Method for manufacturing a solar cell, solar cell and photovoltaic module

Abstract

This application relates to the photovoltaic field, providing a method for fabricating a solar cell, a solar cell, and a photovoltaic module. The method includes: providing a pre-formed silicon wafer with a pre-formed surface; controlling multiple first pulses in a pulsed laser to scan sites on the pre-formed surface to form active sites by activating the sites; controlling multiple second pulses in the pulsed laser to scan the active sites to selectively etch the pre-formed silicon wafer to obtain a silicon wafer; the etched pre-formed surface forms a textured surface, and the selective etching characterizes the etching of portions at the active sites on the pre-formed silicon wafer. The multiple first pulses and multiple second pulses are multiple pulses emitted sequentially by the pulsed laser in the same scanning step, and the energy density of the pulses in the pulsed laser is lower than the energy threshold for polishing the pre-formed surface. This application at least helps to improve the problems of low cell efficiency caused by disordered textured surfaces, large thermal damage, and poor passivation performance in laser texturing in the prior art.

Description

Technical Field

[0001] This application relates to the photovoltaic field, and in particular to a method for preparing a solar cell, a solar cell, and a photovoltaic module. Background Technology

[0002] Current texturing technology for crystalline silicon solar cells mainly relies on wet chemical methods or traditional laser texturing. Traditional laser texturing achieves micro-nano structures through laser ablation, which has advantages such as being pollution-free and fast. However, traditional high-energy laser scanning is prone to forming disordered textured surfaces, resulting in significant thermal damage and severe surface recombination, which affects passivation and cell efficiency. Summary of the Invention

[0003] This application provides a method for preparing a solar cell, a solar cell, and a photovoltaic module, which at least helps to improve the problem of low cell efficiency caused by the disordered texture, large thermal damage, and poor passivation performance of laser texturing in the prior art.

[0004] According to some embodiments of this application, one aspect of this application provides a method for fabricating a solar cell, comprising: providing a pre-existing silicon wafer having a pre-existing surface; controlling a plurality of first pulses in a pulsed laser to scan sites on the pre-existing surface to form active sites by activating the sites; controlling a plurality of second pulses in the pulsed laser to scan the active sites to selectively etch the pre-existing silicon wafer to obtain a silicon wafer; forming a textured surface on the etched pre-existing surface, wherein the selective etching characterizes etching of portions at the active sites on the pre-existing silicon wafer, the plurality of first pulses and the plurality of second pulses are a plurality of pulses emitted sequentially by the pulsed laser in the same scanning step, wherein the energy density of the pulses in the pulsed laser is lower than the energy threshold for polishing the pre-existing surface; and forming a functional layer on the textured surface to obtain a solar cell.

[0005] In some embodiments, the energy density of the pulse in the pulsed laser ranges from 0.18 J / cm² to 0.22 J / cm².

[0006] In some embodiments, the scanning overlap rate of two adjacent pulses in the pulsed laser is greater than or equal to 90%.

[0007] In some embodiments, before scanning sites on the prepared surface with a plurality of first pulses in a controlled pulsed laser, the method further includes: placing the prepared silicon wafer in a texturing chamber and introducing a mixed gas, the mixed gas comprising nitrogen, oxygen and fluorine-based gas, into the texturing chamber.

[0008] In some embodiments, the volume percentage of oxygen in the mixed gas is 1 vol% to 2 vol%, the volume percentage of fluorine-based gas is 0.5 vol% to 1 vol%, and the volume percentage of nitrogen is 97 vol% to 98.5 vol%.

[0009] In some embodiments, the scanning frequency of the pulsed laser ranges from 40 kHz to 80 kHz, and the scanning speed of the pulsed laser ranges from 6 m / s to 8 m / s.

[0010] In some embodiments, the number of the first pulses is 3 to 5, and the number of the second pulses is 5 to 10.

[0011] In some embodiments, during the scanning of the prepared silicon wafer by the pulsed laser, the scanning frequency, scanning speed, scanning overlap rate, and energy density of the pulses in the pulsed laser remain unchanged.

[0012] In some embodiments, the spot diameter of each pulse in the pulsed laser ranges from 0.08 mm to 0.15 mm.

[0013] According to some embodiments of this application, another aspect of this application provides a solar cell, which is prepared using any of the solar cell preparation methods described above.

[0014] According to some embodiments of this application, another aspect of this application provides a photovoltaic module, including: a battery string, formed by connecting a plurality of the aforementioned solar cells; an encapsulating film for covering the surface of the battery string; and a cover plate for covering the surface of the encapsulating film facing away from the battery string.

