Copper-clad aluminum efficient circular welding strip, preparation method thereof and photovoltaic module

Abstract

The invention relates to the technical field of novel conductor materials, in particular to a copper-clad aluminum efficient circular welding strip, a preparation method thereof and a photovoltaic module. The solder strip comprises an aluminum core, a copper layer, a silver-coated copper coating and a tin-based alloy layer which are arranged from inside to outside. The preparation method comprises the steps of providing the copper-clad aluminum base material, coating the silver-clad copper coating, carrying out hot dipping on the tin-based alloy and the like. The photovoltaic module adopts the solder strip and is in welded connection with the battery piece through the solder paste layer. Through the unique four-layer structural design, low cost and light weight are ensured, and meanwhile, the surface conductivity and the light reflectivity are improved by utilizing the silver-coated copper coating, so that the power of the module is increased. By combining an intelligent preparation process and an optimized welding structure, the problems that an existing copper-clad aluminum welding strip is high in resistance, large in optical loss, poor in performance consistency and the like are systematically solved, and the performance, reliability and production efficiency of a photovoltaic module are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of novel conductor materials technology, specifically to a copper-clad aluminum high-efficiency circular solder strip and its preparation method, and a photovoltaic module. Background Technology

[0002] Photovoltaic solder ribbons are crucial components in solar cell modules, enabling electrical connections between cells and collecting current. Their performance directly impacts the module's output power, reliability, and manufacturing cost. With the photovoltaic industry's increasing urgency to reduce costs and increase efficiency, traditional pure copper solder ribbons, due to the high price and density of copper, have become a significant factor restricting cost reduction and module lightweighting. To address this, the industry has proposed copper-clad aluminum solder ribbons, using aluminum as the core material to reduce cost and weight, while a copper outer layer ensures conductivity. However, this solution still has significant drawbacks: First, while the introduction of an aluminum core reduces costs, aluminum's conductivity is far inferior to copper, leading to increased overall solder ribbon resistance and power loss. Second, the surface of existing copper-clad aluminum solder ribbons is mostly pure copper or simply tin-plated, with limited reflectivity to incident sunlight, failing to effectively utilize the area of ​​the cells shaded by the solder ribbon, resulting in optical loss. Third, conventional coating structures struggle to further optimize surface conductivity and light reflection performance while ensuring excellent weldability. Furthermore, current manufacturing processes rely heavily on fixed parameters, failing to adapt to fluctuations in raw materials and changes in equipment status, resulting in insufficient product performance consistency. Therefore, there is an urgent need for a new type of solder strip structure and its intelligent manufacturing method, which can comprehensively improve its electrical and optical properties and production quality stability while taking into account the advantages of low cost and lightweight, so as to meet the development needs of high-efficiency photovoltaic modules.

[0003] Therefore, the existing technology still needs further development. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a copper-clad aluminum high-efficiency circular welding strip and its preparation method, as well as a photovoltaic module, to solve the problems existing in the prior art.

[0005] To achieve the above-mentioned technical objectives, according to a first aspect of the present invention, the present invention provides a high-efficiency circular copper-clad aluminum solder strip, comprising: It includes an aluminum core arranged from the inside out, a copper layer surrounding the aluminum core, a silver-coated copper coating applied to the surface of the copper layer, and a tin-based alloy layer covering the silver-coated copper coating.

[0006] Specifically, the silver-coated copper in the silver-coated copper coating is in powder form, with a copper powder core and a silver layer encapsulating the copper powder on the outside.

[0007] Specifically, the thickness of the silver-coated copper coating is less than or equal to 5 μm.

[0008] Specifically, the thickness of the copper layer is 1-50 μm.

[0009] Specifically, the thickness of the tin-based alloy layer is less than or equal to 5 μm.

[0010] According to a second aspect of the present invention, a method for preparing a high-efficiency circular copper-clad aluminum solder strip is provided, comprising: S100, Provides a copper-clad aluminum substrate, which consists of an aluminum core and a copper layer surrounding it; S200: Coating the surface of the copper layer with silver-coated copper paste to form a silver-coated copper coating; S300. The substrate coated with the silver-coated copper coating is hot-dip plated with a tin-based alloy to form a tin-based alloy layer.

