Back contact solar cell, preparation method thereof and cell module

Abstract

The invention relates to the technical field of solar cells, and discloses a back contact solar cell, a preparation method thereof and a cell module. The back contact solar cell comprises a substrate layer, a first polarity structure, a second polarity structure and an isolation groove, wherein the substrate layer comprises a light receiving surface and a backlight surface which are oppositely arranged; the first polar structure and the second polar structure are alternately formed on one side of the backlight surface of the substrate layer; the isolation groove is formed between the first polar structure and the second polar structure and extends into the substrate layer; a chamfer structure is formed at the end part, close to the first polar structure and / or the second polar structure, of the bottom of the isolation groove, and the chamfer structure is concavely formed from the bottom surface of the isolation groove to one side of the light receiving surface. Compared with the isolation groove, the chamfer structure is deeper, conduction between diffusion atoms with different polarities is effectively blocked, the width of the bottom of the isolation groove can be further reduced, meanwhile, effective internal reflection of incident solar rays by one side of the back face is enhanced, and the optical performance of the cell is improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of solar cells, and in particular to back-contact solar cells, preparation methods thereof, and cell components. Background Art

[0002] Back Contact Solar Cell (BC cell) is a new type of solar cell technology that moves both the positive and negative electrode contacts to the back of the cell. It can eliminate the grid line shading loss on the front of traditional solar cells, significantly improve the cell's light absorption efficiency and appearance consistency, and become an important technical direction in the photovoltaic field.

[0003] To effectively prevent short circuits between regions of different polarity on the back side of existing back-contact solar cells, an isolation region is often formed between the n- and p-region structures. This isolation region is wide and deep, preventing dopant atoms of different polarities from conducting and interconnecting within the isolation region. However, in this structure, an overly wide isolation region reduces the effective passivation area on the back side of the cell, thereby reducing overall surface passivation performance. Furthermore, an overly deep isolation region can induce leakage, which can affect the performance of the back-contact solar cell. Summary of the Invention

[0004] In view of this, the present disclosure provides a back-contact solar cell and a preparation method thereof, as well as a cell assembly, to solve the problem that the isolation region structure of the existing back-contact solar cell affects the cell performance.

[0005] In the first aspect, the present disclosure provides a back-contact solar cell, comprising: a base layer, a first polarity structure, a second polarity structure and an isolation groove, wherein the base layer comprises a light-receiving surface and a backlight surface that are oppositely arranged; the first polarity structure and the second polarity structure are alternately formed on the backlight side of the base layer; the isolation groove is formed between the first polarity structure and the second polarity structure, and penetrates deep into the base layer; the bottom of the isolation groove forms a chamfered structure at the end close to the first polarity structure and / or close to the second polarity structure, and the chamfered structure is concavely formed from the bottom surface of the isolation groove toward the light-receiving side.

[0006] In an optional embodiment, the cross-sectional size of the chamfered structure gradually decreases in a direction from the bottom of the isolation groove toward the light-receiving surface.

[0007] In an optional embodiment, the maximum width of the chamfered structure is greater than zero and less than or equal to 50 μm, and the depth of the chamfered structure is greater than zero and less than or equal to 50 μm.

[0008] In an optional embodiment, a sidewall surface of the isolation groove close to the first polarity structure presents a first slope, and a sidewall surface of the isolation groove close to the second polarity structure presents a second slope.

[0009] In an optional embodiment, the first polarity structure includes: a first tunneling oxide layer and a first doping layer stacked in sequence, the first tunneling oxide layer being relatively close to the backlight surface; the second polarity structure includes: a second tunneling oxide layer and a second doping layer stacked in sequence, the second tunneling oxide layer being relatively close to the backlight surface, and the second doping layer having a conductivity type opposite to that of the first doping layer.

[0010] In an optional embodiment, when the conductivity type of the first polarity structure is p-type and the conductivity type of the second polarity structure is n-type, the second polarity structure extends into the backlight surface of the base layer, and the surface of the first polarity structure is higher than the surface of the second polarity structure.

[0011] In an optional embodiment, the first polarity structure also includes a first inner expansion layer formed in the backlight surface of the base layer, the first inner expansion layer is in contact with the first tunneling oxide layer, and has the same conductivity type as the first doped layer; the second polarity structure also includes a second inner expansion layer formed in the backlight surface of the base layer, the second inner expansion layer is in contact with the second tunneling oxide layer, and has the same conductivity type as the second doped layer.

[0012] In an optional embodiment, the doping depth of the first polarity structure is greater than the doping depth of the second polarity structure.

[0013] In an optional embodiment, the bottom surface of the isolation groove is further provided with a velvet structure.

[0014] In a second aspect, the present disclosure further provides a method for preparing a back-contact solar cell, which is used to prepare the above-mentioned back-contact solar cell, comprising: Providing a base layer, the base layer comprising a light-receiving surface and a backlight surface that are oppositely disposed; A first polarity structure and a second polarity structure are formed on the backlight side of the base layer, and the first polarity structure and the second polarity structure are alternately arranged; An isolation groove is formed between the first polarity structure and the second polarity structure, and the isolation groove penetrates deep into the base layer. The bottom of the isolation groove forms a chamfered structure at the end close to the first polarity structure and / or close to the second polarity structure, and the chamfered structure is concavely formed from the bottom surface of the isolation groove toward the light-receiving surface.

[0015] In an optional embodiment, a chamfered structure is formed in the isolation groove by a wet process or a laser process.

