Solar cell and preparation method therefor

Abstract

The present application relates to a solar cell and a preparation method therefor. The method for preparing a solar cell comprises the following steps: filling a mold with a first slurry to form a first conductive layer; covering the first conductive layer with a second slurry to form a second conductive layer; covering the second conductive layer with a third slurry to form a third conductive layer, wherein the third conductive layer and the first conductive layer jointly coat the second conductive layer to form a laminate; and subjecting the laminate to laser transfer printing onto at least one surface of a bare solar cell, and co-sintering the laminate to form a composite electrode, so as to prepare a solar cell, wherein the first slurry and the third slurry each independently comprise a silver powder, and a conductive metal powder in the second slurry comprises one or more of a copper powder, an aluminum powder, a silver-coated aluminum powder, a silver-coated copper powder, a copper-aluminum alloy powder and a zinc powder. In the present application, the efficiency of the solar cell is improved while the proportion of the costs of the composite electrode is reduced, thereby achieving the win-win effect of cost reduction and efficiency maintenance.

Description

Solar cells and their preparation methods

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on February 28, 2025, with application number 202510237597.X, entitled "Solar Cell and Method for Preparing the Same Thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of photovoltaic technology, and in particular to a solar cell and a method for its fabrication. Background Technology

[0004] In the metallization process of solar cells, a conductive paste is typically printed onto the cell using screen printing, followed by drying and sintering to obtain the metallized electrodes, thereby enabling current output. The conductive paste often uses expensive silver paste, which accounts for a high percentage of the cost and, to some extent, limits the development of solar cells.

[0005] Some studies have used copper or aluminum paste to replace pure silver paste in order to reduce the cost of conductive paste. However, electrodes made from conductive pastes such as copper and aluminum paste have poor conductivity, which reduces the photoelectric conversion efficiency of solar cells and fails to meet the requirements of cost reduction and efficiency. Summary of the Invention

[0006] Therefore, it is necessary to provide a solar cell and its preparation method to solve the problem that electrodes prepared with low-cost conductive paste have poor conductivity and cannot meet the requirements of cost reduction and efficiency.

[0007] The above-mentioned objective of this application is achieved through the following technical solution:

[0008] In a first aspect, this application provides a method for preparing a solar cell, comprising the following steps:

[0009] The first slurry is filled into the mold to form the first conductive layer;

[0010] The second slurry is applied over the first conductive layer to form the second conductive layer;

[0011] A third slurry is applied over the second conductive layer to form a third conductive layer, and the third conductive layer and the first conductive layer together cover the second conductive layer to form a laminate.

[0012] The solar cell is fabricated by laser transfer of the laminate onto at least one surface of the solar cell and co-sintering the laminate to form a composite electrode.

[0013] The first slurry and the third slurry each independently include silver powder, and the conductive metal powder in the second slurry includes one or more of copper powder, aluminum powder, silver-coated aluminum powder, silver-coated copper powder, copper-aluminum alloy powder, and zinc powder.

[0014] In some embodiments, after filling the mold with the first slurry, the following step is further included:

[0015] A first groove is formed on the surface of the first conductive layer, and the second slurry is filled into the first groove to form the second conductive layer; and / or,

[0016] After forming the second conductive layer, the following steps are also included:

[0017] The surface of the second conductive layer is made to form a protrusion, and the third slurry is covered on the protrusion to form the third conductive layer. The third conductive layer forms a second groove on the surface of the second conductive layer that corresponds to the protrusion.

[0018] In some embodiments, the mass fraction of copper in the second slurry is 20% to 80%, and / or the mass fraction of aluminum is 10% to 60%.

[0019] In some embodiments, the specific surface area of ​​the conductive metal powder is 0.5 m². 2 / g~2m 2 / g.

[0020] In some embodiments, the D50 particle size of the conductive metal powder is 0.4 μm to 1.1 μm.

[0021] In some embodiments, the density of the second slurry is 2.5 g / cm³. 3 ~4.5g / cm 3 .

[0022] In some embodiments, the solid content of the second slurry is ≥90%.

[0023] In some embodiments, the viscosity of the second slurry at room temperature is 80 Pa·s to 120 Pa·s.

[0024] In some embodiments, the D50 particle size of the silver powder is 0.4 μm to 1.1 μm.

[0025] In some embodiments, the first slurry further includes a release agent with a mass fraction of 0.1% to 1% and a transfer solvent with a mass fraction of 1% to 5%, wherein the boiling point of the transfer solvent is 100°C to 250°C.

[0026] In some embodiments, the viscosity of the first slurry at room temperature is 50 Pa·s to 70 Pa·s.

[0027] In some embodiments, the density of the first slurry is 1.2 g / cm³. 3 ~1.8g / cm 3 .

[0028] In some embodiments, the viscosity of the third slurry at room temperature is 70 Pa·s to 100 Pa·s.

[0029] In some embodiments, the density of the third slurry is 2 g / cm³. 3 ~4g / cm 3 .

[0030] In some embodiments, the first slurry, the second slurry, and the third slurry each independently include a flexible interface material with a mass fraction of 1% to 5%, the flexible interface material including one or more of lead oxide and zinc oxide.

[0031] In some embodiments, the co-sintering includes the following steps: gradually increasing the temperature in a protective gas atmosphere at a heating rate of 140°C / min to 250°C / min, holding at 650°C to 760°C for 5 min to 10 min, and slowly cooling at a cooling rate of 160°C / min to 200°C / min.

[0032] In some embodiments, the composite electrode is a front-side fine grid with an aspect ratio of 0.6 to 1.2.

[0033] In some embodiments, the composite electrode is a back-side fine grid with an aspect ratio of 0.4 to 0.6.

[0034] In some embodiments, the composite electrode is one or more of the following: the front main gate, the connection line between the front main gate solder joints, and the connection line between the back main gate and the back main gate solder joints, with an aspect ratio of 0.1 to 0.2.

[0035] In some embodiments, the thickness ratio of the first conductive layer, the second conductive layer and the third conductive layer is 1:(1-6):(1-2).

[0036] In some embodiments, the width of the third conductive layer is not less than the width of the second conductive layer, and the width of the second conductive layer is not less than the width of the first conductive layer.

[0037] In a second aspect, this application provides a solar cell manufactured using the solar cell fabrication method described above.

[0038] This application has at least the following beneficial effects:

[0039] This application utilizes a first slurry containing silver powder and a third slurry to prepare a first conductive layer and a third conductive layer with high conductivity and excellent oxidation resistance, respectively. Using a second slurry containing conductive metal powders such as copper and aluminum powder to prepare the second conductive layer not only reduces the amount of silver powder used and lowers the preparation cost, but also ensures that the second conductive layer is completely coated by the first and third conductive layers, effectively enhancing its oxidation resistance and avoiding the problem of conductivity degradation caused by the oxidation of conductive metal powders. This improves the conductivity and service life of the composite electrode.

[0040] Meanwhile, this application achieves precise stacking of multilayer structures through laser transfer technology, resulting in composite electrodes with smaller linewidths and larger aspect ratios. This reduces the amount of conductive paste used, lowers electrode fabrication costs, and improves the current transport performance of the electrodes. Co-sintering optimizes the adhesion and interfacial bonding between conductive layers, preventing delamination due to differences in thermal expansion coefficients and ensuring the continuity of the conductive network.