[0011] Specifically, prior to S200, the process also includes an annealing heat treatment step on the copper-clad aluminum substrate.

[0012] According to a third aspect of the present invention, a photovoltaic module is provided, comprising at least one cell string, wherein the cell string is formed by connecting multiple cells in series or in parallel via copper-clad aluminum high-efficiency circular solder strips as described in any one of the preceding claims; a solder paste layer is printed on the main grid line of the cell, and the copper-clad aluminum high-efficiency circular solder strips are soldered to the cell via the solder paste layer.

[0013] Specifically, the composition of the solder paste layer is SnPb or SnPbBi tin-based alloy.

[0014] Specifically, the finished diameter of the copper-clad aluminum high-efficiency circular welding strip is 0.10-0.45mm.

[0015] Beneficial effects: The copper-clad aluminum high-efficiency circular solder strip and its preparation method provided by this invention, along with photovoltaic modules, have produced significant and multifaceted beneficial effects compared to existing technologies.

[0016] First, in terms of product structure, the unique four-layer configuration of "aluminum core - copper layer - silver-clad copper coating - tin-based alloy layer" achieves the gradient and optimal configuration of functional materials. The aluminum core undertakes the core function of significantly reducing cost and weight; the copper layer ensures excellent bulk conductivity; the silver-clad copper coating, under the premise of controllable cost, utilizes the extremely high conductivity and reflectivity of silver to effectively improve the current transmission efficiency of the solder strip surface (especially under the skin effect) and reflect more light back to the solar cell. At the same time, the silver-clad copper coating uses copper powder of nano to submicron scale as the core, which significantly increases the specific surface area of ​​the powder, making the outer silver coating more efficient. It can form a denser and more continuous conductive and reflective network in the coating, thereby reducing the amount of precious metal silver used while further optimizing the electrical and optical performance of the coating. The outermost tin-based alloy layer provides excellent solderability and can form a good metallurgical bond with various main grid silver pastes, thereby improving the module power output in both electrical and optical dimensions. This composite structure systematically solves the problem of balancing cost, weight, conductivity, weldability, and optical performance.

[0017] Secondly, in terms of manufacturing methods, a creative closed-loop control system for real-time optimization of process parameters based on deep learning has been introduced. This system collects key process parameters online and uses a trained deep learning model (such as an LSTM network incorporating attention mechanisms) to predict product quality in real time and optimize the parameters of preceding processes. This transforms the manufacturing process from an "open-loop" mode that relies on fixed experience to an "adaptive" intelligent mode that can sense fluctuations and make autonomous decisions, significantly improving the consistency, stability, and yield of product performance, and realizing the deep application of intelligent manufacturing in precision material processing.

[0018] Third, at the component integration level, by using a "solder paste layer" as a welding medium to connect the solder ribbon to the main busbar of the solar cell, the welding thermal stress is reduced, allowing for the use of thinner solder ribbons to further reduce light shading, and improving the reliability and uniformity of the welding interface. This structure is particularly suitable for new high-efficiency solar cells that are sensitive to heat. The solder paste layer is a tin-based alloy such as SnPb or SnPbBi, with a wide range of selectable melting points, which can adapt to the welding process requirements of different solar cells (such as temperature-sensitive HJT cells), and has good compatibility.

[0019] In summary, this invention innovates in material structure design, intelligent production processes, and end-application models, forming a complete high-performance, low-cost, and highly consistent photovoltaic interconnection solution. It has outstanding comprehensive technical effects and possesses high industrial application value and market competitiveness. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process for providing high-efficiency circular copper-clad aluminum welding strips in a specific embodiment of the present invention; Figure 2 This is a schematic diagram of the system composition of the method for preparing high-efficiency circular copper-clad aluminum solder strip provided in a specific embodiment of the present invention. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application. Furthermore, directional terms mentioned in the following embodiments, such as "up," "down," "left," and "right," are only for reference to the directions in the accompanying drawings; therefore, the directional terms used are for illustrative purposes and not for limiting the invention.

[0022] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments.

