Phonon dynamics of hybrid organic-inorganic perovskite MAPbBr₃

Metal halide perovskites (MHPs) continue to be a focal point of research due to its wide range of applications in low cost photovoltaic and light emitting devices. These materials exhibit extended charge carrier lifetimes, long carrier diffusion lengths, and exceptional carrier protection from defects. Large polarons were reported to be responsible for the extended charge carrier lifetime. However, the relevant underlying microscopic processes such as phonon melting are still under debate. A recent study of inelastic neutron scattering measurements on CsPbBr₃ confirms the overdamping of transversal acoustic phonons (TA) along the Brillouin zone direction T-M-R-T in both tetragonal and cubic phases. Studies on MAPbI₃ (MA=CH₃NH₃) using inelastic X-Ray scattering at 350K, revealed softening of TA modes along T-M and T-R directions. However, a detailed temperature dependence study to see how the phonons evolve through the structural phase transitions has not been performed. We will show our results from inelastic X-Ray scattering measured on MAPbBr₃. We observed in MAPbBr₃, a phonon mode at Q- [4.14 0.38 L] gets softened at low temperature orthorhombic phase and becomes relatively well defined at room temperature cubic phase. We will also present our results from DFT calculations comparing with evolution of phonon modes in inelastic X-Ray measurements.