[0016] In a third aspect, the present disclosure further provides a back-contact solar cell assembly, comprising the above-mentioned back-contact solar cell.

[0017] Beneficial effects: The present invention forms a downwardly concave chamfered structure at the bottom of the isolation groove near the end of the first polarity structure and / or the second polarity structure. On the one hand, the chamfered structure is deeper than the isolation groove, which effectively blocks the conduction between diffused atoms of different polarities, reduces the conduction risk between different polarity structures on the back of the battery, and ensures the power generation performance of the battery; on the other hand, the setting of the chamfered structure also further narrows the width of the bottom of the isolation groove, and accordingly, the width of the area where the first polarity structure and the second polarity structure doped on both sides are located will be increased, thereby enhancing the effective internal reflection of the incident sunlight on the back side and improving the optical performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 is a schematic structural diagram of a back-contact solar cell according to an embodiment of the present disclosure; Figure 2 is a schematic electron microscope scanning diagram of the isolation groove of the back contact solar cell according to an embodiment of the present disclosure; Figure 3 is a schematic diagram of an optical microscope scanning at an isolation groove of a back contact solar cell according to an embodiment of the present disclosure; Figure 4 is a schematic diagram of a back contact solar cell in an embodiment of the present disclosure in which the cross-sectional shape of the chamfered structure is a rectangle; Figure 5 is a schematic diagram of a back contact solar cell in which the cross-sectional shape of the chamfered structure is an inverted ordinary trapezoid in an embodiment of the present disclosure; Figure 6 is a schematic diagram of a back contact solar cell in which the cross-sectional shape of the chamfered structure is an inverted right-angled trapezoid in an embodiment of the present disclosure; Figure 7 is a schematic diagram of a back contact solar cell according to an embodiment of the present disclosure in which the cross-sectional shape of the chamfered structure is an inverted triangle; Figure 8 is a schematic flow chart of a method for preparing a back-contact solar cell according to an embodiment of the present disclosure; Figure 9 The electrochemical-capacitive voltage curves of the back-contact solar cell of the embodiment of the present disclosure and the conventional back-contact solar cell show that the concentration of phosphorus-doped atoms on the n-poly surface varies with depth.

[0020] Description of reference numerals: 1. Base layer; 11. Light-receiving surface; 12. Backlight surface; 2. First polarity structure; 21. First tunneling oxide layer; 22. First doping layer; 23. First inner extension layer; 3. Second polarity structure; 31. Second tunneling oxide layer; 32. Second doping layer; 33. Second inner extension layer; 4. Isolation groove; 41. First slope; 42. Second slope; 5. Chamfered structure; 51. Extension surface; 52. Chamfered surface; 6. Suede structure. DETAILED DESCRIPTION

[0021] The present disclosure will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are intended only to illustrate the present disclosure and are not intended to limit it. It should also be noted that, for ease of description, the drawings only illustrate some, but not all, structures relevant to the present disclosure. In the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion about the concepts of the present disclosure. The accompanying drawings illustrate various schematic diagrams of structures according to embodiments of the present disclosure. These figures are not drawn to scale; certain details are exaggerated and may be omitted for clarity. The shapes, relative sizes, and positional relationships of the various regions and layers shown in the figures are merely illustrative and may vary in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions based on actual needs. In the context of the present disclosure, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or an intervening layer / element may exist between them. In addition, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element would be "below" the other layer / element.

[0022] In the prior art, back-contact solar cells employ an isolation region between the p-region and n-region structures on the backlight side, typically forming a groove. To effectively prevent conduction between regions of different polarity, the isolation region tends to be wide and deep. However, an overly wide isolation region reduces the area of ​​the structures on either side, weakening the passivation contact performance. During the cell fabrication process, p-type material is typically deposited throughout the entire cell. Laser grooving and wet cleaning are then performed to create space for the n-region structure. Next, n-type material is deposited throughout the entire cell. Finally, laser processing and wet cleaning are performed again to remove the n-type material from the p-region structure and isolation region, ultimately forming the p-region structure, n-region structure, and isolation region. During this process, the p-region material undergoes lateral corrosion during the wet cleaning process, creating voids at the bottom of the p-region material. During the deposition of the n-type material, some of the n-type material enters these voids, making them difficult to remove laterally, resulting in short-circuit leakage. The deeper the isolation region, the longer the wet cleaning time, and the larger the corresponding voids, which exacerbates leakage.

[0023] Based on this, the present disclosure provides a back-contact solar cell and a preparation method thereof, and a back-contact solar cell module to solve the problem of affecting cell performance due to improper isolation area design in related solutions.

[0024] Example 1 refer to Figures 1 to 6 This embodiment provides a back-contact solar cell, including: a base layer 1, a first polarity structure 2, a second polarity structure 3 and an isolation groove 4, the base layer 1 includes a light-receiving surface 11 and a backlight surface 12 arranged opposite to each other, the first polarity structure 2 and the second polarity structure 3 are alternately formed on the backlight surface 12 side of the base layer 1, the isolation groove 4 is formed between the first polarity structure 2 and the second polarity structure 3, and penetrates deep into the base layer 1; the bottom of the isolation groove 4 forms a chamfered structure 5 at the end near the second polarity structure 3, and the chamfered structure 5 is concavely formed from the bottom surface of the isolation groove 4 toward the light-receiving surface 11 side.

