Method for manufacturing a selective emitter, solar cell and method for manufacturing the same

Abstract

This disclosure relates to a method for fabricating a selective emitter, a solar cell, and the same method. The method for fabricating a selective emitter includes: providing a substrate; performing ion diffusion treatment on the substrate to form a doped inner layer extending from the substrate surface into the substrate and a rich-doped layer covering the doped inner layer; laser-treating a non-metallic contact region using a continuous infrared laser to push the dopant element in the rich-doped layer into the substrate, such that the thickness of the doped inner layer in the non-metallic contact region is greater than the thickness of the doped inner layer in the metallic contact region; using the rich-doped layer in the metallic contact region as a barrier layer, etching the substrate to partially or completely remove the doped inner layer in the non-metallic contact region, so that the doping concentration in the non-metallic contact region is less than the doping concentration in the metallic contact region. In this way, the doping profile of the non-metallic contact region can be precisely controlled, and a specific selective emitter can be fabricated.

Description

Technical Field

[0001] This disclosure relates to the field of photovoltaic technology, and in particular to a method for preparing a selective emitter, a solar cell, and a method for preparing the same. Background Technology

[0002] Traditional uniform emitters (such as uniform boron emitters) suffer from a fundamental contradiction: it is difficult to simultaneously control contact resistance and surface carrier recombination. To address this contradiction, laser-doped selective emitters (LDSE) technology uses lasers to achieve zoned doping, differentially controlling the doping concentration in the metal and non-metal contact regions: heavy doping in the metal contact region reduces contact resistance, while light doping in the non-metal contact region improves passivation and reduces carrier recombination. However, existing LDSE technology has limitations, failing to control key parameters such as doping concentration and depth in the non-metal contact region, thus hindering further improvements in the photoelectric conversion efficiency of solar cells. Summary of the Invention

[0003] Therefore, it is necessary to provide a method for preparing a selective emitter to address the problem that existing LDSE technology cannot control key parameters such as doping concentration and doping depth in the non-metallic contact region.

[0004] A method for fabricating a selective emitter includes: providing a substrate; the substrate comprising a metal contact region and a non-metal contact region; performing ion diffusion treatment on the substrate to form a doped inner extension layer extending from the surface of the substrate into the substrate and a rich doped layer covering the doped inner extension layer; performing laser treatment on the non-metal contact region using an infrared continuous laser to advance the dopant element in the rich doped layer into the substrate, such that the thickness of the doped inner extension layer in the non-metal contact region is greater than the thickness of the doped inner extension layer in the metal contact region; using the rich doped layer located in the metal contact region as a barrier layer, performing an etching treatment on the substrate to partially or completely remove the doped inner extension layer located in the non-metal contact region, such that the doping concentration in the non-metal contact region is less than the doping concentration in the metal contact region.

[0005] In one embodiment, during the etching process on the substrate, the etching depth is controlled to be less than the thickness of the doped inner layer located in the non-metallic contact region, so as to remove a portion of the doped inner layer located in the non-metallic contact region, thereby forming a lightly doped region in the non-metallic contact region. This allows the formation of high and low junction units. Maintaining light doping in the non-metallic contact region significantly reduces Auger recombination of charge carriers, lowers the surface recombination rate, and results in a higher passivation effect and open-circuit voltage.

[0006] In one embodiment, during the etching process on the substrate, the etching depth is controlled to be greater than the thickness of the doped inner layer located in the non-metallic contact region, so as to completely remove the doped inner layer located in the non-metallic contact region, thereby forming a doped region in the non-metallic contact region. The doped non-metallic contact region achieves the lowest surface recombination and the highest open-circuit voltage. Furthermore, the pure silicon textured surface structure has optimal anti-reflection characteristics, completely eliminating absorption loss for short-wavelength light, achieving the strongest light capture and the highest blue light response, thereby improving the short-circuit current.

[0007] In one embodiment, the infrared continuous laser is a near-infrared continuous laser with a wavelength of 900nm-1100nm; during the laser processing, the laser energy is 38W-90W, and the spot overlap rate is 30%-80%. Here, the photon energy of the near-infrared laser is highly matched with the intrinsic absorption band of the silicon substrate, and the laser energy can be efficiently absorbed by the richly doped layer and the substrate surface, reducing transmission and reflection losses. During the laser processing, limiting the laser energy to 38W-90W and the spot overlap rate to 30%-80% can achieve uniform and controllable deposition of structural energy, which can provide stable thermal activation power for the diffusion of doped atoms and precisely control the doping depth and concentration gradient, ensuring the uniformity and lattice integrity of the doped layer.

[0008] In one embodiment, during the laser processing, the laser energy is 54W-90W, and the spot overlap rate is 50%-80%; after the laser processing, the doping concentration of the non-metallic contact area is 1E18 atoms / cm². 3 ~1E20atoms / cm 3 The junction depth is 2.0 μm-5.0 μm. By setting the above parameters, a non-metallic contact region with a high doping concentration and a deep junction can be formed.

[0009] In one embodiment, the etching process is wet etching; the wet etching uses a mixed etching solution of hydrofluoric acid and alkaline solution, wherein the concentration of hydrofluoric acid is 2wt%-4wt% and the concentration of alkaline solution is 1wt%-2wt%; the temperature of the wet etching is 60℃-70℃, and the time is 150s-300s; the etching depth of the wet etching is 1.5μm-4.0μm, and the etching depth is less than the junction depth of the non-metallic contact area after the laser treatment. By limiting the concentration of hydrofluoric acid and alkaline solution in the above etching process, and controlling the etching temperature and etching time, the etching process can be precisely controlled, ensuring that the etching depth meets the target requirements, improving the flatness and uniformity of the etched surface, and protecting the integrity of the doped layer and the stability of the silicon wafer lattice structure. In addition, wet etching can also remove laser damage in the laser area, thereby improving the flatness of the laser area and increasing the photoelectric conversion efficiency of the solar cell.

[0010] In one embodiment, during the laser processing, the laser energy is 38W-76W, and the spot overlap rate is 30%-60%; after the laser processing, the doping concentration of the non-metallic contact region is 1E18 atoms / cm². 3 ~5E19atoms / cm 3 The junction depth is 1.0 μm-4.0 μm. By setting the above parameters, a non-metallic contact region with a lower doping concentration and shallower junction depth can be formed.

[0011] In one embodiment, the etching process is wet etching; the wet etching uses a mixed etching solution of hydrofluoric acid and alkaline solution, wherein the concentration of hydrofluoric acid is 2wt%-6wt% and the concentration of alkaline solution is 1wt%-3wt%; the temperature of the wet etching is 60℃-80℃, and the time is 150s-400s; the etching depth of the wet etching is 2.0μm-5.0μm, and the etching depth is greater than the junction depth of the non-metallic contact area after the laser treatment. By limiting the concentration of hydrofluoric acid and alkaline solution in the above etching process, and controlling the etching temperature and etching time, the etching process can be precisely controlled, ensuring that the etching depth meets the target requirements, improving the flatness and uniformity of the etched surface, and protecting the integrity of the doped layer and the stability of the silicon wafer lattice structure. In addition, wet etching can also remove laser damage in the laser area, thereby improving the flatness of the laser area and increasing the photoelectric conversion efficiency of the solar cell.