[0041] Compared to traditional screen printing, this application utilizes the synergistic effect of laser transfer technology and co-sintering treatment to produce a composite electrode with a multi-layer structure. This reduces the cost of the composite electrode while improving battery efficiency, achieving a win-win situation of cost reduction and efficiency. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the disclosed drawings without creative effort.

[0043] Figure 1 is a schematic flowchart of the method for fabricating solar cells in some embodiments;

[0044] Figure 2 is a schematic flowchart of the method for fabricating solar cells in some other embodiments;

[0045] Figure 3 is a schematic diagram of the device structure after step S210 is completed in some embodiments;

[0046] Figure 4 is a schematic diagram of the device structure after step S220 is completed in some embodiments;

[0047] Figure 5 is a schematic diagram of the device structure after step S230 is completed in some embodiments;

[0048] Figure 6 is a schematic diagram of the device structure after step S240 is completed in some embodiments;

[0049] Figure 7 is a schematic diagram of the laser transfer process in step S250 in some embodiments;

[0050] Figure 8 is a schematic diagram of the device structure after step S250 is completed in some embodiments;

[0051] Figure 9 is a schematic diagram of the device structure after step S340 is completed in some embodiments;

[0052] Figure 10 is a schematic diagram of the device structure after step S440 is completed in some embodiments.

[0053] Reference numerals: 10, mold; 20, composite electrode; 21, first conductive layer; 22, second conductive layer; 23, third conductive layer; 30, solar cell. Detailed Implementation

[0054] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0055] 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 be limiting of the application.

[0056] In this application, "and / or" means any and all combinations of one or more of the related listed items. "At least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two, three, etc., unless otherwise expressly and specifically defined. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise expressly and specifically defined.

[0057] When a numerical range is disclosed in this application, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed in this application should be understood to include any and all subranges to which they are included.

[0058] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may 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.

[0059] In this application, "above" or "below" includes the number itself. For example, "below 1" includes 1.

[0060] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0061] In this application, room temperature refers to indoor temperature, normal temperature, or general temperature. Generally, room temperature can be any of the following temperature ranges: 23℃±2℃, 25℃±5℃, or 20℃±5℃.

[0062] In solar cells, conductive paste is typically printed onto the surface of the cell using screen printing, followed by drying and sintering to obtain metallized electrodes. Compared to expensive silver paste, copper and aluminum pastes are less expensive, which helps reduce the cost proportion of conductive paste. However, compared to silver paste, non-silver conductive pastes such as copper paste have the following drawbacks: 1) Copper has lower conductivity than silver, resulting in copper electrodes with inferior conductivity compared to silver electrodes; 2) Copper is easily oxidized in air, degrading the conductivity of the electrodes; 3) The copper-silicon alloy formed at the interface between the cell and the electrode affects the ohmic contact, further degrading the conductivity of the electrodes; 4) Copper electrodes made from copper paste have poor solderability, affecting the reliability and quality of the solar cell. Therefore, while using non-silver conductive pastes such as copper paste helps reduce costs, it hinders rapid current transmission, reduces the photoelectric conversion efficiency of the cell, and fails to meet the requirements of cost reduction and efficiency.

[0063] Based on this, in its first aspect, this application provides a method for preparing a solar cell, which aims to solve the problem that electrodes prepared with low-cost conductive paste have poor conductivity and cannot meet the requirements of cost reduction and efficiency.

[0064] In some embodiments, as shown in FIG1, the method for fabricating a solar cell includes the following steps:

[0065] S110: The first slurry is filled into the mold to form the first conductive layer;

[0066] S120: The second slurry is applied over the first conductive layer to form the second conductive layer;

[0067] S130: The third slurry is applied over the second conductive layer to form the third conductive layer, and the third conductive layer and the first conductive layer together cover the second conductive layer to form a laminate.

[0068] S140: Laser transfer of the laminate onto at least one surface of the solar cell and co-sintering of the laminate to form a composite electrode, thereby producing a solar cell;

[0069] The first and third slurries each independently include silver powder, and the conductive metal powder in the second slurry includes one or more of copper powder, aluminum powder, silver-coated aluminum powder, silver-coated copper powder, copper-aluminum alloy powder, and zinc powder.

[0070] This application utilizes a first slurry containing silver powder and a third slurry to prepare a first conductive layer and a third conductive layer with high conductivity and excellent oxidation resistance, respectively. Using a second slurry containing conductive metal powders such as copper and aluminum powder to prepare the second conductive layer not only reduces the amount of silver powder used and lowers the preparation cost, but also ensures that the second conductive layer is completely coated by the first and third conductive layers, effectively enhancing its oxidation resistance and avoiding the problem of conductivity degradation caused by the oxidation of conductive metal powders. This improves the conductivity and service life of the composite electrode.

[0071] Meanwhile, this application achieves precise stacking of multilayer structures through laser transfer technology, resulting in composite electrodes with smaller linewidths and larger aspect ratios. This reduces the amount of conductive paste used, lowers electrode fabrication costs, and improves the current transport performance of the electrodes. Co-sintering optimizes the adhesion and interfacial bonding between conductive layers, preventing delamination due to differences in thermal expansion coefficients and ensuring the continuity of the conductive network.

[0072] Compared to traditional screen printing, this application utilizes the synergistic effect of laser transfer technology and co-sintering treatment to produce a composite electrode with a multi-layer structure. This reduces the cost of the composite electrode while improving battery efficiency, achieving a win-win situation of cost reduction and efficiency.

[0073] In some embodiments, as shown in FIG2, the method for preparing a solar cell includes the following steps:

[0074] S210: Provide a mold having a receiving groove on its surface for preparing a composite electrode.

[0075] S220: The first slurry is filled into the receiving groove of the mold to form a first conductive layer, and a first groove is formed on the surface of the first conductive layer;

[0076] S230: The second slurry is filled into the first groove to form a second conductive layer, and a protrusion is formed on the surface of the second conductive layer;

[0077] S240: The third slurry is applied over the protrusion to form a third conductive layer, and the surface of the third conductive layer facing the second conductive layer forms a second groove corresponding to the protrusion, thereby obtaining a laminate.

[0078] S250: A solar cell is fabricated by laser transfer of a laminate onto at least one surface of a solar cell and co-sintering the laminate to form a composite electrode.

[0079] The fabrication method of the solar cell shown in Figure 2 will be described in detail below with reference to Figures 3 to 8.

[0080] S210: A mold 10 is provided, the surface of which has a receiving groove for preparing the composite electrode 20.

[0081] Please refer to Figure 3, which is a schematic diagram of the device structure after step S210 is completed in some embodiments.

[0082] In some embodiments, the mold 10 uses a transparent carrier plate, such as a glass carrier plate or a plastic carrier plate.

[0083] In some embodiments, the shape of the receiving groove on the surface of the mold 10 corresponds to the shape of the composite electrode 20. As shown in Figure 3, the cross-sectional shape of the receiving groove is an inverted trapezoid, that is, the width of the receiving groove gradually decreases with the increase of the depth, and the bottom surface of the receiving groove is a plane. During the laser transfer process, the inverted trapezoidal receiving groove can increase the radiation area of ​​the laser beam, which is beneficial to the demolding of the laminate, and can also increase the aspect ratio of the composite electrode 20.

