Anharmonic Lattice Dynamics in CsPbBr3*

CsPbBr₃ is a promising material for use in solar cells and thermoelectrics. The suitability of halide perovskites as photovoltaics derives from the long lifetimes of photoexcited carriers before recombination and it has been theorized that this is due to local polar fluctuations. Furthermore, CsPbBr₃ has been shown to exhibit ultralow thermal conductivity which makes it attractive for use in thermoelectrics. CsPbBr₃ has several lattice instabilities undergoing a cubic to tetragonal transition at ~400K before transforming to an orthorhombic phase at ~360K.

We report inelastic neutron scattering (INS) studies, supported by anharmonic first-principles simulations, on CsPbBr₃ across its three phases. These momentum-resolved measurements allow us to investigate phonon behavior across the Brillouin zone and hence phonon-phonon scattering rates which directly impact thermal conductivity. We find large overall broadening of phonons, even at low temperature, but also a large temperature-dependent anisotropy in the anharmonicity.