Back contact solar cells and photovoltaic modules

Abstract

The utility model discloses back contact solar cell and photovoltaic module. The back light surface of back contact solar cell forms the P area, N area and the interval area between both of them of alternate distribution, the back light surface includes central region and edge area, the area ratio of N area in central region is less than the area ratio of N area in edge area, the area ratio of interval area in central region is greater than the area ratio of interval area in edge area. Therefore, can enhance the edge passivation effect of back contact solar cell to prolong the minority carrier lifetime of edge area, reduce the recombination loss of edge area, improve the passivation uniformity of battery whole, and then be favorable to the promotion battery's efficiency.

Description

Technical Field

[0001] This utility model relates to the field of solar cell technology, specifically to back-contact solar cells and photovoltaic modules. Background Technology

[0002] In the high-temperature passivation process of solar cells, the passivation effect differs significantly between the center and edge of the cell due to uneven thermal field distribution. This results in lower minority carrier lifetime and increased recombination loss in the edge region, thus affecting the cell efficiency. Solutions to these problems include: 1) uniform laser doping: this approach cannot solve the problem of uneven passivation in different regions; 2) adjusting the process temperature: this approach is difficult to control precisely and may introduce new inhomogeneities.

[0003] Therefore, current back-contact solar cells and photovoltaic modules still need improvement. Utility Model Content

[0004] This invention aims to at least alleviate or solve at least one of the aforementioned problems to some extent.

[0005] In one aspect, this invention provides a back-contact solar cell. In some embodiments of this invention, the back surface of the back-contact solar cell has alternating P-regions, N-regions, and intervening regions. The back surface includes a central region and an edge region. The area proportion of the N-region in the central region is smaller than that in the edge region, and the area proportion of the intervening regions in the central region is larger than that in the edge region. This enhances the edge passivation effect of the back-contact solar cell, thereby extending the minority carrier lifetime in the edge region, reducing recombination losses in the edge region, improving the overall passivation uniformity of the cell, and ultimately improving the cell efficiency.

[0006] In some embodiments of this utility model, the area of ​​the N region in the edge region accounts for 40% to 45%.

[0007] In some embodiments of this utility model, the area of ​​the interval zone in the edge region accounts for 25% to 30%.

[0008] In some embodiments of this utility model, the area of ​​the N region in the central region accounts for 30% to 35%.

[0009] In some embodiments of this utility model, the area of ​​the interval zone in the central region accounts for 35% to 40%.

[0010] In some embodiments of this utility model, the area of ​​region P in the edge region accounts for 25% to 30%, and / or the area of ​​region P in the central region accounts for 25% to 30%.

[0011] In some embodiments of this utility model, the backlight surface further includes a transition region, which is located between the central region and the edge region. The area ratio of the N-region in the transition region is between the area ratio of the N-region in the central region and the area ratio of the N-region in the edge region. The area ratio of the interval region in the transition region is between the area ratio of the interval region in the central region and the area ratio of the interval region in the edge region.

[0012] In some embodiments of this utility model, the transition region satisfies at least one of the following conditions: the area ratio of the N region in the transition region is 35% to 40%; the area ratio of the interval region in the transition region is 30% to 35%; and the area ratio of the P region in the transition region is 25% to 30%.

[0013] In some embodiments of this utility model, the area of ​​the central region in the backlight surface accounts for 50% to 55%; and / or, the minimum width of the edge region is ≥ 5 times the thickness of the silicon substrate.

[0014] In another aspect, this utility model provides a photovoltaic module. In some embodiments of this utility model, the photovoltaic module includes the back-contact solar cell described above. Therefore, this photovoltaic module possesses all the features and advantages of the back-contact solar cell described above, which will not be repeated here. In general, this photovoltaic module has a high photoelectric conversion efficiency. Attached Figure Description

[0015] The above and / or additional aspects and advantages of this utility model will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0016] Figure 1 A schematic diagram of the structure of a back-contact solar cell according to an embodiment of the present invention is shown;

[0017] Figure 2 A schematic diagram of the structure of a back-contact solar cell according to another embodiment of the present invention is shown;

[0018] Figure 3 This shows a schematic diagram of the structure of a back-contact solar cell according to yet another embodiment of the present invention;

[0019] Figure 4 A PL (photoluminescence) image of the back-contact solar cell in Comparative Example 1 is shown;

[0020] Figure 5 A PL image of the back-contact solar cell in Example 1 is shown.

[0021] Explanation of reference numerals in the attached figures:

[0022] 1: Central area; 2: Edge area; 3: Transition area. Detailed Implementation

[0023] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0024] In one aspect, this invention provides a back-contact solar cell. In some embodiments of this invention, the back surface of the back-contact solar cell has alternately distributed P-regions, N-regions, and intervening regions, as shown in the reference. Figures 1 to 3 The backlight surface includes a central region 1 and an edge region 2. The area ratio of the N region in the central region 1 is smaller than that in the edge region 2, and the area ratio of the inter-zone in the central region 1 is larger than that in the edge region 2.

