Composite metal electrode and preparation method thereof, solar cell and photovoltaic module

Abstract

The invention provides a composite metal electrode and a preparation method thereof, a solar cell and a photovoltaic module, and relates to the technical field of solar cells. The composite metal electrode comprises a silver seed layer, a composite interface layer, a copper main electrode layer and a metal protection layer, wherein the composite interface layer is a copper-silver metallurgical interlocking layer. According to the invention, a composite electrode structure of three-dimensional interlocking of the thin silver seed layer and the electroplated thick copper layer is adopted, so that atomic-scale metallurgical bonding is realized, nanoscale mechanical occlusion is generated, and ultrahigh-strength adhesion and extremely low contact resistance between the copper layer and the silver layer are realized; therefore, high conductivity, strong adhesion and extremely low silver consumption of the back contact cell are realized.

Description

Technical Field

[0001] This invention relates to the technical field of solar cells, and in particular to a composite metal electrode and its preparation method, as well as solar cells and photovoltaic modules. Background Technology

[0002] Back-contact solar cells effectively eliminate the shading problem caused by front-side grid lines by integrating all electrodes on the back of the cell. This not only significantly improves photoelectric conversion efficiency but also has the outstanding advantage of a neat and aesthetically pleasing appearance, demonstrating promising application prospects in the field of photovoltaic technology.

[0003] Currently, the fabrication of the back electrode for mainstream back-contact batteries mostly employs a process of screen-printing silver paste combined with high-temperature sintering. While this technology is mature, it suffers from two major limitations: firstly, the large consumption of silver paste leads to high production costs; secondly, the aspect ratio of the printed silver grid lines is difficult to improve due to process limitations, directly hindering further optimization of battery conversion efficiency. To overcome this cost bottleneck, the industry is actively exploring electroplated copper as a substitute for silver electrodes. Copper not only has a conductivity close to that of silver, but its material cost is also only about one percent of that of silver, giving it a significant economic advantage. However, copper diffuses rapidly in silicon substrates, easily forming deep-level impurities, which will seriously affect the long-term reliability and lifespan of the battery. This issue has become a key challenge restricting the industrialization of this technology.

[0004] Currently, in the copper plating process of heterojunction batteries, complex transparent conductive oxides are typically used as seed and barrier layers. This technology has compatibility issues with traditional dielectric passivation back contact structures, making it difficult to apply directly. If the intermediate transition layer is omitted and copper is directly electroplated on the silicon substrate or dielectric layer surface of the back contact battery, technical bottlenecks such as insufficient plating adhesion, susceptibility to substrate corrosion, and difficulty in controlling copper ion diffusion will be encountered.

[0005] Therefore, there is an urgent need to design a new electrode structure suitable for back-contact batteries, which can achieve low-cost copper electrodes while ensuring their excellent electrical performance, mechanical reliability and long-term stability.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing solar cell grid lines, a solar cell, and a photovoltaic module, so as to at least solve one of the technical problems existing in the prior art.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a composite metal electrode, the composite metal electrode comprising a silver seed layer, a composite interface layer, a copper main electrode layer and a metal protective layer; The composite interface layer is a copper-silver metallurgical interlocking layer.

[0009] Furthermore, the silver seed layer is a conductive thin film with microscopic roughness and porous morphology.

[0010] Furthermore, the roughness of the silver seed layer is 20~100 nm; Furthermore, the pore size of the silver seed layer is 10~50 nm; Furthermore, the thickness of the silver seed layer is 0.5~3 μm.

[0011] Furthermore, the atomic percentage of copper in the composite interface layer decreases continuously from more than 50% on the side closer to the copper main electrode layer to less than 20% on the side closer to the silver seed layer.

[0012] Furthermore, the thickness of the composite interface layer is 50~500 nm.

[0013] Furthermore, the average grain size of copper in the composite interface layer is less than 100 nm.

[0014] Furthermore, the composite interface layer contains silver-rich nanoparticles dispersed within it.

[0015] Furthermore, the size of the silver-rich nanoparticles is 5~20 nm.

[0016] Furthermore, the copper main electrode layer covers and wraps the upper surface of the composite interface layer, as well as the sidewalls of the silver seed layer and the composite interface layer.

[0017] Furthermore, in a cross-section perpendicular to the length of the metal electrode, the outline of the copper main electrode layer extends outward at positions corresponding to the two side edges of the composite interface layer, forming protrusions, such that the maximum width of the cross-section of the composite metal electrode is greater than the bottom width of the silver seed layer.

[0018] Furthermore, the copper main electrode layer has a columnar crystal structure, and the growth direction of the columnar crystal structure is perpendicular to the surface of the composite interface layer.

[0019] Furthermore, at the interface between the copper main electrode layer and the composite interface layer, there is a defined crystal orientation relationship between the copper grains and the silver grains.

[0020] Furthermore, the columnar crystal structure has a crystallographic orientation in the <110> direction.

[0021] Furthermore, the thickness of the copper main electrode layer is 5~20 μm.

[0022] Furthermore, the thickness of the copper main electrode layer at the edge of the composite interface layer is 10-50% greater than its thickness at the center of the pattern.

[0023] Furthermore, the metal protective layer is a solderable metal layer.

[0024] Furthermore, the material of the solderable metal layer is selected from any one or a combination of at least two of pure tin, pure silver, tin alloy, and silver alloy.

[0025] Furthermore, the thickness of the solderable metal layer is 0.5~2 μm.

[0026] In a second aspect, the present invention provides a method for preparing a composite metal electrode as described in the first aspect, the method comprising: A silver seed layer, a composite interface layer, a copper main electrode layer, and a metal protective layer are prepared on the surface of a substrate to obtain the composite metal electrode.

[0027] Furthermore, the silver seed layer and the composite interface layer are prepared by the following steps: Silver paste is printed onto the surface of a substrate by screen printing, and then sintered to obtain a silver metal layer. The substrate with the silver metal layer is then immersed in a first copper electroplating solution for electroplating, followed by gradient annealing to obtain a silver seed layer and a composite interface layer.

[0028] Furthermore, the sintering temperature is 700~850℃, and the sintering time is 0.5~5 min.

[0029] Furthermore, the thickness of the silver metal layer is 0.5~3 μm.

[0030] Furthermore, the first copper electroplating solution comprises, by mass concentration: 50-80 g / L copper sulfate, 250-350 g / L potassium pyrophosphate, 20-30 g / L ammonium citrate, and 10-20 g / L potassium nitrate, with water as the solvent.

