A method for improving EL darkening at the edges of a cell, a cell, a photovoltaic module and a photovoltaic system

Abstract

The embodiment of the application discloses a method for improving EL darkening of cell edges, a cell, a photovoltaic module and a photovoltaic system. The method comprises the following steps: after one-time sintering and one-time light injection of a cell which has not been sintered and light injected, performing two-time sintering and two-time light injection on the cell with EL darkening edges to improve the brightness of the cell edges; wherein the temperature of the two-time sintering is lower than that of the one-time sintering, and the extension direction of the EL darkening area of the edges during the two-time sintering is perpendicular to the extension direction of the corresponding edge EL darkening area during the one-time sintering. The method continues the two-time sintering and two-time light injection on the cell obtained through the one-time sintering and one-time light injection, and performs the two-time sintering at a relatively lower temperature than the one-time sintering, and meanwhile changes the orientation of the cell during the two-time sintering, thereby improving the problem of EL darkening of the cell edges.

Description

Technical Field

[0001] This application belongs to the field of photovoltaic technology and relates to a method for improving the darkening of the EL at the edge of a battery, a battery cell, a photovoltaic module, and a photovoltaic system. Background Technology

[0002] TOPCon (tunneling oxide passivated contact) cells are a new type of passivated contact solar cell that has attracted widespread attention due to their high conversion efficiency and good stability. However, TOPCon cells can suffer from edge EL (electroluminescence) darkening, which can severely affect the cell's performance. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application provides a method, a solar cell, a photovoltaic module, and a photovoltaic system for improving edge darkening of solar cells. The method involves subjecting the solar cell obtained from a first sintering and a first light injection to a second sintering and a second light injection, and performing the second sintering at a relatively lower temperature than the first sintering. Simultaneously, the orientation of the solar cell is changed during the second sintering, which significantly reduces the edge contact resistivity and improves the edge brightness and local hydrogen passivation effect, thereby improving the problem of edge darkening of solar cells.

[0004] In a first aspect, a method for improving the darkening of the EL (electrode emission) edge of a battery is provided, the method comprising the following steps:

[0005] After performing one sintering and one light injection on the unsintered solar cells, the solar cells with dark edge EL were selected.

[0006] The edge brightness of the solar cell is improved by secondary sintering and secondary light injection.

[0007] The temperature of the secondary sintering is lower than the temperature of the primary sintering;

[0008] The extension direction of the EL darkening region at the edge of the battery cell during the secondary sintering is perpendicular to the extension direction of the corresponding EL darkening region at the edge of the battery cell during the primary sintering.

[0009] The battery cell fabrication is completed after the first sintering and first light injection as described in this application embodiment. However, the battery cell obtained at this time has the problem of darkened edge EL. Therefore, this application performs a second sintering and a second light injection on the battery cell with darkened edge EL. The temperature of the second sintering is lower than that of the first sintering, that is, the second sintering is carried out at a low temperature. In addition, the orientation of the battery cell during the second sintering is different from that during the first sintering. Specifically, the corresponding edge regions of the battery cell are perpendicular to each other during the two sinterings. This allows the darkened area to fully receive the low-temperature second sintering and second light injection. The low-temperature second sintering allows the metal particles (such as silver particles) in the darkened edge region to diffuse and fill more tightly, greatly improving the temperature uniformity, significantly reducing the edge contact resistivity, and increasing the overall edge brightness. At the same time, the second light injection improves the local hydrogen passivation effect at the edge, thereby improving the problem of darkened edge EL of the battery and improving the efficiency and yield of the battery cell.

[0010] In some embodiments, the battery cell in the secondary sintering process is rotated 90° clockwise or counterclockwise relative to the battery cell in the primary sintering process, such that the extension direction of the EL darkening area on the edge of the battery cell in the secondary sintering process is perpendicular to the extension direction of the corresponding EL darkening area on the edge of the battery cell in the primary sintering process.

[0011] In some embodiments, the secondary sintering includes an auxiliary sintering and a main sintering performed sequentially, wherein the temperature of the auxiliary sintering is 160℃-200℃ and the temperature of the main sintering is 200℃-250℃.

