Ferroelectricity of CH₃NH₃PbI₃ Perovskite

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, 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/cm(2) 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.

Effect of Internal Electric Fields on Charge Carrier Dynamics in a Ferroelectric Material for Solar Energy Conversion

“…[7][8][9] The organohalide lead perovskite materials currently yielding very promising photovoltaic device effi ciencies are also reported to be ferroelectric, although the importance of their ferroelectric properties in achieving such high effi ciencies is currently unclear. [10][11][12][13] In almost all cases where enhanced solar conversion performance has been attributed to ferroelectric materials properties, this enhancement has been assigned to reduced recombination losses. [ 11,14,15 ] However to date, to the best of our knowledge, there are no reports directly probing the extent to which spontaneous polarization can indeed increase charge carrier lifetimes.…”

Applications of ferroelectrics in photovoltaic devices

“…They confirmed that ferroelectric properties exist in OTP materials. By performing firstprinciples calculations, combining the classic point charge model and the Berry phase method, Fan et al [85] obtained consistent polarization of~8 µC cm −2 . This result suggests that a ferroelectric structure of~8 µC cm −2 in the mate-rial is the most stable.…”

“…Fan et al [85] concluded that OTP does not exhibit ferroelectricity based on the EP loop and PFM measurements. Beilsten et al [93] studied the conductivity hysteresis of CH3NH3PbI3 films using the double-wave method and obtained results that excluded the impact of the leakage current.…”

Absence of ferroelectricity in methylammonium lead iodide perovskite

“…19,27,28 Recently, there have been numerous conflicting reports regarding ferroelectricity in perovskites. [29][30][31][32] The controversy over the ferroelectricity of methylammonium lead iodide (CH3NH3PbI3) perovskite layer closely resembles the dispute over the ferroelectricity of bananas 33 and highlights the extra care that should be taken in the interpretation of electrical polarization loops and the claim of ferroelectricity. 34 The prerequisite of ferroelectricity of a compound is that the crystal structure must be non-centrosymmetric hence exhibiting a strong optical second harmonic generation (SHG).…”