Solar cell and preparation method thereof

Abstract

The invention provides a solar cell and a preparation method thereof. The preparation method of the solar cell comprises the following steps: forming an auxiliary grid contact short line on a silicon wafer by using first slurry; a main grid connecting line and an auxiliary grid are formed on the silicon wafer through second slurry, the auxiliary grid is perpendicular to and electrically connected with the corresponding auxiliary grid contact short line, the main grid connecting line is perpendicular to and electrically connected with the auxiliary grid, and the mass content of silver in the first slurry is larger than that of silver in the second slurry; and carrying out low-temperature curing at a first temperature less than or equal to 250 DEG C. According to the invention, the auxiliary grid contact short line is formed on the silicon wafer, compared with the continuous auxiliary grid contact line, the usage amount of the first slurry is saved, the shading area is reduced, the usage amount of the silver slurry is saved, and the photovoltaic efficiency is improved. The main grid connecting line and the auxiliary grid are formed by using the second slurry with relatively low silver content, and low-temperature curing is performed, so that the use amount of silver is reduced while the electrical performance is ensured, and the manufacturing cost of the solar cell is greatly reduced.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of new energy, in particular to a solar cell and a preparation method thereof. BACKGROUND

[0002] Generally, the main grid and the auxiliary grid are formed on the silicon wafer of the solar cell by screen printing, wherein the main grid is responsible for the current convergence of the auxiliary grid and the assembly welding, the silver content of the paste used for printing the main grid is 85%-90%, and the auxiliary grid is responsible for forming ohmic contact with silicon and collecting current, the silver content of the paste used for printing the auxiliary grid is 91%-94%. If the silver content of the paste is simply reduced, the sintering ability of the grid line will be reduced, resulting in poor silver-silicon contact and increased grid line resistivity. In the non-silicon cost of the solar cell, the silver paste used for printing the grid line accounts for a large part, for example, in the non-silicon cost of the TOPCon solar cell, the proportion of silver paste is more than 40%. This greatly hinders the further reduction of the cost of the solar cell. It is expected to develop a solar cell that greatly reduces the non-silicon cost without reducing the electrical performance. SUMMARY

[0003] Embodiments of the present disclosure provide a preparation method of a solar cell, comprising: forming auxiliary grid contact short lines on a silicon wafer using a first paste; forming main grid connection lines and auxiliary grids on the silicon wafer using a second paste, wherein the auxiliary grids are perpendicular to and electrically connected to the corresponding auxiliary grid contact short lines, the main grid connection lines and the auxiliary grids are perpendicular and electrically connected, the mass content of silver in the first paste is greater than the mass content of silver in the second paste; and performing low-temperature curing at a first temperature less than or equal to 250°C.

[0004] In some embodiments, the auxiliary grid contact short lines are arranged as a matrix of line segments spaced apart from each other.

[0005] In some embodiments, the mass content of silver in the first paste is 91%-94%.

[0006] In some embodiments, the second paste comprises silver-coated copper, and the mass content of silver in the second paste is 20%-25%.

[0007] In some embodiments, the first temperature is 200°C-250°C.

[0008] In some embodiments, the preparation method further comprises: before forming the main grid connection lines and the auxiliary grids, forming main grid pads on the silicon wafer using a third paste, wherein the main grid connection lines and the auxiliary grids are electrically connected to the main grid pads, and the mass content of silver in the third paste is 85%-90%.

[0009] In some embodiments, the main grid pads are formed before the auxiliary grid contact short lines, and the preparation method further comprises: after forming the main grid pads, performing drying at a second temperature of 200°C-300°C.

[0010] In some embodiments, the preparation method further comprises, after forming the sub-grid contact short line, pre-sintering with a peak temperature of 730-770°C and photo-injection with a light intensity of 8-40 suns and at a third temperature of 500-550°C.

[0011] In some embodiments, the preparation method further comprises, after low-temperature curing, laser-assisted sintering with a scanning direction along the extension direction of the sub-grid contact short line, a laser scanning speed of 40-60 m / s, a laser spot size of 80-100 pm, a laser power setting of 25-33%, a laser rated power of 60 W, and a bias voltage of 13-18 V.