[0025] Specifically, the above-mentioned base layer 1 is a silicon base, which is an n-type base in this embodiment; the first polarity structure 2 and the second polarity structure 3 are structural layers of different polarities diffused on the backlight side of the base layer 1. For example, in this embodiment, the first polarity structure 2 can be a structural layer with a conductivity type of p-type, and the second polarity structure 3 can be a structural layer with a conductivity type of n-type. This case is used as an example in this embodiment. Of course, it is not ruled out that the first polarity structure 2 is an n-type structural layer and the second polarity structure 3 is a p-type structural layer. The above-mentioned isolation groove 4 can be a groove structure obtained by laser etching and wet cleaning, which is relatively recessed in the surface of the first polarity structure 2 and the second polarity structure 3, and the isolation groove in this embodiment penetrates a certain distance into the base layer 1. For example, the height difference between the bottom surface of the isolation groove 4 and the backlight surface 12 of the base layer 1 can be set to be greater than or equal to 2 μm. On this basis, the bottom of the isolation groove 4 in this embodiment forms a locally recessed chamfered structure 5 near the end of the second polarity structure 3 with a conductivity type of n-type, with reference to FIG. Figure 2 and Figure 3 The chamfered structure 5 shown, Figure 1 and Figure 2 Can be regarded as along Figure 3 Schematic diagram of the cross section taken along line aa.

[0026] Furthermore, the chamfered structure 5 may include at least an extension surface 51 and a chamfered surface 52, wherein the extension surface 51 extends from the intersection line of the second polarity structure 3 and the bottom of the isolation groove 4 toward the base layer 1, and the chamfered surface 52 extends from a position at a slight distance from the bottom of the isolation groove 4 and the intersection line toward the base layer 1, and an opening-shaped chamfered structure 5 is formed between the extension surface 51 and the chamfered surface 52. Figures 4 to 7 As shown, the cross-sectional shape of the chamfered structure 5 can be an inverted triangle, an inverted trapezoid or a rectangle. For example, when the extension surface 51 and the chamfered surface 52 are both vertical surfaces, and one end located inside the base layer 1 has a horizontal connecting surface, the cross-sectional shape of the chamfered structure 5 is a rectangle. Figure 4 When the extension surface 51 and the chamfered surface 52 are both inclined surfaces, and one end located inside the base layer 1 has a horizontal connecting surface, the cross-sectional shape of the chamfered structure 5 is an inverted ordinary trapezoid or an inverted isosceles trapezoid, reference Figure 5 When one of the extension surface 51 and the chamfered surface 52 is a vertical surface, the other is an inclined surface, and one end located inside the base layer 1 has a horizontal connecting surface, the cross-sectional shape of the chamfered structure 5 is an inverted right-angled trapezoid, reference Figure 6 When the extension surface 51 and the chamfered surface 52 are both inclined surfaces and are directly connected at one end inside the base layer 1, the cross-sectional shape of the chamfered structure 5 is an inverted triangle, with reference to Figure 7 shown.

[0027] In summary, in the back-contact solar cell in which a chamfered structure 5 is formed at the bottom of the isolation groove 4 in this embodiment, on the one hand, the chamfered structure 5 is deeper than the isolation groove 4, which effectively blocks the conduction between diffused atoms of different polarities, reduces the conduction risk between different polarity structures on the back of the battery, and ensures the power generation performance of the battery; on the other hand, the setting of the chamfered structure 5 also further narrows the width of the bottom of the isolation groove 4, and accordingly, the width of the area where the first polarity structure 2 and the second polarity structure 3 doped on both sides are located will be increased, thereby enhancing the effective internal reflection of the sunlight entering the battery on the back side and improving the optical performance of the battery.

[0028] Further, refer to Figure 8 The process diagram of the method for preparing a back-contact solar cell is shown, and the method for preparing a back-contact solar cell specifically includes the following steps: Step S801 : providing a base layer 1 , wherein the base layer 1 includes a light-receiving surface 11 and a backlight surface 12 that are oppositely disposed.

[0029] For example, a suitable silicon wafer is selected and double-sided polished to remove cutting damage on the surface of the silicon wafer, thereby obtaining a double-sided smooth and clean base layer 1. In this embodiment, the base layer 1 is an n-type silicon wafer.

[0030] Step S802 : forming a first polarity structure 2 and a second polarity structure 3 on the backlight surface 12 of the base layer 1 , wherein the first polarity structure 2 and the second polarity structure 3 are alternately arranged.

[0031] Specifically, an initial first polarity layer may be first deposited on the base layer 1 by LPCVD technology; then the initial first polarity layer may be grooved on the backlight surface 12 side by methods such as laser etching, and this groove treatment will remove part of the base layer 1, followed by alkaline cleaning to remove impurities; thereafter, an initial second polarity layer may be deposited on the grooved base layer 1 again by LPCVD technology as a whole, and the initial second polarity layer may cover the remaining initial first polarity layer and the side walls and bottom base layer 1 of the grooved area; and then in the area adjacent to the initial second polarity layer deposited in the grooved area, the initial second polarity layer on the initial first polarity layer may be removed by methods such as laser etching to form alternating first polarity structures 2 and second polarity structures 3.

[0032] It can be seen that the above-mentioned deposition of the initial first polarity layer and the initial second polarity layer is carried out on the light-receiving surface 11, the backlight surface 12, and the sidewalls of the substrate layer 1, thereby simplifying the processing. Based on this, after removing the initial second polarity layer located on the initial first polarity layer, the deposited material on the light-receiving surface 11 and the sidewalls of the battery is also removed by a chain method.

