Thermal aging-induced interdiffusion and reliability degradation in low-silver electrodes for SHJ solar cells

Silver-coated copper core-shell powders offer a promising route for reducing the cost of electrodes in silicon heterojunction (SHJ) solar cells. However, their limited thermal stability poses challenges to long-term reliability. In this work, the electrical degradation behavior and microstructural evolution of commercial low-silver electrodes with a silver content of ~35 wt% and thin Ag shells (~70 nm) are systematically investigated under accelerated thermal aging at 195 - 240 °C. The results indicate that contact resistivity exhibits significantly higher temperature sensitivity than line resistance, demonstrating that interfacial degradation dominates electrical failure. Microstructural analysis reveals that the thermal aging process is dominated by coupled mechanisms, including Ag-Cu interdiffusion, Kirkendall void formation, and surface diffusion-driven sintering of Ag particles. These processes lead to shell cracking, interfacial pore formation, and disruption of the conductive network. Additionally, an apparent increase in Ag shell thickness is observed, which originates from the attachment and accumulation of sintered Ag particles rather than intrinsic shell growth. Theoretical analysis indicates that the Ag-Cu interdiffusion depth over a 30-year service lifetime reaches approximately 17 nm at 60 °C and 71 nm at 80 °C, values comparable to the initial Ag shell thickness. This suggests that interfacial diffusion may progressively deminish the effective Ag layer and thereby compromise long-term reliability. This work clarifies the degradation mechanisms of low-silver electrodes and provides guidance for the design of cost-effective and reliable SHJ solar modules.