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

Abstract

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 (FAPbI(3)). Specifically, trivalent antimony (Sb-3(+)) and divalent sulfur ions (S-2(-))-alloyed FAPbI(3) 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 degrees C. The introduced Sb-3(+) and S-2(-) ions promote alpha(200)c crystal growth of FAPbI3 and minimize lattice strains that drive humidity- and thermal-induced degradation. Optimized PSCs based on Sb-3(+) and S-2(-) alloyed-FAPbI(3) 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 Sb3+ and S2--alloyed FAPbI3 PSCs retain approximately 94.9% of the initial PCE after 1080 h of storage in the dark (20-40% relative humidity, 25 degrees C). This work pioneers the simultaneous alloying of trivalent Sb3+ and divalent S2- into FAPbI3, establishing a compositional-engineering strategy for more efficient and stable PSCs.