[0012] This disclosure also provides a method for fabricating a solar cell, the method comprising the method for fabricating a selective emitter as described in any of the above embodiments.

[0013] This disclosure also provides a solar cell, which is prepared using the above-described method for preparing solar cells.

[0014] The selective emitter fabrication method provided in this disclosure employs continuous infrared laser to treat the non-metallic contact region. On one hand, the continuous infrared laser can propel the dopant elements in the richly doped layer on the substrate surface to a specific depth within the substrate, making the thickness of the doped inner layer in the non-metallic contact region greater than that in the metallic contact region. This allows for precise control of the doping concentration and depth in the non-metallic contact region. On the other hand, the continuous infrared laser has stable energy output characteristics, resulting in a mild and controllable thermal effect on the substrate, avoiding the instantaneous high-temperature impact of pulsed lasers and preventing damage to the substrate lattice. Furthermore, after laser treatment, the substrate is etched using the richly doped layer in the metallic contact region as a barrier layer to partially or completely remove the doped inner layer in the non-metallic contact region, ensuring that the doping concentration in the non-metallic contact region is lower than that in the metallic contact region. Thus, by combining continuous infrared laser treatment with etching, the doping profile of the non-metallic contact region can be precisely controlled, achieving a low-concentration doped or completely undoped state in the non-metallic contact region, ultimately resulting in a specific selective emitter. In summary, the selective emitter fabrication method provided in this disclosure can reduce laser damage to the substrate and achieve precise control of key parameters such as doping concentration and doping depth in the non-metallic contact area, thereby further improving the photoelectric conversion efficiency of the solar cell. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments or conventional technologies of this disclosure, the accompanying drawings used in the description of the embodiments or conventional technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A schematic flowchart illustrating the method for preparing a selective emitter according to an embodiment of this disclosure;

[0017] Figures 2 to 6 A schematic cross-sectional view of the selective emitter during the fabrication process, as provided in the embodiments of this disclosure;

[0018] Figures 7 to 12 A cross-sectional structural diagram of a solar cell with selective emission and extremely high / low junction units during the fabrication process;

[0019] Figures 13 to 18 A cross-sectional structural diagram of a solar cell with selective emission and localized junction units during the fabrication process.

[0020] In the figure: 10, substrate; 11, metal contact region; 12, non-metal contact region; 21, doped inner expansion layer; 22, richly doped layer; 30, laser-driven doped region; 31, oxide layer; 32, tunneling oxide layer; 33, doped polysilicon layer; 34, doped silicon glass layer; 35, passivation antireflection layer; 36, metal electrode. Detailed Implementation

[0021] To facilitate understanding of this disclosure, it will now be described in more detail. However, it should be understood that this disclosure can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a more thorough and complete understanding of the disclosure.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein in the specification of this disclosure is for the purpose of describing particular implementations or embodiments only and is not intended to be limiting of this disclosure. The optional range of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0023] In this disclosure, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0024] Based on this, the present disclosure provides a method for preparing a selective emitter. Figure 1 A schematic flowchart illustrating a method for preparing a selective emitter according to an embodiment of this disclosure; as shown, the method includes:

[0025] Step S101: Provide a substrate; the substrate includes a metal contact region and a non-metal contact region;

[0026] Step S102: The substrate is subjected to ion diffusion treatment to form a doped inner extension layer extending from the substrate surface into the substrate and a rich doped layer covering the doped inner extension layer.

[0027] Step S103: Use infrared continuous laser to laser process the non-metallic contact area to push the doped elements in the rich doped layer into the substrate, so that the thickness of the doped inner expansion layer in the non-metallic contact area is greater than the thickness of the doped inner expansion layer in the metallic contact area.

[0028] Step S104: Using the rich doped layer in the metal contact region as a barrier layer, the substrate is etched to partially or completely remove the doped inner extension layer in the non-metal contact region, so that the doping concentration in the non-metal contact region is less than the doping concentration in the metal contact region.

[0029] It is understood that the selective emitter fabrication method provided in this disclosure uses continuous infrared laser to treat the non-metallic contact region. On the one hand, the continuous infrared laser can push the doped elements in the richly doped layer on the substrate surface to a specific depth in the substrate, making the thickness of the doped inner layer in the non-metallic contact region greater than that in the metallic contact region, thereby achieving precise control of the doping concentration and doping depth in the non-metallic contact region. On the other hand, the continuous infrared laser has stable energy output characteristics, and the thermal effect on the substrate is mild and controllable, avoiding the instantaneous high-temperature impact of pulsed lasers and preventing damage to the substrate lattice. In addition, after laser treatment, the substrate is etched using the richly doped layer in the metallic contact region as a barrier layer to partially or completely remove the doped inner layer in the non-metallic contact region, so that the doping concentration in the non-metallic contact region is less than that in the metallic contact region. Thus, by combining continuous infrared laser treatment with etching, the doping profile of the non-metallic contact region can be precisely controlled, achieving a low-concentration doped or completely undoped state in the non-metallic contact region, ultimately preparing a specific selective emitter. In summary, the selective emitter fabrication method provided in this disclosure can reduce laser damage to the substrate and achieve precise control of key parameters such as doping concentration and doping depth in the non-metallic contact area, thereby further improving the photoelectric conversion efficiency of the solar cell.

[0030] It should also be understood that although the steps in the above flowchart are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Moreover, at least some of the steps in the above flowchart may include multiple steps or stages, and these steps or stages are not necessarily completed at the same time, nor are they necessarily performed sequentially.

[0031] Figures 2 to 6 This is a schematic cross-sectional view of the selective emitter during the fabrication process, as provided in the embodiments of this disclosure. Below, in conjunction with... Figures 2 to 6 The preparation method of the selective emitter provided in the embodiments of this disclosure and its beneficial effects will be further described in detail.

[0032] First, please refer to Figure 2 Step S101 is executed to provide a substrate 10; the substrate 10 includes a metal contact region 11 and a non-metal contact region 12.

[0033] It is understood that the substrate 10, as the absorption layer and transport carrier of photogenerated carriers, directly affects the open-circuit voltage and overall performance of the solar cell. In this embodiment, the substrate 10 can be a silicon substrate; specifically, the substrate 10 can be an N-type silicon substrate. Compared with a P-type silicon substrate, an N-type silicon substrate has the advantages of natural resistance to light-induced degradation (LID) and low sensitivity to metal impurities, which can effectively improve the long-term stability and photoelectric conversion efficiency of the solar cell.

