Linking Chemistry at the TiO₂/CH₃NH₃PbI₃ Interface to Current-Voltage Hysteresis

We demonstrate that reversible chemical reactions occur at TiO₂/gas and CH₃NH₃PbI₃/gas interfaces on a time scale of seconds to minutes. The chemisorption strongly affects their electronic properties, mainly acting to deplete TiO₂ of free electrons and passivate surface traps on the perovskite. Although the chemistry is not directly probed, we infer that reversible chemistry occurs at the solid-state TiO₂/CH₃NH₃PbI₃ interface. Equilibrium or steady-state concentrations established for adsorbed species associated with each material would be voltage- and illumination-dependent due to free or photocarriers being a main reactant. Interfacial chemistry provides an additional physical mechanism to explain the origins of normal and anomalous hysteretic current-voltage characteristics of perovskite devices. Furthermore, chemical reactions help us to understand why measured perovskite ion-transport properties and the nature of hysteresis are highly dependent on interfaces.