A back contact solar cell repair method

Abstract

The present application belongs to the field of photovoltaic technology, and particularly relates to a back contact solar cell repair method. The present application uses local repair processing of defective solar cell to improve the cell performance by locally connecting the positive and negative electrodes with high resistance, and promotes the reuse of unusable hot spot cell. The repair processing method of the present application only needs to apply conductive material near the hot spot defect to connect the positive and negative electrodes on the cell, which can improve or eliminate the hot spot defect, and the repaired cell can be directly used for the processing and manufacturing of cell modules, thereby improving the overall yield of solar cell production and effectively reducing the production cost. The high resistance connection of the present application helps to ensure that the positive and negative electrodes adjacent to the defect position are in a connected state, thereby effectively reducing the reverse breakdown voltage. At the same time, the low resistance connection is effectively avoided to cause a significant leakage problem between the positive and negative electrodes adjacent to the defect position.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic technology, specifically relating to a method for repairing back-contact solar cells. Background Technology

[0002] Back-contact solar cells have broad application prospects due to their higher photoelectric conversion efficiency. A back-contact solar cell is a type of cell where both the emitter and base contact electrodes are placed on the back of the cell (the non-light-receiving surface). Since the light-receiving surface of this cell is not obstructed by any metal electrodes, this effectively increases the short-circuit current of the cell.

[0003] Due to the high technical difficulty and complex process steps involved in back-contact solar cell technology, various performance defects can easily occur during the fabrication process. Some defects can be detected and reworked during fabrication; others (such as microcracks and hot spots) cannot be detected during fabrication and can only be identified during finished product inspection after all processes are completed. Since the finished product has already undergone metallization, it is necessary to remove the metal electrodes with a strong acid solution before rework, which is costly and environmentally unfriendly.

[0004] When solar cells are connected in series, the total output current is the value of the smallest cell, and the total output voltage is the sum of the voltages of all cells. If one cell's current is less than the others, the output current will be the minimum among all individual cells, and the current of the other cells in the series circuit will also decrease, significantly reducing the overall output power of the circuit. When one cell in a string is shaded, the current of the good cells is reduced, and the additional current generated by the good cells forward-biased them. If the series string is short-circuited, this forward bias across the good cells will reverse-bias the shaded cell. When many series currents cause a large reverse bias on the shaded cell, it can easily lead to significant heat dissipation on the poor cell, resulting in hot spots. Inevitably, all the power generation capacity of the good cells is dissipated in the poor cells. Large power dissipation over a given area causes localized heating or hot spots on the cells, further raising the cell temperature to as high as 150°C. This can lead to permanent and irreversible damage, such as cell or glass cracking, solder melting, or cell degradation.

[0005] Hot spot problems are very common during solar cell manufacturing, accounting for a significant proportion of defective cells. Statistics show that hot spot is the most significant failure mode in photovoltaic modules installed over the past fifteen years. Therefore, a novel solar cell processing technology is urgently needed to improve solar cell performance and increase the overall yield of solar cell production. Summary of the Invention

[0006] The present invention aims to overcome the defects of existing back-contact solar cells, which are prone to localized heating or hot spots, resulting in excessive cell height, permanent and irreversible damage, and difficulty in repair. The invention provides a repair method for back-contact solar cells to overcome the above defects.

[0007] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:

[0008] A method for repairing a back-contact solar cell includes the following steps:

[0009] Defective solar cells are detected and the location of the defects is determined.

[0010] A conductive material is applied between the positive and negative electrodes near the defect location of the battery cell to connect the positive and negative electrodes, thereby forming a conductive connection. The resistivity of the conductive material is greater than 0.5 mΩ•cm.

