Selective emitter and solar cell

Abstract

The invention relates to a selective emitter and a solar cell. The selective emitter comprises a metal grid line area and a non-metal grid line area, and the height of the metal grid line area is different from that of the non-metal grid line area; the doping concentration of the non-metal grid line region is greater than or equal to 0, and the doping concentration of the metal grid line region is greater than that of the non-metal grid line region; the transition region is located between the metal grid line region and the non-metal grid line region; the top surface of the transition region is an inclined surface, and the transition region is undoped. According to the selective emitter provided by the invention, the undoped transition region is formed between the metal grid line region and the non-metal grid line region, so that the problem of carrier recombination aggravation caused by an irregular inclined plane structure can be improved; a tunneling effect and a local breakdown phenomenon caused by doping can be avoided; according to the selective emitter provided by the invention, the open-circuit voltage and the fill factor of the solar cell can be remarkably improved, and the photoelectric conversion efficiency is improved.

Description

Technical Field

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

[0002] Traditional uniform emitters face a trade-off between reducing contact resistance and improving passivation performance. To optimize the electrical performance of solar cell emitters, selective emitter (SE) technology has been introduced. This technology achieves synergistic optimization of minority carrier lifetime, contact performance, and passivation performance by constructing differentiated doping concentration distributions in the metal grid region and the non-metal grid region, thereby improving the conversion efficiency of solar cells.

[0003] However, compared to the fabrication process of a uniform emitter, SE technology adds an additional laser doping step. During the laser patterning process, laser irradiation forms grooves on the silicon wafer surface. The sidewall roughness (Ra) of these grooves is high, which damages the silicon wafer lattice structure and introduces high-density crystal defects and dangling bonds, becoming extremely strong carrier recombination centers. On this basis, when ion doping (such as boron doping) is performed, a large amount of boron impurities accumulate on the sidewalls of the grooves, further inducing new dangling bonds and crystal defects, forming new carrier recombination centers, significantly aggravating carrier recombination losses, resulting in a significant reduction in the open-circuit voltage and fill factor of the solar cell, and consequently, a reduction in the conversion efficiency of the solar cell. Summary of the Invention

[0004] Therefore, it is necessary to provide a selective emitter and a solar cell to address the above problems.

[0005] A selective emitter includes: a metal gate region and a non-metal gate region, the metal gate region and the non-metal gate region having different heights; the doping concentration of the non-metal gate region is greater than or equal to 0, and the doping concentration of the metal gate region is greater than the doping concentration of the non-metal gate region; a transition region located between the metal gate region and the non-metal gate region; the top surface of the transition region is an inclined surface, and the transition region is undoped.

[0006] In one embodiment, a first buffer zone is provided between the metal gate region and the transition region; the first buffer zone has the same height as the metal gate region, and the first buffer zone is undoped. It is understood that by providing a first buffer zone between the metal gate region and the transition region, precise isolation between the highly recombination-active region and the lattice-damaged region of the tilted surface can be achieved; the undoped intrinsic characteristic of the first buffer zone can block the migration path of high-concentration charge carriers to the defect region, thereby avoiding recombination losses of high-concentration charge carriers in the defect region and ensuring effective separation and transport of charge carriers.

[0007] In one embodiment, the width of the first buffer is proportional to the tilt angle of the tilted surface. It is understood that as the tilt angle of the transition region's tilted surface increases, trenches are more likely to appear at the junction of the tilted surface and the metal grid region, leading to increased recombination losses of high-concentration charge carriers in the defect region. Therefore, a wider first buffer is needed to mitigate this increased recombination loss. Conversely, as the tilt angle of the transition region's tilted surface decreases, the recombination losses of high-concentration charge carriers in the defect region decrease, effectively suppressing recombination losses, thus eliminating the need for an excessively wide first buffer. Therefore, the width of the first buffer being proportional to the tilt angle of the transition region's tilted surface ensures that recombination losses remain at a low level while avoiding excessive occupation of the effective light-receiving area of ​​the solar cell, achieving a balance between performance and structure.

[0008] In one embodiment, the width of the first buffer is proportional to the height difference between the metal grid region and the non-metal grid region. It is understood that an increase in the height difference between the metal grid region and the non-metal grid region may lead to an increase in carrier migration distance and a higher probability of carrier recombination, thereby increasing recombination loss. Therefore, a wider first buffer is needed to mitigate the increased recombination loss. Conversely, a smaller height difference between the metal grid region and the non-metal grid region can make the carrier transport path smoother, shortening the carrier migration distance and thus reducing recombination loss. Therefore, an excessively wide first buffer is unnecessary. Thus, a first buffer width proportional to the height difference between the metal grid region and the non-metal grid region ensures that recombination loss remains at a low level, maintaining carrier transport efficiency within the optimal range while avoiding excessive occupation of the effective light-receiving area of ​​the solar cell, achieving a balance between performance and structure.