[0015] The technical solution provided in this application has at least the following advantages:

[0016] First, a pre-existing silicon wafer with a pre-existing surface is provided. Then, multiple first pulses in a pulsed laser are controlled to scan the sites on the pre-existing surface to form active sites by activating the sites. Next, multiple second pulses in the pulsed laser are controlled to scan the active sites to selectively etch the pre-existing silicon wafer to obtain a silicon wafer. The etched pre-existing surface forms a textured surface. Finally, a functional layer is formed on the textured surface to obtain a solar cell. Here, selective etching indicates that the active sites on the pre-existing silicon wafer are etched. The multiple first pulses and multiple second pulses are multiple pulses emitted sequentially by the pulsed laser in the same scanning step. The energy density of the pulses in the pulsed laser is lower than the energy threshold of polishing the pre-existing surface. Compared to existing laser texturing technologies, which suffer from problems such as disordered textured surfaces, significant thermal damage, and poor passivation performance leading to low battery efficiency, this application applies subthreshold pulse energy in stages during a single laser scan. First, multiple first pulses with energy thresholds lower than the polishing preparation surface are used to scan the preparation surface, exciting silicon atoms in local areas to form active sites without actual etching. Then, multiple second pulses with the same energy density continuously bombard the activated sites (i.e., active sites), allowing energy to accumulate naturally and achieving selective etching only on the active sites. This means that controllable micro-nano etching only occurs at the active sites, avoiding disordered etching and forming an ordered textured surface, thereby improving the passivation performance of the battery. This process also avoids the amorphous layer and thermal damage caused by traditional high-energy ablation, ensuring high battery efficiency. Attached Figure Description

[0017] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the drawings in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional art, the drawings used in the embodiments 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 based on these drawings without creative effort.

[0018] Figure 1 A schematic flowchart illustrating a method for fabricating a solar cell according to an embodiment of this application;

[0019] Figure 2 This is a schematic diagram of the textured surface morphology of a solar cell under a scanning electron microscope, provided as an embodiment of this application. Detailed Implementation

[0020] As is known from the background art, existing laser texturing techniques suffer from problems such as disordered texturing surfaces, significant thermal damage, and poor passivation performance, resulting in low battery efficiency. To address these issues, this application provides a method for preparing a solar cell, a solar cell, and a photovoltaic module.

[0021] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0022] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0023] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0024] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0025] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of 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. Therefore, they should not be construed as limitations on the embodiments of this application.

[0026] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0027] In the accompanying drawings corresponding to the embodiments of this application, the thickness and area of ​​the layers are enlarged for better understanding and ease of description. When describing a component (such as a layer, film, region, or substrate) on or on the surface of another component, the component may be "directly" located on the surface of the other component, or there may be a third component between the two components. Conversely, when describing a component on the surface of another component, or when another component is formed or disposed on the surface of a component, it indicates that there is no third component between the two components. Furthermore, when describing a component as being "generally" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a portion of the edge of the entire surface.

[0028] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included. Furthermore, when a component such as a layer, film, region, or plate is referred to as being "on / located" on another component, it can be "directly on" the other component (i.e., located on the surface of the other component with no other components between them), or another component may be present therein. Moreover, when a component such as a layer, film, region, or plate is "directly located" on another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it indicates that no other components are located therein.

[0029] The terminology used in the description of the various embodiments described herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "foreword" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0030] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0031] This application provides a method for preparing a solar cell, such as... Figure 1 As shown, it includes:

[0032] Step S101: Provide a pre-silicon wafer, the pre-silicon wafer having a pre-surface;

[0033] In some embodiments, the material of the prepared silicon wafer may be at least one of monocrystalline silicon, polycrystalline silicon, amorphous silicon, or microcrystalline silicon.

[0034] In some embodiments, the prepared surface may be the front side of the prepared silicon wafer, the back side of the prepared silicon wafer, or both the front and back sides of the prepared silicon wafer. This application does not impose any specific limitations on this.

[0035] Step S102: Control multiple first pulses in the pulsed laser to scan the sites on the prepared surface to form active sites by activating the sites.

[0036] Optionally, an ultraviolet pulsed laser with a wavelength range of 340-360nm can be used. The wavelength of the ultraviolet pulsed laser can be 340nm, 355nm, or 360nm. This application does not impose any specific restrictions on this.

[0037] It should be noted that multiple first pulses only achieve surface pre-activation and generate active sites, without etching or significant morphological changes.