[0011] Common hot-spot defects in solar cells render them unusable for module manufacturing, forcing them to be scrapped or reworked. Since the cells have already undergone metallization, the metal electrodes must be removed with a strong acid solution before cleaning and rework, a very cumbersome process. Even after rework, the cells' performance is often poor. Because a high-resistance conductive connection is established between the positive and negative electrodes near the hot-spot defects on the solar cell, the reverse breakdown voltage can be effectively reduced, thus improving or eliminating the hot-spot problem. Based on this, this invention utilizes localized repair of defective solar cells to create a localized high-resistance conductive connection between the positive and negative electrodes near the defects, thereby improving cell performance and enabling the reuse of unusable hot-spot cells. The rework method of this invention only requires applying a conductive material near the hot-spot defects to connect the positive and negative electrodes, thus improving or eliminating the defects. The process is simple, and the repaired cells can be directly used in the manufacturing of solar modules, improving the overall yield of solar cell production and effectively reducing production costs. The resistivity of the conductive material in this invention is greater than 0.5 mΩ•cm. Using a high-resistance connection helps ensure that the positive and negative electrodes near the defect location remain connected, thereby effectively reducing the reverse breakdown voltage. Simultaneously, it effectively avoids significant leakage problems between the positive and negative electrodes near the defect location caused by a low-resistance connection, thus reducing the impact on the performance of the solar cell.

[0012] As a preferred method, hot spot testing is performed on defective solar cells. The solar cells are photographed and screened using an infrared thermal imager, and the defective locations on the cells are marked according to the heating areas on the infrared thermal imager.

[0013] As a further optimization, hot spot tests and electroluminescence tests are performed on the defective solar cells. The solar cells are photographed using an infrared thermal imager to obtain infrared images of the cells, which are then compared with electroluminescence (EL) test images to locate the defect locations on the cells.

[0014] By using hot spot testing and infrared thermal imaging, non-contact temperature measurement of solar cells can be achieved, enabling a comprehensive scan of the cells in a short time. This allows for the rapid detection of areas with abnormally high local temperatures, improving detection efficiency, reducing detection costs, and enhancing detection accuracy, while effectively avoiding the subjectivity and inaccuracy of human judgment.

[0015] Preferably, the conductive connection is formed either directly or after processing.

[0016] The direct conductive connection method is simple, quick, efficient, and time-saving, enabling precise construction and helping to reduce costs. It also helps reduce potential failure points and signal attenuation and delay, thereby improving conductivity. The pre-treated conductive connection method enhances the strength of the connection points, making them more secure and less prone to detachment. It also facilitates compatibility with different materials, expanding the application range and improving connection accuracy.

[0017] Preferably, the conductive material that directly forms the conductive connection is any one or a combination of metal-ceramic resistive thin film materials, metal compound thin film materials, and non-metallic thin film materials.

[0018] Metal-ceramic resistive thin-film materials possess advantages such as high resistivity and high temperature resistance, exhibiting high stability and maintaining a stable resistance value over a wide temperature range. Metal compound thin-film materials possess excellent electrical and mechanical properties, meeting the conductive connection requirements of electronic devices. They also exhibit excellent corrosion resistance, allowing for long-term use in harsh environments without performance degradation. Non-metallic thin-film materials are typically lightweight and flexible, offering advantages in applications requiring lightweight and flexible connections. Using these materials as the direct conductive materials for forming conductive connections helps improve the reliability and maintain the performance of conductive connections, while reducing production costs.

[0019] As a further preferred embodiment, the metal-ceramic resistive thin film material is composed of a mixture of metal and oxide insulator, wherein the metal is any one or more of silver, copper, zinc, tin, magnesium, aluminum, nickel, cobalt, chromium, tantalum, and ruthenium, and the oxide insulator is any one or more of silicon oxide, aluminum oxide, and calcium oxide.

[0020] As a further preferred embodiment, the metal compound thin film material is any one or a combination of tantalum nitride (TaN), tungsten oxide, Ti2O5, V2O5, LaTiO3, CaVO3, SnOx, NbO, PbO2, and MnO2.

[0021] As a further preferred embodiment, the non-metallic thin film material is a carbon material, and the resistivity of the carbon material is 3~60mΩ•cm.

