Solar cell and preparation method thereof

Abstract

The embodiment of the invention relates to the field of photovoltaic technology, and provides a solar cell and a preparation method thereof, the solar cell comprises a substrate, the substrate is provided with a first surface and a second surface which are opposite, at least one of the first surface and the second surface is provided with a suede, the suede is composed of a plurality of pyramid structures, and the side wall of at least part of the pyramid structures is provided with a wrinkle part; the wrinkle part is composed of a plurality of scaly protrusions, in the direction from the top of the pyramid structure to the bottom of the pyramid structure, the length of the wrinkle part is a first length, the length of the side wall of the pyramid structure is a second length, and the ratio of the first length to the second length is larger than or equal to 0.5. According to the solar cell and the preparation method thereof provided by the embodiment of the invention, the light reflectivity of the solar cell is at least reduced, so that the light conversion efficiency of the solar cell is improved.

Description

Technical Field

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

[0002] At present, with the gradual depletion of fossil energy, solar cells are increasingly used as a new energy alternative. Solar cells are devices that convert sunlight into electrical energy. The working principle of solar cells is based on the photovoltaic effect of the semiconductor PN junction. When light shines on the PN junction, electron-hole pairs are generated. The carriers generated near the PN junction inside the semiconductor are not recombined and reach the space charge region. Attracted by the internal electric field, electrons flow into the N region and holes flow into the P region. As a result, the N region stores excess electrons and the P region has excess holes. They form a photoelectric field in the opposite direction of the potential barrier near the PN junction.

[0003] In the production of solar cells, chemical etching of the substrate is an important process, which aims to reduce the surface reflectivity of the substrate, increase the absorption of light, and increase the density of photogenerated carriers, thereby improving the photoelectric conversion rate of solar cells. The principle of chemical etching of the substrate is to use the anisotropy or isotropy of silicon crystals to make the substrates with different crystal planes or directions corrode at different speeds in the chemical solution, thereby forming a velvet structure composed of pyramid structures of different shapes and sizes on the surface of the substrate.

[0004] However, the textured structure still makes a considerable portion of light unusable, resulting in a still high light reflectivity of the solar cell with the textured structure, thereby making the light conversion efficiency of the solar cell relatively poor. Summary of the invention

[0005] The embodiments of the present application provide a solar cell and a method for preparing the same, which are at least beneficial for reducing the light reflectivity of the solar cell and thereby improving the light conversion efficiency of the solar cell.

[0006] According to some embodiments of the present application, on the one hand, the embodiments of the present application provide a solar cell, including: a substrate, the substrate having a first surface and a second surface relative to each other, at least one of the first surface or the second surface having a velvet surface, the velvet surface being composed of a plurality of pyramid structures, at least part of the side walls of the pyramid structures having a wrinkle portion, the wrinkle portion being composed of a plurality of scaly protrusions, the length of the wrinkle portion in the direction from the top of the pyramid structure to the bottom of the pyramid structure is a first length, the length of the side wall of the pyramid structure is a second length, and the ratio of the first length to the second length is greater than or equal to 0.5.

[0007] In some embodiments, a ratio of the first length to the second length is less than or equal to 0.8.

[0008] In some embodiments, the angle between two inclined surfaces disposed opposite to each other in the pyramid structure is 65° to 70°.

[0009] In some embodiments, a plurality of scale-like protrusions are interconnected to form continuous irregular wavy protrusions, and the plane where the first surface or the second surface is located is used as a reference plane. In a direction perpendicular to the reference plane, the orthographic projection of the irregular wavy protrusions is stamen-shaped.

[0010] In some embodiments, the sidewall of the pyramid structure has a pit, and the wrinkled portion is also located on the inner wall of the pit.

[0011] In some embodiments, it also includes: a passivation layer, the passivation layer is located on the velvet surface and covers the surface of the pyramid structure, the surface of the passivation layer in some areas away from the pyramid structure is conformal to the surface of the wrinkle part, and the surface of the passivation layer in some areas away from the pyramid structure is smoother than the surface of the wrinkle part.

[0012] According to some embodiments of the present application, on the other hand, the embodiments of the present application further provide a method for preparing a solar cell, which is used to prepare a solar cell as in the above-mentioned embodiments, including: providing a substrate, the substrate having a first surface and a second surface relative to each other; performing a first texturing process on at least one of the first surface or the second surface of the substrate to form an initial texturing surface on the first surface or the second surface of the substrate, the initial texturing surface being composed of a plurality of initial pyramid structures; performing a second texturing process on the initial texturing surface to form a texturing surface, the texturing surface being composed of a plurality of pyramid structures, at least part of the pyramid structures having a wrinkle on the side wall, the wrinkle being composed of a plurality of scaly protrusions, the length of the wrinkle in the direction from the top of the pyramid structure to the bottom of the pyramid structure being a first length, the length of the side wall of the pyramid structure being a second length, and the ratio of the first length to the second length being greater than or equal to 0.5; wherein, the alkali concentration in the second texturing agent used in the second texturing process is less than the alkali concentration in the first texturing agent used in the first texturing process; the temperature in the second texturing process is lower than the temperature in the first texturing process.

