Solar cell and preparation method thereof

Abstract

The invention relates to a solar cell and a preparation method thereof. The preparation method of the solar cell comprises the following steps: filling a mold with first slurry to form a first conductive layer; covering the first conductive layer with second slurry to form a second conductive layer; covering the second conductive layer with third slurry to form a third conductive layer, and covering the second conductive layer with the third conductive layer and the first conductive layer to form a laminated body; and performing laser transfer printing on the laminated body to at least one surface of the battery piece, and co-sintering the laminated body to form a composite electrode so as to prepare the solar battery, wherein the first slurry and the third slurry respectively and independently comprise silver powder, and the conductive metal powder in the second slurry comprises one or more of copper powder, aluminum powder, silver-coated aluminum powder, silver-coated copper powder, copper-aluminum alloy powder and zinc powder. The battery efficiency is improved while the cost ratio of the composite electrode is reduced, and the win-win situation of cost reduction and efficiency preservation is realized.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic technology, and in particular to a solar cell and a method for preparing the same. Background Art

[0002] In the metallization process of solar cells, the conductive paste is usually printed on the cell by screen printing, and then dried and sintered to obtain the metallized electrode, thereby achieving current output. Among them, the conductive paste is mostly made of expensive silver paste, which accounts for a high proportion of the cost, and to some extent limits the development of batteries.

[0003] Some studies have used copper paste and aluminum paste to replace pure silver paste to reduce the cost share of conductive paste. However, the conductivity of electrodes prepared from conductive pastes such as copper paste and aluminum paste is poor, which reduces the photoelectric conversion efficiency of solar cells and cannot meet the requirements of cost reduction and efficiency assurance. Summary of the invention

[0004] Based on this, it is necessary to provide a solar cell and a method for preparing the same to solve the problem that electrodes prepared with low-cost conductive pastes have poor conductivity and cannot take into account the requirements of cost reduction and efficiency assurance.

[0005] The above-mentioned purpose of the present application is achieved through the following technical solutions:

[0006] In a first aspect of the present application, a method for preparing a solar cell is provided, comprising the following steps:

[0007] Filling the first slurry into the mold to form a first conductive layer;

[0008] Covering the first conductive layer with a second slurry to form a second conductive layer;

[0009] 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 together cover the second conductive layer to form a laminate;

[0010] Laser transfer the stack onto at least one surface of a cell sheet, and co-sinter the stack to form a composite electrode, thereby producing the solar cell;

[0011] 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.

[0012] In some embodiments, after the first slurry is filled into the mold, the following steps are further included:

[0013] forming a first groove on the surface of the first conductive layer, and filling the first groove with the second slurry to form the second conductive layer; and / or,

[0014] After forming the second conductive layer, the method further comprises the following steps:

[0015] The surface of the second conductive layer is formed with protrusions, and the third slurry is covered on the protrusions to form the third conductive layer, and the surface of the third conductive layer facing the second conductive layer forms a second groove corresponding to the protrusions.

[0016] In some embodiments, the mass fraction of the copper element in the second slurry is 20% to 80%, and / or the mass fraction of the aluminum element is 10% to 60%.

[0017] In some embodiments, the specific surface area of ​​the conductive metal powder is 0.5 m 2 / g~2m 2 / g.

[0018] In some embodiments, the D50 particle size of the conductive metal powder is 0.4 μm to 1.1 μm.

[0019] In some embodiments, the density of the second slurry is 2.5 g / cm 3 ~4.5g / cm 3 .

[0020] In some embodiments, the solid content of the second slurry is ≥ 90%.

[0021] In some embodiments, the viscosity of the second slurry at room temperature is 80 Pa·s to 120 Pa·s.

[0022] In some embodiments, the D50 particle size of the silver powder is 0.4 μm to 1.1 μm.

[0023] 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%, and the boiling point of the transfer solvent is 100° C. to 250° C.

[0024] In some embodiments, the viscosity of the first slurry at room temperature is 50 Pa·s to 70 Pa·s.

[0025] In some embodiments, the density of the first slurry is 1.2 g / cm 3 ~1.8g / cm 3 .

[0026] In some embodiments, the viscosity of the third slurry at room temperature is 70 Pa·s to 100 Pa·s.

[0027] In some embodiments, the density of the third slurry is 2 g / cm 3 ~4g / cm 3 .

[0028] 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%, and the flexible interface material includes one or more of lead oxide and zinc oxide.

[0029] In some embodiments, the co-sintering includes the following steps: in a protective gas atmosphere, gradually heating at a heating rate of 140°C / min to 250°C / min, keeping warm at 650°C to 760°C for 5min to 10min, and slowly cooling at a cooling rate of 160°C / min to 200°C / min.

[0030] In some embodiments, the composite electrode is a front fine grid with an aspect ratio of 0.6 to 1.2.

[0031] In some embodiments, the composite electrode is a back side fine grid with an aspect ratio of 0.4 to 0.6.

[0032] In some embodiments, the composite electrode is one or more of a front main grid, a connecting line between front main grid welding points, and a connecting line between a back main grid and back main grid welding points, and its aspect ratio is 0.1-0.2.

[0033] In some embodiments, a thickness ratio of the first conductive layer, the second conductive layer, and the third conductive layer is 1:(1-6):(1-2).

[0034] 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.

[0035] In a second aspect of the present application, a solar cell is provided, which is manufactured using the solar cell manufacturing method as described above.

[0036] This application has at least the following beneficial effects:

[0037] The present application uses a first slurry and a third slurry containing silver powder to prepare a first conductive layer and a third conductive layer with high conductivity and excellent oxidation resistance. The second conductive layer is prepared using a second slurry containing conductive metal powders such as copper powder and aluminum powder, which can not only reduce the amount of silver powder used and reduce the preparation cost, but also the second conductive layer is completely covered by the first conductive layer and the third conductive layer, effectively improving its oxidation resistance and avoiding the problem of conductivity degradation caused by oxidation of the conductive metal powder, thereby improving the conductive performance and service life of the composite electrode.

[0038] At the same time, the present application realizes the precise stacking of multilayer structures through laser transfer technology, and the obtained composite electrode has a smaller line width and a larger aspect ratio, which reduces the amount of conductive slurry, reduces the preparation cost of the electrode, and is conducive to improving the current transmission performance of the electrode. Through co-sintering treatment, the adhesion and interface bonding performance between the conductive layers are optimized, and the stratification caused by the difference in thermal expansion coefficient is avoided, thereby ensuring the continuity of the conductive network.

