Giant Phonon Tuning Effect via Pressure-Manipulated Polar Rotation in Perovskite MAPbI.

Perovskite MAPbI that exhibits unique optoelectronic properties has emerged as a promising semiconductor material with a potential to revolutionize the photovoltaic industry. Inadequate understanding of the thermal instability and lattice dynamics of MAPbI, however, hinders its practical applications. Herein, combing molecular dynamics with a first-principles-based interatomic potential and inelastic neutron scattering measurements, we have performed an in-depth study of the lattice dynamics of MAPbI. The extremely large line widths of the optical phonons in the tetragonal phase, which prevent direct experimental measurement of the phonon lifetimes, have been obtained for the first time. Our atomic-level study also reveals a giant pressure tuning effect on phonon scattering, which is related to the four-fold rotation of the MA cations around the C-N axis. A hydrostatic pressure as low as 6 kbar can alter the phonon lifetime by more than 1 order of magnitude. This work is expected to pave the way for further phonon engineering and thermal optimization of MAPbI and related perovskites.