Solar cell and solar cell module

Abstract

The present disclosure relates to the technical field of solar cells, and discloses a solar cell and a solar cell module. The solar cell comprises a base layer, a selective emitter structure and a transition structure. The base layer comprises a first surface and a second surface arranged oppositely. The selective emitter structure is formed on one side of the first surface of the base layer. The selective emitter structure comprises contact regions and non-contact regions arranged alternately. The non-contact regions are arranged recessively relative to the contact regions. The contact regions comprise first contact surfaces, and the non-contact regions comprise second contact surfaces. The transition structure comprises a transition part. The present disclosure reduces the carrier recombination rate at the junction area of the selective emitter structure and the base layer, and improves the open circuit voltage and the fill factor.

Description

Technical Field

[0001] This disclosure relates to the field of solar cell technology, and more specifically, to a solar cell and a solar cell module. Background Technology

[0002] Solar cells are semiconductor devices that directly convert light energy into electrical energy and are an important component of the current renewable energy field. Crystalline silicon solar cells have long dominated the market due to their mature technology, high stability, and abundant resources. Among them, tunnel oxide passivated contact (TOPCon) technology has rapidly become one of the mainstream routes for high-efficiency crystalline silicon cells due to its excellent passivation contact performance and high mass production efficiency.

[0003] In the fabrication processes of TOPCon cells, methods such as high-temperature thermal diffusion, ion implantation, or laser doping are typically used to fabricate emitter structures on the front side (i.e., the light-receiving side) of the silicon wafer. For example, a boron-doped emitter can be fabricated on the front side to form a PN junction. However, conventional boron emitters present a trade-off between contact resistance and surface recombination, thus limiting further improvements in TOPCon cell performance. Based on this, related technologies have begun to employ front-side boron-doped selective emitter (SE) technology. SE technology allows for localized doping differentiation in different regions of the emitter, meaning that the doping concentration may vary in different areas.

[0004] However, SE technology typically involves laser doping and wet cleaning processes during fabrication. The combined effects of laser and etching can create defects at the boundaries of different doping concentration regions on the silicon material surface. These defects cause severe lattice damage and are prone to becoming strong carrier recombination centers, thereby lowering the open-circuit voltage and fill factor, and affecting the photoelectric conversion efficiency of the battery. Summary of the Invention

[0005] This disclosure provides a solar cell and a solar cell module to address the problem of high carrier recombination rate at the interface between the selective emitter structure and the substrate.

[0006] In a first aspect, this disclosure provides a solar cell, the solar cell comprising: The base layer includes a first surface and a second surface disposed opposite to each other; A selective emitter structure is formed on one side of a first surface of a substrate layer; the selective emitter structure includes alternating contact areas and non-contact areas, with the non-contact areas recessed relative to the contact areas; the contact areas include a first contact surface relatively far from the second surface of the substrate layer, and the non-contact areas include a second contact surface relatively far from the second surface of the substrate layer. A transition structure is formed on one or two sidewalls of the contact area; the transition structure includes a transition portion, a first connecting portion and a second connecting portion, the first connecting portion connecting the first contact surface and the transition portion, and the second connecting portion connecting the second contact surface and the transition portion.

[0007] Beneficial effects: By setting the transition structure on at least one sidewall of the contact area, with the transition part facing the direction of laser doping and wet cleaning, it has a certain blocking effect, weakening the influence of laser doping and wet cleaning on the interface region between the selective emitter structure and the substrate, and solving the problem of high carrier recombination rate in the interface region.

[0008] In one alternative implementation, the transition portion includes one or more consecutive transition sections; or, the transition portion includes one or more stepped sections.

[0009] Beneficial effects: The continuous transition sections or multiple steps achieve stepwise blocking of laser doping and wet cleaning, further weakening the impact of laser doping and wet cleaning on the selective emitter structure and substrate interface region. Furthermore, setting the transition section as multiple transition sections or multiple steps can reduce the influence of the transition section on the morphology of the contact area and non-contact area, ensuring the smooth formation of the selective emitter structure.

[0010] In one alternative embodiment, the solar cell further includes: The barbed structure is formed at the boundary between one or two sidewalls of the contact area and the second contact surface of the non-contact area, and the barbed structure is recessed inward from the boundary area.

[0011] Beneficial effects: This disclosure adopts a combination of transition structure and barbed structure to reduce the carrier recombination rate at the interface between the selective emitter structure and the substrate, improve the open circuit voltage and fill factor, and ultimately improve the photoelectric conversion efficiency of the cell.

