Composite textured structure of solar cell and method for preparing the same

Abstract

The application discloses a composite textured structure of a solar cell and a preparation method thereof. The composite textured structure comprises a crystalline silicon substrate, and a submicron protrusion is formed on the surface of the crystalline silicon substrate. The surface of the submicron protrusion has a nano stripe, and the extending direction of the nano stripe is perpendicular to or parallel to the extending direction of a ridge line of the submicron protrusion. The micro-nano secondary composite structure of the submicron protrusion and the nano stripe can uniformly reduce the reflectivity of light in a 300 nm-1100 nm wave band without significantly increasing the surface area, and wide wave band light absorption can be realized.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, specifically to a composite textured surface structure for a solar cell and its preparation method. Background Technology

[0002] The photoelectric conversion efficiency of crystalline silicon solar cells largely depends on the substrate surface's ability to capture incident light. Issues such as light reflection loss, surface recombination, and insufficient spectral utilization on the substrate surface are key factors restricting the improvement of cell performance. Most existing conventional crystalline silicon substrates employ a single-morphology microstructure textured surface for anti-reflection treatment. This results in a limited structural form and light modulation dimensions, leading to significant optical-electrical performance contradictions and numerous defects such as insufficient near-infrared light capture, making it difficult to achieve synergistic optimization of light absorption and carrier transport. Summary of the Invention

[0003] The purpose of this application is to provide a composite textured surface structure for solar cells and its preparation method, thereby solving the problems of high light reflectivity and insufficient light capture wavelength in existing solar cells.

[0004] To achieve the objectives of this application, the following technical solution is provided: In a first aspect, the present invention provides a composite textured structure for a solar cell, comprising a crystalline silicon substrate, wherein submicron protrusions are formed on the surface of the crystalline silicon substrate, and the surface of the submicron protrusions has nano-stripes, wherein the extension direction of the nano-stripes is perpendicular to or parallel to the extension direction of the ridges of the submicron protrusions.

[0005] In some embodiments, the height of the submicron protrusion is 0.6 μm to 0.8 μm, and / or the period of the nanostripe is 50 nm to 1000 nm.

[0006] In some embodiments, the nanostripes include low spatial frequency stripes and high spatial frequency stripes, the high spatial frequency stripes being located on the sidewall surface of the low spatial frequency stripes, and the period range of the low spatial frequency stripes being greater than the period range of the high spatial frequency stripes.

[0007] In some embodiments, the submicron protrusion includes a top region and a bottom region along the height direction, wherein the nanostripe density of the top region is greater than that of the bottom region.

[0008] In some embodiments, the density of the nanostripes decreases from the top region to the bottom region along the height direction of the submicron protrusion.

[0009] In some embodiments, the equivalent refractive index of the region containing the nanostripes is greater than the refractive index of air, and the equivalent refractive index of the region containing the nanostripes is less than the bulk refractive index of the submicron protrusion.

[0010] In some embodiments, the equivalent refractive index of the region where the nanostripes are located, the bulk refractive index of the submicron protrusions, and the bulk refractive index of the crystalline silicon substrate are 1.5, 3.0, and 3.5, respectively.

[0011] In some embodiments, the depth of the nanostripes is 10 nm to 200 nm, and the angle formed between the ridges of the submicron protrusions and the surface of the crystalline silicon substrate is 45° to 85°.

[0012] In a second aspect, the present invention provides a method for preparing a composite textured structure for a solar cell. The method is used to prepare the composite textured structure for a solar cell as described in the first aspect. The method includes: step S100, fabricating submicron protrusions on the surface of a crystalline silicon substrate by chemical etching; and step S200, fabricating nano-stripes on the surface of the submicron protrusions by laser-induced periodic surface structure process.

[0013] In some embodiments, in step S200, the wavelength of the laser is 1020 nm to 1064 nm, the pulse width of the laser is 200 fs to 600 fs, and the energy density of the laser is 0.12 J / cm². 2 ~0.30J / cm 2 .

[0014] In some embodiments, in step S200, the scanning speed of the laser is 5 mm / s to 100 mm / s, the polarization direction of the laser is linearly polarized, and the polarization direction forms an angle of 0° to 90° with the scanning direction.

[0015] This invention forms submicron bumps on a crystalline silicon substrate, creating a basic light-trapping structure. The submicron bumps provide the basis for Mie scattering, effectively extending the optical path of incident light, enhancing multi-angle light scattering and coupling absorption, and significantly reducing specular reflection on the battery surface. Simultaneously, nanostripes are formed on the surface of the submicron bumps, creating a micro / nano secondary composite structure of submicron bumps and nanostripes, achieving a dual-scale synergistic effect. Without significantly increasing the surface area, the reflectivity of light in the 300nm~1100nm wavelength band is uniformly reduced, enabling wide-band light absorption, especially near-infrared light. Furthermore, defining the extension direction of the nanostripes ensures structural compatibility between the nanostripes and the submicron bumps, avoiding a decrease in light scattering efficiency due to disordered stripe orientation, further enhancing the light-trapping effect, and facilitating precise control of subsequent laser fabrication processes. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of a composite velvet structure as one implementation method; Figure 2 This is a flowchart illustrating the preparation process of a composite velvet structure in one implementation method. Figure 3 This is a schematic diagram illustrating the preparation process of a composite velvet structure according to one embodiment; Figure 4 This is a schematic diagram illustrating the optical principle of a composite velvet structure in one embodiment; Figure 5 This is a window diagram of laser processing parameters for a composite textured surface structure in one embodiment. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] It should be noted that when a component is said to be "fixed" to another component, it can be directly on the other component or it can be in a middle component. When a component is said to be "connected" to another component, it can be directly connected to the other component or it may be in a middle component.