[0025] In related technologies, the P-region, N-region, and spacer region are uniformly arranged across the entire back surface of a back-contact solar cell, with the area ratio of each region being essentially the same across different areas of the back surface. When back-contact solar cells are fabricated using this arrangement, during the high-temperature passivation process, the central region experiences slower heat dissipation, resulting in a higher and more stable temperature. This heat accumulation allows for the formation of sufficient Si-H bonds in the central region of the back surface, leading to thorough passivation and a longer minority carrier lifetime. Conversely, the edge regions experience faster heat dissipation, resulting in lower temperatures and greater instability. This leads to insufficient hydrogen atom diffusion, more recombination centers, a higher defect state density, and poorer passivation.

[0026] In this invention, the area ratios of the N-region and the spacer region are adjusted in different regions, so that the area ratio of the N-region in the central region is smaller than that in the edge region, and the area ratio of the spacer region in the central region is larger than that in the edge region. Under basic conditions, the passivation effect is N-region ≥ spacer region > P-region. The main reason why the passivation effect of the N-region is better than that of the P-region is that the doping barrier of the N-region is higher than that of the P-region, and the passivation effect at the N-region interface is relatively better. By increasing the area ratio of the N-region in the edge region, the passivation effect in the edge region can be improved.

[0027] In some embodiments of this utility model, the P region may be provided with gate lines (including main gate and fine gate lines) and a P-type doped polysilicon layer, the gate lines of the P region being in contact with the P-type doped polysilicon layer for collecting holes; the N region may be provided with gate lines (including main gate and fine gate lines) and an N-type doped polysilicon layer, the gate lines of the N region being in contact with the N-type doped polysilicon layer for collecting electrons; the spacer region is located between the N region and the P region for separating the N region and the P region.

[0028] In some embodiments of this invention, the area ratio of the N-region in the edge region 2 is 40% to 45%. For example, the area ratio of the N-region in the edge region 2 can be 40%, 41%, 42%, 43%, 44%, 45%, etc. Having the area ratio of the N-region in the edge region within the above range is beneficial for further improving the passivation effect of the edge region and extending the minority carrier lifetime of the edge region.

[0029] In some embodiments of this invention, the area ratio of the spacer region in the edge region 2 is 25% to 30%, for example, the area ratio of the spacer region in the edge region 2 can be 25%, 26%, 27%, 28%, 29%, 30%, etc. This helps to further reduce the recombination rate of charge carriers in the edge region, thereby further improving the passivation effect of the edge region and enhancing the photoelectric conversion efficiency of the battery.

[0030] In some embodiments of this utility model, in the edge region 2, the area of ​​the N region accounts for 40% to 45%, and the area of ​​the interval region accounts for 25% to 30%.

[0031] In some embodiments of this invention, the area ratio of the P region in the edge region 2 is 25% to 30%. For example, the area ratio of the P region in the edge region can be 25%, 26%, 27%, 28%, 29%, 30%, etc. This is beneficial for further improving the overall performance of the battery.

[0032] In some embodiments, in edge region 2, the area of ​​P region accounts for 25% to 30%, the area of ​​N region accounts for 40% to 45%, and the area of ​​interval region accounts for 25% to 30%.

[0033] In some embodiments of this utility model, the area ratio of the N region in the central region 1 is 30% to 35%. For example, the area ratio of the N region in the central region 1 can be 30%, 31%, 32%, 33%, 34%, 35%, etc. This helps to reduce parasitic absorption loss, thereby improving the utilization rate of light and the overall efficiency of the battery.

[0034] In some embodiments of this utility model, the area ratio of the intermediate zone in the central region 1 is 35% to 40%. For example, the area ratio of the intermediate zone in the central region 1 can be 35%, 36%, 37%, 38%, 39%, 40%, etc.

[0035] In some embodiments of this utility model, in the central region 1, the area of ​​the N region accounts for 30% to 35%, and the area of ​​the interval region accounts for 35% to 40%. This can effectively suppress parasitic absorption, thereby improving the overall performance of the battery.

[0036] In some embodiments of this invention, the area ratio of the P-region in the central region 1 is 25% to 30%. For example, the area ratio of the P-region in the central region 1 can be 25%, 26%, 27%, 28%, 29%, 30%, etc. Having the P-region area ratio within the above range is beneficial for balancing the transport paths of electrons and holes in the central region, improving the collection efficiency of electrons and holes, and thus improving the overall efficiency of the battery.

[0037] In some embodiments of this utility model, in the central region 1, the area of ​​region P accounts for 25% to 30%, the area of ​​region N accounts for 30% to 35%, and the area of ​​the interval region accounts for 35% to 40%.