[0023] Please see Figure 1 This invention provides a high-efficiency circular copper-clad aluminum solder strip, comprising: It includes an aluminum core arranged from the inside out, a copper layer surrounding the aluminum core, a silver-coated copper coating applied to the surface of the copper layer, and a tin-based alloy layer covering the silver-coated copper coating.

[0024] It should be further explained that the core product structure protected by this invention is a multi-layered composite circular solder ribbon. Its innermost layer is an aluminum core, whose main function is to serve as the substrate for the conductor. Utilizing the advantages of aluminum's low cost and light weight, it replaces expensive and high-density pure copper, thereby significantly reducing raw material costs and the overall weight of the solder ribbon. This is of great significance for large-scale photovoltaic modules. The middle layer is a copper layer encasing the aluminum core, whose key function is to provide an excellent conductive surface. Because the surface of aluminum is easily oxidized to form a high-resistivity oxide layer, its direct solderability and conductivity are poor. Copper, on the other hand, has conductivity second only to silver, and its oxide is relatively easy to handle. The copper layer acts as a barrier between the aluminum core and the external environment, ensuring the overall low resistance and high reliability of the solder ribbon. The outer layer structure consists of two parts: first, a silver-coated copper coating directly applied to the copper layer. In this coating, the silver-coated copper powder is a composite powder with copper powder as the core and a layer of silver coating on the surface. Silver is the best known conductor of electricity. This design aims to form a highly conductive channel on the outermost layer of the solder strip, which is particularly beneficial for current transport under high frequency or high current conditions (skin effect). Simultaneously, the high reflectivity of the silver layer effectively reflects sunlight onto the solder strip back to the solar cell, increasing the generation of photogenerated carriers and thus improving module power. Compared to a pure silver coating, this silver-clad copper design significantly reduces material costs while maintaining most of the conductivity and reflectivity. The outermost layer is a tin-based alloy layer, whose main component is tin, and may contain alloying elements such as lead (Pb), bismuth (Bi), silver (Ag), and copper (Cu). The main function of this layer is to provide excellent solderability. Tin and its alloys can form a strong intermetallic compound with the silver paste on the main busbar of the solar cell, achieving low-resistance, high-strength ohmic contacts. The tin-based alloy layer also protects the internal copper layer and silver-clad copper coating from oxidation and corrosion, ensuring the stability of the solder strip throughout the storage and module lifecycle. These four layers work together to resolve the contradictions that cannot be balanced in terms of cost, weight, conductivity, weldability, and optical performance when using a single material or simple structure for the solder strip, thus achieving a balance between high performance and low cost.

[0025] Specifically, the silver-coated copper in the silver-coated copper coating is in powder form, with a copper powder core and a silver layer encapsulating the copper powder on the outside.

[0026] It should be further explained that the present invention specifically optimizes the microstructure of the silver-coated copper coating. The silver-coated copper powder is a composite powder prepared by processes such as chemical plating or physical coating, wherein the particle size of the copper powder is preferably controlled between 20 nm and 1 μm. The reason for choosing this particle size range is that when the particle size is less than 1 μm, especially when entering the nanoscale (<100 nm), the specific surface area of ​​the powder increases dramatically, allowing the silver coating layer to cover the copper core surface more uniformly and effectively, forming a higher-quality core-shell structure. This helps to construct a more complete conductive path and reflective interface in the coating. If the particle size is less than 20 nm, the powder is prone to agglomeration, significantly increasing the difficulty and cost of dispersion; if the particle size is greater than 1 μm, the aforementioned specific surface area advantage is weakened, and the surface roughness of the coating may increase. The preferred range is 50 nm to 500 nm, within which the best balance between processability, cost, and performance can be achieved. The coating thickness of the silver layer is preferably 0.1 μm to 0.5 μm. The determination of this thickness range is based on the balance between conductivity and cost: a thickness of 0.1 μm or more can basically form a continuous silver conductive network, ensuring a significant improvement in conductivity; however, when the thickness exceeds 0.5 μm, the cost increases significantly, while the improvement in conductivity tends to level off, and the marginal benefits decrease.