[0020] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items.

[0021] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0022] This invention provides a solar cell, which includes a crystalline silicon substrate, a front passivated emitter, a back passivated contact structure, and a metal electrode. Specifically, the crystalline silicon substrate can be an n-type monocrystalline silicon substrate, which has… <100> The crystal orientation and resistivity of the crystalline silicon substrate are 1 Ω·cm to 3 Ω·cm, with a thickness of 130 μm to 150 μm. The front passivated emitter consists of a boron-doped polycrystalline silicon layer and a passivation layer. The back passivated contact structure includes a tunneling oxide layer (SiO₂). x The metal electrodes consist of a silver gate line on the front side and a copper gate line on the back side.

[0023] In some embodiments, the surface of the crystalline silicon substrate has a composite textured structure; please refer to [reference needed]. Figure 1 The composite textured structure includes submicron protrusions 10, the surface of which has nano-stripes 20, the extension direction of which is perpendicular to or parallel to the extension direction of the ridges of the submicron protrusions 10. Specifically, the surface of the crystalline silicon substrate has multiple submicron protrusions 10, with the ridge line from the top to the bottom of the submicron protrusion 10 being its ridge line; the surface of the submicron protrusions 10 has multiple nano-stripes 20, all of which extend parallel to each other on the surface.

[0024] In a specific embodiment, when incident light irradiates the substrate surface, it first passes through the refraction and reflection of the nano-stripes 20, and then enters the gaps between the submicron protrusions 10 and the pyramid surface. After multiple reflections, it is fully absorbed by the substrate, effectively reducing the light reflectivity and significantly improving the light absorption efficiency.

[0025] In a specific embodiment, please refer to Figure 1 (b) The submicron protrusion 10 can be a boss structure, and the submicron protrusion 10 can include a top surface of a back-to-back passivated contact structure. The top surface of the submicron protrusion 10 has nano-stripes 20. Optionally, the multiple nano-stripes 20 on the top surface extend in the same direction and are spaced apart. Alternatively, the multiple nano-stripes 20 on the top surface can be arranged in multiple rows and columns in a cross pattern. The nano-stripes 20 on the top surface can expand the effective area of ​​light reflection and refraction, reduce the reflection loss of incident light, and improve the light absorption efficiency.

[0026] In a specific embodiment, please refer to Figure 1 (b) The top surface of the submicron protrusion 10 includes a first nanostripes extending along a first direction and a second nanostripes extending along a second direction, the first and second directions being orthogonal. This orthogonal arrangement design further optimizes the light reflection effect of the top surface nanostripes 20. Compared with a stripe arrangement in a single direction, the orthogonal first and second nanostripes can form a three-dimensional reflection network. No matter which direction the incident light shines on the top surface from, it can be fully reflected and refracted by the stripes, minimizing the light reflection loss of the top surface.

[0027] In a specific embodiment, please refer to Figure 1 (b) The submicron protrusion 10 can be a pyramidal structure, and may include four inclined surfaces connected sequentially in a ring-like manner. Each of the four inclined surfaces of the submicron protrusion 10 has nano-stripes 20. Optionally, the multiple nano-stripes 20 on the inclined surfaces extend from the top of the submicron protrusion 10 to its bottom. The nano-stripes 20 on the inclined surfaces further expand the area for light reflection and refraction, while simultaneously balancing optical gain and surface area increase.

[0028] In a specific embodiment, the four inclined surfaces include a first inclined surface and a second inclined surface facing away from each other, as well as a third inclined surface and a fourth inclined surface facing away from each other. The two ends of the first nanostripes on the top surface extend to the first and second inclined surfaces, thereby connecting the nanostripes 20 on the first and second inclined surfaces with the first nanostripes. The two ends of the second nanostripes on the top surface extend to the third and fourth inclined surfaces, thereby connecting the nanostripes 20 on the third and fourth inclined surfaces with the second nanostripes.

[0029] In other embodiments, please refer to Figure 1 In (a) and (c), the submicron protrusion 10 can also be a frustum structure (truncated cone), and the submicron protrusion 10 can include a smooth inclined surface. The first nanostripe and the second nanostripe extend independently to the smooth inclined surface. The smooth inclined surface has both the first nanostripe and the second nanostripe.