[0009] In one embodiment, the width of the first buffer is 20μm-100μm. It is understood that if the width of the first buffer is too large, it will excessively occupy the effective light-receiving area of ​​the solar cell, increasing the carrier transport distance and leading to a decrease in short-circuit current density; if the width of the first buffer is too small, it will be difficult to effectively isolate the doped layer of the metal grid region from the defect region of the tilted surface, easily leading to increased carrier recombination losses and failing to exert the passivation and isolation functions of the buffer. Therefore, the width of the first buffer can be 20μm-100μm, which can fully utilize the passivation and isolation functions of the buffer while avoiding excessive occupation of the effective light-receiving area of ​​the solar cell.

[0010] In one embodiment, when the doping concentration of the non-metallic gate region is greater than 0, a second buffer zone is provided between the non-metallic gate region and the transition region; the second buffer zone has the same height as the non-metallic gate region, and the second buffer zone is undoped. It is understood that by providing a second buffer zone between the non-metallic gate region and the transition region, the undoped design of the second buffer zone can improve the impurity accumulation on the substrate surface, ensure the integrity of the lattice structure in the region, provide a flat substrate for the passivation layer on the doped layer, thereby providing a complete coverage space for the passivation layer. The flat interface can significantly reduce the interface state density between the substrate and the passivation layer, ensuring effective passivation of the interface states. The uniform distribution of interface charge is beneficial to enhancing the stability of the built-in electric field.

[0011] In one embodiment, the width of the second buffer is proportional to the tilt angle of the tilted surface. It is understood that as the tilt angle of the transition region's tilted surface increases, the surface uniformity decreases, potentially leading to insufficient passivation layer coverage and a decrease in passivation level, thus affecting the fill factor and open-circuit voltage. Therefore, a wider second buffer can be provided to improve the problem of insufficient passivation layer coverage. Conversely, as the tilt angle of the transition region's tilted surface decreases, the flatness of the tilted surface improves, and the width of the second buffer can be reduced accordingly. Therefore, the width of the second buffer is proportional to the tilt angle of the transition region's tilted surface, which can prevent a decrease in passivation level while avoiding excessive occupation of the battery's effective light-receiving area, achieving a balance between performance and structure.

[0012] In one embodiment, the width of the second buffer is proportional to the height difference between the metal grid region and the non-metal grid region. It is understood that an increase in the height difference between the metal and non-metal grid regions may lead to an increase in carrier migration distance and recombination probability, resulting in increased recombination loss. Therefore, a wider second buffer is needed to mitigate this increase in recombination loss. Conversely, a decrease in the height difference between the metal and non-metal grid regions can make the carrier transport path smoother, shortening the carrier migration distance and thus reducing recombination loss. Therefore, an excessively wide second buffer is unnecessary. Thus, a second buffer width proportional to the height difference between the metal and non-metal grid regions ensures that recombination loss remains at a low level, maintaining carrier transport efficiency within the optimal range while avoiding excessive occupation of the effective light-receiving area of ​​the solar cell, achieving a balance between performance and structure.

[0013] In one embodiment, the width of the second buffer is 20μm-100μm. It is understood that if the width of the second buffer is too large, it will excessively occupy the effective light-receiving area of ​​the solar cell, increasing the carrier transport distance and leading to a decrease in short-circuit current density; if the width of the second buffer is too small, it may not be able to effectively perform its passivation and isolation functions. Therefore, the width of the second buffer can be 20μm-100μm, balancing the passivation effect with the effective light-receiving area of ​​the solar cell, and avoiding a reduction in the photogenerated carrier collection area due to an excessively wide second buffer.

[0014] This disclosure also provides a solar cell, which includes the selective emitter described in any of the above embodiments.

[0015] The selective emitter disclosed herein, on the one hand, avoids the problem of impurity accumulation on the tilted surface by forming an undoped transition region between the metal grid region and the non-metal grid region, forming a regular tilted surface with low roughness, thereby suppressing the generation of dangling bonds and crystal defects, and improving the problem of intensified carrier recombination caused by irregular tilted surface structure; on the other hand, the transition region is an undoped intrinsic region, which can avoid the tunneling effect and local breakdown phenomenon caused by doping, ensuring the reliability of the electrical performance of the solar cell; the selective emitter disclosed herein can significantly improve the open-circuit voltage and fill factor of the solar cell, thereby improving the photoelectric conversion efficiency. Attached Figure Description

[0016] 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.

[0017] Figure 1 A schematic diagram of the inclined plane structure at the junction of the laser region and the non-laser region, provided for related technologies;

[0018] Figure 2 This is a cross-sectional structural diagram of a high-low junction structure provided in an embodiment of the present disclosure;

[0019] Figure 3 This is a cross-sectional structural diagram of a partial structure provided in an embodiment of the present disclosure;

[0020] Figure 4 This is a cross-sectional structural diagram of another high-low junction structure provided in an embodiment of the present disclosure;

[0021] Figure 5 This is a cross-sectional structural diagram of another local structural feature provided in an embodiment of the present disclosure;

[0022] Figure 6 A cross-sectional schematic diagram of the high-low structure provided for Comparative Example 1;

[0023] Figure 7 A cross-sectional structural diagram of a local structure provided for Comparative Example 2;

[0024] Figure 8 A cross-sectional structural diagram of the high-low junction structure provided for Comparative Example 3;

[0025] Figure 9 A cross-sectional schematic diagram of the local structure provided for Comparative Example 4.

