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Asymmetric Bipolar Resistive Switching of Halide Perovskite Film in Contact with TiO2 Layer.

Halide perovskite materials such as methylammonium lead iodide (CH3NH3PbI3) have attracted considerable interest for the resistive random-access memory applications, which exploit a dramatic change in the resistance by an external electric bias. In many semiconductor films, the drift, accumulation, and chain formation of defects explain the change in the resistance by an external bias. This study demonstrates that the interface of CH3NH3PbI3 with TiO2 has a significant impact on the formation and rupture of defect chains and causes the asymmetric bipolar resistive switching in the Au/CH3NH3PbI3/TiO2/FTO device (FTO = fluorine-doped tin oxide). When a negative bias is applied to the Au electrode, iodine interstitials with the lowest migration activation energy move toward TiO2 in the CH3NH3PbI3 layer and pile up at the CH3NH3PbI3-TiO2 interface. Under the same condition, oxygen vacancies in the TiO2 layer also travel to the CH3NH3PbI3-TiO2 interface and strongly attract iodine interstitials. As a result, a Schottky barrier appears at the CH3NH3PbI3-TiO2 interface, and the resistance of Au/CH3NH3PbI3/TiO2/FTO becomes much larger than that of Au/CH3NH3PbI3/FTO in the high resistance state. The frequency dependence of the capacitance confirms the asymmetric appearance of a large space charge polarization at the CH3NH3PbI3-TiO2 interface, which causes the unique bipolar resistive switching behavior with the on/off ratio (103) and retention time (>104 seconds) at -0.85 V in Au/CH3NH3PbI3/TiO2/FTO film.