[0031] Furthermore, the electroplating is constant current electroplating.

[0032] Furthermore, the current density of the constant current electroplating is 0.5~2.0 A / dm³. 2 The constant current electroplating time is 15~60 s.

[0033] Furthermore, the gradient annealing procedure includes: first heating to 150~250℃ and holding for 15~30 s; then heating to 300~450℃ and holding for 30~60 s.

[0034] Furthermore, the annealing heating rate in the gradient process is 5~10℃ / min.

[0035] Furthermore, the thickness of the silver seed layer is 0.5~3μm; the thickness of the composite interface layer is 50~500 nm.

[0036] Furthermore, the method for preparing the copper main electrode layer includes: The substrate with a silver seed layer and a composite interface layer is immersed in a second copper electroplating solution for main electroplating to obtain a copper main electrode layer.

[0037] Furthermore, the second copper electroplating solution comprises, by mass concentration: 50-80 g / L copper sulfate, 250-350 g / L potassium pyrophosphate, 20-30 g / L ammonium citrate, and 10-20 g / L potassium nitrate, with water as the solvent.

[0038] Furthermore, the main electroplating is constant current electroplating.

[0039] Furthermore, the current density of the constant current electroplating is 5~10 A / dm³. 2 The constant current electroplating time is 5~10 min.

[0040] Furthermore, the method for preparing the metal protective layer includes: The composite metal electrode is obtained by preparing the metal protective layer on the surface of the copper main electrode layer through a chemical immersion plating process.

[0041] Furthermore, the temperature of the chemical immersion plating process is 40~70℃; the time of the chemical immersion plating is 1~5 min; and the thickness of the metal protective layer formed by the chemical immersion plating is 0.5~2 μm.

[0042] Furthermore, the solutions used in the chemical immersion plating process, by mass concentration, include: stannous chloride 15~40 g / L, thiourea 80~150 g / L, concentrated hydrochloric acid 50~100 g / L, sodium hypophosphite 10~30 g / L, and water as the solvent.

[0043] Furthermore, the solution used in the chemical immersion plating process comprises, by mass concentration: 1.5~2.5 g / L silver nitrate, 180~220 g / L sodium thiosulfate, and 15~25 g / L potassium metabisulfite, with water as the solvent.

[0044] In a second aspect, the present invention provides a solar cell, the solar cell comprising a composite metal electrode as described in the first aspect, or a composite metal electrode prepared by the preparation method described in the second aspect.

[0045] Thirdly, the present invention provides a photovoltaic module, the photovoltaic module comprising the solar cell as described in the first aspect.

[0046] Compared with the prior art, the present invention has the following beneficial effects: (1) The composite metal electrode of the present invention adopts a composite interface treatment process. By depositing an ultrathin composite interface layer, the silver seed layer is precisely filled with pores. This not only achieves atomic-level metallurgical bonding of the silver-copper interface, but also forms a nanoscale mechanical interlocking structure. Simultaneously, it achieves a dual technical breakthrough of ultra-high interface adhesion and extremely low contact resistance, solving the technical bottleneck of the traditional structure where conductivity and bonding force are difficult to balance. (2) The composite metal electrode of the present invention optimizes the thick silver grid line that plays the dominant conductive function in the traditional technology into an ultrathin silver layer, retaining only its seed layer and contact layer functions, thereby reducing the amount of silver material consumed by a large order of magnitude and significantly reducing manufacturing costs. (3) The composite metal electrode of the present invention optimizes the deposition process parameters of the copper main electrode layer, so that the copper layer forms a three-dimensional coating on the surface and sidewall of the silver seed layer during the growth process and extends outward in an orderly manner, constructing a gradient structure with "anchoring effect", further strengthening the bonding force of the copper-silver interface. Experimental verification shows that the battery welding pull force is increased by more than 40%, significantly enhancing the long-term reliability of the device. Attached Figure Description

[0047] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art 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 from these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of the structure of the composite metal electrode described in this invention; Figure 2 This is a partially enlarged schematic diagram of the copper main electrode layer described in this invention; Figure 3 This is a schematic diagram of the structure of the solar cell described in this invention; Among them, 10 is the silicon substrate of N-type battery, 20 is the back passivation film, 21 is the front passivation film, 30 is the P+ doped region, 31 is the N+ doped region, 100 is the silver seed layer, 200 is the composite interface layer, 300 is the copper main electrode layer, 301 is the protrusion, and 400 is the metal protective layer. Detailed Implementation

[0049] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0050] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] In a first aspect, the present invention provides a composite metal electrode, such as... Figure 1 As shown, the composite metal electrode includes a silver seed layer 100, a composite interface layer 200, a copper main electrode layer 300, and a metal protective layer 400; wherein, the composite interface layer 200 is a copper-silver metallurgical interlocking layer.

[0052] It should be noted that in the composite metal electrode structure provided by this invention, the thick silver grid lines that play a dominant conductive role in traditional back-contact batteries are replaced with an ultrathin silver layer that only serves as a seed and contact element. This significantly reduces the amount of silver material consumed, lowering manufacturing costs. Simultaneously, a deposited ultrathin composite interface layer is used to fill the pores of the silver seed layer. This composite interface layer is a copper-silver metallurgical interlocking and diffusion-barrier composite layer, achieving atomic-level metallurgical bonding and generating nanoscale mechanical interlocking, resulting in ultra-high adhesion and extremely low contact resistance between the copper and silver layers. Furthermore, the deposited copper main electrode layer forms a three-dimensional coating on the surface and sidewalls of the silver seed layer and extends outwards, creating an "anchoring" effect that improves the bonding force between the copper and silver layers and enhances the welding pull force of the solar cell.

[0053] As an optional implementation, the silver seed layer 100 is a conductive thin film with microscopic roughness and porous morphology.

[0054] It should be noted that the silver seed layer is a conductive thin film with micro-roughness and porous morphology; this micro-roughness and porous morphology significantly increases the specific surface area of ​​the silver seed layer, promotes the uniform deposition and atomic-level metallurgical bonding of the composite interface layer, and enhances the interface adhesion.

[0055] In a preferred embodiment, the roughness of the silver seed layer 100 is 20~100 nm, for example, it can be 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.

[0056] In a preferred embodiment, the pore size of the silver seed layer 100 is 10~50 nm, for example, it can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, etc.

[0057] As an optional implementation, the thickness of the silver seed layer 100 is 0.5~3 μm, for example, it can be 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.5 μm, 3 μm, etc.

