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 due to electron-phonon coupling and thermal expansion. Our results show that the band gap increases with temperature for the two CH₃NH₃PbI₃ phases in excellent agreement with experimental results. We also found that temperature have a significant effect on the effective masses and Rashba coupling especially in the tetragonal phase. At room temperature, electron-phonon coupling is found to enhance the effective mass by a factor of two, and to diminish the Rashba coupling by the same factor compared to T=0 K values.