[0084] However, this application is not limited to this. In other specific examples, the cross-sectional shape of the receiving groove can also be rectangular, U-shaped with a width that remains basically unchanged as the depth increases and a concave arc surface at the bottom, or inverted trapezoidal with a width that gradually decreases as the depth increases and a concave arc surface at the bottom.

[0085] In some embodiments, before preparing the composite electrode 20, the mold 10 is further cleaned and dried to avoid the residual impurities in the mold 10 from negatively affecting the purity, structural morphology and conductivity of the composite electrode 20.

[0086] S220: The first slurry is filled into the receiving groove of the mold 10 to form the first conductive layer 21, and the surface of the first conductive layer 21 is formed with a first groove.

[0087] Please refer to Figure 4, which is a schematic diagram of the device structure after step S220 is completed in some embodiments.

[0088] In some embodiments, the method of filling the receiving groove of the mold 10 with the first slurry includes a scraping method.

[0089] In some embodiments, the method for forming the first groove includes an imprinting method. Specifically, the imprinting method includes the following steps: using a three-roller turnstile to imprint a soft film onto the surface of the first conductive layer 21 to form the first groove. Here, using a soft film with a specific shape as a template allows the elasticity of the soft film to compensate for unevenness between the template and the first conductive layer 21, thereby improving the accuracy and efficiency of the imprinting.

[0090] In this application, after the first conductive layer 21 or the first groove is formed, no drying and curing process is performed to avoid affecting its demolding performance.

[0091] Understandably, different first slurries have different molding properties, release properties, electrical conductivity and oxidation resistance. The following is a detailed description of the component content and physicochemical properties of the first slurry.

[0092] In some embodiments, the first paste includes silver powder, i.e., the first paste is selected from silver paste.

[0093] In some embodiments, the D50 particle size (i.e., median particle size or median diameter) of the silver powder in the first slurry is 0.4 μm to 1.1 μm, including but not limited to 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm or 1.1 μm.

[0094] Therefore, selecting silver powder with a D50 particle size of 0.4μm to 1.1μm is beneficial to improving the density of the first conductive layer 21, enhancing its protective effect on the second conductive layer 22, and making the composite electrode 20 have better oxidation resistance.

[0095] In some embodiments, the first slurry further includes a release agent with a mass fraction of 0.1% to 1% and a transfer solvent with a mass fraction of 1% to 5%, wherein the boiling point of the transfer solvent is 100°C to 250°C. As an example, the mass fraction of the release agent in the first slurry includes, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, and more preferably 0.5%; the mass fraction of the transfer solvent in the first slurry includes, but is not limited to, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, and more preferably 2%; the boiling point of the transfer solvent includes, but is not limited to, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 220°C, 240°C, or 250°C.

[0096] Therefore, adding a release agent helps reduce the adhesion between the first conductive layer 21 and the mold 10, preventing sticking and ensuring effective demolding. Adding a low-boiling-point transfer solvent facilitates heat absorption and evaporation during laser transfer, providing appropriate vapor pressure within the enclosed space of the mold 10, promoting the separation and transfer of the first conductive layer 21 to the surface of the battery cell 30. If the boiling point of the transfer solvent is too low, some of the transfer solvent may evaporate during storage or before transfer, leading to increased viscosity of the first slurry or poor demolding performance; if the boiling point of the transfer solvent is too high, it cannot evaporate quickly during laser transfer, resulting in poor demolding effect and easily causing the first slurry to stick to the mold 10, affecting the integrity of the composite electrode 20.

[0097] In some embodiments, the release agent includes silicone oil, such as methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil, methyl chlorophenyl silicone oil, methyl ethoxy silicone oil, methyl trifluoropropyl silicone oil, methyl vinyl silicone oil, methyl hydroxy silicone oil, ethyl hydrogen silicone oil, hydroxy hydrogen silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, polyether-modified silicone oil, carboxyl-modified silicone oil, etc.

[0098] In some embodiments, the transfer solvent includes one or more of dimethyl glutarate, dimethyl adipate, mixed diesters, diethylene glycol monobutyl ether, and diethylene glycol butyl ether acetate.

[0099] In some embodiments, the first slurry further includes a flexible interface material at a mass fraction of 1% to 5%, the flexible interface material including one or more of lead oxide (PbO) and zinc oxide (ZnO), and more preferably PbO. As an example, the mass fraction of the flexible interface material in the first slurry includes, but is not limited to, 1%, 2%, 3%, 4%, or 5%, and more preferably 2%.

[0100] Therefore, the aforementioned flexible interface material has a low softening point and high elasticity, which can reduce the sintering temperature of the first conductive layer 21, adjust the thermal expansion coefficient of the first conductive layer 21, and optimize its interface bonding performance.

[0101] In some embodiments, the viscosity of the first slurry at room temperature is 50 Pa·s to 70 Pa·s, including but not limited to 50 Pa·s, 52 Pa·s, 55 Pa·s, 58 Pa·s, 60 Pa·s, 62 Pa·s, 65 Pa·s, 68 Pa·s or 70 Pa·s.

[0102] Therefore, the first slurry exhibits good molding properties at the aforementioned viscosity, making it suitable for forming the first groove in the imprinting method. It can also provide support for the subsequent deposition of conductive layers and achieve effective layering of each conductive layer, resulting in better protection of the second conductive layer 22. Simultaneously, the aforementioned viscosity also facilitates uniform deposition and precise demolding in laser transfer printing.

[0103] In some embodiments, the density of the first slurry is 1.2 g / cm³. 3 ~1.8g / cm 3 Including but not limited to 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 Or 1.8g / cm 3 .

[0104] Therefore, the low density of the first slurry reduces the probability of delamination within the first conductive layer 21 during the deposition process.

[0105] In some embodiments, the first paste can be provided by adding 0.1% to 1% by mass of a release agent, 1% to 5% by mass of a transfer solvent, and 1% to 5% by mass of a flexible interface material to the silver paste. Specifically, this can be achieved at [Company Name]. The DK72E paste (silver powder with a D50 particle size of 1μm) contains 0.5% release agent, 2% transfer solvent, and 2% flexible interface material.

[0106] Therefore, the DK72E slurry has a wide low-temperature sintering process window, which is beneficial for reducing the sintering temperature of co-sintering. At the same time, this slurry can support fine-wire grid technology, increase the aspect ratio of the composite electrode 20, reduce the amount of conductive slurry used, reduce the electrode preparation cost, and improve the current transmission performance of the composite electrode 20.

[0107] S230: The second slurry is filled into the first groove to form the second conductive layer 22, and the surface of the second conductive layer 22 is raised.

[0108] Please refer to Figure 5, which is a schematic diagram of the device structure after step S230 is completed in some embodiments.

[0109] In some embodiments, the method of filling the first groove with the second slurry includes a scraping method.

[0110] In some embodiments, forming a protrusion on the surface of the second conductive layer 22 includes the following steps: using a uniform coating technique, filling the first groove with a second slurry, and then using a flexible scraper (with grooves that match the spacing and size of the receiving grooves) to scrape and coat the second conductive layer 22 with a protrusion on the surface, and removing excess slurry that exceeds the receiving groove.