[0039] Compared with the traditional screen printing process, this application uses the synergistic cooperation of laser transfer technology and co-sintering treatment to produce a composite electrode with a multi-layer structure, which reduces the cost share of the composite electrode while improving the battery efficiency, achieving a win-win situation of reducing costs and maintaining efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application and to more completely understand the present application and its beneficial effects, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0041] Figure 1 is a schematic flow chart of a method for preparing a solar cell in some embodiments;

[0042] Figure 2 is a schematic flow chart of a method for preparing a solar cell in some other embodiments;

[0043] Figure 3 Schematic diagram of the structure of the device after step S210 is completed in some embodiments;

[0044] Figure 4 Schematic diagram of the structure of the device after step S220 is completed in some embodiments;

[0045] Figure 5 Schematic diagram of the structure of the device after step S230 is completed in some embodiments;

[0046] Figure 6 Schematic diagram of the structure of the device after step S240 is completed in some embodiments;

[0047] Figure 7 A schematic diagram of the laser transfer process of step S250 in some embodiments;

[0048] Figure 8 Schematic diagram of the structure of the device after step S250 is completed in some embodiments;

[0049] Fig. 9Schematic diagram of the structure of the device after step S340 is completed in some embodiments;

[0050] Fig.10 This is a schematic diagram of the structure of the device after step S440 is completed in some embodiments.

[0051] Reference numerals:

[0052] 10, mold; 20, composite electrode; 21, first conductive layer; 22, second conductive layer; 23, third conductive layer; 30, battery cell. DETAILED DESCRIPTION

[0053] In order to facilitate the understanding of the present application, the present application is further described in detail below in conjunction with specific embodiments. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0055] In the present application, the meaning of "and / or" includes any and all combinations of one or more related listed items. "At least one" means more than one, such as one, two and more than two. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layer" means at least two layers, such as two layers, three layers, etc., unless otherwise clearly and specifically defined. In the description of the present application, "several" means at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0056] When a numerical range is disclosed in this application, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed in this application should be understood to include any and all subranges included therein.

[0057] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0058] In this application, "above" or "below" includes the number itself. For example, "1 below" includes 1.

[0059] The temperature parameters in this application, unless otherwise specified, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0060] In the present application, room temperature refers to indoor temperature, normal temperature or general temperature. Generally speaking, the range of room temperature can be any one of the following temperature intervals: 23°C ± 2°C, 25°C ± 5°C or 20°C ± 5°C.

[0061] In solar cells, a screen printing process is usually used to print the conductive paste onto the surface of the cell, and then the paste is dried and sintered to obtain a metallized electrode. Compared with the expensive silver paste, the cost of copper paste and aluminum paste is lower, which is conducive to reducing the cost share of the conductive paste. However, compared with silver paste, non-silver conductive pastes such as copper paste have the following defects: 1) The conductivity of copper is worse than that of silver, and the conductivity of the prepared copper electrode is not as good as that of the silver electrode; 2) Copper is easily oxidized in the air, which deteriorates the conductivity of the electrode; 3) The copper-silicon alloy formed at the interface between the cell and the electrode will affect the ohmic contact effect, further deteriorating the conductivity of the electrode; 4) The copper electrode prepared by copper paste has poor solderability, which affects the reliability and quality of the finished product of the solar cell. Therefore, although the use of non-silver conductive pastes such as copper paste is conducive to reducing costs, it is not conducive to the rapid transmission of current, reduces the photoelectric conversion efficiency of the battery, and cannot take into account the requirements of cost reduction and efficiency assurance.

[0062] Based on this, in the first aspect of the present application, a method for preparing a solar cell is provided, aiming to solve the problem that electrodes prepared with low-cost conductive pastes have poor conductivity and cannot take into account the requirements of cost reduction and efficiency assurance.

[0063] In some embodiments, Figure 1 As shown, the method for preparing a solar cell comprises the following steps:

[0064] S110: filling the first slurry into the mold to form a first conductive layer;

[0065] S120: Covering the first conductive layer with the second slurry to form a second conductive layer;

[0066] S130: Covering the second conductive layer with the third slurry to form a third conductive layer, wherein the third conductive layer and the first conductive layer together cover the second conductive layer to form a laminate;

[0067] S140: laser transfer the laminate onto at least one surface of the cell, and co-sinter the laminate to form a composite electrode, thereby manufacturing a solar cell;

[0068] 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.

[0069] The present application uses a first slurry and a third slurry containing silver powder to prepare a first conductive layer and a third conductive layer with high conductivity and excellent oxidation resistance. The second conductive layer is prepared using a second slurry containing conductive metal powders such as copper powder and aluminum powder, which can not only reduce the amount of silver powder used and reduce the preparation cost, but also the second conductive layer is completely covered by the first conductive layer and the third conductive layer, effectively improving its oxidation resistance and avoiding the problem of conductivity degradation caused by oxidation of the conductive metal powder, thereby improving the conductive performance and service life of the composite electrode.

[0070] At the same time, the present application realizes the precise stacking of multilayer structures through laser transfer technology, and the obtained composite electrode has a smaller line width and a larger aspect ratio, which reduces the amount of conductive slurry, reduces the preparation cost of the electrode, and is conducive to improving the current transmission performance of the electrode. Through co-sintering treatment, the adhesion and interface bonding performance between the conductive layers are optimized, and the stratification caused by the difference in thermal expansion coefficient is avoided, thereby ensuring the continuity of the conductive network.

[0071] Compared with the traditional screen printing process, this application uses the synergistic cooperation of laser transfer technology and co-sintering treatment to produce a composite electrode with a multi-layer structure, which reduces the cost share of the composite electrode while improving the battery efficiency, achieving a win-win situation of reducing costs and maintaining efficiency.

[0072] In some embodiments, Figure 2 As shown, the method for preparing a solar cell comprises the following steps:

[0073] S210: providing a mold, wherein the surface of the mold has a receiving groove for preparing a composite electrode.