[0038] Step S103: Control the multiple second pulses in the pulsed laser to scan the active sites to selectively etch the prepared silicon wafer to obtain a silicon wafer; the etched prepared surface forms a textured surface; the selective etching characterizes the etching of the portion at the active sites of the prepared silicon wafer; the multiple first pulses and the multiple second pulses are multiple pulses emitted sequentially by the pulsed laser in the same scanning step; the energy density of the pulses in the pulsed laser is lower than the energy threshold for polishing the prepared surface.

[0039] It should be noted that, based on the activated surface, energy naturally accumulates, selectively etching to form an ordered textured surface.

[0040] Step S104: A functional layer is formed on the textured surface to obtain a solar cell.

[0041] In the above embodiments, a pre-existing silicon wafer with a pre-existing surface is first provided. Then, multiple first pulses in a pulsed laser are controlled to scan the sites on the pre-existing surface to form active sites by activating the sites. Then, multiple second pulses in a pulsed laser are controlled to scan the active sites to selectively etch the pre-existing silicon wafer to obtain a silicon wafer. The etched pre-existing surface forms a textured surface. Finally, a functional layer is formed on the textured surface to obtain a solar cell. Here, selective etching indicates that the active sites on the pre-existing silicon wafer are etched. The multiple first pulses and multiple second pulses are multiple pulses emitted sequentially by a pulsed laser in the same scanning step. The energy density of the pulses in the pulsed laser is lower than the energy threshold for polishing the pre-existing surface. Compared to existing laser texturing technologies, which suffer from problems such as disordered textured surfaces, significant thermal damage, and poor passivation performance leading to low battery efficiency, this application applies subthreshold pulse energy in stages during a single laser scan. First, multiple first pulses with energy thresholds lower than the polishing preparation surface are used to scan the preparation surface, exciting silicon atoms in local areas to form active sites without actual etching. Then, multiple second pulses with the same energy density continuously bombard the activated sites (i.e., active sites), allowing energy to accumulate naturally and achieving selective etching only on the active sites. This means that controllable micro-nano etching only occurs at the active sites, avoiding disordered etching and forming an ordered textured surface, thereby improving the passivation performance of the battery. This process also avoids the amorphous layer and thermal damage caused by traditional high-energy ablation, ensuring high battery efficiency.

[0042] In some embodiments, the solar cell described above can be any one of PERC cell (Passivated Emitter and Rear Cell), PERT cell (Passivated Emitter and Rear Totally Diffused Cell), TOPCon cell (Tunnel Oxide Passivated Contact), HIT / HJT cell (Heterojunction Technology), or BC cell (Back Contact). This application does not impose any specific limitations on this.

[0043] In some embodiments, taking a TOPCon battery as an example, the prepared surface is the front side of the prepared silicon wafer. A functional layer is formed on the textured surface, including: a first doped conductive layer, a passivation layer, and a first antireflection film are sequentially formed on the textured surface, and a plurality of spaced first metal electrodes are formed on the surface of the first antireflection film opposite to the silicon wafer; a tunneling oxide layer, a second doped conductive layer, and a second antireflection film are sequentially formed on the surface of the silicon wafer opposite to the emitter, and a plurality of spaced second metal electrodes are formed on the surface of the second antireflection film opposite to the silicon wafer. The silicon wafer is used to receive incident light and generate photogenerated carriers. The first and second metal electrodes are used to collect these photogenerated carriers. The passivation layer prevents oxidation or corrosion of the first doped conductive layer surface, thus improving the stability and lifespan of the solar cell. The tunneling oxide layer provides chemical passivation. Due to interface state defects on the silicon wafer surface, the tunneling oxide layer saturates the dangling bonds on the silicon wafer surface, reducing the defect state density and recombination centers, thereby lowering the carrier recombination rate and resulting in a higher interface state density. This increased density promotes the recombination of photogenerated carriers, increasing the fill factor, short-circuit current, and open-circuit voltage of the solar cell, thus improving its photoelectric conversion efficiency. The first and second antireflective coatings reduce the reflectivity of sunlight on the solar cell surface, allowing more light to be absorbed and converted into electrical energy, thereby improving the light absorption efficiency of the solar cell. Furthermore, the antireflective coating protects the internal structure of the solar cell, preventing environmental pollution and enhancing its stability.