[0013] In some embodiments, the alkali concentration in the first texturing agent is 1.8% to 2.2%; the alkali concentration in the second texturing agent is 0.2% to 0.6%; the temperature of the first texturing process is 80°C to 90°C; the temperature of the second texturing process is 70°C to 80°C.

[0014] In some embodiments, the method further includes placing the substrate in a graphite boat and using plasma chemical vapor deposition to form a passivation layer on the surface of the substrate, wherein the number of contact points between the graphite boat and the substrate is greater than or equal to 5.

[0015] In some embodiments, on the initial suede surface, the surface area of ​​any initial pyramid structure is a first area; on the suede surface, the surface area of ​​any pyramid structure is a second area, and the ratio of the second area to the first area is 1.3 to 1.7.

[0016] The technical solution provided by the embodiments of the present application has at least the following advantages:

[0017] The solar cell and the preparation method thereof provided by the present application are characterized in that the first surface and / or the second surface of the substrate of the solar cell has a velvet surface, the velvet surface is composed of a plurality of pyramid structures, the side of the pyramid structure has a folded portion, the folded portion is composed of a plurality of flaky protrusions, such that the folded portion can increase the roughness of the side wall of the pyramid structure, increase the possibility of multiple reflections of sunlight between the pyramid structures, so that the sunlight is trapped in the surface of the substrate, which not only prolongs the optical path of the incident light in the substrate and increases the spectral effect of the solar cell, but also facilitates more photons to generate electron-hole pairs near the PN junction region on the surface of the substrate, and these electron-hole pairs are more easily separated and collected, thereby increasing the probability of collecting photogenerated carriers and improving the light conversion efficiency of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplified descriptions do not constitute a limitation on the embodiments. Unless otherwise specified, the pictures in the drawings do not constitute a scale limitation. In order to more clearly illustrate the embodiments of the present application or the technical solutions in the traditional technology, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A cross-sectional SEM schematic diagram of a substrate of a solar cell in the related art;

[0020] Figure 2 A scanning electron microscope top view of a substrate of a solar cell in the related art;

[0021] Figure 3 A schematic cross-sectional scanning electron microscope diagram of a substrate of a solar cell provided in an embodiment of the present application;

[0022] Figure 4 A scanning electron microscope top view of a substrate of a solar cell provided in an embodiment of the present application;

[0023] Figure 5 A schematic diagram of a partially enlarged structure of a pyramid structure provided in an embodiment of the present application;

[0024] Figure 6 and Figure 7 Schematic diagram of the structure of two pyramid structures with passivation layers on the surface provided in the embodiments of the present application;

[0025] Figure 8 The reflectivity at different wavelengths corresponding to the various solar cells provided in the embodiments of the present application. DETAILED DESCRIPTION

[0026] As known from the background art, the suede structure still leads to a higher reflectivity of the solar cell, which in turn leads to a lower light conversion efficiency of the solar cell.

[0027] Figure 1 A cross-sectional SEM schematic diagram of a substrate of a solar cell in the related art; Figure 2 This is a scanning electron microscope top view of a substrate of a solar cell in the related art.

[0028] Texturing is the first step in the preparation of solar cells. Conventional mass production processes usually use chemical etching to form a velvet structure on the surface of the substrate to enhance the light trapping effect of the solar cell surface. Since the alkali texturing agent has different etching rates on different crystal faces of the substrate, it will eventually leave four tetrahedral structures composed of (111) crystal faces, also known as pyramid structures (such as Figure 1 and Figure 2 As shown). At present, the alkali texturing process can control the nucleation process of the pyramid structure, effectively reduce the surface tension of the solid-liquid interface, and suppress the further growth of bubbles in the reaction process, so as to achieve the purpose of controlling the reaction rate, and at the same time enable the hydrogen produced by the reaction to quickly leave the surface of the substrate, thereby ensuring the uniformity of the velvet surface. Usually, the aspect ratio between the height of the pyramid structure and the length of the bottom side of the pyramid structure is 0.5:1, or the angle between the inclined surface of the pyramid structure and the bottom of the pyramid structure is 52°~53°. The wide base of the pyramid structure causes a large amount of light to be reflected by the side of the pyramid structure to the outside of the substrate, so that the velvet structure of the substrate still makes a considerable part of the light unusable, resulting in the reflectivity of the solar cell with the substrate having the velvet structure still being high, thereby making the light conversion efficiency of the solar cell poor.

[0029] The reflectivity of the velvet structure composed of the traditional pyramid structure is relatively high (10% to 10.5%), which makes it difficult to efficiently trap light, becoming a shortcoming that limits the improvement of the light conversion efficiency of solar cells. In order to increase the light absorption efficiency of solar cells, nano-velvet structures are currently used, such as black silicon technology (inverted pyramid), which can reduce the reflectivity to 1.5% or even lower, but the velvet surface is messy, the passivation is extremely poor, the efficiency is seriously low, and the process is relatively complicated. In addition, the nano-velvet structure contains metal components, which is costly, easily causes contamination of the tank and the back-end, and is not fully compatible with mass production equipment.