[0030] This invention forms submicron bumps 10 on a crystalline silicon substrate, creating a basic light trapping structure. The submicron bumps 10 provide the basis for Mie scattering, effectively extending the optical path of incident light, enhancing multi-angle light scattering and coupling absorption, and significantly reducing specular reflection on the battery surface. Simultaneously, nano-stripes 20 are formed on the surface of the submicron bumps 10, creating a micro-nano secondary composite structure of the submicron bumps 10 and nano-stripes 20. This achieves a dual-scale synergistic effect, uniformly reducing the reflectivity of light in the 300nm~1100nm wavelength band without significantly increasing the surface area, enabling wide-band light absorption, especially near-infrared light. Furthermore, defining the extension direction of the nano-stripes 20 ensures the structural compatibility between the nano-stripes 20 and the submicron bumps 10, avoiding a decrease in light scattering efficiency due to disordered stripe orientation, further enhancing the light trapping effect, and facilitating precise control of subsequent laser fabrication processes.

[0031] In some embodiments, the height of the submicron bump 10 is 0.6 μm to 0.8 μm. Optionally, the height of the submicron bump 10 can be 0.6 μm, 0.62 μm, 0.64 μm, 0.66 μm, 0.68 μm, 0.7 μm, 0.72 μm, 0.74 μm, 0.76 μm, 0.78 μm, or 0.8 μm; preferably, the height of the submicron bump 10 can be 0.7 μm. This range ensures that the submicron bump 10 has sufficient surface area to enhance light reflection, efficiently couples incident light into the crystalline silicon substrate, and extends the escape angle to achieve quasi-omnidirectional anti-reflection; while avoiding a decrease in structural stability due to excessive height.

[0032] In some embodiments, the period of the nanostripes 20 is 50 nm to 1000 nm. Optionally, the period of the nanostripes 20 can be 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, or 1000 nm; preferably, the period of the nanostripes 20 can be 800 nm. This range ensures the density of the nanostripes 20 to achieve multi-level light reflection, while avoiding situations where the period is too small, leading to mutual compression between stripes and structural instability, or where the period is too large, weakening the light reflection enhancement effect, thereby further improving the light absorption performance of the composite textured surface structure. It should be noted that the nanostripe period refers to the distance between two adjacent nanostripes 20 that extend along a specific direction and are formed on the surface of the submicron protrusion 10 through a laser-induced periodic surface structure process.

[0033] In a specific embodiment, the submicron protrusion 10 has a height of 0.7 μm, and the period of the nanostripes 20 is 800 nm. Their sizes are well-matched and work synergistically. Simultaneously, controlling the height of the submicron protrusion 10 and the period of the nanostripes 20 to be on the same order of magnitude (both in the range of hundreds of nanometers to micrometers), and avoiding a strict integer multiple relationship between them, effectively prevents destructive interference of incident light of specific wavelengths. It should be noted that if their sizes are strictly integer multiples, light of a specific wavelength, after being reflected by the nanostripes 20 and the submicron protrusion 10, is prone to producing reflected light with opposite phases, canceling each other out and leading to light energy loss.

[0034] In some embodiments, the nanostripes include low spatial frequency stripes and high spatial frequency stripes, with the high spatial frequency stripes located on the sidewall surfaces of the low spatial frequency stripes. The period of the low spatial frequency stripes is larger than that of the high spatial frequency stripes. Specifically, the low spatial frequency stripes may be located on the top surface of the submicron protrusion 10, and the high spatial frequency stripes may be located on the four inclined surfaces of the submicron protrusion 10. The periods of the low spatial frequency stripes and the high spatial frequency stripes are different. The high spatial frequency stripes are more densely packed, thus allowing for a smooth transition of the refractive index of light from air to the submicron protrusion 10, thereby fundamentally achieving Fresnel reflection.

[0035] In a specific embodiment, the period of the low spatial frequency stripe is 500nm~1000nm. Optionally, the period of the low spatial frequency stripe can be 500nm, 600nm, 700nm, 800nm, 900nm, or 1000nm; preferably, the period of the low spatial frequency stripe can be 800nm. The period of the high spatial frequency stripe is 50nm~100nm. Optionally, the period of the high spatial frequency stripe can be 50nm, 60nm, 70nm, 80nm, 90nm, or 100nm; preferably, the period of the high spatial frequency stripe can be 80nm.

[0036] For some implementation methods, please refer to Figure 1 The submicron protrusion 10 includes a top region and a bottom region 103 along its height direction. The density of nanostripes 20 in the top region 101 is greater than that in the bottom region 103. Specifically, the top region refers to the tip of the submicron protrusion 10 that is furthest from the crystalline silicon substrate in the height direction. This region is the first point of contact between incident light and the area where light reflection loss is most likely to occur. The bottom region 103 refers to the connection point between the submicron protrusion 10 and the crystalline silicon substrate. This region needs to balance light absorption effect and structural connection stability.

[0037] In a specific embodiment, the number of nanostripes 20 in the top region 101 is greater than the number of nanostripes 20 in the bottom region 103. More nanostripes 20 can increase the number of reflections and refractions of incident light and reduce the loss of light directly reflected from the substrate. Preferably, the spacing between the nanostripes 20 in the top region 101 is smaller than the spacing between the nanostripes 20 in the bottom region 103. The difference in spacing further enhances the density gradient. The narrower stripe spacing at the top can achieve denser light reflection, while the wider stripe spacing at the bottom can avoid structural stress concentration caused by excessive stripe density, and at the same time reserve reasonable space for carrier transport.