[0074] S220: filling the first slurry into the receiving groove of the mold to form a first conductive layer, and forming a first groove on the surface of the first conductive layer;

[0075] S230: filling the first groove with a second slurry to form a second conductive layer, and forming a protrusion on the surface of the second conductive layer;

[0076] S240: Covering the protrusions with a third slurry to form a third conductive layer, and forming a second groove corresponding to the protrusions on a surface of the third conductive layer facing the second conductive layer, thereby obtaining a laminate;

[0077] S250: laser transfer the laminate onto at least one surface of the cell, and co-sinter the laminate to form a composite electrode, thereby manufacturing a solar cell.

[0078] The following reference Figure 3~Figure 8 right Figure 2 The preparation method of the solar cell shown is described in detail.

[0079] S210 : providing a mold 10 , wherein the surface of the mold 10 has a receiving groove for preparing the composite electrode 20 .

[0080] See also Figure 3 , which is a schematic diagram of the structure of the device after step S210 is completed in some embodiments.

[0081] In some embodiments, the mold 10 uses a transparent carrier, such as a glass carrier or a plastic carrier.

[0082] 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. Figure 3 As shown, 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 conducive to the demoulding of the laminate, and can also increase the aspect ratio of the composite electrode 20.

[0083] However, the present application is not limited to this. In some other specific examples, the cross-sectional shape of the accommodating groove can also be a rectangle, a U-shape with a width that remains basically unchanged as the depth increases and a concave arc bottom, or an inverted trapezoid with a width that gradually decreases as the depth increases and a concave arc bottom.

[0084] In some embodiments, before preparing the composite electrode 20 , the mold 10 is also cleaned and dried to prevent residual impurities in the mold 10 from negatively affecting the purity, structural morphology and conductive properties of the composite electrode 20 .

[0085] S220 : filling the first slurry into the receiving groove of the mold 10 to form the first conductive layer 21 , and forming a first groove on the surface of the first conductive layer 21 .

[0086] See also Figure 4 , which is a schematic diagram of the structure of the device after step S220 is completed in some embodiments.

[0087] In some embodiments, the method of filling the first slurry into the receiving groove of the mold 10 includes a doctor blade coating method.

[0088] In some embodiments, the method for forming the first groove includes an embossing method. Specifically, the embossing method includes the following steps: using a three-roller gate machine, and using a soft film to emboss the first groove on the surface of the first conductive layer 21. Among them, using a soft film with a specific shape as a template, the elasticity of the soft film can be used to compensate for the unevenness between the template and the first conductive layer 21, thereby improving the accuracy and efficiency of the embossing.

[0089] In the present application, after the first conductive layer 21 or the first groove is formed, no drying and curing treatment is performed to avoid affecting its demoulding performance.

[0090] It can be understood that different first slurries have different molding properties, demoulding properties, conductive properties and anti-oxidation properties. The component content and physicochemical properties of the first slurry are described in detail below.

[0091] In some embodiments, the first slurry includes silver powder, that is, the first slurry is silver paste.

[0092] In some embodiments, the D50 particle size (ie, 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.

[0093] Therefore, the use of silver powder with a D50 particle size of 0.4 μm to 1.1 μm is beneficial to improving the compactness of the first conductive layer 21 and enhancing its protective effect on the second conductive layer 22 , so that the composite electrode 20 has better anti-oxidation performance.

[0094] 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%, and 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 can be further selected as 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 can be further selected as 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.

[0095] Therefore, adding a release agent is beneficial to reducing the adhesion between the first conductive layer 21 and the mold 10, preventing adhesion, and thus ensuring effective demolding. Adding a transfer solvent with a low boiling point is beneficial to endothermic evaporation during the laser transfer process and providing appropriate vapor pressure in the closed space of the mold 10, which promotes the separation and shedding of the first conductive layer 21 and transfer to the surface of the battery cell 30. If the boiling point of the transfer solvent is too low, part of the transfer solvent may evaporate during the storage process or before transfer, resulting in an increase in the 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, which easily causes the first slurry to adhere to the mold 10, affecting the integrity of the composite electrode 20.

[0096] 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.

[0097] In some embodiments, the transfer solvent includes one or more of dimethyl glutarate, dimethyl adipate, mixed dibasic acid esters, diethylene glycol monobutyl ether, and diethylene glycol butyl ether acetate.

[0098] In some embodiments, the first slurry further includes a flexible interface material with a mass fraction of 1% to 5%, and the flexible interface material includes one or more of lead oxide (PbO) and zinc oxide (ZnO), and further optionally 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 further optionally 2%.

[0099] Therefore, the 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.

[0100] 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.

[0101] Therefore, the first slurry has good molding performance under the above viscosity, is suitable for forming the first groove in the embossing method, and can also provide support for the subsequent deposition of the conductive layer and realize the effective stratification of each conductive layer, thereby better protecting the second conductive layer 22. At the same time, the above viscosity is also conducive to uniform deposition and precise demolding in laser transfer.

[0102] In some embodiments, the density of the first slurry is 1.2 g / cm 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 1.8 g / cm 3 .

[0103] Therefore, the density of the first slurry is low, which can reduce the probability of internal delamination of the first conductive layer 21 during the deposition process.

[0104] In some embodiments, the first slurry 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, 0.5% of a release agent, 2% by mass of a transfer solvent, and 2% by mass of a flexible interface material can be added to DK72E slurry of DKEM® (the D50 particle size of the silver powder is 1 μm).

[0105] Therefore, the DK72E slurry has a wide low-temperature sintering process window, which is conducive to reducing the sintering temperature of co-sintering. At the same time, the slurry can support the fine-line dense grid process, increase the aspect ratio of the composite electrode 20, reduce the amount of conductive slurry, reduce the preparation cost of the electrode, and improve the current transmission performance of the composite electrode 20.

[0106] S230: Filling the first groove with the second slurry to form the second conductive layer 22 , and forming protrusions on the surface of the second conductive layer 22 .

[0107] See also Figure 5 , which is a schematic diagram of the structure of the device after step S230 is completed in some embodiments.

[0108] In some embodiments, the method of filling the second slurry into the first groove includes a doctor blade coating method.

[0109] In some embodiments, forming a protrusion on the surface of the second conductive layer 22 includes the following steps: using a uniform coating technique to fill the second slurry into the first groove, and then using a flexible scraper (with grooves matching the spacing and size of the receiving grooves) to scrape and coat the second conductive layer 22 to form a protrusion on the surface, and removing excess slurry beyond the receiving grooves.

