Solar cell copper electrode composite current collector and preparation method

Abstract

This application relates to the field of solar cell technology, specifically to a composite current collector for copper electrodes in solar cells and its fabrication method. It comprises a first metal layer, an insulating polymer layer, and a second metal layer sequentially stacked along the thickness direction, bonded together by hot-pressing with a hot-melt adhesive. The first metal layer is used for electrical connection to the copper electrode end on one side of the main surface of the solar cell, the second metal layer is used for electrical connection to the copper electrode end on the other side of the main surface, and the insulating polymer layer serves to electrically insulate the first and second metal layers. This composite current collector can be disposed in the non-light-receiving area at the edge of the solar cell, achieving double-sided current collection and extraction at the copper electrode ends on both sides, reducing copper grid current carrying losses, improving interlayer bonding strength, insulation reliability, and the electrical performance and encapsulation stability of the solar cell.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, specifically to a copper electrode composite current collector for solar cells and its preparation method. Background Technology

[0002] As the photovoltaic industry continues to reduce costs and increase efficiency, the proportion of metallization costs in module costs is constantly increasing. Traditional silicon-based solar cells generally use silver paste to form the main grid and fine grid structures. Silver electrode technology is mature and has good welding performance, but the price of silver resources fluctuates significantly, and the unit cost of conductive materials is high, leading to increasing cost pressure on silver paste in high-efficiency cells. Against this backdrop, replacing silver with copper as the conductive electrode material for solar cells has become one of the important technological development directions in the industry.

[0003] From a technological evolution perspective, the metallization structure of silicon-based solar cells has roughly progressed from all-silver screen-printed electrodes, to silver-clad copper or composite conductor electrodes, and finally to direct copper electrode metallization. Compared to silver paste patterning, copper has higher conductivity and lower cost, making it more suitable for forming fine grid lines through electroplating, transfer printing, attachment, or composite conductor construction. To further reduce shading losses and increase the effective light-receiving area, the cell grid structure has evolved from the traditional main grid + fine grid scheme to gridless fine grid structures, multi-main grid fine grid structures, and serpentine copper electrode structures. Especially in the copper grid technology route, because the cross-section of copper fine grids is usually small, the longitudinal resistance of a single grid line is relatively large. Therefore, how to improve the current collection efficiency of copper electrodes, shorten the current carrying path, and reduce series resistance has become a key issue restricting the performance of copper electrode solar cells.

[0004] Existing technologies typically involve placing a busbar or solder strip on one edge of the solar cell to collect current only on the copper electrode. This type of structure largely follows the traditional silver grid single-sided current collection approach, is simple in structure, and is easily compatible with existing module processes. However, for gridless fine-grid copper electrodes or serpentine copper electrodes, the current-carrying path of the grid lines is relatively long, which can easily lead to increased resistance loss, thereby limiting the improvement of short-circuit current, fill factor, and conversion efficiency. On the other hand, solutions to reduce resistance by widening the copper grid or adding additional busbars often result in increased shading area and increased material consumption, making it difficult to achieve a balance between electrical performance, process feasibility, and module reliability. For example, patent application CN116314367A discloses a copper grid solar cell and its corresponding preparation scheme, focusing on the formation of copper grids and their matching with the cell structure. This technology can promote the replacement of silver electrodes with copper electrodes to a certain extent, but its core still focuses on the formation of the grid body and does not consider the high resistance loss problem of copper fine grids or serpentine copper electrodes during long-distance current carrying. Patent application CN116995107A discloses the fabrication and transfer technology of copper grids, which can improve the construction quality of copper grids and adapt to photovoltaic cell manufacturing. However, this technical solution also mainly focuses on the copper grid fabrication process itself and does not mention the current collection and extraction.

[0005] Unlike solar cells, traditional batteries also have current collectors, which are essentially conductive carriers within the electrochemical electrode. Serving as the substrate of the electrode, both sides typically serve the same electrode system, focusing on supporting the active layer, electrolyte resistance, lightweight design, and safety. However, this design did not consider the end-capture problem of the copper electrode in silicon-based solar cells. It failed to anticipate achieving simultaneous current collection from both copper electrodes in the edge region without occupying the effective light-receiving area. Furthermore, it could not guarantee reliable insulation of the conductive layers on both sides within the same composite strip, and could not ensure sufficient peel strength and long-term reliability when welded, hot-pressed, or partially connected to the copper electrode ends.

[0006] Therefore, based on the shortcomings of the existing technology, there is an urgent need for a copper electrode composite current collector for solar cells to achieve more efficient current collection and extraction. Summary of the Invention

[0007] This application aims to overcome at least one of the defects of the prior art and provide a composite current collector for a solar cell copper electrode and a method for its preparation. The composite current collector is disposed in the non-light-receiving area at the edge of the solar cell. It is connected to the copper electrode ends on the two main surfaces of the cell through upper and lower metal layers respectively. An insulating polymer layer is disposed in the middle to achieve electrical insulation between the two metal layers. This improves the current collection efficiency of the copper electrode without increasing the effective light-shielding area and facilitates subsequent connection with adjacent cells or external conductive components.

[0008] In a first aspect, embodiments of this application provide a copper electrode composite current collector for solar cells, achieved through the following technical solution: A composite current collector for a solar cell copper electrode includes a first metal layer, an insulating polymer layer, and a second metal layer sequentially stacked along the thickness direction. The first metal layer, the insulating polymer layer, and the second metal layer are bonded together by hot-pressing with a hot-melt adhesive. The first metal layer is used for electrical connection to the copper electrode end of one of the two main surfaces opposite to the solar cell, the second metal layer is used for electrical connection to the copper electrode end of the other of the two main surfaces opposite to the solar cell, and the insulating polymer layer is used for electrical insulation and isolation between the first metal layer and the second metal layer.

[0009] The solar cell copper electrode composite current collector according to the embodiments of this application has at least the following beneficial effects: This application utilizes a three-layer structure of a first metal layer, an insulating polymer layer, and a second metal layer within the same composite current collector. This allows the copper electrode ends on the two main surfaces of the solar cell to be connected to the upper and lower conductive layers respectively, achieving efficient bi-sided current collection and extraction in the non-light-receiving edge area. This significantly shortens the current-carrying path of the copper electrode, reduces the power loss caused by the high resistance of the copper grid, and thus improves the short-circuit current, fill factor, and conversion efficiency.

[0010] The insulating polymer layer described in this application is located between two metal layers, which can effectively prevent direct conduction between the front and back conductive layers. While achieving double-sided current collection, it ensures electrical insulation and isolation between the front and back of the battery cell, avoids the risk of short circuit, and provides a structural basis for subsequent battery series and parallel design.

[0011] This application employs a specific hot melt adhesive system, which can improve interlayer adhesion strength, peel strength, and interface stability after thermal cycling and damp heat, thereby improving long-term encapsulation reliability.

[0012] The composite current collector of this application can be adapted to various novel copper electrode structures such as gridless fine-grid copper electrodes and serpentine copper electrodes. It can achieve current collection at both ends or form a segmented current collection structure at multiple node positions, and has strong process adaptability and application scalability.

[0013] According to some embodiments of this application, the hot-melt adhesive is composed of polymethyl methacrylate powder, hydrogenated rosin glycerol ester, and polyethylene wax in a weight ratio of 70-80:5-10:5-10. Using the above-mentioned proportioning system, with polymethyl methacrylate powder as the main adhesive component, a continuous and dense bonding interface can be formed, ensuring that the composite current collector has high interlayer bonding strength and good insulation stability. Hydrogenated rosin glycerol ester can improve the wettability and adhesion of the adhesive to the surfaces of the metal layer and the insulating polymer layer, which is beneficial to improving the interfacial adhesion strength. Polyethylene wax can adjust the melt flowability and coating uniformity of the hot-melt adhesive, reducing the risk of interfacial voids and local defects during the composite process. The combination of these three components within the above-mentioned proportion range can better balance bonding strength, processing performance, and long-term reliability, thereby improving the peel strength, hot-pressing composite stability, and interlayer durability of the composite current collector under thermal cycling and humid heat conditions.