[0012] In some embodiments, the solar cell is a TOPCon solar cell, and the sub-grid contact short line forms a direct ohmic contact with the silicon base of the silicon wafer.

[0013] Another embodiment of the present disclosure provides a solar cell, which is obtained according to the above preparation method.

[0014] The present disclosure forms a sub-grid contact short line on a silicon wafer, which on one hand improves the collection ability of photo-generated current, and on the other hand, compared with forming a continuous sub-grid contact line, saves the amount of first paste used, reduces the light-shielding area, thereby saving the amount of silver paste used and improving the photovoltaic efficiency. By using a second paste with a lower silver content to form the main grid connection line and the sub-grid, and performing low-temperature curing, the amount of silver is reduced again while ensuring the electrical performance, thereby greatly reducing the manufacturing cost of the solar cell. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a flowchart of a preparation method of a solar cell according to some embodiments.

[0016] Figure 2 is a schematic plan view of a solar cell according to some embodiments. DETAILED DESCRIPTION

[0017] In order for those skilled in the art to better understand the technical solutions of the present disclosure, the technical solutions of the present disclosure will be described in detail below with reference to the drawings.

[0018] In the following, example embodiments will be described more fully with reference to the accompanying drawings, in which, however, these example embodiments can be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0019] In the case of no conflict, each embodiment of the present disclosure and each feature in the embodiments can be combined with each other.

[0020] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0022] The embodiments described herein can be described with reference to plan views and / or cross-sectional views by virtue of the present disclosure being idealized schematic illustrations. Thus, the example illustrations can be modified according to manufacturing techniques and / or tolerances. Therefore, the embodiments are not limited to the embodiments illustrated in the drawings, but include modifications of configurations formed based on manufacturing processes. Thus, the regions illustrated in the drawings are of a schematic nature and the shapes of the regions shown in the drawings illustrate the specific shapes of the regions of the elements, but are not intended to be limiting.

[0023] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an overly literal or overly formal sense unless expressly so defined herein.

[0024] With the continuous development of the production technology of solar cells, the TOPCon solar cell adopts a tunneling oxide layer passivation contact structure (ultra-thin SiO2 layer + doped polysilicon layer), with excellent interface passivation performance and ultra-high cell efficiency, gradually occupies the market, becomes the mainstream, and in the production process of the TOPCon cell sheet, the main processes are texturing → boron expansion → borosilicate glass (BSG) removal → alkali etching → in-situ doped amorphous silicon → annealing → phosphosilicate glass (PSG) removal → amorphous silicon removal plating → front side generation of aluminum oxide protective film → front and back side silicon nitride film plating → screen printing → pre-sintering → light injection → laser-assisted sintering → testing.

[0025] The present disclosure provides a solar cell and a preparation method thereof, which can greatly reduce the amount of silver paste used, and greatly reduce the non-silicon cost of the solar cell without reducing the electrical performance.

[0026] Embodiments of the present disclosure provide a preparation method of a solar cell, as shown in the following technical scheme. Figure 1 S1, forming a sub-grid contact short line on a silicon wafer using a first paste. In some embodiments, as shown in the following figure, Figure 2 The sub-grid contact short line 2 is in the form of a plurality of short line segments spaced apart from each other, and the plurality of sub-grid contact short lines 2 are on the same straight line, but are discontinuous straight lines, Figure 2 The 5 sub-grid contact short lines 2 are shown on the same straight line, but this is only exemplary and not used to limit the present disclosure. By forming the sub-grid contact short line 2 on the silicon wafer, on the one hand, the collection ability of the photo-generated current is improved, and on the other hand, compared with forming a continuous sub-grid contact line, the amount of the first paste used is saved, and the light shielding area of the sub-grid contact short line is reduced, thereby saving the amount of silver paste used and improving the photovoltaic efficiency. In some embodiments, in the TOPCon solar cell, since the passivation layer adopts a silicon nitride layer, rather than a transparent conductive oxide layer for passivation as in a heterojunction (HJT), the sub-grid contact short line in the TOPCon solar cell needs to go through a high-temperature process of ablating the silicon nitride passivation layer, and the silver-coated copper with low silver content cannot withstand the high temperature in the high-temperature ablation process. Therefore, the sub-grid contact short line 2 of the present disclosure cannot use silver-coated copper paste.

