Back contact solar cell, preparation method thereof and cell module
By forming a chamfered structure at the bottom of the isolation groove, the performance degradation problem caused by the isolation area structure in back-contact solar cells is solved, thereby improving the optical performance and power generation efficiency of the cells.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-31
- Publication Date
- 2026-04-10
Smart Images
Figure CN121843243A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present disclosure relates to the technical field of solar cells, in particular to a back contact solar cell and a preparation method and a cell module thereof. BACKGROUND
[0002] A back contact solar cell (BC cell for short) is a new type of solar cell technology in which the positive and negative electrodes are both moved to the back surface of the cell, which can eliminate the shading loss of the grid lines on the front surface of the traditional solar cell, significantly improve the light absorption efficiency and appearance consistency of the cell, and become an important technical direction in the photovoltaic field.
[0003] In order to effectively prevent short circuit conduction between different polarity regions on the back side of the existing back contact solar cell, an isolation region is often formed between the n region structure and the p region structure when the n region structure and the p region structure are constructed, and the size of the isolation region is relatively wide and the depth is relatively deep, so that the different polarity doping atoms on the two sides cannot be interconnected through the isolation region. However, in this structure, on the one hand, the excessively wide isolation region will reduce the effective passivation area on the back surface of the cell, thereby reducing the overall surface passivation performance, and on the other hand, the excessively deep isolation region will also induce the generation of leakage, thereby affecting the performance of the back contact solar cell. SUMMARY
[0004] Therefore, the present disclosure provides a back contact solar cell and a preparation method and a cell module thereof to solve the problem that the isolation region structure of the existing back contact solar cell affects the performance of the cell.
[0005] In a first aspect, the present disclosure provides a back contact solar cell, comprising: a substrate layer, a first polarity structure, a second polarity structure and an isolation groove, the substrate layer comprising a light-receiving surface and a back surface arranged oppositely; the first polarity structure and the second polarity structure are alternately formed on the back surface side of the substrate layer; the isolation groove is formed between the first polarity structure and the second polarity structure and extends into the substrate layer; a chamfer structure is formed at the end of the bottom of the isolation groove close to the first polarity structure and / or close to the second polarity structure, and the chamfer structure is recessed from the bottom surface of the isolation groove towards the light-receiving surface side.
[0006] In an optional embodiment, the cross-sectional size of the chamfer structure gradually decreases in the direction from the bottom of the isolation groove towards the light-receiving surface side.
[0007] In an optional embodiment, the maximum width size of the chamfer structure is greater than zero and less than or equal to 50 μm, and the depth size of the chamfer structure is greater than zero and less than or equal to 50 μm.
[0008] In an alternative embodiment, the side wall surface of the isolation groove close to the first polarity structure presents a first slope, and the side wall surface of the isolation groove close to the second polarity structure presents a second slope.
[0009] In an alternative embodiment, the first polarity structure comprises a first tunneling oxide layer and a first doped layer which are sequentially stacked, and the first tunneling oxide layer is relatively close to the back light surface; and the second polarity structure comprises a second tunneling oxide layer and a second doped layer which are sequentially stacked, and the second tunneling oxide layer is relatively close to the back light surface, and the second doped layer is opposite to the first doped layer in the conduction type.
[0010] In an alternative embodiment, when the conduction type of the first polarity structure is p-type and the conduction type of the second polarity structure is n-type, the second polarity structure extends into the back light 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 alternative embodiment, the first polarity structure further comprises a first inner extension layer formed in the back light surface of the base layer, the first inner extension layer is in contact with the first tunneling oxide layer and has the same conduction type as the first doped layer; and the second polarity structure further comprises a second inner extension layer formed in the back light surface of the base layer, the second inner extension layer is in contact with the second tunneling oxide layer and has the same conduction type as the second doped layer.
[0012] In an alternative embodiment, the doping depth of the first polarity structure is greater than the doping depth of the second polarity structure.
[0013] In an alternative embodiment, the bottom surface of the isolation groove is further provided with a textured structure.
[0014] In a second aspect, the present disclosure further provides a preparation method of a back contact solar cell, for preparing the above-mentioned back contact solar cell, comprising: providing a base layer, the base layer comprising a light receiving surface and a back light surface arranged oppositely; forming a first polarity structure and a second polarity structure on the back light surface side of the base layer, the first polarity structure and the second polarity structure being arranged alternately; forming an isolation groove between the first polarity structure and the second polarity structure, the isolation groove extending into the base layer, and a chamfer structure being formed at the end of the bottom of the isolation groove close to the first polarity structure and / or close to the second polarity structure, the chamfer structure being recessed from the bottom surface of the isolation groove towards the light receiving surface side.
[0015] In an alternative embodiment, the chamfer 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 module comprising the above-mentioned back contact solar cell.