[0012] In one alternative implementation, the depth of the barb structure is less than or equal to 5 μm.

[0013] Beneficial effects: Limiting the depth of the barbed structure to less than or equal to 5 μm can effectively ensure that charge carriers are fully collected, thereby improving the photoelectric conversion efficiency of solar cells.

[0014] In one optional implementation, the height difference between the first contact surface and the second contact surface ranges from 0.5 μm to 10 μm.

[0015] Beneficial effects: This disclosure limits the height difference range between the first contact surface and the second contact surface. On the one hand, it can avoid the inability to form an effective contact area and non-contact area due to the small height difference. On the other hand, it can solve the problems of passivation difficulty, poor metallization contact and increased stress caused by the large height difference, which increases the risk of fragmentation and affects the battery life.

[0016] In one alternative embodiment, the height difference between the transition portion and the second contact surface ranges from 0.1 μm to 4.5 μm.

[0017] Beneficial effects: On the one hand, it avoids the limitation of optimizing the defects of the barbed structure due to a large height difference; on the other hand, it avoids the reduction of the contact area and the number of charge carriers due to a small height difference, thereby affecting the photoelectric conversion efficiency.

[0018] In one alternative embodiment, the transition portion has a velvety texture; and / or, the width of the transition portion is 1 μm to 20 μm.

[0019] Beneficial effects: The textured surface on the transition section improves the light trapping effect of the battery. This disclosure limits the width range of the transition section, thereby limiting the size of the transition structure. Without affecting the first contact surface and the second contact surface, it can achieve a good cut-off effect.

[0020] In one alternative implementation, the first contact surface is a first velvet structure, and the second contact surface is a second velvet structure.

[0021] Beneficial effects: The first and second velvet structures help enhance the light trapping effect, improve the contact performance between other structural layers and the first and second contact surfaces, and enhance connection reliability.

[0022] In one optional embodiment, the angle between the first connecting portion and the first contact surface is in the range of 90° to 160°; the angle between the second connecting portion and the second contact surface is in the range of 90° to 160°.

[0023] Beneficial effects: The first and second connecting portions formed in this disclosure are in an inclined or vertical state, thereby ensuring that the first and second connecting portions will not sink into the contact area, reducing the influence of the transition structure on the selective emitter structure, and improving the overall performance of the solar cell.

[0024] In one alternative embodiment, the solar cell further includes: A passivated contact structure is formed on the surface of the substrate layer that is relatively away from the selective emitter structure. The passivated contact structure has the opposite conductivity type to the selective emitter structure. A first passivation anti-reflection layer and a second passivation anti-reflection layer are disposed on the selective emitter structure and the second passivation anti-reflection layer is disposed on the passivation contact structure. The first electrode is disposed on the first passivation antireflection layer and connected to the contact area of ​​the selective emitter structure, and the second electrode is disposed on the second passivation antireflection layer and connected to the passivation contact structure.

[0025] Beneficial effects: The passivation contact structure and the selective emitter structure are respectively set on the two sides of the substrate layer, which optimizes the passivation performance at the interface, thereby realizing the full transport of charge carriers. In addition, the weakening or even removal of the barb structure in the junction region further improves the charge carrier transport and collection rate, and increases the open circuit voltage and fill factor. The setting of the first passivation anti-reflection layer and the second passivation anti-reflection layer can further improve the utilization rate of sunlight, thereby improving the overall open circuit voltage and photoelectric conversion efficiency of the battery.

[0026] Secondly, this disclosure also provides a solar cell module, including the aforementioned solar cell. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the specific embodiments of this disclosure or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 A schematic diagram of the structure of the base layer according to an embodiment of the present disclosure is shown; Figure 2 A schematic diagram of a junction region in a solar cell according to an embodiment of the present disclosure is shown; Figure 3 Another structural schematic diagram of the boundary region in a solar cell according to an embodiment of this disclosure is shown; Figure 4 An electron microscope image of a solar cell according to an embodiment of the present disclosure is shown at one angle; Figure 5 An electron microscope image of a solar cell according to an embodiment of the present disclosure is shown from another angle; Figure 6 A schematic diagram of a solar cell in an embodiment of this disclosure is shown, showing that the transition portion is a plurality of transition sections. Figure 7 A schematic flowchart of a method for fabricating a solar cell according to an embodiment of the present disclosure is shown; Figure 8 This illustration shows yet another structural schematic diagram of the boundary region in a solar cell according to an embodiment of the present disclosure; Figure 9 A schematic diagram of the structure of the junction region in a solar cell of comparative example of this disclosure is shown; Figure 10 A schematic diagram of the structure of a solar cell according to an embodiment of the present disclosure is shown.

