High-pressure polyhedral interaction in CsSnI3

In recent years, metal halide perovskites have attracted great interest in various applications because of their excellent properties. Here, we find pressure-induced transformations of edge-sharing Sn−I polyhedra to face-sharing Sn−I polyhedra and subsequently to quasi-two-dimensional layer Sn–I polyhedra in CsSnI3 semiconductor phases at 5.4 and 40 GPa. Our first-principles density functional theory calculations uncover that the phase transformation is due to the variation of Sn atomic coordination accompanied by the Sn–I polyhedral distortion. Both phases are indirect bandgap, which is smaller than the atmospheric phase. Further calculations show that intrapolyhedral Sn−Sn hybridization and interpolyhedral I–I coupling lead to the Sn–I polyhedral distortion. These findings will provide valuable insights into phase transformation of perovskites at high pressures.