Effects of Electron-Phonon Coupling on Electronic Properties of Methylammonium Lead Iodide Perovskites

Temperature can have a dramatic effect on the solar efficiency of methylammonium lead iodide (CH₃NH₃PbI₃) absorbers due to changes in the electronic structure of the system even within the range of stability of a single phase. Herein, using first-principles density functional theory, we investigate the electron band structure of the tetragonal and orthorhombic phases of CH₃NH₃PbI₃ as a function of temperature. The electron-phonon interactions are computed to all orders using a Monte Carlo approach, which is needed considering that the second-order Allen-Heine-Cardona theory in electron-phonon coupling is not adequate. Our results show that the band gap increases with temperature, in excellent agreement with experimental results. We verified that anharmonic effects are only important near the tetragonal-cubic phase transition temperature. We also found that temperature has a significant effect on the effective masses and Rashba coupling. At room temperature, electron-phonon coupling is found to enhance the band effective mass by a factor of 2 and to diminish the Rashba coupling by the same factor compared to T = 0 K values. Our results underscore the significant impact of electron-phonon coupling on electronic properties of the hybrid perovskites.