[0012] In some embodiments, the auxiliary sintering time is 90s-150s.

[0013] In some embodiments, the main sintering time is 2-3 minutes.

[0014] In some embodiments, the heating rate of the main sintering is 5°C / min-10°C / min.

[0015] In some embodiments, the temperature of the first sintering is 250°C-750°C.

[0016] In some embodiments, the sintering time is 100s-120s and the heating rate is 10℃ / s-20℃ / s.

[0017] In some embodiments, the temperature of the first light injection is 450°C-550°C, and the time is 30s-60s.

[0018] In some embodiments, the temperature of the secondary light injection is 450℃-550℃, and the time is 30s-60s.

[0019] In some embodiments, after the first light injection, the resulting solar cells are first tested and sorted, and then solar cells with darkened edge EL are selected.

[0020] In some embodiments, after the secondary light injection is completed, the resulting solar cells are tested and sorted.

[0021] In a second aspect, a battery cell is provided, which is prepared by the method described in the first aspect.

[0022] Thirdly, a photovoltaic module is provided, the photovoltaic module comprising the solar cells as described in the second aspect.

[0023] Fourthly, a photovoltaic system is provided, the photovoltaic system comprising the photovoltaic modules described in the third aspect. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the photovoltaic system provided in this application;

[0025] Figure 2 This is a schematic diagram of the photovoltaic module provided in this application;

[0026] Figure 3 This is an exploded view of the photovoltaic module provided in this application;

[0027] Figure 4 This is a schematic diagram of the structure of the TOPCon solar cell obtained after one sintering and one light injection as described in Embodiment 1 of this application;

[0028] The accompanying drawings are not drawn to scale.

[0029] Reference numerals: 1000-Photovoltaic system, 100-Photovoltaic module, 101-Frame, 102-Front cover plate, 103-First encapsulating film, 104-Cell string layer, 105-Second encapsulating film, 106-Back cover plate, 107-Back cover plate, 1-N-type silicon wafer, 2-P-type doped polycrystalline silicon layer, 3-Alumina layer, 4-Front silicon nitride layer, 5-Front electrode, 6-Silicon dioxide layer, 7-N-type doped polycrystalline silicon layer, 8-Back silicon nitride layer, 9-Back electrode, 10-Fine grid line, 11-Edge EL darkening area. Detailed Implementation

[0030] The descriptions of specific structures or functions implemented according to the concept of this application disclosed in this specification are merely illustrative examples for explaining embodiments based on the concept of this application. Those skilled in the art will understand that embodiments based on the concept of this application can have various variations and forms, and are not limited to the embodiments described in this specification, but also include various modifications, equivalents, or substitutions made within the scope of the purpose, concept, and technology of this application.

[0031] In the description of this application, it should be understood that the use of terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", and "circumferential" indicates the relative orientation or positional relationship between different components, and is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0032] Although the terms "first" or "second" may be used to describe various components or components, the components or components should not be limited by the terms. The terms above are used only for the purpose of distinguishing one component or component from another. For example, without departing from the scope of the claims according to the concept of this application, a first battery cell may be referred to as a second battery cell, and similarly, a second battery cell may be referred to as a first battery cell.

[0033] In this application, unless otherwise expressly specified and limited, the terms "connected," "fixed," "set," etc., should be interpreted broadly. For example, when one component is said to "connect" another component, it should be understood that it can be directly or indirectly connected to the other component, meaning that other components may also be present in between. Similarly, the terms "fixed" and "set" should be interpreted broadly in a similar way. Furthermore, the term "connected" can refer to a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. In this application, unless otherwise expressly specified and limited, the description of "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Moreover, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. The first feature being "below", "under", or "below" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0034] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0035] like Figure 1 As shown, this application provides a photovoltaic system 1000, which can be applied in photovoltaic power plants, such as ground power plants, rooftop power plants, and water-based power plants, and can also be applied to equipment or devices that use solar energy to generate electricity, such as user solar power supplies, solar streetlights, solar cars, or solar buildings, etc.

