Origin of the Temperature-Induced Gap Bowing of Formamidinium-Methylammonium Lead Iodide Perovskites: Role of Cationic Rattlers
By combining temperature and pressure-dependent photoluminescence measurements on FA-MA lead iodide perovskite single crystals, this study identifies that the pronounced temperature-induced gap bowing in low-temperature phases is primarily driven by an anomalous electron-phonon coupling mechanism involving mixed vibrational modes of inorganic cage tilting and formamidinium "rattler" librations.