[0038] For some implementation methods, please refer to Figure 1Along the height direction of the submicron protrusion 10, the density of the nanostripes 20 decreases from the top region 101 to the bottom region 103. Specifically, the submicron protrusion 10 also includes a sloped region 102, which is located between the top region 101 and the bottom region 103 and serves as a transition connecting the top and bottom. Along the height direction of the submicron protrusion 10, the three regions are arranged sequentially as the top region 101, the sloped region 102, and the bottom region 103.

[0039] In a specific embodiment, please refer to Figure 1 In sections b) and d), the density of the nano-stripes 20 also follows the same gradient law, that is, the density of the nano-stripes 20 in the top region 101 is greater than that in the sloping region 102, and the density of the nano-stripes 20 in the sloping region 102 is greater than that in the bottom region 103. This continuously decreasing gradient design allows incident light, after entering from the top region 101, to be gradually reflected and refracted through the nano-stripes 20 of different densities, thus extending the propagation path of the light inside the substrate and maximizing the capture of the incident light.

[0040] In a specific embodiment, no nanostripes 20 are formed in the bottom region 103; instead, nanostripes 20 are formed only in the top region 101 and the sloped region 102, with the nanostripe density in the top region 101 being greater than that in the sloped region 102. The bottom region 103 serves as the connection point between the submicron protrusion 10 and the crystalline silicon substrate, its function being to ensure the stability of the structural connection and the smoothness of the subsequent metal electrodes. Therefore, there is no need to enhance light absorption performance through nanostripes 20.

[0041] In a specific embodiment, the top region 101 may include the top surface as described in the above embodiments, and the sloped region 102 may include the sloped surface as described in the above embodiments. It is understood that the sloped region 102 only includes the first nano-stripes or the second nano-stripes 20 extending from the top region 101, so the number of nano-stripes 20 in the top region 101 is greater than the number of nano-stripes 20 in the sloped region 102. Furthermore, the nano-stripes 20 on the slope extend to the middle position of the slope, that is, the nano-stripes 20 on the slope do not extend to the bottom region 103.

[0042] In some embodiments, the equivalent refractive index of the region containing the nanostripes 20 is greater than the refractive index of air, and the equivalent refractive index of the region containing the nanostripes 20 is less than the bulk refractive index of the submicron protrusions 10. It should be noted that Fresnel reflection mainly arises from the abrupt change in refractive index between the two media. When light is incident from air (low refractive index) to the bulk of the submicron protrusions 10 (high refractive index), the rapid change in refractive index causes some light to be reflected, resulting in light energy loss.

[0043] In a specific embodiment, the gradient design of the refractive index can suppress Fresnel reflection. The equivalent refractive index of the region where the nano-stripes 20 are located is between that of air and the body of the submicron protrusions 10, forming a continuous refractive index transition from air to the body of the submicron protrusions 10, which effectively alleviates the reflection problem caused by the abrupt change in refractive index, thereby suppressing the occurrence of Fresnel reflection.

[0044] In some embodiments, the equivalent refractive index of the region where the nano-stripes 20 are located, the bulk refractive index of the submicron protrusions 10, and the bulk refractive index of the crystalline silicon substrate are 1.5, 3.0, and 3.5, respectively. Specifically, the composite textured structure forms a continuous refractive index transition system from air (refractive index approximately 1.0) → the region of nano-stripes 20 (1.5) → the bulk of the submicron protrusions 10 (3.0) → the bulk of the crystalline silicon substrate (3.5), which completely alleviates the problem of abrupt changes in refractive index between different media and can more efficiently suppress Fresnel reflection.

[0045] In a specific embodiment, the equivalent refractive index of the nano-stripes 20 region 1.5 forms a gentle transition with the air refractive index, the submicron protrusion 103.0 bulk refractive index serves as an intermediate link, and then gradually transitions to the bulk refractive index of the crystalline silicon substrate 3.5. This stepped refractive index distribution not only minimizes the reflection loss of incident light, but also guides the orderly transport of photogenerated carriers, further improving the light absorption efficiency and photoelectric conversion performance of the solar cell.

[0046] In some embodiments, the depth of the nanostripes 20 is 10 nm to 200 nm. Optionally, the depth of the nanostripes 20 can be 10 nm, 20 nm, 30 nm, 50 nm, 100 nm, 150 nm, or 200 nm. This range ensures that the nanostripes 20 has sufficient structural strength, avoiding the problems of easy structural damage and poor refractive index control caused by excessively shallow depths, while also preventing increased fabrication difficulty and material waste caused by excessively deep depths. Furthermore, it synergistically matches the period of the nanostripes 20 and the size of the submicron protrusions 10, ensuring that the nanostripes 20 can effectively suppress Fresnel reflection and enhance light absorption, further improving the overall performance of the composite textured structure.

