Enhanced Lattice Coherences and Improved Structural Stability in Quadruple A‐Site Substituted Lead Bromide Perovskites

Lead halide perovskites (LHPs) are promising materials for efficient photovoltaic devices; however, they often encounter limited structural stability and degradation problems that limit their technological potential. This study investigates a novel perovskite composition consisting of (Cs, MA, FA, GA)PbBr_3, abbreviated as (4cat)PbBr₃, to effectively enhance phase stability and optoelectronic characteristics. The spectroscopic data reveal improved structural order, electronic properties, and dynamic lattice response in a cubic phase, which is uniquely stabilized by the specific cation composition down to 80 K. Superior optoelectronic properties are verified by increased photoluminescence (PL) and 20-fold higher electron mobility, when compared to the single-cation composition, MAPbBr₃. Notably, the ultrafast Terahertz-induced Kerr effect (TKE) reveals a dominating 1.1 THz octahedral twist mode, also observed in MAPbBr₃, however with a doubled phonon coherence time in (4cat)PbBr₃ at 80 K. The observation of higher structural order in the 4-cation composition is thus reflected by the prolonged lattice coherences, indicating enhanced dynamic screening effects that can explain the improved optoelectronic properties of (4cat)PbBr₃. This study therefore sheds light on the influence of the A-site cation composition on the inorganic sublattice and its coherent dynamics, highly relevant to perovskite-based photovoltaic and optoelectronic technologies.