[0110] In some embodiments, the protrusions on the surface of the second conductive layer 22 may also be formed by embossing. Specifically, the embossing method includes the following steps: using a three-roller gate machine, and embossing the surface of the second conductive layer 22 with a soft film to form protrusions.

[0111] In some embodiments, after the second conductive layer 22 is formed with protrusions on its surface, the following steps are further included: drying at 20°C to 50°C for 3s to 30s to semi-solidify the second conductive layer 22 and improve its structural stability, thereby achieving effective stratification between the conductive layers. As an example, the drying temperature may be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, and may further be 40°C; the drying time may be 3s, 5s, 10s, 15s, 20s, 25s or 30s.

[0112] It can be understood that different second slurries have different forming properties and conductive properties. The component content and physicochemical properties of the second slurry are described in detail below.

[0113] 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.

[0114] In some embodiments, the purity of the conductive metal powder in the second slurry is ≥99.9%.

[0115] Therefore, the use of high-purity conductive metal powders such as copper powder and aluminum powder can reduce the obstruction of impurities to the conductive path and improve the conductive performance of the second conductive layer 22.

[0116] In some embodiments, the mass fraction of the copper element in the second slurry is 20% to 80%, and / or the mass fraction of the aluminum element is 10% to 60%. It is understandable that the second slurry may contain only a copper element with a mass fraction of 20% to 80%, or only an aluminum element with a mass fraction of 10% to 60%, or simultaneously contain a copper element with a mass fraction of 20% to 80% and an aluminum element with a mass fraction of 10% to 60%. As an example, the mass fraction of the copper element in the second slurry includes but is not limited to 20%, 30%, 40%, 50%, 60%, 70% or 80%, and / or the mass fraction of the aluminum element in the second slurry includes but is not limited to 10%, 20%, 30%, 40%, 50% or 60%.

[0117] In some embodiments, the specific surface area of ​​the conductive metal powder in the second slurry is 0.5 m 2 / g~2m 2 / g, including but not limited to 0.5m 2 / g, 0.8m 2 / g, 1m 2 / g, 1.2m 2 / g, 1.5m 2 / g, 1.8m 2 / g or 2m 2 / g.

[0118] 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.

[0119] Therefore, the high specific surface area and small D50 particle size of the conductive metal powder are conducive to promoting the close stacking of the conductive metal powder, increasing the contact area between particles, optimizing the stacking density and the conductive path, and providing an efficient conductive path, thereby improving the conductive performance of the second conductive layer 22 while reducing costs.

[0120] In some embodiments, the second slurry further includes a flexible interface material with a mass fraction of 1% to 5%, and the flexible interface material includes one or more of lead oxide (PbO) and zinc oxide (ZnO), and further optionally 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 further optionally 2%.

[0121] Therefore, the above-mentioned 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.

[0122] In some embodiments, the density of the second slurry is 2.5 g / cm 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 .

[0123] 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%.

[0124] Therefore, the second slurry has a high density and a high solid content, which can increase the content of the conductive metal powder and promote the close stacking of the conductive metal powder, thereby improving the conductivity of the second conductive layer 22 .

[0125] 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.

[0126] Therefore, the second slurry has good molding properties under the above viscosity, is suitable for scraping molding to avoid sagging, and is also suitable for shaping the surface with a raised structure by embossing, thereby promoting effective stratification of the second conductive layer 22 and the first conductive layer 21 and the third conductive layer 23.

[0127] In some embodiments, the first slurry can be provided by adding 1% to 5% by mass of the flexible interface material to non-silver conductive slurries such as copper slurry, silver-copper alloy slurry, silver-copper slurry, silver-aluminum slurry and silver-aluminum slurry. Specifically, the first slurry can be provided by adding 1% to 5% by mass of the flexible interface material to non-silver conductive slurries such as copper slurry, silver-copper alloy slurry, silver-copper slurry, silver-aluminum slurry and silver-coated aluminum slurry. 2 / g) and 2% flexible interface material was added.

[0128] Therefore, LF365 copper paste also has a wider low-temperature sintering process window, which is beneficial to reduce the sintering temperature of co-sintering and improve the interface bonding performance between the conductive layers.

[0129] S240: Covering the protrusions with a third slurry to form a third conductive layer 23, and forming a second groove corresponding to the protrusions on the surface of the third conductive layer 23 facing the second conductive layer 22, thereby obtaining a laminated body.

[0130] See also Figure 6 , which is a schematic diagram of the structure of the device after step S240 is completed in some embodiments.

[0131] In some embodiments, the method of coating the third slurry on the protrusions comprises a doctor blade coating method.

[0132] In some embodiments, after forming the third conductive layer 23, the following steps are further included: drying at 20°C to 50°C for 3s to 30s to semi-solidify the third conductive layer 23 and improve its structural stability, thereby achieving effective stratification between the conductive layers. As an example, the drying temperature may be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, and may further be 40°C; the drying time may be 3s, 5s, 10s, 15s, 20s, 25s or 30s.

[0133] It can be understood that different third slurries have different forming properties, conductive properties and anti-oxidation properties. The component content and physicochemical properties of the third slurry are described in detail below.

[0134] In some embodiments, the third paste includes silver powder, that is, the first paste is silver paste.

[0135] 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.

[0136] The silver powder with a D50 particle size of 0.4 μm to 1.1 μm is selected, which can not only form high-quality silver-silicon alloy contact sites to ensure the conduction effect between the composite electrode 20 and the battery cell 30, but also help to improve the compactness of the third conductive layer 23, enhance the protective effect of the third conductive layer 23 on the second conductive layer 22, and make the composite electrode 20 have better anti-oxidation performance. If the D50 particle size of the silver powder is too high, on the one hand, it will lead to poor compactness of the first conductive layer 21 and the third conductive layer 23, poor protection effect on the second conductive layer 22, and the second conductive layer 22 is easy to oxidize and reduce the conductivity of the composite electrode 20; on the other hand, the copper element and aluminum element of the second conductive layer 22 are easy to pass through the third conductive layer 23 and migrate to the surface of the battery cell 30 to form copper-silicon alloy and aluminum-silicon alloy, so that the cross-sectional bonding performance of the composite electrode 20 and the battery cell 30 is deteriorated, and the conductivity is further reduced.