[0022] Preferably, the conductive material is applied in the direct conductive connection process by any one or more of the following methods: 3D printing, laser transfer, selective laser sintering (SLS), selective laser melting (SLM), directed energy deposition (DED), material jetting, and reduction photopolymerization.

[0023] Preferably, the conductive material used to form the conductive connection after processing is a high-resistance conductive paste.

[0024] Preferably, the conductive material forming the conductive connection needs to undergo heat treatment or energy curing treatment.

[0025] Heat treatment of conductive materials forming conductive connections helps optimize their microstructure, thereby improving electron mobility and enhancing conductivity. It also helps reduce internal defects, thus increasing material purity. Energy curing of conductive materials forming conductive connections helps create a stable conductive network, further improving conductivity. It also makes the surface of the conductive material smoother and flatter, reducing surface resistance and further improving conductivity. Furthermore, heat treatment or energy curing effectively strengthens the connection between the conductive material and the positive and negative electrodes near defect sites, thereby reducing failures caused by poor connections.

[0026] As a further preferred embodiment, the heat treatment is infrared fast-burning furnace sintering or laser sintering, and the energy curing treatment is any one or more combinations of thermocuring, photocuring, and electron beam curing.

[0027] Preferably, the high-resistance conductive paste is applied by coating, spraying, direct writing of paste, or dispensing, or any combination of one or more of these methods.

[0028] As a further preferred embodiment, the spraying is directional spraying, and the viscosity of the sprayed high-resistance conductive paste is 10~100cps; the viscosity of the dispensing high-resistance conductive paste is 2000~10000cps; the applied high-resistance conductive paste is in a liquid, colloidal, semi-solid or non-Newtonian fluid state.

[0029] Preferably, the high-resistivity conductive paste is a composition comprising conductive metal particles and a polymeric binder, wherein the mass of the conductive metal particles accounts for 1-25% of the mass of the high-resistivity conductive paste, and the polymeric binder is any one or more combinations of ethylene-vinyl acetate copolymer, polyolefin resin, epoxy resin, polyurethane resin, acrylic resin, and silicone resin, wherein the mass of the polymeric binder accounts for 10-50% of the mass of the high-resistivity conductive paste.

[0030] As a further preferred embodiment, the conductive metal particles are any one or more combinations of silver, aluminum, copper, nickel, silver-plated copper, and nickel.

[0031] Preferably, the high-resistivity conductive paste further includes an inorganic binder, wherein the inorganic binder accounts for 30-50% of the mass of the high-resistivity conductive paste, and the inorganic binder is any two or more combinations selected from TeO2, PbO, Bi2O3, WO3, ZnO, SiO2, Na2O, Li2O, Al2O3, CuO, TiO2, and MoO3.

[0032] The high-resistance conductive paste further includes a solvent, which is any one or a combination of two of water and organic solvents, and the boiling point of the solvent is ≥100℃.

[0033] Inorganic binders provide excellent adhesion, enhancing the adhesion of conductive pastes. They allow for a strong bond with the cell surface during heat treatment, resulting in stable and reliable conductive connections and reducing malfunctions caused by poor bonding. Simultaneously, inorganic binders improve paste stability, effectively preventing stratification and sedimentation during long-term storage or use, thus ensuring stable and reliable conductive connections. Furthermore, the TeO2, PbO, and Bi2O3 components in inorganic binders possess high resistivity, effectively increasing the overall resistivity of the paste.

[0034] High-resistivity conductive pastes include high-boiling-point (≥100℃) solvents, which effectively prevent changes in paste properties due to solvent evaporation and help maintain paste stability. Simultaneously, the viscosity of the paste can be adjusted, ensuring uniform coating of the paste onto the substrate. Furthermore, high-boiling-point organic solvents enhance dispersibility, promoting a more uniform and stable paste.