[0044] In some embodiments, the material of the passivation layer may include one or more of the following: silicon oxide, silicon nitride, silicon oxynitride, silicon carbonitride, titanium oxide, hafnium oxide, or aluminum oxide. The passivation layer may be a single-layer structure or a stacked structure. For example, the single-layer structure may be a single-layer aluminum oxide film, a single-layer silicon oxide film, a single-layer silicon nitride film, or a single-layer silicon oxynitride film. The stacked structure may be composed of at least two layers selected from aluminum oxide film, silicon oxide film, silicon nitride film, or silicon oxynitride film. The silicon wafer can be an N-type semiconductor silicon wafer or a P-type semiconductor silicon wafer. The N-type semiconductor silicon wafer is doped with an N-type dopant element, which can be at least one of group V elements such as phosphorus (P), bismuth (Bi), antimony (Sb), or arsenic (As). The P-type semiconductor silicon wafer is doped with a P-type dopant element, which can be at least one of group III elements such as boron (B), aluminum (Al), gallium (Ga), or indium (In). The material of the tunneling oxide layer can be at least one of silicon oxide, silicon nitride, silicon oxynitride, silicon carbide, or magnesium fluoride.

[0045] In one alternative embodiment, the energy density of the pulses in the aforementioned pulsed laser ranges from 0.18 J / cm² to 0.22 J / cm². In this embodiment, the pulse energy density range (0.18-0.22 J / cm²) is within the subthreshold range, which allows for surface activation and controllable etching through multi-pulse accumulation while avoiding thermal damage and excessive amorphous layer thickness caused by single-pulse high-energy ablation. This results in the synergistic formation of a low-damage, highly uniform ordered microtexture structure in a single scan, further improving passivation quality and battery efficiency.

[0046] In some embodiments, the energy density of the pulse in the pulsed laser is 0.18–0.22 J / cm² (i.e., subthreshold energy), which is lower than the single-pulse etching threshold of 0.26–0.32 J / cm² for pristine polished silicon.

[0047] In another alternative embodiment, the scanning overlap rate of two adjacent pulses in the aforementioned pulsed laser is greater than or equal to 90%. In this embodiment, by setting the scanning overlap rate of adjacent pulses to ≥90%, it can be ensured that each site on the prepared surface stably receives multiple consecutive first pulses and multiple second pulses during a single scan, achieving uniform energy accumulation and realizing the effect of activation followed by cumulative etching. This results in the formation of an ordered, low-damage, and highly uniform micro / nano texturing structure in a single scan, significantly improving passivation compatibility and light absorption performance, and significantly suppressing the problem of local over-etching or under-etching caused by uneven pulse distribution in traditional laser texturing. The scanning overlap rate of the two pulses mentioned above refers to the proportion of the area of ​​the overlapping spots of two adjacent pulses to the area of ​​a single spot.

[0048] In another alternative embodiment, before scanning the sites on the prepared surface using multiple first pulses of the controlled pulsed laser, the method further includes: placing the prepared silicon wafer in a texturing chamber and introducing a mixed gas, including nitrogen, oxygen, and a fluorine-based gas, into the texturing chamber. In this embodiment, by introducing a mixed gas containing nitrogen, oxygen, and a fluorine-based gas into the texturing chamber and placing the silicon wafer in this stable and controllable weakly oxidizing fluorine-containing environment before laser scanning, the synergistic effect of the laser texturing process can be significantly enhanced: nitrogen acts as an inert carrier gas to maintain environmental stability, while oxygen promotes the oxidation of the silicon surface to form SiO₂ that can be selectively etched by fluorine species. x The layer, with fluorine-based gas providing active fluorine atoms for SiO2 reaction. x Layer reaction generates volatile SiF x It is the etching source for forming micro-nano textured surfaces, enabling selective etching of active sites, thereby achieving low-damage chemical-assisted etching.

[0049] According to some exemplary embodiments of this application, in the above-mentioned mixed gas, the volume percentage of oxygen is 1 vol% to 2 vol%, the volume percentage of fluorine-based gas is 0.5 vol% to 1 vol%, and the volume percentage of nitrogen is 97 vol% to 98.5 vol%. In this embodiment, when the oxygen in the mixed gas is controlled at 1-2 vol%, the fluorine-based gas is 0.5-1 vol%, and the nitrogen is supplemented to 97-98.5 vol%, a balance between chemical activity and process stability is achieved: trace amounts of oxygen are sufficient to form a uniform, thin layer of active oxide (SiO2) on the prepared silicon wafer surface. x The fluorine-based gas layer provides controllable sites for selective reaction, promoting directional etching under low temperature and low energy conditions. The concentration of fluorine-based gas is controlled at 0.5-1 vol%, which reduces over-etching or accumulation of gaseous byproducts and ensures that etching only occurs in the laser-activated area. A high proportion of nitrogen gas is used as the main carrier gas to maintain stable chamber pressure, suppress non-target oxidation or contamination, and ensure uniform atmosphere concentration in the laser-activated area. This precise ratio can synergistically achieve precise activation of surface active sites and stable control of selective etching.