[0029] Explanation of reference numerals in the attached figures: 1. Substrate layer; 2. Selective emitter structure; 21. Contact area; 211. First contact surface; 22. Non-contact area; 221. Second contact surface; 3. Barbed structure; 4. Transition structure; 41. Transition portion; 411. First transition portion; 412. Second transition portion; 42. First connecting portion; 43. Second connecting portion; 5. Passivated contact structure; 51. Tunneling oxide layer; 52. Doped polysilicon layer; 6. First passivation antireflection layer; 61. First alumina layer; 62. First silicon nitride layer; 7. Second passivation antireflection layer; 71. Second alumina layer; 72. Second silicon nitride layer; 8. First electrode; 9. Second electrode. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0031] In related technologies, TOPCon cells, when forming the emitter using selective emitter (SE) technology, heavily dopant the electrode contact region 21 and lightly dopant or undopant the non-electrode region, thereby effectively reducing the minority carrier recombination rate and series resistance, and improving the cell's open-circuit voltage and fill factor. During this process, under the combined effects of additional laser doping and wet cleaning, local regions with varying doping concentrations form on the silicon material surface. These regions with different doping concentrations are prone to forming so-called "hook" defects. Compared to a normal textured surface structure, these "hook" defects are deeper and cause severe lattice damage, easily becoming strong carrier recombination centers, thus lowering the open-circuit voltage and fill factor, and affecting the cell's final conversion efficiency.

[0032] Based on this, refer to Figures 1 to 6This disclosure provides a solar cell, which includes a substrate layer 1, a selective emitter structure 2, and a transition structure 4. The substrate layer 1 includes a first surface and a second surface disposed opposite to each other; the selective emitter structure 2 is formed on one side of the first surface of the substrate layer 1, and the selective emitter structure 2 includes alternately arranged contact areas 21 and non-contact areas 22, the non-contact areas 22 being recessed relative to the contact areas 21; the contact areas 21 include a first contact surface 211 relatively far from the second surface of the substrate layer 1, and the non-contact areas 22 include a second contact surface 221 relatively far from the second surface of the substrate layer 1; the transition structure 4 is formed on the sidewall of the contact areas 21, and the transition structure 4 includes a transition portion 41, a first connecting portion 42, and a second connecting portion 43, the first connecting portion 42 connecting the first contact surface 211 and the transition portion 41, and the second connecting portion 43 connecting the second contact surface 221 and the transition portion 41.

[0033] That is, in this disclosure, the transition structure 4 is disposed on the side wall of the contact area 21, and the transition part 41 faces the direction of laser doping and wet cleaning, which has a certain blocking effect, weakens the influence of laser doping and wet cleaning on the interface region between the selective emitter structure 2 and the substrate layer 1, and solves the problem of high carrier recombination rate in the interface region.

[0034] The direction in which the contact area 21 and the non-contact area 22 are alternately arranged is defined as the first direction, and the direction perpendicular to the first direction is defined as the second direction. Both the first direction and the second direction are located in a plane parallel to the first surface of the substrate layer 1. In some embodiments, the solar cell further includes a barb structure 3, which is formed at the junction of the sidewall of the contact area 21 and the second contact surface 221 of the non-contact area 22, and the barb structure 3 is recessed inward from the junction area.

[0035] In some embodiments, along the first direction, barb structures 3 are formed at the junction of the two sidewalls of the contact area 21 and the second contact surface. Correspondingly, transition structures 4 are formed on both sidewalls of the contact area 21. For example, barb structures 3 and transition structures 4 are formed on the left side of the contact area 21, and barb structures 3 and transition structures 4 are formed on the right side of the contact area 21. In some embodiments, along the first direction, barb structures 3 are formed at the junction of the two sidewalls of the contact area 21 and the second contact surface. Correspondingly, transition structures 4 are formed on only one sidewall of the contact area 21. For example, barb structures 3 and transition structures 4 are formed on the left side of the contact area 21, and barb structures 3 are formed only on the right side of the contact area 21. In some embodiments, along the first direction, a barb structure 3 is formed on only one sidewall of the contact area 21 at the boundary between the second contact surface and the first sidewall. Correspondingly, a transition structure 4 is formed on only one sidewall of the contact area 21. For example, the barb structure 3 and the transition structure 4 are formed on the left side of the contact area 21, while the barb structure 3 and the transition structure 4 are not formed on the right side of the contact area 21. In some embodiments, such as Figure 6 As shown, the transition portion 41 is composed of multiple continuous transition sections, i.e., multiple stepped sections. These continuous transition sections or stepped sections achieve a step-by-step blocking of laser doping and wet cleaning, further weakening the impact of laser doping and wet cleaning on the interface region between the selective emitter structure 2 and the substrate layer 1. Furthermore, by setting the transition portion 41 as multiple transition sections, the influence of the transition portion 41 on the morphology of the contact area 21 and the non-contact area 22 can be reduced, ensuring the smooth formation of the selective emitter structure 2. In some embodiments, such as... Figure 2 and 3 As shown, the transition section 41 consists of only one transition section, namely a step section.

