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 ferroelectric behavior through our proposed ways. Our results clarify the controversy of the ferroelectricity in MAPbI₃ and also provide valuable guidance for future studies on this active topic