[0014] Furthermore, the average particle size of the polymethyl methacrylate (PMMA) powder is 0.5-1 μm. Controlling the PMMA powder within this particle size range is beneficial for achieving better dispersion uniformity and consistent melting under heat in the hot-melt adhesive system, thereby improving film formation uniformity during coating and wetting effect on the metal and insulating polymer layers during hot-pressing. Simultaneously, this particle size range helps the adhesive fully fill the micro-rough structure of the interface and form a stable bonding layer, thereby improving interlayer adhesion strength and peel strength, reducing localized adhesive shortages, voids, or stress concentrations, and enhancing the composite stability and long-term reliability of the composite current collector.

[0015] Further, the preparation of the hot melt adhesive includes the following steps: In a reaction vessel, polymethyl methacrylate powder, hydrogenated rosin glycerol ester, and polyethylene wax are added, heated to 140-150℃, and stirred until uniformly mixed to obtain the hot melt adhesive. Using polymethyl methacrylate powder, hydrogenated rosin glycerol ester, and polyethylene wax to melt-blend at 140-150℃ to prepare the hot melt adhesive allows for thorough mixing of the components and the formation of a stable and uniform adhesive system. Polymethyl methacrylate provides the main adhesive strength, hydrogenated rosin glycerol ester helps improve the wettability and initial tack of the metal layer and the insulating polymer layer, and polyethylene wax helps regulate melt flow and coating uniformity. This allows the adhesive to spread more fully and penetrate the interfacial microstructure during hot pressing, further improving the composite adhesion strength, interlayer bonding stability, and product processing consistency between the first metal layer, the insulating polymer layer, and the second metal layer.

[0016] According to some embodiments of this application, the first metal layer and the second metal layer are each independently selected from at least one of copper, nickel, tin, silver, copper alloy, and nickel alloy.

[0017] Furthermore, the first metal layer and the second metal layer are each independently selected from a copper alloy and a nickel alloy, for example, the first metal layer is a copper alloy. Copper alloys have high conductivity, which is beneficial for reducing current collection resistance and transmission loss; nickel alloys have good corrosion resistance and interface stability, which is beneficial for improving the long-term reliability of the composite current collector.

[0018] According to some embodiments of this application, the surface of the first metal layer away from the insulating polymer layer is covered with a first solderable surface layer, and / or the surface of the second metal layer away from the insulating polymer layer is covered with a second solderable surface layer. Covering with a solderable surface layer can effectively improve the welding compatibility between the composite current collector and the copper electrode end of the solar cell, adjacent cells, or external conductive components, reducing the risk of an excessively narrow welding temperature window, insufficient wetting, and poor soldering or desoldering.

[0019] Furthermore, the first solderable surface layer and the second solderable surface layer are each independently selected from at least one of tin and tin alloys. Tin or tin alloy surface layers have good solderability and interface compatibility, which is beneficial for forming a stable and dense connection interface, reducing contact resistance, improving current transmission stability, and can also enhance the oxidation resistance of the metal layer surface to a certain extent, thereby improving the connection reliability of the composite current collector during the welding process and long-term use.

[0020] According to some embodiments of this application, the surface of the first metal layer and / or the second metal layer near the insulating polymer layer is subjected to surface treatment, including sequential roughening treatment and plasma treatment.

[0021] Roughening treatment creates a micro-uneven structure on the metal layer surface, increasing the actual contact area and improving mechanical interlocking. Further plasma treatment effectively removes surface contaminants, increases surface energy, and introduces active groups, thereby improving the wettability and bonding ability of the hot-melt adhesive to the metal layer surface. This significantly improves the adhesion and peel strength between the metal layer and the insulating polymer layer, reduces the risk of delamination and warping after hot-pressing, and enhances the structural stability and long-term reliability of the composite current collector under welding, thermal cycling, and humid conditions.

[0022] Further, the surface treatment includes the following steps: placing the surface of the first metal layer and / or the second metal layer near the insulating polymer layer in a sodium persulfate solution with a concentration of 60 g / L, and treating it at 20-30°C for 23-27 s to form a micro-roughened structure on the surface of the metal layer. After cleaning and drying, it is placed in a low-pressure plasma device, and under a vacuum of 35-45 Pa, argon gas is first introduced and treated at 250 W power for 25-35 s, and then oxygen is introduced and treated at 200 W power for 18-22 s.

[0023] Sodium persulfate treatment can form a uniform micro-coarsened structure on the metal surface, increase the actual contact area of ​​the interface, and enhance the mechanical interlocking of the hot melt adhesive. Subsequently, the surface is cleaned by argon plasma to remove the weak boundary layer, and then oxygen plasma is used to further introduce active groups, improve surface energy and wettability, thereby significantly improving the interfacial bonding state between the metal layer and the insulating polymer layer, improving interlayer adhesion strength, peel strength and hot pressing composite stability, and helping to improve the long-term reliability of the composite current collector in welding, thermal cycling and humid heat environments.

[0024] According to some embodiments of this application, the surface of the insulating polymer layer is modified by the following steps: immersing the insulating polymer layer in a 2wt% sodium hydroxide solution at 45-55°C for 25-35 seconds, then neutralizing it with a 1wt% hydrochloric acid solution for 18-22 seconds, washing it with deionized water and drying it; subsequently performing double-sided oxygen plasma treatment for 55-65 seconds to obtain an activated insulating polymer layer; immersing the activated insulating polymer layer in a 1wt% aqueous solution of γ-aminopropyltriethoxysilane in ethanol, wherein the mass of ethanol in the aqueous solution is 95%, then drying it at 90-110°C for 2-4 minutes to obtain a surface-modified insulating polymer layer.

[0025] By sequentially subjecting the insulating polymer layer to alkali treatment, acid neutralization, oxygen plasma activation, and silane coupling modification, the inert layer and residual impurities on the base film surface can be effectively removed, and active groups such as hydroxyl and carboxyl groups can be introduced on the surface, significantly improving surface energy and wettability. γ-aminopropyltriethoxysilane can form a stable coupling interface on the surface of the insulating polymer layer, with one end bonding to the activated polymer surface and the other end forming a stronger interfacial interaction with the hot melt adhesive and metal layer, thereby improving the bonding strength and peel strength between the insulating polymer layer and the metal layer, suppressing problems such as interlayer delamination and warping after hot pressing, and helping to improve the interfacial stability and long-term reliability of the composite current collector under welding, thermal cycling, and humid heat environments.

[0026] According to some embodiments of this application, the insulating polymer layer comprises the following raw materials in parts by weight: 90-110 parts polymer resin, 2-4 parts surface-modified nano-silica, 0.2-1 parts heat-resistant stabilizer, and 0.4-0.6 parts epoxy chain extender. Using the above formulation system, the polymer resin provides basic insulation, flexibility, and film-forming properties; the surface-modified nano-silica improves the heat resistance, dimensional stability, and mechanical strength of the insulating polymer layer, and improves its interfacial bonding with the metal layer and hot-melt adhesive; the heat-resistant stabilizer inhibits thermo-oxidative degradation during processing and hot pressing, ensuring stable material properties; and the epoxy chain extender improves molecular chain integrity and melt strength, enhancing processability and interlayer composite reliability. This allows the insulating polymer layer to possess excellent electrical insulation, heat resistance, and interfacial bonding properties, which is beneficial for improving the interlayer adhesion strength, anti-delamination ability, and long-term stability of the composite current collector.

[0027] Furthermore, the heat-resistant stabilizer is composed of a mixture of phosphite stabilizers and hindered phenolic stabilizers in a weight ratio of 2-3:1.