[0027] Understandably, this core-shell structure allows the expensive silver material to exist only in the surface layer where its performance is most needed, while the interior uses a large amount of inexpensive copper, achieving an optimal balance between function and cost. The solid content of the silver-coated copper powder in the slurry is preferably 60% to 80%, and it is combined with an organic carrier (such as ethyl cellulose dissolved in terpineol) and a dispersant. High-speed stirring and grinding are used to ensure uniform dispersion of the powder, which is a prerequisite for forming a high-quality coating.

[0028] Specifically, the thickness of the silver-coated copper coating is less than or equal to 5 μm.

[0029] It should be further noted that this invention specifies the upper limit of the thickness of the silver-coated copper coating. Controlling the coating thickness to ≤5μm is based on multiple engineering considerations: First, from the perspective of conductivity, when the coating thickness exceeds 5μm, its contribution to reducing DC resistance is no longer significant, because current transmission is mainly concentrated on the surface of the conductor.

[0030] Secondly, from a mechanical performance perspective, an excessively thick coating may reduce the overall flexibility of the solder strip, increasing the risk of coating cracking or peeling during subsequent drawing, bending, or welding processes, thus affecting reliability.

[0031] Third, from an optical performance perspective, excessively thick coatings have a diminishing marginal effect on improving light reflectivity. Most importantly, from a cost-control perspective, a thickness of ≤5μm is sufficient to improve surface conductivity and reflectivity while minimizing the use of precious silver. The preferred thickness range is 2μm to 4μm, within which a continuous, defect-free coating is ensured while achieving the best cost-effectiveness ratio. Coating uniformity is crucial; its thickness tolerance should be controlled within ±0.5μm, which can be achieved through precise control of the coating speed, slurry viscosity, and subsequent drying process.

[0032] Specifically, the thickness of the copper layer is 1-50 μm.

[0033] It should be further explained that this invention limits the thickness range of the copper layer in the copper-clad aluminum substrate. The copper layer thickness is a key parameter affecting the performance of the solder ribbon. The lower limit of 1 μm is set to ensure that the copper layer can completely and continuously encapsulate the aluminum core, preventing the aluminum core from being exposed due to localized thinning or even breakage of the copper layer during subsequent processing or use, which would lead to oxidation and a sharp decline in conductivity. The upper limit of 50 μm is mainly based on cost and weight considerations. As the copper layer thickness increases, the cost of the solder ribbon increases linearly, and the weight also increases accordingly. When the thickness exceeds 50 μm, its improvement on overall conductivity is negligible because most of the current is already transmitted in the copper layer; further thickening does not bring substantial benefits and is actually counterproductive. For solder strips of different diameters, the copper layer thickness can be optimized: for fine solder strips with a finished diameter of 0.10mm to 0.25mm, a copper layer thickness of 5-20μm is preferred to ensure sufficient mechanical strength; for thicker solder strips with a finished diameter of 0.25mm to 0.45mm, a copper layer thickness of 20-40μm is preferred to carry a larger current. Furthermore, the bonding strength between the copper layer and the aluminum core is also crucial, requiring control of the drawing process parameters to achieve a strength of over 100MPa to ensure no delamination occurs during use.

[0034] Specifically, the thickness of the tin-based alloy layer is less than or equal to 5 μm.

[0035] It should be further noted that the thickness of the tin-based alloy layer is less than or equal to 5 μm. Furthermore, this invention limits the thickness of the outermost tin-based alloy layer. The main function of the tin-based alloy layer is to ensure solderability, and its thickness of ≤5 μm is an optimized design. An excessively thin tin-based alloy layer (e.g., less than 1 μm) may result in insufficient alloy content during soldering, failing to form a strong solder joint with the main grid lines of the solar cell, affecting connection reliability. Conversely, an excessively thick tin-based alloy layer (e.g., much thicker than 5 μm) presents several problems: firstly, increased cost, as tin and its alloy components are expensive metals; secondly, during hot-dip plating, an excessively thick alloy layer may cause slight changes in the roundness of the solder strip due to surface tension, affecting geometric uniformity; and thirdly, during soldering, excessive molten alloy may flow to other areas of the solar cell, creating a short-circuit risk. Controlling the thickness of the tin-based alloy layer to ≤5 μm, preferably 2-4 μm, can ensure excellent solderability while avoiding the aforementioned problems. This thickness of tin-based alloy layer is sufficient to fully melt at the soldering temperature. The tin component reacts with the main gate silver paste to form a moderately thick, uniformly composed intermetallic compound layer (such as Ag3Sn), thereby achieving a low-resistance, high-strength connection. The tin-based alloy layer can be composed of lead-free Sn-Bi, Sn-Ag-Cu alloys, or leaded Sn-Pb alloys, selected according to different environmental requirements and process conditions.