[0034] It should be noted that, for ease of description, this disclosure divides the substrate 10 into a metal contact region 11 and a non-metal contact region 12, which are arranged adjacent to each other. It is important to emphasize that the aforementioned metal contact region 11 and non-metal contact region 12 are not pre-defined during the substrate 10 fabrication stage, but are defined after the selective emitter is formed on the substrate 10, based on the arrangement of the selective emitter. This disclosure merely introduces the concepts of metal contact region 11 and non-metal contact region 12 in advance for ease of description and understanding of the scheme provided in this disclosure, and is not intended to limit the fabrication method provided in this disclosure. Furthermore, the metal contact region 11 can also be referred to as a "metal gate line contact region," and the non-metal contact region 12 can also be referred to as a "non-metal gate line contact region."

[0035] It should also be noted that in the selective emitter fabrication method provided in this disclosure, multiple selective emitters can be fabricated on a single substrate 10 as needed. Furthermore, the number of metal contact regions 11 and non-metal contact regions 12 in the selective emitter can also be set to multiple, and the metal contact regions 11 and non-metal contact regions 12 can be alternately distributed according to the arrangement pattern of the selective emitters. It should be emphasized that the accompanying drawings and related descriptions in this application are only schematically illustrating the structure and fabrication of a single selective emitter and do not constitute a limitation on the number or arrangement of selective emitters fabricated on the substrate.

[0036] In some embodiments, please refer to Figure 2 The method for fabricating the selective emitter may further include: texturing the substrate 10 to form a pyramidal textured surface on the surface of the substrate 10; specifically, anisotropic etching of the surface of the substrate 10 can be performed in a chain or trough apparatus using an alkaline solution of specific concentration and temperature to form a dense micron-scale pyramidal textured surface on the surface of the substrate 10. The size of the pyramidal textured surface can be 1.0 μm-5.0 μm; for example, the size of the pyramidal textured surface can be 1.0 μm, 2.0 μm, 3.0 μm, 4.0 μm, or 5.0 μm, etc. This increases the light trapping efficiency of the substrate 10 surface.

[0037] In some specific embodiments, the alkaline solution can be a sodium hydroxide (NaOH) or potassium hydroxide (KOH) solution; the concentration of the alkaline solution can be 0.5wt%-3.0wt%, for example, the concentration of the alkaline solution can be 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, or 3.0wt%, etc.; the temperature of the alkaline solution can be 70℃-85℃, for example, the temperature of the alkaline solution can be 70℃, 75℃, 80℃, or 85℃, etc.

[0038] Then, please refer to Figure 3 Step S102 is performed to perform ion diffusion treatment on the substrate 10 to form a doped inner extension layer 21 extending from the surface of the substrate 10 into the substrate 10 and a rich doped layer 22 covering the doped inner extension layer 21.

[0039] In some embodiments, the doping type of the doped inner extension layer 21 and the rich doped layer 22 can be P-type. Specifically, the doped inner extension layer 21 can be a boron-doped inner extension layer, and the rich doped layer 22 can be a borosilicate glass (BSG) layer. Here, the main function of the boron-doped inner extension layer is to form hole-conducting regions in the silicon crystal by using boron atoms (B) as acceptor impurities, so as to construct an efficient PN junction and achieve effective separation of photogenerated carriers; the borosilicate glass layer is a boron-rich glassy film formed on the surface of the substrate 10 after ion diffusion, mainly composed of a mixture of boron oxide (B2O3) and silicon dioxide (SiO2), and its function is to provide a uniform diffusion of boron atoms into the substrate 10 as a boron doping source and control the doping concentration gradient; the borosilicate glass layer can serve as a doping source for subsequent laser processing, supplying boron impurities for laser processing, thereby accurately forming the ideal P-type layer. + Emitter or local contact area.

[0040] In some specific embodiments, ion diffusion treatment of substrate 10 may include: performing boron ion diffusion (boron diffusion) on the front side of substrate 10 to form a boron-doped inner extension layer extending from the front side of substrate 10 into the substrate 10. At the same time, boron elements that do not participate in diffusion combine with silicon oxide on the surface of substrate 10 to form a borosilicate glass layer in situ above the boron-doped inner extension layer.

[0041] In practice, the specific steps for forming a boron-doped inner diffusion layer may include: placing the texturized substrate 10 into a tube diffusion furnace, introducing a boron-containing gas (such as boron tribromide (BBr3) or boron trichloride (BCl3)), and allowing boron atoms to diffuse into the surface of the substrate 10 at a high temperature of 800℃-1050℃, forming a fully surface-doped P layer. +Layer (P-type heavily doped emitter); the sheet resistance after boron diffusion is 200 ohms-400 ohms, and the diffusion concentration is 3E17 atoms / cm. 3 -4E19atoms / cm 3 The junction depth is 0.8μm-2μm.

[0042] It should be noted that during the boron diffusion process, the boron-containing gas can indiscriminately contact the back and sides of the substrate 10, causing some of the boron source to deposit on the back and sides of the substrate 10 and diffuse shallowly into the substrate 10, thereby forming a boron-doped inner diffusion layer and a borosilicate glass layer. This wrapped-around structure can be completely removed by subsequent etching processes, so there is no need to add an additional mask or shielding process before boron diffusion, which simplifies the overall fabrication process.

[0043] Then, please refer to Figure 4 In step S103, the non-metallic contact area 12 is laser-processed using an infrared continuous laser to push the doped elements in the rich doped layer 22 into the substrate 10, so that the thickness of the doped inner expansion layer 21 in the non-metallic contact area 12 is greater than the thickness of the doped inner expansion layer 21 in the metallic contact area 11.

[0044] Understandably, this disclosure employs continuous infrared laser as the doping driving force, acting directionally on the non-metallic contact region 12. The core mechanism for selective doping (regional doping) is to utilize the continuous thermal effect of the infrared beam to drive the diffusion of impurity atoms. Specifically, a high-energy laser beam locally irradiates the silicon substrate surface coated with the dopant source (rich doped layer 22), instantly generating high temperatures that cause the impurity source to decompose and diffuse into the silicon lattice. Compared with traditional high-temperature diffusion doping, continuous infrared laser can selectively advance the high-concentration doped atoms on the surface of the silicon substrate to a specific depth, thereby achieving precise doping of the non-metallic contact region 12. This precise doping capability is beneficial for simultaneously forming heavily doped and lightly doped (or undoped) regions of the selective emitter in subsequent fabrication processes, constructing high and low junction units or local junction units with differentiated doping concentrations and junction depths, thereby reducing parasitic absorption and lowering contact resistance.

[0045] It is also understandable that, compared with open-film laser, infrared continuous laser can effectively reduce the damage of laser to substrate 10, thereby avoiding the problem of solar cell conversion efficiency loss, because the two have fundamentally different mechanisms of action.

[0046] Specifically, laser ablation typically employs high-energy-density nanosecond or picosecond laser beams to selectively and precisely process the surface of a silicon substrate. When the laser is focused on the silicon substrate surface, silicon atoms absorb photon energy and rapidly heat up to their melting or vaporization point, locally removing material through thermal ablation to form pre-defined patterned trenches or openings. When such high-energy-density lasers irradiate silicon materials, the thermo-mechanical coupling effect caused by the sudden surge in localized temperature and rapid cooling leads to structural damage to the material, resulting in a molten surface, microcrack networks, debris, and abnormal diffusion of dopants. This significantly increases the surface recombination rate of minority carriers, leading to a decrease in the open-circuit voltage of the solar cell and a loss of conversion efficiency.