[0027] In some embodiments, as shown in the following figure, Figure 1 The preparation method of the present disclosure further comprises: S2, forming a main grid connection line and a sub-grid on the silicon wafer using a second paste. As shown in the following figure, Figure 2 In some embodiments, the sub-grid 4 is perpendicular to and electrically connected with the corresponding sub-grid contact short line 2, the main grid connection line 3 and the sub-grid 4 are perpendicular and electrically connected, and the current collected by the sub-grid contact short line 2 is transmitted out through the main grid connection line 3 and the sub-grid 4. In some embodiments, the mass content of silver in the first paste is greater than the mass content of silver in the second paste. Since the sub-grid contact short line 2 formed by the first paste forms a direct ohmic contact with the silicon matrix in the silicon wafer, by using the first paste with high silver content, the ohmic contact resistance between the sub-grid contact short line 2 and the silicon wafer can be reduced, and the resistivity of the sub-grid contact short line 2 can be reduced. Since the main grid connection line 3 and the sub-grid 4 of the present disclosure can not form an ohmic contact with the silicon wafer, but are responsible for transmitting the current collected by the sub-grid contact short line 2 out (i.e., carrier collection and lateral transmission by the sub-grid contact short line 2), by using the second paste with lower silver content, the use amount of silver can be greatly reduced while ensuring the electrical performance of the solar cell, thereby greatly reducing the manufacturing cost of the solar cell.

[0028] In some embodiments, as shown in the following figure, Figure 1As shown, the preparation method disclosed herein further includes: S3, low-temperature curing at a first temperature less than or equal to 250°C. Since the second slurry has a low silver content, it is generally not resistant to high temperatures. When the first temperature is higher than 250°C, it will affect the stability of the second slurry and the formation height of the main grid connection line 3 and the auxiliary grid 4, thereby reducing the electrical performance of the solar cell. By performing low-temperature curing at a first temperature less than 250°C, the formation height of the main grid connection line 3 and the auxiliary grid 4 can be increased, thereby increasing the cross-section of the main grid connection line 3 and the auxiliary grid 4, reducing the resistivity of the main grid connection line 3 and the auxiliary grid 4, and improving the electrical performance of the solar cell.

[0029] like Figure 2 As shown, in some embodiments, the auxiliary grid contact stubs 2 are arranged in a matrix of spaced-apart line segments. In some embodiments, the first spacing between the auxiliary grid contact stubs 2 in a first direction parallel to the auxiliary grid 4 is equal to the second spacing between the auxiliary grid contact stubs 2 in a second direction perpendicular to the auxiliary grid 4 or along the direction in which the line segments of the auxiliary grid contact stubs 2 extend. In this case, the distribution of the individual line segments of the auxiliary grid contact stubs 2 is relatively uniform, and the current collection efficiency can be optimized accordingly. In some embodiments, the width of the auxiliary grid contact stubs 2 is 14 μm to 16 μm, for example, 15 μm; the first spacing and the second spacing between the auxiliary grid contact stubs 2 are 0.3 mm to 1 mm, for example, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, or other suitable values ​​therebetween.

