Ferroelectricity of CH3NH3PbI3 Perovskite.

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, CH3NH3PbI3 (MAPbI3), 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/cm2 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+ groups and the semiconducting nature of MAPbI3 at room temperature. Therefore, we conclude that MAPbI3 is not ferroelectric at room temperature; however, it is possible to induce and experimentally observe apparent ferroelect...