Enhanced stability and efficiency in perovskite solar cells via mixed-metal chalcohalide-alloyed formamidinium lead iodide.

Achieving long-term stability in halide perovskite solar cells (PSCs) remains challenging due to their susceptibility to environmental degradation. Enhancing material stability at the intrinsic level offers a pathway to more durable solutions. This study addresses the instability of halide perovskites by enhancing ionic binding energy and alleviating lattice strain through the mixed metal chalcohalide into formamidinium lead tri-iodide (FAPbI₃). Specifically, trivalent antimony (Sb³⁺) and divalent sulfur ions (S²⁻)-alloyed FAPbI₃ thin films are formed using a sequential ambient-air process, applying a formamidinium iodide (FAI) solution over a spin-coated SbCl₃-thiourea (Sb-TU) complex with PbI₂ at 150 °C. The introduced Sb³⁺ and S²⁻ ions promote α(200)c crystal growth of FAPbI and minimize lattice strains that drive humidity- and thermal-induced degradation. Optimized PSCs based on Sb³⁺ and S²⁻ alloyed-FAPbI₃ achieve a power conversion efficiency (PCE) of 25.07% under standard conditions, comparable to the highest PCE of PSCs fabricated in the atmosphere. The unencapsulated Sb and S-alloyed FAPbI PSCs retain approximately 94.9% of the initial PCE after 1080 h of storage in the dark (20-40% relative humidity, 25 °C). This work pioneers the simultaneous alloying of trivalent Sb and divalent S into FAPbI, establishing a compositional-engineering strategy for more efficient and stable PSCs.