[0026] In the figure: 10, substrate; 11, metal gate region; 12, non-metal gate region; 13, transition region; 21, first buffer zone; 22, second buffer zone; 31, doped layer; 32, passivation layer; 33, passivation antireflection layer; 34, metal electrode. Detailed Implementation

[0027] 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.

[0028] 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.

[0029] 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.

[0030] Figure 1A schematic diagram of the inclined plane structure at the junction of the laser region and the non-laser region, provided for related technologies.

[0031] During laser patterning, the laser energy distribution density typically exhibits a Gaussian distribution (high energy at the center, low energy at the edges). This uneven energy absorption leads to explosive removal of the material rather than smooth evaporation, leaving a rough surface with unevenness and poor recrystallization quality at the boundary of the laser-scanned area (laser zone). Therefore, the sidewall roughness of the grooves formed by laser irradiation in both metal and non-metal grid areas is relatively high. After laser patterning, when wet etching is performed on the laser zone, the initial surface unevenness causes slight differences in the residence time and etching rate of the etching solution at the protrusions and depressions. This difference amplifies the original unevenness of the sidewalls, exacerbating the roughness and inhomogeneity.

[0032] It is evident that the irregular inclined surface (i.e., the groove sidewall) structure at the junction of the laser area and the non-laser area is the result of the combined effect of the inherent characteristics of the laser and the anisotropy of wet etching.

[0033] Specifically, the irregular inclined surface at the junction of the laser area and the non-laser area exhibits a non-uniform, sawtooth, or corrugated structure (e.g. Figure 1 As shown in Figure (a), the increased surface roughness of the irregular slope disrupts the silicon wafer's lattice structure, introducing high-density crystal defects and dangling bonds, creating extremely strong carrier recombination centers. During subsequent ion doping, a large number of impurities tend to accumulate on the irregular slope surface, further increasing sidewall roughness, generating numerous dangling bonds and crystal defects, forming even more carrier recombination centers. This results in a large number of photogenerated carriers recombinating in the irregular slope region, unable to transport to the bottom electrode, leading to a significant decrease in open-circuit voltage. Furthermore, the PN junction is exposed at the edge of the irregular slope. The rough, irregular slope makes the junction surface of the PN junction uneven, with many tiny "peaks" and "depressions," causing localized electric field concentration, making tunneling and localized breakdown more likely, resulting in a significant decrease in the fill factor.

[0034] In addition, vertical "V"-shaped grooves may form at the bottom of irregular slopes (such as...). Figure 1 (as shown in Figure (b)) or a horizontal "<" shaped gap (such as...) Figure 1 As shown in Figure (c), under the influence of ion doping, these trench and interstitial regions are prone to forming impurity accumulation regions, which can also lead to an increase in carrier recombination.

[0035] Based on this, embodiments of the present disclosure provide a selective emitter. Figure 2 A cross-sectional structural diagram of a high-low junction structure provided in this embodiment of the present disclosure is shown in the figure; the selective emitter includes:

[0036] Metal gate region 11 and non-metal gate region 12 have different heights; the doping concentration of non-metal gate region 12 is greater than or equal to 0, and the doping concentration of metal gate region 11 is greater than the doping concentration of non-metal gate region 12.

[0037] The transition region 13 is located between the metal gate region 11 and the non-metal gate region 12; the top surface of the transition region 13 is an inclined surface, and the transition region 13 is undoped.

[0038] It is understood that the selective emitter provided in this disclosure, on the one hand, by forming an undoped transition region 13 between the metal grid region 11 and the non-metal grid region 12, can avoid the problem of impurity accumulation on the tilted surface, forming a regular tilted surface with low roughness, thereby suppressing the generation of dangling bonds and crystal defects, and improving the problem of intensified carrier recombination caused by irregular tilted surface structure; on the other hand, the transition region 13 is an undoped intrinsic region, which can avoid the tunneling effect and local breakdown phenomenon caused by doping, ensuring the reliability of the electrical performance of the solar cell; the selective emitter provided in this disclosure can significantly improve the open-circuit voltage and fill factor of the solar cell, thereby improving the photoelectric conversion efficiency.

[0039] In some embodiments, the metal gate region 11 and the non-metal gate region 12 are located on the substrate 10; the metal gate region 11 is the area on the surface of the substrate 10 that forms an ohmic contact with the metal electrode 34, and its main function is to achieve efficient collection and export of photogenerated carriers; the non-metal gate region 12 refers to the area on the surface of the substrate that is not in direct contact with the metal electrode 34, and its core function is to significantly reduce carrier recombination loss through high-quality surface passivation.