[0028] The heat-resistant stabilizer is a compound of phosphite stabilizers and hindered phenolic stabilizers in a weight ratio of 2-3:1, which can form a good synergistic stabilizing effect. The phosphite stabilizers preferentially decompose peroxides generated during processing and thermal aging, inhibiting polymer thermo-oxidative degradation; the hindered phenolic stabilizers capture free radicals, delaying polymer backbone breakage. Using both within the above-mentioned ratio range helps to balance processing stability and long-term heat resistance, reducing yellowing, embrittlement, and molecular weight decay of the insulating polymer layer during melt extrusion, biaxial stretching, heat setting, and subsequent hot-pressing composite processes. This helps maintain the mechanical properties, dimensional stability, and electrical insulation properties of the insulating polymer layer, and further improves the interlayer bonding stability and long-term reliability of the composite current collector.

[0029] Furthermore, the phosphite stabilizer is selected from at least one of bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite and tris(2,4-di-tert-butylphenyl) phosphite.

[0030] Furthermore, the hindered phenolic stabilizer is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene.

[0031] Furthermore, the polymer resin includes at least one of polyethylene terephthalate, polyimide, polytetrafluoroethylene (PTFE), and polyethylene naphthalate. All of the above polymer resins possess good electrical insulation, film-forming properties, and thermal stability, meeting the dimensional stability and insulation requirements of the composite current collector during hot-pressing, welding, and component encapsulation processes. Polyethylene terephthalate and polyethylene naphthalate exhibit good mechanical strength and processing adaptability, polyimide possesses excellent heat resistance, and PTFE possesses excellent chemical corrosion resistance and insulation properties. Using one or more of the above polymer resins as the substrate for the insulating polymer layer is beneficial for improving the interlayer composite stability, environmental aging resistance, and long-term reliability of the composite current collector.

[0032] Further, the preparation of the surface-modified nano silica includes the following steps: adding nano silica to a mixed solution of ethanol and deionized water, ultrasonically dispersing for 25-35 min, adding γ-glycidoxypropyltrimethoxysilane accounting for 2-3% of the mass of nano silica, adjusting the pH to 5, stirring and reacting at 55-65℃ for 1.5-2.5 h, filtering and drying after the reaction to obtain surface-modified nano silica.

[0033] By performing the aforementioned surface modification treatment on nano-silica, γ-glycidoxypropyltrimethoxysilane can form a stable coupling layer on the surface of nano-silica. On the one hand, this reduces the agglomeration tendency caused by hydroxyl groups on the surface of nano-silica, improving its dispersion uniformity in polymer resins. On the other hand, its active groups can enhance the interfacial compatibility and bonding force between nano-silica and the polymer matrix. This effectively improves the mechanical properties, heat resistance, and dimensional stability of the insulating polymer layer, and reduces local stress concentration and interfacial defects caused by poor dispersion of inorganic fillers. This is beneficial for further improving the interlayer bonding strength, processing stability, and long-term reliability of the composite current collector.

[0034] Furthermore, the epoxy chain extender is a styrene-glycidyl acrylate copolymer.

[0035] According to some embodiments of this application, the preparation of the insulating polymer layer includes the following steps: S1. Mix the polymer resin, surface-modified nano silica, heat-resistant stabilizer and epoxy chain extender evenly according to the weight parts, add them to a twin-screw extruder, melt-blend and extrude at 250-270℃, cool and granulate to obtain modified polymer resin granules; S2. Place the modified polymer resin granules in a dehumidifying drying oven and dry them at 120-180℃ for 2-8 hours. Then, obtain the insulating polymer layer by extrusion casting and biaxial stretching and heat setting at 210℃.

[0036] Using the above preparation steps, the polymer resin, surface-modified nano-silica, heat-resistant stabilizer, and epoxy chain extender are first fully melt-blended at 250-270℃ via twin-screw extrusion. This allows the inorganic filler to be more uniformly dispersed in the resin matrix and promotes chain extension reaction and improved interfacial compatibility, thereby enhancing the mechanical strength, heat resistance, and dimensional stability of the insulating polymer layer. Subsequently, dehumidification drying, extrusion casting, biaxial stretching, and heat setting at 210℃ further improve the film orientation structure and density, reduce internal defects and processing residual stress, resulting in an insulating polymer layer with high insulation performance, heat resistance, and film formation consistency. This also helps maintain good interfacial bonding strength and long-term reliability during subsequent hot-pressing lamination with a metal layer.

[0037] According to some embodiments of this application, the thickness of the insulating polymer layer is 30-100 μm, the thickness of the first metal layer and the second metal layer are 20-70 μm respectively, and the width of the composite current collector is 0.5-5 mm.

[0038] The above limitations facilitate a better balance between conductivity, insulation reliability, flexibility, and structural strength. Specifically, when the thickness of the insulating polymer layer is within the above range, it ensures sufficient electrical insulation between the upper and lower metal layers while avoiding excessive thickness that would increase overall thickness and reduce bending adaptability. When the metal layer thickness is within the above range, it satisfies the conductivity and welding strength required for current collection and lead-out, while avoiding excessively thin metal layers that would increase resistance or excessively thick metal layers that would increase material costs and make forming difficult. When the width of the composite current collector is within the above range, it is convenient to place it in the non-light-receiving area at the edge of the solar cell, reducing the impact on the effective light-receiving area, and also meets the process requirements for connection to the copper electrode end and subsequent interconnection.

[0039] Secondly, this application provides a method for preparing a copper electrode composite current collector for solar cells, which is achieved through the following technical solution: A method for preparing a copper electrode composite current collector for solar cells includes the following steps: S1 modifies the surface of the insulating polymer layer to obtain a surface-modified insulating polymer layer; S2 The first metal layer, the surface-modified insulating polymer layer and the second metal layer are laid in sequence. During the laying, the contact surfaces of each layer are uniformly coated with hot melt adhesive, pre-pressed and molded, and then hot-pressed and bonded to obtain the copper electrode composite current collector for solar cells. The first metal layer is used to connect the copper electrode end of one side of the two main surfaces of the solar cell that are arranged opposite each other, and the second metal layer is used to connect the copper electrode end of the other side of the two main surfaces of the solar cell that are arranged opposite each other, so as to realize the collection and extraction of the photocurrent generated by the solar cell.

[0040] The method for preparing the copper electrode composite current collector for solar cells according to the embodiments of this application has at least the following beneficial effects: The preparation method of this application first modifies the surface of the insulating polymer layer to improve its surface activity and interfacial bonding ability with adjacent layers. Then, by coating a hot-melt adhesive between the first metal layer, the surface-modified insulating polymer layer, and the second metal layer, and performing pre-pressing and hot-pressing composite bonding, stable composite bonding of the materials in each layer can be achieved, thereby obtaining a composite current collector with high interlayer adhesion strength, good structural stability, and reliable insulation isolation between the conductive layers on both sides. The composite current collector obtained by this preparation method can be connected to the copper electrode ends of the two main surfaces of the solar cell, which is beneficial to achieve efficient collection and extraction of photocurrent, and improves product consistency, processing adaptability, and long-term reliability.

[0041] According to some embodiments of this application, the temperature of hot pressing composite in step S2 is 140-150°C.

[0042] According to some embodiments of this application, the pressure for hot-pressing composite in step S2 is 2-5 MPa.

[0043] According to some embodiments of this application, the hot pressing time in step S2 is 3-7 minutes.

[0044] By controlling the hot-pressing composite process conditions, the hot-melt adhesive can fully melt and uniformly wet the interface between the first metal layer, the insulating polymer layer, and the second metal layer. At the same time, it avoids thermal shrinkage, warping, or performance degradation of the insulating polymer layer due to excessively high temperature, and also avoids insufficient interlayer adhesion due to insufficient pressure or too short holding time. As a result, the composite current collector can obtain high interlayer adhesion strength, good dimensional stability, and stable electrical insulation performance, and is conducive to improving the consistency of product preparation and the reliability of subsequent welding and packaging processes.

[0045] According to some embodiments of this application, the coating thickness of the hot melt adhesive in step S2 is 1-2 μm. Within this thickness range, the hot melt adhesive can fully wet the contact interface of the first metal layer, the insulating polymer layer, and the second metal layer during hot pressing, forming a continuous and uniform adhesive layer, thereby effectively improving interlayer adhesion strength and peel strength. At the same time, this thickness can avoid problems such as interface stress concentration, increased total thickness of the composite current collector, decreased flexibility, and increased thermal resistance caused by excessive adhesive layer thickness, and reduce the adverse effects of adhesive overflow during hot pressing on the subsequent welding area and the stability of conductive connection. This is beneficial to balance the structural stability, electrical connection reliability, and subsequent processing adaptability of the composite current collector.