[0036] It is understandable that the application scenarios of the PV system 1000 are not limited to this; that is to say, the PV system 1000 can be applied in all fields that require solar power generation. Taking a PV power generation system as an example, the PV system 1000 may include a PV array, a combiner box, and an inverter. The PV array may be an array combination of multiple PV modules. For example, multiple PV modules can form multiple PV arrays. The PV array is connected to the combiner box, which can collect the current generated by the PV array. The collected current flows through the inverter and is converted into AC power required by the mains power grid before being connected to the mains power grid to realize solar power supply.

[0037] like Figure 2 and Figure 3 As shown, a photovoltaic module 100 is a device that directly converts light energy into electrical energy through the photoelectric effect or photochemical effect. The photovoltaic module 100 is typically a stacked encapsulation structure, comprising at least the following from the light-facing side to the backlight-facing side: a front cover plate 102, a first encapsulating film 103, a cell string layer 104, a second encapsulating film 105, and a back cover plate 106, as well as a frame 101 surrounding the stacked structure and a back cover plate 107 disposed on one side of the back cover plate 106.

[0038] The front cover 102 may be made of a material with excellent light transmittance, impact resistance, corrosion resistance, and weather resistance, and may optionally include at least one of the following materials: tempered glass, plexiglass, transparent ceramics, organic fibers, or polymers. In some embodiments, the front cover may include at least one of an insulating barrier layer, a fluorinated weather-resistant layer, and a transition adhesive layer.

[0039] The back cover 106 typically needs to possess insulation, water resistance, aging resistance, weather resistance, and corrosion resistance. It may optionally include at least one of the following composite back covers as the substrate: tempered glass, acrylic glass, metal back cover, or PET film. Among these, PET-based composite back covers may be selected from various types, such as composite (e.g., TPT / KPK, TPE / KPE), coated (e.g., TPC, KPC, CPC), and co-extruded (e.g., PO), depending on the needs of different applications.

[0040] It is understandable that the material selection of the front cover 102 and the back cover 106 does not affect each other, and the same or different materials can be selected according to different application scenarios of the components (such as residential photovoltaics and building-integrated photovoltaics).

[0041] The first encapsulating film 103 and the second encapsulating film 105 can be selected from at least one of ethylene-vinyl acetate copolymer (EVA) film, polyvinyl octene coelastomer (POE) film, EVA-POE-EVA co-extruded film (EPE), PVB (polyvinyl butyral), polyethylene terephthalate (PET) film, or liquid silicone. In some embodiments, the first encapsulating film 103 and the second encapsulating film 105 may also include one or more functional additives selected from the group consisting of crosslinking agents, coupling agents, antioxidants, or ultraviolet absorbers, to improve the degree of crosslinking, weather resistance, adhesive strength, and anti-aging properties of the film. It is understood that the first encapsulating film 103 and the second encapsulating film 105 can be made of the same or different materials.

[0042] The battery string layer 104 includes multiple battery strings, which can be combined in series, parallel, or series-parallel configurations to achieve current collection and output. Further, each battery string is formed by sequentially connecting multiple battery cells via connectors. In some embodiments, at least a portion of the connector is electrically connected to the back electrode of one battery cell, and at least another portion is electrically connected to the front or back electrode of another battery cell to form a battery string. The connectors may optionally include conductive elements such as solder strips, busbars, or metal clips. In some embodiments, to improve welding performance, oxidation resistance, and weather resistance, the connector material may preferably be a highly conductive metal material, such as at least one of silver, copper, tin, or nickel, or an alloy thereof. In some embodiments, to balance conductivity and cost control, the connector material may also be at least one of metal-clad composite materials such as silver-coated copper, copper-coated silver, copper-coated aluminum, aluminum-coated copper, tin-plated copper, or nickel-plated copper. Electrical connections may be made using one of the following methods: laser welding, spot welding, bonding, ultrasonic welding, resistance welding, or brazing.