[0017] Beneficial effects: the disclosure forms a downwardly recessed chamfer 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 chamfer structure is deeper than the depth of the isolation groove, effectively blocking the conduction between the diffusion atoms of different polarities, reducing the risk of conduction between different polarity structures on the back of the battery, and ensuring the power generation performance of the battery; on the other hand, the setting of the chamfer structure also narrows the width of the bottom of the isolation groove, so correspondingly, the width of the region where the doped first polarity structure and the second polarity structure on both sides are located will increase, which enhances the effective internal reflection of the incident sunlight on the back side, and improves the optical performance of the battery. BRIEF DESCRIPTION OF DRAWINGS
[0018] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present disclosure, the drawings needed in the specific embodiment or prior art description will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present disclosure, and other drawings can also be obtained by those skilled in the art without creative labor.
[0019] Figure 1 is a structural schematic diagram of a back contact solar cell of an embodiment of the present disclosure; Figure 2 is an electron microscope scanning schematic diagram of the isolation groove of the back contact solar cell of the embodiment of the present disclosure; Figure 3 is an optical microscope scanning schematic diagram of the isolation groove of the back contact solar cell of the embodiment of the present disclosure; Figure 4 is a schematic diagram of the chamfer structure in the back contact solar cell of the embodiment of the present disclosure, the cross-sectional shape of which is a rectangle; Figure 5 is a schematic diagram of the chamfer structure in the back contact solar cell of the embodiment of the present disclosure, the cross-sectional shape of which is an inverted ordinary trapezoid; Figure 6 is a schematic diagram of the chamfer structure in the back contact solar cell of the embodiment of the present disclosure, the cross-sectional shape of which is an inverted right-angle trapezoid; Figure 7 is a schematic diagram of the chamfer structure in the back contact solar cell of the embodiment of the present disclosure, the cross-sectional shape of which is an inverted triangle; Figure 8 is a flowchart schematic diagram of the preparation method of the back contact solar cell of the embodiment of the present disclosure; Figure 9 is an electrochemical-capacitance voltage curve of the n-poly surface phosphorus doping atom concentration change with depth of the back contact solar cell of the embodiment of the present disclosure and a conventional back contact solar cell.
[0020] Explanation of reference numerals in the attached figures: 1. Base layer; 11. Light-receiving surface; 12. Backlight-receiving surface; 2. First polar structure; 21. First tunneling oxide layer; 22. First doped layer; 23. First inner extension layer; 3. Second polar structure; 31. Second tunneling oxide layer; 32. Second doped layer; 33. Second inner expansion layer; 4. Isolation groove; 41. First slope; 42. Second slope; 5. Chamfered structure; 51. Extended surface; 52. Chamfered surface; 6. Felt texture. Detailed Implementation
[0021] The present disclosure will be further described in detail below with reference to the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the present disclosure and not intended to limit it. It should also be noted that, for ease of description, only the parts relevant to the present disclosure are shown in the drawings, not all structures. In the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concepts of the present disclosure. The accompanying drawings show various structural schematic diagrams according to embodiments of the present disclosure. These drawings are not drawn to scale, and some details are enlarged for clarity and may be omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed. In the context of this 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 there may be an intermediate layer / element between them. Additionally, if one layer / component is "above" another layer / component in one orientation, then when the orientation is reversed, that layer / component can be "below" that other layer / component.
[0022] In related technologies, back-contact solar cells have an isolation region, typically a groove-like structure, between the p-region and n-region structures on the back surface. To effectively prevent conduction between regions of different polarities, the isolation region tends to be wide and deep. However, an excessively wide isolation region reduces the area of the structural regions on both sides, weakening the passivation contact performance. The cell fabrication process usually involves first depositing p-type material monolithically, then creating space for the n-region structure through laser grooving and wet cleaning, followed by monolithic deposition of n-type material, and finally another laser treatment and wet cleaning to remove the n-type material from the p-region structure and the isolation region, ultimately forming the p-region structure, n-region structure, and isolation region. During this process, lateral corrosion of the p-region material during wet cleaning creates voids at the bottom. During the deposition of n-type material, some n-type material can enter these voids and become difficult to remove, leading to short circuits and leakage. The deeper the isolation region, the longer the wet cleaning time, and the larger the corresponding voids, exacerbating the leakage phenomenon.
[0023] Based on this, this disclosure provides a back-contact solar cell and its preparation method, as well as a back-contact solar cell module, to solve the problem of battery performance being affected by 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 substrate layer 1, a first polar structure 2, a second polar structure 3, and an isolation groove 4. The substrate layer 1 includes a light-receiving surface 11 and a back-lighting surface 12 disposed opposite to each other. The first polar structure 2 and the second polar structure 3 are alternately formed on one side of the back-lighting surface 12 of the substrate layer 1. The isolation groove 4 is formed between the first polar structure 2 and the second polar structure 3 and extends into the substrate layer 1. The bottom of the isolation groove 4 has a chamfered structure 5 formed at the end near the second polar structure 3. The chamfered structure 5 is recessed from the bottom surface of the isolation groove 4 toward the light-receiving surface 11.
