Ferroelectricity of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Perovskite
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Abstract
Ferroelectricity
has been believed to be an important but controversial
origin of the excellent photovoltaic performance of organometal trihalide
perovskites (OTPs). Here we investigate the ferroelectricity of a
prototype OTP, CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> (MAPbI<sub>3</sub>), both theoretically and experimentally. Our first-principles
calculations based on 3-D periodic boundary conditions reveal that
a ferroelectric structure with polarization of ∼8 μC/cm<sup>2</sup> is the globally stable one among all possible tetragonal
structures; however, experimentally no room-temperature ferroelectricity
is observed by using polarization–electric field hysteresis
measurements and piezoresponse force microscopy. The discrepancy between
our theoretical and experimental results is attributed to the dynamic
orientational disorder of MA<sup>+</sup> groups and the semiconducting
nature of MAPbI<sub>3</sub> at room temperature. Therefore, we conclude
that MAPbI<sub>3</sub> is not ferroelectric at room temperature; however,
it is possible to induce and experimentally observe apparent ferroelectric
behavior through our proposed ways. Our results clarify the controversy
of the ferroelectricity in MAPbI<sub>3</sub> and also provide valuable
guidance for future studies on this active topic