[0058] It should be noted that the thickness of the silver seed layer in this invention is controlled at 0.5~3 μm, which can significantly reduce the amount of silver material used and greatly reduce electrode costs while ensuring conductivity and the quality of the electroplating starting interface. At the same time, this thickness range is conducive to the uniform coverage of the subsequent composite interface layer and the good adhesion of the copper layer, taking into account both process feasibility and electrode reliability.

[0059] As an optional implementation, the atomic percentage of copper in the composite interface layer 200 decreases continuously from more than 50% on the side closer to the copper main electrode layer to less than 20% on the side closer to the silver seed layer.

[0060] It should be noted that this gradient-distributed composite interface is achieved through a gradient annealing process following copper electroplating. Copper gradually diffuses into the silver layer in a gradient manner during the annealing process (temperature and annealing time), resulting in a continuous decrease in the percentage of copper atoms from over 50% near the copper main electrode layer to below 20% towards the silver seed layer. This gradient-distributed composite interface achieves a smooth compositional transition between copper and silver, effectively mitigating interfacial stress concentration caused by thermal expansion coefficients and lattice mismatch between the two metals, significantly improving bonding strength and suppressing interfacial crack formation. Simultaneously, the gradient structure weakens the rapid diffusion channels of copper atoms, forming an effective diffusion barrier effect, preventing copper migration to the silicon substrate and thus avoiding material contamination and a decrease in minority carrier lifetime. Furthermore, this design helps reduce interfacial resistance, improve carrier transport efficiency, and provide a good crystallographic matching environment for subsequent epitaxial growth of the copper layer, thereby ensuring the conductivity, stability, and long-term reliability of the electrode, balancing high performance and high durability requirements.

[0061] As an optional implementation, the thickness of the composite interface layer 200 is 50~500 nm, for example, it can be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc.

[0062] As an optional implementation, the average grain size of copper in the composite interface layer 200 is less than 100 nm, for example, it can be 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, etc.

[0063] As an optional implementation, the composite interface layer 200 is internally dispersed with silver-rich nanoparticles.

[0064] As an optional implementation, the size of the silver-rich nanoparticles is 5~20 nm, for example, it can be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, etc.

[0065] As an optional implementation method, such as Figure 1 As shown, the copper main electrode layer 300 covers and wraps the upper surface of the composite interface layer 200, as well as the sidewalls of the silver seed layer 100 and the composite interface layer 200.

[0066] It should be noted that this three-dimensional coating structure achieves full-circumferential sealing of the silver seed layer and composite interface layer by the copper main electrode, effectively blocking the erosion paths of moisture and oxygen and inhibiting electrochemical corrosion; at the same time, it forms an "anchoring" effect, significantly enhancing the mechanical bonding force between layers, preventing peeling and falling off, and improving the integrity of the electrode structure and the reliability of welding.

[0067] As an optional implementation method, such as Figure 2 As shown, in a cross-section perpendicular to the length of the metal electrode, the outline of the copper main electrode layer 300 extends outward at positions corresponding to the two side edges of the composite interface layer, forming a protrusion 301, such that the maximum width of the cross-section of the composite metal electrode is greater than the bottom width of the silver seed layer.

[0068] As an optional implementation method, such as Figure 2 As shown, the thickness of the copper main electrode layer 300 at the edge of the pattern of the composite interface layer 200 is 10-50% greater than its thickness at the center of the pattern.

[0069] As an optional implementation, the copper main electrode layer has a columnar crystal structure, and the growth direction of the columnar crystal structure is perpendicular to the surface of the composite interface layer.

[0070] As an optional implementation, at the interface between the copper main electrode layer and the composite interface layer, there is a defined crystal orientation relationship between the copper grains and the silver grains.

[0071] As an optional implementation, the columnar crystal structure has a crystallographic orientation in the <110> direction.

[0072] As an optional implementation, the thickness of the copper main electrode layer 300 is 5~20 μm, for example, it can be 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, etc.

[0073] As an optional implementation, the metal protective layer 400 is a solderable metal layer.

[0074] As an optional implementation, the material of the solderable metal layer is selected from any one or a combination of at least two of pure tin, pure silver, tin alloy, and silver alloy.

[0075] As an optional implementation, the thickness of the solderable metal layer is 0.5~2 μm, for example, it can be 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, etc.

[0076] In a second aspect, the present invention provides a method for preparing a composite metal electrode as described in the first aspect, the method comprising: A silver seed layer, a composite interface layer, a copper main electrode layer, and a metal protective layer are prepared on the surface of a substrate to obtain the composite metal electrode.

[0077] As an optional implementation, the silver seed layer and the composite interface layer are prepared by the following steps: Silver paste is printed onto the surface of a substrate by screen printing, and then sintered to obtain a silver metal layer. The substrate with the silver metal layer is then immersed in a first copper electroplating solution for electroplating, followed by gradient annealing to obtain a silver seed layer and a composite interface layer.

[0078] As an optional implementation, the sintering temperature is 700~850℃, for example, it can be 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, 820℃, 840℃, 850℃, etc., and the sintering time is 0.5~5 min, for example, it can be 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, etc.

[0079] As an optional implementation, the thickness of the silver metal layer is 0.5~3 μm, for example, it can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, etc.

[0080] As an optional implementation, the first copper electroplating solution comprises, by mass concentration: 50-80 g / L copper sulfate (e.g., 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, etc.), 250-350 g / L potassium pyrophosphate (e.g., 250 g / L, 260 g / L, 280 g / L, 300 g / L, 320 g / L, 340 g / L, 350 g / L, etc.), 20-30 g / L ammonium citrate (e.g., 20 g / L, 22 g / L, 24 g / L, 26 g / L, 28 g / L, 30 g / L, etc.), and 10-20 g / L potassium nitrate (e.g., 10 g / L, 12 g / L, 14 g / L, 16 g / L, 18 g / L, 20 g / L, etc.), with water as the solvent.

[0081] As an optional implementation, the process of immersing the substrate with the silver metal layer in the first copper electroplating solution for electroplating is a constant current electroplating.

[0082] As an optional implementation, the step of immersing the substrate with the silver metal layer in a first copper electroplating solution for electroplating is a constant current electroplating; the current density of the constant current electroplating is 0.5~2.0 A / dm³. 2 For example, it could be 0.5 A / dm 2 0.6A / dm 2 0.8 A / dm 2 1 A / dm 2 1.2 A / dm 2 1.4 A / dm 2 1.6 A / dm 2 1.8 A / dm 2 2.0 A / dm 2 The constant current electroplating time is 15~60 s, for example, it can be 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, 50 s, 55 s, 60 s, etc.