[0036] For ease of description and understanding, two transition sections are used as examples. The transition section closer to the non-contact area 22 is defined as the first transition section 411, and the transition section adjacent to the first transition section 411 is defined as the second transition section 412. The distance between the first transition section 411 and the second contact surface 221 is less than the distance between the second transition section 412 and the second contact surface 221.

[0037] The number of transition sections can be three, four, five, or even more. Similarly, the distances between the third, fourth, and fifth transition sections and the second contact surface 221 increase sequentially.

[0038] In some embodiments, the barb structure 3 extends a certain length along the second direction. In some embodiments, the barb structure 3 is present along the second direction on the sidewall of the contact area 21 and the entire boundary region of the second contact surface 221 of the non-contact area 22. In some embodiments, one or more transition structures 4 are provided on the sidewall of the contact area 21 along the second direction, and the multiple transition structures 4 are spaced apart or connected. The barb structure 3 is formed under the action of laser doping and wet cleaning. Since the barb structure 3 is recessed inward from the boundary region, this recess will increase the carrier recombination in the boundary region. In order to reduce the carrier recombination rate, the inventors creatively proposed to adopt the setting of the transition structure 4 to minimize the amount of recess (i.e., depth) of the barb structure 3.

[0039] This disclosure employs a combination of transition structure 4 and barbed structure 3 to reduce the carrier recombination rate at the interface between selective emitter structure 2 and substrate layer 1, thereby increasing the open-circuit voltage and fill factor, and ultimately improving the photoelectric conversion efficiency of the battery.

[0040] In some embodiments, the distance between the transition portion 41 and the second contact surface 221 is positively correlated with the depth of the barb structure 3. The smaller the distance between the transition portion 41 and the second contact surface 221, the shallower the depth of the barb structure 3. For example, the solar cell described above can be a TOPCon cell, wherein the first surface is the upper surface of the substrate layer 1, i.e., the light-receiving surface, and the second surface is the lower surface of the substrate layer 1, i.e., the backlight surface; the substrate layer 1 can be a silicon wafer with N-type polarity or conductivity. A P-type selective emitter structure 2 is formed on the light-receiving side of the substrate layer 1 through boron doping, i.e., forming the front emitter of the TOPCon cell. A PN junction is formed between the selective emitter structure 2 and the substrate layer 1 to achieve the photovoltaic effect; wherein the non-contact area 22 is the laser area, and the contact area 21 is the non-laser area. The contact area 21 is higher than the non-contact area 22, facilitating efficient connection with the electrode paste in the future. The aforementioned barbed structure 3 is deeper than the second contact surface 221, which can provide a certain degree of electrical isolation, but it results in significant lattice loss. Overall, the location of the barbed structure 3 is prone to becoming a strong carrier recombination center, thereby lowering the open-circuit voltage and fill factor, and affecting the battery efficiency. Based on this, this disclosure forms a transition structure 4 on the sidewall of the contact region 21. By forming a physical-level truncation structure on the sidewall of the contact region 21, the doping gradient is optimized, alleviating or even eliminating the defects at the junction of different doped regions, i.e., optimizing the barbed structure 3. In other words, by combining the transition structure 4 and the barbed structure 3, the depth of the barbed structure 3 is adjusted by utilizing the distance between the transition portion 41 and the second contact surface 221. Reducing the depth of the barbed structure 3 lowers the carrier recombination rate at the interface between the selective emitter structure 2 and the substrate layer 1, increasing the open-circuit voltage and fill factor, and ultimately improving the photoelectric conversion efficiency of the battery.