[0047] In some embodiments, the angle formed between the ridge of the submicron protrusion 10 and the surface of the crystalline silicon substrate is 45° to 85°. Optionally, the angle formed between the ridge of the submicron protrusion 10 and the surface of the crystalline silicon substrate is 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, or 85°. This range ensures that the submicron protrusion 10 has sufficient surface slope to achieve multi-level light reflection and extend the propagation path of incident light inside the substrate, while avoiding weakened light reflection due to an excessively small angle or decreased structural stability due to an excessively large angle.

[0048] This invention also provides a method for preparing a composite textured structure for solar cells. This method is used to prepare the composite textured structure for solar cells as described in the above embodiments. Please refer to... Figure 2 and Figure 3 The preparation methods include: Step S100: Submicron bumps are fabricated on the surface of a crystalline silicon substrate using a chemical etching process; In step S200, nano-stripes are created on the submicron raised surface using a laser-induced periodic surface structure process.

[0049] In a specific embodiment, please refer to Figure 3 In step S100 (a), an alkaline etching system (such as sodium hydroxide and isopropanol, NaOH / IPA) can be used. By controlling parameters such as etching temperature, etching time, and etching solution concentration, the size, morphology, and uniformity of the submicron bumps can be precisely controlled, ensuring that parameters such as the height and edge angle of the submicron bumps meet the design requirements. Chemical etching has the advantages of simple operation, low cost, and strong adaptability to large-scale production, and can achieve uniform preparation of submicron bumps on the surface of crystalline silicon substrates.

[0050] In a specific embodiment, in step S200, please refer to... Figure 3 In sections b) and c), the LIPSS process is used to induce periodic nanostripes on the surface of submicron protrusions by utilizing the interference effect of lasers and the self-organizing properties of materials. This process has the advantages of high preparation precision, good structural uniformity, and minimal damage to materials. It can precisely control parameters such as the period, depth, and orientation of nanostripes to ensure the structural compatibility of nanostripes with submicron protrusions, while avoiding damage to the structure of submicron protrusions and ensuring the overall performance of the composite textured surface structure.

[0051] In some embodiments, in step S200, the wavelength of the laser is 1020 nm to 1064 nm. Optionally, the wavelength of the laser can be 1020 nm, 1030 nm, 1040 nm, 1050 nm, 1060 nm, or 1064 nm; preferably, the wavelength of the laser can be 1030 nm. Lasers in this wavelength range have good absorption effects on crystalline silicon materials, effectively inducing the formation of periodic nanostripes on the material surface, while avoiding excessive ablation of the material due to excessively short wavelengths or uneven stripe periods due to excessively long wavelengths.

[0052] In some embodiments, in step S200, the pulse width of the laser is 200 fs to 600 fs. Optionally, the pulse width of the laser can be 200 fs, 300 fs, 400 fs, 500 fs, or 600 fs; preferably, the pulse width of the laser can be 300 fs to 500 fs. This pulse width falls within the category of femtosecond lasers. Femtosecond lasers have the advantages of short pulse duration, high peak power, and low thermal damage, enabling cold processing on the surface of crystalline silicon materials. This avoids problems such as surface amorphization and increased defects caused by thermal effects, ensuring the structural integrity and optical performance of the nanofibers.

[0053] For some implementation methods, please refer to Figure 5 In step S200, the energy density of the laser is 0.12 J / cm². 2 ~0.30J / cm 2 Optionally, the laser energy density can be 0.12 J / cm². 2 0.14J / cm 2 0.16J / cm 2 0.18J / cm 2 0.20J / cm 2 0.25J / cm 2 0.30J / cm 2 Preferably, the energy density of the laser can be 0.15 J / cm². 2 ~0.25J / cm 2 This energy density range is near the LIPSS induction threshold of crystalline silicon materials, which can ensure the successful induction of nanostripes while avoiding material ablation and structural damage caused by excessive energy density.

[0054] For some implementation methods, please refer to Figure 5 In step S200, the laser scanning speed is 5 mm / s to 100 mm / s. Optionally, the laser scanning speed can be 5 mm / s, 10 mm / s, 20 mm / s, 30 mm / s, 40 mm / s, 50 mm / s, 60 mm / s, 70 mm / s, 80 mm / s, 90 mm / s, or 100 mm / s; alternatively, the laser scanning speed can be 10 mm / s to 50 mm / s. This range ensures both the quality of the nanostripe fabrication and production efficiency, adapting to the needs of large-scale production.

[0055] In some embodiments, in step S200, the laser is linearly polarized, and the polarization direction forms an angle of 0° to 90° with the scanning direction. Optionally, the angle between the polarization direction and the scanning direction is 10°, 20°, 30°, 40°, 50°, 60°, 70°, or 80°; preferably, the polarization direction forms an angle of 45° with the scanning direction. By controlling the angle between the polarization direction and the scanning direction, the extension direction of the nanofibers can be precisely controlled, making it perpendicular or parallel to the extension direction of the ridges of the submicron protrusions, ensuring the optical performance of the composite textured structure, and adapting to the fabrication requirements of submicron protrusions of different sizes and morphologies.