[0030] The present application provides a solar cell and a preparation method thereof, wherein the first surface and / or the second surface of a substrate in the solar cell has a velvet surface, the velvet surface is composed of a plurality of pyramid structures, and the side of the pyramid structure has a folded portion, the folded portion is composed of a plurality of scaly protrusions, such that the folded portion can increase the roughness of the side wall of the pyramid structure, increase the possibility of multiple reflections of sunlight between the pyramid structures, so that the sunlight is trapped in the surface of the substrate, which not only prolongs the optical path of the incident light in the substrate and increases the spectral effect of the solar cell, but also facilitates more photons to generate electron-hole pairs near the PN junction region on the surface of the substrate, and these electron-hole pairs are more easily separated and collected, thereby increasing the probability of collecting photogenerated carriers and improving the light conversion efficiency of the solar cell.

[0031] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0032] In the description of the embodiments of the present application, “plurality” means more than two, unless otherwise clearly and specifically defined.

[0033] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0034] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0035] In the description of the embodiments of the present application, technical terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0036] In the accompanying drawings corresponding to the embodiments of the present application, the thickness and area of ​​the layer are magnified for better understanding and ease of description. When describing a component on another component or on the surface of another component, the component may be "directly" located on the surface of the other component, or a third component may be present between the two components. On the contrary, when describing a component on the surface of another component or when another component is formed or provided on the surface of a component, it means that there is no third component between the two components. In addition, when describing a component as "substantially" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a partial edge of the entire surface.

[0037] In the description of the embodiments of the present application, when a certain component “includes” another component, unless otherwise stated, other components are not excluded and other components may be further included.

[0038] The terms used in the description of the various described embodiments herein are used only to describe specific embodiments and are not intended to be limiting. As used in the description of the various described embodiments and the appended claims, "components" are also intended to include plural forms unless the context clearly indicates otherwise.

[0039] The following will describe the various embodiments of the present application in detail with reference to the accompanying drawings. However, it will be appreciated by those skilled in the art that in the various embodiments of the present application, many technical details are provided in order to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solution claimed in the present application can be implemented.

[0040] Figure 3 A schematic cross-sectional scanning electron microscope diagram of a substrate of a solar cell provided in an embodiment of the present application; Figure 4 A scanning electron microscope top view of a substrate of a solar cell provided in an embodiment of the present application; Figure 5 A partially enlarged structural schematic diagram of a pyramid structure provided in an embodiment of the present application.

[0041] The solar cell provided in the embodiment of the present application includes: a substrate, the substrate having a first surface and a second surface opposite to each other, and at least one of the first surface or the second surface has a velvet surface. Figure 3 and Figure 4 The velvet surface is composed of a plurality of pyramid structures, and at least part of the side walls of the pyramid structures have wrinkles, and the wrinkles are composed of a plurality of scale-like protrusions. Figure 5In the direction from the top of the pyramid structure 10 to the bottom of the pyramid structure 10, the length of the folded portion 11 is a first length L1, the length of the side wall of the pyramid structure 10 is a second length L2, and the ratio of the first length L1 to the second length L2 is greater than or equal to 0.5, and specifically can be 0.5, 0.56, 0.6, 0.64, 0.7, 0.75, 0.8, 0.96 or 1.

[0042] In the solar cell provided in the embodiment of the present application, the first surface and / or the second surface of the substrate has a velvet surface, the velvet surface is composed of a plurality of pyramid structures, the side of the pyramid structure has a wrinkle portion, the wrinkle portion is composed of a plurality of scaly protrusions, such that the wrinkle portion can increase the roughness of the side wall of the pyramid structure, increase the possibility of multiple reflections of sunlight between the pyramid structures, so that the sunlight is trapped in the surface of the substrate, which not only prolongs the optical path of the incident light in the substrate and increases the spectral effect of the solar cell, but also facilitates more photons to generate electron-hole pairs near the PN junction area on the surface of the substrate, and these electron-hole pairs are more easily separated and collected, thereby increasing the probability of collecting photogenerated carriers and improving the light conversion efficiency of the solar cell.

[0043] It should be noted that the reference Figure 3 Since the degree of wrinkles is different at different positions from the top to the bottom of the pyramid structure, from the appearance, the scale-like protrusions corresponding to the wrinkle part located at the top of the pyramid structure are less obvious than the scale-like protrusions corresponding to the wrinkle part located in the middle of the pyramid structure.

[0044] In some embodiments, the solar cell can be any one of a PERC cell (Passivated Emitter and Rear Cell), a PERT cell (Passivated Emitter and Rear Totally-diffused cell), a TOPCon cell (Tunnel Oxide Passivated Contact), a HIT / HJT cell (Heterojunction Technology), or a BC cell (Back Contact).

[0045] In some embodiments, the solar cell can be a monocrystalline silicon solar cell, a polycrystalline silicon solar cell, an amorphous silicon solar cell or a multi-compound solar cell. The multi-compound solar cell can specifically be a cadmium sulfide solar cell, a gallium arsenide solar cell, a copper indium selenide solar cell or a perovskite solar cell.

[0046] Figure 6 and Figure 7 Schematic diagram of the structure of two pyramid structures with surface covered passivation layers provided in the embodiments of the present application.