[0111] In some embodiments, the method for forming the protrusions on the surface of the second conductive layer 22 can also employ an imprinting method. Specifically, the imprinting method includes the following steps: using a three-roller turnstile, and using a soft film to imprint protrusions onto the surface of the second conductive layer 22.

[0112] In some embodiments, after forming protrusions on the surface of the second conductive layer 22, the method further includes the following step: drying at 20°C to 50°C for 3 to 30 seconds to semi-cure the second conductive layer 22, thereby improving its structural stability and enabling effective delamination between the conductive layers. As an example, the drying temperature can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, or 50°C, and more preferably 40°C; the drying time can be 3 seconds, 5 seconds, 10 seconds, 15 seconds, 20 seconds, 25 seconds, or 30 seconds.

[0113] Understandably, different second slurries have different molding properties and electrical conductivity. The following is a detailed description of the component content and physicochemical properties of the second slurries.

[0114] In some embodiments, the conductive metal powder in the second slurry includes one or more of copper powder, aluminum powder, silver-coated aluminum powder, silver-coated copper powder, copper-aluminum alloy powder, and zinc powder.

[0115] In some embodiments, the purity of the conductive metal powder in the second slurry is ≥99.9%.

[0116] Therefore, by selecting high-purity conductive metal powders such as copper powder and aluminum powder, the obstruction of the conductive path by impurities can be reduced, thereby improving the conductivity of the second conductive layer 22.

[0117] In some embodiments, the second slurry contains 20% to 80% copper by mass and / or 10% to 60% aluminum by mass. It is understood that the second slurry may contain only 20% to 80% copper by mass, only 10% to 60% aluminum by mass, or both 20% to 80% copper by mass and 10% to 60% aluminum by mass. As examples, the mass fraction of copper in the second slurry includes, but is not limited to, 20%, 30%, 40%, 50%, 60%, 70%, or 80%, and / or the mass fraction of aluminum in the second slurry includes, but is not limited to, 10%, 20%, 30%, 40%, 50%, or 60%.

[0118] In some embodiments, the specific surface area of ​​the conductive metal powder in the second slurry is 0.5 m². 2 / g~2m 2 / g, including but not limited to 0.5m 2 / g, 0.8m 2 / g、1m 2 / g, 1.2m2 / g, 1.5m 2 / g, 1.8m 2 / g or 2m 2 / g.

[0119] In some embodiments, the D50 particle size of the conductive metal powder in the second slurry is 0.4 μm to 1.1 μm, including but not limited to 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm or 1.1 μm.

[0120] Therefore, the high specific surface area and small D50 particle size of the conductive metal powder are conducive to the close packing of the conductive metal powder, increasing the contact area between particles, optimizing the packing density and conductive path, and providing an efficient conductive path, thereby improving the conductivity of the second conductive layer 22 while reducing costs.

[0121] In some embodiments, the second slurry further includes a flexible interface material at a mass fraction of 1% to 5%, the flexible interface material including one or more of lead oxide (PbO) and zinc oxide (ZnO), and more preferably PbO. As an example, the mass fraction of the flexible interface material in the second slurry includes, but is not limited to, 1%, 2%, 3%, 4%, or 5%, and more preferably 2%.

[0122] Therefore, the aforementioned flexible interface material has a low softening point and high elasticity, which can reduce the sintering temperature of the second conductive layer 22, adjust the thermal expansion coefficient of the second conductive layer 22, and optimize its interface bonding performance.

[0123] In some embodiments, the density of the second slurry is 2.5 g / cm³. 3 ~4.5g / cm 3 including but not limited to 2.5g / cm 3 2.8g / cm 3 3g / cm 3 3.2g / cm 3 3.5g / cm 3 3.8g / cm 3 4g / cm 3 4.2g / cm 3 Or 4.5g / cm 3 .

[0124] In some embodiments, the solid content of the second slurry is ≥90%, including but not limited to 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%.

[0125] Therefore, the high density and high solid content of the second slurry can increase the content of conductive metal powder, promote the dense stacking of conductive metal powder, and thus improve the conductivity of the second conductive layer 22.

[0126] In some embodiments, the viscosity of the second slurry at room temperature is 80 Pa·s to 120 Pa·s, including but not limited to 80 Pa·s, 85 Pa·s, 90 Pa·s, 95 Pa·s, 100 Pa·s, 105 Pa·s, 110 Pa·s, 115 Pa·s or 120 Pa·s.

[0127] Therefore, the second slurry has good molding properties at the above viscosity, is suitable for scraping molding, avoids sagging, and is also suitable for molding a raised structure on the surface by embossing, so as to promote the effective separation of the second conductive layer 22 with the first conductive layer 21 and the third conductive layer 23.

[0128] In some embodiments, the first paste can be provided by adding a flexible interface material at a mass fraction of 1% to 5% to a non-silver conductive paste such as copper paste, silver-copper alloy paste, silver-coated copper paste, silver-aluminum paste, and silver-coated aluminum paste. Specifically, COPPRINT's LF365 copper paste (copper powder with a D50 particle size of 1 μm and a specific surface area of ​​0.67 m²) can be used. 2 Add 2% flexible interface material to / g).

[0129] Therefore, LF365 copper paste also has a wide low-temperature sintering process window, which is beneficial to reducing the sintering temperature of co-sintering and improving the interfacial bonding performance between each conductive layer.

[0130] S240: The third slurry is applied over the protrusion to form a third conductive layer 23, and a second groove corresponding to the protrusion is formed on the surface of the third conductive layer 23 facing the second conductive layer 22, thereby obtaining a laminate.

[0131] Please refer to Figure 6, which is a schematic diagram of the device structure after step S240 is completed in some embodiments.

[0132] In some embodiments, the method of covering the protrusion with a third slurry includes a scraping method.

[0133] In some embodiments, after forming the third conductive layer 23, the method further includes the following step: drying at 20°C to 50°C for 3s to 30s to semi-cure the third conductive layer 23, thereby improving its structural stability and enabling effective delamination between the conductive layers. As an example, the drying temperature can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, or 50°C, and more preferably 40°C; the drying time can be 3s, 5s, 10s, 15s, 20s, 25s, or 30s.

[0134] Understandably, different third slurries have different molding properties, electrical conductivity, and antioxidant properties. The following is a detailed description of the component content and physicochemical properties of the third slurries.

[0135] In some embodiments, the third paste includes silver powder, i.e., the first paste is selected from silver paste.

[0136] In some embodiments, the D50 particle size of the silver powder in the third slurry is 0.4 μm to 1.1 μm, including but not limited to 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm or 1.1 μm.

[0137] Using silver powder with a D50 particle size of 0.4μm to 1.1μm not only forms high-quality silver-silicon alloy contact sites, ensuring conductivity between the composite electrode 20 and the solar cell 30, but also improves the density of the third conductive layer 23, enhancing its protective effect on the second conductive layer 22 and improving the oxidation resistance of the composite electrode 20. If the D50 particle size of the silver powder is too high, on the one hand, it will lead to poor density of the first conductive layer 21 and the third conductive layer 23, resulting in poor protection of the second conductive layer 22, making it prone to oxidation and reducing the conductivity of the composite electrode 20; on the other hand, copper and aluminum elements in the second conductive layer 22 can easily penetrate the third conductive layer 23 and migrate to the surface of the solar cell 30, forming copper-silicon alloys and aluminum-silicon alloys, which worsens the cross-sectional bonding performance between the composite electrode 20 and the solar cell 30, further reducing conductivity.