[0025] Specifically, the aforementioned substrate 1 is a silicon substrate, specifically an n-type substrate in this embodiment. The first polar structure 2 and the second polar structure 3 are structural layers of different polarities diffused on the backlight side of the substrate 1. For example, in this embodiment, the first polar structure 2 can be a p-type conductive layer, and the second polar structure 3 can be an n-type conductive layer. This is the case used for illustration in this embodiment. Of course, it is also possible that the first polar structure 2 is an n-type structural layer and the second polar structure 3 is a p-type structural layer. The aforementioned isolation groove 4 can be a trench structure that is relatively recessed in the surfaces of the first polar structure 2 and the second polar structure 3, obtained by laser etching and wet cleaning. In this embodiment, the isolation trench extends a certain distance into the substrate 1. For example, the height difference between the bottom surface of the isolation groove 4 and the backlight surface 12 of the substrate 1 can be greater than or equal to 2 μm. Based on this, in this embodiment, the bottom of the isolation groove 4 forms a locally recessed chamfered structure 5 at the end near the n-type conductive second polar structure 3, as shown in the reference. Figure 2 and Figure 3 The chamfered structure 5 shown is... Figure 1 and Figure 2 Both can be seen as along Figure 3 A schematic diagram of the cross section cut by aa.
[0026] Furthermore, the chamfer structure 5 may include at least an extending surface 51 and a chamfer surface 52. The extending surface 51 extends from the intersection line of the second polar structure 3 and the bottom of the isolation groove 4 toward the base layer 1. The chamfer surface 52 extends from the bottom of the isolation groove 4 at a position with a small gap from the intersection line toward the base layer 1. An open chamfer structure 5 is formed between the extending surface 51 and the chamfer surface 52. (Refer to...) Figures 4 to 7 As shown, the cross-sectional shape of the chamfer structure 5 can be an inverted triangle, an inverted trapezoid, or a rectangle. For example, when both the extension surface 51 and the chamfer surface 52 are vertical surfaces, and one end located inside the base layer 1 has a horizontal connecting surface, the cross-sectional shape of the chamfer structure 5 is rectangular. (Refer to...) Figure 4 As shown; when both the extension surface 51 and the chamfered surface 52 are 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, as shown in the reference. Figure 5 As shown; when one of the extension surface 51 and the chamfered surface 52 is a vertical surface and 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 a chamfered right trapezoid, as shown in the reference. Figure 6 As shown; when both the extension surface 51 and the chamfered surface 52 are inclined surfaces, and one end located inside the base layer 1 is directly connected, the cross-sectional shape of the chamfered structure 5 is an inverted triangle, as shown in the reference. Figure 7 As shown.
[0027] In summary, in this embodiment of a back-contact solar cell with a chamfered structure 5 formed at the bottom of the isolation groove 4, on the one hand, the chamfered structure 5 is deeper than the isolation groove 4, effectively blocking the conduction between diffusion atoms of different polarities, reducing the risk of conduction between different polarity structures on the back of the cell, and ensuring the power generation performance of the cell; on the other hand, the chamfered structure 5 also further narrows the width of the bottom of the isolation groove 4, so correspondingly, the width of the area where the first polarity structure 2 and the second polarity structure 3 are doped on both sides will be increased, thus enhancing the effective internal reflection of sunlight entering the cell from the back side and improving the optical performance of the cell.
[0028] Further, refer to Figure 8 The flowchart shown illustrates the fabrication method of a back-contact solar cell. The fabrication method specifically includes the following steps: Step S801: Provide a substrate layer 1, which includes a light-receiving surface 11 and a backlight surface 12 disposed opposite to each other.
[0029] For example, a suitable silicon wafer is selected and polished on both sides to remove cutting damage on the surface of the silicon wafer, resulting in a flat and clean substrate layer 1 on both sides. In this embodiment, the substrate layer 1 is an n-type silicon wafer.
[0030] In step S802, a first polar structure 2 and a second polar structure 3 are formed on one side of the backlight surface 12 of the substrate layer 1, and the first polar structure 2 and the second polar structure 3 are alternately arranged.
[0031] Specifically, an initial first polar layer may first be deposited on the substrate layer 1 using LPCVD technology; then, the initial first polar layer may be grooved on one side of the backlight surface 12 by means such as laser etching, which will remove part of the substrate layer 1, followed by alkaline cleaning to remove impurities; then, an initial second polar layer may be deposited on the grooved substrate layer 1 again using LPCVD technology, which covers the remaining initial first polar layer as well as the sidewalls and bottom substrate layer 1 of the grooved area; then, in the area adjacent to the initial second polar layer deposited in the grooved area, the initial second polar layer located on the initial first polar layer may be removed by means such as laser etching, forming an alternating first polar structure 2 and second polar structure 3.
[0032] It is understood that the aforementioned deposition forming of the initial first polar layer and the initial second polar layer is carried out omnidirectionally on the light-receiving surface 11, the back-lighting surface 12, and the sidewalls of the substrate layer 1, simplifying the processing technology. Based on this, after removing the initial second polar layer located on the initial first polar layer, the deposition material on one side of the light-receiving surface 11 and the sidewall surface of the battery is also removed by a chain method.