[0137] In some embodiments, the third slurry further includes a flexible interface material with a mass fraction of 1% to 5%, and the flexible interface material includes one or more of lead oxide (PbO) and zinc oxide (ZnO), and further optionally 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 further optionally 2%.

[0138] Therefore, the 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.

[0139] 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.

[0140] Therefore, the third slurry has good molding performance under the above viscosity, is suitable for the coating of fine grid lines, ensures the smoothness of the edge of the composite electrode 20, and thus improves the conductive effect of the composite electrode 20.

[0141] In some embodiments, the density of the third slurry is 2 g / cm 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 .

[0142] Therefore, the third slurry has a high density, which can increase the density of the third conductive layer 23 and improve its conductive property, anti-oxidation property and mechanical stability.

[0143] In some embodiments, the third slurry can be provided by adding 1% to 5% by mass of the flexible interface material to the silver slurry. Specifically, 2% by mass of the flexible interface material can be added to DK72E slurry of DKEM® (the D50 particle size of the silver powder is 1 μm).

[0144] Therefore, DK72E slurry has the following advantages: 1) The low-temperature sintering process window is wide, which is conducive to reducing the sintering temperature of co-sintering; 2) It supports fine-line and dense-grid process, increases the aspect ratio of the composite electrode 20, reduces the amount of conductive slurry, reduces the preparation cost of the electrode, and improves the current transmission performance of the composite electrode 20; 3) It precisely controls the fluidity and etching ability of the glass powder, greatly reduces the damage to the passivation layer during the sintering process, and forms high-quality silver-silicon alloy contact sites within a limited etching channel.

[0145] S250: laser transfer the laminate onto at least one surface of the cell sheet 30, and co-sinter the laminate to form a composite electrode 20, thereby manufacturing a solar cell.

[0146] See also Figure 7 and Figure 8 , Figure 7 is a schematic diagram of the laser transfer process of step S250 in some embodiments, Figure 8 Schematic diagram of the structure of the device after step S250 is completed in some embodiments.

[0147] In some embodiments, laser transfer includes the following steps: using an infrared wavelength laser beam, scanning the surface of the mold 10 away from the laminate at a scanning speed of 1m / s~50m / s at a power of 10W~50W, so that the laminate is transferred to at least one surface of the battery 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.

[0148] After laser transfer, the third conductive layer 23 in the stack is arranged to face the battery cell 30, the first conductive layer 21 is arranged to face away from the battery cell 30, and the second conductive layer 22 is coated 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 battery cell 30 to prevent the formation of copper-silicon alloy or aluminum-silicon alloy and improve the conductive effect of the composite electrode 20, but also the composite electrode 20 has excellent antioxidant properties, and its weldability and adhesion are better than those of copper electrodes or aluminum electrodes, thereby improving the reliability, finished product quality and service life of solar cells.

[0149] In some embodiments, co-sintering includes the following steps: in a protective gas atmosphere, gradually heating at a heating rate of 140°C / min to 250°C / min, keeping warm at 650°C to 760°C for 5min to 10min, and slowly cooling at a cooling rate of 160°C / min to 200°C / min.

[0150] As an example, the protective gas can be one or more of nitrogen, helium, neon, argon, krypton and xenon, and can further be nitrogen or argon; the heating rate can be 140°C / min, 150°C / min, 160°C / min, 170°C / min, 180°C / min, 190°C / min, 200°C / min, 210°C / min, 220°C / min, 230°C / min, 240°C / min or 250°C / min. 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.

[0151] Therefore, co-sintering under a protective atmosphere can improve the purity of each conductive layer, prevent oxidation of metal elements such as silver, copper, and aluminum, and improve the uniformity and density of sintering. Sintering at 650℃~760℃ can prevent oxidation of metal elements caused by excessive sintering temperature, and can ensure that each layer softens and completes interface bonding under the action of flexible interface materials, so that the thermal expansion coefficients of each conductive layer tend to be consistent, avoiding stratification caused by different thermal expansion coefficients, and making the adhesion and interface bonding performance of each conductive layer excellent.

[0152] In the traditional sintering process, the temperature rise process from room temperature to sintering temperature is usually completed within 1 minute, and after sintering, the temperature is quickly cooled from the sintering temperature to room temperature. In comparison, the present application controls the heating rate at 140℃ / min~250℃ / min, realizes gradual heating, and reduces the thermal shock caused by rapid temperature changes; controls the cooling rate at 160℃ / min~200℃ / min, reduces the accumulation of thermal stress through slow cooling, and improves the structural stability of each conductive layer.

[0153] The following reference Fig. 9 and Fig.10 The preparation methods of solar cells in other embodiments are described.

[0154] In some embodiments, a method for preparing a solar cell comprises the following steps:

[0155] S310 : providing a mold 10 , wherein the surface of the mold 10 has a receiving groove for preparing the composite electrode 20 .

[0156] S320: Filling the first slurry into the receiving groove of the mold 10 to form the first conductive layer 21, and forming a first groove on the surface of the first conductive layer 21;

[0157] S330: Filling the first groove with a second slurry to form a second conductive layer 22;

[0158] S340: Cover the second conductive layer 22 with the third slurry to form a 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. The resulting structure is as shown in FIG. Fig. 9 As shown;

[0159] S350: laser transfer the laminate onto at least one surface of the cell 30, and co-sinter the laminate to form a composite electrode 20, thereby manufacturing a solar cell.

[0160] In some embodiments, a method for preparing a solar cell comprises the following steps:

[0161] S410 : providing a mold 10 , wherein the surface of the mold 10 has a receiving groove for preparing the composite electrode 20 .

[0162] S420: Filling the first slurry into the receiving groove of the mold 10 to form the first conductive layer 21;

[0163] S430: Covering the first conductive layer 21 with the second slurry to form the second conductive layer 22, and forming protrusions on the surface of the second conductive layer 22;

[0164] S440: Cover the protrusions with the third slurry to form a third conductive layer 23, and form a second groove corresponding to the protrusions on the surface of the third conductive layer 23 facing the second conductive layer 22, thereby obtaining a laminate. The obtained structure is as follows: Fig.10 As shown;

[0165] S450: laser transfer the laminate onto at least one surface of the cell sheet 30, and co-sinter the laminate to form a composite electrode 20, thereby manufacturing a solar cell.