[0047] refer to Figure 6 and Figure 7 In some embodiments, the solar cell further comprises a passivation layer 12, the passivation layer 12 is located on the velvet surface and covers the surface of the pyramid structure 10, Figure 6 , the surface of the passivation layer 12 in a part of the area away from the pyramid structure 10 is conformal to the surface of the wrinkle portion 11; or, Figure 7 , the surface of the passivation layer 12 in some areas away from the pyramid structure 10 is smoother than the surface of the wrinkle part 11. On the velvet surface of the base, the roughness of the wrinkle part 11 on the side wall of the pyramid structure 10 in different areas is different. When the undulation of the wrinkle part 11 relative to the side wall of the pyramid structure 10 is large or obvious, and the thickness of the passivation layer 11 covering all parts of the surface of the pyramid structure 10 is relatively uniform, the surface of the passivation layer 12 away from the pyramid structure 10 is conformal to the surface of the wrinkle part 11 (such as Figure 6 ); when the undulation of the wrinkle portion 11 relative to the side wall of the pyramid structure 10 is small or not obvious, and the thickness of the passivation layer 11 covering the surface of the pyramid structure 10 is relatively uniform, the coverage of the passivation layer 12 will weaken the undulation relative to the side wall of the pyramid structure 10, and thus the surface of the passivation layer 12 away from the pyramid structure 10 is smoother than the surface of the wrinkle portion 11 (as shown in FIG. Figure 7 shown).

[0048] In some embodiments, the passivation layer includes a first passivation layer and a second passivation layer, wherein the first passivation layer is located on a side of the substrate close to the first surface, and the second passivation layer is located on a side of the substrate close to the second surface. The first passivation layer and the second passivation layer can prevent oxidation or corrosion of the substrate surface to improve the stability and life of the battery cell.

[0049] The material of the first passivation layer may include at least one of aluminum oxide, silicon oxide, silicon nitride or silicon oxynitride. The first passivation layer may be a single-layer structure or a stacked-layer structure. For example, the single-layer structure may be a single-layer aluminum oxide film layer, a single-layer silicon oxide film layer, a single-layer silicon nitride film layer or a single-layer silicon oxynitride film layer; the stacked-layer structure may be composed of at least two film layers stacked among an aluminum oxide film layer, a silicon oxide film layer, a silicon nitride film layer or a silicon oxynitride film layer.

[0050] The material of the second passivation layer may include at least one of aluminum oxide, silicon oxide, silicon nitride or silicon oxynitride. The second passivation layer may be a single-layer structure or a stacked-layer structure. For example, the single-layer structure may be a single-layer aluminum oxide film layer, a single-layer silicon oxide film layer, a single-layer silicon nitride film layer or a single-layer silicon oxynitride film layer; the stacked-layer structure may be composed of at least two film layers of an aluminum oxide film layer, a silicon oxide film layer, a silicon nitride film layer or a silicon oxynitride film layer stacked together.

[0051] In some embodiments, the substrate may have an emitter, and the emitter may be located on a side of the substrate close to the first passivation layer and in contact with the first passivation layer, or the emitter may be located on a side of the substrate close to the second passivation layer and in contact with the second passivation layer. The doping element type of the emitter is opposite to the doping element type of the substrate. For example, if the doping element of the substrate is a P-type doping element, the doping element of the emitter is an N-type doping element; if the doping element of the substrate is an N-type doping element, the doping element of the emitter is a P-type doping element, thus forming a PN junction with the substrate. The PN junction can receive incident light irradiated to the surface of the substrate and generate electron-hole pairs. For example, when the substrate is an N-type substrate, the separated electrons move into the substrate, and the separated holes move into the emitter, thus forming a current.

[0052] The substrate may be an N-type semiconductor substrate or a P-type semiconductor substrate. The N-type semiconductor substrate is doped with an N-type doping element, which may be any one of the V-group elements such as phosphorus (P), bismuth (Bi), antimony (Sb), or arsenic (As). The P-type semiconductor substrate is doped with a P-type element, which may be any one of the III-group elements such as boron (B), aluminum (Al), gallium (Ga), or indium (In).

[0053] The material of the substrate may be at least one of single crystal silicon, polycrystalline silicon, amorphous silicon or microcrystalline silicon.

[0054] If the solar cell is a single-sided cell, the velvet surface can be formed only on one side of the substrate, and the other side of the substrate can be a polished surface, that is, the polished surface of the substrate is flatter than the velvet surface. It should be noted that for a single-sided cell, the velvet surface can also be formed on both sides of the substrate. If the solar cell is a double-sided cell, the velvet surface can be formed on both sides of the substrate.