[0043] The solar cell may include a semiconductor substrate, a first emitter of a first conductivity type, and a second emitter of a second conductivity type. It is understood that one of the first and second conductivity types is P-type, and the other is N-type. The semiconductor substrate may include an N-type silicon substrate or a P-type silicon substrate. N-type silicon substrates are typically formed by doping with Group V elements such as phosphorus, arsenic, or antimony, and have the characteristic that the majority carriers are electrons; P-type silicon substrates are typically formed by doping with Group III elements such as boron, gallium, or aluminum, and have the characteristic that the majority carriers are holes.

[0044] The solar cell can employ a grid line design with no main grid (OBB), multiple main grid (MBB), or super-multiple main grid (SMBB). In some embodiments, the grid line material can be selected as at least one of silver-based conductive paste or silver-coated copper composite paste. The paste uses highly conductive metal powder as the conductive substrate, and the substrate can be at least one of silver powder, copper powder, or silver-coated copper composite powder. To improve the ohmic contact performance, conductivity, and long-term weather resistance of the electrodes, a composite functional layer can be formed on the surface of the substrate or in the grid line structure. The functional layer material includes at least one of glass powder, organic carrier, nickel-based barrier layer, tin-based alloy layer, or anti-oxidation and corrosion-resistant coating.

[0045] It is understood that the solar cell can be at least one of the following commonly used in the field: TOPCon (Tunnel Oxide Passivated Contact) cell, HJT (Heterojunction with Intrinsic Thin-film) cell, BC (Back Contact) cell, or perovskite-crystalline silicon tandem solar cell.

[0046] The frame 101 surrounds the periphery of the stacked structure and is typically made of aluminum alloy or steel alloy. In some embodiments, the frame 101 may also be a fiberglass frame 101 or a plastic frame 101. The inner side of the frame 101 usually has grooves for filling with sealant to achieve a sealed bond with the stacked components formed by the front cover 102, the first encapsulating film 103, the battery string layer 104, the second encapsulating film 105, and the back cover 106, thereby blocking moisture and buffering external impacts. In some embodiments, the frame 101 can be assembled using corner brackets.

[0047] A back cover 107 is disposed on one side of the back cover 106 and is electrically connected to the terminals of the bus electrodes in the battery string layer 104 via a lead-out busbar for energy extraction. The back cover 107 typically includes a housing and cover made of weather-resistant insulating material, conductive connecting tabs disposed within the housing, and one or more bypass diodes. The bypass diodes are connected in parallel with sub-units of the battery string. The electrical leads of the back cover 107 include photovoltaic-specific connectors and cables. The cables preferably use cross-linked polyethylene insulation sheaths and tinned copper core wires. In some embodiments, the interior of the back cover 107 may also be filled and encapsulated with potting compound to achieve insulation, thermal conductivity, moisture protection, and fixation.

[0048] TOPCon cells typically consist of a silicon wafer. The front side of the silicon wafer has a boron diffusion layer, a passivation layer, a front anti-reflection layer, and a front electrode. The back side of the silicon wafer has a tunneling oxide layer, a doped polycrystalline silicon layer, a back anti-reflection layer, and a back electrode. In other words, a tunneling oxide layer is first prepared on the back side of the TOPCon cell, and then a doped polycrystalline silicon layer is deposited. The two together form a passivation contact structure, providing good interface passivation for the back side of the silicon wafer, which enables TOPCon cells to have high conversion efficiency.

[0049] However, due to numerous defects in the silicon substrate material and production process, TOPCon solar cells still exhibit edge EL (electroluminescence) darkening even after undergoing normal full-process manufacturing. Edge EL darkening severely affects the performance of the cells.

[0050] Based on this, this application provides a method for improving the darkening of the edge EL of a battery cell. The method can perform local edge repair on the darkened EL of the battery cell, improve the edge EL brightness, and improve the battery cell efficiency and yield.

[0051] This application provides a method for improving the darkening of the EL (electrode emission index) at the edge of a battery, the method comprising the following steps:

[0052] After performing one sintering and one light injection on the unsintered solar cells, the solar cells with dark edge EL were selected.

