Halide perovskites (ABX3) attracted much of attention in the last years due to their excellent photovoltaic activity. They are unique in the sense that they exhibit long carrier lifetime despite having many apparent structural defects. Recent studies in our group concluded that this unique behavior is due to strong coupling between the electronic band structure and the strongly anharmonic motion of the atoms within the crystal. Therefore, it is imperative to understand the source of anharmonic atomic motion in this class of materials. Studies have indicated the B-cation lone pair to be a possible source for strong anharmonic behavior in the perovskite crystals. In order to understand the anharmonic behavior and its origin, I investigated a series of perovskites with different lone pair stereoactivity. Using low frequency Raman spectroscopy, I quantified the level of anharmonicity and determined the influence of the B-cation lone pair on the structural dynamics.