[0046] Thirdly, embodiments of this application provide a solar cell, achieved through the following technical solution: A solar cell includes a solar cell, copper electrodes disposed opposite to each other on two main surfaces of the solar cell, and a solar cell copper electrode composite current collector disposed in a non-light-receiving area at the edge of the solar cell. The first metal layer of the composite current collector is connected to the copper electrode end of one side of the two main surfaces of the solar cell that are opposite to each other, and the second metal layer of the composite current collector is connected to the copper electrode end of the other side of the two main surfaces of the solar cell that are opposite to each other. The insulating polymer layer electrically insulates and isolates the copper electrodes of the two main surfaces of the solar cell that are opposite to each other.

[0047] The solar cell according to the embodiments of this application has at least the following beneficial effects: By placing the aforementioned copper electrode composite current collector in the non-light-receiving area at the edge of the solar cell, the ends of the copper electrodes on the two opposing main surfaces of the cell are connected to the first and second metal layers of the composite current collector, respectively. This achieves synchronous current collection and extraction of the copper electrodes on both sides without occupying additional effective light-receiving area. Simultaneously, the insulating polymer layer provides reliable electrical insulation isolation between the copper electrodes on the two main surfaces, effectively preventing short circuits in the conductive layers on both sides. This structure is particularly suitable for gridless fine-grid copper electrodes or serpentine copper electrodes, shortening the current transmission path, reducing series resistance and current collection losses, thus improving the current collection capability, fill factor, and photoelectric conversion efficiency of the solar cell, and enhancing the flexibility of cell interconnect design.

[0048] According to some embodiments of this application, the copper electrode of the solar cell is a gridless fine-grid copper electrode or a serpentine copper electrode, and the composite current collector is disposed in two opposite edge regions of the solar cell to connect with the two ends of the copper electrode of the solar cell to form a double-ended current collector structure. Attached Figure Description

[0049] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is a schematic diagram of the cross-sectional structure of the copper electrode composite current collector for solar cells in an embodiment of this application; Figure 2 This is a schematic diagram showing the connection relationship between the composite current collector and the copper electrode ends on the front and back of the solar cell in an embodiment of this application; Figure 3 This is a schematic diagram of the front and back busbars of the solar cell in Comparative Example 4 of this application; Figure 4 This is a schematic diagram of the solar cell busbar in Embodiment 6 of this application.

[0051] Explanation of reference numerals in the attached figures: 1. Insulating polymer layer; 2. First metal layer; 3. Second metal layer; 4. First solderable surface layer; 5. Second solderable surface layer; 6. Copper grid line; 7. Battery cell; 8. Busbar; 9. Composite current collector. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of this application clearer, a further detailed description will be provided below in conjunction with specific embodiments. The embodiments described herein are merely some examples of this application and should not be construed as limiting the scope of protection of this application. Unless otherwise specified, the raw materials used in the embodiments are all commercially available, and the equipment and testing methods used are conventional equipment and methods in the art.

[0053] In this application, "two main surfaces arranged opposite each other" refers to the main surface of the solar cell that receives light and the other main surface that receives light away from it. It can also be understood as two large surfaces opposite each other in the thickness direction of the cell. "Copper electrode end" refers to the end position of the copper electrode located on the front or back of the cell in the edge region. This end can be the end of a gridless fine grid, the confluence position, or the two ends of a serpentine copper electrode and the corresponding connection position of a local inflection point. "The composite current collector is arranged in the edge non-light-receiving area" means that the structure is preferably arranged in the edge region that does not participate in the main light-receiving and power generation, thereby avoiding a significant increase in shading loss.

[0054] Example 1 This embodiment provides a composite current collector for a solar cell with a copper electrode. The composite current collector comprises, from top to bottom, a first metal layer, an insulating polymer layer, and a second metal layer. Both the first and second metal layers are made of C2720 copper alloy foil with a thickness of 40 μm. The surface of the C2720 copper alloy foil away from the insulating polymer layer is electroplated to form a tin layer with a thickness of about 2 μm, serving as the first solderable surface layer and the second solderable surface layer.

[0055] The insulating polymer layer is a polyethylene terephthalate-based insulating layer, and its raw materials, by weight, include: 100 parts polyethylene terephthalate, 3 parts surface-modified nano silica, 0.6 parts heat stabilizer, and 0.5 parts styrene-glycidyl acrylate copolymer. The heat stabilizer is obtained by mixing bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] in a weight ratio of 2.5:1.

[0056] The preparation process of surface-modified nano silica is as follows: nano silica is added to a mixed solution of ethanol and deionized water, ultrasonically dispersed for 30 min, γ-glycidyl etheroxypropyltrimethoxysilane accounting for 2.5% of the mass of nano silica is added, the pH is adjusted to 5, and the reaction is stirred at 60℃ for 2 h. After filtration and drying, surface-modified nano silica is obtained.

[0057] The preparation steps of the insulating polymer layer are as follows: the above raw materials are mixed evenly and then added to a twin-screw extruder. The mixture is melt-blended and extruded at 260°C, cooled and pelletized to obtain modified polyethylene terephthalate granules. The granules are dried at 150°C for 5 hours and then subjected to extrusion casting, biaxial stretching and heat setting at 210°C to obtain a polyethylene terephthalate-based insulating layer with a thickness of 65 μm.

[0058] The hot melt adhesive is prepared by mixing polymethyl methacrylate powder, hydrogenated rosin glycerol ester, and polyethylene wax in a weight ratio of 75:8:8, wherein the average particle size of the polymethyl methacrylate powder is 0.7 μm. During preparation, the above components are added to a reaction vessel, heated to 145°C, and stirred for 30 min to obtain a uniformly mixed hot melt adhesive.

[0059] The first and second metal layers are first surface-treated on the side closest to the insulating polymer layer: placed in an 8% sodium hydroxide solution, cleaned at 50°C for 60 seconds, rinsed with deionized water, dried with hot air at 80°C for 2 minutes, placed in a 60g / L sodium persulfate solution, treated at 25°C for 25 seconds, cleaned and dried, and then placed in a low-pressure plasma device. Under a vacuum of 40Pa, argon gas is first introduced at 250W for 30 seconds, followed by oxygen gas at 200W for 20 seconds.

[0060] The surface modification treatment of the insulating polymer layer is as follows: the polyethylene terephthalate-based insulating layer is immersed in a 2wt% sodium hydroxide solution at 50°C for 30s, then removed and neutralized in a 1wt% hydrochloric acid solution for 20s, then washed with deionized water and dried; subsequently, it undergoes double-sided oxygen plasma treatment for 60s to obtain an activated polyethylene terephthalate-based insulating layer; then it is immersed in a 1wt% ethanol aqueous solution of γ-aminopropyltriethoxysilane, wherein the ethanol mass fraction in the aqueous solution is 95%, and after removal, it is dried at 100°C for 3min to obtain a surface-modified insulating polymer layer.

[0061] During hot-pressing composite, the first metal layer, the surface-modified insulating polymer layer, and the second metal layer are sequentially stacked. Each contact surface is uniformly coated with a 1.5 μm thick hot melt adhesive. The process is first pre-pressed and then hot-pressed at 145℃ and 3MPa for 5 minutes. After cooling, a composite current collector is obtained with a width of 2 mm.

[0062] Example 2 This embodiment provides a copper electrode composite current collector for solar cells. The composite current collector comprises, from top to bottom, a first metal layer, an insulating polymer layer, and a second metal layer. Both the first and second metal layers are made of Inconel 600 nickel alloy foil with a thickness of 70 μm. The surface of the Inconel 600 nickel alloy foil away from the insulating polymer layer is electroplated to form a tin layer with a thickness of approximately 2 μm, serving as the first and second solderable surface layers.

