solar cell

Abstract

Solar cell, comprehensive: a substrate that includes a first surface and a second surface that are opposite each other; wherein at least one of the first surface and the second surface is designed as a textured surface that includes a plurality of pyramidal structures (10), and at least some of the plurality of pyramidal structures (10) have sidewalls with folded sections (11), and wherein each folded section of the folded sections (11) of each side wall of the side walls has a first length (L1) and includes one or more scale-like projections within the first length, the respective side wall has 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.

Description

TECHNICAL AREA

[0001] Embodiments of the present disclosure relate to the field of photovoltaic technologies, in particular to a solar cell. BACKGROUND

[0002] Given the gradual depletion of fossil fuels, solar cells are increasingly being used as a new energy alternative. A solar cell is a device that converts sunlight into electrical energy. In terms of its operation, the solar cell is based on the photovoltaic effect of a PN junction in a semiconductor. When light strikes the PN junction, electron-hole pairs are generated. The charge carriers generated at the PN junction in the semiconductor do not recombine to reach a space charge region. Under the influence of an internal electric field, electrons flow into an N-region and holes flow into a P-region. As a result, excess electrons accumulate in the N-region and excess holes in the P-region, creating a photogenerated electric field opposite to the direction of a potential barrier near the PN junction.

[0003] In the manufacturing process of solar cells, chemical texturing of substrates by etching is a crucial step. This process serves to reduce the surface reflection of the substrates, improve light absorption, and increase the density of photogenerated charge carriers, thereby enhancing the photovoltaic conversion efficiency of the solar cells. The principle of chemical texturing of substrates is based on the anisotropy or isotropy of silicon crystals, meaning that in a chemical solution, the etching rates vary across the crystal planes or orientations of a substrate. In this way, texturing structures, including pyramidal structures of various shapes and sizes, can be formed on the substrate surfaces.

[0004] However, the texturing structures still prevent a significant amount of light from being utilized, resulting in relatively high light reflection from solar cells with such texturing structures. Consequently, the photovoltaic conversion efficiency of these solar cells remains low. SUMMARY

[0005] Embodiments of the present disclosure provide a solar cell and a method for manufacturing it, which at least contribute to reducing the light reflection of the solar cell and thereby improving the photovoltaic conversion efficiency of the solar cell.

[0006] Some embodiments of the present disclosure provide a solar cell. The solar cell includes a substrate, and the substrate includes a first surface and a second surface facing each other. At least one of the first surface and the second surface is configured as a textured surface that includes a plurality of pyramidal structures, and at least some of the plurality of pyramidal structures have sidewalls with folded sections. Each folded section of a sidewall has a first length and includes at least one scale-like projection within the first length. The sidewall has 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, the ratio of the first length to the second length is less than or equal to 0.8.

[0008] In some embodiments, an enclosed angle formed between two opposing side walls of each pyramidal structure of at least some of the plurality of pyramidal structures lies in a range of 65° to 70°.

[0009] In some embodiments, the respective folded section comprises a plurality of interconnected scale-like projections, and the plurality of scale-like projections exhibit a form of continuous irregular waves. An orthogonal projection of scale-like projections of a corresponding pyramidal structure of the plurality of pyramidal structures enclosing the respective folded section along a direction perpendicular to the first surface or the second surface exhibits a bud shape.

[0010] In some embodiments, a recess is formed on the side wall that encloses the respective folded section, and the respective folded section is formed on an inner wall of the recess.

[0011] In some embodiments, the solar cell further includes a passivation layer formed on the textured surface, covering the surfaces of the plurality of pyramidal structures. The passivation layer comprises first sections and second sections corresponding to the folded sections, wherein the surfaces of the first sections, located away from the plurality of pyramidal structures, exhibit shapes similar to those of the folded section surfaces, while the surfaces of the second sections, located away from the plurality of pyramidal structures, have a higher degree of smoothness than the folded section surfaces.

[0012] Some embodiments of the present disclosure provide a method for manufacturing a solar cell which is applicable to manufacturing the solar cell as in the embodiments described above.The method includes: providing a substrate, wherein the substrate includes a first surface and a second surface facing each other; forming at least one initial textured surface by performing a first texturing process on at least one of the first and second surfaces of the substrate, wherein the at least one initial textured surface includes a plurality of initial pyramidal structures; and forming at least one textured surface by performing a second texturing process on the at least one initial textured surface, wherein the at least one textured surface includes a plurality of pyramidal structures and at least some of the plurality of pyramidal structures have sidewalls with folded sections.Each folded section of a sidewall has a first length and includes at least one scale-like projection within the first length. The sidewall has a second length, and the ratio of the first length to the second length is greater than or equal to 0.5. A first texturizing agent is used in the first texturizing process, a second texturizing agent is used in the second texturizing process, and the alkali concentration in the second texturizing agent is lower than the alkali concentration in the first texturizing agent. The temperature for the second texturizing process is lower than the temperature for the first texturizing process.

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

[0014] In some embodiments, the method further includes: arranging the substrate in a graphite boat; and forming a passivation layer on at least one surface of the substrate using plasma-enhanced chemical vapor deposition. The number of contact points between the graphite boat and the substrate is greater than or equal to 5.

[0015] In some embodiments, each initial pyramidal structure of the plurality of initial pyramidal structures has a first surface area, each pyramidal structure of the plurality of pyramidal structures has a second surface area, and a ratio of the second surface area to the first surface area is in the range of 1.3 to 1.7.