[0083] As an optional implementation, the gradient annealing process includes: first heating to 150~250℃ (e.g., 150℃, 160℃, 180℃, 200℃, 220℃, 240℃, 250℃, etc.), and holding at that temperature for 15~30 s (e.g., 15 s, 16 s, 18 s, 20 s, 22 s, 24 s, 25 s, 26 s, 28 s, 30 s, etc.); then heating to 300~450℃ (e.g., 300℃, 320℃, 340℃, 350℃, 360℃, 380℃, 400℃, 420℃, 440℃, 450℃, etc.), and holding at that temperature for 30~60 s (e.g., 30 s, 35 s, 40 s, 45 s, 50 s, 55 s, 60 s, etc.).

[0084] As an optional implementation, the annealing heating rate in the gradient program is 5~10℃ / min, for example, it can be 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min, etc.

[0085] As an optional implementation, the gradient annealing process may further include a cooling step after completion.

[0086] As an optional implementation, the cooling is natural cooling to room temperature.

[0087] As an optional implementation, the thickness of the silver seed layer is 0.5~3 μm; the thickness of the composite interface layer is 50~500 nm.

[0088] As an optional implementation, the method for preparing the copper main electrode layer includes: The substrate with a silver seed layer and a composite interface layer is immersed in a second copper electroplating solution for main electroplating to obtain a copper main electrode layer.

[0089] As an optional implementation, the second copper electroplating solution comprises, by mass concentration: copper sulfate 50-80 g / L (e.g., 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, etc.), potassium pyrophosphate 250-350 g / L (e.g., 250 g / L, 260 g / L, 280 g / L, 300 g / L, 320 g / L, 340 g / L, 350 g / L, etc.), ammonium citrate 20-30 g / L (e.g., 20 g / L, 22 g / L, 24 g / L, 25 g / L, 26 g / L, 28 g / L, 30 g / L, etc.), and potassium nitrate 10-20 g / L (e.g., 10 g / L, 12 g / L, 14 g / L, 15 g / L, 16 g / L, 18 g / L, 20 g / L, etc.). (g / L, etc.), with water as the solvent.

[0090] As an optional implementation, the main electroplating is constant current electroplating.

[0091] As an optional implementation, the main electroplating is constant current electroplating; the current density of the constant current electroplating is 5~10 A / dm³. 2 For example, it could be 5 A / dm 2 6 A / dm 2 7 A / dm 2 8 A / dm 2 9 A / dm 2 10 A / dm 2 The constant current electroplating time is 5~10 min, for example, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc.

[0092] As an optional implementation, the method for preparing the metal protective layer includes: The composite metal electrode is obtained by preparing the metal protective layer on the surface of the copper main electrode layer through a chemical immersion plating process.

[0093] As an optional implementation, the temperature of the chemical immersion plating process is 40~70℃, for example, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, etc.; the chemical immersion plating time is 1~5 min, for example, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, etc.; the thickness of the metal protective layer formed by the chemical immersion plating is 0.5~2 μm, for example, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, etc.

[0094] As an optional implementation, the solutions used in the chemical immersion plating process, by mass concentration, include: stannous chloride 15~40 g / L (e.g., 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, etc.), thiourea 80~150 g / L (e.g., 80 g / L, 85 g / L, 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L, 125 g / L, 130 g / L, 135 g / L, 140 g / L, 145 g / L, 150 g / L, etc.), concentrated hydrochloric acid 50~100 g / L (e.g., 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, etc.). Sodium hypophosphite at concentrations of 10-30 g / L (e.g., 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, etc.), with water as the solvent.

[0095] As an optional implementation, the concentrated hydrochloric acid has a mass percentage content of 36-38%.

[0096] As an optional implementation, the solutions used in the chemical immersion plating process, by mass concentration, include: silver nitrate 1.5~2.5 g / L (e.g., 1.5 g / L, 1.6 g / L, 1.8 g / L, 2.0 g / L, 2.2 g / L, 2.4 g / L, 2.5 g / L, etc.), sodium thiosulfate 180~220 g / L (e.g., 180 g / L, 190 g / L, 200 g / L, 210 g / L, 220 g / L, etc.), and potassium metabisulfite 15~25 g / L (e.g., 15 g / L, 16 g / L, 18 g / L, 20 g / L, 22 g / L, 24 g / L, 25 g / L, etc.), with water as the solvent.

[0097] In a second aspect, the present invention provides a solar cell, the solar cell comprising a composite metal electrode as described in the first aspect, or a composite metal electrode prepared by the preparation method described in the second aspect.

[0098] As an optional implementation method, such as Figure 3 As shown, the solar cell includes an N-type silicon substrate 10; the front side of the N-type silicon substrate 10 has a front passivation film 21, and the back side has a back passivation film 20; the back side of the N-type silicon substrate 10 also has alternating, mutually insulated P+ doped regions 30 and N+ doped regions 31; and the composite metal electrode is respectively disposed above the P+ doped region 30 and the N+ doped region 31; the composite metal electrode includes a silver seed layer 100, a composite interface layer 200, a copper main electrode layer 300, and a metal protective layer 400; wherein, the composite interface layer 200 is a copper-silver metallurgical interlocking layer.

[0099] Thirdly, the present invention provides a photovoltaic module, the photovoltaic module comprising the solar cell as described in the first aspect.

[0100] The present invention will be further illustrated below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0101] Example 1 This embodiment provides a back-contact solar cell with a composite metal electrode; the solar cell includes an N-type silicon substrate; the front side of the N-type silicon substrate has a front passivation film and the back side has a back passivation film; the back side of the N-type silicon substrate also has alternately arranged, mutually insulated P+ doped regions and N+ doped regions; wherein, the composite metal electrode is respectively disposed above the P+ doped region and the N+ doped region; the composite metal electrode includes a silver seed layer, a composite interface layer, a copper main electrode layer and a metal protective layer.

[0102] The conductive thin film with microscopic roughness and porous morphology has a roughness of 60 nm, a pore size of 30 nm, and a thickness of 0.8 μm.

[0103] The composite interface layer is a copper-silver metallurgical interlocking and diffusion barrier composite layer with a thickness of 200 nm. The atomic percentage of copper in the composite interface layer decreases continuously from 50% near the copper main electrode layer to 20% near the silver seed layer. The average grain size of copper in the composite interface layer is 80 nm, and silver-rich nanoparticles with an average size of 10 nm are dispersed inside it.