[0063] The insulating polymer layer is a polyethylene naphthalate-based insulating layer, and its raw materials, by weight, include: 90 parts of polyethylene naphthalate, 4 parts of surface-modified nano silica, 0.2 parts of heat stabilizer, and 0.6 parts of styrene-glycidyl acrylate copolymer. The heat stabilizer is obtained by mixing tris(2,4-di-tert-butylphenyl) phosphite and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene in a weight ratio of 2:1.

[0064] The preparation process of surface-modified nano silica is as follows: nano silica is added to a mixed solution of ethanol and deionized water, ultrasonically dispersed for 35 min, γ-glycidyl etheroxypropyltrimethoxysilane accounting for 2% of the mass of nano silica is added, the pH is adjusted to 5, and the reaction is stirred at 65℃ for 1.5 h. After filtration and drying, surface-modified nano silica is obtained.

[0065] The preparation steps of the insulating polymer layer are as follows: the above raw materials are mixed evenly and then added to a twin-screw extruder. The mixture is melt-blended and extruded at 270°C, cooled and granulated to obtain modified polyethylene naphthalate granules. The granules are dried at 120°C for 8 hours and then subjected to extrusion casting, biaxial stretching and heat setting at 210°C to obtain a polyethylene naphthalate-based insulating layer with a thickness of 30 μm.

[0066] The hot melt adhesive is prepared by mixing polymethyl methacrylate powder, hydrogenated rosin glycerol ester, and polyethylene wax in a weight ratio of 80:5:10, wherein the average particle size of the polymethyl methacrylate powder is 0.5 μm. During preparation, the above components are added to a reaction vessel, heated to 150°C, and stirred for 30 min to obtain a uniformly mixed hot melt adhesive.

[0067] The first and second metal layers, on the side closest to the insulating polymer layer, undergo surface treatment: they are placed in an 8% sodium hydroxide solution and cleaned at 45°C for 65 seconds. After rinsing with deionized water, they are dried with hot air at 75°C for 2.5 minutes. Then, they are placed in a 60g / L sodium persulfate solution and treated at 20°C for 27 seconds. After cleaning and drying, they are placed in a low-pressure plasma device and treated at 35Pa vacuum. Argon gas is first introduced at 250W for 35 seconds, followed by oxygen gas at 200W for 18 seconds.

[0068] The surface modification treatment of the insulating polymer layer is as follows: the polyethylene naphthalate-based insulating layer is immersed in a 2wt% sodium hydroxide solution at 55°C for 25s, then removed and neutralized in a 1wt% hydrochloric acid solution for 22s, then washed with deionized water and dried; subsequently, it is subjected to double-sided oxygen plasma treatment for 55s to obtain an activated polyethylene naphthalate-based insulating layer; then it is immersed in a 1wt% ethanol aqueous solution of γ-aminopropyltriethoxysilane, wherein the ethanol mass fraction in the aqueous solution is 95%, and then removed and dried at 110°C for 2min to obtain a surface-modified insulating polymer layer.

[0069] During hot-pressing composite, the first metal layer, the surface-modified insulating polymer layer, and the second metal layer are sequentially stacked. A 2μm thick hot melt adhesive is uniformly coated on each contact surface. The mixture is first pre-pressed and then hot-pressed at 140℃ and 5MPa for 3 minutes. After cooling, a composite current collector is obtained with a width of 3mm.

[0070] Example 3 This embodiment provides a composite current collector for a solar cell with a copper electrode. The composite current collector comprises, from top to bottom, a first metal layer, an insulating polymer layer, and a second metal layer. Both the first and second metal layers are made of C2720 copper alloy foil with a thickness of 20 μm. The surface of the C2720 copper alloy foil away from the insulating polymer layer is electroplated to form a tin layer with a thickness of about 2 μm, serving as the first solderable surface layer and the second solderable surface layer.

[0071] The insulating polymer layer is a polyethylene terephthalate-based insulating layer, and its raw materials, by weight, include: 110 parts polyethylene terephthalate, 2 parts surface-modified nano silica, 1 part heat stabilizer, and 0.4 parts styrene-glycidyl acrylate copolymer. The heat stabilizer is obtained by mixing bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene in a weight ratio of 3:1.

[0072] The preparation process of surface-modified nano silica is as follows: nano silica is added to a mixed solution of ethanol and deionized water, ultrasonically dispersed for 25 min, γ-glycidyl etheroxypropyltrimethoxysilane accounting for 3% of the mass of nano silica is added, the pH is adjusted to 5, and the reaction is stirred at 55℃ for 2.5 h. After filtration and drying, surface-modified nano silica is obtained.

[0073] The preparation steps of the insulating polymer layer are as follows: the above raw materials are mixed evenly and then added to a twin-screw extruder. The mixture is melt-blended and extruded at 250°C, cooled and pelletized to obtain modified polyethylene terephthalate granules. The granules are dried at 180°C for 2 hours and then subjected to extrusion casting, biaxial stretching and heat setting at 210°C to obtain a polyethylene terephthalate-based insulating layer with a thickness of 100 μm.

[0074] The hot melt adhesive is prepared by mixing polymethyl methacrylate powder, hydrogenated rosin glycerol ester, and polyethylene wax in a weight ratio of 70:10:5, wherein the average particle size of the polymethyl methacrylate powder is 1 μm. During preparation, the above components are added to a reaction vessel, heated to 140°C, and stirred for 30 min to obtain a uniformly mixed hot melt adhesive.

[0075] The first and second metal layers, on the side closest to the insulating polymer layer, undergo surface treatment: they are placed in an 8% sodium hydroxide solution and cleaned at 55°C for 55 seconds. After rinsing with deionized water, they are dried with hot air at 85°C for 1.5 minutes. Then, they are placed in a 60g / L sodium persulfate solution and treated at 30°C for 23 seconds. After cleaning and drying, they are placed in a low-pressure plasma device and treated with argon gas at 250W for 25 seconds under a vacuum of 45Pa. Then, oxygen gas is introduced and treated with 200W for 22 seconds.

[0076] The surface modification treatment of the insulating polymer layer is as follows: the polyethylene terephthalate-based insulating layer is immersed in a 2wt% sodium hydroxide solution at 45°C for 35s, then removed and placed in a 1wt% hydrochloric acid solution for 18s, then washed with deionized water and dried; subsequently, it is subjected to double-sided oxygen plasma treatment for 65s to obtain an activated polyethylene terephthalate-based insulating layer; then it is immersed in a 1wt% ethanol aqueous solution of γ-aminopropyltriethoxysilane, wherein the ethanol mass fraction in the aqueous solution is 95%, and then removed and dried at 90°C for 4min to obtain a surface-modified insulating polymer layer.

[0077] During hot-pressing composite, the first metal layer, the surface-modified insulating polymer layer, and the second metal layer are sequentially stacked. Each contact surface is uniformly coated with a 1μm thick hot melt adhesive. The process is first pre-pressed, and then hot-pressed at 150℃ and 2MPa for 7 minutes. After cooling, a composite current collector is obtained with a width of 2mm.

[0078] Example 4 This embodiment provides a composite current collector for a solar cell with a copper electrode. The composite current collector comprises, from top to bottom, a first metal layer, an insulating polymer layer, and a second metal layer. Both the first and second metal layers are made of Inconel 600 nickel alloy foil with a thickness of 30 μm. The surface of the Inconel 600 nickel alloy foil away from the insulating polymer layer is electroplated to form a tin layer with a thickness of approximately 2 μm, serving as the first and second solderable surface layers.

[0079] The insulating polymer layer is a polyethylene naphthalate-based insulating layer, and its raw materials, by weight, include: 105 parts polyethylene naphthalate, 3 parts surface-modified nano silica, 0.5 parts heat stabilizer, and 0.5 parts styrene-glycidyl acrylate copolymer. The heat stabilizer is obtained by mixing tris(2,4-di-tert-butylphenyl) phosphite and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] at a weight ratio of 2.8:1.