[0033] In step S803, an isolation groove 4 is formed between the first polarity structure 2 and the second polarity structure 3. The isolation groove 4 extends deep into the base layer 1. The bottom of the isolation groove 4 forms a chamfered structure 5 near the end of the second polarity structure 3. The chamfered structure 5 is concavely formed from the bottom surface of the isolation groove 4 toward the light-receiving surface 11.

[0034] After forming the first polarity structure 2 and the second polarity structure 3 as described above, an isolation groove 4 can be formed between the first polarity structure 2 and the second polarity structure 3 by methods such as laser etching or wet etching. Simultaneously, a deeper chamfered structure 5 is formed at the bottom edge of the isolation groove 4. In this embodiment, the chamfered structure 5 can be formed only on the side proximal to the n-type second polarity structure 3. On the one hand, the chamfered structure 5, which is deeper than the isolation groove 4, effectively blocks conduction between diffused atoms of different polarities, reducing the risk of conduction between structures of different polarities on the back side of the cell and effectively ensuring the power generation performance of the cell. On the other hand, the provision of the chamfered structure 5 further narrows the width of the bottom of the isolation groove 4. Consequently, the width of the region where the first polarity structure 2 and the second polarity structure 3 are doped on both sides is increased. This enhances the effective internal reflection of sunlight entering the cell on the back side, improving the optical performance of the cell.

[0035] In another embodiment, the chamfered structure 5 may be provided only at one end of the bottom of the isolation groove 4 close to the first polarity structure 2 of the p-type conductivity type; or at both ends of the bottom of the isolation groove 4 .

[0036] It can be seen that when forming the chamfered structure 5 only on the side closest to the n-type second polarity structure 3, or only on the side closest to the p-type first polarity structure 2, or both sides, laser etching can be used to complete the process. The appropriate wavelength of laser can be selected according to the depth requirements. For example, when a long wavelength laser such as infrared light is selected, the penetration depth is deeper, while when a short wavelength laser such as ultraviolet light is selected, the penetration depth is shallower. However, in this embodiment, when forming the chamfered structure 5 only on the side closest to the n-type second polarity structure 3, a wet etching process can also be preferably used. Specifically, on the one hand, when the initial second polarity layer is deposited, an initial second polarity layer is also deposited on the sides of the initial first polarity layer, and the subsequent laser is difficult to completely remove the initial second polarity structure 3 layer on the sides of the first polarity structure 2. As a result, during the wet etching process to form the isolation groove 4, the etching rate of the sides of the first polarity structure 2 is slower than that of the second polarity structure 3. On the other hand, during the wet etching reaction process, the diffusion layer with a higher dopant atomic concentration and an electronic conductivity type is more likely to react. Therefore, the portion of the second polarity structure 3 close to the n-type has a higher phosphorus atom doping concentration and an electronic conductivity type, thus forming the chamfered structure 5 more quickly. This method of forming the chamfered structure 5 by wet etching is compatible with the subsequent wet cleaning step and has a simpler process than laser etching.

[0037] Example 2 On the basis of Example 1, in the back contact solar cell of Example 2, in the direction from the bottom of the isolation groove 4 toward the light receiving surface 11, that is, along Figure 1 The cross-sectional dimensions of the chamfered structure 5 decrease gradually from top to bottom as shown by the arrow in the middle. Specifically, the cross-sectional dimensions include the dimensions of the figure obtained by cutting the chamfered structure 5 in the horizontal direction. Figure 3 It can include length and width. The length is the extension size of the chamfered structure 5 in the second direction, and the width is the size in the first direction. Since the change in the length is very small, the change in the cross-sectional size of the chamfered structure 5 can be considered as the change in the width. Figure 1 、 Figures 5 to 7 That is, at least one of the extended surface 51 and the chamfered surface 52 of the chamfered structure 5 is set as an inclined surface. As the depth dimension gradually increases, the cross-sectional dimension of the chamfered structure 5 gradually decreases, which helps to reduce the area of ​​the concave part, ensure the uniform stress distribution of the entire battery, and improve the strength of the battery.

[0038] Example 3 On the basis of Example 2, in the back contact solar cell of this Example 3, the maximum width dimension of the chamfered structure 5 is greater than zero and less than or equal to 50 μm, and the depth dimension of the chamfered structure 5 is greater than zero and less than or equal to 50 μm.

[0039] That is, when the chamfered structure 5 as a whole presents a structure in which the cross-sectional dimension gradually decreases from top to bottom, the cross-sectional dimension of the bottom of the isolation groove 4, i.e., the uppermost plane, is the largest. Figure 1 At the viewing angle shown, the maximum cross-sectional dimension is within a horizontal width range of 50 μm, while the vertical depth of the chamfered structure 5 is within a vertical depth range of 50 μm. Within these limits, the chamfered structure 5 can achieve optimal performance for the trench structure, the first polarity structure 2, and the second polarity structure 3, thereby achieving efficient power generation for the back-contact solar cell. It can be seen that the width of the isolation trench is set to range from 50 to 100 μm. Therefore, compared to providing a chamfered structure 5 at either end of the bottom of the isolation trench 4, providing a chamfered structure 5 at both ends of the bottom of the isolation trench 4 can appropriately reduce the width of the chamfered structure 5.

[0040] Example 4 On the basis of Example 1, in the back contact solar cell of Example 4, as Figure 1 and Figure 2 As shown, the sidewall surface of the isolation groove 4 close to the first polarity structure 2 presents a first slope 41 , and the sidewall surface of the isolation groove 4 close to the second polarity structure 3 presents a second slope 42 .