[0016] The technical solutions provided in the embodiments of the present disclosure have the following advantageous effects.

[0017] In the solar cell and the method for manufacturing the solar cell provided in the embodiments of the present disclosure, at least one of the first surface and the second surface of the substrate of the solar cell is configured as a textured surface that includes a plurality of pyramidal structures. Sidewalls of at least some of the plurality of pyramidal structures are configured with folded sections, and each folded section includes at least one scale-like projection. The folded sections can increase the roughness of the sidewalls of the pyramidal structures and increase the probability of multiple reflections of sunlight between the pyramidal structures, thereby trapping the sunlight at the surface(s) of the substrate.In this way, the optical path length of incident light in the substrate can be increased, improving the spectral effects of the solar cell and enabling more photons to generate electron-hole pairs at a PN junction on the substrate surface(s). The generated electron-hole pairs are more easily separated and collected, increasing the probability of photogenerated charge carrier collection and improving the photovoltaic conversion efficiency of the solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Exemplary representations of one or more embodiments are provided by reference to the images in the corresponding accompanying drawings. These exemplary representations do not constitute a limitation of the embodiments. The drawings do not represent a scale limitation unless otherwise indicated. For a clearer illustration of the technical solutions in related technologies or in the embodiments of this disclosure, the drawings to be used in the embodiments are briefly described below. It is evident that the drawings mentioned in the following description are only some embodiments of this disclosure. Persons skilled in the art can derive other drawings from these drawings without inventive effort. Fig.Figure 1 is a schematic diagram of a cross-section of a substrate of a solar cell according to the prior art, obtained using a scanning electron microscope (SEM); Fig. Figure 2 is a schematic top view of the substrate of the solar cell according to the prior art, obtained using a SEM; Fig. Figure 3 is a schematic diagram of a cross-section of a substrate of a solar cell according to some embodiments of the present disclosure, obtained using a SEM; Fig. 4 is a schematic top view of the substrate of the solar cell according to some embodiments of the present disclosure, obtained using a SEM; Fig. Figure 5 is a schematic enlarged view of a local structure of a pyramidal structure according to some embodiments of the present disclosure; Fig. 6 and Fig.Figure 7 shows schematic structural diagrams of two pyramid-shaped structures, each of whose surfaces is covered with a corresponding passivation layer, according to some embodiments of the present disclosure; and Fig. Figure 8 is a diagram showing the reflection of the solar cells according to some embodiments of the present disclosure, measured at different wavelengths. Fig. Figure 9 is a flowchart of a method for manufacturing a solar cell according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE EXECUTION FORMS

[0019] As is known from the prior art, the texturing structures lead to a relatively high light reflection of the solar cells, which results in a low photovoltaic conversion efficiency of the solar cells.

[0020] Fig.Figure 1 is a schematic diagram of a cross-section of a substrate of a solar cell according to the state of the art, obtained using a SEM, and Fig. Figure 2 is a schematic top view of the substrate of the solar cell according to the state of the art, obtained using a SEM.

[0021] In the texturing process, the first step in solar cell manufacturing, chemical etching is typically used to form texturing structures on the surface(s) of a substrate in conventional mass production to enhance the light-trapping effect of the solar cell's surface(s). Due to the fact that the etch rates of alkaline texturing agents vary across the crystal planes of the substrate, square-shaped pyramidal structures (also known as pyramidal structures, as in...) are ultimately formed. Fig. 1 and Fig.(2 illustrated) are formed, each exhibiting four (111) crystal planes. Currently, an alkaline texturizing process can control a nucleation process of the pyramidal structures, effectively reducing the surface tension at a solid-liquid interface and suppressing further expansion of bubbles during the reaction. This controls the reaction rate and allows the hydrogen gas generated during the reaction to escape rapidly from the substrate surface(s). In this way, the uniformity of the textured surface can be ensured. Typically, the ratio of the height of a pyramidal structure to the length of a base edge of the pyramidal structure is 0.5:1, or the included angle formed between an inclined face of the pyramidal structure and a base of the pyramidal structure is in the range of 52° to 53°.The pyramid-shaped structures, which feature relatively large substrate dimensions, cause a significant amount of light to be reflected through the lateral surfaces of these structures to the outer surface of the substrate. Consequently, the textured substrate further prevents a considerable amount of light from being utilized, resulting in relatively high light reflection from the solar cells with such textured structures. As a result, the photovoltaic conversion efficiency of these solar cells is low.

[0022] Conventional texturing structures, which are designed as pyramid-shaped structures, exhibit relatively high reflectance (10% to 10.5%) and cannot efficiently capture light, thus hindering improvements in the photovoltaic conversion efficiency of solar cells. To increase the light absorption efficiency of solar cells, nanotexturing structures such as black silicon technology (inverted pyramid) have been used, which can reduce reflectance to as low as 1.5% or even less. However, the nanotextured surfaces are disordered, exhibit poor passivation, and suffer from significantly reduced efficiency. Additionally, the process is more complex. Furthermore, the nanotexturing structures contain metallic components, leading to higher costs and contamination of the tank and post-processing stages, and therefore not being fully compatible with mass production equipment.