[0104] The copper main electrode layer covers and wraps the upper surface of the composite interface layer, as well as the sidewalls of the silver seed layer and the composite interface layer. The thickness of the copper main electrode layer is 10 μm. The thickness of the copper main electrode layer at the edge of the composite interface layer pattern is 30% greater than its thickness at the center of the pattern. The copper main electrode layer has a columnar crystal structure, and the growth direction of the columnar crystals is perpendicular to the surface of the composite interface layer. On a cross-section perpendicular to the length of the metal electrode, the outline of the copper main electrode layer extends outward at positions corresponding to the two sides of the composite interface layer, forming protrusions, such that the maximum width of the electrode cross-section is greater than the width of the bottom of the composite interface layer. The columnar crystals mainly have a crystallographic orientation in the <110> direction. At the interface between the copper main electrode layer and the composite interface layer, there is a definite crystallographic orientation relationship between the copper grains and the silver grains.

[0105] The metal protective layer is a tin metal layer, and the thickness of the metal protective layer is 1 μm.

[0106] The back-contact solar cell with composite metal electrodes described in this embodiment is prepared by the following steps: (1) Silver paste is printed onto a silicon substrate with P+ and N+ doped regions by screen printing, and then sintered to obtain a silver metal layer. The silver paste is DK93H high-temperature sintering conductive silver paste provided by Dike Technology Co., Ltd.; the consumption of the silver paste is 1.5 mg / W; the sintering temperature is 750℃; the sintering time is 2 min; and the thickness of the silver metal layer is 0.82 μm.

[0107] (2) The substrate with the silver metal layer was immersed in the first copper electroplating solution for electroplating, and then subjected to gradient annealing to obtain a silver seed layer of 0.8 μm and a composite interface layer of 200 nm. The first copper electroplating solution comprises, by mass concentration: 65 g / L copper sulfate pentahydrate, 300 g / L potassium pyrophosphate, 25 g / L ammonium citrate, and 15 g / L potassium nitrate; the solvent is purified. The electroplating is constant current electroplating, with a current density of 1.0 A / dm³. 2 The constant current electroplating time is 40 s; the gradient annealing procedure includes: first heating to 200℃ at 8℃ / min and holding for 20 s; then heating to 400℃ at 8℃ / min and holding for 45 s, and finally cooling naturally to room temperature.

[0108] (3) Immerse the substrate with the silver seed layer and the composite interface layer into the second copper electroplating solution for main electroplating to obtain the copper main electrode layer. The second copper electroplating solution comprises, by mass concentration: 65 g / L copper sulfate pentahydrate, 300 g / L potassium pyrophosphate, 25 g / L ammonium citrate, and 15 g / L potassium nitrate, with purified water as the solvent; the main electroplating is constant current electroplating, with a current density of 7.5 A / dm³. 2 The constant current electroplating time is 7.5 min.

[0109] (4) The metal protective layer is prepared on the surface of the copper main electrode layer by chemical immersion plating process to obtain the composite metal electrode; The chemical immersion plating process uses a solution comprising, by mass concentration: 30 g / L stannous chloride, 115 g / L thiourea, 75 g / L concentrated hydrochloric acid (with a mass fraction of 37%), and 20 g / L sodium hypophosphite, with purified water as the solvent; the temperature of the chemical immersion plating process is 55°C; and the time of the chemical immersion plating is 2.5 min.

[0110] Example 2 This embodiment provides a back-contact solar cell with a composite metal electrode; the solar cell includes an N-type silicon substrate; the front side of the N-type silicon substrate has a front passivation film and the back side has a back passivation film; the back side of the N-type silicon substrate also has alternately arranged, mutually insulated P+ doped regions and N+ doped regions; wherein, the composite metal electrode is respectively disposed above the P+ doped region and the N+ doped region; the composite metal electrode includes a silver seed layer, a composite interface layer, a copper main electrode layer and a metal protective layer.

[0111] The conductive thin film with micro-roughness and porous morphology has a silver seed layer with a roughness of 40 nm, a pore size of 20 nm, and a thickness of 0.5 μm.

[0112] The composite interface layer is a copper-silver metallurgical interlocking and diffusion barrier composite layer with a thickness of 50 nm. The atomic percentage of copper in the composite interface layer decreases continuously from 55% near the copper main electrode layer to 15% near the silver seed layer. The average grain size of copper in the composite interface layer is 50 nm, and silver-rich nanoparticles with an average size of 5 nm are dispersed inside it.

[0113] The copper main electrode layer covers and wraps the upper surface of the composite interface layer, as well as the sidewalls of the silver seed layer and the composite interface layer. The thickness of the copper main electrode layer is 5 μm. The thickness of the copper main electrode layer at the edge of the composite interface layer pattern is 10% greater than its thickness at the center of the pattern. The copper main electrode layer has a columnar crystal structure, and the growth direction of the columnar crystals is perpendicular to the surface of the composite interface layer. On a cross-section perpendicular to the length of the metal electrode, the outline of the copper main electrode layer extends outward at positions corresponding to the two sides of the composite interface layer, forming protrusions, such that the maximum width of the electrode cross-section is greater than the width of the bottom of the composite interface layer. The columnar crystals mainly have a crystallographic orientation in the <110> direction. At the interface between the copper main electrode layer and the composite interface layer, there is a definite crystallographic orientation relationship between the copper grains and the silver grains.

[0114] The metal protective layer is a tin metal layer, and the thickness of the metal protective layer is 0.5 μm.

[0115] The back-contact solar cell with composite metal electrodes described in this embodiment is prepared by the following steps: (1) Silver paste is printed onto a silicon substrate with P+ and N+ doped regions by screen printing, and then sintered to obtain a silver metal layer. The silver paste is DK93H high-temperature sintering conductive silver paste provided by Dike Technology Co., Ltd.; the consumption of the silver paste is 1 mg / W; the sintering temperature is 750℃; the sintering time is 1 min; and the thickness of the silver metal layer is 0.55μm.

[0116] (2) The substrate with the silver metal layer is immersed in the first copper electroplating solution, electroplated, and then subjected to gradient annealing to obtain a 0.5 μm silver seed layer and a 50 nm composite interface layer. The first copper electroplating solution comprises, by mass concentration: 50 g / L copper sulfate pentahydrate, 250 g / L potassium pyrophosphate, 20 g / L ammonium citrate, and 10 g / L potassium nitrate; the solvent is purified. The electroplating is constant current electroplating, with a current density of 0.5 A / dm³. 2 The constant current electroplating time is 60 s; the gradient annealing procedure includes: first heating to 150℃ at 5℃ / min and holding for 30 s; then heating to 300℃ at 5℃ / min and holding for 60 s, and finally cooling naturally to room temperature.