[0080] The preparation process of surface-modified nano silica is as follows: nano silica is added to a mixed solution of ethanol and deionized water, ultrasonically dispersed for 32 min, γ-glycidyl etheroxypropyltrimethoxysilane accounting for 2.4% of the mass of nano silica is added, the pH is adjusted to 5, and the reaction is stirred at 62℃ for 2 h. After filtration and drying, surface-modified nano silica is obtained.

[0081] The preparation steps of the insulating polymer layer are as follows: the above raw materials are mixed evenly and then added to a twin-screw extruder. The mixture is melt-blended and extruded at 260°C, cooled and pelletized to obtain modified polyethylene naphthalate granules. The granules are dried at 150°C for 5 hours and then subjected to extrusion casting, biaxial stretching and heat setting at 210°C to obtain a polyethylene naphthalate-based insulating layer with a thickness of 60 μm.

[0082] The hot melt adhesive is prepared by mixing polymethyl methacrylate powder, hydrogenated rosin glycerol ester, and polyethylene wax in a weight ratio of 75:7:8, wherein the average particle size of the polymethyl methacrylate powder is 0.8 μm. During preparation, the above components are added to a reaction vessel, heated to 145°C, and stirred for 30 min to obtain a uniformly mixed hot melt adhesive.

[0083] The first and second metal layers are first surface-treated on the side closest to the insulating polymer layer: placed in an 8% sodium hydroxide solution, cleaned at 50°C for 60 seconds, rinsed with deionized water, dried with hot air at 80°C for 2 minutes, placed in a 60g / L sodium persulfate solution, treated at 26°C for 25 seconds, cleaned and dried, and then placed in a low-pressure plasma device. Under a vacuum of 40Pa, argon gas is first introduced at 250W for 30 seconds, followed by oxygen gas at 200W for 20 seconds.

[0084] The surface modification treatment of the insulating polymer layer is as follows: the polyethylene naphthalate-based insulating layer is immersed in a 2wt% sodium hydroxide solution at 50°C for 30s, then removed and neutralized in a 1wt% hydrochloric acid solution for 20s, then washed with deionized water and dried; subsequently, it undergoes double-sided oxygen plasma treatment for 60s to obtain an activated polyethylene naphthalate-based insulating layer; then it is immersed in a 1wt% ethanol aqueous solution of γ-aminopropyltriethoxysilane, wherein the ethanol aqueous solution has an ethanol mass fraction of 95%, and then dried at 95°C for 3min to obtain a surface-modified insulating polymer layer.

[0085] During hot-pressing composite, the first metal layer, the surface-modified insulating polymer layer, and the second metal layer are sequentially stacked. Each contact surface is uniformly coated with a 1.5 μm thick hot melt adhesive. The process is first pre-pressed and then hot-pressed at 145℃ and 4MPa for 4 minutes. After cooling, a composite current collector is obtained with a width of 3 mm.

[0086] Example 5 This embodiment provides a solar cell. The solar cell includes an N-type silicon-based solar cell, copper electrodes formed on the front and back main surfaces of the cell, and a composite current collector disposed on two opposite edge regions of the cell. The composite current collector uses the product obtained in Embodiment 1 and is connected to the ends of multiple gridless fine-grid copper electrodes on the front and back surfaces of the cell to form a dual-end current collector structure.

[0087] Example 6 This embodiment provides a solar cell. The solar cell includes an N-type silicon-based solar cell, copper electrodes formed on the front and back main surfaces of the cell, and a composite current collector disposed on two opposite edge regions of the cell. The composite current collector uses the product obtained in Embodiment 1 and is connected to multiple inflection points of the serpentine copper electrodes on the front and back surfaces of the cell to form a multi-node segmented current collection structure.

[0088] Comparative Example 1 (The difference from Example 1 is that the roughening and plasma treatment of the side of the first metal layer and the second metal layer near the insulating layer are not performed) This comparative example provides a copper electrode composite current collector for a solar cell. The composite current collector comprises, from top to bottom, a first metal layer, an insulating polymer layer, and a second metal layer. Both the first and second metal layers are made of C2720 copper alloy foil with a thickness of 40 μm. The surface of the C2720 copper alloy foil away from the insulating polymer layer is electroplated to form a tin layer with a thickness of about 2 μm, serving as the first solderable surface layer and the second solderable surface layer.

[0089] The insulating polymer layer is a polyethylene terephthalate-based insulating layer, and its raw materials, by weight, include: 100 parts polyethylene terephthalate, 3 parts surface-modified nano silica, 0.6 parts heat stabilizer, and 0.5 parts styrene-glycidyl acrylate copolymer. The heat stabilizer is obtained by mixing bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] in a weight ratio of 2.5:1.

[0090] The preparation process of surface-modified nano silica is as follows: nano silica is added to a mixed solution of ethanol and deionized water, ultrasonically dispersed for 30 min, γ-glycidyl etheroxypropyltrimethoxysilane accounting for 2.5% of the mass of nano silica is added, the pH is adjusted to 5, and the reaction is stirred at 60℃ for 2 h. After filtration and drying, surface-modified nano silica is obtained.

[0091] The preparation steps of the insulating polymer layer are as follows: the above raw materials are mixed evenly and then added to a twin-screw extruder. The mixture is melt-blended and extruded at 260°C, cooled and pelletized to obtain modified polyethylene terephthalate granules. The granules are dried at 150°C for 5 hours and then subjected to extrusion casting, biaxial stretching and heat setting at 210°C to obtain a polyethylene terephthalate-based insulating layer with a thickness of 65 μm.

[0092] The hot melt adhesive is prepared by mixing polymethyl methacrylate powder, hydrogenated rosin glycerol ester, and polyethylene wax in a weight ratio of 75:8:8, wherein the average particle size of the polymethyl methacrylate powder is 0.7 μm. During preparation, the above components are added to a reaction vessel, heated to 145°C, and stirred for 30 min to obtain a uniformly mixed hot melt adhesive.

[0093] The first and second metal layers are first surface-treated on the side closest to the insulating polymer layer: placed in an 8% sodium hydroxide solution, cleaned at 50°C for 60 seconds, rinsed with deionized water, and then dried with hot air at 80°C for 2 minutes.

[0094] The surface modification treatment of the insulating polymer layer is as follows: the polyethylene terephthalate-based insulating layer is immersed in a 2wt% sodium hydroxide solution at 50°C for 30s, then removed and neutralized in a 1wt% hydrochloric acid solution for 20s, then washed with deionized water and dried; subsequently, it undergoes double-sided oxygen plasma treatment for 60s to obtain an activated polyethylene terephthalate-based insulating layer; then it is immersed in a 1wt% ethanol aqueous solution of γ-aminopropyltriethoxysilane, wherein the ethanol mass fraction in the aqueous solution is 95%, and after removal, it is dried at 100°C for 3min to obtain a surface-modified insulating polymer layer.

[0095] During hot-pressing composite, the first metal layer, the surface-modified insulating polymer layer, and the second metal layer are sequentially stacked. Each contact surface is uniformly coated with a 1.5 μm thick hot melt adhesive. The process is first pre-pressed and then hot-pressed at 145℃ and 3MPa for 5 minutes. After cooling, a composite current collector is obtained with a width of 2 mm.

[0096] Comparative Example 2 (The difference from Example 1 is that the insulating polymer layer is not surface modified). This comparative example provides a copper electrode composite current collector for a solar cell. The composite current collector comprises, from top to bottom, a first metal layer, an insulating polymer layer, and a second metal layer. Both the first and second metal layers are made of C2720 copper alloy foil with a thickness of 40 μm. The surface of the C2720 copper alloy foil away from the insulating polymer layer is electroplated to form a tin layer with a thickness of about 2 μm, serving as the first solderable surface layer and the second solderable surface layer.

[0097] The insulating polymer layer is a polyethylene terephthalate-based insulating layer, and its raw materials, by weight, include: 100 parts polyethylene terephthalate, 3 parts surface-modified nano silica, 0.6 parts heat stabilizer, and 0.5 parts styrene-glycidyl acrylate copolymer. The heat stabilizer is obtained by mixing bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] in a weight ratio of 2.5:1.