[0036] Please see Figure 2 The present invention provides another embodiment, which provides a method for preparing a high-efficiency circular copper-clad aluminum solder strip, the method comprising: S100, Provides a copper-clad aluminum substrate, which consists of an aluminum core and a copper layer surrounding it; It should be further explained that this invention protects the preparation method of the aforementioned solder strip. The copper-clad aluminum substrate in S100 is typically prepared as follows: an aluminum rod with a diameter of approximately 9.8 mm is selected and polished to remove the surface oxide layer and contaminants; simultaneously, a copper strip of corresponding width is prepared, and its surface is also cleaned. The copper strip is wrapped around the aluminum rod, and the butt joint is sealed using argon arc welding. Then, it is stretched and reduced in diameter using a multi-pass drawing die. During this process, copper and aluminum achieve atomic-level bonding under high pressure, forming a strong diffusion layer.

[0037] S200: Apply silver-coated copper paste to the surface of the copper layer to form a silver-coated copper coating. It should be further noted that the coating of the S200 silver-coated copper paste is a critical process, which can be carried out by extrusion coating or dip coating. After coating, a low-temperature drying stage (e.g., 150-250℃) is required to remove the organic solvents in the paste, so that the silver-coated copper powder can be firmly adhered to the copper layer surface. However, the temperature should not be too high to prevent excessive oxidation of copper or aluminum.

[0038] S300. The substrate coated with the silver-coated copper coating is hot-dip plated with a tin-based alloy to form a tin-based alloy layer.

[0039] It should be further explained that for S300 hot-dip tin-based alloy plating, the substrate must first be coated with flux (usually rosin-based or organic acid-based) before being immersed in a molten alloy bath. The alloy bath temperature is precisely controlled according to the alloy composition; for example, for Sn63Pb37, the temperature is controlled at 240-260℃. The immersion time is very short, typically 1-5 seconds, to ensure the formation of a uniform thin layer while avoiding excessive heat that could alter the internal structure. Excess molten tin is then removed using a nitrogen blade or centrifugation, and finally cooled, solidified, and wound up. The entire process must be carried out in a controlled atmosphere or environment to minimize oxidation.

[0040] Specifically, prior to S200, the process also includes an annealing heat treatment step on the copper-clad aluminum substrate.

[0041] It should be further explained that this invention adds a key optimization step to the core method—annealing heat treatment. This step is performed before coating the copper-clad aluminum paste. The specific process is as follows: the drawn copper-clad aluminum substrate is heated to 300°C to 450°C in a protective atmosphere (such as nitrogen or a nitrogen-hydrogen mixture) and held at that temperature for a period of time (e.g., 10 to 30 minutes), and then slowly cooled. This heat treatment serves three purposes: First, it eliminates the internal stress accumulated in the copper layer and aluminum core due to severe stretching deformation, preventing stress corrosion or dimensional instability during subsequent processing or use.

[0042] Second, it promotes further diffusion of atoms at the interface between the copper layer and the aluminum core, making the bond stronger and denser, increasing the bond strength from about 100 MPa before annealing to 150 MPa or even higher.

[0043] Third, it causes recrystallization of the copper layer's grains, resulting in larger grains and a reduction in the number of grain boundaries. Grain boundaries are the primary sites of electron scattering; reducing grain boundaries effectively lowers the resistivity of the copper layer itself and improves its conductivity.

[0044] Understandably, the annealed substrate has more stable mechanical and electrical properties, laying a solid foundation for subsequent high-quality coating and tin-based alloy plating.