[0041] The sidewalls of the isolation groove 4 in this embodiment 4 are formed into inclined surfaces near the first polarity structure 2 and the second polarity structure 3, resulting in the overall isolation groove 4 presenting an "inverted trapezoidal" shape. Compared to the vertical sidewalls of the isolation groove 4, the sidewalls of the isolation groove 4 in this embodiment are formed into slopes. On the one hand, the distance between the first polarity structure 2 and the second polarity structure 3 remains unchanged in the bottom area of ​​the isolation groove 4, while the distance between the two is increased in the top area. This can more effectively prevent the first polarity structure 2 and the second polarity structure 3 from short-circuiting and reducing the risk of leakage. On the other hand, this design with a larger port opening size is more conducive to the uniform deposition of the passivation film on the backlight surface 12.

[0042] Example 5 Based on Example 1, Figure 1 In the back-contact solar cell of this embodiment 5, the first polarity structure 2 includes: a first tunneling oxide layer 21 and a first doping layer 22 stacked in sequence, and the first tunneling oxide layer 21 is relatively close to the backlight surface 12; the second polarity structure 3 includes: a second tunneling oxide layer 31 and a second doping layer 32 stacked in sequence, the second tunneling oxide layer 31 is relatively close to the backlight surface 12, and the conductivity type of the second doping layer 32 is opposite to that of the first doping layer 22.

[0043] Exemplarily, the first tunneling oxide layer 21 is ultra-thin silicon oxide, and the first doping layer 22 is boron-doped p-type polysilicon; the second tunneling oxide layer 31 is also ultra-thin silicon oxide, and the second doping layer 32 is phosphorus-doped n-type polysilicon, that is, the passivation contact structure of the backlight surface 12 of the back-contact battery disclosed in the present invention adopts a combination of a tunneling oxide layer and a polysilicon layer, and the first polarity structure 2 and the second polarity structure 3 of different polarities are alternately arranged, which effectively reduces carrier recombination and thereby improves battery performance.

[0044] Example 6 On the basis of Example 5, Figure 1 and Figure 2 As shown, in the back-contact solar cell of this embodiment 6, when the conductivity type of the first polarity structure 2 is p-type and the conductivity type of the second polarity structure 3 is n-type, the second polarity structure 3 extends into the backlight surface 12 of the base layer 1, and the surface of the first polarity structure 2 is higher than the surface of the second polarity structure 3.

[0045] In this embodiment, the p-type first polarity structure 2 is arranged higher than the n-type first polarity structure 2 based on the order of the fabrication processes. Specifically, during the fabrication process, the p-type first polarity structure 2 is fabricated first, followed by the n-type second polarity structure 3. After the p-type first polarity structure 2 is fabricated, laser grooving is performed to remove a portion of the base layer 1, and then the n-type second polarity structure 3 is formed at the beginning of the grooving. The thicknesses of the first polarity structure 2 and the second polarity structure 3 are typically set to be the same. Therefore, the first polarity structure 2 is taller than the second polarity structure 3, which helps improve the overall passivation performance of the p-type first polarity structure 2 and the n-type second polarity structure 3. Specifically, the p-type first polarity structure 2, especially the p-type first doped layer 22 (also known as p-poly), is fabricated at a higher process temperature, typically between 950 and 1050°C, while the n-type second polarity structure 3, especially the n-type second doped layer 32 (also known as n-poly), is fabricated at a lower process temperature, typically between 850 and 950°C. If n-poly is prepared first and then p-poly, the high temperature during the preparation of p-poly will have a secondary effect on n-poly, seriously damaging the initial passivation performance of n-poly; while if p-poly is prepared first and then n-poly, the temperature of n-poly is lower than that of p-poly, so the secondary effect is smaller, making the passivation performance of the overall p-poly and n-poly films better.

[0046] As a preferred embodiment, the process of subsequently forming the second polar structure 3 may specifically include the following steps: In step P1, a low-pressure chemical vapor deposition (LPCVD) device is used to deposit the first sublayer of the second tunnel oxide layer 31 at low temperature, wherein the flow rate of the introduced oxygen is in the range of 2000-10000 sccm, the flow rate of the introduced nitrogen is in the range of 5000-20000 sccm, the temperature range of the deposition process is 300-500°C, the time range is 50-200 s, and the thickness of the formed first sublayer is in the range of 0.1-1 nm.

[0047] Specifically, because the tunnel oxide layer is relatively thin, it's necessary to ensure that the oxide layer grown on the silicon wafer is uniform across all regions within the tube during deposition. Conventional tunnel oxide deposition processes operate at temperatures between 500°C and 700°C, using only oxygen. This approach can lead to severely uneven oxide layer growth across different regions of the silicon wafer. The reasons for this are: First, the tubes in LPCVD equipment are relatively long (typically 2-3 meters) and have a relatively large diameter (typically 0.4-0.5 meters). During tunnel oxide deposition, the oxygen introduced cannot diffuse evenly throughout the LPCVD tube within a short period of time. Consequently, the oxygen concentration in different regions varies, resulting in uneven oxide layer growth across different regions of the silicon wafer. Second, higher process temperatures can also accelerate the reaction between oxygen and the silicon wafer surface. Inconsistent oxygen concentrations within the tube further exacerbate the uneven oxide layer growth across different regions of the silicon wafer. Secondly, if oxygen is directly introduced into the tube, the oxygen concentration near the oxygen pipe mouth will generally be higher, which will directly cause the oxide layer on the surface of the silicon wafer near the pipe mouth to be thicker. If the oxygen flow rate is reduced, the oxygen diffusion rate will also be slower, and it will be difficult to diffuse evenly throughout the tube in a short time.

