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CH 3NH 3PbI 3 due to the build-up of space charges close to the contacts originating from ionic displacement.[12, 13] Xiao et al.[12] showed that photocurrent direction in CH 3NH 3PbI 3 films could be switched repeatedly by applying a small electric field of< 1 V µm–1, which was explained by the formation of reversible p–i–n structures induced by ion drift in the perovskite layer. Although the exact defect nature is still elusive, recent studies have shown that negatively charged Pb and CH 3NH 3 vacancies and positively charged I vacancies are the predominant ionic species.[14, 15] More excitingly, the rotational motion of the A-site organic cation can provide structural flexibility and even ferroelectric behavior on the nanoscale.[16, 17] Figure 1a depicts the rotational motion of the CH 3NH 3 cation in the unit cell of CH 3NH 3PbI 3. Unlike the spherical Pb cation and I anion, the MA cation is asymmetric dumbbell-shaped. At the ground state, the CH 3NH 3 cation tilts toward the diagonal direction by≈ 30.[17, 18] Since the molecule is polar, the CH 3NH 3 cation may rotate with an external electric field. Especially, when the external electric field is applied along the c-axis, the CH 3NH 3 cation can rotate and align with the external bias. For the room temperature cubic phase of CH 3NH 3PbI 3, the fast rotational dynamics of the CH 3NH 3 cations in picosecond time scale was predicted.[19, 20] Such a molecular rotational motion can lead to lowering the barrier for the migration of point defects including vacancies and interstitials. This unique nature of CH 3NH 3PbI 3 motivated us to explore whether the OHP can be used as a resistive switching material …