Junke’s second first-author manuscript entitled “Atomistic and Electronic Origin of Phase Instability of Metal Halide Perovskites” is published on ACS Applied Energy Materials. By using DFT calculations, Junke provides insights for the undesired phase transition of pristine perovskites (FAPbI3, CsPbI3, and CsSnI3) and reveal the mechanisms of the improved phase stability of the mixed compounds (CsxFA1-xPbI3, CsSnyPb1-yI3, and CsSn(BrzI1-z)3). 

Junke identifies that the phase transition is correlated with the relative strength of the metal-halide bonds as well as that of the hydrogen bonds (for hybrid compositions) in perovskite and non-perovskite phases. The phase transition can be suppressed by mixing ions, giving rise to either increased bond strength for the perovskite or decreased bond strength in their non-perovskite counterparts, or suppressed vacancy defect formation for Sn-Pb mixed perovskites. These results present a comprehensive understanding of the mechanisms for the phase instability of metal halide perovskites and provide design rules for engineering phase-stable perovskite compositions.