[0038] In some embodiments of this utility model, reference is made to Figure 2 The back surface of a back-contact solar cell can be composed of a central region 1 and an edge region 2. In this invention, reference... Figure 2 The central region 1 is a region formed by extending outward from the center of the backlight surface by a certain radius or length, and the edge region 2 can be a region on the backlight surface other than the central region.

[0039] In this invention, the structures of the central region 1 and the edge region 2 differ. When the differences are significant, there may be uneven stress on the silicon wafer, which can lead to surface stress, potentially causing the silicon wafer to bend or other problems, and increasing the breakage rate.

[0040] To further improve the yield of back-contact solar cells, in some other embodiments of this invention, reference is made to... Figure 1 and Figure 3 The backlight surface may also include a transition region 3, located between the central region 1 and the edge region 2. The area ratio of the N-region in the transition region 3 is between that of the N-region in the central region 1 and the N-region in the edge region 2. The area ratio of the spacing region in the transition region 3 is between that of the spacing region in the central region 1 and the spacing region in the edge region 2. This reduces the breakage rate and improves the battery yield.

[0041] In some embodiments of this invention, the area ratio of the N region in the transition region 3 is 35% to 40%. For example, the area ratio of the N region in the transition region 3 can be 35%, 36%, 37%, 38%, 39%, 40%, etc. Therefore, the transition region can serve as a transition from the central region to the edge region, which is beneficial for balancing stress and improving the yield of the battery.

[0042] In some embodiments of this invention, the area ratio of the interstitial spacer in the transition region 3 is 30% to 35%. For example, the area ratio of the interstitial spacer in the transition region 3 can be 30%, 31%, 32%, 33%, 34%, 35%, etc. This helps to further balance stress, thereby further improving the yield of the battery.

[0043] In some embodiments of this invention, the area of ​​region P in transition region 3 accounts for 25% to 30%. This is beneficial for further improving the overall performance of the battery.

[0044] In some embodiments, in transition region 3, the area of ​​region P accounts for 25% to 30%, the area of ​​region N accounts for 35% to 40%, and the area of ​​interval region accounts for 30% to 35%.

[0045] In some embodiments, reference Figure 1 and Figure 3 The central region 1 can be a region extending outward from the center of the backlight surface by a certain length or radius. The transition region 3 can be a ring-shaped region extending outward from the edge of the central region 1 by a certain length. The edge region 2 is a region extending from the outer edge of the transition region 3 to the edge of the backlight surface. In the actual fabrication process, the division of each region can be adjusted according to the real-time PL.

[0046] In some embodiments of this utility model, the area ratio of the central region 1 in the back surface of the back contact solar cell can be 50% to 55%. For example, the area ratio of the central region 1 can be 50%, 51%, 52%, 53%, 54%, 55%, etc. This is beneficial to balancing the overall passivation effect and photoelectric conversion efficiency of the battery, and is beneficial to further improving the overall performance of the battery.

[0047] In some specific embodiments, in the central region 1, the area proportions of the N-region, the spacer region, and the P-region are 30%, 40%, and 30%, respectively; in the transition region 3, the area proportions of the N-region, the spacer region, and the P-region are 35%, 35%, and 30%, respectively; and in the edge region 2, the area proportions of the N-region, the spacer region, and the P-region are 40%, 30%, and 30%, respectively. In other specific embodiments, in the central region 1, the area proportions of the N-region, the spacer region, and the P-region are 33%, 39%, and 28%, respectively; in the transition region 3, the area proportions of the N-region, the spacer region, and the P-region are 38%, 34%, and 28%, respectively; and in the edge region 2, the area proportions of the N-region, the spacer region, and the P-region are 43%, 29%, and 28%, respectively. This effectively improves the overall passivation uniformity of the battery, reduces the minority carrier lifetime difference between the edge and central regions, and is beneficial to improving the photoelectric conversion efficiency of the battery.

[0048] In some embodiments of this utility model, reference is made to Figures 1 to 3 Back-contact solar cells can be square cells. Of course, those skilled in the art can also select and set the shape and size of the cells as needed.

[0049] In some embodiments of this invention, the back-contact solar cell has a silicon substrate. To further reduce the fragmentation rate, reference is made. Figure 1 The minimum width d of the edge region can be ≥ 5 times the thickness of the silicon substrate.

[0050] In some embodiments, reference Figure 1 The back-contact solar cell is a square cell. The following description, based on the dimensions of the square cell, describes the area ratio of the edge region, transition region, and center region on the backlight surface in some specific embodiments.

[0051] In some specific embodiments, reference is made to Figure 1 The length L of the battery can be 166mm, the area ratio of the central region 1 can be 52%, the area ratio of the transition region 3 can be 28%, the area ratio of the edge region 2 can be 20%, and the minimum width d of the edge region 2 can be 8mm.