[0138] In some embodiments, the third slurry further includes a flexible interface material at a mass fraction of 1% to 5%, the flexible interface material including one or more of lead oxide (PbO) and zinc oxide (ZnO), and more preferably PbO. As an example, the mass fraction of the flexible interface material in the third slurry includes, but is not limited to, 1%, 2%, 3%, 4%, or 5%, and more preferably 2%.

[0139] Therefore, the aforementioned flexible interface material has a low softening point and high elasticity, which can reduce the sintering temperature of the third conductive layer 23, adjust the thermal expansion coefficient of the third conductive layer 23, and optimize its interface bonding performance.

[0140] In some embodiments, the viscosity of the third slurry at room temperature is 70 Pa·s to 100 Pa·s, including but not limited to 70 Pa·s, 75 Pa·s, 80 Pa·s, 85 Pa·s, 90 Pa·s, 95 Pa·s or 100 Pa·s.

[0141] Therefore, the third slurry has good molding properties at the above viscosity, is suitable for coating fine grid lines, ensures the smoothness of the edges of the composite electrode 20, and thus improves the conductivity of the composite electrode 20.

[0142] In some embodiments, the density of the third slurry is 2 g / cm³. 3 ~4g / cm 3 including but not limited to 2g / cm 3 2.2g / cm 3 2.5g / cm 3 2.8g / cm 3 3g / cm 3 3.2g / cm 3 3.5g / cm 3 3.8g / cm 3 or 4g / cm 3 .

[0143] Therefore, the high density of the third slurry can improve the density of the third conductive layer 23, thereby improving its conductivity, oxidation resistance and mechanical stability.

[0144] In some embodiments, the third paste can be provided by adding a flexible interface material at a mass fraction of 1% to 5% to the silver paste. Specifically, this can be achieved at [Company Name]. The DK72E slurry (with a D50 particle size of 1 μm for silver powder) was supplemented with 2% by mass of flexible interface material.

[0145] Therefore, DK72E paste has the following advantages: 1) It has a wide low-temperature sintering process window, which is conducive to reducing the sintering temperature of co-sintering; 2) It supports fine-line grid process, increases the aspect ratio of composite electrode 20, reduces the amount of conductive paste, reduces the preparation cost of electrode, and improves the current transmission performance of composite electrode 20; 3) It precisely controls the fluidity and etching ability of glass powder, greatly reduces the damage to the passivation layer during sintering, and forms high-quality silver-silicon alloy contact sites within the limited etching channel.

[0146] S250: The laminate is laser-transferred onto at least one surface of the solar cell 30, and the laminate is co-sintered to form a composite electrode 20, thereby obtaining a solar cell.

[0147] Please refer to Figures 7 and 8. Figure 7 is a schematic diagram of the laser transfer process in step S250 in some embodiments, and Figure 8 is a schematic diagram of the device structure after step S250 is completed in some embodiments.

[0148] In some embodiments, laser transfer includes the following steps: selecting an infrared wavelength laser beam, scanning the surface of the mold 10 away from the laminate at a power of 10W to 50W and a scanning speed of 1m / s to 50m / s, so that the laminate is transferred to at least one surface of the solar cell 30. As an example, the wavelength of the laser beam can be 1064nm, the power of the laser beam can be 10W, 20W, 30W, 40W, or 50W, and the scanning speed of the laser beam can be 1m / s, 5m / s, 10m / s, 20m / s, 30m / s, 40m / s, or 50m / s.

[0149] After laser transfer, the third conductive layer 23 in the laminate faces the solar cell 30, the first conductive layer 21 faces away from the solar cell 30, and the second conductive layer 22 covers the space between the first conductive layer 21 and the third conductive layer 23. This not only forms a silver-silicon alloy contact point between the composite electrode 20 and the solar cell 30, preventing the formation of copper-silicon alloy or aluminum-silicon alloy and improving the conductivity of the composite electrode 20, but also gives the composite electrode 20 excellent oxidation resistance, weldability, and adhesion compared to copper or aluminum electrodes, thereby improving the reliability, product quality, and lifespan of the solar cell.

[0150] In some embodiments, co-sintering includes the following steps: gradually increasing the temperature in a protective gas atmosphere at a heating rate of 140°C / min to 250°C / min, holding at 650°C to 760°C for 5 min to 10 min, and slowly cooling at a cooling rate of 160°C / min to 200°C / min.

[0151] As an example, the protective gas can be one or more of nitrogen, helium, neon, argon, krypton, and xenon, and can be further selected as nitrogen or argon; the heating rate can be 140℃ / min, 150℃ / min, 160℃ / min, 170℃ / min, 180℃ / min, 190℃ / min, 200℃ / min, 210℃ / min, 220℃ / min, 230℃ / min, 240℃ / min, or 250℃ / min. The sintering temperature can be 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃ or 760℃; the holding time can be 5min, 6min, 7min, 8min, 9min or 10min; the cooling rate can be 160℃ / min, 170℃ / min, 180℃ / min, 190℃ / min or 200℃ / min.

[0152] Therefore, co-sintering under a protective atmosphere can improve the purity of each conductive layer, prevent the oxidation of metal elements such as silver, copper, and aluminum, and improve the uniformity and density of sintering. Holding the sintering temperature at 650℃~760℃ prevents excessively high sintering temperatures from causing oxidation of the metal elements. Furthermore, it ensures that each layer softens and completes interfacial bonding under the action of a flexible interface material, resulting in a more uniform thermal expansion coefficient among the conductive layers. This avoids delamination caused by different thermal expansion coefficients, leading to excellent adhesion and interfacial bonding performance of each conductive layer.

[0153] In traditional sintering processes, the heating process from room temperature to sintering temperature is typically completed within 1 minute, followed by rapid cooling from the sintering temperature back to room temperature after sintering. In contrast, this application controls the heating rate at 140℃ / min to 250℃ / min, achieving gradual heating and reducing thermal shock caused by rapid temperature changes; and controls the cooling rate at 160℃ / min to 200℃ / min, reducing the accumulation of thermal stress through slow cooling and improving the structural stability of each conductive layer.

[0154] The fabrication methods of solar cells in other embodiments are described below with reference to Figures 9 and 10.

[0155] In some embodiments, a method for preparing a solar cell includes the following steps:

[0156] S310: Provide a mold 10, the surface of which has a receiving groove for preparing the composite electrode 20.

[0157] S320: The first slurry is filled into the receiving groove of the mold 10 to form the first conductive layer 21, and the surface of the first conductive layer 21 is formed with a first groove.

[0158] S330: The second slurry is filled into the first groove to form the second conductive layer 22;

[0159] S340: The third slurry is applied over the second conductive layer 22 to form the third conductive layer 23. The third conductive layer 23 and the first conductive layer 21 together cover the second conductive layer 22 to form a laminate, and the resulting structure is shown in Figure 9.

[0160] S350: The laminate is laser-transferred onto at least one surface of the solar cell 30 and the laminate is co-sintered to form a composite electrode 20, thereby producing a solar cell.