[0023] The embodiments of the present disclosure provide a solar cell and a method for manufacturing solar cells, wherein at least one of the first surface and the second surface of the substrate of the solar cell is configured as a textured surface that includes a plurality of pyramidal structures. Sidewalls of at least some of the plurality of pyramidal structures are configured with folded sections, and each folded section includes at least one scale-like projection. The folded sections can increase the roughness of the sidewalls of the pyramidal structures and increase the probability of multiple reflections of sunlight between the pyramidal structures, thereby capturing the sunlight at the surface(s) of the substrate.In this way, the optical path length of incident light in the substrate can be increased, improving the spectral effects of the solar cell and enabling more photons to generate electron-hole pairs at a PN junction on the substrate surface(s). The generated electron-hole pairs are more easily separated and collected, increasing the probability of photogenerated charge carrier collection and improving the photovoltaic conversion efficiency of the solar cell.

[0024] In the description of the embodiments of the present disclosure, the technical terms “first”, “second” and the like serve only to distinguish different objects and are not to be understood as an indication or suggestion of the relative importance or as an implicit reference to the number, the specific order or the dominant-subordinate relationship of the specified technical features.

[0025] In the description of the embodiments of the present disclosure, “a plurality of” means two or more, unless expressly stated otherwise.

[0026] The term “elaboration” as used herein means that certain features, structures, or properties described in combination with the embodiments may be included in at least one embodiment of this disclosure. Terms appearing at different points in the description do not refer to the same embodiment, nor to separate or alternative embodiments that are mutually exclusive with other embodiments. Persons skilled in the art understand, expressly and implicitly, that the embodiments described herein may be combined with other embodiments.

[0027] In the description of the embodiments of the present disclosure, the term "and / or" herein merely denotes an associative relationship that describes related objects and indicates that three relationships are possible. For example, A and / or B indicates that there are three cases: A alone, A and B together, and B alone. Furthermore, the symbol " / " herein generally indicates an "or" relationship between the related objects.

[0028] In the description of the embodiments of the present disclosure, the orientation or position relationships indicated by the technical terms "central", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "from", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like are based on the orientation or position relationships shown in the accompanying drawings and serve only to facilitate the description of the present disclosure and to simplify the description, rather than indicating or implying that the device or element in question must have a particular orientation or be designed and operated in a particular orientation, and are therefore not to be interpreted as limiting the embodiments of the present disclosure.

[0029] In the drawings corresponding to the embodiments of this disclosure, the thickness and area of ​​a layer are exaggerated for clarity and to simplify the description. When a component is described as being on top of another component or on a surface of another component, the component may be "directly" on the surface of the other component, or a third component may be present between the two components. Conversely, when a component is described as being on the surface of another component, or when the other component is formed or provided on a surface of a component, no third component is present between the two components.Furthermore, if one component is described as being formed “essentially” on the other component, this means that the component is formed neither on the entire surface (or a front face) of the other component nor on part of an edge of the entire surface.

[0030] If, in the description of the embodiments of the present disclosure, one component “includes” another component, other components are not excluded and may, unless otherwise stated, also be included.

[0031] The terms used in the description of the embodiments described herein serve only to describe specific embodiments and are not to be understood as limiting. As used in the description of the described embodiments and in the accompanying claims, "component" is intended to include the plural form unless the context clearly indicates otherwise.

[0032] Various embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details are provided in the embodiments of the present disclosure to facilitate readers' understanding of these embodiments. Nevertheless, the technical solutions claimed in the embodiments of the present disclosure can also be implemented without these technical details and with various changes and modifications based on the following embodiments.

[0033] Fig. Figure 3 is a schematic diagram of a cross-section of a substrate of a solar cell according to some embodiments of the present disclosure, obtained using a SEM; Fig.4 is a schematic top view of the substrate of the solar cell according to some embodiments of the present disclosure, obtained using a SEM; and Fig. Figure 5 is a schematic enlarged view of a local structure of a pyramidal structure according to some embodiments of the present disclosure.

[0034] The solar cell according to some embodiments of the present disclosure includes a substrate comprising a first surface and a second surface opposite each other, wherein at least one of the first surface and the second surface is a textured surface. Referring to Fig. 3 and Fig.4. The textured surface includes a multitude of pyramid-shaped structures. Sidewalls of at least some of the multitude of pyramid-shaped structures are formed with folded sections. Each folded section includes at least one scale-like projection. Referring to Fig.In Figure 5, each folded section of the folded sections 11 has a first length L1, a side wall enclosing the folded section, and 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; for example, the ratio may be 0.5, 0.56, 0.6, 0.64, 0.7, 0.75, 0.8, 0.96, or 1. The first length L1 is measured along a perpendicular line from a vertex of each pyramidal structure of the plurality of pyramidal structures to a base edge of each pyramidal structure.In a direction extending from the vertex to the base edge of the respective pyramidal structure, a starting position for measuring the first length L1 is defined at a first scale-like projection of the respective folded section, and an end position for measuring the first length L1 is defined at the last scale-like projection of the respective folded section.

[0035] In the solar cell according to the embodiments of the present disclosure, at least one of the first and the second surfaces of the substrate of the solar cell is configured as a textured surface that includes a plurality of pyramidal structures. Sidewalls of at least some of the plurality of pyramidal structures are configured with folded sections, and each folded section includes at least one scale-like projection. The folded sections can increase the roughness of the sidewalls of the pyramidal structures and increase the probability of multiple reflections of sunlight between the pyramidal structures, thereby capturing the sunlight at the surface(s) of the substrate.In this way, the optical path length of incident light in the substrate can be increased, improving the spectral effects of the solar cell and enabling more photons to generate electron-hole pairs at a PN junction on the substrate surface(s). The generated electron-hole pairs are more easily separated and collected, increasing the probability of photogenerated charge carrier collection and improving the photovoltaic conversion efficiency of the solar cell.