[0166] It can be understood that the slurry and process selected in steps S310~S350 and steps S410~S450 can refer to steps S210~S250, and this application will not elaborate on them here.

[0167] The following combination Figure 8 The structural parameters of the composite electrode 20 are described in detail.

[0168] In the present application, the cell 30 has a front side and a back side opposite to each other, and the composite electrode 20 can be prepared on the front side as the front main grid or the front fine grid, and the composite electrode 20 can also be prepared on the back side as the back main grid or the back fine grid. In addition, the composite electrode 20 can also be used as a connecting line between the front main grid welding points, or as a connecting line between the back main grid welding points.

[0169] When the composite electrode 20 is used as different gate line electrodes, its aspect ratio may be the same or different. At the same time, the width of the same composite electrode 20 may be the same or different. When calculating the aspect ratio, the average width of the composite electrode 20 may be used for calculation, that is, aspect ratio = height ÷ width (same width) ≈ height ÷ average width (different width).

[0170] In some embodiments, the composite electrode 20 is a front fine grid, and its aspect ratio is 0.6-1.2, including but not limited to 0.6, 0.7, 0.8, 0.9, 1, 1.1 or 1.2.

[0171] Specifically, the composite electrode 20 is a front fine grid, whose height is 6μm~12μm, including but not limited to 6μm, 7μm, 8μm, 9μm, 10μm, 11μm or 12μm; its width (or average width) is 10μm~20μm, including but not limited to 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0172] In some embodiments, the composite electrode 20 is a back side fine grid, and its aspect ratio is 0.4-0.6, including but not limited to 0.4, 0.42, 0.45, 0.48, 0.5, 0.52, 0.55, 0.58 or 0.6.

[0173] Specifically, the composite electrode 20 is a back fine grid, whose height is 5μm~10μm, including but not limited to 5μm, 6μm, 7μm, 8μm, 9μm or 10μm; its width (or average width) is 20μm~40μm, including but not limited to 20μm, 22μm, 25μm, 28μm, 30μm, 32μm, 35μm, 38μm or 40μm.

[0174] In some embodiments, the composite electrode 20 is one or more of a front main grid, a connecting line between front main grid welding points, and a connecting line between a back main grid and a back main grid welding point, and its aspect ratio is 0.1 to 0.2, including but not limited to 0.1, 0.12, 0.14, 0.16, 0.18 or 0.2.

[0175] Specifically, the composite electrode 20 is one or more of the front main grid, the connecting line between the front main grid welding points, and the connecting line between the back main grid and the back main grid welding points, and its height is 2μm~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.

[0176] 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 can be understood that the thickness of each conductive layer refers to the 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.

[0177] 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, and this structure is conducive to laser transfer and can increase the aspect ratio of the composite electrode 20, thereby reducing the consumption of the conductive paste.

[0178] In some embodiments, the composite electrode 20 is a front fine grid, and the thickness of each conductive layer is as follows:

[0179] The first conductive layer 21 has an average thickness of 1 μm to 3 μm (maximum thickness of 3 μm to 7 μm) and an average width of 3 μm to 20 μm. If the first conductive layer 21 has a first groove, the depth of the first groove is 1.5 μm to 6 μm.

[0180] The second conductive layer 22 has an average thickness of 2 μm to 15 μm and an average width of 5 μm to 12 μm. Figure 8 In a specific example, the cross section of the second conductive layer 22 is elliptical, the minor axis size along the thickness direction thereof is 3 μm-12 μm, and the major axis size along the width direction thereof is 5 μm-18 μm.

[0181] The third conductive layer 23 has an average thickness of 1 μm to 4 μm (maximum width of 5 μm to 11 μm), and an average width of 7 μm to 25 μm. If the third conductive layer 23 has a second groove, the depth of the second groove is 1.5 μm to 6 μm.

[0182] The advantages of the composite electrode provided by the present application are further illustrated by an example below.

[0183] There are reports that a release layer is prepared by using copper paste (or other non-silver conductive paste) with a release agent and a low-boiling point solvent, and a silver layer that is conductive to the battery cell is prepared by using silver paste, and a double-layer electrode is obtained by laser transfer and co-sintering. However, this double-layer electrode has the following problems: 1) The release layer is directly exposed to the air, and the copper element is easily oxidized; 2) During the laser transfer process, the release agent absorbs heat and evaporates, resulting in more holes and defects in the release layer, which is not conducive to the densification sintering of the release layer and interrupts the conductive path; 3) The release agent may cause side reactions with the copper powder (or aluminum powder) of the release layer and affect the conductive properties of the electrode.

[0184] In contrast, the present application uses a scraping method, laser transfer technology and co-sintering treatment to prepare a composite electrode with a three-layer structure. In the composite electrode, the first conductive layer provides demoulding, support, and anti-oxidation functions, the second conductive layer focuses on efficient conduction and cost reduction, and the third conductive layer provides anti-oxidation and conduction with the battery cell. The functions of different conductive layers are separated and do not interfere with each other, ensuring the optimal comprehensive performance of the composite electrode. At the same time, the layered stacking design is conducive to separately optimizing the slurry composition and process parameters of each layer, reducing side reactions, and improving the sintering effect, so that the density and uniformity of each conductive layer are effectively improved, thereby improving the accuracy, stability and conductivity of the composite electrode, and thus achieving the effect of reducing costs and maintaining efficiency.

[0185] In a second aspect of the present application, a solar cell is provided, which is manufactured using the solar cell manufacturing method as described above.

[0186] In some embodiments, the solar cell includes one or more of a silicon solar cell, a compound solar cell, and an organic solar cell. Among them, the crystalline silicon solar cell includes one or more of an emitter and back passivated cell (PassivatedEmitter and Rear Solar Cell, referred to as PERC cell), a tunnel oxide passivated contact solar cell (TunnelOxide Passivated Contact Solar Cell, referred to as TOPCon cell), an intrinsic thin film heterojunction cell (Heterojunction with Intrinsic Thin-film Solar Cell, referred to as HJT cell or HIT cell), and an interdigitated back contact cell (Interdigitated Back Contact Solar Cell, referred to as IBC cell). The compound solar cell includes a perovskite solar cell (referred to as PSC cell), a copper indium gallium selenide solar cell (referred to as CIGS cell), a cadmium telluride solar cell (referred to as CdTe cell), and a gallium arsenide solar cell (referred to as AsGa cell).