[0033] In step S803, an isolation groove 4 is formed between the first polar structure 2 and the second polar structure 3. The isolation groove 4 extends into the base layer 1. A chamfer structure 5 is formed at the bottom of the isolation groove 4 near the end of the second polar structure 3. The chamfer structure 5 is recessed from the bottom surface of the isolation groove 4 toward the light-receiving surface 11.
[0034] After forming the first polar structure 2 and the second polar structure 3 as described above, an isolation groove 4 can be formed between the first polar structure 2 and the second polar structure 3 by means such as laser etching or wet etching. At the same time, a deeper chamfer structure 5 is formed at the bottom edge of the formed isolation groove 4. In this embodiment, the chamfer structure 5 can be formed only on the side closer to the n-type second polar structure 3. On the one hand, the formed chamfer structure 5 is deeper than the isolation groove 4, which effectively blocks the conduction between diffusion atoms of different polarities, reduces the risk of conduction between different polarity structures on the back of the battery, and effectively ensures the power generation performance of the battery. On the other hand, the setting of the chamfer structure 5 also further narrows the width of the bottom of the isolation groove 4. Accordingly, the width of the area where the first polar structure 2 and the second polar structure 3 are doped on both sides will be increased. This enhances the effective internal reflection of sunlight entering the battery from the back side and improves the optical performance of the battery.
[0035] In another embodiment, the chamfer structure 5 may be provided only at the bottom of the isolation groove 4 near one end of the first polar structure 2 with a conductivity type of p; or it may be provided at both ends of the bottom of the isolation groove 4.
[0036] It is known that when the chamfer structure 5 is formed only on the side near the second polar structure 3 of the n-type, or only on the side near the first polar structure 2 of the p-type, or on both sides, the laser etching process can be used to complete the process. The appropriate wavelength of the laser is selected based on the different depth requirements; for example, long-wavelength lasers such as infrared light result in deeper penetration, while short-wavelength lasers such as ultraviolet light result in shallower penetration. However, in this embodiment, when the chamfer structure 5 is formed only on the side near the second polar structure 3 of the n-type, a wet etching process is preferable. Specifically, on the one hand, since the initial second polar layer is deposited on the side of the initial first polar layer, and the subsequent laser cannot completely remove the initial second polar structure 3 layer on the side of the first polar structure 2, the corrosion rate of the side of the first polar structure 2 is slower than that of the second polar structure 3 during the wet etching process to form the isolation groove 4. On the other hand, in the wet etching reaction process, the diffusion layer with a higher concentration of doped atoms and electron conductivity is more likely to react. Therefore, the part near the n-type second polar structure 3 has a higher phosphorus doping concentration and electron conductivity, thus forming the chamfer structure 5 more quickly. This method of forming the chamfer structure 5 by wet etching is compatible with the subsequent wet cleaning steps and is simpler than laser etching.
[0037] Example 2 Based on Example 1, in the back-contact solar cell of Example 2, the direction from the bottom of the isolation groove 4 toward the light-receiving surface 11, that is, along... Figure 1 As indicated by the middle arrow, the cross-sectional dimensions of the chamfered structure 5 gradually decrease from top to bottom. Specifically, the cross-sectional dimensions include the dimensions of the shape obtained by cutting the chamfered structure 5 in the horizontal direction, as shown in the reference. Figure 3 This can include length and width dimensions. The length dimension is the extension dimension of the chamfered structure 5 in the second direction, while the width dimension is the dimension in the first direction. Since the change in the length dimension is very small, the change in the cross-sectional dimension of the chamfered structure 5 can be considered as a change in the width dimension. (Reference) Figure 1 , Figures 5 to 7 That is, at least one of the extension surface 51 and the chamfer surface 52 of the chamfer structure 5 is set as an inclined surface. As the depth dimension gradually increases, the cross-sectional dimension of the chamfer structure 5 gradually decreases, which helps to reduce the area of the recessed part, ensure the uniform stress distribution of the battery as a whole, and improve the strength of the battery.
[0038] Example 3 Based on Example 2, in the back contact solar cell of Example 3, the maximum width dimension of the chamfer structure 5 is greater than zero and less than or equal to 50 μm, and the depth dimension of the chamfer structure 5 is greater than zero and less than or equal to 50 μm.
[0039] That is, when the chamfered structure 5 presents a structure with cross-sectional dimensions gradually decreasing from top to bottom, its cross-sectional dimension is largest at the bottom, i.e., the uppermost plane of the isolation groove 4. Figure 1 From the shown perspective, the maximum cross-sectional dimension has a horizontal width range of less than 50 μm, and the chamfered structure 5 has a vertical depth range of less than 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 high-efficiency power generation of the back-contact solar cell. It is known that the width of the isolation trench is set to 50~100 μm. Therefore, compared to setting the chamfered structure 5 at only one end of the bottom of the isolation trench 4, setting the chamfered structure 5 at both ends of the bottom of the isolation trench 4 allows for a suitable reduction in the width of the chamfered structure 5.