[0040] Here, substrate 10 can be a silicon substrate; in this embodiment, substrate 10 can be an N-type silicon substrate. Substrate 10 can serve as an absorption layer and transport carrier for photogenerated carriers. The quality of substrate 10 directly affects the open-circuit voltage and overall performance of the solar cell. In this embodiment, substrate 10 uses an N-type silicon substrate. Compared with P-type silicon substrates, N-type silicon substrates have 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 solar cells.

[0041] In some embodiments, the top surface of the transition region 13 located between the metal gate region 11 and the non-metal gate region 12 is an inclined surface that smoothly extends from the metal gate region 11 to the non-metal gate region 12. The inclined surface connects the top surfaces of the metal gate region 11 and the non-metal gate region 12 in a continuous and gradual manner, so that the surface profile of the selective emitter presents a continuous and smooth shape, effectively reducing the risk of surface stress concentration. At the same time, the transition region 13 adopts an undoped design: on the one hand, the defect density of the undoped transition region 13 itself is at an extremely low level, and no new carrier recombination centers are introduced, which can ensure that the carriers maintain a long carrier lifetime during the process of crossing the transition region 13; on the other hand, the surface state density of the undoped transition region 13 is lower, which can form a tighter interface bond with the passivation layer 32, thereby significantly enhancing the passivation effect and greatly reducing the recombination loss of surface photogenerated carriers.

[0042] Figure 3 This is a cross-sectional structural diagram of a partial structure provided in an embodiment of the present disclosure; Figure 4 This is a cross-sectional structural diagram of another high-low junction structure provided in an embodiment of the present disclosure; Figure 5 This is a cross-sectional structural diagram of another local structure provided in an embodiment of this disclosure.

[0043] In some embodiments, please refer to Figure 2 or Figure 4 The doping concentration of the non-metallic gate region 12 is greater than 0, and the doping concentration of the metallic gate region 11 is greater than that of the non-metallic gate region 12; thus, a high-low gradient doped high-low junction structure can be formed. Here, the metallic gate region 11 adopts a high-doped deep diffusion design. On the one hand, high doping can reduce the contact resistance of the metal-semiconductor interface, reduce the transport loss of charge carriers at the interface between the metal electrode 34 and the emitter, and provide a low-resistance channel for rapid carrier outflow; on the other hand, deep diffusion can provide sufficient doping buffer to effectively prevent the metal paste from burning through the PN junction during high-temperature sintering, thereby ensuring the electrical stability of the solar cell and ultimately achieving a reduction in the overall series resistance of the device and a significant improvement in the fill factor. Meanwhile, the non-metallic gate region 12 adopts a shallow junction and light doping design. On the one hand, it greatly suppresses Auger recombination of charge carriers, reduces the surface recombination rate, and brings higher passivation effect and open circuit voltage. On the other hand, the shallow junction structure weakens the "dead layer" effect in this region, significantly improves the absorption and utilization of short-wavelength light, effectively enhances the short-wavelength light response, and ultimately optimizes the short-circuit current.

[0044] In some embodiments, please refer to Figure 3 or Figure 5The doping concentration of the non-metallic gate region 12 is zero, while the doping concentration of the metallic gate region 11 is greater than that of the non-metallic gate region 12; thus, a locally doped local junction structure can be formed. Here, the metallic gate region 11 is a doped region, which can form an excellent ohmic contact with the metal electrode 34 with low contact resistance, which is beneficial to improving the fill factor. At the same time, the non-metallic gate region 12 adopts an undoped design, which is beneficial to completely eliminate Auger recombination and defect recombination caused by high doping in this region, achieving the lowest surface recombination and the highest open-circuit voltage.

[0045] In some embodiments, the substrate 10 is covered with a doped layer 31. Specifically, in a high-low junction structure, the doped layer 31 is located in the metal gate region 11 and the non-metal gate region 12, and the doped layer 31 exhibits a differentiated distribution of concentration and junction depth in different regions. In a local junction structure, the doped layer 31 in the non-metal gate region 12 is completely removed, and the surface of the non-metal gate region 12 is a pristine, undoped silicon textured surface. The pure silicon textured surface structure has optimal 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. Here, the doped layer 31 can be a boron doped layer, which, as the core doped layer of the P-type doping system, can form a stable PN junction with the N-type substrate.

[0046] It should be noted that, in addition to the doping concentration distribution, the morphology and height of the metal gate region 11 and the non-metal gate region 12 can also be flexibly adjusted according to actual process requirements; in some specific embodiments, please refer to... Figure 2 or Figure 3 The height of the metal gate region 11 is higher than the height of the non-metal gate region 12, which helps to increase the contact area between the metal electrode 34 and the emitter, further reducing the contact resistance; in other embodiments, please refer to Figure 4 or Figure 5 The height of the metal grid region 11 can also be lower than the height of the non-metal grid region 12. This reduces the overall height of the metal electrode 34, shrinking its projected area on the light-receiving surface of the solar cell. This effectively reduces the shading of incident light by the metal electrode 34, lowering the loss of photogenerated carriers caused by shading, and laying the foundation for improving the short-circuit current of the solar cell. This disclosure does not impose specific limitations on the specific morphology and height of the metal grid region 11 and the non-metal grid region 12.