[0161] In some embodiments, a method for preparing a solar cell includes the following steps:

[0162] S410: A mold 10 is provided, the surface of which has a receiving groove for preparing the composite electrode 20.

[0163] S420: The first slurry is filled into the receiving groove of the mold 10 to form the first conductive layer 21;

[0164] S430: The second slurry is applied over the first conductive layer 21 to form a second conductive layer 22, and a protrusion is formed on the surface of the second conductive layer 22.

[0165] S440: The third slurry is applied over the protrusion to form a third conductive layer 23. The surface of the third conductive layer 23 facing the second conductive layer 22 forms a second groove corresponding to the protrusion, thereby obtaining a laminate. The resulting structure is shown in Figure 10.

[0166] S450: The laminate is laser-transferred onto at least one surface of the solar cell 30 and the laminate is co-sintered to form a composite electrode 20, thereby obtaining a solar cell.

[0167] Understandably, the slurry and process used in steps S310 to S350 and S410 to S450 can be found in steps S210 to S250, and will not be repeated here.

[0168] The structural parameters of the composite electrode 20 are described in detail below with reference to Figure 8.

[0169] In this application, the solar cell 30 has a front side and a back side. A composite electrode 20 can be fabricated on the front side as a front main grid or a front fine grid, and also on the back side as a back main grid or a back fine grid. Furthermore, the composite electrode 20 can also serve as a connecting line between the front main grid solder joints or as a connecting line between the back main grid solder joints.

[0170] When the composite electrode 20 is used as different grid line electrodes, its aspect ratio can be the same or different. At the same time, the width of the same composite electrode 20 can be the same or different. When calculating the aspect ratio, the average width of the composite electrode 20 can be used, that is: Aspect Ratio = Height ÷ Width (same width) ≈ Height ÷ Average Width (different widths).

[0171] In some embodiments, the composite electrode 20 is a front-side fine grid with an aspect ratio of 0.6 to 1.2, including but not limited to 0.6, 0.7, 0.8, 0.9, 1, 1.1 or 1.2.

[0172] Specifically, the composite electrode 20 is a front-side fine grid with a height of 6μm to 12μm, including but not limited to 6μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm; and a width (or average width) of 10μm to 20μm, including but not limited to 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0173] In some embodiments, the composite electrode 20 is a back-side fine grid with an aspect ratio of 0.4 to 0.6, including but not limited to 0.4, 0.42, 0.45, 0.48, 0.5, 0.52, 0.55, 0.58 or 0.6.

[0174] Specifically, the composite electrode 20 is a back-side fine grid with a height of 5μm to 10μm, including but not limited to 5μm, 6μm, 7μm, 8μm, 9μm or 10μm; and a width (or average width) of 20μm to 40μm, including but not limited to 20μm, 22μm, 25μm, 28μm, 30μm, 32μm, 35μm, 38μm or 40μm.

[0175] In some embodiments, the composite electrode 20 is one or more of the following: the front main gate, the connection line between the front main gate solder joints, and the connection line between the back main gate and the back main gate solder joints, with an aspect ratio of 0.1 to 0.2, including but not limited to 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2.

[0176] Specifically, the composite electrode 20 is one or more of the following: the front main grid, the connection line between the front main grid solder joints, and the connection line between the back main grid and the back main grid solder joints. Its height is 2μm to 5μm, including but not limited to 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm; its width (or average width) is 20μm, 25μm, 30μm, 35μm, 40μm, 45μm or 50μm.

[0177] In some embodiments, the thickness ratio of the first conductive layer 21, the second conductive layer 22, and the third conductive layer 23 is 1:(1-6):(1-2). It is understood that the thickness of each conductive layer refers to its average thickness. As an example, the average thickness ratio of the first conductive layer 21 and the second conductive layer 22 can be 1:1, 1:2, 1:3, 1:4, 1:5, or 1:6, and the average thickness ratio of the first conductive layer 21 and the second conductive layer 22 can be 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, or 1:2.

[0178] In some embodiments, the width of the third conductive layer 23 is not less than the width of the second conductive layer 22, and the width of the second conductive layer 22 is not less than the width of the first conductive layer 21. Thus, along the direction away from the battery cell 30, the width of the composite electrode 20 gradually decreases. This structure is beneficial for laser transfer and can increase the aspect ratio of the composite electrode 20, thereby reducing the consumption of conductive paste.

[0179] In some embodiments, the composite electrode 20 is a front-side fine grid, and the thickness of each conductive layer is as follows:

[0180] First conductive layer 21: average thickness of 1μm to 3μm (maximum thickness of 3μm to 7μm), average width of 3μm to 20μm; if the first conductive layer 21 has a first groove, the depth of the first groove is 1.5μm to 6μm.

[0181] The second conductive layer 22 has an average thickness of 2μm to 15μm and an average width of 5μm to 12μm. In the specific example in Figure 8, the cross-section of the second conductive layer 22 is elliptical, with a minor axis dimension of 3μm to 12μm along its thickness direction and a major axis dimension of 5μm to 18μm along its width direction.

[0182] The third conductive layer 23 has an average thickness of 1μm to 4μm (maximum width of 5μm to 11μm) and an average width of 7μm to 25μm; if the third conductive layer 23 has a second groove, the depth of the second groove is 1.5μm to 6μm.

[0183] The advantages of the composite electrode provided in this application are further illustrated by the following example.

[0184] Reports indicate that a release layer is prepared using copper paste (or other non-silver conductive paste) with added release agents and low-boiling-point solvents, and a silver layer conductive to the solar cell is prepared using silver paste. A double-layer electrode is then fabricated via laser transfer and co-sintering. However, this double-layer electrode presents the following problems: 1) The release layer is directly exposed to air, making copper prone to oxidation; 2) During laser transfer, the release agent absorbs heat and volatilizes, resulting in numerous pores and defects in the release layer, hindering its densification and interrupting the conductive path; 3) The release agent may react with copper powder (or aluminum powder) in the release layer, affecting the electrode's conductivity.

[0185] In contrast, this application utilizes a blade coating method, laser transfer technology, and co-sintering to fabricate a composite electrode with a three-layer structure. In this composite electrode, the first conductive layer provides demolding, support, and oxidation resistance; the second conductive layer focuses on high-efficiency conductivity and cost reduction; and the third conductive layer provides oxidation resistance and conductivity with the solar cell. The separation of functions among the different conductive layers ensures optimal overall performance of the composite electrode. Furthermore, the layered stacking design facilitates individual optimization of the slurry composition and process parameters for each layer, reducing side reactions and improving sintering results. This effectively improves the density and uniformity of each conductive layer, thereby enhancing the precision, stability, and conductivity of the composite electrode, ultimately achieving cost reduction and efficiency improvement.

[0186] In a second aspect, this application provides a solar cell manufactured using the solar cell fabrication method described above.

[0187] In some embodiments, the solar cell includes one or more of silicon solar cells, compound solar cells, and organic solar cells. Crystalline silicon solar cells include one or more of the following: Passivated Emitter and Rear Solar Cell (PERC), Tunnel Oxide Passivated Contact Solar Cell (TOPCon), Intrinsic Thin-Junction with Intrinsic Thin-Film Solar Cell (HJT or HIT), and Interdigitated Back Contact Solar Cell (IBC). Compound solar cells include perovskite solar cells (PSC), copper indium gallium selenide solar cells (CIGS), cadmium telluride solar cells (CdTe), and gallium arsenide solar cells (AsGa).