[0052] In other specific embodiments, reference is made to... Figure 1 The length L of the battery can be 182mm, the area ratio of the central region 1 can be 55%, the area ratio of the transition region 3 can be 25%, the area ratio of the edge region 2 can be 20%, and the minimum width d of the edge region 2 can be 10mm.

[0053] In other specific embodiments, reference is made to... Figure 1The length L of the battery can be 210mm, the area ratio of the central region 1 can be 50%, the area ratio of the transition region 3 can be 30%, the area ratio of the edge region 2 can be 20%, and the minimum width d of the edge region 3 can be 12mm.

[0054] As battery size increases, the transition area can be appropriately enlarged to better balance stress, reduce breakage rate, and improve battery yield.

[0055] In this invention, the shapes of the central region, transition region, and edge region are not specifically limited, and those skilled in the art can set and adjust them according to actual conditions. For example, refer to... Figure 1 The central region 1 can be elliptical or approximately circular, the transition region can be annular, and the edge of the transition region 3 away from the central region 1 can be elliptical, or, refer to... Figure 3 The central region 1 can be a rectangle, and the edge of the transition region 3 away from the central region 1 can be a rectangle.

[0056] This invention provides a method for fabricating the aforementioned back-contact solar cell. In some embodiments of this invention, the method for fabricating the aforementioned back-contact solar cell may include the following steps:

[0057] S10: Provides a silicon substrate.

[0058] The silicon substrate has a front side and a back side that are arranged opposite to each other. The back side of the silicon substrate includes a central region and an edge region. Both the central region and the edge region include an N-region, a P-region and a spacer region. The spacer region is located between the N-region and the P-region.

[0059] In some embodiments of this invention, the silicon substrate can be an N-type silicon wafer. In some embodiments, the resistivity of the silicon substrate can be 3 Ω·cm. 2 -30Ω·cm 2 .

[0060] In some embodiments of this invention, an alkaline solution can be used to polish the silicon substrate on both sides to form a tower base with a size of 10μm-20μm on the silicon substrate.

[0061] S20: A P-type doped polycrystalline silicon layer and a borosilicate glass layer are formed on the back surface of a silicon substrate.

[0062] In some embodiments, a polycrystalline silicon layer (containing silicon atoms and hydrogen atoms in the raw material, some of which can form Si-H bonds during subsequent high-temperature processing) is formed on the back surface of a silicon substrate, and then boron diffusion is performed to transform the polycrystalline silicon layer into a P-type doped polycrystalline silicon layer; subsequently, a borosilicate glass layer (BSG layer) is formed by oxidation or annealing, and the borosilicate glass layer is located on the side of the P-type doped polycrystalline silicon layer away from the silicon substrate.

[0063] In some embodiments, step S20 may include steps S21 and S22.

[0064] S21: Prepare a first polycrystalline silicon layer on the surface of a silicon substrate.

[0065] In some specific embodiments, a first polycrystalline silicon layer with a thickness of 50nm-400nm can be deposited using one or more of LPCVD (low-pressure chemical vapor deposition), PECVD (plasma-enhanced chemical vapor deposition), and PVD (physical vapor deposition).

[0066] S22: Forms a P-type doped polycrystalline silicon layer and a borosilicate glass layer.

[0067] After the first polycrystalline silicon layer is formed, boron diffusion is performed using BCl3 and / or BBr3 as the boron source, and boron deposition is carried out at 900℃-1000℃ to form a surface doping concentration of 1×10⁻⁶. 20 / cm 3 -5×10 20 / cm 3 A P-type doped polycrystalline silicon layer is formed, and then a borosilicate glass layer with high reflectivity is formed by oxidation or annealing.

[0068] S30: Perform the first laser treatment to remove the borosilicate glass layer in the N-region and the spacer region.

[0069] In the first laser processing, the laser powers acting on the central and edge regions are W1 and W2, respectively, where W1 < W2. Using a relatively low-power laser to scan the central region helps reduce laser damage; using a relatively high-power laser to scan the edge region generates more heat, promoting the full diffusion of hydrogen atoms, reducing the defect state density in the edge region, thereby improving the passivation effect in the edge region and enhancing the passivation uniformity of the battery.

[0070] In some embodiments, W1 = 80%W2 to 90%W2. For example, W1 can be 80%W2, 82%W2, 85%W2, 87%W2, 90%W2, etc. Thus, the power of the laser acting on the central region and the edge region has a certain difference. The laser energy density in the edge region is about 10% to 20% higher than that in the central region, which can enhance the passivation effect in the edge region and help improve the overall passivation uniformity of the battery.