[0041] The aforementioned positive correlation specifically means that when the distance between the transition portion 41 and the second contact surface 221 decreases, the depth of the barb structure 3 decreases, and vice versa. This disclosure utilizes the distance between the transition portion 41 and the second contact surface 221 to adjust the depth of the barb structure 3, thereby reducing the distance between the transition portion 41 and the second contact surface 221 to achieve the purpose of reducing the depth of the barb structure 3.

[0042] In some embodiments, the depth of the barb structure 3 is ≤5 μm. When the distance between the transition portion 41 and the second contact surface 221 is within a preset range, the depth of the barb structure 3 approaches zero, or even the barb structure 3 does not exist. The inventors have found that the provision of the transition structure 4 can optimize the barb structure 3.

[0043] Specifically, the depth of the barbed structure 3 is limited to greater than or equal to 0. If the depth of the barbed structure 3 is equal to 0, it means that the barbed structure 3 does not exist and the recombination rate in the boundary region is the lowest. The depth of the barbed structure 3 is limited to ≤5 μm, such as 0.5 μm, 1 μm, 2 μm, 3 μm and 4 μm, which can effectively ensure that the charge carriers are fully collected and improve the photoelectric conversion efficiency of the solar cell.

[0044] In some embodiments, the height difference between the transition portion 41 and the second contact surface 221 is greater than zero and less than the height difference between the first contact surface 211 and the second contact surface 221.

[0045] Specifically, such as Figure 2 and Figure 3 As shown, the height difference between the first contact surface 211 and the second contact surface 221 is defined as h, and the height difference between the transition portion 41 and the second contact surface 221 is defined as d, where 0 < d < h. That is, this disclosure sets the height difference range between the transition portion 41 and the second contact surface 221 to ensure that the transition portion 41 is located between the second contact surface 221 and the first contact surface 211, thereby allowing the doping concentration to further increase the gradient transition in the vertical direction. Figure 6 As shown, the distance between the transition portion 41 and the second contact surface 221 has multiple values, including the distance d1 between the first transition portion 411 and the second contact surface 221, and the distance d2 between the second transition portion 412 and the second contact surface 221.

[0046] In some embodiments, the height difference between the first contact surface 211 and the second contact surface 221 ranges from 0.5 μm to 10 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, and 9 μm. This disclosure limits the range of the height difference between the first contact surface 211 and the second contact surface 221. On the one hand, this avoids the inability to form an effective contact area 21 and non-contact area 22 due to an excessively small height difference. On the other hand, it solves the problems of passivation difficulties, poor metallization contact, and increased stress caused by an excessively large height difference, which increases the risk of fragmentation and affects battery life.

[0047] In some embodiments, the height difference between the transition portion 41 and the second contact surface 221 ranges from 0.1 μm to 4.5 μm, for example, it can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.2 μm, etc. This avoids both excessively large height differences that could limit the optimization of defects in the barbed structure 3 and excessively small height differences that could reduce the area of ​​the contact region 21 and the number of charge carriers therein, thereby affecting the photoelectric conversion efficiency. Therefore, this disclosure defines the specific height position of the transition portion 41 by limiting the height difference range mentioned above, ensuring that the transition portion 41 forms a suitable gradient value between the doping concentrations of the contact region 21 and the non-contact region 22, effectively mitigating carrier recombination in the barbed structure 3, while ensuring the number of charge carriers and transport efficiency. It also simplifies the fabrication process and reduces costs, ensures effective light trapping and battery lifespan, and ultimately ensures the photoelectric conversion efficiency of the battery.

[0048] When there are multiple values ​​for the distance between the transition portion 41 and the second contact surface 221, the minimum value is taken as the limit value for the height difference. For example, if the height difference is limited to 1.5 μm, then the distance d1 between the first transition portion 411 and the second contact surface 221 is 1.5 μm.

[0049] In some embodiments, such as Figure 6 As shown, the transition portion 41 has a textured surface; and / or, the width of the transition portion 41 is 1 μm to 20 μm, for example, it can be 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, and 18 μm, etc. The textured surface on the transition portion 41 improves the light-trapping effect of the battery. This disclosure limits the width range of the transition portion 41, thereby limiting the size of the transition structure 4, and achieving a good cutoff effect without affecting the first contact surface 211 and the second contact surface 221. Figure 2 , Figure 3 and Figure 6 As shown, the width of the transition section 41 is defined as w.

[0050] In some embodiments, the first contact surface 211 has a first textured surface structure, and the second contact surface 221 has a second textured surface structure. The first textured surface structure and the second textured surface structure help to enhance the light trapping effect, improve the contact performance between other structural layers and the first contact surface 211 and the second contact surface 221, and enhance the connection reliability.