[0047] Infrared continuous lasers have stable energy output characteristics, and the thermal effect on the substrate 10 is more gentle and controllable. They can avoid the instantaneous high temperature impact of pulsed lasers and prevent damage to the lattice of the substrate 10. They can also precisely control the temperature range of the substrate 10 surface, so that doped atoms migrate from the rich doped layer 22 into the interior of the substrate 10 at a stable rate, forming a doped inner expansion layer 21 with a gentle concentration gradient, which provides favorable conditions for the uniform diffusion of doped elements.

[0048] In some embodiments, an infrared continuous laser with specific power and wavelength can be used to precisely scan the patterned area of ​​the non-metallic contact area 12. Specifically, the laser can be a near-infrared continuous laser, and the laser used for laser processing is a near-infrared continuous laser with a wavelength of 900nm-1100nm, for example, the laser wavelength can be 900nm, 950nm, 1000nm, 1050nm, 1100nm, etc.

[0049] Understandably, near-infrared lasers with wavelengths of 900nm-1100nm are chosen as the doping laser because the photon energy of the near-infrared laser is highly matched with the intrinsic absorption band of the silicon substrate. The laser energy can be efficiently absorbed by the borosilicate glass layer and the surface of the silicon substrate, reducing transmission and reflection losses. In contrast, mid-infrared, far-infrared, or other continuous lasers in the ultraviolet or visible bands are prone to causing etching damage to the surface of the silicon substrate due to excessively high photon energy, or to wasting a lot of energy due to low absorption rate. Both of these methods make it difficult to achieve precise control of doping depth and concentration gradient.

[0050] In some specific embodiments, during laser processing, the laser energy can be 38W-90W, for example, 38W, 40W, 50W, 60W, 70W, 80W, 90W, etc.; the spot overlap rate can be 30%-80%, for example, 30%, 40%, 50%, 60%, 70%, 80%, etc. Based on the synergistic control of the above parameters, the laser energy can instantly melt the silicon surface layer of the scanning area and accelerate the diffusion of boron atoms into the silicon substrate to a specific depth, precisely controlling the doping concentration and junction depth of the non-metallic contact region 12. Ultimately, the doping concentration of the laser-driven doped region 30 formed in the non-metallic contact region 12 can reach 1E18 atoms / cm². 3 -1E20atoms / cm 3 The junction depth can be 1.0μm-5.0μm.

[0051] Understandably, if the laser energy is below 38W, the migration drive of boron atoms may be insufficient, making it impossible to form the target junction depth and doping concentration. If the laser energy is above 90W, excessive local energy accumulation can cause high temperatures, potentially damaging the substrate 10 lattice and leading to disordered deep diffusion of boron atoms, disrupting the smoothness of the concentration gradient. Furthermore, if the spot overlap rate is below 30%, laser scanning may have energy blind zones, resulting in discontinuous doping on the substrate 10 surface and localized insufficient doping defects. If the spot overlap rate is above 80%, excessive spot overlap may lead to localized energy accumulation, causing excessively deep doping in that area and reducing overall doping uniformity. Therefore, limiting the laser energy to 38W-90W and the spot overlap rate to 30%-80% during laser processing allows for uniform and controllable deposition of structural energy. This provides stable thermal activation for dopant atom diffusion and allows for precise control of doping depth and concentration gradient, ensuring the uniformity and lattice integrity of the doped layer.

[0052] It should be noted that the laser-driven doping region 30 refers to the region where the doped inner extension layer 21 of the non-metallic contact region 12 is located. This region is formed by first creating an initial doped region on the surface of the substrate 10 through ion diffusion treatment, and then promoting secondary diffusion of doped atoms into the substrate 10 through laser treatment, ultimately resulting in a doped region with increased doping depth. Since the infrared continuous laser only acts on the non-metallic contact region 12, the doping depth of the doped inner extension layer 21 of the metallic contact region 11 is the same as the depth of the initial doped region formed by ion diffusion treatment. Therefore, the thickness of the doped inner extension layer 21 of the non-metallic contact region 12 is greater than the thickness of the doped inner extension layer 21 of the metallic contact region 11, and the doping depth of the non-metallic contact region 12 directly affects the type and effect of the subsequent selective emitter.

[0053] In some embodiments, the area ratio of the laser region to the non-laser region can be 24%-48%; for example, the area ratio of the laser region to the non-laser region can be 24%, 30%, 36%, 42%, 48%, etc.

[0054] Understandably, by limiting the area ratio of the laser region to the non-laser region, the area ratio of the non-metallic contact region 12 to the metallic contact region 11 can be limited. If the area ratio of the non-metallic contact region 12 to the metallic contact region 11 is too large, it may lead to an extended lateral transport distance for charge carriers, resulting in lateral resistance loss and a significant increase in series resistance. Simultaneously, charge carriers need to migrate a greater distance to be collected by the grid electrodes, which also increases recombination loss. If the area ratio of the non-metallic contact region 12 to the metallic contact region 11 is too small, the increased density of the grid electrodes reduces the effective light-receiving area of ​​the solar cell, leading to a decrease in short-circuit current and open-circuit voltage. Therefore, limiting the area ratio of the non-metallic contact region 12 to the metallic contact region 11 within a certain range can achieve synergistic suppression of lateral resistance loss and charge carrier recombination loss, while ensuring the effective light-receiving area of ​​the solar cell.

[0055] In this embodiment of the disclosure, when the richly doped layer 22 located in the non-metallic contact region 12 is laser-processed using an infrared continuous laser, the doping depth and doping concentration of the non-metallic contact region 12 are proportional to the laser energy of the infrared continuous laser and also proportional to the beam overlap rate. That is, the thickness of the doped inner extension layer 21 located in the non-metallic contact region 12 (or the junction depth of the non-metallic contact region 12) increases with increasing laser energy and beam overlap rate. Therefore, in the following embodiments, two examples are provided for controlling the doping depth and doping concentration of the non-metallic contact region 12 by adjusting laser parameters.

[0056] In some embodiments, when a non-metallic contact region 12 with a high doping concentration and deep junction depth is required, the laser energy for laser treatment can be 54W-90W, and the spot overlap rate can be 50%-80%; after laser treatment, the doping concentration of the non-metallic contact region 12 is 1E18 atoms / cm². 3 -1E20atoms / cm 3 The junction depth is 2.0μm-5.0μm.

[0057] In other embodiments, when a non-metallic contact region 12 with a lower doping concentration and shallower junction depth is required, the laser energy for laser processing can be 38W-76W, and the spot overlap rate can be 30%-60%; after laser processing, the doping concentration of the non-metallic contact region 12 is 1E18 atoms / cm². 3 -5E19atoms / cm 3The junction depth is 1.0 μm-4.0 μm. It should be noted that the lower doping concentration and shallower junction depth here are relative to the process parameters for forming the non-metallic contact region 12 with higher doping concentration and deeper junction depth as described in the above embodiments, and are not specific to the doping concentration and junction depth of the non-metallic contact region 12, nor do they refer to general standard values ​​in the art.

