Modeling of Thermal Effect on the Electronic Properties of Photovoltaic Perovskite CH3NH3PbI3: The Case of Tetragonal Phase

Hybrid organic-inorganic perovskites are semiconductors with disordered structures and remarkable properties for photovoltaic applications. Many theoretical investigations have attempted to obtain structural models of the high-temperature phases, but most of them are focused on the mobility of organic components and their implications in material properties. Herein we propose a set of geometric variables to evaluate the conformation of the inorganic framework at each phase of methylammonium lead iodide perovskite. We show that the analysis of these variables is required to ensure consistent structural models of the tetragonal phase. We explore the theoretical ingredients needed to achieve good models of this phase. Ab initio molecular dynamic simulation, under canonical ensemble at the experimental unit cell volume, leads to representative states of the phase. Under this scheme, PBE and van der Waals density functional approaches provide similar models of the tetragonal phase. We find that this perovskite has a highly mobile inorganic framework due to the thermal effect regardless of movement of the organic cations. Consequently, the electronic structure shows significant movements of the bands with large bandgap variations.