[0030] In some embodiments, the mass content of silver in the first paste is 91% to 94%. In some embodiments, the high silver content of the first paste can provide better electrical conductivity. Silver is one of the best known conductors, and using a high proportion of silver can effectively reduce resistance, thereby improving current collection efficiency and overall electrical performance. In addition, since the sub-grid contact short line 2 forms an ohmic contact with the silicon substrate of the silicon wafer, the high silver content of the first paste can form an effective ohmic contact, and in order to achieve efficient current collection, the sub-grid contact short line 2 needs to form a low resistance ohmic contact with the surface of the silicon wafer. In addition, high silver content helps to penetrate the silicon nitride passivation layer during sintering and form a direct ohmic contact with the silicon substrate, which is essential for high-performance solar cells. Silver paste with high silver content generally has better durability and environmental stability, which can increase the service life of the solar panel. In addition, silver also has good oxidation resistance and can maintain its electrical properties under long-term outdoor use conditions. Maintaining a high silver content without changing the existing production process can ensure process stability and product consistency. Of course, the mass content of silver in the first paste cannot be too high, as too high a content will reduce the content of glass powder and some organic carriers (e.g., leveling agents, etc.) in the first paste, affecting the ability of the first paste to ablate the passivation layer. In some embodiments, the mass content of silver in the first paste can be 91%, 92%, 93%, 94%, or any suitable value therebetween.

[0031] In some embodiments, the second paste includes silver-coated copper, and the mass content of silver in the second paste is 20% to 25%. As described above, in the present disclosure, the main grid connection line 3 and the sub-grid 4 formed by the second paste do not form an ohmic contact with the silicon wafer, but are responsible for transmitting the current collected by the sub-grid contact short line 2. By using a second paste with a lower silver content, the use of silver can be significantly reduced while ensuring the electrical performance of the solar cell, thereby significantly reducing the manufacturing cost of the solar cell. In some embodiments, the silver-coated copper has a copper particle as the core and a layer of silver on the surface. This structure takes advantage of the excellent conductivity and oxidation resistance of silver, while also taking advantage of the cost-effectiveness of copper to reduce the use of expensive silver. If the mass content of silver in the second paste is too small, the conductivity and oxidation resistance of the silver-coated copper will be insufficient, which will not be conducive to the stability of the silver-coated copper structure. If the mass content of silver in the second paste is too high, the effect of improving the conductivity and oxidation resistance of the silver-coated copper will no longer be significant, and the cost-effectiveness will be inhibited. In some embodiments, the mass content of silver in the second paste can be 20%, 21%, 22%, 23%, 24%, 25%, or any suitable value therebetween. In some embodiments, the mass content of copper in the second paste can be 70% to 75%.

[0032] In the paste of the present disclosure, in addition to the silver powder or silver-coated copper powder, glass powder and organic carrier can also be included, the mass content of the glass powder can be 1% to 4%, and the mass content of the organic carrier can be 4% to 15%. The glass powder and the organic carrier can adopt the commonly used glass powder and organic carrier in the art, for example, the glass powder can include silicon dioxide and some additives (for example, Na2O), and the organic carrier can include resin material (for example, phenolic resin). In some embodiments, the second paste can not contain glass powder.

[0033] In some embodiments, the first temperature is 200°C to 250°C. In some embodiments, the first temperature can be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, or any suitable value therebetween. Since the second paste adopts silver-coated copper, under high temperature conditions, the copper can be softened or melted, which not only affects the shape and integrity of the grid lines, but also causes the electrical performance to decline. In addition, too high a temperature will also cause the problem of copper oxidation, reducing the conductivity. Although the silver coating layer can provide a certain anti-oxidation protection, at too high a temperature, the silver coating layer can not be enough to completely prevent the oxidation or morphological change of the copper core. Especially in the process of manufacturing solar cells, if the high-temperature sintering process conventionally used for pure silver paste is adopted, the copper part in the silver-coated copper paste can not be able to withstand such a temperature, thereby affecting the quality and performance of the final product. By adopting a first temperature of 200°C to 250°C for low-temperature curing, good electrical connection between the main grid connection line 3 and the sub-grid 4 and the sub-grid contact short line 2 is ensured, while avoiding the problems of copper oxidation and damage to the chemical structure of other organic carriers caused by high temperature.

[0034] In some embodiments, as described above, the sub-grid contact short line 2 forms a direct ohmic contact with the silicon matrix of the silicon wafer. In some embodiments, the solar cell is a TOPCon solar cell. The silver-coated copper process for heterojunction (HJT) cells is already quite mature, but the silver-coated copper paste for HJT cells is printed and cured above the conductive layer and is in direct contact with the oxide conductive layer, so that the current can be collected. However, the TOPCon solar cell requires the paste to sinter through the silicon nitride passivation film at high temperature, and form a direct ohmic contact with the silicon matrix to collect the current. Therefore, the printing method of HJT and the silver-coated copper paste cannot be applied in TOPCon.