[0048] Based on this, this embodiment first uses a low-temperature deposition method to pre-grow an oxide layer to form the first sublayer of the second tunnel oxide layer 31. Due to the low reaction temperature, the oxidation reaction rate on the silicon wafer surface is also slow, which helps to reduce the thickness difference between the oxide layers in different areas of the silicon wafer surface. Secondly, this embodiment uses nitrogen and oxygen together. On the one hand, it can reduce the concentration of oxygen entering the tube, so that the initial oxygen concentration difference between different areas is not too large. On the other hand, nitrogen will carry oxygen into the tube at the same time, with a higher flow rate, and will diffuse to various areas within the tube in a shorter time. Therefore, the initial low-temperature pre-deposition of a portion of the second tunnel oxide layer helps to grow a more uniform oxide layer between the silicon wafers in various areas within the tube.

[0049] In step P2, the temperature inside the tube is increased without changing the flow rate of the introduced gas, thereby accelerating the formation of the second sublayer of the second tunneling oxide layer 31 at a higher temperature. The temperature range of the precipitation process is 500-700°C, the time range is 20-300 seconds, and the thickness of the formed second sublayer is 1-3 nm.

[0050] Since the oxygen concentration in each area of ​​the tube has become consistent after step P1, directly increasing the temperature on this basis can increase the growth rate of the oxide layer on the silicon wafer surface, shorten the process time, and also ensure that there is no significant difference in the thickness of the oxide layer between different areas of the silicon wafer.

[0051] Step P3: Subsequently, a second intrinsic polysilicon layer is deposited at low temperature using LPCVD. The flow rate of silane (SiH4) is in the range of 300-2000 sccm, the deposition temperature is in the range of 350-550°C (conventional process temperature is 550-600°C), the time is in the range of 2-6 hours, the working pressure is in the range of 100-500 mTorr, and the thickness of the second intrinsic polysilicon layer is in the range of 100-300 nm.

[0052] First, low-temperature deposition reduces the impact of thermal stress on the base layer 1 and other functional layers, avoiding lattice defects or interface degradation caused by high temperatures. Second, low-temperature processes slow the decomposition of silane and its deposition rate on the silicon wafer surface, relieving stress concentration between silicon atoms and reducing hydrogen bond breakage, significantly reducing the probability of film explosion and resulting in a higher-quality second intrinsic polysilicon layer.

[0053] Step P4: The temperature inside the tube is raised to perform a high-temperature pre-annealing crystallization treatment. The pre-annealing crystallization treatment first helps increase the initial film grain size of the second intrinsic polysilicon layer, improve the crystallization rate, reduce the grain boundary density, improve the film quality, and improve the subsequent gold / semiconductor contact performance. Secondly, it can also adjust the stoichiometric ratio and valence state of silicon atoms and oxygen atoms in the second tunneling oxide layer 31, thereby obtaining a higher quality second tunneling oxide layer 31. In addition, it can also increase the phosphorus atom doping concentration of the second intrinsic polysilicon layer during the subsequent phosphorus diffusion process (most of the atoms in the initial second intrinsic polysilicon layer exist in an amorphous and disordered form, making it difficult for dopant atoms to replace or embed within or between silicon atoms, resulting in a reduced doping level). An increase in the phosphorus doping concentration, that is, an increase in the number of electrons, can increase the high-low junction (n→n+→n++) concentration difference between the n-type doped layer and the base layer 1, improving field passivation performance and also facilitating subsequent gold / semiconductor contact. Furthermore, an increase in the electron concentration and the reaction rate also facilitate the formation of the chamfered structure 5 near the second polarity structure 3 during the laser processing + wet cleaning process, ultimately improving the isolation performance of the isolation groove 4.

[0054] Because step P3 is a low-temperature deposition process, the corresponding second intrinsic polysilicon layer has smaller grain size and more grain boundaries. If high-temperature annealing is performed directly in step P5, it is easy to cause the initial intrinsic polysilicon layer to crystallize too quickly, insufficiently releasing internal stress, causing lattice distortion and affecting film quality. To this end, after depositing the second intrinsic polysilicon layer, a high-temperature pre-annealing treatment is performed in the tube at a temperature range of 550-700°C for 1-3 hours, while simultaneously introducing an inert gas atmosphere such as nitrogen or argon.

[0055] In step P5, the silicon wafer with the second intrinsic polysilicon layer, which has undergone a high-temperature pre-annealing crystallization treatment, is moved to the phosphorus diffusion tube and subjected to another high-temperature annealing treatment before phosphorus diffusion. This further increases and improves the grain size and crystallization rate of the second intrinsic polysilicon layer. The two gradient annealing pre-crystallization treatments can significantly reduce the risk of insufficient stress release between the crystal lattices caused by high temperatures and improve film quality. This high-temperature annealing treatment is performed at a temperature range of 900-1050°C for a time range of 2-6 hours, and an inert gas atmosphere is also introduced.