[0050] In some embodiments, nitrogen may be replaced with other inert gases, and this application does not impose specific limitations on this. In the embodiments of this application, the fluorine-based gas is NF3 and / or SF6.

[0051] It should be noted that nitrogen is a carrier gas and also has a protective function, preventing uncontrollable natural oxidation, water vapor adsorption, and impurity contamination on the silicon wafer surface, and ensuring uniform atmosphere concentration in the laser-activated area. A trace amount of oxygen is used to act on the dangling bond sites (i.e., active sites) of the silicon surface after laser pre-activation, preferentially forming an ultrathin controllable oxide layer at the active sites, improving the site reactivity, reducing the potential barrier, and allowing subsequent fluorine-based gas to preferentially etch only at these active sites. Fluorine-based gas can provide F free radicals, which react with the ultrathin controllable oxide layer to generate volatile fluorides, which are the etching source for forming micro-nano textured surfaces, achieving site-selective anisotropic etching.

[0052] According to some exemplary embodiments of this application, the scanning frequency of the pulsed laser ranges from 40 kHz to 80 kHz, and the scanning speed of the pulsed laser ranges from 6 m / s to 8 m / s. In this embodiment, within this parameter range, the number of pulses received by the sites on the prepared surface is uniformly maintained at a fixed number (i.e., the sum of the number of first pulses and the number of second pulses). Multiple first pulses effectively activate the atomic bonding of the silicon surface layer, and multiple second pulses trigger selective etching under the synergistic effect of a weakly oxidizing fluorine-containing atmosphere, thus avoiding insufficient etching caused by low frequency and low speed or heat accumulation and disordered melting caused by high frequency and high speed.

[0053] According to some other exemplary embodiments of this application, the number of the first pulses is 3 to 5, and the number of the second pulses is 5 to 10. In this embodiment, when the number of the first pulses is limited to 3 to 5 and the number of the second pulses is 5 to 10, the precise allocation of laser energy in the two stages of surface activation and selective etching is achieved: 3 to 5 subthreshold pulses are sufficient to induce a sufficient density of active sites on the silicon surface, but not enough to cause significant etching or thermal damage. Subsequently, 5 to 10 pulses accumulate energy on the activated surface, triggering controllable micro-nano etching in conjunction with a weakly oxidizing fluorine-containing atmosphere to form a uniform and ordered textured surface structure. This precise pulse segmentation control ensures stable synergy between damage-free activation and efficient etching in a single scan, further improving the uniformity of the textured surface and passivation compatibility.

[0054] In practical applications, those skilled in the art can set the number of the first pulse and the number of the second pulse based on experience, or obtain them through multiple experiments. This application does not impose any specific restrictions on this.

[0055] According to some other exemplary embodiments of this application, during the scanning of the prepared silicon wafer by the pulsed laser, the scanning frequency, scanning speed, scanning overlap rate, and energy density of the pulses in the pulsed laser remain unchanged. In this embodiment, by keeping the scanning frequency, scanning speed, scanning overlap rate, and single-pulse energy density constant during the scanning of the prepared silicon wafer by the pulsed laser, stable and controllable laser process parameters are achieved, ensuring that every point on the silicon wafer surface receives the same number of subthreshold pulses uniformly, thereby precisely and collaboratively completing the two-stage process of front-end activation and back-end cumulative etching.

[0056] According to some other exemplary embodiments of this application, the spot diameter of each pulse in the aforementioned pulsed laser ranges from 0.08 mm to 0.15 mm. In this embodiment, this size range ensures that the effective overlap area between adjacent pulses is stable and controllable under high overlap scanning conditions, avoiding insufficient pulse overlap and energy dispersion caused by excessively small spots, and also preventing thermal accumulation runaway and surface disorder caused by excessively large spots.

[0057] It should be noted that if the spot diameter is too small, although the spatial resolution can be improved, it will significantly prolong the single-wafer scanning cycle, reduce the production line cycle time, and due to the limited scanning path density, the number of pulses received at each point on the prepared surface of the silicon wafer will be uneven (the number of pulses at the edge is prone to be uneven), resulting in insufficient activation or etching in local areas. If the spot diameter is too large, the laser energy density per unit area will be reduced due to energy diffusion. In addition, the energy attenuation at the edge of the Gaussian beam is significant, which can easily cause the energy density in the center of the silicon wafer to be higher than that at the edge, resulting in inconsistent activation and etching levels between the center and the edge of the silicon wafer, and poor texture uniformity.