[0047] In some embodiments, a first buffer zone 21 is provided between the metal gate region 11 and the transition region 13; the first buffer zone 21 has the same height as the metal gate region 11, and the first buffer zone 21 is undoped. Here, the height of the first buffer zone 21 is consistent with the height of the metal gate region 11, and this region is an undoped intrinsic semiconductor region without the introduction of any doping atoms. The first buffer zone 21 has the core characteristics of uniform electrical properties and complete crystal structure, which can provide a basis for optimizing the electrical performance of solar cells.

[0048] Understandably, by setting a first buffer zone 21 between the metal gate region 11 and the transition region 13, precise isolation between the highly active recombination region and the lattice-damaged region of the tilted surface can be achieved. Specifically, the doped layer 31 of the metal gate region 11 has the characteristics of a large carrier concentration gradient and high lattice stress, making it prone to becoming an active region for carrier recombination. The tilted surface of the transition region 13 is formed by laser processing and wet etching, and it has a lattice-damaged region, which is prone to inducing new dangling bonds and crystal defects. The undoped intrinsic characteristics of the first buffer zone 21 can block the migration path of high-concentration carriers to the defect region, thereby avoiding recombination loss of high-concentration carriers in the defect region and ensuring the effective separation and transport of carriers.

[0049] In some embodiments, the width D1 of the first buffer 21 is proportional to the tilt angle of the inclined surface of the transition region 13.

[0050] Understandably, as the tilt angle of the inclined surface of the transition region 13 increases, trenches are more likely to appear at the junction of the inclined surface and the metal grid region 11, leading to increased recombination losses of high-concentration carriers in the defect region. Therefore, a wider first buffer zone 21 is needed to mitigate the increased recombination losses. Conversely, as the tilt angle of the inclined surface of the transition region 13 decreases, the recombination losses of high-concentration carriers in the defect region decrease, effectively suppressing recombination losses. In this case, an excessively wide first buffer zone 21 is unnecessary. Therefore, the width D1 of the first buffer zone 21 is proportional to the tilt angle of the inclined surface of the transition region 13, ensuring that recombination losses remain at a low level while avoiding excessive occupation of the effective light-receiving area of ​​the solar cell, thus achieving a balance between performance and structure.

[0051] In some embodiments, the width D1 of the first buffer 21 is proportional to the height difference between the metal gate area 11 and the non-metal gate area 12.

[0052] It is understandable that an increase in the height difference between the metal grid region 11 and the non-metal grid region 12 may lead to an increase in carrier migration distance and a higher probability of carrier recombination, thereby increasing recombination loss. Therefore, a wider first buffer zone 21 is needed to mitigate the increased recombination loss. Conversely, a decrease in the height difference between the metal grid region 11 and the non-metal grid region 12 can make the carrier transport path smoother, shorten the carrier migration distance, and thus reduce recombination loss. Therefore, an excessively wide first buffer zone 21 is unnecessary. Thus, the width D1 of the first buffer zone 21 is proportional to the height difference between the metal grid region 11 and the non-metal grid region 12, which ensures that recombination loss remains at a low level, maintains carrier transport efficiency within the optimal range, and avoids excessive occupation of the effective light-receiving area of ​​the solar cell, achieving a balance between performance and structure.

[0053] In some embodiments, the width D1 of the first buffer 21 can be 20μm-100μm; for example, the width D1 of the first buffer 21 can be 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, etc.

[0054] Understandably, if the width D1 of the first buffer zone 21 is too large, it will excessively occupy the effective light-receiving area of ​​the solar cell, increasing the carrier transport distance and leading to a decrease in short-circuit current density. If the width D1 of the first buffer zone 21 is too small, it will be difficult to effectively isolate the doped layer 31 of the metal grid region 11 from the defect region of the tilted surface, easily leading to increased carrier recombination loss and failing to exert the passivation and isolation functions of the buffer zone. Therefore, the width D1 of the first buffer zone 21 can be 20μm-100μm, which can fully exert the passivation and isolation functions of the buffer zone while avoiding excessive occupation of the effective light-receiving area of ​​the solar cell.

[0055] In some embodiments, please refer to Figure 2 or Figure 4 When the doping concentration of the non-metallic gate region 12 is greater than 0, a second buffer zone 22 is provided between the non-metallic gate region 12 and the transition region 13. The second buffer zone 22 has the same height as the non-metallic gate region 12, and the second buffer zone 22 is undoped. Here, the height of the second buffer zone 22 is consistent with the height of the non-metallic gate region 12, and this region is an undoped intrinsic semiconductor region without the introduction of any doping atoms. The second buffer zone 22 has the core characteristics of uniform electrical properties and complete crystal structure, which can provide a basis for optimizing the electrical performance of solar cells.