[0036] It should be noted that with regard to Fig.3. The degree of folding differs at various positions on the side walls of a pyramidal structure. Therefore, the pyramidal structure has an appearance in which the scale-like projections corresponding to the folded sections at the apex of the pyramidal structure are less pronounced than those corresponding to the folded sections in the middle of the pyramidal structure.

[0037] In some embodiments, the solar cell can be one of the following: a passivated emitter and backside cell (PERC cell), a passivated emitter and backside total diffusion cell (PERT cell), a tunnel oxide passivated contact cell (TOPCon cell), a heterojunction technology cell (HIT / HJT cell), or a back contact cell (BC cell).

[0038] 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-component composite solar cell. The multi-component composite solar cell can be a cadmium sulfide solar cell (CdS solar cell), a gallium arsenide solar cell (GaAs solar cell), a copper indium selenide solar cell (CIS solar cell), or a perovskite solar cell.

[0039] Fig. 6 and Fig. Figure 7 are schematic structural diagrams of two pyramid-shaped structures, the surfaces of which are each covered with a corresponding passivation layer, according to some embodiments of the present disclosure.

[0040] Referring to Fig. 6 and Fig.7 In some embodiments, the solar cell further includes a passivation layer 12, which is formed on the textured surface and covers surfaces of the plurality of pyramidal structures 10. The passivation layer 12 includes first sections and second sections corresponding to the folded sections, wherein with reference to Fig. 6. Surfaces of the first sections, which are removed from the multitude of pyramidal structures 10, have shapes similar to the shapes of the surfaces of the folded sections 11; or, referring to Fig.7. The surfaces of the second sections, located away from the multitude of pyramidal structures 10, exhibit a higher degree of smoothness than the surfaces of the folded sections 11. On the textured surface of the substrate, the folded sections 11 exhibit varying degrees of roughness at the sidewalls of the pyramidal structures 10 in different regions. If the waviness of the folded sections 11 is relatively large or pronounced relative to the sidewalls of the pyramidal structures 10, and the passivation layer 12 is applied uniformly over the surfaces of the pyramidal structures 10, the surface of the passivation layer 12, located away from the multitude of pyramidal structures 10, exhibits shapes similar to the shapes of the surfaces of the folded sections 11 (as shown in Figure 1). Fig.6 illustrated). Conversely, if the waviness of the folded sections 11 relative to the side walls of the pyramidal structures 10 is relatively small or non-existent, and the passivation layer 12 is applied uniformly over the surfaces of the pyramidal structures 10, the coverage of the passivation layer 12 reduces the waviness effect of the folded sections 11 relative to the side walls of the pyramidal structures 10. Therefore, the surface of the passivation layer 12 furthest from the pyramidal structures 10 exhibits a higher degree of smoothness than the surfaces of the folded sections 11 (as illustrated in Figure 6). Fig. 7 illustrated).

[0041] In some embodiments, the passivation layer comprises a first passivation layer and a second passivation layer. The first passivation layer is located on the first surface, and the second passivation layer is located on the second surface. The first and second passivation layers can prevent oxidation or corrosion of the substrate surfaces, thereby improving the stability and lifespan of the solar cell.

[0042] The first passivation layer can consist of at least one of aluminum oxide, silicon oxide, silicon nitride, or silicon oxynitride. The first passivation layer can have either a single-layer or a multi-layer structure. For example, the single-layer structure can be a single layer of aluminum oxide, a single layer of silicon oxide, a single layer of silicon nitride, or a single layer of silicon oxynitride. The multi-layer structure can include a stack of at least two layers, selected from an aluminum oxide layer, a silicon oxide layer, a silicon nitride layer, and a silicon oxynitride layer.

[0043] The second passivation layer can consist of at least one of aluminum oxide, silicon oxide, silicon nitride, or silicon oxynitride. The second passivation layer can have either a single-layer or a multi-layer structure. For example, the single-layer structure can be a single layer of aluminum oxide, a single layer of silicon oxide, a single layer of silicon nitride, or a single layer of silicon oxynitride. The multi-layer structure can include a stack of at least two layers, selected from an aluminum oxide layer, a silicon oxide layer, a silicon nitride layer, and a silicon oxynitride layer.

[0044] In some embodiments, the substrate may include an emitter. The emitter may be located on the side of the substrate facing the first passivation layer and may be in contact with it. Alternatively, the emitter may be located on the side of the substrate facing the second passivation layer and may be in contact with it. The doping type of the emitter is the opposite of that of the substrate. For example, if the substrate is doped with a p-type dopant, the emitter is doped with an n-type dopant; and conversely, if the substrate is doped with an n-type dopant, the emitter is doped with a p-type dopant. In this way, a pn junction is formed between the emitter and the substrate.The pn junction can receive and absorb incident light that is shone onto the surface of the substrate, generating electron-hole pairs. If, for example, the substrate is an n-type substrate, separate electrons move into the substrate and separate holes into the emitter, thus generating an electric current.