[0117] (3) Immerse the substrate with the silver seed layer and the composite interface layer into the second copper electroplating solution for main electroplating to obtain the copper main electrode layer. The second copper electroplating solution comprises, by mass concentration: 50 g / L copper sulfate pentahydrate, 250 g / L potassium pyrophosphate, 20 g / L ammonium citrate, and 10 g / L potassium nitrate, with purified water as the solvent; the main electroplating is constant current electroplating, with a current density of 5 A / dm³. 2 The constant current electroplating time is 10 min.

[0118] (4) The metal protective layer is prepared on the surface of the copper main electrode layer by chemical immersion plating process to obtain the composite metal electrode; The chemical immersion plating process uses a solution comprising, by mass concentration: 15 g / L stannous chloride, 80 g / L thiourea, 50 g / L concentrated hydrochloric acid (with a mass fraction of 37%), and 10 g / L sodium hypophosphite, with purified water as the solvent; the temperature of the chemical immersion plating process is 40°C; and the time of the chemical immersion plating is 5 min.

[0119] Example 3 This embodiment provides a back-contact solar cell with a composite metal electrode; the solar cell includes an N-type silicon substrate; the front side of the N-type silicon substrate has a front passivation film and the back side has a back passivation film; the back side of the N-type silicon substrate also has alternately arranged, mutually insulated P+ doped regions and N+ doped regions; wherein, the composite metal electrode is respectively disposed above the P+ doped region and the N+ doped region; the composite metal electrode includes a silver seed layer, a composite interface layer, a copper main electrode layer and a metal protective layer.

[0120] The conductive thin film with microscopic roughness and porous morphology has a silver seed layer with a roughness of 80 nm, a pore size of 40 nm, and a thickness of 1.5 μm.

[0121] The composite interface layer is a copper-silver metallurgical interlocking and diffusion barrier composite layer with a thickness of 150 nm. The atomic percentage of copper in the composite interface layer decreases continuously from 60% near the copper main electrode layer to 10% near the silver seed layer. The average grain size of copper in the composite interface layer is 100 nm, and silver-rich nanoparticles with an average size of 20 nm are dispersed inside it.

[0122] The copper main electrode layer covers and wraps the upper surface of the composite interface layer, as well as the sidewalls of the silver seed layer and the composite interface layer. The thickness of the copper main electrode layer is 20 μm. The thickness of the copper main electrode layer at the edge of the composite interface layer pattern is 50% greater than its thickness at the center of the pattern. The copper main electrode layer has a columnar crystal structure, and the growth direction of the columnar crystals is perpendicular to the surface of the composite interface layer. On a cross-section perpendicular to the length of the metal electrode, the outline of the copper main electrode layer extends outward at positions corresponding to the two sides of the composite interface layer, forming protrusions, such that the maximum width of the electrode cross-section is greater than the width of the bottom of the composite interface layer. The columnar crystals mainly have a crystallographic orientation in the <110> direction. At the interface between the copper main electrode layer and the composite interface layer, there is a definite crystallographic orientation relationship between the copper grains and the silver grains.

[0123] The metal protective layer is a tin metal layer, and the thickness of the metal protective layer is 2 μm.

[0124] The back-contact solar cell with composite metal electrodes described in this embodiment is prepared by the following steps: (1) Silver paste is printed onto a silicon substrate with P+ and N+ doped regions by screen printing, and then sintered to obtain a silver metal layer. The silver paste is DK93H high-temperature sintering conductive silver paste provided by Dike Technology Co., Ltd.; the consumption of the silver paste is 2 mg / W; the sintering temperature is 750℃; the sintering time is 2.5 min; and the thickness of the silver metal layer is 1.65 μm.

[0125] (2) The substrate with the silver metal layer is immersed in the first copper electroplating solution, electroplated, and then subjected to gradient annealing to obtain a 1.5 μm silver seed layer and a 150 nm composite interface layer. The first copper electroplating solution comprises, by mass concentration: 80 g / L copper sulfate pentahydrate, 350 g / L potassium pyrophosphate, 30 g / L ammonium citrate, and 20 g / L potassium nitrate; the solvent is purified. The electroplating is constant current electroplating, with a current density of 2.0 A / dm³. 2 The constant current electroplating time is 15 s; the gradient annealing procedure includes: first heating to 250℃ at 10℃ / min and holding for 15 s; then heating to 450℃ at 10℃ / min and holding for 30 s, and finally cooling naturally to room temperature.

[0126] (3) Immerse the substrate with the silver seed layer and the composite interface layer into the second copper electroplating solution for main electroplating to obtain the copper main electrode layer. The second copper electroplating solution comprises, by mass concentration: 80 g / L copper sulfate pentahydrate, 350 g / L potassium pyrophosphate, 30 g / L ammonium citrate, and 20 g / L potassium nitrate, with purified water as the solvent; the main electroplating is constant current electroplating, with a current density of 5 A / dm³. 2 The constant current electroplating time is 10 min.

[0127] (4) The metal protective layer is prepared on the surface of the copper main electrode layer by chemical immersion plating process to obtain the composite metal electrode; The chemical immersion plating process uses a solution comprising, by mass concentration: 40 g / L stannous chloride, 150 g / L thiourea, 100 g / L concentrated hydrochloric acid (with a mass fraction of 37%), and 30 g / L sodium hypophosphite, with purified water as the solvent; the temperature of the chemical immersion plating process is 70°C; and the time of the chemical immersion plating is 1 min.

[0128] Example 4 This embodiment provides a back-contact solar cell with a composite metal electrode. The only difference from Embodiment 1 is that the atomic percentage of copper in the composite interface layer decreases continuously from 40% near the copper main electrode layer to 20% near the silver seed layer; other settings are the same as in Embodiment 1.

[0129] Example 5 This embodiment provides a back-contact solar cell with a composite metal electrode. The only difference from Embodiment 1 is that the atomic percentage of copper in the composite interface layer decreases continuously from 50% near the copper main electrode layer to 30% near the silver seed layer; other settings are the same as in Embodiment 1.