[0053] The edge brightness of the solar cell is improved by secondary sintering and secondary light injection.

[0054] The temperature of the secondary sintering is lower than the temperature of the primary sintering;

[0055] The extension direction of the EL darkening region at the edge of the battery cell during the secondary sintering is perpendicular to the extension direction of the corresponding EL darkening region at the edge of the battery cell during the primary sintering.

[0056] The solar cell fabrication is completed after the first sintering and first light injection as described in this application. However, the solar cell obtained at this time has the problem of darkened edge EL. Therefore, this application performs a second sintering and a second light injection on the solar cell with darkened edge EL. The temperature of the second sintering is lower than that of the first sintering, that is, the second sintering is carried out at a low temperature. In addition, the orientation of the solar cell during the second sintering is different from that during the first sintering. Specifically, the corresponding edge regions of the solar cell are perpendicular to each other during the two sintering processes. This allows the darkened area to fully receive the low-temperature second sintering and second light injection. The low-temperature second sintering allows the metal particles (such as silver particles) in the darkened edge region to diffuse and fill more tightly, greatly improving the temperature uniformity, significantly reducing the edge contact resistivity, and increasing the overall edge brightness. At the same time, the second light injection improves the local hydrogen passivation effect at the edge, thereby improving the problem of darkened edge EL of the solar cell and improving the efficiency and yield of the solar cell.

[0057] Since the fabrication method of solar cells typically includes texturing, sequentially fabricating a tunneling oxide layer and a doped polycrystalline silicon layer on the back side, fabricating a passivation and antireflection layer on the front side, screen printing, sintering, and light injection, the solar cells described in this application that have not undergone sintering and light injection refer to solar cells that have not undergone sintering and light injection after screen printing.

[0058] In some embodiments, the solar cell in the secondary sintering process is rotated 90° clockwise or counterclockwise relative to the solar cell in the primary sintering process (meaning rotated 90° clockwise or counterclockwise around the center of the solar cell), such that the extension direction of the EL darkening area on the edge of the solar cell in the secondary sintering process is perpendicular to the extension direction of the corresponding EL darkening area on the edge of the solar cell in the primary sintering process.

[0059] This application adds an offline sintering furnace and a light injection furnace to the existing battery manufacturing production line. A cell feeder and a 90° cell rotation device are installed in front of the sintering furnace. Cells with darkened EL are manually placed on the feeder. After the cells are rotated 90° from their initial sintering position, they enter the sintering furnace for a second low-temperature sintering. Then, they are passed into the light injection furnace for a second light injection (with the cell orientation unchanged). This allows for localized repair of the darkened EL areas at the edges, improving the edge EL brightness and increasing the efficiency and yield of the cells.

[0060] In some embodiments, the secondary sintering includes an auxiliary sintering and a main sintering performed sequentially. The temperature of the auxiliary sintering is 160℃-200℃, for example, 160℃, 170℃, 180℃, 190℃ or 200℃. The temperature of the main sintering is 200℃-250℃, for example, 200℃, 210℃, 220℃, 230℃, 240℃ or 250℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] This application performs secondary sintering at a lower temperature. The main sintering temperature affects the improvement effect on the edge EL darkening area. If the main sintering temperature of the secondary sintering is too high, it will damage the contact and cause the battery performance to decline. If the main sintering temperature of the secondary sintering is too low, the improvement effect on resistance and edge EL darkening will decrease.