[0055] In some embodiments, the solar cell may further include a tunneling layer and a doped conductive layer, wherein the tunneling layer is located on the side surface of the substrate away from the emitter, and the doped conductive layer is located on the surface of the tunneling layer away from the substrate. The tunneling layer and the doped conductive layer are used to form a passivation contact structure, and the tunneling layer can play a chemical passivation effect. Due to the presence of interface state defects on the substrate surface, the tunneling layer can saturate the dangling bonds on the substrate surface, reduce the defect state density on the substrate surface, and reduce the recombination center on the substrate surface to reduce the carrier recombination rate, so that the interface state density on the substrate surface is relatively large. The increase in the interface state density will promote the recombination of photogenerated carriers, increase the filling factor, short-circuit current and open-circuit voltage of the solar cell, so as to improve the photoelectric conversion efficiency of the solar cell; the doped conductive layer can have a field passivation effect, and the doped conductive layer can form an electrostatic field, so that the minority carriers escape from the interface, reduce the concentration of the minority carriers, so that the carrier recombination rate at the substrate interface is relatively low, and the open-circuit voltage, short-circuit current and filling factor of the solar cell are increased, so as to improve the photoelectric conversion efficiency of the solar cell.

[0056] The material of the tunneling layer may include at least one of silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, or magnesium fluoride.

[0057] The material of the doped conductive layer may include at least one of amorphous silicon, polycrystalline silicon or silicon carbide. The doped conductive layer has the same doping element as the substrate. If the doping element type of the substrate is P-type, the doping element type in the doped conductive layer is also P-type; if the doping element type of the substrate is N-type, the doping element type in the doped conductive layer is also N-type.

[0058] refer to Figure 5 In some embodiments, a ratio of the first length L1 to the second length L2 is less than or equal to 0.8.

[0059] Table 1 shows the reflectivity of various solar cells provided in the embodiments of the present application.

[0060] Table 1 Reflectivity of different solar cells

[0061]

[0062] As shown in Table 1, the substrate surfaces of the solar cells corresponding to Comparative Examples 1 and 2 have conventional velvet surfaces, and the side walls of the pyramid structures on the velvet surfaces are smooth surfaces without wrinkles. The substrate surfaces of the solar cells corresponding to Examples 1 to 4 have wrinkles, wherein the ratio of the first length L1 of the wrinkles to the tower length L2 of the pyramid structure increases successively.

[0063] Referring to Table 1, by comparing Comparative Example 2 and Examples 1 to 4, it can be found that, compared with conventional velvet, when the substrate surface of the solar cell has a wrinkle portion, the reflectivity of the solar cell is reduced. By comparing Examples 1 to 4, it can be found that when the ratio of the first length L1 to the second length L2 is small, the reflectivity reduction effect on the solar cell is slight; as the ratio of the first length L1 to the second length L2 increases, the area of ​​the side wall of the pyramid structure occupied by the wrinkle portion increases, so that the reflectivity reduction effect of the solar cell increases; when the ratio of the first length L1 to the second length L2 continues to increase to the entire side wall of the pyramid structure, the reflectivity reduction gain of the solar cell is not obvious. Therefore, when the ratio of the first length L1 to the second length L2 exceeds 0.5 and does not exceed 0.8, it is beneficial to keep the reflectivity of the solar cell at a low level. In addition, when the ratio of the first length L1 to the second length L2 is too large, the corresponding process time for forming the wrinkle portion increases, which easily leads to the deterioration of the uniformity of the wrinkle portion, and when the reflectivity reduction gain of the solar cell is not obvious, it will also lead to a decrease in the preparation efficiency of the solar cell. Therefore, a ratio of the first length L1 to the second length L2 within an appropriate range can be beneficial to maintaining a high uniformity and a low reflectivity of the velvet surface, and can also be beneficial to improving the preparation efficiency of solar cells.

[0064] Continuing to refer to Table 1, by comparing Comparative Example 1 and Comparative Example 2, it is found that for conventional velvet, compared with the reflectivity of the solar cell when the top angle of the pyramid structure (i.e., the angle between the two inclined planes arranged opposite to each other in the pyramid structure) is in the range of 70° to 75°, the reflectivity of the solar cell when the top angle of the pyramid structure is in the range of 65° to 70° is lower. This is because the sharper the top angle of the pyramid structure, the more conducive it is for sunlight to be reflected between adjacent pyramid structures, which makes it easier for sunlight to sink into the substrate surface, achieving a better light trapping effect, and thus improving the light conversion efficiency of the solar cell.

[0065] Figure 8 The reflectivity at different wavelengths corresponding to the various solar cells provided in the embodiments of the present application. Figure 8 a in is the curve corresponding to Comparative Example 1 in Table 1; Figure 8 b in Table 1 is the curve corresponding to Example 3.

[0066] Combined with reference table 1 and Figure 8Compared with conventional velvet surfaces, in the solar cell provided in this embodiment, when the side wall of the pyramid structure has a wrinkled portion, the angle between the two relatively arranged inclined surfaces in the pyramid structure, that is, the tower top angle is maintained at 65° to 70°, which can further enhance the light trapping effect of the substrate surface. In different wavelength ranges, the reflectivity of the solar cell is reduced, thereby further improving the light conversion efficiency of the solar cell.