[0071] In some embodiments, W2 = 20W to 120W, for example, W2 can be 20W, 30W, 50W, 80W, 100W, 120W, etc. This is beneficial to increase the thermal effect of the edge region, allowing more heat to accumulate in the edge region, promoting the diffusion of hydrogen atoms, forming more Si-H bonds in the edge region, and improving the passivation effect of the edge region.

[0072] In the first laser processing, the frequencies of the lasers acting on the central and edge regions are f1 and f2, respectively. In some embodiments of this invention, f1 ≤ f2, and f2 = 50 kHz to 1000 kHz. For example, f2 can be 50 kHz, 100 kHz, 300 kHz, 500 kHz, 700 kHz, 1000 kHz, etc. Using a relatively high-frequency laser to process the edge region can increase the thermal effect in the edge region, accumulate more heat in the edge region, promote the formation of Si-H bonds, and improve the passivation effect; using a relatively low-frequency laser to process the central region helps to reduce laser damage.

[0073] In some embodiments of this invention, during the first laser processing, the interval region in the central region may be scanned at least twice. Using a lower-power laser to scan the interval region in the central region multiple times is more beneficial for removing the borosilicate glass layer in the interval region and optimizing the passivation effect. In some embodiments, during the first laser processing, the interval region in the central region may be subjected to two, three, or more laser scans.

[0074] In some embodiments of this invention, during the first laser processing, the power of the laser acting on the transition region is W5, where W1 < W5 < W2. This is beneficial for further improving the overall passivation uniformity of the battery and for balancing thermal stress, thereby increasing the battery's fabrication yield.

[0075] In some embodiments of this invention, the backlight surface further includes a transition region. During the first laser processing, the frequency of the laser acting on the transition region is f5, where f1≤f5≤f2. This is beneficial for further improving the overall passivation uniformity of the battery and for balancing thermal stress, thereby improving the battery manufacturing yield.

[0076] In some embodiments, during the first laser processing, the frequency of the laser acting on region N in the edge region may be higher than the frequency of the laser in other regions on the backlight surface.

[0077] In some embodiments, during the first laser processing, the single-pulse energy of the laser can be 50μJ-200μJ, and the pulse width can be 0.1µs-5µs.

[0078] In some embodiments, during the first laser processing, a green picosecond laser, an ultraviolet picosecond laser, a green femtosecond laser, or an ultraviolet femtosecond laser can be used for patterning.

[0079] S40: Remove the P-type doped polysilicon layer from the N-region and spacer region.

[0080] In some embodiments, an alkaline solution (5%-10% NaOH solution + 5%-10% hydrogen peroxide solution) can be used to remove the P-type doped polysilicon layer in the N-region and spacer region, as well as laser damage.

[0081] During the fabrication of the P-type doped polysilicon layer and BSG layer on the backlight surface, the P-type doped polysilicon layer and BSG layer are also formed on the front and side surfaces of the silicon substrate. After the first laser treatment and before step S40, the BSG layers on the front and side surfaces can be removed using an HF (50% concentration) solution.

[0082] S50: An N-type doped polycrystalline silicon layer and a phosphosilicate glass layer are formed on the back surface of a silicon substrate.

[0083] In some embodiments, a polycrystalline silicon layer is formed on the back surface of a silicon substrate, and then phosphorus diffusion is performed to transform the polycrystalline silicon layer into an N-type doped polycrystalline silicon layer; subsequently, a phosphosilicate glass layer (PSG layer) is formed by oxidation or annealing, the phosphosilicate glass layer being located on the side of the N-type doped polycrystalline silicon layer away from the silicon substrate.

[0084] In some embodiments, step S50 may include steps S51 to S53.

[0085] S51: Prepare a second polycrystalline silicon layer on the back surface of a silicon substrate.

[0086] In some embodiments, a second polycrystalline silicon layer with a thickness of 50nm-400nm can be deposited using one or more of LPCVD, PECVD, and PVD methods.

[0087] S52: Perform phosphorus diffusion to transform the second polycrystalline silicon layer prepared in step S51 into an N-type doped polycrystalline silicon layer.

[0088] In some embodiments of this invention, phosphorus oxychloride can be used as a phosphorus source for phosphorus diffusion to dope the second polycrystalline silicon layer, forming a surface doping concentration of 1×10⁻⁶. 20 / cm 3 -5×10 21 / cm 3 N-type doped polycrystalline silicon layer.

[0089] S53: Oxidation or annealing is performed to form a phosphosilicate glass layer, which is located on the side of the N-type doped polycrystalline silicon layer away from the silicon substrate.

[0090] S60: Perform a second laser treatment to remove the phosphorosilicate glass layer in the P-region and the spacer region.