[0058] Understandably, adjusting the laser parameters to control the doping concentration and depth of the non-metallic contact region 12 significantly reduces the difficulty of subsequent etching processes, thereby reducing process time and production costs, and improving production efficiency. The core reason is that precise control of the doping depth directly optimizes the precision of the etching amount, avoiding problems such as incomplete etching due to excessively deep doped inner layer 21, or damage to the substrate 10 lattice due to over-etching. By using this differentiated parameter control to form regions with different doping depths, the type of selective emitter structure obtained can be precisely controlled.

[0059] Finally, please refer to Figure 5 and Figure 6 In step S104, the substrate 10 is etched using the rich doped layer 22 located in the metal contact region 11 as a barrier layer to partially or completely remove the doped inner extension layer 21 located in the non-metal contact region 12, so that the doping concentration of the non-metal contact region 12 is less than the doping concentration of the metal contact region 11.

[0060] In some embodiments, the richly doped layer 22 of the metal contact region 11 is not laser-treated, retaining its original uniform and dense structure without lattice damage. Therefore, during etching, the etching rate of the metal contact region 11 is much lower than that of the non-metallic contact region 12, and the richly doped layer 22 of the metal contact region 11 can precisely protect the metal contact region 11, achieving selective etching.

[0061] In some embodiments, the etching process can employ a wet etching process to partially or completely remove the doped inner layer 21 of the non-metallic contact region 12 and re-fabricate a pyramidal textured surface on the surface of the non-metallic contact region 12. The metallic contact region 11, protected by the richly doped layer 22, retains heavy doping, forming selective emitter high-low junction units (such as…). Figure 5 (as shown) or local junction units (such as Figure 6 (As shown).

[0062] In some specific embodiments, when etching the substrate 10, the etching depth can be controlled to be less than the thickness of the doped inner extension layer 21 located in the non-metallic contact region 12, so as to partially remove the doped inner extension layer 21 located in the non-metallic contact region 12, thereby forming a lightly doped region in the non-metallic contact region 12. In this way, high and low junction units can be formed with the metal contact region 11 heavily doped and the non-metallic contact region 12 lightly doped; the non-metallic contact region 12 remains lightly doped, which greatly reduces Auger recombination of charge carriers, reduces the surface recombination rate, and brings higher passivation effect and open circuit voltage.

[0063] In other specific embodiments, when etching the substrate 10, the etching depth can be controlled to be greater than the thickness of the doped inner extension layer 21 located in the non-metallic contact region 12, so as to completely remove the doped inner extension layer 21 located in the non-metallic contact region 12, making the non-metallic contact region 12 an undoped region. In this way, a local junction unit with heavily doped metal contact region 11 and undoped non-metallic contact region 12 can be formed; the undoped non-metallic contact region 12 can achieve the lowest surface recombination and the highest open-circuit voltage, and the pure silicon textured surface structure has the best anti-reflection characteristics, with no absorption loss of short-wavelength light, which can achieve the strongest light capture and the highest blue light response, thereby improving the short-circuit current.

[0064] Here, the high and low junction units are characterized by: the metal contact region 11 being highly doped to reduce the contact resistance of the metal-semiconductor interface, while deep diffusion provides sufficient doping buffer to effectively prevent the metal paste from burning through the PN junction during subsequent high-temperature sintering, ultimately achieving low series resistance and high fill factor. The doped inner extension layer 21 of the non-metallic contact region 12 is partially removed, and the non-metallic contact region 12 remains a shallow junction with light doping, which greatly reduces Auger recombination of charge carriers, lowers the surface recombination rate, and brings higher passivation effect and open-circuit voltage. Moreover, the "dead layer" effect in this region is weaker, allowing for more complete absorption and utilization of short-wavelength light, thereby increasing the short-circuit current.

[0065] The characteristics of the local junction unit are: the metal contact region 11 retains a highly doped structure, ensuring excellent, low-resistance ohmic contact with the metal electrode, which is beneficial for obtaining a high fill factor. The doped inner extension layer 21 of the non-metallic contact region 12 has been completely removed, exposing the original, undoped silicon textured surface, completely eliminating Auger recombination and defect recombination caused by high doping in this region, achieving the lowest surface recombination and the highest open-circuit voltage. Moreover, the pure silicon textured surface structure has the best anti-reflection characteristics, with no absorption loss for short-wavelength light, achieving the strongest light capture and the highest blue light response, thereby improving the short-circuit current.

[0066] In some embodiments, a specific method for forming high and low junction units may include: based on forming a non-metallic contact region 12 with a higher doping concentration and a deeper junction depth, performing wet etching on the substrate. The wet etching uses a mixed etching solution of hydrofluoric acid and an alkaline solution, wherein the concentration of hydrofluoric acid is 2wt%-4wt% and the concentration of alkaline solution is 1wt%-2wt%; for example, the concentration of hydrofluoric acid may be 2wt%, 2.5wt%, 3wt%, 3.5wt%, or 4wt%, etc., and the concentration of alkaline solution may be 1wt%, 1.2wt%, 1.5wt%, or 1.8wt%. Or 2wt%, etc.; the wet etching temperature is 60℃-70℃, and the time is 150s-300s; for example, the wet etching temperature can be 60℃, 62℃, 65℃, 68℃ or 70℃, etc., and the time can be 150s, 180s, 200s, 250s, 280s or 300s, etc.; the wet etching depth is 1.5μm-4.0μm, for example, the etching depth can be 1.5μm, 2.0μm, 3.0μm or 4.0μm, etc.; and the etching depth is less than the junction depth of the non-metallic contact area after laser treatment. The non-metallic contact area 12 textured surface obtained by this method still has some light doping, with a doping concentration of 1E17 atoms / cm. 3 -3E18atoms / cm 3 The junction depth is 0.2μm-0.7μm.

[0067] In other embodiments, the specific method for forming local junction units may include: based on the formation of a non-metallic contact region 12 with a low doping concentration and shallow junction depth, performing wet etching on the substrate. The wet etching uses a mixed etching solution of hydrofluoric acid and an alkaline solution, wherein the concentration of hydrofluoric acid is 2wt%-6wt% and the concentration of alkaline solution is 1wt%-3wt%; for example, the concentration of hydrofluoric acid can be 2wt%, 3wt%, 4wt%, 5wt%, or 6wt%, etc., and the concentration of alkaline solution can be 1wt%, 1.5wt%, 2wt%, 2.5wt%, or... The etching process involves using a wet etching temperature of 60℃-80℃ and a time of 150s-400s. For example, the wet etching temperature can be 60℃, 65℃, 70℃, 75℃, or 80℃, and the time can be 150s, 200s, 250s, 300s, 350s, or 400s. The etching depth is 2.0μm-5.0μm, and can be 2.0μm, 3.0μm, 4.0μm, or 5.0μm. The etching depth is greater than the junction depth of the non-metallic contact area after laser treatment. The non-metallic contact area 12 obtained by this method is an undoped pure pyramid-textured silicon substrate.