[0067] refer to Figure 4 In some embodiments, a plurality of scale-like protrusions are interconnected to form continuous irregular wavy protrusions, and the plane where the first surface or the second surface is located is used as a reference plane. In the direction perpendicular to the reference plane, the orthographic projection of the irregular wavy protrusions is stamen-shaped. The irregular stamen-shaped structure is conducive to irregular reflection of incident light between adjacent pyramid structures, thereby extending the optical path of the incident light in the substrate, increasing the spectral effect of the solar cell, and facilitating more photons to generate electron-hole pairs near the PN junction region on the surface of the substrate, increasing the probability of collecting photogenerated carriers, and improving the light conversion efficiency of the solar cell.

[0068] refer to Figure 3 In some embodiments, the sidewalls of the pyramid structure have pits due to etching (eg Figure 3 The folded portion may also be located on the inner wall of the pit. The pit can increase the surface area of ​​the side wall of the pyramid structure, and the folded portion exists in the pit at the same time, which can also increase the roughness of the inner wall of the pit, thereby facilitating the light trapping effect of the velvet surface and improving the light conversion efficiency of the solar cell.

[0069] In the solar cell provided in the embodiment of the present application, the first surface and / or the second surface of the substrate has a velvet surface, the velvet surface is composed of a plurality of pyramid structures, the side of the pyramid structure has a wrinkle portion, the wrinkle portion is composed of a plurality of scaly protrusions, such that the wrinkle portion can increase the roughness of the side wall of the pyramid structure, increase the possibility of multiple reflections of sunlight between the pyramid structures, so that the sunlight is trapped in the surface of the substrate, which not only prolongs the optical path of the incident light in the substrate and increases the spectral effect of the solar cell, but also facilitates more photons to generate electron-hole pairs near the PN junction area on the surface of the substrate, and these electron-hole pairs are more easily separated and collected, thereby increasing the probability of collecting photogenerated carriers and improving the light conversion efficiency of the solar cell.

[0070] Correspondingly, another embodiment of the present application also provides a method for preparing a solar cell, which can be used to manufacture the solar cell provided in the above embodiment. For the parts that are the same or corresponding to the previous embodiment, reference can be made to the corresponding description of the previous embodiment, and will not be described in detail below.

[0071] The method for preparing a solar cell provided in an embodiment of the present application comprises:

[0072] Step S1: providing a substrate, wherein the substrate has a first surface and a second surface opposite to each other;

[0073] Step S2: performing a first texturing process on at least one of the first surface or the second surface of the substrate to form an initial texturing surface on the first surface or the second surface of the substrate, wherein the initial texturing surface is composed of a plurality of initial pyramid structures.

[0074] Step S3: Perform a second texturing process on the initial velvet surface to form a velvet surface, wherein the velvet surface is composed of a plurality of pyramid structures, and at least part of the pyramid structures have side walls with wrinkles, and the wrinkles are composed of a plurality of scale-like protrusions, and in the direction from the top of the pyramid structure to the bottom of the pyramid structure, the length of the wrinkles is a first length, and the length of the side walls of the pyramid structure is a second length, and the ratio of the first length to the second length is greater than or equal to 0.5; wherein the alkali concentration in the second texturing agent used in the second texturing process is less than the alkali concentration of the first texturing agent used in the first texturing process; and the temperature in the second texturing process is lower than the temperature in the first texturing process.

[0075] In the preparation method of the solar cell provided in the embodiment of the present application, a first texturing process is firstly used to form an initial velvet surface on the first surface and / or the second surface of the substrate, the initial velvet surface is composed of a plurality of initial pyramid structures, and the initial velvet surface can increase the surface roughness of the substrate and reduce the degree of reflection of the incident light on the substrate surface; further, a second texturing process is also used to form a folded portion on the side wall of the initial pyramid structure, the folded portion is composed of a plurality of scaly protruding structures, and in the direction from the top to the bottom of the pyramid structure, the length of the folded portion is at least greater than or equal to 0.5 of the length of the pyramid structure body, the folded portion can increase the roughness of the side wall of the pyramid structure, increase the possibility of multiple reflections of sunlight between the pyramid structures, so that the sunlight is trapped in the substrate surface, which not only prolongs the optical path of the incident light in the substrate and increases the spectral effect of the solar cell, but also facilitates more photons to generate electron-hole pairs near the PN junction region on the substrate surface, these electron-hole pairs are more easily separated and collected, and the collection probability of photogenerated carriers is increased, thereby improving the light conversion efficiency of the solar cell. In the first texturing process, the size of the initial pyramid structure to be formed is relatively large; in the second texturing process, the wrinkles to be formed are located on the side wall of the initial pyramid structure, with a relatively fine morphology and a relatively small size. Therefore, the temperature and alkali concentration required in the first texturing process are uniformly higher than those in the second texturing process. The alkali concentration refers to the mass ratio of the alkali to the total mass of the texturing agent.

[0076] Specifically, the alkali concentration in the first texturing agent is 1.8% to 2.2%, for example, it can be 1.8%, 1.9%, 2%, 2.1% or 2.2%; the alkali concentration in the second texturing agent is 0.2% to 0.6%, for example, it can be 0.2%, 0.3%, 0.4%, 0.5% or 0.6%; the temperature of the first texturing process is 80℃ to 90℃, for example, it can be 80℃, 82℃, 83℃, 85℃, 86℃, 88℃ or 90℃; the temperature of the second texturing process is 70℃ to 80℃, for example, it can be 70℃, 72℃, 73℃, 75℃, 77℃, 79℃ or 80℃.