[0040] Example 4 Based on Example 1, in the back-contact solar cell of Example 4, as follows: Figure 1 and Figure 2 As shown, the side wall of the isolation groove 4 near the first polar structure 2 forms a first slope 41, and the side wall of the isolation groove 4 near the second polar structure 3 forms a second slope 42.
[0041] In this embodiment 4, the isolation groove 4 has its sidewalls near the first polar structure 2 and the second polar structure 3 both formed as slopes, thus giving the overall isolation groove 4 an "inverted trapezoidal" shape. Compared to the vertical sidewalls of the isolation groove 4, the sloped sidewalls of the isolation groove 4 in this embodiment ensure that the distance between the first polar structure 2 and the second polar structure 3 remains constant in the bottom region of the isolation groove 4, while the distance between them increases in the top region. This more effectively prevents short circuits between the first polar structure 2 and the second polar structure 3, 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, and referring to Figure 1 In the back-contact solar cell of this embodiment 5, the first polar structure 2 includes a first tunneling oxide layer 21 and a first doped layer 22 stacked sequentially, with the first tunneling oxide layer 21 being relatively close to the back light surface 12; the second polar structure 3 includes a second tunneling oxide layer 31 and a second doped layer 32 stacked sequentially, with the second tunneling oxide layer 31 being relatively close to the back light surface 12, and the second doped layer 32 having the opposite conductivity type to the first doped layer 22.
[0043] For example, the first tunneling oxide layer 21 is ultrathin silicon oxide, and the first doped layer 22 is boron-doped p-type polycrystalline silicon; the second tunneling oxide layer 31 is also ultrathin silicon oxide, and the second doped layer 32 is phosphorus-doped n-type polycrystalline silicon. That is, the passivation contact structure of the back contact battery back surface 12 of this disclosure adopts a combination of tunneling oxide layer and polycrystalline silicon layer, and the first polarity structure 2 and the second polarity structure 3 of different polarities are alternately arranged to effectively reduce carrier recombination and thus improve battery performance.
[0044] Example 6 Based on Example 5, such as Figure 1 and Figure 2 As shown, in the back-contact solar cell of this embodiment 6, when the conductivity type of the first polar structure 2 is p-type and the conductivity type of the second polar structure 3 is n-type, the second polar structure 3 extends into the back-light surface 12 of the substrate layer 1, and the surface of the first polar structure 2 is higher than the surface of the second polar structure 3.
[0045] In this embodiment, the p-type first polar structure 2 is positioned higher than the n-type first polar structure 2 based on the order of the fabrication processes. That is, during the fabrication process, the p-type first polar structure 2 is fabricated first, followed by the n-type second polar structure 3. Since the p-type first polar structure 2 is fabricated, and a portion of the substrate layer 1 is removed by laser grooving, the n-type second polar structure 3 is formed at the initial stage of grooving. The thicknesses of the first polar structure 2 and the second polar structure 3 are typically set to be the same. Therefore, the higher thickness of the first polar structure 2 compared to the second polar structure 3 helps improve the overall passivation performance of both the p-type first polar structure 2 and the n-type second polar structure 3. Specifically, the p-type first polar structure 2, especially the p-type first doped layer 22 (i.e., p-poly), is fabricated at a higher temperature, typically between 950 and 1050 °C, while the n-type second polar structure 3, especially the n-type second doped layer 32 (i.e., n-poly), is fabricated at a lower temperature, typically between 850 and 950 °C. If n-poly is prepared first and then p-poly, the high temperature during the p-poly preparation process will have a secondary impact on n-poly, severely damaging the initial passivation performance of n-poly. However, if p-poly is prepared first and then n-poly, the temperature of n-poly is relatively lower than that of p-poly, so the secondary impact is smaller, resulting in better passivation performance of both p-poly and n-poly films.
[0046] As a preferred embodiment, the process of forming the second polar structure 3 in the latter stage may specifically include the following steps: In step P1, a first sublayer of the second tunneling oxide layer 31 is deposited at low temperature using a low-pressure chemical vapor deposition (LPCVD) device. The flow rate of oxygen introduced ranges from 2000 to 10000 sccm, the flow rate of nitrogen ranges from 5000 to 20000 sccm, the temperature range of the deposition process ranges from 300 to 500 ℃, the time ranges from 50 to 200 s, and the thickness of the first sublayer formed ranges from 0.1 to 1 nm.
[0047] Specifically, because the tunneling oxide layer is relatively thin, it is necessary to ensure that the oxide layer grown on the silicon wafers is consistent across all regions within the tube during deposition. Conventional tunneling oxide deposition processes operate at temperatures between 500 and 700 °C, and only oxygen is introduced. This method leads to severe inhomogeneity of the oxide layer grown on different regions of the silicon wafer. The reasons are as follows: First, LPCVD equipment has a relatively long tube (typically 2-3 meters) and a large diameter (typically 0.4-0.5 meters). During tunneling oxide deposition, the introduced oxygen cannot diffuse evenly to all parts of the LPCVD tube in a short time, resulting in varying oxygen concentrations in different regions and thus uneven oxide layer growth between different areas of the silicon wafer. Second, the higher process temperature also accelerates the reaction between oxygen and the silicon wafer surface. Given the inconsistent oxygen concentrations in different regions of the tube, this further exacerbates the inhomogeneity of the grown oxide layer between different areas of the silicon wafer. Furthermore, if oxygen is directly introduced into the tube, the oxygen concentration near the oxygen inlet will generally be higher, which will directly result in a thicker oxide layer on the silicon wafer surface near the inlet. If the oxygen flow rate is reduced, the oxygen diffusion rate will also be slower, making it difficult to diffuse evenly throughout the tube in a short time.