[0056] It is understandable that by setting a second buffer zone 22 between the non-metallic gate region 12 and the transition region 13, the undoped design of the second buffer zone 22 can improve the impurity accumulation on the surface of the substrate 10, ensure the integrity of the lattice structure in the region, provide a flat substrate for the passivation layer 32 on the doped layer 31, thereby providing a complete coverage space for the passivation layer 32. The flat interface can significantly reduce the interface state density between the substrate 10 and the passivation layer 32, ensure effective passivation of the interface states, and the uniform distribution of interface charge is beneficial to enhancing the stability of the built-in electric field.

[0057] In some embodiments, the width D2 of the second buffer 22 is proportional to the tilt angle of the inclined surface of the transition region 13.

[0058] Understandably, as the tilt angle of the transition region 13 increases, the surface uniformity of the tilted surface decreases, which can easily lead to insufficient coverage of the passivation layer 32, resulting in a decrease in the passivation level and thus affecting the fill factor and open-circuit voltage. Therefore, a wider second buffer zone 22 can be provided to improve the problem of insufficient coverage of the passivation layer 32. Conversely, as the tilt angle of the transition region 13 decreases, the flatness of the tilted surface improves, and the width D2 of the second buffer zone 22 can be reduced accordingly. Therefore, the width D2 of the second buffer zone 22 is proportional to the tilt angle of the transition region 13, which can prevent a decrease in the passivation level and avoid excessive occupation of the effective light-receiving area of ​​the battery, achieving a balance between performance and structure.

[0059] In some embodiments, the width D2 of the second buffer 22 is proportional to the height difference between the metal gate region 11 and the non-metal gate region 12.

[0060] Understandably, an increased height difference between the metal grid region 11 and the non-metal grid region 12 may lead to an increase in carrier migration distance and recombination probability, resulting in increased recombination loss. Therefore, a wider second buffer zone 22 is needed to mitigate the increased recombination loss. Conversely, a smaller height difference between the metal grid region 11 and the non-metal grid region 12 can create a smoother carrier transport path, shortening the carrier migration distance and thus reducing recombination loss. In this case, an excessively wide second buffer zone 22 is unnecessary. Therefore, the width D2 of the second buffer zone 22 is proportional to the height difference between the metal grid region 11 and the non-metal grid region 12, ensuring that recombination loss remains at a low level, maintaining carrier transport efficiency within the optimal range, while avoiding excessive occupation of the effective light-receiving area of ​​the solar cell, thus achieving a balance between performance and structure.

[0061] In some embodiments, the width D2 of the second buffer 22 is 20μm-100μm; for example, the width D2 of the second buffer 22 can be 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, etc.

[0062] Understandably, if the width D2 of the second buffer zone 22 is too large, it will excessively occupy the effective light-receiving area of ​​the solar cell, increasing the carrier transport distance and leading to a decrease in short-circuit current density. If the width D2 of the second buffer zone 22 is too small, it may not be able to perform its passivation and isolation functions. Therefore, the width D2 of the second buffer zone 22 can be 20μm-100μm, which can balance the passivation effect and the effective light-receiving area of ​​the solar cell, avoiding the reduction of the photogenerated carrier collection area due to the second buffer zone 22 being too wide.

[0063] It should be noted that the width D1 of the first buffer zone 21 is also called the "first doping / sloping passivation buffer spacing," which refers to the buffer spacing between the doped layer 31 in the metal gate region 11 and the sloping surface of the transition region 13. The width D2 of the second buffer zone 22 is also called the "second doping / sloping passivation buffer spacing," which refers to the buffer spacing between the doped layer 31 in the non-metal gate region 12 and the sloping surface of the transition region 13. Here, the width D1 of the first buffer zone 21 and the width D2 of the second buffer zone 22 are respectively the dimensions of the first buffer zone 21 and the second buffer zone 22 along the arrangement direction of the metal gate region 11 and the non-metal gate region 12.

[0064] In some embodiments, the passivation layer 32 on the doped layer 31 can be an aluminum oxide (Al2O3) passivation layer, whose core function is surface passivation to solve the carrier recombination problem caused by dangling bonds on the substrate 10 surface; the passivation antireflection layer 33 on the passivation layer 32 can be silicon nitride (SiN). x Passivation and anti-reflection layer.

[0065] In some embodiments, the metal electrode 34 located in the metal gate region 11 can form a good ohmic contact with the doped layer 31 in the metal gate region 11.

[0066] This disclosure provides a solar cell, which includes the selective emitter described in any of the above embodiments.

[0067] In some embodiments, the solar cell can be a TOPCon (tunnel oxide passivated contact) cell; specifically, the solar cell can be an N-type TOPCon cell. With the photovoltaic industry's continuous pursuit of higher conversion efficiency and lower manufacturing costs, TOPCon technology has rapidly replaced PERC (passivated emitter and back contact) technology, becoming the mainstream high-efficiency cell technology. The embodiments of this disclosure, by optimizing the selective emitter structure, can improve the problem of increased carrier recombination caused by irregular sloped structures, avoid tunneling effects and local breakdown phenomena caused by doping, and thus significantly improve the open-circuit voltage and fill factor of the solar cell, achieving an increase in photoelectric conversion efficiency.