[0098] The preparation process of surface-modified nano silica is as follows: nano silica is added to a mixed solution of ethanol and deionized water, ultrasonically dispersed for 30 min, γ-glycidyl etheroxypropyltrimethoxysilane accounting for 2.5% of the mass of nano silica is added, the pH is adjusted to 5, and the reaction is stirred at 60℃ for 2 h. After filtration and drying, surface-modified nano silica is obtained.

[0099] The preparation steps of the insulating polymer layer are as follows: the above raw materials are mixed evenly and then added to a twin-screw extruder. The mixture is melt-blended and extruded at 260°C, cooled and pelletized to obtain modified polyethylene terephthalate granules. The granules are dried at 150°C for 5 hours and then subjected to extrusion casting, biaxial stretching and heat setting at 210°C to obtain a polyethylene terephthalate-based insulating layer with a thickness of 65 μm.

[0100] The hot melt adhesive is prepared by mixing polymethyl methacrylate powder, hydrogenated rosin glycerol ester, and polyethylene wax in a weight ratio of 75:8:8, wherein the average particle size of the polymethyl methacrylate powder is 0.7 μm. During preparation, the above components are added to a reaction vessel, heated to 145°C, and stirred for 30 min to obtain a uniformly mixed hot melt adhesive.

[0101] The first and second metal layers are first surface-treated on the side closest to the insulating polymer layer: placed in an 8% sodium hydroxide solution, cleaned at 50°C for 60 seconds, rinsed with deionized water, dried with hot air at 80°C for 2 minutes, placed in a 60g / L sodium persulfate solution, treated at 25°C for 25 seconds, cleaned and dried, and then placed in a low-pressure plasma device. Under a vacuum of 40Pa, argon gas is first introduced at 250W for 30 seconds, followed by oxygen gas at 200W for 20 seconds.

[0102] During hot-pressing composite, the first metal layer, the insulating polymer layer, and the second metal layer are sequentially stacked, and each contact surface is uniformly coated with a 1.5 μm thick hot melt adhesive. The mixture is first pre-pressed and then hot-pressed at 145℃ and 3MPa for 5 minutes. After cooling, a composite current collector is obtained with a width of 2 mm.

[0103] Comparative Example 3 (different from Example 1 in that the hot melt adhesive is prepared from a single polymethyl methacrylate powder and does not contain hydrogenated rosin glycerol ester and polyethylene wax) This comparative example provides a copper electrode composite current collector for a solar cell. The composite current collector comprises, from top to bottom, a first metal layer, an insulating polymer layer, and a second metal layer. Both the first and second metal layers are made of C2720 copper alloy foil with a thickness of 40 μm. The surface of the C2720 copper alloy foil away from the insulating polymer layer is electroplated to form a tin layer with a thickness of about 2 μm, serving as the first solderable surface layer and the second solderable surface layer.

[0104] The insulating polymer layer is a polyethylene terephthalate-based insulating layer, and its raw materials, by weight, include: 100 parts polyethylene terephthalate, 3 parts surface-modified nano silica, 0.6 parts heat stabilizer, and 0.5 parts styrene-glycidyl acrylate copolymer. The heat stabilizer is obtained by mixing bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] in a weight ratio of 2.5:1.

[0105] The preparation process of surface-modified nano silica is as follows: nano silica is added to a mixed solution of ethanol and deionized water, ultrasonically dispersed for 30 min, γ-glycidyl etheroxypropyltrimethoxysilane accounting for 2.5% of the mass of nano silica is added, the pH is adjusted to 5, and the reaction is stirred at 60℃ for 2 h. After filtration and drying, surface-modified nano silica is obtained.

[0106] The preparation steps of the insulating polymer layer are as follows: the above raw materials are mixed evenly and then added to a twin-screw extruder. The mixture is melt-blended and extruded at 260°C, cooled and pelletized to obtain modified polyethylene terephthalate granules. The granules are dried at 150°C for 5 hours and then subjected to extrusion casting, biaxial stretching and heat setting at 210°C to obtain a polyethylene terephthalate-based insulating layer with a thickness of 65 μm.

[0107] The hot melt adhesive is prepared from polymethyl methacrylate powder with an average particle size of 0.7 μm. During preparation, the above components are added to a reaction vessel, heated to 145°C, and stirred for 30 min to obtain a uniformly mixed hot melt adhesive.

[0108] The first and second metal layers are first surface-treated on the side closest to the insulating polymer layer: placed in an 8% sodium hydroxide solution, cleaned at 50°C for 60 seconds, rinsed with deionized water, dried with hot air at 80°C for 2 minutes, placed in a 60g / L sodium persulfate solution, treated at 25°C for 25 seconds, cleaned and dried, and then placed in a low-pressure plasma device. Under a vacuum of 40Pa, argon gas is first introduced at 250W for 30 seconds, followed by oxygen gas at 200W for 20 seconds.

[0109] The surface modification treatment of the insulating polymer layer is as follows: the polyethylene terephthalate-based insulating layer is immersed in a 2wt% sodium hydroxide solution at 50°C for 30s, then removed and neutralized in a 1wt% hydrochloric acid solution for 20s, then washed with deionized water and dried; subsequently, it undergoes double-sided oxygen plasma treatment for 60s to obtain an activated polyethylene terephthalate-based insulating layer; then it is immersed in a 1wt% ethanol aqueous solution of γ-aminopropyltriethoxysilane, wherein the ethanol mass fraction in the aqueous solution is 95%, and after removal, it is dried at 100°C for 3min to obtain a surface-modified insulating polymer layer.

[0110] During hot-pressing composite, the first metal layer, the surface-modified insulating polymer layer, and the second metal layer are sequentially stacked. Each contact surface is uniformly coated with a 1.5 μm thick hot melt adhesive. The process is first pre-pressed and then hot-pressed at 145℃ and 3MPa for 5 minutes. After cooling, a composite current collector is obtained with a width of 2 mm.

[0111] Comparative Example 4 This comparative example provides a solar cell. It adopts a conventional single-sided current collector structure, that is, a conventional metal busbar is set only on one edge of the cell to collect current to the front copper electrode, without using the composite current collector structure of this application.

[0112] Experimental Example The composite current collectors for solar cells with copper electrodes prepared in Examples 1-4 and Comparative Examples 1-3 were tested for their 180° peel strength, insulation resistance, and resistance to damp heat aging. The test methods are as follows: The 180° peel strength between layers was tested according to the test principle specified in GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes". The sample was cut and tested in combination with the composite current collector structure. The test speed was 300 mm / min, and the average value of 5 parallel samples was taken. Insulation resistance was measured using an insulation resistance tester. A DC test voltage of 100V was applied between the first metal layer and the second metal layer, and the stable insulation resistance value was recorded. The sample was placed in an environment of 23℃ and 50% relative humidity for 24 hours before testing. Damp heat aging test: Aging at 85℃ and 85% relative humidity for 500h, and test the peel strength retention rate and insulation resistance value after damp heat aging.

[0113] The test data is shown in Table 1 below: Table 1. Test results of copper electrode composite current collector performance in solar cells.

[0114] Reference Figures 1-2As can be seen from Table 1, the copper electrode composite current collectors for solar cells prepared in Examples 1-4 of this application have good interlayer 180° peel strength, insulation resistance, and resistance to damp heat aging.

[0115] In the preparation of the copper electrode composite current collector for solar cells in Comparative Example 1, roughening and plasma treatment were not performed on the side of the first and second metal layers closest to the insulating layer. All other aspects were the same as in Example 1. The 180° peel strength and resistance to damp heat aging of the copper electrode composite current collector for solar cells prepared in Comparative Example 1 showed a significant decrease. This indicates that the roughening treatment in this application can form a micro-uneven structure on the surface of the metal layer, increasing the actual contact area at the interface and improving the mechanical interlocking effect. Further plasma treatment can effectively remove surface contaminants, increase surface energy, and introduce active groups on the surface, thereby improving the wettability and bonding ability of the hot-melt adhesive to the surface of the metal layer. This significantly improves the adhesion and peel strength between the metal layer and the insulating polymer layer, reduces the risk of delamination and warping after hot-pressing, and helps improve the structural stability and long-term reliability of the composite current collector under welding, thermal cycling, and damp heat environments.