[0051] In some embodiments, the angle between the first connecting portion 42 and the first contact surface 211 ranges from 90° to 160°, such as 100°, 110°, 120°, 130°, 140°, and 150°; the angle between the second connecting portion 43 and the second contact surface 221 ranges from 90° to 160°, such as 100°, 110°, 120°, 130°, 140°, and 150°. The first connecting portion 42 and the second connecting portion 43 formed in this disclosure are inclined or vertical, thereby ensuring that the first connecting portion 42 and the second connecting portion 43 do not sink into the contact area 21, reducing the influence of the transition structure 4 on the selective emitter structure 2, and improving the overall performance of the solar cell. Specifically, the first connecting portion 42 is a first inclined surface or a first vertical surface; the second connecting portion 43 is a second inclined surface or a second vertical surface. That is, the first connecting portion 42 and the second connecting portion 43 can be either inclined surfaces or vertical surfaces.

[0052] If the first connecting part 42 is a first inclined surface and the second connecting part 43 is a second inclined surface, the first inclined surface and the second inclined surface are respectively set at an angle to the laser doping direction.

[0053] If the first connecting part 42 is a first vertical surface and the second connecting part 43 is a second vertical surface, both the first vertical surface and the second vertical surface are arranged parallel to the laser doping direction.

[0054] The texturing process of the substrate layer 1 typically includes the fabrication of a first texturing structure, a second texturing structure, and a transition structure 4. The transition structure 4 is used to adjust the depth of the barb structure 3, which has the advantages of effectively reducing carrier recombination and high process compatibility. The first and second texturing structures help to enhance the light trapping effect, improve the contact performance between other structural layers and the first contact surface 211 and the second contact surface 221, and enhance the connection reliability.

[0055] See Figure 3 and Figure 10 In some embodiments, the solar cell further includes a passivated contact structure 5, a first passivation antireflection layer 6, a second passivation antireflection layer 7, a first electrode 8, and a second electrode 9.

[0056] A passivation contact structure 5 is formed on the surface of the substrate layer 1 that is opposite to the selective emitter structure 2. The passivation contact structure 5 has the opposite conductivity type to the selective emitter structure 2. A first passivation antireflection layer 6 is disposed on the selective emitter structure 2, and a second passivation antireflection layer 7 is disposed on the passivation contact structure 5. A first electrode 8 is disposed on the first passivation antireflection layer 6 and connected to the contact area 21 of the selective emitter structure 2, and a second electrode 9 is disposed on the second passivation antireflection layer 7 and connected to the passivation contact structure 5.

[0057] For example, the passivation contact structure 5 includes a tunneling oxide layer 51 and a doped polysilicon layer 52 stacked together. The doped polysilicon layer 52 is phosphorus-doped (P) polysilicon with N-type polarity. The first passivation antireflection layer 6 uses a first alumina layer 61 (Al2O3) and a first silicon nitride layer 62 (SiN). x The second passivation antireflection layer 7 adopts a second alumina layer 71 (Al2O3) and a second silicon nitride layer 72 (SiN). x The passivated contact structure 5 and the selective emitter structure 2 are respectively disposed on the two sides of the substrate layer 1 to optimize the passivation performance at the interface, thereby achieving full transport of charge carriers. In addition, the weakening or even removal of the barbed structure 3 in the boundary region further improves the charge carrier transport and collection rate, and increases the open-circuit voltage and fill factor. The setting of the first passivation anti-reflection layer 6 and the second passivation anti-reflection layer 7 can further improve the utilization rate of sunlight, thereby improving the overall open-circuit voltage and photoelectric conversion efficiency of the battery.

[0058] This disclosure uses set parameters for laser doping and wet cleaning to obtain a barbed structure 3 with a lower depth, thereby reducing the carrier recombination rate in the interface region and improving the photoelectric conversion efficiency.

[0059] refer to Figures 1 to 7 This disclosure also provides a method for preparing a solar cell, used to prepare the aforementioned solar cell. Figure 7 The diagram below illustrates the process of this preparation method, which specifically includes the following steps: S100, a base layer 1 is provided, the base layer 1 including a first surface and a second surface disposed opposite to each other.

[0060] refer to Figure 1 The substrate 1 disclosed herein is a silicon substrate, which is formed by polishing and cleaning both sides of a silicon wafer to create a silicon substrate for fabricating solar cells.