[0045] The substrate can be an N-type or a P-type semiconductor substrate. The N-type semiconductor substrate is doped with an N-type dopant. The N-type dopant can be one of the elements in Group V, such as potassium (K), bismuth (Bi), antimony (Sb), arsenic (As), or the like. The P-type semiconductor substrate is doped with a P-type dopant. The P-type dopant can be one of the elements in Group III, such as boron (B), aluminum (Al), gallium (Ga), indium (In), or the like.

[0046] The substrate can consist of at least one of monocrystalline silicon, polycrystalline silicon, amorphous silicon or microcrystalline silicon.

[0047] If the solar cell is a monofacial solar cell, one side of the substrate can have a textured surface, while the other side can be a polished surface; that is, the polished surface of the substrate is flatter and smoother compared to the textured surface. It should be noted that in a monofacial solar cell, textured surfaces can be present on both sides of the substrate. If the solar cell is a bifacial solar cell, textured surfaces can be present on both sides of the substrate.

[0048] In some embodiments, the solar cell may further comprise a tunnel layer and a doped conductive layer. The tunnel layer is located on a surface of the substrate away from the emitter, and the doped conductive layer is located on a surface of the tunnel layer away from the substrate. The tunnel layer and the doped conductive layer are configured to form a passivated contact structure. The tunnel layer can achieve a chemical passivation effect. Due to the presence of interfacial defects on the surface of the substrate, the tunnel layer can saturate detached bonds on the surface of the substrate, reduce the defect density on the surface of the substrate, and decrease recombination centers on the surface of the substrate to lower the recombination rate of charge carriers, thus increasing the interfacial density of states on the surface of the substrate.Increasing the interfacial density of states promotes the recombination of photogenerated charge carriers, thereby increasing the fill factor, short-circuit current, and open-circuit voltage of the solar cell, thus improving its photoelectric conversion efficiency. The doped conductive layer can achieve a field passivation effect. It can generate an electrostatic field that causes minority charge carriers to escape from the interface, reducing their concentration. This, in turn, reduces the recombination rate of charge carriers at the substrate interface, thereby increasing the open-circuit voltage, short-circuit current, and fill factor of the solar cell, thus improving its photoelectric conversion efficiency.

[0049] The tunnel layer can consist of at least one of silicon oxide, silicon nitride, silicon oxynitride, silicon carbide or magnesium fluoride.

[0050] The doped conductive layer can consist of at least one of amorphous silicon, polycrystalline silicon, or silicon carbide. The doped conductive layer comprises a dopant of the same type as the one in the substrate. If the dopant in the substrate is phosphorus (P-type), the dopant in the doped conductive layer is also phosphorus (P-type). If the dopant in the substrate is nitric oxide (N-type), the dopant in the doped conductive layer is also nitric oxide (N-type).

[0051] Referring to Fig. In some embodiments, the ratio of the first length L1 to the second length L2 is less than or equal to 0.8.

[0052] Table 1 lists the reflectance corresponding to various solar cells provided in the embodiments of the present disclosure. Table 1: Reflectance of various solar cells Example of implementation With folded sections or not? Ratio of the first length to the second length (L1 / L2) Vertical angle Reflectance Comparative example 1 No / 70° to 75° 10% to 10.5% Comparative example 2 No / 65° to 70° 7% to 8% Example 1 Yes 1 / 5 6.8% to 7% Example 2 Yes 1 / 3 6% to 7% Example 3 Yes 2 / 3 3% to 5% Example 4 Yes 1 3% to 5%

[0053] As shown in Table 1, the substrates of the solar cells according to Comparative Example 1 and Comparative Example 2 have conventional textured surfaces, with the sidewalls of the pyramidal structures on the textured surfaces being smooth and lacking any folded sections on the sidewalls. In contrast, the solar cells according to Examples 1 to 4 have folded sections on the substrate surfaces, and the ratio of the first length L1 of a respective folded section to the length L2 of a sidewall of a corresponding pyramidal structure increases progressively.

[0054] Referring to Table 1, a comparison between Example 2 and Examples 1 to 4 shows that when folded sections are formed on the surfaces of the solar cell substrates, the reflectance of the solar cells is reduced compared to the conventional textured surface. A comparison of Examples 1 to 4 shows that at a relatively small ratio of the first length L1 to the second length L2, the reduction in the reflectance of the solar cells is small. As the ratio of the first length L1 to the second length L2 increases, the areas occupied by the folded sections on the sidewalls of the pyramidal structures increase, resulting in a more significant reduction in the reflectance of the solar cells.However, if the ratio of the first length L1 to the second length L2 increases further until the entire side walls of the pyramidal structures are occupied, the additional reduction in the reflectance of the solar cells becomes less pronounced. Therefore, if the ratio of the first length L1 to the second length L2 is greater than 0.5 and less than or equal to 0.8, the reflectance of the solar cells can be kept at a relatively low level. Furthermore, if the ratio of the first length L1 to the second length L2 is too large, the processing time required to form the folded sections increases, leading to a deterioration in the uniformity of the folded sections. This does not significantly reduce the reflectance of the solar cells, but it does decrease their manufacturing efficiency.Therefore, a ratio of the first length L1 to the second length L2 that lies within a suitable range is conducive to providing a relatively high uniformity and a relatively low reflectance of the textured surfaces, as well as improving the manufacturing efficiency of the solar cells.