[0035] As a further preferred embodiment, the solvent is any one or a combination of water, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monobutyl ether, ethylene glycol methyl ether acetate, methyl lactate, ethyl lactate, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, γ-butyrolactone, terpineol, ethyl acetoacetate, N-methylpyrrolidone, N,N-dimethylimidazolinone, N,N-dimethylformamide, N,N-dimethylacetamide, toluene, xylene, propylene glycol tert-butyl ether, acetylacetone, propylene glycol n-butyl ether, or 3-methoxy-3-methylbutanol.

[0036] Therefore, the present invention has the following beneficial effects:

[0037] (1) The present invention utilizes the local repair treatment of defective solar cells to make the positive and negative electrodes near the defects conduct locally with high resistance to improve the performance of the battery and enable the unusable hot spot solar cells to be reused.

[0038] (2) The rework method of the present invention only requires the application of conductive material near the hot spot defect on the battery cell to connect the positive and negative electrodes, which can improve or eliminate the hot spot defect. The process is simple, and the repaired battery cell can be directly used for the processing and manufacturing of battery modules, which improves the overall yield of solar cell production and effectively reduces production costs.

[0039] (3) The resistivity of the conductive material of the present invention is greater than 0.5 mΩ•cm. Using high resistance connection helps to ensure that the positive and negative electrodes near the defect location are connected, thereby effectively reducing the reverse breakdown voltage. At the same time, it can effectively avoid the problem of significant leakage between the positive and negative electrodes near the defect location caused by using low resistance connection, thereby reducing the impact on the performance of the battery cell. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of a back-contact solar cell structure in Example 1.

[0041] Figure 2 This is a schematic diagram of a back-contact solar cell structure in Example 2.

[0042] Figure 3 This is a schematic diagram of the structure at the defect location on the back of the solar cell repaired in Example 1. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0044] Example

[0045] A method for repairing a back-contact solar cell includes the following steps:

[0046] Defective solar cells are detected and the location of the defects is determined.

[0047] A conductive material is applied between the positive and negative electrodes near the defect location of the battery cell to connect the positive and negative electrodes, thereby forming a conductive connection. The resistivity of the conductive material is greater than 0.5 mΩ•cm.

[0048] Hot spot testing is performed on back-contact solar cells. This involves applying a reverse voltage (e.g., -12V) to the cell, placing it in a reverse bias state, and then using an infrared thermal imager to capture the temperature rise. By comparing the temperature changes, cells whose temperature exceeds the initial baseline temperature (3°C or 5°C) are selected, and the corresponding locations of the heated areas on the infrared thermal imager are marked. Since the heated areas can be large, to accurately locate defects on the solar cell, both hot spot testing and electroluminescence (EL) testing can be performed on the defective cells. The infrared images of the cells captured by the infrared thermal imager are then compared with the EL images to determine the type and specific location of the defects. Defects causing hot spots on solar cells may include broken grids, microcracks, or black edges, which can be detected in the EL images.

[0049] By using hot spot testing and infrared thermal imaging, non-contact temperature measurement of solar cells can be achieved, enabling a comprehensive scan of the cells in a short time. This allows for the rapid detection of areas with abnormally high local temperatures, improving detection efficiency, reducing detection costs, and enhancing detection accuracy, while effectively avoiding the subjectivity and inaccuracy of human judgment.

[0050] A conductive material is applied between the positive and negative electrodes near the defect location on the solar cell to connect them, thus forming a conductive connection. The purpose of this repair process is to connect the positive and negative electrodes near the defect location on the solar cell, forming a diode with a relatively low reverse breakdown voltage at the connection point. This is beneficial for the solar cell to have a relatively low reverse breakdown voltage when it is shaded.

[0051] In one implementation method, the applied conductive material is a resistive material with a certain resistivity. After application, a conductive connection can be formed directly, or it can be formed after processing. The direct conductive connection method is simple, quick, efficient, and time-saving, enabling precise construction and helping to reduce costs. It also helps reduce potential failure points and signal attenuation and delay, thereby improving conductivity. The method of forming a conductive connection after processing helps to enhance the strength of the connection, making it more secure and less prone to detachment. It also allows for adaptation to different materials, expanding the application range and improving connection accuracy.

