Response of Methylammonium Lead Iodide to External Stimuli and Caloric Effects from Molecular Dynamics Simulations

Abstract

The power conversion efficiency for solar cells fabricated using organometal halide perovskites (OMHPs) has risen to more than 20% in a short span of time, making OMHPs promising solar materials for harnessing energy from sunlight. The hybrid perovskite architecture that consists of organic molecular cations and an inorganic lattice could also potentially serve as a robust platform for materials design to realize functionalities beyond photovoltaic applications. Taking methylammonium lead iodide (MAPbI3) as an example, we explore the response of organometal halide perovskites to various stimuli, using all-atom molecular dynamics simulations with a first-principles-based interatomic potential. We find that a large electric field is necessary to introduce a sizable molecular ordering at room temperature in unstrained MAPbI3. Molecular dipoles in epitaxially strained MAPbI3 are more susceptible to an electric field. We also report various caloric effects in MAPbI3. The adiabatic thermal change is estimated directly by introducing different driving fields in the simulations. We find that MAPbI3 exhibits both electrocaloric and mechanocaloric effects at room temperature. Local structural analysis reveals that the rearrangement of molecular cations in response to electric and stress fields is responsible for the caloric effects. The enhancement of caloric response could be realized through strain engineering and chemical doping.