0076] In the description of 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. "First feature" and "second feature" may include one or more of the indicated feature.

[0077] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0078] In this application, the order in which the steps are written does not imply a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0079] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a back electrode of a solar cell, characterized in that, include: A conductive silver paste is used to perform a first screen printing process on the surface of the solar cell backsheet to obtain a solar cell backsheet with silver paste main grids printed on it. The conductive silver paste comprises: 50-90 parts by weight of conductive silver powder, 0.5-10 parts by weight of glass powder, 1-20 parts by weight of organic carrier, 2-20 parts by weight of solvent, and 0.5-10 parts by weight of additives, wherein the specific surface area of ​​the conductive silver powder is 1.0 m². 2 / g-1.5m 2 / g; The conductive silver paste contains 75%-85% silver; the conductive silver powder has a Dv50 particle size of 0.5μm-1.5μm and a tap density of 3g / cm³. 3 -10g / cm 3 The sintering temperature of the conductive silver powder is 200℃-300℃. The solar cell backsheet with silver paste grids printed on it is subjected to drying and sintering processes in sequence to obtain a solar cell backsheet with silver grids printed on it. A second screen printing process and drying process are performed on the solar cell backsheet with silver main grid printed with aluminum paste to obtain a solar cell backsheet with aluminum secondary grid printed with aluminum. A glass paste is printed over an aluminum sub-grid and then dried and sintered in sequence to prepare the back electrode of the solar cell.

2. The method according to claim 1, characterized in that, The mesh count of the screen used for the first screen printing process is 200-300 mesh; and / or, The mesh count of the screen used for the second screen printing process is 300-400 mesh.

3. The method according to claim 1 or 2, characterized in that, The conductive silver paste comprises: 75-85 parts by weight of conductive silver powder, 1-5 parts by weight of glass powder, 1-10 parts by weight of organic carrier, 2-20 parts by weight of solvent, and 1-5 parts by weight of additives.

4. The method according to claim 1 or 2, characterized in that, The glass powder includes at least one of Te2O-Bi2O3-PbO glass, PbO-SiO2 glass powder, and lead-free glass powder, wherein the Dv50 particle size of the glass powder is 0.5μm-10μm; and / or, The organic carrier includes at least one of ethyl hydroxyethyl cellulose, nitrocellulose, a mixture of ethyl cellulose and phenolic resin, phenolic resin, acrylate resin, xylene resin, polybutene resin, polyester resin, urea resin, vinyl acetate resin, rosin, or polymethyl methacrylate of alcohol.

5. The method according to claim 1 or 2, characterized in that, The solvent comprises at least one selected from diethylene glycol diethyl ether, butyl carbitol (diethylene glycol monobutyl ether), diethylene glycol butyl ether acetate, carbitol butyl ether acetate, diacetone alcohol, terpineol, benzyl alcohol, cyclohexanone, methyl ethyl ketone, divalent ester, 2,2,4-trimethyl-1,3-pentanediol monoisobutyl ester, and 2,2,4-trimethyl-1,3-pentanediol diisobutyl ester; and / or, The adjuvant includes a dispersant, which includes at least one of sorbitan trioleate, dimethylacetamide, TDO, BYK-110, and BYK-111.

6. A solar cell, characterized in that, The solar cell includes the back electrode of a solar cell prepared by the method of any one of claims 1-5.

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