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Liu, Shi; Cohen, R. E. (2016): Response of Methylammonium Lead Iodide to External Stimuli and Caloric Effects from Molecular Dynamics Simulations. In: Journal of Physical Chemistry C, Vol. 120, No. 31: pp. 17274-17281
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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 methyl ammonium lead iodide (MAPbI(3)) 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 MAPbI(3). Molecular dipoles in epitaxially strained MAPbI(3) are more susceptible to an electric field. We also report various caloric effects in MAPbI(3). The adiabatic thermal change is estimated directly by introducing different driving fields in the simulations. We find that MAPbI(3) 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.