[0048] Based on this, this embodiment first employs a low-temperature deposition method to pre-grow an oxide layer, forming the first sublayer of the second tunneling oxide layer 31. Due to the lower reaction temperature, the oxidation reaction rate on the silicon wafer surface is also slower, which helps to reduce the thickness difference between oxide layers in different areas of the silicon wafer surface. Secondly, this embodiment uses both nitrogen and oxygen in the same gas path. On the one hand, this reduces the concentration of oxygen introduced into the tube, preventing excessive differences in oxygen concentration between initial regions. On the other hand, nitrogen carries oxygen into the tube simultaneously, resulting in a higher flow rate and faster diffusion to all areas within the tube. Therefore, the initial low-temperature pre-deposition of a portion of the second tunneling oxide layer helps to grow a more uniform oxide layer between silicon wafers in different areas of the tube.
[0049] Step P2 involves heating the inside of the tube without changing the gas flow rate, 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 ℃, the time range is 20~300 s, and the thickness of the formed second sublayer ranges from 1 to 3 nm.
[0050] Since the oxygen concentration in each area of the tube has become more uniform after step P1, directly raising 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 300~2000 sccm, the deposition temperature is 350~550 ℃ (the conventional process temperature is 550~600 ℃), the deposition time is 2~6 h, the working pressure is 100~500 mTorr, and the thickness of the second intrinsic polysilicon layer is 100~300 nm.
[0052] First, low-temperature deposition reduces the thermal stress on the substrate layer 1 and other functional layers, avoiding lattice defects or interface degradation caused by high temperatures. Second, under low-temperature processes, the decomposition of silane and the deposition rate on the silicon wafer surface are slower, which alleviates stress concentration between silicon atoms and reduces hydrogen bond breaking, thereby significantly reducing the probability of film bursting and resulting in a higher quality second intrinsic polycrystalline silicon layer.
[0053] Step P4: Heat the tube to perform a high-temperature pre-annealing crystallization treatment. Pre-annealing crystallization treatment firstly helps to increase the initial thin film grain size of the second intrinsic polycrystalline silicon layer, improve the crystallinity, reduce the grain boundary density, improve the film quality, and improve the subsequent gold / semiconductor contact performance. Secondly, it can also adjust the stoichiometry and valence state of silicon and oxygen atoms in the second tunneling oxide layer 31 to obtain a higher quality second tunneling oxide layer 31. In addition, it can increase the phosphorus atom doping concentration of the second intrinsic polycrystalline silicon layer in the subsequent phosphorus diffusion process (most atoms in the initial second intrinsic polycrystalline silicon layer exist in an amorphous disordered form, and it is difficult for doped atoms to replace or embed in or between silicon atoms, resulting in a decrease in doping amount). When the phosphorus doping concentration increases, that is, the number of electrons increases, it can, on the one hand, increase the high-low junction (n→n+→n++) concentration difference between the n-type doped layer and the substrate layer 1, improve the field passivation performance, and also benefit the subsequent gold / semiconductor contact. On the other hand, the increased electron concentration and reaction rate also help to form the chamfer structure 5 near the second polar structure 3 during the laser treatment + wet cleaning process, ultimately improving the isolation performance of the isolation groove 4.
[0054] Since step P3 is a low-temperature deposition process, the corresponding second intrinsic polysilicon layer has a small grain size and many grain boundaries. If high-temperature annealing is performed directly in step P5, the initial intrinsic polysilicon layer will easily crystallize too quickly, resulting in insufficient internal stress release, lattice distortion, and affecting the film quality. Therefore, after depositing the second intrinsic polysilicon layer, a high-temperature pre-annealing treatment is performed simultaneously in the tube, with a temperature range of 550~700 ℃ and a time range of 1~3 h, while simultaneously introducing an inert gas atmosphere, such as nitrogen or argon.
[0055] Step P5 involves transferring the silicon wafer with the second intrinsic polycrystalline silicon layer, after a first high-temperature pre-annealing crystallization treatment, to a phosphorus diffusion tube. A second high-temperature annealing treatment is then performed before phosphorus diffusion to further increase and improve the grain size and crystallinity of the second intrinsic polycrystalline silicon layer. These two gradient annealing pre-crystallization treatments significantly reduce the risk of insufficient stress release between the crystal lattices caused by high temperatures, thus improving film quality. The temperature range for this high-temperature annealing treatment is 900–1050 °C, and the time range is 2–6 h, all while being conducted in an inert gas atmosphere.