[0058] In one possible embodiment, the specific process of solar cell fabrication is as follows: 1) Preparation of pre-treated silicon wafers: Take N-type monocrystalline pre-treated silicon wafers (compatible with sizes from 182mm×182mm to 183.75×213mm), clean and dry them routinely to remove surface oil, impurities, and the natural oxide layer; 2) Establishment of atmospheric environment: Send the pre-treated silicon wafers into the texturing chamber, and introduce a stable mixed gas: N2 + trace O2 + trace fluorine-based gas (NF3 / SF6). Maintain a single stable atmosphere throughout the process, without switching or partitioning, and use an ambient pressure environment to ensure stable etching reaction; 3) Laser parameter setting: Use a 355nm ultraviolet pulsed laser with a power density of 0.18-0.22J / cm² (lower than the original polished silicon single-pulse etching threshold of 0.26-0.32J / cm²), a scanning frequency of 40-80kHz, and perform high-speed left-right reciprocating scanning. The speed is 6-8m / s, and the scanning overlap rate is ≥90% (ensuring that each point receives multiple pulses continuously); 4) Single-scan texturing: The first 3-5 pulses (i.e., multiple first pulses): Subthreshold energy is applied to the surface layer of the prepared silicon wafer (within 10nm), which only achieves surface pre-activation and generates active sites. No etching or obvious morphological changes occur; The subsequent 5-10 pulses (i.e., multiple second pulses): On the basis of surface activation, energy accumulates naturally. Combined with the synergistic effect of a weakly oxidizing fluorine-containing atmosphere, selective etching is triggered to form an ordered microtextured structure (i.e., textured surface). The prepared silicon wafer is formed into a silicon wafer; The laser power, scanning frequency, pulse parameters and double scanning are not switched throughout the process. Texturing can be completed in a single wafer pass. The production capacity is completely consistent with the existing single-laser texturing, while achieving low damage and ordered textured surface; 5) Unloading: After texturing is completed, the silicon wafer is unloaded by conveyor belt and enters the next process.

[0059] It should be noted that single-pass reciprocating scanning refers to the laser head performing only one complete scanning motion during the laser texturing process (i.e., moving from one end of a row on the pre-existing silicon wafer to the other end, and then moving in the opposite direction to scan the next row). Throughout this entire scanning stroke, the laser pulse continuously acts on the surface of the pre-existing silicon wafer without stopping or performing a second scan. This method, through high-speed reciprocating motion (e.g., 6-8 m / s) combined with a high overlap rate (≥90%), ensures that each position on the pre-existing silicon wafer is continuously irradiated by multiple laser pulses in a single pass. This achieves uniform activation and cumulative etching without adding process steps, balancing efficiency and texture quality.

[0060] It should be noted that the texturing of crystalline silicon cells is currently divided into two main categories: (1) wet chemical texturing: using alkali to anisotropically etch different crystal planes of silicon to form a pyramidal textured surface. The process is mature, but it has problems such as large acid and alkali consumption, large amount of waste liquid, large equipment space required, need for regular liquid replacement, and difficulty in controlling the stability of the solution in the early, middle and late stages; (2) traditional laser texturing: achieving micro-nano structures through laser ablation, with advantages such as no pollution and high speed. However, traditional high-energy laser scanning is prone to forming disordered textured surfaces, thick amorphous layers, and serious surface recombination, which affects passivation and cell efficiency. Wet chemical texturing relies on the anisotropy of chemical etching. The equipment occupies a large area and needs to be used in conjunction with waste liquid and waste gas discharge pipelines, resulting in additional waste treatment costs. The process cycle is long, and the etching ability of the solution varies in the early, middle and late stages, making it difficult to control the process stability. Traditional laser texturing has problems such as disordered textured surfaces, deep thermal damage, thick amorphous layers, and poor passivation compatibility.

[0061] In some embodiments, addressing the problem of single-pulse high-energy ablation caused by traditional laser texturing, this application employs a 355nm ultraviolet pulsed laser in a uniform weakly oxidizing fluorine-containing atmosphere, performing a single-round reciprocating scan with a high overlap rate using subthreshold single-pulse energy. Utilizing the high overlap characteristic of the scan, multiple pulses are continuously received at the same point on the silicon wafer surface, achieving uniform texturing. This application proposes for the first time a high-overlap subthreshold multi-pulse accumulation mode, completing surface activation first in a single laser scan, followed by in-situ etching, achieving single-scan texturing. This differs from the single-pulse high-energy ablation and low-energy ineffectiveness problems of existing single-laser methods, avoiding thermal damage, achieving uniform texturing, and featuring simple equipment, low cost, and good mass production compatibility.