[0187] In a third aspect of the present application, a stacked cell is provided, comprising a bottom cell and a top cell, wherein the bottom cell and / or the top cell is the solar cell as described above.

[0188] In a fourth aspect of the present application, a photovoltaic module is provided, comprising a first packaging panel, a first packaging film, a battery string, a second packaging film and a second packaging panel stacked in sequence, wherein the battery string is formed by electrically connecting a plurality of solar cells as described above, or by electrically connecting a plurality of stacked batteries as described above.

[0189] The following is further described in conjunction with specific embodiments and comparative examples. The raw materials involved in the following specific embodiments and comparative examples, unless otherwise specified, can all be commercially available, the instruments used, unless otherwise specified, can all be commercially available, and the processes involved, unless otherwise specified, are all routinely selected by those skilled in the art.

[0190] Example 1

[0191] The preparation method of the TOPCon battery of this embodiment is as follows:

[0192] (1) Screening and grouping of battery cells: All blue film battery cells are subjected to minority carrier lifetime tests, and the minority carrier lifetime data of each battery cell is recorded. The battery cells are grouped according to the test data to ensure that the mean minority carrier lifetime of each group of battery cells remains consistent, so as to ensure that the subsequent processes are comparable between the groups.

[0193] (2) Preparation of back busbar, back fine grid and front busbar: Using a screen printer, print the back busbar paste onto the back side of the cell, and then dry it at 120°C for 1 min for pre-curing to obtain the back busbar; print the back fine grid paste onto the back side of the cell, and then dry it at 120°C for 1 min for pre-curing to obtain the back fine grid; print the front busbar paste onto the front side of the cell, and then dry it at 120°C for 1 min for pre-curing to obtain the front busbar; wherein, the back busbar paste, back fine grid paste and front busbar paste are all commercially available pastes.

[0194] (3) Preparation of front fine grid:

[0195] ①Prepare template and slurry:

[0196] A glass carrier is provided as a mold, wherein the surface of the glass carrier has an inverted trapezoidal receiving groove, the height (depth) of which is 7.1 μm, the average width is 7.3 μm, and the aspect ratio is 0.97;

[0197] 0.5% of release agent (methyl silicone oil), 2% of transfer solvent (diethylene glycol monobutyl ether, boiling point at 101.3 kPa is about 230.4 ° C) and 2% of flexible interface material (PbO) were added to DK72E slurry of DKEM® (the D50 particle size of silver powder is 1 μm) to obtain the first slurry, which has a viscosity of 69 Pa·s and a density of 1.5 g / cm at room temperature. 3 ;

[0198] In COPPRINT's LF365 copper paste (copper powder with a D50 particle size of 1 μm and a specific surface area of ​​0.67 m 2 / g) was added with 2% of a flexible interface material (PbO) to obtain a second slurry, which had a viscosity of 106 Pa·s at room temperature and a density of 4.5 g / cm 3 ;

[0199] 2% of the flexible interface material (PbO) was added to DK72E slurry of DKEM® (the D50 particle size of the silver powder was 1 μm) to obtain the third slurry, which had a viscosity of 92 Pa·s and a density of 3 g / cm at room temperature. 3 ;

[0200] By controlling the viscosity and density of the three slurries, it is beneficial to achieve effective stratification, difficult mixing, and easy molding, so that each layer of slurry is evenly filled in the containing tank to form a preset coating structure.

[0201] ②Preparation of laminated body:

[0202] The uniform coating technology is adopted to fill the first slurry into the receiving groove of the template, and the excess slurry in the flattened area is removed by a scraper, so that a first conductive layer with a thickness of about 3μn is retained in the receiving groove; the first groove is formed on the surface of the first conductive layer through soft film extrusion of the three-roller gate machine; wherein, the average thickness of the first conductive layer is 3μm (the maximum thickness is 3.6μm), the average width is 6.3μm, and the depth of the first groove is 3.2μm.

[0203] The uniform coating technology is adopted to fill the second slurry into the first groove, and then a flexible scraper (provided with a semi-elliptical groove matching the spacing and size of the receiving groove) is used for scraping to form a second conductive layer with a protrusion on the surface, and the excess slurry exceeding the receiving groove is removed, followed by drying at 40°C for 3s for pre-curing; wherein, the cross-section of the second conductive layer is elliptical, with a short axis dimension of 6.4μm along its thickness direction and a long axis dimension of 7.5μm along its width direction.

[0204] The third slurry is coated on the surface of the second conductive layer by a uniform coating technology, and the final coating thickness is controlled by a scraper to ensure that the outer surface of the mold is clean and the third conductive layer completely covers the second conductive layer. A second groove corresponding to the protrusion is formed on the surface of the third conductive layer facing the second conductive layer; wherein the average thickness of the third conductive layer is 3μm (the maximum thickness is 3.5μm), the average width is 10μm, and the depth of the second groove is 3.2μm.

[0205] The laminate was then dried at 40° C. for 3 seconds for pre-curing to obtain a laminate.

[0206] ③Laser transfer:

[0207] The mold filled with the laminate is aligned and fixed to the front side of the battery cell, and the third conductive layer is arranged facing the battery cell. A fiber laser is selected with set wavelength of 1064nm, laser power of 15W, exposure time of 200ns, scanning speed of 1.5m / s and 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 battery cell through local heating.

[0208] ④ Co-sintering:

[0209] After transfer, directly enter the sintering and annealing integrated furnace (or chain furnace), and sinter and anneal according to the following temperature curve under the protection of nitrogen with an oxygen content of ≤10ppm:

[0210] Heating from 25°C to 400°C within 1.5 min (heating rate: 250°C / min);

[0211] Heating from 400°C to 760°C in 2.5 min (heating rate: 144°C / min);

[0212] Keep at 760℃ for 5min;

[0213] Slowly cool from 760°C to 25°C within 4 minutes (cooling rate is about 184°C / min);

[0214] To ensure that each layer of slurry softens and fuses evenly during the heating process, the thermal shock is small, the glass powder flows fully and the metal powder particles are densely combined during the insulation stage, the thermal stress accumulation is reduced during the cooling stage, and the structural stability of each layer is good, so that the stack forms a composite electrode with excellent density, conductivity and interface bonding strength, while effectively preventing interface problems caused by the diffusion of copper elements into the silicon wafer.