[0068] Understandably, by limiting the concentrations of hydrofluoric acid and alkali, and controlling the etching temperature and time during wet etching, precise control of the etching process can be achieved. This ensures that the etching depth meets the target requirements, improves the flatness and uniformity of the etched surface, and protects the integrity of the doped layer and the stability of the silicon wafer lattice structure. In addition, wet etching can also remove laser damage in the laser region, thereby improving the flatness of the laser region and increasing the photoelectric conversion efficiency of the solar cell.

[0069] In some embodiments, since the laser acts on the non-metallic grid region, the height of the metallic contact region 11 is higher than the height of the non-metallic contact region 12. This increases the contact area between the subsequently formed metallic electrode and the emitter, further reducing the contact resistance.

[0070] It should be noted that since multiple selective emitters can be fabricated on a single substrate 10 as needed, the doping of the metal contact region 11 and non-metal contact region 12 corresponding to each selective emitter can be flexibly adjusted according to the actual device design requirements. Therefore, multiple non-metal contact regions 12 can all adopt a uniform fabrication process to form a high-low junction or local junction with a uniform structure (that is, to form a full-surface local junction unit or a full-surface high-low junction unit); or different non-metal contact regions can be controlled separately to achieve a hybrid structure in which some areas are high-low junctions and some areas are local junctions, and the proportion of high-low junctions in the hybrid structure can be 20%-80%, and correspondingly, the proportion of local junctions can be 20%-80%.

[0071] In summary, by optimizing the aforementioned laser process parameters and coordinating them with wet etching, this disclosure enables precise control of the doping profile of the substrate 10, achieving a low-concentration doped or completely undoped state in the non-metallic contact region 12. Local junction units or high-low junction units can be selectively fabricated according to actual design requirements. The selective emitter fabricated in this embodiment is a front-side selective emitter, specifically a front-side boron-doped selective emitter.

[0072] Based on this, the present disclosure also provides a method for preparing a solar cell, including the method for preparing a selective emitter provided in any of the above embodiments.

[0073] Figures 7 to 12 A cross-sectional structural diagram of a solar cell with selective emission and extremely high / low junction units during the fabrication process.

[0074] In some embodiments, please refer to Figure 7After forming the selective emitter, the fabrication method of the solar cell may include: thermally annealing the substrate 10 to form an oxide layer 31 on the surface of the non-metallic contact region 12, wherein the oxide layer 31 covers the surface of the remaining doped inner extension layer 21 of the non-metallic contact region 12; the material of the oxide layer 31 may include silicon oxide (SiO2). x ).

[0075] Here, thermal annealing can repair defects on the surface of substrate 10, and at the same time, push the doped elements in the rich doped layer 22 on the surface of metal contact region 11 into substrate 10, further increasing the doping concentration and doping depth of metal contact region 11.

[0076] In some embodiments, please refer to Figure 8 After the substrate 10 is subjected to thermal annealing, the method for fabricating a solar cell may further include: placing the thermally annealed substrate 10 into an HF chain cleaning tank to remove the rich doped layer 22 deposited around the back and sides of the substrate 10; then, placing the acid-washed substrate 10 into an alkaline polishing tank, and under the action of the alkaline polishing solution, removing the doped inner diffusion layer 21 deposited around the back and sides of the substrate 10 and polishing it; the alkaline polishing solution in the alkaline polishing tank may be a mixed solution including sodium hydroxide (NaOH) and polishing additives.

[0077] In some embodiments, please refer to Figure 9 After removing the rich doped layer 22 and the doped inner extension layer 21 deposited on the back and sides of the substrate 10, the method for fabricating the solar cell may further include: growing a tunneling oxide layer 32 on the back of the substrate 10 using low-pressure chemical vapor deposition (LPCVD); depositing an amorphous silicon layer on the tunneling oxide layer 32, and then crystallizing the amorphous silicon layer by high temperature and ion doping to form a doped polycrystalline silicon layer 33; and covering the surface of the doped polycrystalline silicon layer 33 with a doped silicon glass layer 34.

[0078] In some specific embodiments, the thickness of the tunneling oxide layer 32 can be 1.1 nm to 2.0 nm, including the endpoint values; the tunneling oxide layer 32 can be a silicon dioxide layer. The doping type of the doped polysilicon layer 33 can be N-type; specifically, the doped polysilicon layer 33 can be a phosphorus-doped polysilicon layer (N-poly); the thickness of the doped polysilicon layer 33 can be 80 nm to 150 nm, including the endpoint values; the doped silicon glass layer 34 can be a phosphosilicate glass layer.

[0079] It should be noted that when the doped polysilicon layer 33 and the doped silicon glass layer 34 are formed on the back side of the substrate 10, the doped polysilicon layer 33 and the doped silicon glass layer 34 are also deposited around the side and front side of the substrate 10.

[0080] In some embodiments, please refer to Figure 10The method for fabricating a solar cell may include: performing an RCA cleaning process on a substrate 10 to remove the doped silicon glass layer 34 deposited around the front and sides of the substrate 10 in an HF chain cleaning tank; then, placing the acid-washed substrate 10 into an alkaline polishing tank, and removing the doped polycrystalline silicon layer 33 deposited around the front and sides of the substrate 10 under the action of an alkaline polishing solution and polishing; the alkaline polishing solution in the alkaline polishing tank may be a mixed solution including sodium hydroxide (NaOH) and polishing additives; finally, using an acid washing solution to clean and remove the remaining doped layer 22 and oxide layer 31 on the front side of the substrate 10, and micro-etching the PN junction at the edge.

[0081] In some embodiments, please refer to Figure 11 The method for fabricating solar cells may further include: forming a passivation antireflection layer 35 on the front and back sides of the substrate 10; specifically, depositing a uniform aluminum oxide (Al₂O₃) layer using atomic layer deposition (ALD) technology. x A layer is then formed; subsequently, a silicon nitride antireflection and passivation film, such as silicon nitride (SiN), is deposited using plasma-enhanced chemical vapor deposition (PECVD). x ) / Silicon oxynitride (SiNO) / Silicon oxide (SiO) x (Layering)

[0082] In some embodiments, please refer to Figure 12 After the passivation antireflection layer 35 is formed, the method for fabricating a solar cell may further include: performing a screen printing process to print grid lines on the substrate 10, with the grid lines precisely aligned with the metal contact area 11; then, rapidly sintering in a high-temperature furnace, so that the paste on the front side penetrates the passivation antireflection layer 35 and forms a low-ohmic contact with the doped inner expansion layer 21, and the doped inner expansion layer 21 (selective emitter) and the doped polycrystalline silicon layer 33 draw out current through the metal electrode 36; finally, applying high-intensity light to repair defects caused by sintering.

[0083] In some embodiments, the solar cell provided in this disclosure can be a TOPCon (Tunnel Oxide Passivated Contact) cell; specifically, the solar cell can be an N-type Topcon cell. Currently, TOPCon cells, with their superior passivation effect provided by the tunnel oxide layer 32 and doped polycrystalline silicon layer 33 on the back side, have become the mainstream high-efficiency cell technology, meeting the photovoltaic industry's continuous pursuit of higher conversion efficiency and lower manufacturing costs.