[0188] In a third aspect, this application provides a tandem solar cell, comprising a bottom cell and a top cell, wherein the bottom cell and / or the top cell are solar cells as described above.

[0189] In a fourth aspect, this application provides a photovoltaic module, comprising a first encapsulation panel, a first encapsulation film, a battery string, a second encapsulation film, and a second encapsulation panel stacked sequentially, wherein the battery string is formed by electrically connecting multiple solar cells as described above, or by electrically connecting multiple stacked batteries as described above.

[0190] The following description is further illustrated with specific embodiments and comparative examples. Unless otherwise specified, the raw materials involved in the following specific embodiments and comparative examples are all commercially available. Unless otherwise specified, the instruments used are all commercially available. Unless otherwise specified, the processes involved are conventionally selected by those skilled in the art.

[0191] Example 1

[0192] The method for preparing the TOPCon battery in this embodiment is as follows:

[0193] (1) Screening and grouping of solar cells: minority carrier lifetime test is performed on all blue film solar cells, the minority carrier lifetime data of each solar cell is recorded, and the solar cells are grouped according to the test data to ensure that the average minority carrier lifetime of each group of solar cells is consistent, so as to ensure that the subsequent processes are comparable between groups.

[0194] (2) Preparation of back grid, back grid and front grid: The back grid paste is printed onto the back of the cell using a screen printing machine and then pre-cured at 120°C for 1 min to obtain the back grid; the back grid paste is printed onto the back of the cell and then pre-cured at 120°C for 1 min to obtain the back grid; the front grid paste is printed onto the front of the cell and then pre-cured at 120°C for 1 min to obtain the front grid; the back grid paste, the back grid paste and the front grid paste are all commercially available pastes.

[0195] (3) Fabrication of the front-side fine grating:

[0196] ①Prepare the template and grout:

[0197] A glass carrier plate is provided as a mold. The surface of the glass carrier plate has an inverted trapezoidal receiving groove with a height (depth) of 7.1 μm, an average width of 7.3 μm, and an aspect ratio of 0.97.

[0198] In Dico To obtain a first slurry, 0.5% of a release agent (methyl silicone oil), 2% by mass of a transfer solvent (diethylene glycol monobutyl ether, boiling point approximately 230.4℃ at 101.3 kPa), and 2% by mass of a flexible interface material (PbO) were added to a DK72E slurry (silver powder with a D50 particle size of 1 μm). This slurry had a viscosity of 69 Pa·s and a density of 1.5 g / cm³ at room temperature. 3 ;

[0199] The LF365 copper paste from Copprin (copper powder with a D50 particle size of 1 μm and a specific surface area of ​​0.67 m²) 2 To obtain a second slurry, 2% flexible interface material (PbO) was added to the mixture (g) to obtain a slurry with a viscosity of 106 Pa·s and a density of 4.5 g / cm³ at room temperature. 3 ;

[0200] In Dico A third slurry was obtained by adding 2% flexible interface material (PbO) to DK72E slurry (silver powder with a D50 particle size of 1 μm). This slurry had a viscosity of 92 Pa·s and a density of 3 g / cm³ at room temperature. 3 ;

[0201] By controlling the viscosity and density of the three slurries, it is beneficial to achieve effective stratification, prevent mixing, and facilitate molding, so that each layer of slurry is evenly filled in the receiving tank to form the preset coating structure.

[0202] ②Preparation of laminates:

[0203] Using a uniform coating technique, the first slurry is filled into the receiving groove of the template. Excess slurry in the flat area is removed by a scraper, leaving a first conductive layer of about 3 μm thickness in the receiving groove. The soft membrane is extruded by a three-roller gate, forming a first groove on the surface of the first conductive layer. The average thickness of the first conductive layer is 3 μm (maximum thickness is 3.6 μm), the average width is 6.3 μm, and the depth of the first groove is 3.2 μm.

[0204] Using a uniform coating technique, the second slurry is filled into the first groove, and then coated with a flexible scraper (with a semi-elliptical groove that matches the spacing and size of the receiving groove) to form a second conductive layer with raised surfaces. Excess slurry extending beyond the receiving groove is removed, and then pre-cured by drying at 40°C for 3 seconds. The cross-section of the second conductive layer is elliptical, with a minor axis dimension of 6.4 μm along its thickness direction and a major axis dimension of 7.5 μm along its width direction.

[0205] Using a uniform coating technique, a third slurry is applied to the surface of the second conductive layer. The final coating thickness is controlled by a scraper to ensure the cleanliness of the outer surface of the mold and to ensure that the third conductive layer completely covers the second conductive layer. The third conductive layer forms a second groove corresponding to the protrusion on the surface of the second conductive layer. The average thickness of the third conductive layer is 3μm (maximum thickness is 3.5μm), the average width is 10μm, and the depth of the second groove is 3.2μm.

[0206] The laminate is then pre-cured by drying at 40°C for 3 seconds to obtain the laminate.

[0207] ③ Laser transfer:

[0208] The mold filled with the laminate is aligned and fixed with the front side of the solar cell, with the third conductive layer facing the solar cell. A fiber laser is selected, with a wavelength of 1064nm, a laser power of 15W, an exposure time of 200ns, a scanning speed of 1.5m / s, and a focusing diameter of 80μm. The back side of the mold is scanned according to the preset pattern, and the laminate is transferred to the front side of the solar cell by local heating.

[0209] ④ Co-sintering:

[0210] After transfer, the material is directly fed into a sintering and annealing integrated furnace (or chain furnace), and sintered and annealed under nitrogen protection with an oxygen content ≤10ppm, according to the following temperature curve:

[0211] The temperature was increased from 25°C to 400°C in 1.5 minutes (heating rate of 250°C / min);

[0212] The temperature was increased from 400℃ to 760℃ in 2.5 minutes (heating rate of 144℃ / min);

[0213] Keep warm at 760℃ for 5 minutes;

[0214] The temperature was slowly cooled from 760°C to 25°C within 4 minutes (cooling rate was approximately 184°C / min);

[0215] To ensure uniform softening and fusion of each layer of slurry during the heating process, minimize thermal shock, ensure full flow of glass powder and dense bonding of metal powder particles during the heat preservation stage, reduce thermal stress accumulation during the cooling stage, and ensure good structural stability of each layer, the laminate forms a composite electrode with excellent density, conductivity and interfacial bonding strength, while effectively preventing interface problems caused by the diffusion of copper elements into the silicon wafer.

[0216] Examples 2-3

[0217] Please refer to Table 1. The preparation methods of the TOPCon batteries in Examples 2 and 3 are the same as those in Example 1, except that the aspect ratios of the composite electrodes are different.

[0218] Comparative Examples 1-3

[0219] Please refer to Table 1. The preparation methods of the TOPCon cells in Comparative Examples 1-3 are the same as those in Example 1, except that the front-side fine grids in Comparative Examples 1-3 are made of DIC material. The DK72E paste (silver powder with a D50 particle size of 1μm) was prepared by screen printing.

[0220] Test case

[0221] (1) Morphology detection: The cross-section of the composite electrode was characterized by a 3D optical microscope, and the height, width and structural parameters of each layer of the composite electrode were recorded.