[0215] Embodiment 2-3

[0216] Please refer to Table 1. The preparation method of the TOPCon battery of Examples 2 to 3 is the same as the preparation method of the TOPCon battery of Example 1, except that the aspect ratios of the composite electrodes are different.

[0217] Comparative Examples 1 to 3

[0218] Please refer to Table 1. The preparation method of the TOPCon battery of Comparative Examples 1 to 3 is the same as that of the TOPCon battery of Example 1, except that the front fine grid of Comparative Examples 1 to 3 is prepared by screen printing using DK72E slurry of DKEM® (the D50 particle size of the silver powder is 1 μm).

[0219] Test Case

[0220] (1) Morphology detection: A 3D optical microscope was used to characterize the cross section of the composite electrode and record the height, width, and height and width of each layer of the composite electrode.

[0221] (2) Slurry consumption: Before preparing all the gate electrodes, the battery cell is weighed to obtain a mass G1. After preparing all the gate electrodes, the cell is weighed again to obtain a mass G2. The slurry consumption of a single cell (referred to as unit consumption) is: unit consumption = G2-G1.

[0222] (3) Electrical performance test: The electrical performance of the TOPCon battery was tested using a 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.

[0223] The above test results are shown in Tables 1 and 2. In Table 2, the test results of Example 1 are the average values ​​of 443 parallel experiments, and the test results of Comparative Example 1 are the average values ​​of 465 parallel experiments. The difference between the average values ​​of Example 1 and the average value of Comparative Example 1 is obtained to verify the performance variation of Example 1. The other two columns of data in Table 2 are also processed in a similar way.

[0224] Table 1. Height, width and aspect ratio of the front side fine grid

[0225]

[0226] Table 2. TOPCon battery unit consumption and electrical performance

[0227]

[0228] As shown in Table 1, in Examples 1 to 3, the height of the front fine grid is 4.9 μm to 7.1 μm (average value is 5.87 μm), the width is 7.2 μm to 7.3 μm (average value is 7.27 μm), and the aspect ratio is 0.67 to 0.97 (average value is 0.81). Compared with the front fine grids of Comparative Examples 1 to 3, the width of the front fine grid of Example 1 is greatly reduced, and the aspect ratio is greatly improved, which shows that the composite electrode with a multilayer structure prepared in this application has a stronger winding capability.

[0229] As can be seen from Table 2, in the TOPCon battery prepared in Example 1, the slurry consumption of each cell is lower, and the slurry consumption of each cell can be reduced by 3mg~13mg, which is due to the narrowing of the composite electrode line. At the same time, in the composite electrode, the second conductive layer uses copper paste instead of expensive silver paste, which reduces the amount of silver powder per cell by 30%~50%. Therefore, the composite electrode with a multilayer structure provided in this application can effectively reduce the preparation cost of the battery.

[0230] Because the width of the front fine grid of Example 1 is reduced and the aspect ratio is larger, the photoelectric conversion efficiency (Eta), open circuit voltage (Uoc) and short circuit current (Isc) of the TOPCon battery are improved, but the fill factor (FF) is reduced due to the influence of 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, and the resistance increases.

[0231] In summary, the method for preparing solar cells provided in the present application provides a composite electrode having a narrower width and a larger aspect ratio, which is beneficial to reducing the unit dosage of conductive paste and silver powder, while also improving the photoelectric conversion efficiency, open circuit voltage and short circuit current of the battery, thereby playing a role in reducing costs and maintaining efficiency.

[0232] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0233] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of protection of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the scope of protection of the present application. Therefore, the scope of protection of the present application shall be subject to the attached claims.

Claims

1. A method for preparing a solar cell, characterized in that: The following steps are involved: Filling the first slurry into the mold 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 together cover the second conductive layer to form a laminate; Laser transfer the stack onto at least one surface of a cell sheet, and co-sinter the stack to form a composite electrode, thereby producing the solar cell; 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 according to claim 1, characterized in that: After the first slurry is filled into the mold, the following steps are also included: forming a first groove on the surface of the first conductive layer, and filling the first groove with the second slurry to form the second conductive layer; and / or, After forming the second conductive layer, the method further comprises the following steps: The surface of the second conductive layer is formed with protrusions, and the third slurry is covered on the protrusions to form the third conductive layer, and the surface of the third conductive layer facing the second conductive layer forms a second groove corresponding to the protrusions.

3. The method for preparing a solar cell according to claim 1, wherein: The second slurry satisfies one or more of the following conditions: (1) The mass fraction of the copper element in the second slurry is 20% to 80%, and / or the mass fraction of the aluminum element is 10% to 60%; (2) The specific surface area of ​​the conductive metal powder is 0.5 m 2 / g~2m 2 / g; (3) The D50 particle size of the conductive metal powder is 0.4 μm to 1.1 μm; (4) The density of the second slurry is 2.5 g / cm 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, characterized in that: 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 3, characterized in that: 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%, and 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 3, characterized in that: One or more of the following conditions are 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 / cm 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 / cm 3 ~4g / cm 3 .

7. The method for preparing a solar cell according to any one of claims 1 to 3, characterized in that: 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%, and 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 3, characterized in that: The co-sintering comprises the following steps: In a protective gas atmosphere, the temperature is gradually increased at a heating rate of 140°C / min-250°C / min, kept at 650°C-760°C for 5min-10min, and slowly cooled at a cooling rate of 160°C / min-200°C / min.

9. The method for preparing a solar cell according to any one of claims 1 to 3, characterized in that: One or more of the following conditions are met: (1) The composite electrode is a front fine grid with a height-to-width ratio of 0.6 to 1.2; (2) The composite electrode is a back-side fine grid with an aspect ratio of 0.4 to 0.6; (3) The composite electrode is one or more of the front main grid, the connecting wire between the front main grid welding points, and the connecting wire between the back main grid and the back main grid welding points, and its aspect ratio is 0.1-0.2; (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, characterized in that: The solar cell is prepared by the method for preparing the solar cell according to any one of claims 1 to 9.

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