[0055] Referring to Table 1, a comparison between Example 1 and Example 2 shows that for conventional textured surfaces, the reflectance of the solar cells is lower when the apex angle of the pyramidal structures (i.e., the angle enclosed between two opposite sides of a pyramidal structure) is in the range of 65° to 70°, compared to a case where the apex angle of the pyramidal structures is in the range of 70° to 75°. This is because a more acute apex angle of the pyramidal structures favors multiple reflections of sunlight between adjacent pyramidal structures, so that sunlight is more likely to be captured at the substrate surfaces, resulting in a better light-trapping effect and improving the photovoltaic conversion efficiency of the solar cell.

[0056] Fig.Figure 8 is a diagram showing the reflection of the solar cells according to some embodiments of the present disclosure, measured at different wavelengths. The curve labeled “a” in Fig. 8 corresponds to the data for comparison example 1 in Table 1, and the curve labeled “b” in Fig. 8 corresponds to the data for Example 3 in Table 1.

[0057] Referring to Table 1 and Fig.Figure 8 shows that, compared to conventional textured surfaces, in the solar cell according to the embodiments, which has folded sections on the side walls of the pyramidal structures, the angle enclosed between the two opposing side walls of a pyramidal structure is maintained, namely an apex angle in the range of 65° to 70°. In this way, the light-trapping effect on the substrate surfaces can be further improved. As a result, the reflectance of the solar cells at different wavelengths can be reduced, thereby improving the photovoltaic conversion efficiency of the solar cells.

[0058] Referring to Fig.4 In some embodiments, each folded section comprises a plurality of interconnected scale-like projections, and the plurality of scale-like projections exhibit a form of continuous irregular waves. An orthogonal projection of scale-like projections of a corresponding pyramidal structure of the plurality of pyramidal structures enclosing the respective folded section along a direction perpendicular to the first or second surface exhibits a bud shape. The irregular bud-like structure facilitates irregular reflections of incident light between adjacent pyramidal structures, which helps to lengthen the optical path of the incident light in the substrate and enhance the spectral effects of the solar cell.This results in more photons being excited to generate electron-hole pairs at a PN junction region on the surface(s) of the substrate, thereby increasing the probability of collecting photogenerated charge carriers and improving the photovoltaic conversion efficiency of the solar cell.

[0059] Referring to Fig. 3 is in some embodiments a recess (like the one in Fig.3. Textures (indicated by the dashed circle) are formed on the side wall of a pyramidal structure, each enclosing a folded section due to etching. These folded sections are located on the inner wall of the recess. The recesses increase the surface area of ​​the pyramidal structure's side walls. The folded sections, also present within the recesses, increase the roughness of the recess walls. This enhances the light-trapping effect of the textured surfaces and, consequently, the photovoltaic conversion efficiency of the solar cell.

[0060] In the solar cell provided in the embodiments of the present disclosure, at least one of the first and second surfaces of the substrate of the solar cell is configured as a textured surface that includes a plurality of pyramidal structures. Sidewalls of at least some of the plurality of pyramidal structures are configured with folded sections, and each folded section includes at least one scale-like projection. The folded sections can increase the roughness of the sidewalls of the pyramidal structures and increase the probability of multiple reflections of sunlight between the pyramidal structures, thereby capturing the sunlight at the surface(s) of the substrate.In this way, the optical path length of incident light in the substrate can be increased, improving the spectral effects of the solar cell and enabling more photons to generate electron-hole pairs at a PN junction on the substrate surface(s). The generated electron-hole pairs are more easily separated and collected, increasing the probability of photogenerated charge carrier collection and improving the photovoltaic conversion efficiency of the solar cell.

[0061] Accordingly, some embodiments of the present disclosure further provide a method for manufacturing a solar cell. This method can be used to manufacture the solar cell according to the foregoing embodiments. It should be noted that for those parts which are similar to or correspond to those in the foregoing embodiments, reference may be made to the corresponding description of the foregoing embodiments, which is not repeated here.

[0062] The method for manufacturing the solar cell according to the embodiments of the present disclosure comprises the following operations.

[0063] In S1, a substrate is provided, the substrate comprising a first surface and a second surface that are opposite each other.

[0064] In S2, at least one initial textured surface is formed by performing a first texturing process on at least one of the first surface and the second surface of the substrate, wherein the at least one initial textured surface includes a plurality of initial pyramidal structures.

[0065] In S3, at least one textured surface is formed by performing a second texturing process on the at least one initial textured surface, wherein the at least one textured surface includes a plurality of pyramidal structures, and sidewalls of at least some of the plurality of pyramidal structures are formed with folded sections. Each folded section of the folded sections has a first length and includes at least one scale-like projection within the first length, wherein a sidewall enclosing the respective folded section has a second length, and the ratio of the first length to the second length is greater than or equal to 0.5.A first texturizing agent is used in the first texturizing process, a second texturizing agent is used in the second texturizing process, and the alkali concentration in the second texturizing agent is lower than the alkali concentration in the first texturizing agent. The temperature for the second texturizing process is lower than the temperature for the first texturizing process.