[0035] In some embodiments, the preparation method further includes: before forming the main grid connection line 3 and the sub-grid 4, using a third paste to form a main grid pad 1 (or main grid pad point) on the silicon wafer, as shown in FIG. 1B. Figure 2As shown, the main grid connecting lines 3 and the sub-grid 4 are electrically connected to the main grid pads 1. Since high-temperature baking is involved after the formation of the main grid pads 1, which can destroy the structural stability of silver-coated copper, the main grid pads 1 are formed before the main grid connecting lines 3 and the sub-grid 4. In some embodiments, the mass content of silver in the third paste is 85% to 90%. In some embodiments, the mass content of silver in the third paste is 85%, 86%, 87%, 88%, 89%, 90%, or any suitable value therebetween. In some embodiments, the main grid connecting lines aggregate and conduct the current received from the sub-grid from the individual main grid pads 1, and finally connect to the external circuit through the solder ribbon, completing the current output. The main grid pad is a structure for connecting the solder ribbon. In the present disclosure, the main grid pads 1 are printed using the third paste with high silver content to ensure good soldering performance and sufficient mechanical strength. This ensures that the battery piece can be firmly connected to other components (such as other battery pieces or backplanes) through the soldering process in the subsequent component manufacturing process, providing the necessary electrical connection and mechanical support. Since the main grid pad uses silver paste with high silver content, it has a lower resistivity, which helps to reduce energy loss during current transmission and improve overall electrical performance. This is crucial for maintaining or even improving the overall conversion efficiency of solar cells. By using the third paste with high silver content, the main grid pad can improve its long-term stability and durability, which helps to ensure the required pulling force and good solderability during component soldering. This is because silver has excellent oxidation and corrosion resistance, and can maintain good electrical conductivity even after long-term exposure to various environmental conditions outdoors.

[0036] In some embodiments, the main grid pads 1 are formed before the sub-grid contact short lines 2. In some embodiments, the main grid pads 1 are formed first, making the entire manufacturing process simpler and smoother, while also being well compatible with existing production line equipment and technology. There is no need to modify the existing production line, reducing the difficulty and cost of technical implementation. In addition, the role of the sub-grid contact short line is to form effective contact with the surface of the battery piece during the laser sintering process, so as to facilitate the extraction of carriers and complete the lateral transmission. If these sub-grid contact short lines are printed first, the subsequent printing of the main grid pads may damage the sub-grid contact short lines or affect their contact effect with the battery piece. Therefore, ensuring the stability and reliability of the main grid pads first, and then forming the sub-grid contact short lines, is beneficial to ensure the quality of the final battery. Therefore, printing the main grid pads first and then printing the sub-grid contact short lines not only helps to improve the electrical performance and reliability of solar cells, but also simplifies the production process and reduces manufacturing costs.

[0037] In some embodiments, the preparation method further comprises baking at a second temperature of 200-300°C after the formation of the main grid pad 1. In some embodiments, the second temperature is 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, or any suitable value therebetween. The third paste usually contains a certain proportion of organic carriers (such as resins, solvents, etc.), which need to be effectively removed before subsequent curing or sintering. 200-300°C is a relatively ideal temperature range, which can ensure that the organic carrier is sufficiently volatilized, while avoiding the problems caused by rapid evaporation due to excessively high temperature. Within this temperature range, the silver particles in the third paste can be effectively controlled from being excessively oxidized, maintaining their good electrical conductivity. If the temperature is too low, it is not sufficient to completely volatilize the organic carrier; while a temperature that is too high can lead to the oxidation of the silver surface, affecting the final electrical performance. In addition, this temperature range meets the need of removing the organic carrier, and does not have too much impact on production efficiency. It can complete the baking process within a reasonable time, and is compatible with existing production line equipment and technical conditions, which is conducive to improving production efficiency and stability. If the baking temperature is too low, the organic carrier in the third paste may not be completely volatilized, and the residual organic matter can produce gas during subsequent high-temperature processing, forming bubbles or voids, affecting the mechanical strength and electrical performance of the battery. If the baking temperature is too high, the silver paste surface can be oxidized, increasing the contact resistance and damaging the electrical performance. Therefore, baking within the temperature range of 200-300°C can effectively remove the organic carrier in the silver paste, and avoid the adverse effects of excessively high or low temperature, ensuring the stability and efficiency of the solar cell manufacturing process.