[0062] It should be noted that while some existing lasers can achieve multi-pulse scanning, they can only perform low overlap scanning (overlap ≤ 60%). The number of pulses received at the same point on the silicon wafer surface is scattered and uneven, with some areas receiving fewer than 3 pulses (unable to complete activation) and others receiving excessive pulses (leading to over-damage and disordered etching). Furthermore, there is no step of activation followed by selective etching; it is merely a disordered accumulation of single energy, either failing to trigger etching or resulting in a chaotic etching process, ultimately failing to form a uniform textured surface. This application employs a high overlap scanning of ≥ 90%, ensuring that every point across the entire silicon wafer can continuously receive 8-15 pulses (uniformly numbered and distributed). By precisely controlling the subthreshold energy of each pulse, the first 3-5 pulses stably complete activation, and the subsequent 5-10 pulses stably complete cumulative etching, creating a synergistic effect. Simultaneously, a weakly oxidizing fluorine-containing atmosphere ensures that the etching reaction occurs only at the active sites, avoiding disordered etching and ultimately achieving a uniform textured surface. This is a core design not addressed or achievable by existing multi-pulse lasers.

[0063] In summary, compared with wet texturing, this application is free of acids and alkalis, produces no wastewater, is environmentally friendly and has low costs, produces a uniform and controllable textured surface, allows for more precise control of reflectivity, improves cycle time, and requires less floor space. Compared with traditional laser texturing, this application is non-high-energy ablation, significantly reduces thermal damage and amorphous layers, produces a more uniform textured surface distribution density, and has stronger passivation compatibility. It also results in lower surface recombination and a longer minority carrier lifetime.

[0064] To verify the technical effect of this application, both the traditional laser texturing method (prepared silicon wafer insertion into the cavity → high-energy laser scanning ablation / remelting → forming a textured surface) and the solar cell fabrication method of the photovoltaic cell of this application were used to texture 100 prepared silicon wafers with the same process parameters (all prepared silicon wafers were 182mm×182mm N-type polished single crystal silicon wafers). The laser used in this application was a 355nm ultraviolet picosecond pulsed laser with a power density of 0.20J / cm², a scanning frequency of 60kHz, a scanning speed of 8m / s, a scanning overlap rate of 92%, and a pulse spot diameter of 0.1mm. Each point on the surface of the prepared silicon wafer received 10 pulses (the first 4 pulses were used for activation, and the last 6 pulses were used for cumulative etching). The atmosphere in the texturing chamber was 97.7 vol% N₂ + 1.5 vol% O₂ + 0.8 vol% NF₃, and the pressure in the texturing chamber was at atmospheric pressure steady state. The textured surface after texturing in this application is as follows: Figure 2 As shown, the textured surface has an ordered conical structure with a preferred arrangement of quasi-crystalline directions. Table 1 shows a comparison of key performance indicators of silicon wafers textured by traditional laser texturing and textured wafers of this application, including reflectivity, amorphous layer thickness, minority carrier lifetime, textured surface uniformity, and photoelectric conversion efficiency, to objectively quantify the significant advantages of this application.

[0065] Table 1

[0066]

[0067] This application also provides a solar cell, which is prepared using any of the above-described methods for preparing solar cells.

[0068] In the above embodiments, the solar cell is prepared using a solar cell fabrication method. In the solar cell fabrication method, a pre-prepared silicon wafer with a pre-prepared surface is first provided. Then, multiple first pulses in a pulsed laser are controlled to scan the sites on the pre-prepared surface to activate the sites and form active sites. Then, multiple second pulses in a pulsed laser are controlled to scan the active sites to selectively etch the pre-prepared silicon wafer to obtain a silicon wafer. The etched pre-prepared surface forms a textured surface. Finally, a functional layer is formed on the textured surface to obtain a solar cell. Here, selective etching indicates that the active sites on the pre-prepared silicon wafer are etched. The multiple first pulses and multiple second pulses are multiple pulses emitted sequentially by a pulsed laser in the same scanning step. The energy density of the pulses in the pulsed laser is lower than the energy threshold for polishing the pre-prepared surface. Compared to existing laser texturing technologies, which suffer from problems such as disordered textured surfaces, significant thermal damage, and poor passivation performance leading to low battery efficiency, this application applies subthreshold pulse energy in stages during a single laser scan. First, multiple first pulses with energy thresholds lower than the polishing preparation surface are used to scan the preparation surface, exciting silicon atoms in local areas to form active sites without actual etching. Then, multiple second pulses with the same energy density continuously bombard the activated sites (i.e., active sites), allowing energy to accumulate naturally and achieving selective etching only on the active sites. This means that controllable micro-nano etching only occurs at the active sites, avoiding disordered etching and forming an ordered textured surface, thereby improving the passivation performance of the battery. This process also avoids the amorphous layer and thermal damage caused by traditional high-energy ablation, ensuring high battery efficiency.