[0056] Step P6 involves performing phosphorus diffusion within a phosphorus diffusion tube to transform the surface and inner layers of the second intrinsic polycrystalline silicon layer into a PSG layer and a phosphorus diffusion layer, respectively. The phosphorus diffusion layer is also known as the second doped layer 32. The diffusion temperature ranges from 750 to 850 °C, the diffusion time ranges from 5 to 30 min, the flow rate of phosphorus oxychloride (POCl3) carried by nitrogen gas ranges from 500 to 1200 sccm, and the flow rate of oxygen ranges from 500 to 1000 sccm. Oxygen is then introduced for oxidation propagation, with a temperature range of 850 to 950 °C, a propagation time range of 20 to 60 min, and an oxygen flow rate range of 1000 to 10000 sccm, resulting in a PSG layer with a thickness ranging from 30 to 70 nm.
[0057] refer to Figure 9 Compared to the traditional approach of directly diffusing the intrinsic polysilicon layer, this embodiment uses the above two steps to form the second tunneling oxide layer 31 and two pre-annealing steps before diffusion to finally form the second polar structure 3. The doping concentration of the second doped layer 32 is relatively larger, 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 polar structure 2 further includes a first inner expansion layer 23 formed in the back-light surface 12 of the substrate 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 doped layer 22. The second polar structure 3 further includes a second inner expansion layer 33 formed in the back-light surface 12 of the substrate 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 doped layer 32.
[0059] Specifically, during boron or phosphorus diffusion of intrinsic polycrystalline silicon, some of the diffused atoms will enter the substrate layer 1 to form an inner expansion layer, thereby forming a p-type first inner expansion layer 23 of the p-type first polar structure 2 and an n-type second inner expansion layer 33 of the n-type second polar structure 3. This enhances the carrier collection and transport capabilities, improves the contact performance between the substrate layer 1 and the passivation contact structure, reduces the recombination rate on the surface of the substrate layer 1, and improves the open-circuit voltage and conversion efficiency of the battery.
[0060] Based on this, step S802, which forms the first polar structure 2 and the second polar structure 3, may include the following steps: Step S8021: Deposit an ultrathin silicon oxide on the substrate layer 1 to form an initial first tunneling oxide layer; Step S8022: A first intrinsic polycrystalline silicon layer is deposited on the initial first tunneling oxide layer; Step S8023: The first intrinsic polysilicon layer is subjected to boron diffusion treatment 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 expansion layer on the surface of the substrate layer 1. Step S8024, first laser processing, sequentially removes part of the borosilicate glass layer, part of the initial first doped layer, part of the initial first tunneling oxide layer and at least part of the initial first inner expansion layer 23 to form a groove; Step S8025: Deposit ultrathin silicon oxide again to form an initial second tunneling oxide layer, which covers the borosilicate glass layer and the trench. Step S8026: A second intrinsic polysilicon layer is formed on the initial second tunneling oxide layer; Step S8027: The second intrinsic polysilicon layer is subjected to phosphorus diffusion treatment to form an initial second doped layer with phosphorus doping, a phosphorus silicon glass layer (PSG layer) located on the outer surface of the initial second doped layer, and an initial second inner expansion layer on the surface of the substrate layer 1. Step S8028, a second laser treatment, removes the phosphorosilicon glass layer, the initial second doped layer, and the initial second tunneling oxide layer at the preset position of the first polar structure 2, exposing the first polar structure 2. The groove contains the second polar structure 3, thus forming an alternating arrangement of the first polar structure 2 and the second polar structure 3. Of course, the first polar structure 2 and the second polar structure 3 in this step are connected to each other, and need to be isolated from each other by subsequent de-coating and wet processing to form isolation grooves 4.
[0061] Example 8 Based on Example 7, in the back contact solar cell of Example 8, the doping depth of the first polar structure 2 is greater than the doping depth of the second polar structure 3.
[0062] In other words, the depth of boron diffusion in step S8023 is greater than the depth of phosphorus diffusion in step S8027. Specifically, in this embodiment, the depth of boron diffusion is set to 1~2 μm, while the depth of phosphorus diffusion is set to 0.2~0.6 μm. In this way, with the surface of the first polar structure 2 being higher than the surface of the second polar structure 3, this different setting of doping depth reduces the horizontal height difference of the internally diffused boron / phosphorus atoms, which helps to balance the separation and migration rate of electron-hole pairs in the p-region and n-region generated by the substrate 1, and improves the carrier transport and collection performance. Moreover, the diffusion depth of each doped atom is also an effective means of controlling the cleaning intensity in the wet process. The doped region is often more easily corroded by wet process than the undoped region. The higher surface of the first polar structure 2 and the deeper doping depth of boron atoms can make the corrosion of the first polar structure 2 and the second polar structure 3 approximately at the same horizontal plane after the wet cleaning process, so that no obvious step structure is formed between them, which is conducive to the uniform coverage of the subsequent passivation film.
[0063] Example 9 Based on any one of the above embodiments 1 to 8, in the back contact solar cell of this embodiment 9, the bottom surface of the isolation groove 4 is further provided with a textured surface structure 6.
