1、 Technical principles and composition
Silver coated copper technology is a composite metal material technology, and its core product silver coated copper powder is composed of copper in the core and silver shell covering its surface. A typical silver layer thickness is between 50-200 nanometers, with a silver content (mass ratio) of 5% -30%. In this structure, the copper core plays a role in providing low cost and high conductivity, while the silver shell is crucial in ensuring that the particles resist oxidation during processes such as pulping and printing, while forming good ohmic contact with the battery silicon wafer or TCO film. After sintering, the silver shell acts as a conductive medium, ensuring low contact resistance and reliable adhesion of the electrode, while the copper core reduces material costs while endowing the slurry with certain mechanical strength and thermal stability.
2、 Application Fields
（1） In the photovoltaic industry, silver copper technology is mainly applied in the metallization process of batteries. Currently widely used in HJT heterojunction batteries. On the HJT battery production line, a 30% silver content silver coated copper fine grid slurry has been introduced for mass production, and it is expected that a 20% silver content silver coated copper slurry will also be introduced for mass production in the future. By using silver in copper technology while maintaining the same efficiency, the amount of pure silver used per watt can be reduced from 6mg to 0.5mg, and the amount of pure silver used per HJT battery can be reduced from around 30mg to less than 3mg, a decrease of over 90%. However, in battery technologies such as TOPCon and XBC that require high-temperature sintering, the introduction of silver coated copper paste is still in the experimental verification stage.
（2） Silver coated copper powder, as a highly conductive filler in other electronic fields, can be added to materials such as coatings (paints), adhesives (binders), inks, polymer slurries, plastics, rubber, etc., to make various conductive and electromagnetic shielding products. Widely used in the fields of conductivity and electromagnetic shielding in industrial sectors such as electronics, mechatronics, communication, printing, aerospace, and weapons, such as computers, mobile phones, electronic medical equipment, electronic instruments and meters, and other electronic, electrical, and communication products.
3、 Technological advantages and challenges
（1） Excellent performance advantage: Within the appropriate range of silver content, silver coated copper paste can achieve conductivity and battery efficiency similar to pure silver paste. Batch verification by multiple companies shows that HJT batteries use silver coated copper fine grid paste with a silver content of about 30%, and the conversion efficiency only slightly decreases compared to pure silver paste, with a range of less than 0.1 percentage points. And the screen printing adaptability of silver coated copper paste is good, with printing grid line fineness (20 μ m level), aspect ratio and other indicators not much different from traditional low-temperature silver paste. Significant cost-effectiveness: The biggest advantage of silver coated copper paste is that it significantly reduces the amount of precious metal silver used, and the cost advantage is particularly prominent when silver prices are high. When the silver price reaches 8000 yuan/kg, if HJT batteries fully use silver coated copper paste with 30% silver content and cooperate with non main gate technology, the cost of silver paste per watt can be saved by about 0.04 yuan compared to traditional TOPCon batteries. Starting from April 2024, the industry will adjust the pricing mechanism for silver coated copper paste to "silver price x silver content+fixed processing markup". When silver prices rise, battery manufacturers using silver coated copper paste can gain greater cost advantages.
（2） Challenging conductivity and reliability issues: In terms of ultimate performance, the conductivity and oxidation resistance of silver coated copper powder are slightly inferior to pure silver powder. When the silver content decreases even lower (such as<20%), the gate line resistance may significantly increase, affecting the battery fill factor and efficiency. Meanwhile, due to the presence of copper, the moisture resistance and electrochemical corrosion resistance of the components have received attention. At present, the industry is improving reliability through measures such as thickening the silver envelope coating, optimizing the glass flux formula, and packaging protection, but long-term empirical data verification is still needed. Difficulty in process control: The preparation process of silver coated copper powder is complex, and chemical electroplating is usually used to uniformly deposit a silver layer on the surface of micrometer sized copper powder. This requires precise control of parameters such as plating solution composition, reaction temperature, and time to ensure stable and uniform coating of the product. If the silver layer is too thin or uneven, some copper will be exposed and oxidized prematurely; If the silver layer is too thick, it increases costs and reduces the copper content in the slurry, which is not conducive to cost reduction. Finding the optimal silver layer thickness between cost and performance and achieving consistency in large-scale production is a challenge faced by silver coated copper powder manufacturers. Poor adaptability to high-temperature processes: At present, silver coated copper paste is mainly suitable for low-temperature processes such as HJT. To promote high-temperature sintered batteries such as TOPCon and XBC, it is necessary to address the issue of copper protection at high temperatures. At present, there are research and development directions such as using low-temperature sintered silver coated copper paste+subsequent laser assisted heating, or adding nanoscale protective coatings (such as graphene, palladium, etc.) outside the silver layer, but they are not yet mature. Market awareness needs to be improved: As an emerging technology, the acceptance of silver coated copper paste in the upstream and downstream of the industry chain requires time to cultivate. Component manufacturers and end customers have doubts about its long-term reliability, and production line processes (such as printing parameter adjustments, welding process compatibility, etc.) also need to be optimized through break in. Some traditional manufacturers that use pure silver paste will wait and see more cases and data before following up for stability considerations.
With the continuous advancement and improvement of technology, silver clad copper technology is expected to be applied in more battery technology routes. It is expected that by 2030, the global demand for silver coated copper paste will reach 1166 tons, corresponding to a market space of over 3.5 billion yuan. In the future, silver clad copper is expected to gradually extend to more routes such as TOPCon and passivated contact back contact (BC), bringing more comprehensive cost reduction effects to the photovoltaic industry. Meanwhile, with the expansion of its application scope in other electronic fields, the market size is expected to further expand. But to achieve these goals, it still requires joint efforts from all parties in the industry chain to solve technical problems, enhance market awareness and acceptance.
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