[0038] In some embodiments, the method of manufacturing further comprises, after forming the subgrid contact stubs 2, performing a pre-sintering and a photo-injection, the pre-sintering having a peak temperature of 730°C to 770°C, and the photo-injection having a light intensity of 8 suns to 40 suns (e.g., 16 suns) and being performed at a third temperature of 500°C to 550°C. In some embodiments, the main purpose of the pre-sintering is to perform a preliminary solidification process on the printed subgrid contact stubs. By heating, the organic components in the silver paste are volatilized, and the metal particles begin to form preliminary connections among them, enhancing their mechanical strength and electrical conductivity. In addition, pre-sintering helps to improve the contact quality between the silver paste and the surface of the silicon wafer, preparing for subsequent laser-assisted sintering. Proper pre-sintering can ensure that, at the final sintering, the silver can better penetrate the passivation layer and form a low-resistance ohmic contact with the silicon substrate, which is crucial for improving current collection efficiency. In some embodiments, the peak temperature of the pre-sintering is 730°C, 740°C, 750°C, 760°C, 770°C, or any suitable value therebetween. Such a temperature range can both ensure that the silver paste is sufficiently preliminarily solidified and not be too high to cause unnecessary material changes or damage.

[0039] In some embodiments, the photo-injection is a heat treatment process usually performed under conditions of light illumination (e.g., LED lamp) of a certain intensity. It can accelerate the diffusion and activation of dopant atoms by providing additional energy, thereby increasing the carrier concentration in the semiconductor material and optimizing the cell performance. In addition, photo-injection can also help to repair certain defects in the crystal structure, such as dangling bonds, dislocations, etc., which can become recombination centers, reducing carrier lifetime and cell efficiency. By photo-injection, such defects can be effectively reduced, and the overall performance of the cell can be improved. In the present disclosure, the photo-injection is performed at a third temperature of 500°C to 550°C, at which the photo-injection can further improve the interface properties between the metal and the semiconductor, such as reducing the interface state density and enhancing the charge transport capability, which is very important for achieving high-efficiency energy conversion. In some embodiments, too high a light intensity can cause unnecessary thermal stress on the surface or inside of the silicon wafer, and even possibly cause physical damage. While a light intensity range of 8 suns to 40 suns (preferably, 15 suns to 17 suns, e.g., 16 suns) is an ideal interval that can both effectively activate the dopant and not cause damage to the material. In some embodiments, the third temperature can be 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, or any suitable value therebetween. By choosing this relatively low temperature (compared to some high-temperature processing steps), the activation effect can be ensured while reducing the problem of thermal stress caused by rapid heating or high-temperature processing. This helps to maintain the integrity of the silicon wafer and its surface passivation layer, preventing cracks or other forms of damage due to differences in thermal expansion coefficients.