[0056] In step P6, phosphorus diffusion is performed within the phosphorus diffusion tube to transform the surface and inner layers of the second intrinsic polysilicon layer into a PSG layer and a phosphorus diffusion layer, respectively. The phosphorus diffusion layer is also the second doped layer 32. The diffusion temperature range is 750-850°C, the diffusion time range is 5-30 minutes, the flow rate of phosphorus oxychloride (POCl3) carried by nitrogen is 500-1200 sccm, and the flow rate of oxygen is 500-1000 sccm. Oxygen is then introduced for oxidation advancement at a temperature range of 850-950°C, the advancement time range is 20-60 minutes, and the oxygen flow rate range is 1000-10000 sccm, resulting in a PSG layer with a thickness ranging from 30 to 70 nm.

[0057] refer to Figure 9 Compared with the conventional solution of directly diffusing the intrinsic polysilicon layer, this embodiment adopts the above-mentioned two-step method of forming the second tunneling oxide layer 31 and the two-step pre-annealing treatment before diffusion to finally form the second polarity structure 3. The doping concentration of the second doping layer 32 is relatively higher, and the chamfer structure 5 can be formed simultaneously.

[0058] Example 7 Based on Example 6, see Figure 1In the back-contact solar cell of this embodiment 7, the first polarity structure 2 further includes a first inner expansion layer 23 formed in the backlight surface 12 of the base layer 1, the first inner expansion layer 23 is in contact with the first tunneling oxide layer 21, and has the same conductivity type as the first doping layer 22; the second polarity structure 3 further includes a second inner expansion layer 33 formed in the backlight surface 12 of the base layer 1, the second inner expansion layer 33 is in contact with the second tunneling oxide layer 31, and has the same conductivity type as the second doping layer 32.

[0059] Specifically, when boron or phosphorus is diffused into the intrinsic polysilicon, some of the diffused atoms will enter the base layer 1 to form an inner diffusion layer, thereby forming a p-type first inner diffusion layer 23 of the p-type first polarity structure 2, and an n-type second inner diffusion layer 33 of the n-type second polarity structure 3, thereby enhancing the carrier collection ability and transmission performance, improving the contact performance between the base layer 1 and the passivation contact structure, reducing the recombination rate on the surface of the base layer 1, and improving the open circuit voltage and conversion efficiency of the battery.

[0060] On this basis, the step S802 of forming the first polarity structure 2 and the second polarity structure 3 may include the following steps: Step S8021, depositing ultra-thin silicon oxide on the base layer 1 to form an initial first tunneling oxide layer; Step S8022, depositing a first intrinsic polysilicon layer on the initial first tunnel oxide layer; Step S8023 , performing boron diffusion treatment on the first intrinsic polysilicon layer to form a boron-doped initial first doped layer, a borosilicate glass layer (BSG layer) located on the outer surface of the initial first doped layer, and an initial first inner diffusion layer on the surface of the base layer 1 ; Step S8024: performing a first laser treatment to sequentially remove a portion of the borosilicate glass layer, a portion of the initial first doped layer, a portion of the initial first tunneling oxide layer, and at least a portion of the initial first inner extension layer 23 to form a notch; Step S8025, depositing ultra-thin silicon oxide again to form an initial second tunneling oxide layer, where the initial second tunneling oxide layer covers the borosilicate glass layer and the notch; Step S8026, forming a second intrinsic polysilicon layer on the initial second tunneling oxide layer; Step S8027 , performing phosphorus diffusion treatment on the second intrinsic polysilicon layer to form a phosphorus-doped initial second doped layer, a phosphorus-silicate glass layer (PSG layer) located on the outer surface of the initial second doped layer, and an initial second inner diffusion layer on the surface of the base layer 1 ; Step S8028, a second laser treatment, removes the phosphosilicate glass layer, the initial second doped layer, and the initial second tunneling oxide layer at the location of the preset first polarity structure 2, exposing the first polarity structure 2. The second polarity structure 3 is located in the notch, thereby forming an alternating arrangement of the first polarity structure 2 and the second polarity structure 3. Of course, the first polarity structure 2 and the second polarity structure 3 in this step are connected to each other, and subsequent de-plating and wet processing are required to form isolation grooves 4 to achieve isolation.

[0061] Example 8 On the basis of Example 7, in the back-contact solar cell of Example 8, the doping depth of the first polarity structure 2 is greater than the doping depth of the second polarity structure 3 .

[0062] That is to say, the depth of the boron diffusion in the above-mentioned step S8023 is greater than the depth of the phosphorus diffusion in step S8027. Specifically, in this embodiment, the depth range of the boron diffusion is set to 1~2 μm, and the depth range of the phosphorus diffusion is set to 0.2~0.6 μm. In this way, under the premise that the surface of the first polarity structure 2 is higher than the surface of the second polarity structure 3, the different settings of the doping depth reduce the horizontal height difference of the internally diffused boron / phosphorus atoms, which helps to balance the separation and migration rate of the electron-hole pairs generated by the base layer 1 to the p-region and the n-region, and improve the carrier transport and collection performance; moreover, the diffusion depth of each doping atom is also an effective means of controlling the cleaning intensity during the wet process. The doped area is often more susceptible to wet etching than the non-doped area. The higher surface of the first polarity structure 2 and the deeper doping depth of the boron atoms can make the etching of the first polarity structure 2 and the second polarity structure 3 after the wet cleaning process approximately at the same level, so that no obvious step-like structure is formed between the two, which is conducive to uniform coverage of the subsequent passivation film.

[0063] Example 9 On the basis of any one of the above-mentioned embodiments 1 to 8, in the back-contact solar cell in this embodiment 9, a velvet structure 6 is further provided on the bottom surface of the isolation groove 4 .