[0084] Figures 13 to 18 A cross-sectional structural diagram of a solar cell with selective emission and localized junction units during the fabrication process.

[0085] The method for fabricating a solar cell with selective emission and localized junction units in this embodiment is basically the same as the method for fabricating a solar cell with selective emission and high / low junction units in terms of overall process. The only difference between the two is the thermal annealing step: after the previous process, the doped inner layer 21 of the non-metallic contact region 12 is completely removed, and the oxide layer 31 formed in the thermal annealing stage of this embodiment directly and completely covers the exposed surface of the substrate 10 (see details in [reference]). Figure 13 ).

[0086] Based on this, the present disclosure also provides a solar cell, which is prepared using the solar cell preparation method provided in any of the above embodiments.

[0087] The present disclosure will be further explained below with reference to specific embodiments and comparative examples.

[0088] Example 1

[0089] Step 1, texturing: The surface of the N-type silicon wafer is texturized to form a dense, micron-scale pyramidal texture. Specifically, anisotropic etching can be performed using an alkaline solution of NaOH or KOH at a reaction temperature of 70℃-85℃ to form a random pyramidal microstructure on the surface.

[0090] Step 2, Front-side boron diffusion: The texturized silicon wafer is placed in a tube diffusion furnace, and a boron-containing gas (BCl3 or BBr3) is introduced. At a high temperature of 800℃-1050℃, boron atoms are diffused into the front side of the silicon wafer, forming a heavily doped boron-doped inner diffusion layer across the entire surface. Furthermore, a borosilicate glass layer is formed on top of this boron-doped inner diffusion layer. The sheet resistance after boron diffusion is 200 ohms-400 ohms, and the diffusion concentration is 3E17 atoms / cm². 3 -4E19atoms / cm 3 The junction depth is 0.8μm-2.0μm.

[0091] Step 3, Laser Doping: Using a near-infrared continuous laser with a wavelength in the range of 900nm to 1100nm, the non-metallic grid pattern area is precisely scanned. The laser energy is 54W-90W, the spot overlap rate is 50%-80%, and the area ratio of the laser-treated area to the non-laser-treated area is 24%-48%. The laser energy accelerates the diffusion of surface boron atoms into the silicon mass, with a diffusion concentration of 1E18 atoms / cm³. 3 -1E20atoms / cm 3 The junction depth is 2.0μm-5.0μm.

[0092] Step 4, Secondary texturing: The non-metallic contact areas after laser treatment are re-textured into a pyramidal texture using a wet etching process. The hydrofluoric acid concentration is 2wt%-4wt%, the alkali concentration is 1wt%-2wt%, the etching temperature is 60℃-70℃, and the etching time is 150s-300s; the etching depth is 1.5μm-4.0μm; after etching, each non-metallic contact area retains some light boron doping on the textured surface, with a doping concentration of 1E17 atoms / cm. 3 -3E18atoms / cm 3 The junction depth is 0.2μm-0.7μm; the metal contact area still retains P due to the protection of the borosilicate glass layer. + Layered doping allows for the formation of a complete and uniform high-low junction on the front side of the substrate.

[0093] Step 5, Annealing: Perform thermal annealing on the silicon wafer with a selective emitter structure having a high-low junction structure to form a silicon oxide layer in the non-metallic gate contact area and repair defects on the silicon wafer surface (surface passivation); the annealing temperature is 700℃-900℃.

[0094] Step 6, Backside Polishing: Remove the borosilicate glass layer deposited around the back and sides of the silicon wafer during the boron diffusion process in the HF chain cleaning tank; remove the boron-doped inner diffusion layer deposited around the back and sides of the silicon wafer in the alkaline polishing tank, and polish the back and sides of the silicon wafer; the alkaline polishing solution in the alkaline polishing tank can be a mixed solution including sodium hydroxide and polishing additives.

[0095] Step 7, Oxidation and Phosphorus Diffusion: A very thin layer of silicon dioxide is grown on the back side of the silicon wafer as a tunneling oxide layer using low-pressure chemical vapor deposition; an amorphous silicon layer is deposited on the tunneling oxide layer, and then the amorphous silicon layer is crystallized into a phosphorus-doped polycrystalline silicon layer by high temperature and phosphorus doping, and a phosphorus-silicon glass layer is formed on the phosphorus-doped polycrystalline silicon layer.

[0096] Step 8, RCA cleaning: Remove the phosphorus-silicon glass layer deposited on the front and sides of the silicon wafer during the phosphorus diffusion process in the HF chain cleaning tank; place the acid-washed silicon wafer into the alkaline cleaning tank to remove the phosphorus-doped polycrystalline silicon layer deposited on the front and sides of the silicon wafer. The alkaline cleaning solution in the alkaline cleaning tank is a mixed solution including sodium hydroxide and additives; place the silicon wafer into the acid cleaning tank, and clean it with the acid cleaning solution to remove the borosilicate glass layer on the front of the silicon wafer, and micro-etch the PN junction at the edge.

[0097] Step 9, preparation of passivation and antireflection layer: A uniform aluminum oxide layer is formed on the surface of the silicon wafer using atomic layer deposition technology; silicon nitride antireflection and passivation films are deposited on the front and back sides of the silicon wafer by plasma-enhanced chemical vapor deposition.

[0098] Step 10, screen printing: Print grid lines on the front and back of the silicon wafer, with the grid lines precisely aligned with the metal grid line contact area on the front of the silicon wafer; rapidly sinter in a high-temperature furnace, allowing the paste on the front to penetrate the dielectric layer and form a low-ohmic contact with the boron-doped inner layer, and selectively emitter and phosphorus-doped polycrystalline silicon layer to draw current through metal electrodes; then apply high-intensity light to repair defects caused by sintering, and the fabrication of the solar cell is completed.

[0099] Example 2

[0100] Example 2 is basically the same as Example 1, except that:

[0101] Step 3, Laser Doping: Using a near-infrared continuous laser with a wavelength in the range of 900nm to 1100nm, the non-metallic grid pattern area is precisely scanned. The laser energy is 38W-76W, the spot overlap rate is 30%-60%, and the area ratio of the laser-treated area to the non-laser-treated area is 24%-48%. The laser energy accelerates the diffusion of surface boron atoms into the silicon mass, with a diffusion concentration of 1E18 atoms / cm³. 3 -5E19atoms / cm 3 The junction depth is 1.0μm-4.0μm.

[0102] Step 4, Secondary texturing: The non-metallic contact area after laser treatment is re-textured into a pyramidal textured surface using a wet etching process. The hydrofluoric acid concentration is 2wt%-6wt%, the alkali concentration is 1wt%-3wt%, the etching temperature is 60℃-80℃, and the etching time is 150s-400s; the etching depth is 2.0μm-5.0μm. After etching, the non-metallic contact area is an undoped pure pyramidal textured silicon substrate, while the metallic contact area retains P due to the protection of the borosilicate glass layer. + Layered doping allows for the formation of complete and uniform local junctions on the front side of the substrate.