[0056] For some implementation methods, please refer to Figure 4 In step S200, the present invention uses a femtosecond laser to act on the submicron protruding surface. Due to the lightning rod effect, the electric field is significantly localized and focused at the top of the submicron protrusion (radius of curvature < 50 nm), achieving a 3-5 times directional enhancement of the local electric field intensity. Relying on the spatially differentiated energy distribution, the selective and controllable construction of multi-region microstructures is achieved. In this way, dense and ordered nanostripes are formed in the top region; sparse nanostripes are formed in the sloping region, which moderately increases the specific surface area while taking into account the material's optical absorption and optical gain performance, achieving a synergistic balance of functional characteristics; in the bottom region, the electric field has no focusing gain and the laser energy density is lower than the critical threshold for structural modification, and the original submicron morphology of the substrate is completely preserved, providing a flat contact surface for subsequent metal electrode deposition and ensuring electrode adhesion and conductive contact stability.

[0057] The technical solution of the present invention will be described in detail below through specific embodiments.

[0058] Example 1 This embodiment provides a solar cell and its fabrication method. This embodiment uses an N-type silicon wafer with dimensions of 182×182mm as the substrate. The resistivity of the silicon wafer is 1Ω·cm to 3Ω·cm, and the thickness of the silicon wafer is 130μm. The crystalline silicon substrate of the solar cell has a composite textured structure, which includes submicron protrusions (0.7μm in height) and nanoscale stripes (800nm ​​period). The specific steps of the fabrication method include the following: Step (1), silicon wafer cleaning and alkaline etching to prepare submicron pyramids: After the N-type single crystal silicon wafer is cleaned by RCA standard, it is immersed in etching solution. The etching solution is a mixed aqueous solution of 3wt% NaOH and 5vol% IPA. The etching temperature is 82℃ and the etching time is 12min. After etching, it is rinsed with deionized water and dried with nitrogen to obtain a crystalline silicon substrate with submicron pyramid protrusions on the surface. The pyramid height is 0.7μm and the angle between the edge and the bottom surface is 54.7°.

[0059] Step (2), femtosecond laser-induced nanostripes: A linearly polarized femtosecond laser with a wavelength of 1030 nm, a pulse width of 300 fs, an energy density of 0.18 J / cm², a scanning speed of 20 mm / s, and a polarization direction at a 45° angle to the scanning direction was used to induce the formation of nanostripes with a period of 800 nm and a depth of 50 nm on the surface of the submicron pyramid. After laser treatment, the surface debris was removed by ultrasonic cleaning with acetone for 5 min.

[0060] Step (3), Preparation of tunneling oxide layer and back polycrystalline silicon layer: A 1.2 nm SiO layer is grown on the back side of the silicon wafer using thermal oxidation. x The oxide layer is tunneled through, and then a 150 nm phosphorus-doped amorphous silicon layer is deposited using PECVD. After annealing and crystallization at 900 °C, a phosphorus-doped polycrystalline silicon layer is formed.

[0061] Step (4), preparation of front-side emitter and passivation layer: A boron-doped p+ emitter is formed on the front side using BBr3 tubular diffusion, with sheet resistance controlled at 120 Ω / sq; a 15 nm Al2O3 passivation layer is deposited using ALD, followed by a 75 nm SiN layer deposited using PECVD. x Anti-reflective coating.

[0062] Step (5), metal electrode preparation and sintering: silver grid lines are printed on the front side and copper grid lines are printed on the back side by screen printing. Ohmic contacts are formed by rapid sintering to obtain solar cells.

[0063] The performance test results of this solar cell include: under standard test conditions (AM1.5G, 100mW / cm²) 2 At 25℃, the battery conversion efficiency was measured to be 25.3%, the open-circuit voltage to be 721mV, and the short-circuit current density to be 41.2mA / cm². 2 The fill factor is 85.2%; the weighted average reflectance in the 300nm~1100nm band is 2.8%.

[0064] Example 2 This embodiment provides a solar cell and its fabrication method. This embodiment uses an N-type silicon wafer with dimensions of 182×182mm as the substrate. The resistivity of the silicon wafer is 1Ω·cm to 3Ω·cm, and the thickness of the silicon wafer is 130μm. The crystalline silicon substrate of the solar cell has a composite textured structure, which includes submicron protrusions (0.6μm in height) and nanoscale stripes (500nm period). The specific steps of the fabrication method include the following: Step (1), silicon wafer cleaning and alkaline etching to prepare submicron pyramids: After cleaning the N-type single crystal silicon wafer with RCA standard, it is immersed in an etching solution. The etching solution is a mixed aqueous solution of 2.5wt% NaOH and 6vol% IPA. The etching temperature is 80℃ and the etching time is 10min, resulting in submicron protrusions with a pyramid height of 0.6μm.

[0065] Step (2), femtosecond laser-induced nanostripes: A linearly polarized femtosecond laser with a wavelength of 1030 nm, a pulse width of 250 fs, an energy density of 0.15 J / cm², a scanning speed of 15 mm / s, and a polarization direction at a 0° angle to the scanning direction was used to induce the formation of nanostripes with a period of 500 nm and a depth of 30 nm on the surface of the pyramid. After laser treatment, the surface was ultrasonically cleaned with acetone for 5 min.

