title: Temperature Dependence of the Energy Levels of Methylammonium Lead Iodide Perovskite from First-Principles.
abstract: Environmental effects and intrinsic energy-loss processes lead to fluctuations in the operational temperature of solar cells, which can profoundly influence their power conversion efficiency. Here we determine from first-principles the effects of temperature on the band gap and band edges of the hybrid pervoskite CH3NH3PbI3by accounting for electron-phonon coupling and thermal expansion. From 290 to 380 K, the computed band gap change of 40 meV coincides with the experimental change of 30-40 meV. The calculation of electron-phonon coupling in CH3NH3PbI3is particularly intricate as the commonly used Allen-Heine-Cardona theory overestimates the band gap change with temperature, and excellent agreement with experiment is only obtained when including high-order terms in the electron-phonon interaction. We also find that spin-orbit coupling enhances the electron-phonon coupling strength but that the inclusion of nonlocal correlations using hybrid functionals has little effect. We reach similar conclusions in the metal-halide perovskite CsPbI3. Our results unambiguously confirm for the first time the importance of high-order terms in the electron-phonon coupling by direct comparison with experiment.
authors.affiliation: Department of Mechanical Engineering and Materials Science, University of Pittsburgh , Pittsburgh, Pennsylvania, 15261, United States.
authors.forename: Wissam A
authors.identifier: http://orcid.org/0000-0001-6714-4832
authors.initials: WA
authors.lastname: Saidi
authors.affiliation: Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom.
authors.forename: Samuel
authors.initials: S
authors.lastname: Poncé
authors.affiliation: Department of Physics and Astronomy, Rutgers University , Piscataway, New Jersey 08854-8019, United States.|TCM Group, Cavendish Laboratory, University of Cambridge , J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
authors.forename: Bartomeu
authors.initials: B
authors.lastname: Monserrat