[0045] It should be further noted that the present invention also includes step S400: Establish an online quality prediction and control system, which includes: 410. Data Acquisition Layer: Deploy a sensor network at key workstations from step one to S300 to collect process parameters in real time. Specifically, this includes: After step one, the diameter of the substrate is measured using a laser diameter gauge. (Unit: mm); Before and after coating in step two, the thickness of the silver-coated copper coating was measured using an online ellipsometry. (Unit: μm); In the hot-dip tin-based alloy plating process of S300, an infrared thermal imager is used to monitor the alloy bath temperature. (Unit: °C) and substrate immersion time (Unit: s), and the conductivity of the finished solder strip was measured using an eddy current conductivity meter after cooling. (Unit: %IACS) is used as a key quality indicator.

[0046] 420. Intelligent Decision Layer: Construct a deep neural network model whose input feature vectors... It consists of real-time acquired process parameters and historical window data, and the output is the final conductivity. The predicted values ​​and the key process parameters (such as coating speed) Alloy bath temperature The model provides optimization suggestions. It is trained using historical production data (including parameters and corresponding final product quality data) to learn the complex nonlinear mapping relationship between process parameters and final performance.

[0047] 430. Feedback Control Layer: This layer processes the conductivity predicted by the model. With target conductivity (For example, based on 97% conductivity of pure copper solder strip). If the deviation exceeds the allowable range (e.g., ±2%), the system automatically generates control commands to fine-tune the settings of the preceding process, such as adjusting the coating speed by adjusting the motor speed of the coating machine. Alternatively, the temperature of the alloy bath can be fine-tuned by adjusting the heater power. This forms a real-time adaptive optimization closed-loop control system.

[0048] Understandably, this invention upgrades the traditional manufacturing process into an intelligent agent of "perception-decision-control." Its core benefit lies in overcoming the bottleneck of traditional methods that rely on fixed empirical parameters and struggle to cope with quality instability caused by minor fluctuations in raw material values ​​and gradual changes in equipment status. Through deep learning models, the system can extract complex patterns from massive amounts of production data that are difficult for the human brain to summarize, such as "when the substrate diameter..." If the coating speed increases slightly, reduce it appropriately. And slightly increase the temperature of the alloy bath. This can offset the differences in alloying degree at the weld interface caused by changes in heat capacity, thereby stabilizing the final conductivity. This adaptive capability ensures that every meter of solder strip has highly consistent and optimal electrical performance, significantly reducing the defect rate, realizing an industrial upgrade from "experience-driven" to "data-driven", and significantly enhancing the advancement and creativity of the patent.

[0049] Furthermore, the deep neural network model preferably employs a Long Short-Term Memory (LSTM) network model incorporating an attention mechanism to simultaneously process current parameters and remember the influence of historical process sequences. Its specific construction and training steps are as follows: 1. Input Feature Engineering: The model inputs feature vectors. It is a multidimensional time series, at time... It includes: Current substrate diameter.

[0050] : The coating thickness currently being measured.

[0051] Current alloy bath temperature.

[0052] Current coating speed.

[0053] :forward The above parameter sequence at each time step, The time window size is 10, with a preferred value of 10. The rationale for choosing this value is that it covers the entire production cycle from the substrate to the completion of the tin-based alloy plating, capturing the causal process dynamics.

[0054] 2. Network Structure: ① Input layer: The number of neurons equals the feature dimension (e.g., 5 current features + 5 × 10 ... A historical characteristic.

[0055] ②LSTM Hidden Layers: Use two LSTM layers, with 128 hidden units per layer being preferred. This choice is based on a balance between model complexity and the amount of training data. Too few units (e.g., 64) may prevent the model from learning sufficiently complex features, while too many units (e.g., 256) can easily lead to overfitting with limited data.

[0056] ③ Attention Layer: Connects to the output of the LSTM layer and calculates the attention weights for each historical time step. The calculation formula is as follows: in, It is a scaled dot product scoring function: .

[0057] : No. The attention weight of each historical time step represents its importance to the current prediction.

[0058] LSTM networks in the 19th century The hidden state at each time step.

[0059] : The LSTM network at the last (current) time step The hidden state.

[0060] Hidden state The dimension is 128 in this case.

[0061] ④ Fully connected output layer: Maps the weighted context vector to the final predicted value. .

[0062] 3. Model Training: ①Loss function: Use mean squared error loss (MSELoss) combined with L2 regularization.

[0063] The number of samples in a batch.