[0062] In some embodiments, the auxiliary sintering time is 90s-150s, for example, it can be 90s, 100s, 110s, 120s, 130s, 140s or 150s, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0063] In some embodiments, the main sintering time is 2 min to 3 min, for example, it can be 2 min, 2.2 min, 2.4 min, 2.6 min, 2.8 min or 3 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0064] In some embodiments, the heating rate of the main sintering is 5℃ / min-10℃ / min, for example, it can be 5℃ / min, 5.5℃ / min, 6℃ / min, 6.5℃ / min, 7℃ / min, 7.5℃ / min, 8℃ / min, 8.5℃ / min, 9℃ / min, 9.5℃ / min or 10℃ / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0065] In some embodiments, the temperature of the first sintering is 250°C-750°C, for example, it can be 250°C, 350°C, 450°C, 550°C, 650°C or 750°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0066] In some embodiments, the sintering time is 100s-120s, for example, 100s, 105s, 110s, 115s or 120s, and the heating rate is 10℃ / s-20℃ / s, for example, 10℃ / s, 12℃ / s, 14℃ / s, 16℃ / s, 18℃ / s or 20℃ / s, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0067] In some embodiments, the temperature of the first light injection is 450°C-550°C, for example, 450°C, 470°C, 490°C, 510°C, 530°C or 550°C, and the time is 30s-60s, for example, 30s, 40s, 50s or 60s, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0068] In some embodiments, the temperature of the secondary light injection is 450℃-550℃, for example, 450℃, 470℃, 490℃, 510℃, 530℃ or 550℃, and the time is 30s-60s, for example, 30s, 40s, 50s or 60s, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0069] In some implementations, after the first light injection, the resulting solar cells are first tested and sorted, and then solar cells with darkened edge EL are selected.

[0070] In some implementations, after the secondary light injection is completed, the resulting solar cells are tested and sorted.

[0071] The following specific embodiments provide a more detailed description of this application, but should not be construed as limiting the application. Any modifications or substitutions made to the methods, steps, or conditions of this application without departing from the spirit and substance of this application are within the scope of this application.

[0072] Example 1

[0073] This embodiment provides a method for improving the darkening of the edge EL of a TOPCon battery, the method including the following steps:

[0074] After screen printing, TOPCon solar cells that have not undergone sintering and light injection are subjected to one sintering and one light injection. TOPCon solar cells with darkened edge EL are then selected. A structural diagram of a TOPCon solar cell with darkened edge EL is shown below. Figure 4 As shown, it includes an N-type silicon wafer 1, a P-type doped polysilicon layer 2, an aluminum oxide layer 3, a front silicon nitride layer 4 and a front electrode 5 on the front side of the N-type silicon wafer 1, a silicon dioxide layer 6, an N-type doped polysilicon layer 7, a back silicon nitride layer 8, a back electrode 9 and a fine gate line 10 on the back side of the N-type silicon wafer 1, and an edge EL darkening region 11 on the side of the N-type silicon wafer 1;

[0075] The temperature of the first sintering is 700℃, the time is 110s, and the heating rate is 15℃ / s; the temperature of the first light injection is 500℃, and the time is 40s.

[0076] The TOPCon solar cells with darkened edge EL are placed in front of the offline sintering furnace for loading. After being rotated 90° clockwise, they are conveyed into the sintering furnace for secondary sintering. This ensures that the extension direction of the darkened edge EL region of the TOPCon solar cell during the secondary sintering is perpendicular to the extension direction of the corresponding edge EL region of the TOPCon solar cell during the primary sintering. After the secondary sintering is completed, the solar cells are cooled and then enter the light injection furnace for secondary light injection.

[0077] The conveyor belt has a conveying speed of 100 mm / s. The secondary sintering includes first assisted sintering at 180°C for 120 s, and then main sintering at 250°C for 2.5 min at a heating rate of 8°C / min. The radiation intensity of the secondary light injection is 500°C and the time is 40 s.

[0078] Example 2

[0079] This embodiment provides a method for improving the darkening of the edge EL of a TOPCon battery, the method including the following steps:

[0080] After screen printing, TOPCon solar cells that have not undergone sintering and light injection are subjected to one sintering and one light injection. TOPCon solar cells with darkened edge EL are then selected. A structural diagram of a TOPCon solar cell with darkened edge EL is shown below. Figure 4 As shown, it includes an N-type silicon wafer 1, a P-type doped polysilicon layer 2, an aluminum oxide layer 3, a front silicon nitride layer 4 and a front electrode 5 on the front side of the N-type silicon wafer 1, a silicon dioxide layer 6, an N-type doped polysilicon layer 7, a back silicon nitride layer 8, a back electrode 9 and a fine gate line 10 on the back side of the N-type silicon wafer 1, and an edge EL darkening region 11 on the side of the N-type silicon wafer 1;

[0081] The temperature of the first sintering is 550℃, the time is 100s, and the heating rate is 20℃ / s; the temperature of the first light injection is 450℃, and the time is 60s.