[0066] Step (3), Preparation of tunneling oxide layer and back polycrystalline silicon layer: A 1.0 nm SiO layer is grown on the back side of the silicon wafer using thermal oxidation. x The oxide layer is tunneled through, and then a 120 nm phosphorus-doped amorphous silicon layer is deposited by PECVD, followed by annealing and crystallization at 920 °C.

[0067] Step (4), preparation of front-side emitter and passivation layer: A boron-doped p+ emitter is formed on the front side using BBr3 tubular diffusion, with a sheet resistance of 110 Ω / sq; a 12 nm Al2O3 passivation layer is deposited using ALD, followed by an 80 nm SiN layer deposited using PECVD. x Anti-reflective coating.

[0068] Step (5), metal electrode preparation and sintering: same as in Example 1, to obtain a solar cell.

[0069] The performance test results of this solar cell include: under standard test conditions (AM1.5G, 100mW / cm²) 2 At 25℃, the battery conversion efficiency was measured to be 25.6%, the open-circuit voltage to be 725mV, and the short-circuit current density to be 41.5mA / cm². 2 The fill factor is 85.1%; the weighted average reflectance in the 300nm~1100nm band is 2.5%.

[0070] Example 3 This embodiment provides a solar cell and its fabrication method. This embodiment uses an N-type silicon wafer with dimensions of 210×210mm as the substrate. The resistivity of the silicon wafer is 1Ω·cm to 3Ω·cm, and the thickness of the silicon wafer is 150μm. The crystalline silicon substrate of the solar cell has a composite textured structure, which includes submicron protrusions (0.8μm in height) and nanoscale stripes (1000nm period). The specific steps of the fabrication method include the following: Step (1), silicon wafer cleaning and alkaline etching to prepare submicron pyramids: after cleaning the N-type single crystal silicon wafer with RCA standard, it is immersed in an etching solution, which is a mixed aqueous solution of 4wt% NaOH and 4vol% IPA. The etching temperature is 85℃ and the etching time is 15min, resulting in submicron protrusions with a pyramid height of 0.8μm.

[0071] Step (2), femtosecond laser-induced nanostripes: A linearly polarized femtosecond laser with a wavelength of 1064nm, a pulse width of 500fs, an energy density of 0.25J / cm², a scanning speed of 50mm / s, and a polarization direction at a 90° angle to the scanning direction was used to induce the formation of nanostripes with a period of 1000nm and a depth of 80nm on the surface of the pyramid. After laser treatment, the surface was ultrasonically cleaned with acetone for 5min.

[0072] Step (3), Preparation of tunneling oxide layer and back polycrystalline silicon layer: A 1.5 nm SiO layer is grown on the back side of the silicon wafer using thermal oxidation. x The oxide layer is tunneled through, and then a 180 nm phosphorus-doped amorphous silicon layer is deposited by PECVD, followed by annealing and crystallization at 880 °C.

[0073] Step (4), preparation of front-side emitter and passivation layer: A boron-doped p+ emitter is formed on the front side using BBr3 tubular diffusion, with a sheet resistance of 130 Ω / sq; an 18 nm Al2O3 passivation layer is deposited using ALD, followed by a 70 nm SiN layer deposited using PECVD. x Anti-reflective coating.

[0074] Step (5), metal electrode preparation and sintering: same as in Example 1, to obtain a solar cell.

[0075] The performance test results of this solar cell include: under standard test conditions (AM1.5G, 100mW / cm²) 2 At 25℃, the battery conversion efficiency was measured to be 25.1%, the open-circuit voltage to be 718mV, and the short-circuit current density to be 40.8mA / cm². 2 The fill factor is 85.5%; the weighted average reflectance in the 300nm~1100nm band is 3.1%.

[0076] Comparative Example 1 This comparative example provides a solar cell and its fabrication method. The comparative example uses an N-type silicon wafer with dimensions of 182×182mm as the substrate. The resistivity of the silicon wafer is 1Ω·cm to 3Ω·cm, and the thickness of the silicon wafer is 130μm. The crystalline silicon substrate of the solar cell has a textured structure, which includes submicron protrusions (0.7μm in height). The laser processing in step (2) is omitted from the fabrication method; the remaining steps are the same as in Example 1.

[0077] The performance test results of this solar cell include: under standard test conditions (AM1.5G, 100mW / cm²) 2 At 25℃, the battery conversion efficiency was measured to be 24.4%, the open-circuit voltage to be 724mV, and the short-circuit current density to be 39.6mA / cm². 2 The fill factor is 85.0%; the weighted average reflectance in the 300nm~1100nm band is 5.2%.

[0078] Comparative Example 2 This comparative example provides a solar cell and its fabrication method. The comparative example uses an N-type silicon wafer with dimensions of 182×182mm as the substrate. The resistivity of the silicon wafer is 1Ω·cm to 3Ω·cm, and the thickness of the silicon wafer is 130μm. The solar cell has a single-level nanostructure on its crystalline silicon substrate. In the fabrication method, the alkaline etching in step (1) is omitted; instead, a femtosecond laser is used to directly induce the formation of nanostripes with a period of 800nm ​​on the planar silicon surface. The remaining steps are the same as in Example 1.