[0052] As one implementation method, the resistivity of the applied conductive material needs to be greater than 0.5 mΩ•cm. Using a high-resistance connection helps ensure that the positive and negative electrodes near the defect location are connected, thereby effectively reducing the reverse breakdown voltage. At the same time, it can effectively avoid the significant leakage problem between the positive and negative electrodes near the defect location caused by using a low-resistance connection, thus reducing the impact on the performance of the solar cell.

[0053] As one implementation method, the conductive material that can directly form a conductive connection after application is any one or a combination of metal ceramic resistive thin film materials, metal compound thin film materials, and non-metallic thin film materials.

[0054] Metal-ceramic resistive thin-film materials possess advantages such as high resistivity and high temperature resistance, exhibiting high stability and maintaining a stable resistance value over a wide temperature range. Metal compound thin-film materials possess excellent electrical and mechanical properties, meeting the conductive connection requirements of electronic devices. They also exhibit excellent corrosion resistance, allowing for long-term use in harsh environments without performance degradation. Non-metallic thin-film materials are typically lightweight and flexible, offering advantages in applications requiring lightweight and flexible connections. Using these materials as conductive materials for directly forming conductive connections helps improve the reliability and maintain the performance of the conductive connections, while reducing production costs. These materials, when applied between the positive and negative electrodes on the surface of the solar cell, form a conductive connection without any further processing, simplifying the process and enabling precise installation.

[0055] In another embodiment, the metal-ceramic resistive thin film material is composed of a mixture of metal and oxide insulator. The metal is any one or more of silver, copper, zinc, tin, magnesium, aluminum, nickel, cobalt, chromium, tantalum, and ruthenium, and the oxide insulator is any one or more of silicon oxide, aluminum oxide, and calcium oxide.

[0056] As another embodiment, the metal compound thin film material is any one or a combination of tantalum nitride (TaN), tungsten oxide, Ti2O5, V2O5, LaTiO3, CaVO3, SnOx, NbO, PbO2, and MnO2.

[0057] As another implementation method, the non-metallic thin film material is a carbon material with a resistivity of 3~60mΩ•cm.

[0058] As one implementation method, the conductive material is applied in the direct conductive connection process by any one or more combinations of 3D printing, laser transfer, selective laser sintering (SLS), selective laser melting (SLM), directed energy deposition (DED), material jetting, and reduction photopolymerization.

[0059] As one implementation method, the conductive material that needs to be processed after application to form a conductive connection is a high-resistance conductive paste.

[0060] As one implementation method, conductive materials that need to be processed to form conductive connections need to undergo heat treatment or energy curing treatment.

[0061] Heat treatment of conductive materials forming conductive connections helps optimize their microstructure, thereby improving electron mobility and enhancing conductivity. It also helps reduce internal defects, thus increasing material purity. Energy curing of conductive materials forming conductive connections helps create a stable conductive network, further improving conductivity. It also makes the surface of the conductive material smoother and flatter, reducing surface resistance and further improving conductivity. Furthermore, heat treatment or energy curing effectively strengthens the connection between the conductive material and the positive and negative electrodes near defect sites, thereby reducing failures caused by poor connections.

[0062] As another implementation, the heat treatment is infrared rapid-fire furnace sintering or laser sintering. Laser sintering is preferred because it allows for rapid sintering at localized locations. The energy curing process is any one or a combination of thermosetting, photocuring, and electron beam curing.

[0063] As one implementation method, the high-resistivity conductive paste is applied by coating, spraying, direct writing (DIW), or dispensing, or any combination of one or more of these methods.