[0040] In some embodiments, the preparation method further comprises, after low-temperature curing, performing laser-assisted sintering, the scanning direction of the laser-assisted sintering being along the extension direction of the auxiliary grid contact short line, the laser scanning speed being 40 m / s-60 m / s, the laser spot size being 80 μm-100 μm, the laser power being set to 25%-33%, the laser rated power being 60 W, and the bias voltage being 13 V-18 V. By performing laser-assisted sintering, high-quality ohmic contact between the metal electrode and the semiconductor material can be achieved, and the current collection efficiency can be optimized. Specifically, by laser-assisted sintering, a high energy density can be provided in the local area, so that the first paste can effectively penetrate the silicon nitride passivation layer and form a direct ohmic contact with the silicon substrate. During laser-assisted sintering, due to the effect of local high temperature, the fusion between silver particles and the good bonding between silver and copper can be promoted, thereby reducing the contact resistance and improving the overall conductivity. Compared with the traditional global high-temperature sintering method, laser-assisted sintering is a local heating technology that only heats the specific area that needs to be processed, reducing the impact on the surrounding material and avoiding unnecessary thermal stress and possible material damage. By making the scanning direction of the laser-assisted sintering along the extension direction of the auxiliary grid contact short line, a high energy density can be provided in the local area where the auxiliary grid contact short line contacts the silicon wafer, so that the first paste can effectively penetrate the silicon nitride passivation layer and form a direct ohmic contact with the silicon substrate, while reducing the impact on the surrounding material. By using the above laser scanning speed, laser power and bias voltage, both good sintering effect and minimal negative impact on the material can be ensured.

[0041] Another embodiment of the present disclosure provides a solar cell, which is obtained according to the above preparation method.

[0042] The present disclosure uses a third paste with high silver content to print the main grid pad, ensuring the welding tension and weldability of the photovoltaic module, and uses a first paste with high silver content to print the auxiliary grid contact short line, ensuring the effective ohmic contact between the auxiliary grid contact short line and the silicon wafer. In addition, silver-coated copper paste is used for printing instead of high-silver-content paste to print the main grid connection line and the auxiliary grid, ensuring the collection and lateral transmission of carriers. Compared with the existing process route, the present disclosure only needs to add one printing and low-temperature curing process to print the main grid connection line 3 and the auxiliary grid 4, and the other processes are consistent with the existing process route, so that the electrical performance is not weaker than that of the existing process route, but the silver content can be greatly reduced, wherein the silver content of the main grid connection line 3 and the auxiliary grid 4 is reduced from 85%-90% to 20%-25% and from 91%-94% to 20%-25% respectively, greatly reducing the non-silicon cost of the solar cell.

[0043] The technical solutions of the present disclosure will be described below in conjunction with specific embodiments.

[0044] As shown in Tables 1-3, which are a comparison table of parameters and electrical properties of solar cells prepared by the process method of the present disclosure and the existing conventional process method, Table 1 shows the parameters of the process method of the present disclosure, Table 2 shows the parameters of the existing process method, and Table 3 shows the comparison of their electrical properties. In slurry A, the mass content of glass powder (SiO2) is 2%, and the mass content of organic carrier (phenolic resin) is 15%; in slurry B, the mass content of glass powder (SiO2) is 3%, and the mass content of organic carrier (phenolic resin) is 6%; in slurry C, the mass content of organic carrier (phenolic resin) is 5%. They all use n-type monocrystalline silicon wafers as substrates, the size of the silicon wafers is 182.2 mm x 183.75 mm, the thickness of the silicon wafers is 110-130 μm, and the resistivity of the silicon wafers is 0.3-2.1 Ω·cm. On the front surface of the n-type silicon wafer substrate, a P-N junction is formed by diffusion, a composite passivation film layer of aluminum oxide and silicon nitride is deposited, and on the back surface of the n-type silicon wafer substrate, doped polysilicon and silicon nitride are deposited in sequence; then the existing process prints silver grid lines (main grid connection line width 20 μm, main grid pad size 0.6 mm*0.8 mm, and sub-grid width 16 μm) on the front and back surfaces by screen printing technology, and after drying and sintering, a metal silver electrode with good ohmic contact is formed, and finally a TOPCon solar cell is prepared.

[0045] In the process method of the present disclosure, the existing sub-grid is replaced by a sub-grid contact short line (first interval 1 mm, second interval 0.3 mm), and slurry C is used to print the main grid connection line and the sub-grid, and the others are the same as the existing process method. The solar cell photoelectric conversion efficiency difference (including Eta, Voc, Isc, FF parameters) is tested by using a May electrical performance tester (complying with IEC60904 series industry standards) under standard test conditions (STC) (i.e. light intensity 1000 W / m 2 , spectrum AM1.5, temperature 25℃).