[0064] Specifically, the process of forming the isolation groove 4 using a wet process also includes forming a textured surface 6 at the bottom of the isolation groove 4 to facilitate the formation of the chamfered structure 5. It is understood that a larger textured surface 6 can also be formed on the light-receiving surface 11 of the substrate layer 1, enhancing 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 module of this embodiment includes a plurality of back-contact solar cells. Each back-contact solar cell has a chamfered structure 5 formed in the isolation groove 4 of the back surface 12. The bottom of the isolation groove 4 has a downwardly recessed chamfered structure 5 at the end near the second polar structure 3 of the n-type conductivity. On the one hand, the chamfered structure 5 is deeper than the isolation groove 4, which effectively blocks the conduction between diffusion atoms of different polarities, reduces the risk of conduction between different polarity structures on the back of the cell, and ensures the power generation performance of the cell. On the other hand, the setting of the chamfered structure 5 also further narrows the width of the bottom of the isolation groove 4. Accordingly, the width of the area where the first polarity structure 2 and the second polarity structure 3 are doped on both sides will be increased. This enhances the effective internal reflection of sunlight entering the cell from the back side, improves the optical performance of the cell, and ultimately improves the performance of the back-contact solar cell module.
[0067] Further functional descriptions of the above structures are the same as those of the corresponding embodiments described above, and will not be repeated here.
[0068] The above description does not provide detailed explanations of the technical aspects of each layer's patterning, etching, etc. However, those skilled in the art should understand that various technical means can be used to form layers and regions of the desired shape. Furthermore, to form the same structure, those skilled in the art can also design methods that are not entirely identical to those described above. Additionally, although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination.
[0069] 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 back-contact solar cell, characterized in that, include: The base layer includes a light-receiving surface and a backlighting surface that are positioned opposite to each other; A first polar structure and a second polar structure are alternately formed on one side of the backlight surface of the substrate layer; An isolation groove is formed between the first polar structure and the second polar structure and extends into the base layer; The bottom of the isolation groove has a chamfered structure at the end near the first polar structure and / or near the second polar structure. The chamfered structure is recessed from the bottom surface of the isolation groove toward the light-receiving surface. 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.
2. The back-contact solar cell according to claim 1, characterized in that, The cross-sectional dimensions of the chamfered structure gradually decrease from the bottom of the isolation groove toward the light-receiving surface.
3. The back-contact solar cell according to claim 1, characterized in that, The isolation groove forms a first slope near the side wall of the first polar structure, and the isolation groove forms a second slope near the side wall of the second polar structure.
4. The back-contact solar cell according to claim 1, characterized in that, The first polar structure includes: a first tunneling oxide layer and a first doped layer stacked sequentially, wherein the first tunneling oxide layer is relatively close to the backlight surface; The second polar structure includes: a second tunneling oxide layer and a second doped layer stacked sequentially, the second tunneling oxide layer being relatively close to the backlight surface, and the second doped layer having the opposite conductivity type to the first doped layer.
5. The back-contact solar cell according to claim 4, characterized in that, When the conductivity type of the first polar structure is p-type and the conductivity type of the second polar structure is n-type, the second polar structure extends into the back surface of the substrate layer, and the surface of the first polar structure is higher than the surface of the second polar structure.
6. The back-contact solar cell according to claim 5, characterized in that, The first polar structure further includes a first inner expansion layer formed in the backlight surface of the substrate layer, the first inner expansion layer being in contact with the first tunneling oxide layer and having the same conductivity type as the first doped layer; The second polar structure further includes a second inner expansion layer formed within the back surface of the substrate layer, the second inner expansion layer being in contact with the second tunneling oxide layer and having the same conductivity type as the second doped layer.
7. The back-contact solar cell according to claim 6, characterized in that, The doping depth of the first polar structure is greater than that of the second polar structure.
8. The back-contact solar cell according to any one of claims 1-7, characterized in that, The bottom surface of the isolation groove is also provided with a velvety structure.
9. A method for preparing a back-contact solar cell, used to prepare the back-contact solar cell according to any one of claims 1-8, characterized in that, include: A substrate layer is provided, the substrate layer comprising a light-receiving surface and a backlight surface disposed opposite to each other; A first polar structure and a second polar structure are formed on one side of the backlight surface of the substrate layer, and the first polar structure and the second polar structure are alternately arranged. An isolation groove is formed between the first polar structure and the second polar structure, the isolation groove extending into the substrate layer. The bottom of the isolation groove has a chamfered structure at the end near the first polar structure and / or near the second polar structure. The chamfered structure is recessed from the bottom surface of the isolation groove toward the light-receiving surface. The distance between the bottom of the chamfered structure and the backlight surface is greater than the distance between the bottom of the isolation groove and the backlight surface.
10. The method for preparing a back-contact solar cell according to claim 9, characterized in that, The chamfered structure is formed in the isolation groove by a wet process or a laser process.
11. A back-contact solar cell module, characterized in that, include: The back-contact solar cell according to any one of claims 1-8.