Pressure-Induced Piezochromism and Structure Transitions in Lead-Free Layered Cs₄MnBi₂Cl₁₂ Quadruple Perovskite

Lead-free all-inorganic halide perovskites with an outstanding stability and a nontoxic nature are promising substitutes for hybrid lead halide counterparts in optoelectronic devices and solar cells. Herein, we investigate the relationship between the structure and optical properties of quadruple halide perovskite Cs4MnBi2Cl12 via a high-pressure technique, and in situ spectroscopic analyses with density functional theory calculations as well. Cs4MnBi2Cl12 undergoes two distinct band gap narrowing processes and a sharp piezochromic transition upon compression, accompanied by two pressure-induced phase transitions. Our findings provide a unique strategy to tune lead-free quadruple perovskites with suitable band gaps for better optoelectronic and photovoltaic applications.