[0064] In another implementation, the spraying is directional spraying, and the viscosity of the sprayed high-resistance conductive paste is 10~100 cps. The viscosity of the dispensing high-resistance conductive paste is 2000~10000 cps. The applied high-resistance conductive paste is in a liquid, gel, semi-solid, or non-Newtonian fluid state.

[0065] In one embodiment, the high-resistivity conductive paste is a composition comprising conductive metal particles and a polymeric binder. The conductive metal particles account for 1-25% of the mass of the high-resistivity conductive paste. The polymeric binder is any one or more combinations of ethylene-vinyl acetate copolymer, polyolefin resin, epoxy resin, polyurethane resin, acrylic resin, and silicone resin. The polymeric binder accounts for 10-50% of the mass of the high-resistivity conductive paste.

[0066] In another implementation, the conductive metal particles are any one or more combinations of silver, aluminum, copper, nickel, silver-coated copper, and nickel.

[0067] In one embodiment, the high-resistivity conductive paste also includes an inorganic binder, the inorganic binder accounting for 30-50% of the mass of the high-resistivity conductive paste. The inorganic binder is any combination of two or more of TeO2, PbO, Bi2O3, WO3, ZnO, SiO2, Na2O, Li2O, Al2O3, CuO, TiO2, and MoO3.

[0068] Inorganic binders provide excellent adhesion, enhancing the adhesion of conductive pastes. They allow for a strong bond with the cell surface during heat treatment, resulting in stable and reliable conductive connections and reducing malfunctions caused by poor bonding. Simultaneously, inorganic binders improve paste stability, effectively preventing stratification and sedimentation during long-term storage or use, thus ensuring stable and reliable conductive connections. Furthermore, the TeO2, PbO, and Bi2O3 components in inorganic binders possess high resistivity, effectively increasing the overall resistivity of the paste.

[0069] As one implementation method, the high-resistivity conductive paste also includes a solvent, which is any one or a combination of two of water and organic solvents. For improved workability, the solvent preferably has a boiling point ≥100°C.

[0070] High-resistivity conductive pastes include high-boiling-point (≥100℃) solvents, which effectively prevent changes in paste properties due to solvent evaporation and help maintain paste stability. Simultaneously, the viscosity of the paste can be adjusted, ensuring uniform coating of the paste onto the substrate. Furthermore, high-boiling-point organic solvents enhance dispersibility, promoting a more uniform and stable paste.

[0071] As another embodiment, the solvent is any one or a combination of water, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol monobutyl ether, ethylene glycol methyl ether acetate, methyl lactate, ethyl lactate, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol methyl ether acetate, γ-butyrolactone, terpineol, ethyl acetoacetate, N-methylpyrrolidone, N,N-dimethylimidazolinone, N,N-dimethylformamide, N,N-dimethylacetamide, toluene, xylene, propylene glycol tert-butyl ether, acetylacetone, propylene glycol n-butyl ether, or 3-methoxy-3-methylbutanol.

[0072] As one implementation method, for a large number of hot spot areas on the solar cell that are relatively large or dispersed, more than one repair connection can be set on the isolation area on the surface of the solar cell to provide multiple current paths and make the temperature distribution on the surface of the solar cell more uniform.

[0073] Example 1

[0074] like Figure 1 As shown, this embodiment provides a back-contact solar cell structure, wherein the substrate is an n-type or p-type monocrystalline silicon wafer, and p-type and n-type doped regions are disposed on the back side of the silicon substrate. The p-type doped regions can be formed by localized doping on the back side of the silicon substrate using a dopant containing a p-type dopant (e.g., boron), and the n-type doped regions can be formed by localized doping on the back side of the silicon substrate using a dopant containing an n-type dopant (e.g., phosphorus). The p-type and n-type doped regions are alternately distributed on the back side of the silicon substrate and separated by an isolation region, which is an undoped silicon substrate.