[0222] (2) Slurry consumption: Before preparing all grid electrodes, the cell is weighed to obtain mass G1. After preparing all grid electrodes, it is weighed again to obtain mass G2. The slurry consumption of a single cell (abbreviated as unit consumption) is: Unit consumption = G2 - G1.

[0223] (3) Electrical performance test: The electrical performance of the above TOPCon battery was tested by HALM IV tester, and its photoelectric conversion efficiency (Eta), open circuit voltage (Uoc), short circuit current (Isc), fill factor (FF), series resistance (Rser), parallel resistance (Rsh) and reverse leakage current (Irev2) were recorded.

[0224] The test results are shown in Tables 1 and 2. In Table 2, the test results for Example 1 are the average of 443 parallel experiments, and the test results for Comparative Example 1 are the average of 465 parallel experiments. The difference between the average of Example 1 and the average of Comparative Example 1 is obtained by subtracting the average of Comparative Example 1 from the average of Example 1 to verify the performance variation of Example 1. The data in the other two columns of Table 2 are processed in a similar way.

[0225] Table 1. Height, width, and aspect ratio of the front grille

[0226] Table 2. Power consumption and electrical performance of TOPCon batteries

[0227] As shown in Table 1, in Examples 1-3, the height of the front-side fine grid is 4.9 μm to 7.1 μm (average 5.87 μm), the width is 7.2 μm to 7.3 μm (average 7.27 μm), and the aspect ratio is 0.67 to 0.97 (average 0.81). Compared with the front-side fine grids of Comparative Examples 1-3, the width of the front-side fine grid in Example 1 is significantly reduced, and the aspect ratio is significantly increased. This indicates that the composite electrode with a multilayer structure prepared in this application has a stronger wire-gathering ability.

[0228] As shown in Table 2, the TOPCon battery prepared in Example 1 has a lower paste consumption per cell, which can be reduced by 3mg to 13mg. This is due to the narrowing of the composite electrode line shape. Furthermore, in the composite electrode, copper paste is used instead of expensive silver paste for the second conductive layer, reducing the amount of silver powder used per cell by 30% to 50%. Therefore, the multilayer composite electrode provided in this application can effectively reduce the manufacturing cost of the battery.

[0229] Because the width of the front fine grid in Example 1 is smaller and the aspect ratio is larger, the photoelectric conversion efficiency (Eta), open circuit voltage (Uoc), and short circuit current (Isc) of the TOPCon cell are improved. However, the fill factor (FF) is less affected by the line shape, and the series resistance (Rser) and parallel resistance (Rsh) are affected by the narrowing of the line shape and the second conductive layer, resulting in increased resistance.

[0230] In summary, the solar cell fabrication method provided in this application produces a composite electrode with a narrower width and a larger aspect ratio, which helps to reduce the unit amount of conductive paste and silver powder, while also improving the photoelectric conversion efficiency, open-circuit voltage and short-circuit current of the cell, thereby achieving the effect of cost reduction and efficiency improvement.

[0231] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0232] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a solar cell, comprising the following steps: The first slurry is filled into the mold to form the first conductive layer; The second slurry is applied over the first conductive layer to form the second conductive layer; A third slurry is applied over the second conductive layer to form a third conductive layer, and the third conductive layer and the first conductive layer together cover the second conductive layer to form a laminate. The solar cell is fabricated by laser transfer of the laminate onto at least one surface of the solar cell and co-sintering the laminate to form a composite electrode. The first slurry and the third slurry each independently include silver powder, and the conductive metal powder in the second slurry includes one or more of copper powder, aluminum powder, silver-coated aluminum powder, silver-coated copper powder, copper-aluminum alloy powder, and zinc powder.

2. The method for preparing a solar cell as described in claim 1, wherein, After the first slurry is filled into the mold, the following steps are also included: A first groove is formed on the surface of the first conductive layer, and the second slurry is filled into the first groove to form the second conductive layer; and / or, After forming the second conductive layer, the following steps are also included: The surface of the second conductive layer is made to form a protrusion, and the third slurry is covered on the protrusion to form the third conductive layer. The third conductive layer forms a second groove on the surface of the second conductive layer that corresponds to the protrusion.

3. The method for preparing a solar cell according to any one of claims 1 to 2, wherein, The second slurry satisfies one or more of the following conditions: (1) The mass fraction of copper in the second slurry is 20% to 80%, and / or the mass fraction of aluminum is 10% to 60%; (2) The specific surface area of ​​the conductive metal powder is 0.5 m². 2 / g~2m 2 / g; (3) The D50 particle size of the conductive metal powder is 0.4μm to 1.1μm; (4) The density of the second slurry is 2.5 g / cm³. 3 ~4.5g / cm 3 ; (5) The solid content of the second slurry is ≥90%; (6) The viscosity of the second slurry at room temperature is 80 Pa·s to 120 Pa·s.

4. The method for preparing a solar cell according to any one of claims 1 to 3, wherein, The D50 particle size of the silver powder is 0.4 μm to 1.1 μm.

5. The method for preparing a solar cell according to any one of claims 1 to 4, wherein, The first slurry also includes a release agent with a mass fraction of 0.1% to 1% and a transfer solvent with a mass fraction of 1% to 5%, wherein the boiling point of the transfer solvent is 100°C to 250°C.

6. The method for preparing a solar cell according to any one of claims 1 to 5, wherein, One or more of the following conditions must be met: (1) The viscosity of the first slurry at room temperature is 50 Pa·s to 70 Pa·s; (2) The density of the first slurry is 1.2 g / cm³. 3 ~1.8g / cm 3 ; (3) The viscosity of the third slurry at room temperature is 70 Pa·s to 100 Pa·s; (4) The density of the third slurry is 2 g / cm³. 3 ~4g / cm 3 .

7. The method for preparing a solar cell according to any one of claims 1 to 6, wherein, The first slurry, the second slurry, and the third slurry each independently include a flexible interface material with a mass fraction of 1% to 5%, wherein the flexible interface material includes one or more of lead oxide and zinc oxide.

8. The method for preparing a solar cell according to any one of claims 1 to 7, wherein, The co-sintering includes the following steps: In a protective gas atmosphere, the temperature is gradually increased at a rate of 140℃ / min to 250℃ / min, held at 650℃ to 760℃ for 5 min to 10 min, and then slowly cooled at a rate of 160℃ / min to 200℃ / min.

9. The method for preparing a solar cell according to any one of claims 1 to 8, wherein, One or more of the following conditions must be met: (1) The composite electrode is a front-side fine grid with an aspect ratio of 0.6 to 1.2; (2) The composite electrode is a fine grid on the back side with an aspect ratio of 0.4 to 0.6; (3) The composite electrode is one or more of the following: the front main grid, the connecting line between the front main grid solder joints, and the connecting line between the back main grid and the back main grid solder joints, with an aspect ratio of 0.1 to 0.

2. (4) The thickness ratio of the first conductive layer, the second conductive layer and the third conductive layer is 1:(1~6):(1~2); (5) The width of the third conductive layer is not less than the width of the second conductive layer, and the width of the second conductive layer is not less than the width of the first conductive layer.

10. A solar cell, wherein, The solar cell is prepared by any one of the methods described in claims 1 to 9.

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