[0066] In the method for manufacturing the solar cell according to the embodiments of the present disclosure, at least one of the first and the second surfaces of the substrate is formed using the first texturing process as at least one initial textured surface, which includes a plurality of initial pyramidal structures. The at least one initial textured surface can increase the roughness of at least one surface of the substrate and reduce the reflectance of incident light on the surface of the substrate. Then, sidewalls of at least some of the plurality of initial pyramidal structures are formed using the second texturing process with folded sections. Each folded section includes at least one scale-like projection.The length of each folded section is at least greater than or equal to half the length of a sidewall of a corresponding pyramidal structure enclosing the folded section. The folded sections can increase the roughness of the pyramidal structures' sidewalls and thus increase the probability of multiple reflections of sunlight between the pyramidal structures, thereby trapping sunlight at the substrate surface(s). This increases the optical path length of incident light within the substrate and improves the solar cell's spectral effects, allowing more photons to generate electron-hole pairs at a PN junction on the substrate surface(s).The generated electron-hole pairs are more easily separated and collected, thereby increasing the probability of photogenerated charge carrier collection and improving the photovoltaic conversion efficiency of the solar cell. In the first texturing process, the initial pyramidal structures formed have relatively large dimensions. In the second texturing process, the folded sections on the sidewalls of the initial pyramidal structures are formed and exhibit relatively fine morphologies and relatively small dimensions. Therefore, the temperature and alkali concentration required in the first texturing process are higher than those in the second. Here, alkali concentration refers to the mass ratio of alkali to the total mass of the texturing agent.

[0067] In some embodiments, the alkali concentration in the first texturizing agent is in the range of 1.8% to 2.2%, for example, 1.8%, 1.9%, 2%, 2.1%, or 2.2%. The alkali concentration in the second texturizing agent is in the range of 0.2% to 0.6%, for example, 0.2%, 0.3%, 0.4%, 0.5%, or 0.6%. The temperature for the first texturizing process is in the range of 80°C to 90°C, for example, 80°C, 82°C, 83°C, 85°C, 86°C, 88°C, or 90°C. The temperature for the second texturizing process is in the range of 70°C to 80°C, for example, 70°C, 72°C, 73°C, 75°C, 77°C, 79°C, or 80°C.

[0068] The duration of the first texturing process can range from 100 s to 900 s, for example 100 s, 150 s, 200 s, 230 s, 300 s, 340 s, 400 s, 460 s, 500 s, 520 s, 600 s, 670 s, 700 s, 740 s, 800 s, 850 s or 900 s.

[0069] The duration of the second texturing process can range from 100 s to 900 s, for example 100 s, 150 s, 200 s, 230 s, 300 s, 340 s, 400 s, 460 s, 500 s, 520 s, 600 s, 670 s, 700 s, 740 s, 800 s, 850 s or 900 s.

[0070] In some embodiments, the substrate has a first mass before the first texturing process and a second mass after the first texturing process, the difference between the first mass and the second mass being in the range of 0.3 g to 0.4 g, for example 0.3 g, 0.33 g, 0.36 g, 0.39 g, or 0.4 g. The substrate has a third mass after the second texturing process, and the difference between the second mass and the third mass being in the range of 0.03 g to 0.04 g, for example 0.03 g, 0.033 g, 0.035 g, 0.038 g, or 0.04 g. The difference between the first mass and the second mass can serve as a monitoring tool for the first texturing process and help to determine the extent of the formation of the initial textured surface on the substrate using the first texturing process, thus preventing over-etching or under-etching.Similarly, the difference between the second mass and the third mass can serve as a monitoring tool for the second texturing process, helping to determine the extent of the formation of the folded sections using the second texturing process, thus preventing over-etching or under-etching.

[0071] The alkali used in the first texturizing process can be at least one of sodium hydroxide or potassium hydroxide.

[0072] The alkali used in the second texturizing process can be at least one of sodium hydroxide or potassium hydroxide.

[0073] In some embodiments, a selective etchant can also be used in the second texturing process. The selective etchant can be at least one polyether compound or sodium lignosulfonate. The selective etchant promotes the selective etching of the sidewalls of the initial pyramidal structures in the second texturing process, thereby promoting the formation of the folded sections.

[0074] The concentration of the selective etchant (a ratio of the mass of the selective etchant to the total mass of the etchant) can be in the range of 0.1% to 0.2%, for example 0.1%, 0.13%, 0.15%, 0.18% or 0.25%.

[0075] In some embodiments, the method further comprises a first cleaning process prior to the first texturizing process. This first cleaning process is configured to remove contaminants from the substrate surfaces. The first cleaning process uses at least alkali and hydrogen peroxide. The concentration of alkali used in the first cleaning process is in the range of 0.4% to 0.6%, for example, 0.4%, 0.45%, 0.5%, 0.55%, or 0.6%. The concentration of hydrogen peroxide is in the range of 3% to 5%, for example, 3%, 3.3%, 4%, 4.4%, or 5%. The temperature for the first cleaning process can be in the range of 25°C to 50°C, for example, 25°C, 30°C, 35°C, 40°C, 45°C, or 50°C. The duration of the first cleaning process can range from 30 s to 200 s, for example 30 s, 50 s, 80 s, 100 s, 140 s, 180 s or 200 s.

[0076] The alkali used in the first cleaning process can be at least one of sodium hydroxide or potassium hydroxide.

[0077] In some embodiments, the process following the second texturizing process further comprises a second cleaning process, which includes water washing or acid washing.