[0068] The present disclosure will be further explained below with reference to specific embodiments and comparative examples.

[0069] Example 1

[0070] Please refer to Figure 2 This embodiment provides a solar cell. The solar cell has a selective emitter, which includes: a metal grid region 11 and a non-metal grid region 12, wherein the height of the metal grid region 11 is higher than the height of the non-metal grid region 12; the doping concentration of the non-metal grid region 12 is greater than 0, and the doping concentration of the metal grid region 11 is greater than the doping concentration of the non-metal grid region 12; a transition region 13 is located between the metal grid region 11 and the non-metal grid region 12; the top surface of the transition region 13 is an inclined surface, and the transition region 13 is undoped.

[0071] In this embodiment, a first buffer zone is provided between the metal gate line region 11 and the transition region 13; the first buffer zone has the same height as the metal gate line region 11, and the first buffer zone is undoped. A second buffer zone is provided between the non-metal gate line region 12 and the transition region 13; the second buffer zone has the same height as the non-metal gate line region 12, and the second buffer zone is undoped.

[0072] It should be noted that the selective emission provided in this embodiment is a high-low junction structure; in this structure, the metal gate region 11 is higher than the non-metal gate region 12 because the laser acts on the non-metal gate region 12.

[0073] It should also be noted that the non-metallic grid region 12 is the area where the solar cell collects photogenerated carriers. Laser action here, forming grooves, will first cause physical damage. The irregular groove sidewalls and the textured pyramid structure at the bottom will be disrupted, introducing high-density crystal defects and dangling bonds, becoming extremely strong carrier recombination centers, leading to a decrease in the fill factor. To remove this laser-damaged area, when using laser patterning to process a silicon wafer with uniform doping on the front side, laser parameters can be precisely controlled to reduce the laser-damaged area. Then, wet cleaning is used to further remove the damage and retexturize the surface, forming a patterned groove across the entire front side, resulting in the high-low junction structure.

[0074] Example 2

[0075] Please refer to Figure 3This embodiment provides a solar cell. The solar cell has a selective emitter, which includes: a metal grid region 11 and a non-metal grid region 12, wherein the height of the metal grid region 11 is higher than the height of the non-metal grid region 12; the doping concentration of the non-metal grid region 12 is equal to 0, and the doping concentration of the metal grid region 11 is greater than the doping concentration of the non-metal grid region 12; a transition region 13 is located between the metal grid region 11 and the non-metal grid region 12; the top surface of the transition region 13 is an inclined surface, and the transition region 13 is undoped.

[0076] In this embodiment, a first buffer zone is provided between the metal gate line region 11 and the transition region 13; the first buffer zone and the metal gate line region 11 have the same height, and the first buffer zone is undoped.

[0077] It should be noted that the selective emission provided in this embodiment is a localized junction structure; in this structure, the metal gate region 11 is higher than the non-metal gate region 12 because the laser acts on the non-metal gate region 12.

[0078] Example 3

[0079] Please refer to Figure 4 This embodiment provides a solar cell. The solar cell has a selective emitter, which includes: a metal grid region 11 and a non-metal grid region 12, wherein the height of the metal grid region 11 is lower than the height of the non-metal grid region 12; the doping concentration of the non-metal grid region 12 is greater than 0, and the doping concentration of the metal grid region 11 is greater than the doping concentration of the non-metal grid region 12; a transition region 13 is located between the metal grid region 11 and the non-metal grid region 12; the top surface of the transition region 13 is an inclined surface, and the transition region 13 is undoped.

[0080] In this embodiment, a first buffer zone is provided between the metal gate line region 11 and the transition region 13; the first buffer zone has the same height as the metal gate line region 11, and the first buffer zone is undoped. A second buffer zone is provided between the non-metal gate line region 12 and the transition region 13; the second buffer zone has the same height as the non-metal gate line region 12, and the second buffer zone is undoped.

[0081] It should be noted that the selective emission provided in this embodiment is a high-low junction structure; in this structure, the metal gate region 11 is lower than the non-metal gate region 12 because the laser acts on the metal gate region 11.

[0082] Specifically, the laser acts on the metal grid region 11, creating a laser-damaged area. This area, upon contact with the slurry, leads to unstable transmission current and a decrease in the fill factor. To remove this laser-damaged area, the laser parameters can be precisely controlled to reduce its impact. Then, wet cleaning further removes the damage and re-texturing is performed to form a patterned groove on the entire front surface, resulting in the high-low junction structure.