[0061] S200, a selective emitter structure 2 is formed on one side of the first surface of the substrate 1. The selective emitter structure 2 includes alternating contact areas 21 and non-contact areas 22. A transition structure 4 is formed on the sidewall of the contact area 21. The non-contact area 22 is recessed relative to the contact area 21. The contact area 21 includes a first contact surface 211 that is relatively far from the second surface of the substrate 1. The non-contact area 22 includes a second contact surface 221 that is relatively far from the second surface of the substrate 1. The transition structure 4 includes a transition portion 41, a first connecting portion 42, and a second connecting portion 43. The first connecting portion 42 connects the first contact surface 211 and the transition portion 41. The second connecting portion 43 connects the second contact surface 221 and the transition portion 41. The distance between the transition portion 41 and the second contact surface 221 is positively correlated with the depth of the barb structure 3.

[0062] In some embodiments, the boundary region between the sidewall of the contact area 21 and the second contact surface 221 of the non-contact area 22 has a barb structure 3, which is recessed inward from the boundary region.

[0063] Specifically, the light-receiving surface of the substrate layer 1 is first grouted with laser to form alternating contact areas 21 and non-contact areas 22, which have an uneven morphology. Then, laser doping is performed, with a high doping concentration in the contact areas 21 and a low doping concentration in the non-contact areas 22. Finally, wet cleaning is performed.

[0064] This disclosure combines the transition structure 4 and the barb structure 3, thereby adjusting the depth of the barb structure 3 by utilizing the distance between the transition portion 41 and the second contact surface 221, thereby reducing the depth value of the barb structure 3, thereby reducing the carrier recombination rate at the interface between the selective emitter structure 2 and the substrate layer 1, increasing the open-circuit voltage and fill factor, and improving the photoelectric conversion efficiency of the battery.

[0065] In some embodiments, the barb structure 3 and the transition structure 4 are formed using laser processing and wet processing. The height of the transition structure 4 is adjusted by configuring the parameters of the laser processing and wet processing. For example, in the laser processing, the higher the laser power parameter, the smaller the distance between the transition portion 41 and the second contact surface 221, and the shallower the depth of the barb structure 3. Similarly, in the wet processing, the higher the additive concentration, the smaller the distance between the transition portion 41 and the second contact surface 221, and the shallower the depth of the barb structure 3.

[0066] This disclosure utilizes laser technology and a wet process to obtain solar cells with a transition structure 4, which is convenient to fabricate and saves costs. The wet process uses NaOH solution.

[0067] This disclosure utilizes additives of varying concentrations to regulate the corrosion rate (frequency conversion). The additives can inhibit or accelerate the corrosion of specific materials by NaOH solution, thereby precisely controlling the morphology and forming the desired transition structure. Furthermore, the additives improve surface quality, helping to obtain a more uniform and smoother surface, or preventing recontamination of cleaned surfaces. The additives also have an auxiliary cleaning function, helping to remove specific types of contaminants.

[0068] The additives include, but are not limited to, chemical agents composed of sodium benzoate, sodium dodecyl sulfonate, sodium polystyrene sulfonate, polyethylene glycol, and deionized water. The different concentrations of the additives mentioned above refer to the proportion of the additives to the NaOH solution and the total amount of additives.

[0069] The laser process uses an infrared laser with a laser power range of 50 W to 75 W, a laser frequency of 20 kHz, a marking speed of 25,000 mm / s, a spot uniformity of <3%, and an overlap rate of 40% to 60%. The wet process uses a temperature of 75 ℃ to 80 ℃, a NaOH concentration of 1% to 1.5%, an additive concentration range of 0.5% to 0.8%, and a cleaning time of 450 s to 550 s.

[0070] In one embodiment, the laser process uses an infrared laser with a laser power of 70 W, a laser frequency of 20 KHz, a marking speed of 25000 mm / s, a spot uniformity of 1.5%, and an overlap rate of 50%. The wet process uses a temperature of 78 ℃, a NaOH concentration of 1.3%, an additive concentration of 0.55%, and a cleaning time of 480 s.

[0071] In the solar cell fabricated according to the above parameters, the height difference between the transition portion 41 and the second contact surface 221 is 0.85 μm, and the depth of the barb structure 3 is close to 0. For ease of description, this cell is referred to as the cell of Example 1.