[0078] In some embodiments, the process, after forming the textured surface(s) on the substrate, further includes: arranging the substrate in a graphite boat and forming a passivation layer on at least one surface of the substrate using plasma-enhanced chemical vapor deposition (PEC). The number of contact points between the graphite boat and the substrate is greater than or equal to five. Due to the relatively high surface roughness of the textured surface on the substrate, the number of free bonds on the substrate surfaces increases, leading to an increase in the recombination rate of charge carriers on the substrate surfaces. With the increase in solar cell area and the rise in industrial production demand, the volume of a graphite boat used in PEC also gradually increases.During the formation of the passivation layer using plasma-enhanced chemical vapor deposition (PEC), the discharge power is limited, making it difficult to achieve both optimal uniformity across the entire boat and optimal passivation layer thickness on a single substrate. Typically, the substrate and the graphite boat are in contact via contact points. To achieve a denser and more uniform passivation layer, comparable to the textured surface described in the preceding embodiments, the number of contact points on the graphite boat for PEC can be increased. This increases the contact area between the graphite boat and the substrate, thereby enhancing the actual discharge power of a plasma exciter and resulting in a more uniform discharge.In this way, the deposition rate and density of the passivation layer can be improved, and the hydrogen passivation effect can also be improved, thereby improving the efficiency of the solar cell by over 0.15%.

[0079] In some embodiments, each initial pyramidal structure of the plurality of initial pyramidal structures has a first surface, each pyramidal structure of the plurality of pyramidal structures has a second surface, and the ratio of the second surface to the first surface is in the range of 1.3 to 1.7, for example 1.3, 1.4, 1.5, 1.6, or 1.7. By forming the folded sections on the sidewalls of the initial pyramidal structures, the specific surface area of ​​each individual pyramidal structure can be further increased, thereby improving the light-trapping effect of the substrate and the photovoltaic conversion efficiency of the solar cell.

[0080] In the method for manufacturing the solar cell according to the embodiments of the present disclosure, at least one of the first and the second surfaces of the substrate is formed using the first texturing process as at least one initial textured surface, which includes a plurality of initial pyramidal structures. The at least one initial textured surface can increase the roughness of at least one surface of the substrate and reduce the reflectance of incident light on the surface of the substrate. Then, sidewalls of at least some of the plurality of initial pyramidal structures are formed using the second texturing process with folded sections. Each folded section includes at least one scale-like projection.The length of each folded section is at least greater than or equal to half the length of a sidewall of a corresponding pyramidal structure enclosing the folded section. The folded sections can increase the roughness of the pyramidal structures' sidewalls and thus increase the probability of multiple reflections of sunlight between the pyramidal structures, thereby trapping sunlight at the substrate surface(s). This increases the optical path length of incident light within the substrate and improves the solar cell's spectral effects, allowing more photons to generate electron-hole pairs at a PN junction on the substrate surface(s).The generated electron-hole pairs are more easily separated and collected, thereby increasing the probability of collecting photogenerated charge carriers and improving the photovoltaic conversion efficiency of the solar cell.

[0081] Those skilled in the art will understand that the embodiments mentioned above are specific examples for implementing the present disclosure. In practice, various changes to the form and details can be made without altering the scope of protection of the present disclosure. Therefore, the scope of patent protection of the present disclosure is subject to the scope of protection defined in the accompanying claims.

Claims

[1] Solar cell, comprising: a substrate that includes a first surface and a second surface that are opposite each other; wherein at least one of the first surface and the second surface is designed as a textured surface that includes a plurality of pyramidal structures (10), and at least some of the plurality of pyramidal structures (10) have sidewalls with folded sections (11), and wherein each folded section of the folded sections (11) of each side wall of the side walls has a first length (L1) and includes one or more scale-like projections within the first length, the respective side wall has 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. [2] Solar cell according to claim 1, wherein the ratio of the first length (L1) to the second length (L2) is less than or equal to 0.

8. [3] Solar cell according to claim 1 or claim 2, wherein an enclosed angle formed between two opposing side walls of each pyramidal structure of at least some of the plurality of pyramidal structures (10) is in the range of 65° to 70°. [4] Solar cell according to one of claims 1 to 3, wherein the respective folded section includes a plurality of interconnected scale-like projections, and the plurality of scale-like projections has a form of continuous irregular waves. [5] Solar cell according to claim 4, wherein an orthogonal projection of scale-like projections of a corresponding pyramidal structure of the plurality of pyramidal structures (10) enclosing the respective folded section along a direction perpendicular to the first surface or the second surface has a bud shape. [6] Solar cell according to one of claims 1 to 5, wherein a recess is formed on the side wall which encloses the respective folded section. [7] Solar cell according to claim 6, wherein the respective folded section is formed on an inner wall of the recess. [8] Solar cell according to any one of claims 1 to 7, further comprising a passivation layer (12) formed on the textured surface and covering surfaces of the plurality of pyramid-shaped structures (10); and wherein the passivation layer (12) includes first sections corresponding to the folded sections (11), and surfaces of the first sections located away from the plurality of pyramidal structures (10) have shapes similar to the shapes of the surfaces of the folded sections (11). [9] Solar cell according to claim 8, wherein the passivation layer (12) further includes second sections corresponding to the folded sections (11), and surfaces of the second sections that are away from the plurality of pyramidal structures (10) have a higher degree of smoothness than the surfaces of the folded sections (11). [10] Solar cell according to claim 8 or 9, wherein the passivation layer (12) comprises a first passivation layer arranged on the first surface and a second passivation layer arranged on the second surface, and wherein both the first passivation layer and the second passivation layer contain at least one of aluminium oxide, silicon oxide, silicon nitride or silicon oxynitride.

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