[0091] In some embodiments of this invention, during the second laser processing, the laser powers acting on the central region and the edge region are W3 and W4, respectively, where W3 < W4. Therefore, using a lower-power laser to etch the central region reduces damage to the film layer in the central region, which is beneficial for improving the passivation effect of the central region. Using a higher-power laser to etch the edge region increases the thermal effect in the edge region, causing more heat to accumulate, promoting hydrogen atom diffusion, and thus generating more Si-H bonds, reducing defects in the edge region, thereby improving the passivation effect and extending the minority carrier lifetime of the edge region.

[0092] In some embodiments, W3 = 80%W4 to 90%W4. For example, W3 can be 80%W4, 83%W4, 85%W4, 88%W4, 90%W4, etc. Thus, using lasers of different powers to act on the edge and center regions is beneficial to improving the overall passivation effect and passivation uniformity of the battery.

[0093] In some embodiments, W4 = 20W to 120W, for example, W4 can be 20W, 30W, 50W, 80W, 100W, 120W, etc. Therefore, the higher power of the laser acting on the edge region allows more heat to accumulate in the edge region, promoting the diffusion of hydrogen atoms and forming more Si-H bonds, thereby further improving the passivation effect of the edge region.

[0094] In the second laser processing, the laser frequencies acting on the central and edge regions are f3 and f4, respectively. In some embodiments of this invention, f3 ≤ f4, and f4 = 50 kHz to 1000 kHz. For example, f4 can be 50 kHz, 200 kHz, 400 kHz, 600 kHz, 800 kHz, 1000 kHz, etc. Using a higher frequency laser to process the edge region is beneficial for heat accumulation in the edge region, promoting hydrogen atom diffusion, thereby improving the passivation effect of the edge region. Using a lower frequency laser to process the central region is beneficial for reducing laser damage and improving the overall performance of the battery.

[0095] In some embodiments of this invention, during the second laser processing, the spacer region in the central region may be scanned at least twice. Performing multiple laser scans at lower power can improve the removal effect of the phosphosilicate glass layer in the spacer region, which is beneficial for optimizing the passivation effect of the spacer region. In some embodiments, during the second laser processing, the spacer region in the central region may be scanned two, three, four, or more times.

[0096] In some embodiments, the backlight surface further includes a transition region. During the first laser processing, the power of the laser acting on the transition region is W6, where W3 < W6 < W4. This is beneficial for improving the passivation uniformity and fabrication yield of the battery.

[0097] In some embodiments, during the second laser processing, the frequency of the laser acting on the transition region is f6, where f3 ≤ f6 ≤ f4. This is beneficial for further improving the overall passivation uniformity and fabrication yield of the battery.

[0098] In some embodiments, during the second laser processing, the single-pulse energy of the laser can be 50μJ-200μJ, and the pulse width can be 0.1µs-5µs.

[0099] In some embodiments, during the second laser processing, a green picosecond laser, an ultraviolet picosecond laser, a green femtosecond laser, or an ultraviolet femtosecond laser can be used for patterning.

[0100] In some embodiments of this invention, the method for preparing the aforementioned back-contact solar cell may further include the following steps:

[0101] S70: Remove the N-type doped polysilicon layer from the P-region and spacer region.

[0102] In some embodiments, the PSG layers on the front and sides can be washed away first with an HF solution (concentration can be 50%), and then the N-type doped polysilicon layers in the P region and spacer region can be removed with an alkaline solution to repair laser damage. At the same time, the front side is texturized to form a tower base with a size of 20-30 micrometers to increase the utilization rate of light.

[0103] S80: Preparation of positive membrane.

[0104] Before preparing the positive film, the PSG layer in the N region and the BSG layer in the P region can be removed using an HF solution, while retaining the N-type doped polysilicon layer in the N region and the P-type doped polysilicon layer in the P region.

[0105] In some specific embodiments of this utility model, the coating process temperature of the positive film can be 540℃, and it is divided into 6 layers. The deposition sequence from the silicon substrate outward is as follows: first silicon nitride layer, second silicon nitride layer, third silicon nitride layer, first silicon oxynitride layer, second silicon oxynitride layer, and first silicon oxide layer. The difference between the silicon nitride and silicon oxynitride layers is their refractive index. The thickness of each layer is between 10nm and 25nm, and the final overall thickness of the film is 75±5nm with a refractive index of 2.10±0.05.

[0106] S90: Preparation of backsheet.

[0107] In some embodiments of this utility model, the coating process temperature of the back film can be 530℃, and it is divided into 3 layers. The deposition order from the silicon substrate outward is the fourth silicon nitride layer, the fifth silicon nitride layer, and the sixth silicon nitride layer. The difference between the silicon nitride layers is the refractive index. The thickness of each layer is between 10nm and 30nm. The final overall thickness of the film is 84±6nm, and the refractive index is 2.12±0.05.

[0108] S100: Electrode preparation.