[0072] In another embodiment, the laser process uses an infrared laser with a laser power of 50 W, a laser frequency of 20 kHz, a marking speed of 25,000 mm / s, a spot uniformity of 1.5%, and an overlap rate of 50%. The wet process uses a temperature of 78 ℃, a NaOH concentration of 1.3%, an additive concentration of 0.65%, and a cleaning time of 480 s.

[0073] In the solar cell fabricated according to the above parameters, the height difference between the transition portion 41 and the second contact surface 221 is 2.9 μm, and the depth of the barb structure 3 is 0.5 μm. For ease of description, this cell is referred to as the cell of Example 2.

[0074] Please see Figure 9 In addition, a comparative battery was selected, wherein the comparative battery adopted the same passivation contact structure 5 as the battery of Example 1 and Example 2, but the comparative battery formed a large barb structure 3 at the junction of the side wall of the contact area 21 and the second contact surface 221 of the non-contact area 22, and did not form a transition structure 4. The depth of the barb structure 3 was 5.5 μm.

[0075] Based on this, see Figures 3 to 9 The batteries from Examples 1, 2, and the comparative example were subjected to electrical performance tests, and the data are shown in the table below:

[0076] As can be seen from the table above, the cells of Examples 1 and 2 are superior to the comparative example in terms of various current performance parameters such as implicit open-circuit voltage (iVoc) and implicit fill factor (iFF). That is, the formation of transition structure 4 on substrate layer 1 in Examples 1 and 2 can effectively improve the photoelectric conversion efficiency of solar cells.

[0077] In some embodiments, this disclosure also provides a solar cell module, including a plurality of solar cells as described in any of the above embodiments, an encapsulation plate, and an encapsulation film. In this module, a front encapsulation plate, a front encapsulation film, a plurality of solar cells, a back encapsulation film, and a back encapsulation plate are stacked.

[0078] Although embodiments of the present disclosure have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present disclosure, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A solar cell, characterized in that, include: A base layer, the base layer including a first surface and a second surface disposed opposite to each other; A selective emitter structure is formed on one side of the first surface of the substrate layer; the selective emitter structure includes alternating contact areas and non-contact areas, the non-contact areas being recessed relative to the contact areas; the contact areas include a first contact surface relatively far from the second surface of the substrate layer, and the non-contact areas include a second contact surface relatively far from the second surface of the substrate layer; A transition structure is formed on one or both sidewalls of the contact area; the transition structure includes a transition portion, a first connecting portion and a second connecting portion, the first connecting portion connecting the first contact surface and the transition portion, and the second connecting portion connecting the second contact surface and the transition portion.

2. The solar cell according to claim 1, characterized in that, The transition section includes one or more continuous transition segments; or, the transition section includes one or more stepped sections.

3. The solar cell according to claim 1, characterized in that, Also includes: A barb structure is formed at the junction of one or two sidewalls of the contact area and a second contact surface of the non-contact area, the barb structure being recessed inward from the junction area.

4. The solar cell according to claim 3, characterized in that, The depth of the barb structure is less than or equal to 5 μm.

5. The solar cell according to claim 1, characterized in that, The height difference between the first contact surface and the second contact surface ranges from 0.5 μm to 10 μm.

6. The solar cell according to claim 1, characterized in that, The height difference between the transition section and the second contact surface ranges from 0.1 μm to 4.5 μm.

7. The solar cell according to claim 1, characterized in that, The transition portion has a velvety texture; and / or the width of the transition portion is 1 μm to 20 μm.

8. The solar cell according to claim 1, characterized in that, The first contact surface has a first velvet structure, and the second contact surface has a second velvet structure.

9. The solar cell according to claim 1, characterized in that, The angle between the first connecting part and the first contact surface is in the range of 90° to 160°; the angle between the second connecting part and the second contact surface is in the range of 90° to 160°.

10. The solar cell according to any one of claims 1 to 9, characterized in that, Also includes: A passivated contact structure is formed on the surface of the substrate layer on the side opposite to the selective emitter structure, and the passivated contact structure has the opposite conductivity type to the selective emitter structure; A first passivation anti-reflection layer and a second passivation anti-reflection layer, wherein the first passivation anti-reflection layer is disposed on the selective emitter structure and the second passivation anti-reflection layer is disposed on the passivation contact structure; A first electrode and a second electrode, wherein the first electrode is disposed on the first passivation antireflection layer and connected to the contact area of ​​the selective emitter structure, and the second electrode is disposed on the second passivation antireflection layer and connected to the passivation contact structure.

11. A solar cell module, characterized in that, include: The solar cell according to any one of claims 1 to 10.

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