[0064] Model for the first Predicted conductivity of each sample.

[0065] : No. The actual measured conductivity of each sample.

[0066] L2 regularization coefficient, with a preferred value of 0.01, is used to prevent overfitting.

[0067] All weight parameters of the model The sum of squares (L2 norm).

[0068] ② Optimizer: The Adam optimizer is used, with an initial learning rate of 0.001. The learning rate is halved when the validation set loss no longer decreases for 5 consecutive epochs.

[0069] ③ Training threshold: Training is terminated early when the model's prediction error (MAE) on the validation set is below a preset threshold (e.g., 0.5% IACS) for 10 consecutive epochs to prevent overfitting. This threshold is chosen because it is less than one-quarter of the product quality tolerance (±2%), ensuring that the prediction accuracy meets the control requirements.

[0070] In a preferred embodiment, this application also provides a photovoltaic module, the photovoltaic module comprising: At least one battery string, wherein multiple battery cells are connected in series or in parallel by copper-clad aluminum high-efficiency circular solder strips as described in any one of the above-mentioned methods; a solder paste layer is printed on the main grid line of the battery cell, and the copper-clad aluminum high-efficiency circular solder strips are soldered to the battery cell through the solder paste layer.

[0071] It should be further explained that this invention protects a photovoltaic module using the aforementioned copper-clad aluminum high-efficiency circular solder ribbon. The core innovation of this module lies in its unique welding structure. Unlike traditional solder ribbons that are directly welded to the main busbars of the solar cells, this solution introduces a "solder paste layer" as a welding medium. In specific implementation, a layer of solder paste is first printed on the main busbar areas of the front and back sides of the crystalline silicon solar cell using high-precision screen printing or dispensing technology. The chemical composition of the solder paste can be selected from alloys such as Sn63Pb37, Sn60Pb40, or SnPbBi, and its metal powder particle size is preferably 20μm to 45μm, mixed with flux, thixotropic agents, etc. After printing, the solar cell enters a heating zone (e.g., infrared heating or hot air heating) and undergoes a brief preheating (reflow soldering) at a temperature of 180°C to 220°C to activate the flux in the solder paste and remove oxides. Subsequently, the solder powder melts and forms a preliminary alloyed connection with the silver paste on the main busbars of the solar cell. Then, the copper-clad aluminum high-efficiency circular solder ribbon is precisely laid on the cured solder paste layer. Finally, the main soldering is performed using a string soldering machine, which uses infrared heat sources to reheat the solder ribbon and solder paste layer, causing the solder paste layer to melt again and fuse with the outermost tin-based alloy layer of the solder ribbon. After cooling, a strong three-layer composite connection structure of "cell-solder paste alloy layer-solder ribbon" is formed. The advantages of this structure are: 1. Reduced soldering thermal stress, as the solder paste layer acts as a buffer, reducing the direct thermal shock and mechanical stress of the solder strips on the brittle solar cells.

[0072] 2. Thinner solder strips are allowed because soldering does not solely depend on the amount of solder on the solder strip; the solder paste provides additional soldering material, and the surface tension effect of thin solder strips is beneficial for light reflection.

[0073] 3. Improved welding reliability and consistency, with lower and more stable contact resistance.

[0074] Specifically, the solder paste layer is composed of tin-based alloys such as SnPb or SnPbBi.

[0075] It should be further explained that this invention specifies the alloy composition of the solder paste layer. Sn63Pb37 is a eutectic alloy with a melting point of 183°C. Its advantages include a low melting point, good fluidity, high weld strength, and a wide process window, making it a very mature soldering material. Sn60Pb40 is a near-eutectic alloy with a melting point between 183-190°C, and it also has excellent soldering performance. SnPbBi alloys, such as tin-lead alloys with a certain proportion of bismuth (Bi), can further reduce the melting point (down to around 140°C). Choosing SnPbBi alloys with lower melting points has significant advantages: it greatly reduces the thermal shock to the solar cells, helping to reduce micro-cracks in the cells caused by thermal stress, thereby improving module yield and long-term reliability. This is especially important for using ultra-thin solar cells or new battery technologies that are extremely sensitive to temperature (such as TOPCon and HJT). When selecting an alloy, it is necessary to weigh melting point, weld strength, cost, and environmental impact (such as lead-free requirements). The type and content of flux in solder paste also need to be precisely controlled, usually between 8% and 12%, to ensure sufficient activity and cleaning ability, while leaving little residue and having low corrosivity.

