Ferroelectricity of CH₃NH₃PbI₃ Perovskite

Abstract

Ferroelectricity\nhas been believed to be an important but controversial\norigin of the excellent photovoltaic performance of organometal trihalide\nperovskites (OTPs). Here we investigate the ferroelectricity of a\nprototype OTP, CH₃NH₃PbI₃ (MAPbI₃), both theoretically and experimentally. Our first-principles\ncalculations based on 3-D periodic boundary conditions reveal that\na ferroelectric structure with polarization of ∼8 μC/cm² is the globally stable one among all possible tetragonal\nstructures; however, experimentally no room-temperature ferroelectricity\nis observed by using polarization–electric field hysteresis\nmeasurements and piezoresponse force microscopy. The discrepancy between\nour theoretical and experimental results is attributed to the dynamic\norientational disorder of MA⁺ groups and the semiconducting\nnature of MAPbI₃ at room temperature. Therefore, we conclude\nthat MAPbI₃ is not ferroelectric at room temperature; however,\nit is possible to induce and experimentally observe apparent ferroelectric\nbehavior through our proposed ways. Our results clarify the controversy\nof the ferroelectricity in MAPbI₃ and also provide valuable\nguidance for future studies on this active topic.