[0069] This application also provides a photovoltaic module, including: a battery string, which is formed by connecting multiple solar cells as described above; an encapsulating film for covering the surface of the battery string; and a cover plate for covering the surface of the encapsulating film away from the battery string.

[0070] It should be noted that the connection between solar cells can be achieved through techniques such as welding, with the aim of converging the current generated by the solar cells to form a greater output power; the encapsulating film is an important component inside the photovoltaic module, playing a role in sealing and bonding. The encapsulating film can be EVA (ethylene vinyl acetate copolymer), POE (polyolefin elastomer), or other special materials, which can effectively block the influence of external factors such as moisture and dust on the solar cells, while maintaining the physical stability of the solar cells; the cover plate is usually transparent tempered glass, located on the outermost layer of the photovoltaic module, directly exposed to the external environment. It not only needs to have good light transmittance and mechanical strength, but also needs to have properties such as UV protection, high temperature resistance, and impact resistance to protect the internal solar cells from damage.

[0071] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A method for producing a solar cell, characterized by, include: A pre-existing silicon wafer is provided, the pre-existing silicon wafer having a pre-existing surface; Multiple first pulses in a controlled pulsed laser are used to scan sites on the prepared surface to form active sites by activating the sites. Multiple second pulses in the pulsed laser are controlled to scan the active sites to selectively etch the prepared silicon wafer to obtain the silicon wafer; The etched preparatory surface forms a textured surface. The selective etching characterizes the etching of a portion of the active sites on the preparatory silicon wafer. The plurality of first pulses and the plurality of second pulses are multiple pulses emitted sequentially by the pulsed laser in the same scanning step. The energy density of the pulse in the pulsed laser is lower than the energy threshold for polishing the preparatory surface. A functional layer is formed on the velvet surface to obtain a solar cell.

2. The method of producing a solar cell according to claim 1, wherein The energy density of the pulse in the pulsed laser ranges from 0.18 J / cm² to 0.22 J / cm².

3. The method for preparing a solar cell according to claim 1, characterized in that, The scanning overlap rate of two adjacent pulses in the pulsed laser is greater than or equal to 90%.

4. The method of producing a solar cell according to claim 3, wherein Before controlling a plurality of first pulses in a pulsed laser to scan sites on the prepared surface, the method further includes: The prepared silicon wafer is placed in a texturing chamber, and a mixed gas, comprising nitrogen, oxygen and fluorine-based gas, is introduced into the texturing chamber.

5. The method for preparing a solar cell according to claim 4, characterized in that, In the mixed gas, the oxygen has a volume percentage of 1 vol% to 2 vol%, the fluorine-based gas has a volume percentage of 0.5 vol% to 1 vol%, and the nitrogen has a volume percentage of 97 vol% to 98.5 vol%.

6. The method for preparing a solar cell according to claim 5, characterized in that, The scanning frequency of the pulsed laser ranges from 40 kHz to 80 kHz, and the scanning speed of the pulsed laser ranges from 6 m / s to 8 m / s.

7. The method for preparing a solar cell according to claim 1, characterized in that, The number of the first pulse is 3 to 5, and the number of the second pulse is 5 to 10.

8. The method for preparing a solar cell according to claim 1, characterized in that, During the scanning process of the prepared silicon wafer by the pulsed laser, the scanning frequency, scanning speed, scanning overlap rate, and energy density of the pulses in the pulsed laser remain unchanged.

9. The method for preparing a solar cell according to claim 1, characterized in that, The diameter of the spot of each pulse in the pulsed laser ranges from 0.08 mm to 0.15 mm.

10. A solar cell, characterized in that, The solar cell is prepared using the solar cell preparation method according to any one of claims 1 to 9.

11. A photovoltaic module, characterized in that, include: A battery string, consisting of multiple solar cells as described in claim 10 connected together; An encapsulating film is used to cover the surface of the battery string; A cover plate is used to cover the surface of the encapsulating film that faces away from the battery string.

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