[0077] The time of the first texturing process can be 100s to 900s, for example, 100s, 150s, 200s, 230s, 300s, 340s, 400s, 460s, 500s, 520s, 600s, 670s, 700s, 740s, 800s, 850s or 900s.

[0078] The time of the second texturing process can be 100s to 900s, for example, 100s, 150s, 200s, 230s, 300s, 340s, 400s, 460s, 500s, 520s, 600s, 670s, 700s, 740s, 800s, 850s or 900s.

[0079] In some embodiments, before the first texturing process is performed, the mass of the substrate is the first mass; after the first texturing process, the mass of the substrate is the second mass, and the difference between the first mass and the second mass is 0.3g to 0.4g, for example, it can be 0.3g, 0.33g, 0.36g, 0.39g or 0.4g; after the second texturing process is performed, the mass of the substrate is the third mass, and the difference between the second mass and the third mass is 0.03 to 0.04g, for example, it can be 0.03g, 0.033g, 0.035g, 0.038g or 0.04g. By obtaining the difference between the first mass and the second mass, it can be used as a monitoring means for the first texturing process, and then it can assist in judging the degree of the initial velvet surface formed on the surface of the substrate by the first texturing process, avoiding the problem of excessive etching or low etching degree; similarly, by obtaining the difference between the second mass and the third mass, it can be used as a monitoring means for the second texturing process, and then it can assist in judging the degree of the wrinkled portion formed by the second texturing process, avoiding the problem of excessive etching or low etching degree.

[0080] The alkali in the first texturing process can be selected from at least one of sodium hydroxide and potassium hydroxide.

[0081] The alkali in the second texturing process can be selected from at least one of sodium hydroxide and potassium hydroxide.

[0082] In some embodiments, a selective etchant may be added to the second texturing process. The selective etchant may be selected from at least one of polyether compounds or sodium lignin sulfonate. The selective etchant may be beneficial for selectively etching the side walls of the initial pyramid structure in the second texturing process, thereby promoting the formation of the wrinkled portion.

[0083] The concentration of the selective etchant (the ratio of the mass of the selective etchant to the total mass of the etchant) may be 0.1% to 0.2%, for example, 0.1%, 0.13%, 0.15%, 0.18% or 0.25%.

[0084] In some embodiments, before the first texturing process is performed, it also includes: a first cleaning process, the first cleaning process is used to remove impurities on the surface of the substrate. The alkali concentration of the first cleaning process is 0.4% to 0.6%, for example, it can be 0.4%, 0.45%, 0.5%, 0.55% or 0.6%; the concentration of hydrogen peroxide is 3% to 5%, for example, it can be 3%, 3.3%, 4%, 4.4% or 5%. The temperature used in the first cleaning process can be 25℃ to 50℃, for example, it can be 25℃, 30℃, 35℃, 40℃, 45℃ or 50℃; the time of the first cleaning process can be 30s to 200s, for example, it can be 30s, 50s, 80s, 100s, 140s, 180s or 200s.

[0085] The alkali in the first cleaning process may be selected from at least one of sodium hydroxide and potassium hydroxide.

[0086] In some embodiments, after the second texturing process, the method further includes: a second cleaning process, wherein the second cleaning process includes water washing or acid washing.

[0087] In some embodiments, after the velvet is formed on the substrate, the method further includes: placing the substrate in a graphite boat and using plasma chemical vapor deposition to form a passivation layer on the surface of the substrate, wherein the number of contact points between the graphite boat and the substrate is greater than or equal to 5. Due to the large velvet roughness of the surface of the substrate, the number of dangling bonds on the surface of the substrate is increased, resulting in an increase in the recombination rate of carriers at the surface of the substrate. In addition, with the increase in the area of ​​solar cells and the increase in demand for production in the industry, the volume of the graphite boat used for plasma chemical vapor deposition has gradually increased. When the plasma chemical vapor deposition forms a passivation layer, the discharge power is limited, and the uniformity of the entire boat and the thickness of the passivation layer on the monolithic substrate are difficult to achieve two-way optimization. Usually, the substrate and the graphite boat are contacted in a card point manner. For the velvet in the above embodiment that requires a denser and more uniform passivation film to match, by increasing the number of card points of the graphite boat for plasma chemical vapor deposition, the contact area between the graphite boat and the substrate can be increased, thereby increasing the actual discharge power of the plasma exciter, and the discharge is more uniform, which is conducive to increasing the deposition rate and the density of the passivation layer, improving the hydrogen passivation effect, and thus increasing the battery efficiency by more than 0.15%.

[0088] In some embodiments, on the initial velvet surface, the surface area of ​​any initial pyramid structure is the first area; on the velvet surface, the surface area of ​​any pyramid structure is the second area, and the ratio of the second area to the first area is 1.3 to 1.7, for example, 1.3, 1.4, 1.5, 1.6 or 1.7. By forming a wrinkled portion on the side wall of the initial pyramid structure, the specific surface area of ​​a single pyramid structure is further increased, thereby improving the light trapping effect of the substrate and improving the light conversion efficiency of the solar cell.