[0109] Silver paste is printed in the N region and Al / Ag electrode paste is printed in the P region. The paste is then sintered at high temperature and laser-assisted sintering is performed to reduce metal recombination and improve the fill factor (FF) of the battery.

[0110] In summary, this invention improves the overall passivation effect of the battery by dividing the area of ​​the N-region and the spacer region into distinct zones and using lasers of different powers to treat different regions. Adjusting the distribution ratio of the N-region, spacer region, and P-region in different areas further balances parasitic absorption and passivation uniformity, thus enhancing the overall performance of the battery. The fabrication method proposed in this invention has promising application prospects and is suitable for the efficient fabrication and mass production of back-contact solar cells, improving battery yield and efficiency. Compared to technical solutions where the N-region and spacer region have the same proportion in different regions, the technical solution of this invention improves the overall passivation uniformity of the battery, reducing the minority carrier lifetime difference between the edge and center regions from >15% to <10%. Experimental verification shows an absolute efficiency improvement of 0.2%–0.3%. Furthermore, by limiting the N-region area ratio to ≤45%, parasitic absorption is controllable, and infrared light loss is <3%.

[0111] In another aspect, this invention provides a photovoltaic module. In some embodiments of this invention, the photovoltaic module includes the aforementioned back-contact solar cell. Therefore, this photovoltaic module exhibits good passivation effect and high photoelectric conversion efficiency.

[0112] In some embodiments of this invention, the photovoltaic module may include multiple back-contact solar cells.

[0113] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the following specific embodiments are merely illustrative and do not limit the scope of the present invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the materials and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the later embodiments, conditions and methods known in the art can be used for processing.

[0114] Example 1

[0115] (1) Double-sided polishing: The silicon substrate (N-type silicon wafer) is polished with alkaline solution to form a tower base with a size of 10μm-20μm.

[0116] The back surface of the silicon substrate is divided into a central region, a transition region, and an edge region. The area ratio of the N region and the area ratio of the P region are different in each of the above regions. The specific ratios are recorded in Table 1.

[0117] Table 1. Proportion (area share) and laser parameters of different regions

[0118]

[0119]

[0120] (2) Preparation of the first polycrystalline silicon layer: The first polycrystalline silicon layer with a thickness of 300 nm was deposited by LPCVD.

[0121] (3) First boron diffusion: Using BCl3 as the boron source, boron deposition (doping the first polycrystalline silicon layer) was performed at 950℃ to form a surface doping concentration of 3×10⁻⁶. 20 / cm 3 The P-type doped polycrystalline silicon layer is oxidized to form a borosilicate glass layer with high reflectivity.

[0122] (4) First laser processing: Patterning is performed using a green picosecond laser with a pulse width of 1 microsecond to remove the borosilicate glass layer in the N-region and the spacer region; according to the proportions, laser parameters and... in Table 1 Figure 1 The partitions are laser-processed.

[0123] (5) Wet treatment: Use a 50% HF solution to remove the borosilicate glass layer on the front and side sides, and then use an alkaline solution (5% NaOH solution + 5% hydrogen peroxide solution) to remove the P-type doped polysilicon layer and laser damage in the N region and spacer region.

[0124] (6) Preparation of the second polycrystalline silicon layer: A second polycrystalline silicon layer with a thickness of 300 nm was deposited using LPCVD.

[0125] (7) Phosphorus diffusion: Phosphorus oxychloride was used as the phosphorus source for doping the second polycrystalline silicon layer, resulting in a surface doping concentration of 5 × 10⁻⁶. 20 / cm 3 The N-type doped polycrystalline silicon layer is then oxidized to form a phosphosilicate glass (PSG) layer, which is located on the side of the N-type doped polycrystalline silicon layer away from the silicon substrate.

[0126] (8) Second laser processing: Patterning is performed using a green picosecond laser with a pulse width of 1 microsecond to remove the phosphorosilicate glass layer in the P-region and the interstitial region; according to the proportions, laser parameters and... in Table 1 Figure 1 The partitions are laser-processed.

[0127] (9) Wet treatment: The PSG layers on the front and sides are washed away with a 50% HF solution. The damage is cleaned and repaired by a texturing tank (removing the N-type doped polysilicon layers in the P region and the spacer region). At the same time, the front side is texturized to form a tower base with a size of 20-30 micrometers. The PSG layer in the N region and the BSG layer in the P region are removed with HF solution.

[0128] (10) Preparation of positive film: The coating process temperature is 540℃, and it is divided into 6 layers. The deposition order from the silicon substrate outward is the first silicon nitride layer, the second silicon nitride layer, the third silicon nitride layer, the first silicon oxynitride layer, the second silicon oxynitride layer, and the first silicon oxide layer.

[0129] (11) Preparation of back film: The coating process temperature is 530℃, and it is divided into 3 layers. The deposition order from the silicon substrate outward is the fourth silicon nitride layer, the fifth silicon nitride layer, and the sixth silicon nitride layer.