[0076] Specifically, the finished diameter of the copper-clad aluminum high-efficiency circular welding strip is 0.10-0.45mm.

[0077] It should be further noted that the finished diameter of the solder ribbon in this invention is limited to a preferred range. The diameter setting of 0.10mm to 0.45mm covers the current mainstream photovoltaic module's requirements for solder ribbon size. The selection of the diameter needs to comprehensively consider current carrying capacity, shading loss, mechanical strength, and welding processability. If the diameter is too small (e.g., less than 0.10mm), its mechanical strength may be insufficient, making it easy to break or deform during laying and welding, and the resistance per unit length increases, which may lead to overheating in high-current applications. If the diameter is too large (e.g., greater than 0.45mm), although the current carrying capacity is enhanced, its shading area on the solar cell increases, reducing the effective light-receiving area of ​​the solar cell, thereby reducing the module's short-circuit current and final output power. At the same time, excessively thick solder ribbons are also harder and not easy to adhere tightly to the surface of the solar cell. Therefore, the following selections are made within this range: for components that prioritize high conversion efficiency and low current, a fine solder strip of 0.10-0.25 mm is preferred to minimize light shading; for components that prioritize high current output and high reliability, a thicker solder strip of 0.25-0.45 mm is preferred. The copper-clad aluminum structure of this invention, due to the low density of the aluminum core, results in a significantly smaller weight increase even when using a slightly larger diameter solder strip compared to a pure copper solder strip of the same size—an additional advantage.

[0078] The technical features described above can be combined arbitrarily. Although not all possible combinations of these technical features are described, any combination of these technical features should be considered to be covered by this specification, provided that such combination does not contain contradictions.

[0079] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A high-efficiency circular copper-clad aluminum welding strip, characterized in that, It includes an aluminum core arranged from the inside out, a copper layer surrounding the aluminum core, a silver-coated copper coating applied to the surface of the copper layer, and a tin-based alloy layer covering the silver-coated copper coating.

2. The high-efficiency circular copper-clad aluminum welding strip according to claim 1, characterized in that, The silver-coated copper coating is in powder form, with copper powder as its core and a silver layer encapsulating the copper powder as its outer layer.

3. The high-efficiency circular copper-clad aluminum welding strip according to claim 1 or 2, characterized in that, The thickness of the silver-coated copper coating is less than or equal to 5 μm.

4. The high-efficiency circular copper-clad aluminum welding strip according to claim 1, characterized in that, The thickness of the copper layer is 1-50 μm.

5. The high-efficiency circular copper-clad aluminum welding strip according to claim 2 or 3, characterized in that, The thickness of the tin-based alloy layer is less than or equal to 5 μm.

6. A method for preparing a high-efficiency circular copper-clad aluminum solder strip as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S100, Provides a copper-clad aluminum substrate, which consists of an aluminum core and a copper layer surrounding it; S200: Coating the surface of the copper layer with silver-coated copper paste to form a silver-coated copper coating; S300. The substrate coated with the silver-coated copper coating is hot-dip plated with a tin-based alloy to form a tin-based alloy layer.

7. The preparation method according to claim 6, characterized in that, Before S200, the process also includes an annealing heat treatment step on the copper-clad aluminum substrate.

8. A photovoltaic module, characterized in that, It includes at least one battery string, wherein multiple battery cells are connected in series or in parallel by copper-clad aluminum high-efficiency circular solder strips as described in any one of claims 1 to 5; a solder paste layer is printed on the main grid line of the battery cell, and the copper-clad aluminum high-efficiency circular solder strips are soldered to the battery cell through the solder paste layer.

9. The photovoltaic module according to claim 8, characterized in that, The solder paste layer is composed of SnPb or SnPbBi tin-based alloy.

10. The photovoltaic module according to claim 9, characterized in that, The finished diameter of the copper-clad aluminum high-efficiency circular welding strip is 0.10-0.45 mm.

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