[0075] Silicon nitride is deposited on the back side of a silicon substrate to form a passivation layer. The silicon nitride preferably has a relatively large positive fixed charge density to allow the silicon surface below the trench to accumulate and provide good surface passivation. As one embodiment, the silicon nitride is formed to a thickness of approximately 40–100 nm using plasma-enhanced chemical vapor deposition (PECVD).

[0076] The p-type and n-type metal electrodes can pass through silicon nitride to form electrical connections with the p-type and n-type doped regions, respectively.

[0077] The passivation antireflection layer is formed by depositing 4-8 nm Al2O3 using ALD and then depositing approximately 80 nm silicon nitride using PECVD.

[0078] This embodiment provides a repair method for a back-contact solar cell as described above.

[0079] like Figure 3As shown, a rework method for a back-contact solar cell includes the following steps:

[0080] Under a reverse bias of -12V, hot spot detection was performed on defective solar cells. Infrared thermal imagers captured the temperature rise of the cells, and by comparing the temperature changes, cells with temperatures exceeding the initial temperature (baseline temperature) by 3°C or 5°C were selected. The locations of the heated areas on the infrared thermal imagers were marked on the cells, thus pinpointing the defect locations. Before repair, the temperature at the defective area on the solar cell was 27.3°C.

[0081] 3D-printed carbon material was used to connect the adjacent positive and negative electrodes (i.e., p-type and n-type electrodes) near the defect location of the solar cell, thus directly forming a conductive connection. The resistivity of the applied carbon material was 5 mΩ•cm. After the repair connection was completed, the defect location of the solar cell was inspected again, and the temperature rise of the cell was captured by an infrared thermal imager. The results showed that the temperature at the defect location of the repaired solar cell was 23.1℃.

[0082] The repair significantly reduced the temperature at the defect site on the solar cell, indicating that electrical coupling was formed between the p-type and n-type doped regions of the solar cell through the conductive material, resulting in a relatively low reverse breakdown voltage. This improves the safety of the cell and module when the solar cell is shaded.

[0083] Example 2

[0084] The difference between this embodiment and Embodiment 1 is that:

[0085] The back-contact solar cell structure provided in this embodiment is different. For example... Figure 2 As shown, a back-contact solar cell structure is disclosed, wherein the substrate is an n-type or p-type monocrystalline silicon wafer, and p-type and n-type doped regions are disposed on the back side of the silicon substrate. The p-type and n-type doped regions are formed on a tunneling layer, which comprises silicon dioxide thermally grown on the surface of the silicon substrate or an ultrathin silicon dioxide layer deposited on the silicon substrate, with a thickness of 0.5 nm to 5 nm. The tunneling layer may also comprise silicon nitride, aluminum oxide, or silicon oxynitride.

[0086] Silicon nitride is deposited on the back side of a silicon substrate to form a passivation layer. The silicon nitride preferably has a relatively large positive fixed charge density to allow the silicon surface below the trench to accumulate and provide good surface passivation. As one embodiment, the silicon nitride is formed to a thickness of approximately 40–100 nm using plasma-enhanced chemical vapor deposition (PECVD).

[0087] The p-type and n-type metal electrodes can pass through silicon nitride to form electrical connections with the p-type and n-type doped regions, respectively.

[0088] This embodiment also provides a repair method for back-contact solar cells as described above.

[0089] A method for repairing a back-contact solar cell includes the following steps:

[0090] Under a reverse bias of -12V, hot spot detection was performed on defective solar cells. Infrared thermal imagers captured the temperature rise of the cells, and by comparing the temperature changes, cells with temperatures exceeding the initial temperature (baseline temperature) by 3°C or 5°C were selected. The locations of the heated areas on the infrared thermal imager were marked on the cells, thus pinpointing the defect locations. Before repair, the temperature at the defective area on the solar cell was 28.6°C.