[0083] Example 4

[0084] Please refer to Figure 5 This embodiment provides a solar cell. The solar cell has a selective emitter, which includes: a metal grid region 11 and a non-metal grid region 12, wherein the height of the metal grid region 11 is lower than the height of the non-metal grid region 12; the doping concentration of the non-metal grid region 12 is equal to 0, and the doping concentration of the metal grid region 11 is greater than the doping concentration of the non-metal grid region 12; a transition region 13 is located between the metal grid region 11 and the non-metal grid region 12; the top surface of the transition region 13 is an inclined surface, and the transition region 13 is undoped.

[0085] In this embodiment, a first buffer zone is provided between the metal gate line region 11 and the transition region 13; the first buffer zone and the metal gate line region 11 have the same height, and the first buffer zone is undoped.

[0086] It should be noted that the selective emission field provided in this embodiment is a localized junction structure; in this structure, the metal gate region 11 is lower than the non-metal gate region 12 because the laser acts on the metal gate region 11.

[0087] Comparative Example 1

[0088] Figure 6 A cross-sectional structural diagram of the high-low structure provided for Comparative Example 1; please refer to it. Figure 6 This embodiment provides a solar cell. This embodiment is basically the same as Embodiment 1, except that the transition region 13 in this embodiment is a doped region, and this embodiment does not provide a first buffer zone between the metal grid region 11 and the transition region 13, nor does it provide a second buffer zone between the non-metal grid region 12 and the transition region 13.

[0089] Comparative Example 2

[0090] Figure 7 A cross-sectional structural diagram of the local structure provided for Comparative Example 2; please refer to... Figure 7 This embodiment provides a solar cell. This embodiment is basically the same as embodiment 2, except that the transition region 13 in this embodiment is a doped region, and the first buffer zone is not provided between the metal grid region 11 and the transition region 13 in this embodiment.

[0091] Comparative Example 3

[0092] Figure 8 A cross-sectional structural diagram of the high-low structure provided for Comparative Example 3; please refer to it. Figure 8This embodiment provides a solar cell. This embodiment is basically the same as embodiment 3, except that the transition region 13 in this embodiment is a doped region, and this embodiment does not provide a first buffer zone between the metal grid region 11 and the transition region 13, nor does it provide a second buffer zone between the non-metal grid region 12 and the transition region 13.

[0093] Comparative Example 4

[0094] Figure 9 A cross-sectional structural diagram of the local structure provided for Comparative Example 4; please refer to... Figure 9 This embodiment provides a solar cell. This embodiment is basically the same as embodiment 4, except that the transition region 13 in this embodiment is a doped region, and the first buffer zone is not provided between the metal grid region 11 and the transition region 13 in this embodiment.

[0095] 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 are tested, and the test results are shown in Table 1.

[0096] Table 1

[0097]

[0098] As shown in Table 1, the conversion efficiencies of Examples 1-4 are higher than those of Comparative Examples 1-4 with the same structure. Furthermore, the conversion efficiency improvement effect of the high-low junction structure is better than that of the local junction structure. It can be seen that the effective operating region of the buffer in the high-low junction structure is much larger than that in the local junction structure. In the high-low junction structure, the first buffer and the second buffer work together to more efficiently suppress the recombination behavior of high-concentration carriers at lattice defects, significantly reduce recombination losses, and at the same time, greatly enhance the effective passivation effect of interface states and the stability of the built-in electric field.

[0099] 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.

[0100] 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 selective emitter, characterized in that, The selective emitter includes: The regions are a metal gate region and a non-metal gate region, wherein the metal gate region and the non-metal gate region have different heights; the doping concentration of the non-metal gate region is greater than or equal to 0, and the doping concentration of the metal gate region is greater than the doping concentration of the non-metal gate region. The transition region is located between the metal gate region and the non-metal gate region; the top surface of the transition region is an inclined surface, and the transition region is undoped.

2. The selective emitter according to claim 1, characterized in that, A first buffer zone is provided between the metal gate line region and the transition region; the first buffer zone and the metal gate line region have the same height, and the first buffer zone is undoped.

3. The selective emitter according to claim 2, characterized in that, The width of the first buffer is proportional to the tilt angle of the inclined surface.

4. The selective emitter according to claim 2, characterized in that, The width of the first buffer is proportional to the height difference between the metal gate area and the non-metal gate area.

5. The selective emitter according to claim 2, characterized in that, The width of the first buffer is 20μm-100μm.

6. The selective emitter according to claim 1 or 2, characterized in that, When the doping concentration of the non-metallic gate region is greater than 0, a second buffer is provided between the non-metallic gate region and the transition region; the second buffer has the same height as the non-metallic gate region, and the second buffer is undoped.

7. The selective emitter according to claim 6, characterized in that, The width of the second buffer is proportional to the tilt angle of the inclined surface.

8. The selective emitter according to claim 6, characterized in that, The width of the second buffer is proportional to the height difference between the metal gate area and the non-metal gate area.

9. The selective emitter according to claim 6, characterized in that, The width of the second buffer is 20μm-100μm.

10. A solar cell, characterized in that, The solar cell includes a selective emitter as described in any one of claims 1 to 9.

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