Wide-Bandgap CsPbIBr₂ Perovskite Indoor Photovoltaics Enabled by Dynamic Hot-Air Processing and FAI Interlayer Engineering

Inorganic halide perovskites are promising light absorbers due to their thermal stability, high absorption, and tunable optoelectronic properties. CsPbIBr₂, with a suitable bandgap and robust phase stability, is particularly attractive for indoor photovoltaics (IPVs). However, achieving uniform, defect-minimized films remains challenging. Here, we report a synergistic strategy combining hot-air processing and formamidinium iodide (FAI) post-treatment to improve the structural and photovoltaic properties of the CsPbIBr₂ films. Hot-air processing promotes uniform crystallization by controlling solvent evaporation, while FAI treatment induces surface reconstruction and ionic defect passivation. These modifications result in denser microstructures, reduced lattice strain, and suppressed nonradiative recombination. The optimized device, treated with 4 mg/mL FAI, delivers a power conversion efficiency of 7.01% under 1000 lx illumination. This work demonstrates that coupling thermal crystallization with mild chemical treatments offers a practical and scalable route toward improved performance in perovskite-based IPV devices.