[0130] (12) Metallization: Print Ag paste in the N region and Al / Ag electrode in the P region.

[0131] (13) Sintering + Laser-assisted sintering: First, the printed paste is sintered at high temperature, and then laser-assisted sintering is performed.

[0132] Comparative Example 1

[0133] In Comparative Example 1, the N-region, P-region, and spacer region are uniformly distributed on the back surface of the battery. The area of ​​the N-region accounts for 40%, the area of ​​the P-region accounts for 40%, and the area of ​​the spacer region accounts for 20%. During the first and second laser processing, the frequency is 550 kHz, the power is 48 W, and the pulse width is 1 microsecond. Each region is scanned only once. The conditions for other steps in Comparative Example 1 are the same as in Example 1.

[0134] The batteries prepared in Example 1 and Comparative Example 1 were subjected to performance tests, including PL (photoluminescence) test, minority carrier lifetime, open circuit voltage (iVoc), fill factor (iFF), and recombination current density (Jo). The test results are recorded in Table 2.

[0135] Table 2. Battery performance test results for Example 1 and Comparative Example 1

[0136] Comparative Example 1 23532 3721 734.3 85.3 12 Example 1 25354 4137.5 740.5 86 9.8

[0137] In Table 1, the PL test data are grayscale values, which only represent relative signal strength. The larger the PL grayscale value, the higher the relative minority carrier lifetime. As can be seen from Table 1, compared with the battery of Comparative Example 1, the battery of Example 1 has a larger PL grayscale value, improved minority carrier lifetime, improved open-circuit voltage and fill factor, and a smaller recombination current density. Therefore, it can be seen that the overall passivation effect of the battery of Example 1 is significantly improved.

[0138] Figure 4 and Figure 5 The images shown are PL test pictures of the batteries in Comparative Example 1 and Example 1, respectively, by... Figure 4 As can be seen, the edge areas in Comparative Example 1 are noticeably darker, indicating a poor passivation effect; Figure 5 As can be seen, the battery in Example 1 is generally bright, with virtually no darkening at the edges, demonstrating excellent passivation. In practical applications, it can be determined according to... Figure 4 To adjust the central area, transition area, and edge area. Figure 4 The bright yellow area in the middle can be used as the central area, the red area can be used as the transition area, and the purple area can be used as the edge area. In order to reduce the fragmentation rate, the minimum width of the edge area is set to at least 5 times the thickness of the silicon substrate.

[0139] In the description of this utility model, the terms "front", "backlight", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing this utility model and do not require that this utility model must be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this utility model.

[0140] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," and "other embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0141] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A back-contact solar cell, wherein the back surface of the back-contact solar cell has alternating P-regions, N-regions, and intervening regions located between them, characterized in that, The backlight surface includes a central region and an edge region. The area ratio of the N-zone in the central region is smaller than that in the edge region, and the area ratio of the spacer zone in the central region is larger than that in the edge region.

2. The back-contact solar cell according to claim 1, characterized in that, The area of ​​region N in the edge region accounts for 40% to 45%.

3. The back-contact solar cell according to claim 1, characterized in that, The area of ​​the intervening zone in the edge region accounts for 25% to 30%.

4. The back-contact solar cell according to claim 1, characterized in that, The area of ​​zone N in the central region accounts for 30% to 35%.

5. The back-contact solar cell according to claim 1, characterized in that, The area of ​​the intermediate zone in the central region accounts for 35% to 40%.

6. The back-contact solar cell according to any one of claims 1 to 5, characterized in that, The area of ​​region P in the edge region accounts for 25% to 30%, and / or the area of ​​region P in the central region accounts for 25% to 30%.

7. The back-contact solar cell according to any one of claims 1 to 5, characterized in that, The backlight surface also includes a transition area, which is located between the central area and the edge area. The area ratio of the N-zone in the transition area is between the area ratio of the N-zone in the central area and the area ratio of the N-zone in the edge area. The area ratio of the interval area in the transition area is between the area ratio of the interval area in the central area and the area ratio of the interval area in the edge area.

8. The back-contact solar cell according to claim 7, characterized in that, The transition region satisfies at least one of the following conditions: The area of ​​region N in the transition region accounts for 35% to 40%; The area of ​​the interval zone in the transition region accounts for 30% to 35%; The area of ​​zone P in the transition region accounts for 25% to 30%.

9. The back-contact solar cell according to any one of claims 1 to 5 and 8, characterized in that, In the backlight surface, the area of ​​the central region accounts for 50% to 55%; and / or, the minimum width of the edge region is ≥ 5 times the thickness of the silicon substrate.

10. A photovoltaic module, characterized in that, Includes the back-contact solar cell according to any one of claims 1 to 9.

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