[0064] Specifically, the process of forming the isolation groove 4 by the wet process also includes forming a velvet structure 6 at the bottom of the isolation groove 4 to facilitate the formation of the chamfer structure 5. It can be seen that a larger velvet structure 6 can also be formed on the light-receiving surface 11 of the base layer 1 at the same time to enhance the light trapping ability of the light-receiving surface 11.

[0065] Example 10 This embodiment provides a back-contact solar cell module, including the back-contact solar cells described in Embodiments 1-9.

[0066] The back-contact solar cell assembly of this embodiment includes a plurality of back-contact solar cells, each of which has a chamfered structure 5 formed in the isolation groove 4 on the backlight surface 12. The bottom of the isolation groove 4 forms a downwardly concave chamfered structure 5 at one end close to the second polarity structure 3 of the n-type conductivity type. On the one hand, the chamfered structure 5 is deeper than the isolation groove 4, which effectively blocks the conduction between diffused atoms of different polarities, reduces the conduction risk between different polarity structures on the back of the battery, and ensures the power generation performance of the battery; on the other hand, the setting of the chamfered structure 5 also further narrows the width of the bottom of the isolation groove 4, and accordingly, the width of the area where the first polarity structure 2 and the second polarity structure 3 doped on both sides are located will be increased, thereby enhancing the effective internal reflection of the sunlight entering the battery on the back side, improving the optical performance of the battery, and ultimately improving the performance of the back-contact solar cell assembly.

[0067] The further functional description of each of the above structures is the same as that of the above corresponding embodiments and will not be repeated here.

[0068] While the above description does not provide detailed technical details regarding patterning and etching of each layer, those skilled in the art will appreciate that various technical means can be employed to form layers, regions, and the like in desired shapes. Furthermore, those skilled in the art may devise methods that differ from those described above to form the same structure. Furthermore, while each embodiment has been described separately, this does not mean that the measures in each embodiment cannot be advantageously combined.

[0069] Although the embodiments of the present disclosure have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present disclosure, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A back contact solar cell, characterized in that: include: A base layer comprising a light-receiving surface and a backlight surface that are oppositely disposed; A first polarity structure and a second polarity structure are alternately formed on the backlight side of the base layer; an isolation groove formed between the first polarity structure and the second polarity structure and extending deep into the base layer; The bottom of the isolation groove forms a chamfered structure at an end close to the first polarity structure and / or close to the second polarity structure. The chamfered structure is concavely formed from the bottom surface of the isolation groove toward the light receiving surface.

2. The back contact solar cell according to claim 1, wherein: The cross-sectional size of the chamfered structure gradually decreases in a direction from the bottom of the isolation groove toward the light receiving surface.

3. The back contact solar cell according to claim 2, characterized in that The maximum width of the chamfered structure is greater than zero and less than or equal to 50 μm, and the depth of the chamfered structure is greater than zero and less than or equal to 50 μm.

4. The back contact solar cell according to claim 1, wherein: A sidewall surface of the isolation groove close to the first polarity structure presents a first slope, and a sidewall surface of the isolation groove close to the second polarity structure presents a second slope.

5. The back contact solar cell according to claim 1, wherein: The first polarity structure includes: a first tunneling oxide layer and a first doping layer stacked in sequence, wherein the first tunneling oxide layer is relatively close to the backlight surface; The second polarity structure includes: a second tunneling oxide layer and a second doping layer stacked in sequence, the second tunneling oxide layer is relatively close to the backlight surface, and the second doping layer has a conductivity type opposite to that of the first doping layer.

6. The back contact solar cell according to claim 5, characterized in that When the conductivity type of the first polarity structure is p-type and the conductivity type of the second polarity structure is n-type, the second polarity structure extends into the backlight surface of the base layer, and the surface of the first polarity structure is higher than that of the second polarity structure.

7. The back contact solar cell according to claim 6, characterized in that The first polarity structure further includes a first inner extension layer formed in the backlight surface of the base layer, the first inner extension layer is in contact with the first tunneling oxide layer and has the same conductivity type as the first doping layer; The second polarity structure further includes a second inner extension layer formed in the backlight surface of the base layer, the second inner extension layer is in contact with the second tunneling oxide layer, and has the same conductivity type as the second doping layer.

8. The back contact solar cell according to claim 7, characterized in that The doping depth of the first polarity structure is greater than the doping depth of the second polarity structure.

9. The back-contact solar cell according to any one of claims 1 to 8, characterized in that The bottom surface of the isolation groove is further provided with a suede structure.

10. A method for preparing a back-contact solar cell, for preparing the back-contact solar cell according to any one of claims 1 to 9, characterized in that: include: Providing a base layer, the base layer comprising a light-receiving surface and a backlight surface disposed opposite to each other; forming a first polarity structure and a second polarity structure on a backlight side of the base layer, wherein the first polarity structure and the second polarity structure are alternately arranged; An isolation groove is formed between the first polarity structure and the second polarity structure, and the isolation groove extends deep into the base layer. The bottom of the isolation groove forms a chamfered structure near the end of the first polarity structure and / or near the second polarity structure, and the chamfered structure is concavely formed from the bottom surface of the isolation groove toward the light-receiving surface.

11. The method for preparing a back-contact solar cell according to claim 10, wherein: The chamfered structure is formed in the isolation groove by a wet process or a laser process.

12. A back contact solar cell module, characterized in that: include: The back-contact solar cell according to any one of claims 1 to 9.

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