[0130] Example 6 This embodiment provides a back-contact solar cell with a composite metal electrode. The only difference from Embodiment 1 is that the copper main electrode layer only covers and wraps the upper surface of the composite interface layer (using a lower current density and special additives, so that copper ions can only grow preferentially in the vertical direction on the existing conductive surface (the upper surface of the composite interface layer), suppressing their lateral epitaxial growth and precipitation, so that the maximum width of the cross-section of the composite metal electrode is equal to the bottom width of the silver seed layer). Other settings are the same as in Embodiment 1.

[0131] Example 7 This embodiment provides a back-contact solar cell with a composite metal electrode. The only difference from Embodiment 1 is that the thickness of the copper main electrode layer at the edge of the composite interface layer pattern is 5% greater than the thickness at the center of the pattern; other settings are the same as in Embodiment 1.

[0132] Example 8 This embodiment provides a back-contact solar cell with a composite metal electrode. The only difference from Embodiment 1 is that the thickness of the copper main electrode layer at the edge of the composite interface layer pattern is 55% greater than the thickness at the center of the pattern; other settings are the same as in Embodiment 1.

[0133] Example 9 This embodiment provides a back-contact solar cell with a composite metal electrode. The only difference from Embodiment 1 is that in step (4), the metal protective layer is a pure silver layer; the solution used in the chemical immersion plating process includes, by mass concentration: 2 g / L silver nitrate, 200 g / L sodium thiosulfate, 20 g / L potassium metabisulfite, and purified water as the solvent.

[0134] Example 10 This embodiment provides a back-contact solar cell with a composite metal electrode. The only difference from Embodiment 1 is that in step (4), the metal protective layer is a pure silver layer; the solution used in the chemical immersion plating process includes, by mass concentration: 1.5 g / L silver nitrate, 180 g / L sodium thiosulfate, 15 g / L potassium metabisulfite, and purified water as the solvent.

[0135] Example 11 This embodiment provides a back-contact solar cell with a composite metal electrode. The only difference from Embodiment 1 is that in step (4), the metal protective layer is a pure silver layer; the solution used in the chemical immersion plating process includes, by mass concentration: 2.5 g / L silver nitrate, 220 g / L sodium thiosulfate, 25 g / L potassium metabisulfite, and purified water as the solvent.

[0136] Comparative Example 1 This comparative example provides a back-contact solar cell, which differs from Example 1 only in that the composite interface layer is no longer provided; the other settings are the same as in Example 1.

[0137] Comparative Example 2 This comparative example provides a back-contact solar cell, which differs from Example 1 only in that the composite interface layer is replaced with a copper layer; in step (2) of the preparation process, gradient annealing is no longer performed after copper electroplating; other settings are the same as in Example 1.

[0138] Test Example 1 Test samples: Back-contact solar cells with composite metal electrodes provided in Examples 1-11, and back-contact solar cells (G12 size) provided in Comparative Examples 1-2.

[0139] Test method: (1) Contact resistivity test: The back contact solar cell is cut into strips along the main grid direction, and the sheet resistance of the metal electrodes in the P region and N region is measured by the four-probe method. The contact resistivity (mΩ·cm²) is calculated. (2) Electrical performance tests (photoelectric conversion efficiency, open circuit voltage, series resistance, fill factor); specifically, the tests were conducted at AM1.5G spectrum, 1000 W / m² light intensity, and 25°C battery temperature. (3) Welding tensile test: Welding tensile test (300~350℃) is performed on the PAD points on the metal electrode (the tensile force on the back of the BC battery is ≥0.8N on average of 12 PAD points to be qualified).

[0140] The test results are shown in Table 1 below: Table 1

[0141] As shown in Table 1, the composite metal electrode structure provided by this invention replaces the thick silver grid lines, which play a dominant conductive role in traditional back-contact batteries, with an ultrathin silver layer that only serves as a seed and contact element. This significantly reduces silver material consumption and lowers manufacturing costs. Simultaneously, a deposited ultrathin composite interface layer fills the pores of the silver seed layer. This composite interface layer is a copper-silver metallurgical interlocking and diffusion-barrier composite layer, achieving atomic-level metallurgical bonding and generating nanoscale mechanical interlocking, resulting in ultra-high adhesion and extremely low contact resistance between the copper and silver layers. Furthermore, the deposited copper main electrode layer forms a three-dimensional coating on the surface and sidewalls of the silver seed layer and extends outwards, creating an "anchoring" effect that improves the bonding force between the copper and silver layers and enhances the welding pull force of the solar cell.

[0142] The comparison between Examples 1 and Examples 4-5 shows that when the gradient range of the percentage of copper atoms in the composite interface layer of Examples 4-5 deviates from more than 50% to less than 20%, the contact resistivity increases and the electrical properties and welding pull decrease compared to Example 1. This indicates that the gradient distribution plays a key role in the interfacial bonding strength and electrical conductivity. Exceeding this range will weaken the metallurgical interlocking effect and diffusion barrier ability, affecting the reliability of the electrode.

[0143] A comparison of Examples 1 and 6 shows that when the copper main electrode layer only covers the upper surface of the composite interface layer without sidewall coverage or protrusions, the contact resistivity increases significantly and the welding pull decreases. This indicates that the three-dimensional coating structure and the "anchoring" effect are crucial for improving interface adhesion and reducing contact resistance. The absence of this structure will weaken the mechanical bond and electrical performance, affecting the overall reliability of the electrode.

[0144] A comparison of Examples 1 and 7-8 shows that when the edge thickness increment of the copper main electrode layer is less than 10% or more than 50%, both welding tensile strength and electrical properties decrease. This indicates that a moderate edge thickness increase (10-50%) can optimize stress distribution and enhance the "anchoring" effect; too small an increase results in insufficient coverage, while too large an increase exacerbates lattice distortion and affects interface stability. This range is the key process window for achieving a synergistic improvement in both adhesion and resistance.

[0145] A comparison of Examples 1 and 9-11 shows that when a pure silver metal protective layer is used, the contact resistivity increases slightly and the welding pull force decreases. This indicates that the tin-based protective layer is superior to the silver-based layer in terms of solderability and interfacial conductivity, which may be related to its better wettability and lower interfacial barrier.

[0146] As can be seen from the comparison between Example 1 and Comparative Example 1, the contact resistivity increases significantly after omitting the composite interface layer, and the photoelectric conversion efficiency, open circuit voltage and welding pull force all decrease significantly. This indicates that the copper-silver metallurgical interlocking layer is crucial for forming atomic-level bonding, reducing interface resistance and enhancing adhesion. The absence of this layer leads to weakened copper-silver interface bonding, diffusion control failure, and seriously affects the electrical performance and mechanical reliability of the electrode.