[0116] In Comparative Example 2, the insulating polymer layer was not surface-modified during the preparation of the solar cell copper electrode composite current collector, and all other processes were the same as in Example 1. The 180° peel strength, insulation resistance, and resistance to humid heat aging of the solar cell copper electrode composite current collector prepared in Comparative Example 2 were significantly reduced. This indicates that by sequentially performing alkali treatment, acid neutralization, oxygen plasma activation, and silane coupling modification on the insulating polymer layer, the inert layer and residual impurities on the base film surface can be effectively removed, and active groups such as hydroxyl and carboxyl groups can be introduced on the surface, significantly improving surface energy and wettability. γ-aminopropyltriethoxysilane can form a stable coupling interface on the surface of the insulating polymer layer, with one end bonding to the activated polymer surface and the other end forming a stronger interfacial interaction with the hot melt adhesive and metal layer. This improves the bonding strength and peel strength between the insulating polymer layer and the metal layer, suppresses problems such as delamination and warping after hot pressing, and helps to improve the interfacial stability and long-term reliability of the composite current collector under welding, thermal cycling, and humid heat environments.

[0117] In Comparative Example 3, the hot-melt adhesive for the copper electrode composite current collector of the solar cell was prepared using a single polymethyl methacrylate powder, without hydrogenated rosin glycerol ester and polyethylene wax. All other aspects were the same as in Example 1. The 180° peel strength and resistance to damp heat aging of the copper electrode composite current collector prepared in Comparative Example 3 showed a significant decrease. This indicates that the hot-melt adhesive of this application uses a specific ratio system, with polymethyl methacrylate powder as the main adhesive component, which can form a continuous and dense bonding interface, ensuring that the composite current collector has high interlayer bonding strength and good insulation stability. Hydrogenated rosin glycerol ester can improve the wettability and adhesion of the adhesive to the surfaces of the metal layer and the insulating polymer layer, which is beneficial to improving the interfacial adhesion strength. Polyethylene wax can adjust the melt flowability and coating uniformity of the hot-melt adhesive, reducing the risk of interfacial voids and local defects during the composite process. When these three components are used in combination within the above-mentioned ratio range, they can better balance bonding strength, processing performance, and long-term reliability, thereby improving the peel strength, hot-pressing composite stability, and interlayer durability under thermal cycling and damp heat conditions of the composite current collector.

[0118] The electrical performance of the solar cells in Examples 5-6 and Comparative Example 4 was tested using a solar simulator under standard test conditions, namely, a light intensity of 1000 W / m². The test parameters included AM1.5 spectrum and 25℃, and included short-circuit current, open-circuit voltage, fill factor, conversion efficiency, and series resistance. The test methods followed GB / T 6495.1-2025 "Photovoltaic Devices - Part 1: Measurement of Photovoltaic Current-Voltage Characteristics" and related photovoltaic test specifications. Test data are shown in Table 2 below. Table 2. Test results of the electrical performance of solar cells

[0119] Reference Figures 1-4 As shown in Table 2, compared to Comparative Example 4, the open-circuit voltage changes in Examples 5 and 6 are relatively small, indicating that the composite current collector has little impact on the battery junction characteristics. Its main function is to optimize the current collection path and reduce resistance loss. Meanwhile, the short-circuit current, fill factor, and conversion efficiency of Examples 5 and 6 are significantly improved, while the series resistance decreases sequentially, indicating that the composite current collector can effectively shorten the current-carrying path and improve the current collection efficiency. In particular, the electrical performance of Example 6 is further superior to that of Example 5, demonstrating that for the serpentine copper electrode, connecting multiple inflection points to form segmented current collection can further reduce resistance loss, resulting in better conductivity and higher conversion efficiency.

[0120] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions or alterations can be made to these embodiments without departing from the principles and spirit of this application, and the technical solutions resulting from such changes, modifications, substitutions or alterations will all fall within the protection scope of this application.

Claims

1. A copper electrode composite current collector for solar cells, characterized in that, It includes a first metal layer, an insulating polymer layer, and a second metal layer that are sequentially stacked along the thickness direction; The first metal layer, the insulating polymer layer, and the second metal layer are bonded together by hot-pressing with a hot-melt adhesive. The first metal layer is used for electrical connection to the copper electrode end of one of the two main surfaces opposite to the solar cell, the second metal layer is used for electrical connection to the copper electrode end of the other of the two main surfaces opposite to the solar cell, and the insulating polymer layer is used for electrical insulation and isolation between the first metal layer and the second metal layer.

2. The composite current collector for a solar cell copper electrode according to claim 1, characterized in that, The hot melt adhesive is composed of polymethyl methacrylate powder, hydrogenated rosin glycerol ester and polyethylene wax in a weight ratio of 70-80:5-10:5-10.

3. The composite current collector for a solar cell copper electrode according to claim 1, characterized in that, The first metal layer and the second metal layer are each independently selected from at least one of copper, nickel, tin, silver, copper alloy, and nickel alloy.

4. The composite current collector for a solar cell copper electrode according to claim 1, characterized in that, The surface of the first metal layer away from the insulating polymer layer is covered with a first solderable surface layer, and / or the surface of the second metal layer away from the insulating polymer layer is covered with a second solderable surface layer.

5. A composite current collector for a solar cell copper electrode according to claim 1, characterized in that, The surface of the first metal layer and / or the second metal layer near the insulating polymer layer is subjected to surface treatment, including roughening treatment and plasma treatment in sequence.

6. The composite current collector for a solar cell copper electrode according to claim 1, characterized in that, The surface of the insulating polymer layer is modified by the following steps: immersing the insulating polymer layer in a 2wt% sodium hydroxide solution at 45-55℃ for 25-35s, then neutralizing it with a 1wt% hydrochloric acid solution for 18-22s, washing it with deionized water and drying it; subsequently performing double-sided oxygen plasma treatment for 55-65s to obtain an activated insulating polymer layer; immersing the activated insulating polymer layer in a 1wt% ethanol aqueous solution of γ-aminopropyltriethoxysilane, wherein the mass of ethanol in the ethanol aqueous solution is 95%, then drying it at 90-110℃ for 2-4min to obtain a surface-modified insulating polymer layer.

7. A composite current collector for a solar cell with a copper electrode according to claim 1, characterized in that, The insulating polymer layer comprises the following raw materials in parts by weight: 90-110 parts polymer resin, 2-4 parts surface-modified nano silica, 0.2-1 parts heat-resistant stabilizer, and 0.4-0.6 parts epoxy chain extender.

8. A composite current collector for a solar cell copper electrode according to claim 7, characterized in that, The heat-resistant stabilizer is composed of a mixture of phosphite stabilizers and hindered phenolic stabilizers in a weight ratio of 2-3:

1.

9. A composite current collector for a solar cell with a copper electrode according to claim 7, characterized in that, The polymer resin includes at least one of polyethylene terephthalate, polyimide, polytetrafluoroethylene, and polyethylene naphthalate.

10. A method for preparing a copper electrode composite current collector for solar cells as described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1 modifies the surface of the insulating polymer layer to obtain a surface-modified insulating polymer layer; S2 The first metal layer, the surface-modified insulating polymer layer and the second metal layer are laid in sequence. During the laying, the contact surfaces of each layer are uniformly coated with hot melt adhesive, pre-pressed and molded, and then hot-pressed and bonded to obtain the copper electrode composite current collector for solar cells. The first metal layer is used to connect the copper electrode end of one side of the two main surfaces of the solar cell that are arranged opposite each other, and the second metal layer is used to connect the copper electrode end of the other side of the two main surfaces of the solar cell that are arranged opposite each other, so as to realize the collection and extraction of the photocurrent generated by the solar cell.

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