Correlating the Composition-Dependent Structural and Electronic Dynamics of Inorganic Mixed Halide Perovskites

Inorganic halide perovskites have attracted intensive research focus for next-generation photovoltaic applications, but their low thermal and humidity stabilities still remain to be surmounted for practical applications. Compositional engineering, such as mixing of two different halogen anions, has been explored as one strategy to enhance thermodynamic stabilities, with an extra benefit of band gap tuning. However, a thorough examination on how anion engineering affects the structural dynamics, which governs many physical behaviors of mixed halide perovskites, remains elusive. Here, by combining density functional theory calculations with statistical learning, we explore the critical correlation between composition-dependent structural and electronic dynamics of cubic CsPb(I1–xBrx)3 across 24 different compositions, which encompasses multiple degrees of freedom (composition, time, and atomistic and electronic structures). We show that the anharmonic vibrations of halogen atoms are stronger (weaker) in I (Br)-rich phases. The dynamics of Pb–halogen octahedral coordination environments, as revealed from the machine-learned coordinates, follows largely the opposite composition-dependent trend of the vibrational anharmonicity of halogen atoms. Nevertheless, for all mixed halide perovskites, a much faster decoherence in electronic band gap at 300 K is observed, signifying a stronger electron–phonon coupling in these systems. This may lead to lower photostabilities and carrier mobilities in these materials.