[0147] A comparison of Example 1 and Comparative Example 2 shows that when the composite interface layer is replaced with a pure copper layer without gradient annealing, the contact resistivity increases significantly, and the electrical properties and weld pull strength decrease markedly. This indicates that the copper layer formed without annealing lacks a copper-silver metallurgical interlocking structure and compositional gradient, resulting in weak interfacial bonding, poor diffusion control, and a tendency to produce voids and stress concentrations. The metallurgical interlocking layer formed by gradient annealing is the key to achieving low resistance and high adhesion.

[0148] This demonstrates that the absence of a composite metal layer (metallic interlocking layer) results in a purely physical contact between the copper and silver interfaces, leading to a high-resistivity interface and micro-gap, which increases the carrier transport barrier. Furthermore, the weak interface adhesion makes it prone to peeling under thermal stress, causing a surge in resistivity and electrical failure.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite metal electrode, characterized in that, It includes a silver seed layer, a composite interface layer, a copper main electrode layer, and a metal protective layer; The composite interface layer is a copper-silver metallurgical interlocking layer.

2. The composite metal electrode according to claim 1, characterized in that, The silver seed layer is a conductive thin film with microscopic roughness and porous morphology. Preferably, the roughness of the silver seed layer is 20~100 nm; Preferably, the pore size of the silver seed layer is 10~50 nm; Preferably, the thickness of the silver seed layer is 0.5~3 μm.

3. The composite metal electrode according to claim 1, characterized in that, The atomic percentage of copper in the composite interface layer decreases continuously from more than 50% on the side closer to the copper main electrode layer to less than 20% on the side closer to the silver seed layer. Preferably, the thickness of the composite interface layer is 50~500 nm; Preferably, the average grain size of copper in the composite interface layer is less than 100 nm; Preferably, the composite interface layer contains silver-rich nanoparticles dispersed within it. Preferably, the size of the silver-rich nanoparticles is 5~20 nm.

4. The composite metal electrode according to claim 1, characterized in that, The copper main electrode layer covers and wraps the upper surface of the composite interface layer, as well as the sidewalls of the silver seed layer and the composite interface layer. Preferably, in a cross-section perpendicular to the length of the metal electrode, the outline of the copper main electrode layer extends outward at positions corresponding to the two side edges of the composite interface layer to form a protrusion, such that the maximum width of the cross-section of the composite metal electrode is greater than the bottom width of the silver seed layer. Preferably, the thickness of the copper main electrode layer is 5~20 μm; Preferably, the thickness of the copper main electrode layer at the edge of the composite interface layer is 10-50% greater than its thickness at the center of the pattern.

5. The composite metal electrode according to claim 1, characterized in that, The metal protective layer is a solderable metal layer; Preferably, the material of the solderable metal layer is selected from any one or a combination of at least two of pure tin, pure silver, tin alloy, and silver alloy; Preferably, the thickness of the solderable metal layer is 0.5~2 μm.

6. A method for preparing a composite metal electrode according to any one of claims 1 to 5, characterized in that, The preparation method includes: A silver seed layer, a composite interface layer, a copper main electrode layer, and a metal protective layer are prepared on the surface of a substrate to obtain the composite metal electrode.

7. The method for preparing the composite metal electrode according to claim 6, characterized in that, The silver seed layer and the composite interface layer are prepared by the following steps: Silver paste is printed onto the surface of a substrate by screen printing, and then sintered to obtain a silver metal layer. The substrate with the silver metal layer is immersed in a first copper electroplating solution for electroplating, and then subjected to gradient annealing to obtain a silver seed layer and a composite interface layer. Preferably, the sintering temperature is 700~850℃, and the sintering time is 0.5~5 min; Preferably, the thickness of the silver metal layer is 0.5~3 μm; Preferably, the first copper electroplating solution comprises, by mass concentration: 50-80 g / L copper sulfate, 250-350 g / L potassium pyrophosphate, 20-30 g / L ammonium citrate, and 10-20 g / L potassium nitrate, with water as the solvent; Preferably, the electroplating is constant current electroplating; Preferably, the current density of the constant current electroplating is 0.5~2.0 A / dm³. 2 The constant current electroplating time is 15~60s; Preferably, the gradient annealing process includes: first heating to 150~250℃ and holding for 15~30 s; then heating to 300~450℃ and holding for 30~60 s; Preferably, the annealing heating rate in the gradient program is 5~10℃ / min; Preferably, the thickness of the silver seed layer is 0.5~3 μm; and the thickness of the composite interface layer is 50~500 nm.

8. The method for preparing the composite metal electrode according to claim 6, characterized in that, The method for preparing the copper main electrode layer includes: The substrate with a silver seed layer and a composite interface layer is immersed in a second copper electroplating solution for main electroplating to obtain a copper main electrode layer. Preferably, the second copper electroplating solution comprises, by mass concentration: 50-80 g / L copper sulfate, 250-350 g / L potassium pyrophosphate, 20-30 g / L ammonium citrate, and 10-20 g / L potassium nitrate, with water as the solvent; Preferably, the main electroplating is constant current electroplating; Preferably, the current density of the constant current electroplating is 5~10 A / dm³. 2 The constant current electroplating time is 5~10 min; Preferably, the method for preparing the metal protective layer includes: The composite metal electrode is obtained by preparing the metal protective layer on the surface of the copper main electrode layer through a chemical immersion plating process. Preferably, the temperature of the chemical immersion plating process is 40~70℃; the chemical immersion plating time is 1~5 min; and the thickness of the metal protective layer formed by the chemical immersion plating is 0.5~2 μm. Preferably, the solution used in the chemical immersion plating process comprises, by mass concentration: 15-40 g / L stannous chloride, 80-150 g / L thiourea, 50-100 g / L concentrated hydrochloric acid, 10-30 g / L sodium hypophosphite, and water as the solvent; Preferably, the solution used in the chemical immersion plating process comprises, by mass concentration: 1.5~2.5 g / L silver nitrate, 180~220 g / L sodium thiosulfate, and 15~25 g / L potassium metabisulfite, with water as the solvent.

9. A solar cell, characterized in that, The solar cell includes a composite metal electrode as described in any one of claims 1 to 5, or a composite metal electrode prepared by the preparation method as described in any one of claims 6 to 8.

10. A photovoltaic module, characterized in that, The photovoltaic module includes the solar cell as described in claim 9.

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