Upcycling bullets into solar cells converts lead waste into a green energy source

Global lead waste streams contain millions of tons of secondary lead, while perovskite solar cells require high-purity lead iodide for terawatt-scale deployment. Here, we report a two-step upcycling process that converts contaminated lead waste into photovoltaic-grade PbI2 via electrochemical synthesis in acetonitrile and inverse temperature crystallization for purification. Testing with centuries-old bullets as challenging feedstock, we achieve 94% electrochemical conversion efficiency and 204% higher yields through process optimization and reduce metal impurities to commercial-grade levels. Upcycled lead solar cells reach 21% power conversion efficiency, matching devices fabricated using commercial high-purity (5N) PbI2 controls statistically. This method transforms hazardous waste into clean energy precursors, potentially supplying substantial PbI2 demand from secondary sources while eliminating environmental disposal burdens for sustainable photovoltaic manufacturing.