[0089] In the preparation method of the solar cell provided in the embodiment of the present application, a first texturing process is firstly used to form an initial velvet surface on the first surface and / or the second surface of the substrate, the initial velvet surface is composed of a plurality of initial pyramid structures, and the initial velvet surface can increase the surface roughness of the substrate and reduce the degree of reflection of the incident light on the substrate surface; further, a second texturing process is also used to form a folded portion on the side wall of the initial pyramid structure, the folded portion is composed of a plurality of scaly protruding structures, and in the direction from the top to the bottom of the pyramid structure, the length of the folded portion is at least greater than or equal to 0.5 of the length of the pyramid structure body, the folded portion can increase the roughness of the side wall of the pyramid structure, increase the possibility of multiple reflections of sunlight between the pyramid structures, so that the sunlight is trapped in the substrate surface, which not only prolongs the optical path of the incident light in the substrate and increases the spectral effect of the solar cell, but also facilitates more photons to generate electron-hole pairs near the PN junction region on the substrate surface, these electron-hole pairs are more easily separated and collected, and the collection probability of photogenerated carriers is increased, thereby improving the light conversion efficiency of the solar cell.

[0090] Those skilled in the art will appreciate that the above-mentioned embodiments are specific examples for implementing the present application, and in practical applications, various changes may be made to the embodiments in form and detail without departing from the spirit and scope of the present application. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present application, and therefore the scope of protection of the present application shall be subject to the scope defined in the claims.

Claims

1. A solar cell, characterized in that: include: A substrate, wherein the substrate has a first surface and a second surface relative to each other, at least one of the first surface or the second surface has a velvet surface, the velvet surface is composed of a plurality of pyramid structures, at least part of the side walls of the pyramid structures have a folded portion, the folded portion is composed of a plurality of scale-like protrusions, in a direction from the top of the pyramid structure to the bottom of the pyramid structure, the length of the folded portion is a first length, the length of the side wall of the pyramid structure is a second length, and the ratio of the first length to the second length is greater than or equal to 0.

5.

2. The solar cell according to claim 1, characterized in that A ratio of the first length to the second length is less than or equal to 0.

8.

3. The solar cell according to claim 1, characterized in that The angle between the two inclined surfaces arranged opposite to each other in the pyramid structure is 65° to 70°.

4. The solar cell according to claim 1, characterized in that A plurality of the scale-like protrusions are interconnected to form continuous irregular wavy protrusions. Taking the plane where the first surface or the second surface is located as a reference surface, the orthographic projection of the irregular wavy protrusions in a direction perpendicular to the reference surface is stamen-shaped.

5. The solar cell according to claim 1, characterized in that: The side wall of the pyramid structure has a pit, and the wrinkled portion is also located on the inner wall of the pit.

6. The solar cell according to claim 1, characterized in that Also includes: A passivation layer, the passivation layer is located on the velvet surface and covers the surface of the pyramid structure, the surface of the passivation layer in some areas away from the pyramid structure is conformal to the surface of the folded portion, and the surface of the passivation layer in some areas away from the pyramid structure is smoother than the surface of the folded portion.

7. A method for preparing a solar cell, for preparing the solar cell according to any one of claims 1 to 6, characterized in that: include: providing a substrate having opposing first and second sides; Performing a first texturing process on at least one of the first surface or the second surface of the substrate to form an initial velvet surface on the first surface or the second surface of the substrate, wherein the initial velvet surface is composed of a plurality of initial pyramid structures; Performing a second texturing process on the initial velvet surface to form a velvet surface, wherein the velvet surface is composed of a plurality of pyramid structures, and at least a portion of the side walls of the pyramid structures have wrinkles, and the wrinkles are composed of a plurality of scale-like protrusions. In a direction from the top of the pyramid structure to the bottom of the pyramid structure, the length of the wrinkles is a first length, and the length of the side wall of the pyramid structure is a second length, and the ratio of the first length to the second length is greater than or equal to 0.5; The alkali concentration of the second texturing agent used in the second texturing process is lower than the alkali concentration of the first texturing agent used in the first texturing process; and the temperature in the second texturing process is lower than the temperature in the first texturing process.

8. The method for preparing a solar cell according to claim 7, characterized in that: The alkali concentration in the first texturing agent is 1.8% to 2.2%; the alkali concentration in the second texturing agent is 0.2% to 0.6%; the temperature of the first texturing process is 80°C to 90°C; the temperature of the second texturing process is 70°C to 80°C.

9. The method for preparing a solar cell according to claim 7, characterized in that: Also includes: The substrate is placed in a graphite boat and a passivation layer is formed on the surface of the substrate by plasma chemical vapor deposition, wherein the number of contact points between the graphite boat and the substrate is greater than or equal to 5.

10. The method for preparing a solar cell according to claim 7, characterized in that: On the initial velvet surface, the surface area of ​​any initial pyramid structure is a first area; on the velvet surface, the surface area of ​​any pyramid structure is a second area, and the ratio of the second area to the first area is 1.3 to 1.7.

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