[0082] The TOPCon solar cells with darkened edge EL are placed in front of the offline sintering furnace for loading. After being rotated 90° clockwise, they are conveyed into the sintering furnace for secondary sintering. This ensures that the extension direction of the darkened edge EL region of the TOPCon solar cell during the secondary sintering is perpendicular to the extension direction of the corresponding edge darkened edge EL region of the TOPCon solar cell during the primary sintering. After the secondary sintering, the solar cells are cooled and then placed in the light injection furnace for secondary light injection to improve the brightness of the TOPCon solar cell edge.

[0083] The conveyor belt has a conveying speed of 100 mm / s. The secondary sintering includes first auxiliary sintering at 200°C for 90 s, and then main sintering at 250°C for 2 min at a heating rate of 5°C / min. The radiation intensity of the secondary light injection is 550°C and the time is 30 s.

[0084] Example 3

[0085] This embodiment provides a method for improving the darkening of the edge EL of a TOPCon battery, the method including the following steps:

[0086] After screen printing, TOPCon solar cells that have not undergone sintering and light injection are subjected to one sintering and one light injection. TOPCon solar cells with darkened edge EL are then selected. A structural diagram of a TOPCon solar cell with darkened edge EL is shown below. Figure 4 As shown, it includes an N-type silicon wafer 1, a P-type doped polysilicon layer 2, an aluminum oxide layer 3, a front silicon nitride layer 4 and a front electrode 5 on the front side of the N-type silicon wafer 1, a silicon dioxide layer 6, an N-type doped polysilicon layer 7, a back silicon nitride layer 8, a back electrode 9 and a fine gate line 10 on the back side of the N-type silicon wafer 1, and an edge EL darkening region 11 on the side of the N-type silicon wafer 1;

[0087] The temperature of the first sintering is 250℃, the time is 120s, the heating rate is 10℃ / s, and the radiation intensity of the first light injection is 550℃ for 30s.

[0088] The TOPCon solar cells with darkened edge EL are placed in front of the offline sintering furnace for loading. After being rotated 90° clockwise, they are conveyed into the sintering furnace for secondary sintering. This ensures that the extension direction of the darkened edge EL region of the TOPCon solar cell during the secondary sintering is perpendicular to the extension direction of the corresponding edge darkened edge EL region of the TOPCon solar cell during the primary sintering. After the secondary sintering, the solar cells are cooled and then placed in the light injection furnace for secondary light injection to improve the brightness of the TOPCon solar cell edge.

[0089] The conveyor belt has a conveying speed of 100 mm / s. The secondary sintering includes first assisted sintering at 160°C for 150 s, and then heating to 200°C at a heating rate of 10°C / min for main sintering for 3 mins. The radiation intensity of the secondary light injection is 450°C, and the time is 60 s.

[0090] Example 4

[0091] This embodiment provides a method to improve the darkening of the edge EL of TOPCon battery. Except for the main sintering temperature of 300°C for secondary sintering, the method is the same as that in Embodiment 1.

[0092] Example 5

[0093] This embodiment provides a method to improve the darkening of the edge EL of a TOPCon battery. Except for the fact that the auxiliary sintering temperature is not increased during the secondary sintering and the main sintering temperature is 110°C, the method is the same as that in Embodiment 1.

[0094] Comparative Example 1

[0095] This comparative example provides a method for improving the darkening of the edge EL of a TOPCon battery. The method is the same as in Example 1, except that the main sintering temperature of the secondary sintering is the same as that of the primary sintering temperature (both are 700°C).

