Electrochemical and Thermal Etching of Indium Tin Oxide by Solid-State Hybrid Organic-Inorganic Perovskites

We show that tin-doped indium oxide (ITO) can be thermally etched by the Brønsted acid salts methylammonium iodide (MAI), methylammonium lead triiodide (MAPbI₃), and formamidinium lead triiodide (FAPbI₃) in solid-state films and devices at common processing temperatures. More importantly, a series of reactions within an ITO/hybrid perovskite/Au device can be electrochemically induced near room temperature by applied cathodic voltages as low as -1.2 V. Cyclic voltammetry in this range leads to eventual In³⁺ leaching into the perovskite layer in the form of InI₃, unambiguously identified by a binding energy signature of 445.9-446.3 eV measured by X-ray photoelectron spectroscopy. Furthermore, the etching is exacerbated by defects generated by O₂-plasma treatment of the ITO compared to UV-ozone cleaning, lowering the reaction potential and the electrochemical stability window of an ITO/MAPbI₃/Au device. Low-temperature, electrochemical reactivity at this interface has implications on operational stability, fundamental studies of hybrid perovskite materials, electron (or hole) transport layer free perovskite devices, reverse bias degradation, and other applications where ITO/hybrid perovskite contact is possible.