Origin of Hysteresis in CH3NH3PbI3 Perovskite Thin Films

Organic-inorganic hybrid perovskite solar cells are attracting the attention of researchers owing to the high level of performance they exhibit in photovoltaic device applications. However, the attainment of an even higher level of performance is hindered by their anomalous current-voltage (I-V) hysteresis behavior. Even though experimental and theoretical studies have suggested that the perovskite materials may have a ferroelectric nature, it is still far from being fully understood. In this study, the origin of the hysteresis behavior in CH3NH3PbI3 perovskite thin films is investigated. The behavior of ferroelectricity using piezoresponse force microscopy is first examined. Then, by comparing the scan-rate-dependent nano/macroscopic I-V curves, it is found that ion migration assisted by the grain boundaries is a dominant origin of I-V hysteresis from a macroscopic viewpoint. Consequently, the observations suggest that, even though ferroelectricity exists in the CH3NH3PbI3 perovskite materials, ion migration primarily contributes to the macroscopic I-V hysteresis. The presented results can provide fundamental guidelines to the resolution of hysteresis issues in organic-inorganic hybrid perovskite materials.