Recovery of silver and silicon from spent solar cells by direct separation driven by galvanic and chemical etching in molten chloride

The rapid expansion of photovoltaic (PV) deployment underscores the critical need for sustainable silver (Ag) and silicon (Si) recycling from retired modules. However, alkaline etching methods inevitably attack both the SiO₂ and Si. In this study, the Ag/Si interface and SiN_x layer were removed within 1 min via galvanic and chemical etching using molten NaCl-CaCl₂. Galvanic etching occurred between the Al back layer anode and the SiO₂ at the Ag/Si interface cathode within the molten NaCl-CaCl₂ electrolyte. During galvanic etching, Al was oxidized to Al₂O₃ and SiO₂ was reduced to Si with volume shrinkage, leading to Ag separation from the Si. Simultaneously, chemical etching was enabled by the reaction of CaCO₃/CaO with SiO₂ and SiN_x, resulting in Ag and SiN_x removal. This method achieved 99.0% Ag and Si recovery efficiency because Si is almost inert to the etching agent. Furthermore, life cycle assessment (LCA) and life cycle costing (LCC) confirmed a reduction of 11.0 kg CO₂-eq and a benefit of $14.04 per kg for recycled cells. Overall, the molten salt provides a selective medium that allows both galvanic and chemical etching with lower material consumption, offering a technically viable circular pathway for PVs.