[0096] Comparative Example 2

[0097] This comparative example provides a method for improving edge EL darkening of TOPCon cells. The method is the same as in Example 1, except that the extension direction of the edge EL darkening region of the TOPCon cell during the second sintering is parallel to the extension direction of the corresponding edge EL darkening region of the TOPCon cell during the first sintering (i.e., the orientation of the cell is the same during the two sinterings, and the cell is not rotated 90° during the second sintering feeding).

[0098] With 100 battery cells as a group, after improvements to the methods described in the above embodiments and comparative examples, the proportion of battery cells with darkened edge EL is shown in Table 1. EL imaging detection of the battery cells was performed using an EL tester to determine the degree of edge EL darkening.

[0099] Table 1

[0100]

[0101] As can be seen from Table 1 above:

[0102] As can be seen from Examples 1-5 and Comparative Example 1, the secondary sintering of the present invention needs to be carried out at a lower temperature to promote the denser diffusion and filling of metal particles in the darkened edge area, reduce the decrease in edge contact resistivity, and at the same time improve the brightness of the edge cell, thus significantly reducing the dark cell ratio. As can be seen from Examples 1-5 and Comparative Example 2, the orientation of the cell during the secondary sintering of the present invention is different from that during the primary sintering. The corresponding edge areas of the cell are perpendicular to each other during the two sintering processes, which allows the darkened area after the primary sintering to fully receive the low-temperature secondary sintering and secondary light injection, thus improving the darkening of the edge EL. As can be seen from Examples 1 and Examples 4-5, the main sintering temperature of the secondary sintering of the present invention affects the effect of improving the darkening of the edge EL, and the main sintering temperature is preferably within a specific range.

[0103] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for improving the darkening of the EL (electrode aperture) at the edge of a battery, characterized in that, The method includes the following steps: After performing one sintering and one light injection on the unsintered solar cells, the solar cells with dark edge EL were selected. The edge EL of the battery cell is sintered and light injected twice to improve the brightness of the TOPCon battery edge. The temperature of the secondary sintering is lower than the temperature of the primary sintering; The extension direction of the EL darkening region at the edge of the battery cell during the secondary sintering is perpendicular to the extension direction of the corresponding EL darkening region at the edge of the battery cell during the primary sintering.

2. The method according to claim 1, characterized in that, The battery cell in the second sintering process is rotated 90° clockwise or counterclockwise compared to the battery cell in the first sintering process, so that the extension direction of the EL darkening area on the edge of the battery cell in the second sintering process is perpendicular to the extension direction of the corresponding EL darkening area on the edge of the battery cell in the first sintering process.

3. The method according to claim 1 or 2, characterized in that, The secondary sintering includes auxiliary sintering and main sintering performed sequentially. The temperature of the auxiliary sintering is 160℃-200℃, and the temperature of the main sintering is 200℃-250℃.

4. The method according to claim 3, characterized in that, The auxiliary sintering time is 90s-150s; Preferably, the main sintering time is 2-3 minutes.

5. The method according to claim 3, characterized in that, The heating rate of the main sintering is 5℃ / min-10℃ / min.

6. The method according to claim 1 or 2, characterized in that, The temperature for the first sintering is 250℃-750℃; Preferably, the sintering time is 100s-120s and the heating rate is 10℃ / s-20℃ / s.

7. The method according to claim 1 or 2, characterized in that, The temperature of the first light injection is 450℃-550℃, and the time is 30s-60s.

8. The method according to claim 1 or 2, characterized in that, The temperature of the secondary light injection is 450℃-550℃, and the time is 30s-60s.

9. The method according to claim 1 or 2, characterized in that, After the first light injection, the resulting solar cells are first tested and sorted, and then solar cells with dark edges (EL) are selected.

10. The method according to claim 1 or 2, characterized in that, After the secondary light injection is completed, the resulting solar cells are tested and sorted.

11. A battery cell, characterized in that, The battery cell is prepared by the method described in any one of claims 1-10.

12. A photovoltaic module, characterized in that, The photovoltaic module includes the solar cells as described in claim 11.

13. A photovoltaic system, characterized in that, The photovoltaic system includes the photovoltaic module as described in claim 12.

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