[0103] Example 3

[0104] Example 3 is basically the same as Example 1, except that:

[0105] Step 3, Laser Doping: Using a near-infrared continuous laser with a wavelength in the range of 900nm to 1100nm, the non-metallic grid pattern area is precisely scanned. The laser energy is 38W-90W, the spot overlap rate is 30%-80%, and the area ratio of the laser-treated area to the non-laser-treated area is 24%-48%. The laser energy accelerates the diffusion of surface boron atoms into the silicon mass, with a diffusion concentration of 1E18 atoms / cm³. 3 -1E20atoms / cm 3 The junction depth is 1.0μm-5.0μm.

[0106] Step 4, Secondary texturing: The non-metallic contact area after laser treatment is re-textured into a pyramidal texture using a wet etching process. The hydrofluoric acid concentration is 2wt%-6wt%, the alkali concentration is 1wt%-3wt%, the etching temperature is 60℃-80℃, and the etching time is 150s-400s; the etching depth is 1.5μm-5.0μm. After etching, all or part of the light boron doping on the non-metallic contact area is removed, while the borosilicate glass layer protects the boron doping in the metallic contact area. + Layer doping; thus, a hybrid structure including high-low junctions and local junctions can be formed on the front side of the substrate, wherein the high-low junction accounts for 20%-80% and the local junction accounts for 20%-80%.

[0107] Comparative Example

[0108] The comparative example is basically the same as Example 1, except that:

[0109] Step 3, Laser treatment: Select ultraviolet picosecond laser to treat the non-metallic contact area. Since the ultraviolet picosecond laser is a film-opening laser, it does not have the doping propulsion effect. It only vaporizes or loosens the borosilicate glass layer on the boron-doped surface of the non-metallic contact area to prepare for subsequent selective etching.

[0110] Step 4, Secondary texturing: Use acid solution to clean away the borosilicate glass layer and the laser area loss layer, perform initial repair on the laser area, and etch the laser area to a depth of 1.0μm-5.0μm to remove part or all of the residual PN junction in the laser area; high and low junctions and local junctions appear randomly and cannot be controlled according to actual needs.

[0111] The solar cells prepared in the above embodiments and comparative examples were then subjected to performance tests, and the test results are shown in Tables 1 and 2.

[0112] Table 1 shows the test results of the passivation level of the non-metallic contact area on the front side of the silicon wafer of the solar cells prepared in the above embodiments and comparative examples. The passivation level of the non-metallic contact area on the front side of the silicon wafer can be obtained by WCT120 testing. Table 2 shows the test results of the conversion efficiency (Eta), open circuit voltage (Uoc), fill factor (FF), short circuit current (Isc), and series resistance (Rs) of the solar cells prepared in the above embodiments and comparative examples.

[0113] Table 1

[0114]

[0115] Table 2

[0116]

[0117] As can be seen from Tables 1 and 2, the passivation level and electrical performance of the non-metallic contact area treated by infrared continuous laser are significantly better than those treated by open-film laser. This is because in the front-side selective emitter structure, the damage to the silicon wafer caused by infrared continuous laser is relatively small, and key parameters such as doping concentration and doping depth of the non-metallic contact area can be precisely controlled. Furthermore, the subsequent wet cleaning removes all laser damage, further improving the photoelectric conversion efficiency of the solar cell and bringing positive benefits to the solar cell efficiency.

[0118] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0119] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a selective emitter, characterized in that, The method for preparing the selective emitter includes: A substrate is provided; the substrate includes metal contact areas and non-metal contact areas; The substrate is subjected to ion diffusion treatment to form a doped inner extension layer extending from the surface of the substrate into the substrate and a rich doped layer covering the doped inner extension layer; The non-metallic contact area is laser-processed using infrared continuous laser to push the doped elements in the rich doped layer into the substrate, so that the thickness of the doped inner expansion layer in the non-metallic contact area is greater than the thickness of the doped inner expansion layer in the metallic contact area. Using the richly doped layer located in the metal contact region as a barrier layer, the substrate is etched to partially or completely remove the doped inner extension layer located in the non-metal contact region, so that the doping concentration in the non-metal contact region is less than the doping concentration in the metal contact region.

2. The method for preparing a selective emitter according to claim 1, characterized in that, When the substrate is etched, the etching depth is controlled to be less than the thickness of the doped inner layer located in the non-metallic contact region, so as to remove part of the doped inner layer located in the non-metallic contact region and form a lightly doped region in the non-metallic contact region.

3. The method for preparing a selective emitter according to claim 1, characterized in that, When the substrate is etched, the etching depth is controlled to be greater than the thickness of the doped inner layer located in the non-metallic contact region, so as to completely remove the doped inner layer located in the non-metallic contact region and form an undoped region in the non-metallic contact region.

4. The method for preparing a selective emitter according to claim 1, characterized in that, The infrared continuous laser is a near-infrared continuous laser with a wavelength of 900nm-1100nm; during the laser processing, the laser energy is 38W-90W and the spot overlap rate is 30%-80%.

5. The method for preparing a selective emitter according to claim 1, characterized in that, During the laser treatment, the laser energy is 54W-90W, and the spot overlap rate is 50%-80%; after the laser treatment, the doping concentration of the non-metallic contact area is 1E18 atoms / cm². 3 ~1E20atoms / cm 3 The junction depth is 2.0μm-5.0μm.

6. The method for preparing a selective emitter according to claim 5, characterized in that, The etching process is wet etching; the wet etching uses a mixed etching solution of hydrofluoric acid and alkaline solution, wherein the concentration of hydrofluoric acid is 2wt%-4wt% and the concentration of alkaline solution is 1wt%-2wt%; the temperature of the wet etching is 60℃-70℃ and the time is 150s-300s; the etching depth of the wet etching is 1.5μm-4.0μm, and the etching depth is less than the junction depth of the non-metallic contact area after the laser treatment.

7. The method for preparing a selective emitter according to claim 1, characterized in that, During the laser treatment, the laser energy is 38W-76W, and the spot overlap rate is 30%-60%. After the laser treatment, the doping concentration of the non-metallic contact area is 1E18 atoms / cm². 3 ~5E19atoms / cm 3 The junction depth is 1.0μm-4.0μm.

8. The method for preparing a selective emitter according to claim 7, characterized in that, The etching process is wet etching; the wet etching uses a mixed etching solution of hydrofluoric acid and alkaline solution, wherein the concentration of hydrofluoric acid is 2wt%-6wt% and the concentration of alkaline solution is 1wt%-3wt%; the temperature of the wet etching is 60℃-80℃ and the time is 150s-400s; the etching depth of the wet etching is 2.0μm-5.0μm, and the etching depth is greater than the junction depth of the non-metallic contact area after the laser treatment.

9. A method for preparing a solar cell, characterized in that, The method for preparing the solar cell includes the method for preparing the selective emitter as described in any one of claims 1 to 8.

10. A solar cell, characterized in that, The solar cell is prepared using the solar cell preparation method described in claim 9.

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