[0079] The performance test results of this solar cell include: under standard test conditions (AM1.5G, 100mW / cm²) 2 At 25℃, the battery conversion efficiency was measured to be 23.0%, the open-circuit voltage to be 715mV, and the short-circuit current density to be 38.5mA / cm². 2 The fill factor is 83.5%; the weighted average reflectance in the 300nm~1100nm band is 6.0%.

[0080] The test results of Example 1 and Comparative Example 1 show that, in the process of fabricating solar cells using the same silicon wafer as the substrate, the process of creating submicron bumps on the surface of the crystalline silicon substrate through chemical etching has an impact on the performance of the solar cell. This is because nanoscale stripes can form a micro-nano secondary composite structure with the submicron bumps, achieving a dual-scale synergistic effect. Without significantly increasing the surface area, this uniformly reduces the reflectivity of light in the 300nm~1100nm wavelength band, enabling wide-band light absorption, especially near-infrared light. Therefore, the reflectivity of Example 1 is only 2.8%, while the reflectivity of Comparative Example 1 is as high as 5.2%, and the overall performance of the solar cell in Comparative Example 1 is significantly lower.

[0081] The test results from Example 1 and Comparative Example 2 show that, in the process of fabricating solar cells using the same silicon wafer as the substrate, the process of creating nano-stripes on the surface of the submicron protrusions through laser-induced periodic surface structure technology has an impact on the performance of the solar cells. This is because chemical etching can initially form submicron protrusions, creating a basic light trap structure on the crystalline silicon substrate. These submicron protrusions provide the basis for Mie scattering, effectively extending the optical path of incident light, enhancing multi-angle light scattering and coupling absorption, and significantly reducing specular reflection on the cell surface. Therefore, the reflectivity of Example 1 is only 2.8%, while the reflectivity of Comparative Example 2 is as high as 6.0%, and the overall performance of the solar cell in Comparative Example 2 is significantly lower.

[0082] The test results of Examples 1 and 2 show that, in the process of fabricating solar cells using the same silicon wafer as a substrate, the performance of the solar cells is affected by adaptively adjusting the parameters of the submicron bumps and nanostripes. Therefore, the parameters of the submicron bumps and nanostripes need to be within a suitable range; excessively high or low parameters (height or period) will significantly affect the performance of the solar cells. The test results of Examples 1 and 3 show that the preparation method provided by this invention can be adapted to solar cells of different specifications. Therefore, the preparation method provided by this invention has universality for solar cells and significant industrial value.

[0083] In the description of the embodiments of this application, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and other indicators are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0084] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A composite textured surface structure for a solar cell, characterized in that, The invention includes a crystalline silicon substrate, wherein submicron protrusions are formed on the surface of the crystalline silicon substrate, and the surface of the submicron protrusions has nano-stripes, the extension direction of which is perpendicular to or parallel to the extension direction of the ridges of the submicron protrusions.

2. The composite textured surface structure of the solar cell according to claim 1, characterized in that, The height of the submicron protrusion is 0.6μm to 0.8μm, and / or the period of the nanostripe is 50nm to 1000nm.

3. The composite textured surface structure of the solar cell according to claim 1, characterized in that, The nanostripes include low spatial frequency stripes and high spatial frequency stripes, with the high spatial frequency stripes located on the sidewall surface of the low spatial frequency stripes, and the period range of the low spatial frequency stripes being larger than that of the high spatial frequency stripes.

4. The composite textured surface structure of the solar cell according to claim 1, characterized in that, The submicron protrusion includes a top region and a bottom region along the height direction, and the nanostripe density of the top region is greater than that of the bottom region.

5. The composite textured surface structure of the solar cell according to claim 3, characterized in that, Along the height direction of the submicron protrusion, the density of the nanostripes decreases from the top region to the bottom region.

6. The composite textured surface structure of the solar cell according to claim 1, characterized in that, The equivalent refractive index of the region containing the nanostripes is greater than the refractive index of air, and the equivalent refractive index of the region containing the nanostripes is less than the bulk refractive index of the submicron protrusion.

7. The composite textured surface structure of the solar cell according to claim 1, characterized in that, The depth of the nanostripes is 10nm~200nm, and the angle formed between the submicron protrusions and the surface of the crystalline silicon substrate is 45°~85°.

8. A method for preparing a composite textured surface structure for a solar cell, characterized in that, The preparation method is used to prepare a composite textured structure for a solar cell as described in any one of claims 1-7, and the preparation method includes: Step S100: Submicron bumps are fabricated on the surface of a crystalline silicon substrate using a chemical etching process; In step S200, nano-stripes are created on the surface of the submicron protrusions using a laser-induced periodic surface structure process.

9. The preparation method according to claim 8, characterized in that, In step S200, the wavelength of the laser is 1020 nm to 1064 nm, the pulse width of the laser is 200 fs to 600 fs, and the energy density of the laser is 0.12 J / cm². 2 ~0.30J / cm 2 .

10. The preparation method according to claim 8, characterized in that, In step S200, the scanning speed of the laser is 5 mm / s to 100 mm / s, the polarization direction of the laser is linearly polarized, and the polarization direction forms an angle of 0° to 90° with the scanning direction.

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