Impact of Electron-Phonon Scattering on Optical Properties of CH₃NH₃PbI₃ Hybrid Perovskite Material

We numerically investigate the impact of electron-phonon scattering on the optical properties of a perovskite material (CH₃NH₃PbI₃). Using nonequilibrium Green function formalism, we calculate the local density of states for several values of the electron-phonon scattering strength. We report an Urbach-like penetration of the density of states in the band gap due to scattering. A physical analytical model allows us to attribute this behavior to a multiphonon process. Values of Urbach energy up to 9.5 meV are obtained, meaning that scattering contribution to the total experimental Urbach energy of 15 meV is quite important. We also show that the open-circuit voltage V_oc, for a solar cell assuming such a material as an absorber, depends on the scattering strength. V_oc loss increases with the scattering strength, up to 41 mV. Finally, an unexpected result of this study, is that the impact of electron-phonon scattering on Urbach tail and V_oc increases with the phonon energy. This low value in perovskite (8 meV) is therefore an advantage for photovoltaic applications.