[0046] Table 1

[0047] Print position Type of paste Silver mass content % Copper mass content % Wet weight mg Silver consumption mg Main grid pad A 83％ / 3 2.49 Sub grid contact stub B 91％ / 10 9.1 Main grid connection line and sub grid sub grid C 25％ 70％ 39 9.75

[0048] Table 2

[0049] Print position Type of paste Silver mass content % Copper mass content % Wet weight mg Silver consumption mg Main grid connection line and main grid pad A 83％ / 7 5.81 Sub grid B 91％ / 35 31.85

[0050] Table 3

[0051]

[0052] From Table 3, it can be seen that the electrical performance of the solar cell prepared by the process method of the present disclosure is little different from that prepared by the existing process method, and is basically equivalent. By the preparation method of the present disclosure, a cell piece is printed, except that silver-coated copper paste C is added, other paste types are consistent, the total wet weight is increased by 10 mg, but the silver consumption is reduced by 16.32 mg, the silver consumption is reduced by 43.3%, the copper consumption is increased by 27.3 mg, the copper unit price is 0.077 yuan / g, the silver unit price is 8.1 yuan / g, the single cell piece saves cost 0.13 yuan, according to 8W of single cell piece, 1GW saves cost 1625 million.

[0053] Example embodiments have been disclosed herein and, although the use of specific terms is expressly used herein, they are intended in the sense only of general descriptive purpose and should not be construed as limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics or / and elements described in connection with a particular embodiment can be used in conjunction with other embodiments unless otherwise explicitly noted. As such, those skilled in the art will appreciate that various changes can be made in form and detail without departing from the scope of the disclosure as set forth in the appended claims.

Claims

1. A method for producing a solar cell, characterized by, Comprising: forming sub-grid contact stubs on a silicon wafer using a first paste; forming main-grid connection lines and sub-grids on the silicon wafer using a second paste, wherein the sub-grids are perpendicular to and electrically connected with corresponding sub-grid contact stubs, the main-grid connection lines and the sub-grids are perpendicular and electrically connected, the mass content of silver in the first paste is greater than the mass content of silver in the second paste; performing low-temperature curing at a first temperature less than or equal to 250℃.

2. The method of producing a solar cell according to claim 1, wherein The sub-grid contact stubs are arranged as a matrix of line segments spaced apart from each other.

3. The method of claim 1, wherein the method further comprises: The mass content of silver in the first paste is 91% to 94%.

4. The method of producing a solar cell according to claim 1, wherein The second paste comprises silver-coated copper, and the mass content of silver in the second paste is 20% to 25%.

5. The method of producing a solar cell according to claim 1, wherein The first temperature is 200℃ to 250℃.

6. The method of producing a solar cell according to claim 1, wherein Further comprising: forming main-grid pads on the silicon wafer using a third paste before forming the main-grid connection lines and the sub-grids, wherein the main-grid connection lines and the sub-grids are electrically connected to the main-grid pads, and the mass content of silver in the third paste is 85% to 90%.

7. The method of producing a solar cell according to claim 6, wherein Further comprising: performing drying at a second temperature of 200℃ to 300℃ after forming the main-grid pads.

8. The method of producing a solar cell according to claim 1, wherein Further comprising: performing pre-sintering and photo-injection after forming the sub-grid contact stubs, the peak temperature of the pre-sintering is 730℃ to 770℃, the light intensity of the photo-injection is 8suns to 40suns, and the third temperature is 500℃ to 550℃.

9. The method of producing a solar cell according to claim 1, wherein Further comprising: performing laser-assisted sintering after the low-temperature curing, the scanning direction of the laser-assisted sintering is along the extension direction of the sub-grid contact stubs, the laser scanning speed is 40m / s-60m / s, the laser spot size is 80μm-100μm, the laser power is set to 25%-33%, the laser rated power is 60W, and the bias voltage is 13V-18V.

10. The method of producing a solar cell according to claim 1, wherein The solar cell is a TOPCon solar cell, and the sub-grid contact stubs form a direct ohmic contact with a silicon base of the silicon wafer.

11. A solar cell, characterized by, The solar cell is obtained by the preparation method according to any one of claims 1 to 10.

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