[0091] In a solar cell, a nickel conductive paste is applied between the positive and negative electrodes (i.e., p-type and n-type electrodes) near the defect location to connect adjacent positive and negative electrodes. This connection is then formed through laser heat treatment (i.e., laser sintering). The resistivity of the nickel conductive paste after laser heat treatment is 3 mΩ•cm. The viscosity of the colloidal nickel conductive paste is 5000 cps. The nickel conductive paste is a composition comprising nickel conductive particles and a polymeric binder. The nickel conductive particles account for 70% of the mass of the nickel conductive paste. The polymeric binder is acrylic resin, accounting for 12% of the mass of the nickel conductive paste. The nickel conductive paste also includes an inorganic binder, accounting for 10% of the mass of the nickel conductive paste. The inorganic binder is a combination of PbO, Bi₂O₃, ZnO, SiO₂, and Li₂O. The nickel conductive paste also includes a solvent, accounting for 8% of the mass of the nickel conductive paste. The solvent is diethylene glycol monobutyl ether.

[0092] The repair significantly reduced the temperature at the defect site on the solar cell, indicating that electrical coupling was formed between the p-type and n-type doped regions of the solar cell through the conductive material, resulting in a relatively low reverse breakdown voltage. This improves the safety of the cell and module when the solar cell is shaded.

[0093] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A method for repairing back-contact solar cells, characterized in that, Includes the following steps: The defective solar cell is detected and the location of the defect is determined. The defect is a hot spot defect. A conductive material is applied between the positive and negative electrodes near the defect location of the battery cell to connect the positive and negative electrodes, thereby forming a conductive connection. The resistivity of the conductive material is greater than 0.5 mΩ•cm. The conductive connection can be formed by applying a conductive material directly to form a conductive connection or by applying a conductive material and then processing it to form a conductive connection.

2. The rework method for a back-contact solar cell according to claim 1, characterized in that, Hot spot tests are performed on defective solar cells. The solar cells are photographed and screened using an infrared thermal imager, and the defect locations on the cells are marked according to the heating areas on the infrared thermal imager.

3. The rework method for a back-contact solar cell according to claim 1, characterized in that, The conductive material that directly forms the conductive connection is any one or a combination of metal-ceramic resistive thin film materials, metal compound thin film materials, and non-metallic thin film materials.

4. A method for repairing a back-contact solar cell according to claim 1 or 3, characterized in that, The conductive material is applied in the process of directly forming a conductive connection by any one or more of the following methods: 3D printing, laser transfer, selective laser sintering, selective laser melting, directional energy deposition, material jetting, and reduction photopolymerization.

5. The rework method for a back-contact solar cell according to claim 1, characterized in that, The conductive material that forms a conductive connection after processing is a high-resistance conductive paste.

6. The rework method for a back-contact solar cell according to claim 5, characterized in that, Conductive materials that form conductive connections need to undergo heat treatment or energy curing treatment.

7. The rework method for a back-contact solar cell according to claim 5, characterized in that, The high-resistance conductive paste is applied by coating, spraying, direct writing of paste, or dispensing, or any combination of one or more of these methods.

8. A method for repairing a back-contact solar cell according to claim 5 or 7, characterized in that, The high-resistance conductive paste is a composition comprising conductive metal particles and a polymeric binder. The conductive metal particles account for 1-25% of the mass of the high-resistance conductive paste. The polymeric binder is any one or more of ethylene-vinyl acetate copolymer, polyolefin resin, epoxy resin, polyurethane resin, acrylic resin, and silicone resin. The polymeric binder accounts for 10-50% of the mass of the high-resistance conductive paste.

9. A method for repairing a back-contact solar cell according to claim 8, characterized in that, The high-resistance conductive paste also includes an inorganic binder, the inorganic binder accounting for 30-50% of the mass of the high-resistance conductive paste, and the inorganic binder being any two or more combinations selected from TeO2, PbO, Bi2O3, WO3, ZnO, SiO2, Na2O, Li2O, Al2O3, CuO, TiO2, and MoO3. The high-resistance conductive paste further includes a solvent, which is any one or a combination of two of water and organic solvents, and the boiling point of the solvent is ≥100℃.

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