Ambient Air Stability of Hybrid Perovskite Thin‐Film Transistors by Ambient Air Processing

Abstract Despite the widespread research on organic–inorganic hybrid perovskites, the ambient air instability and ion migration‐induced hysteresis in the current–voltage characteristics of their devices remain unsolved. Here, it is shown that stable ambient air operation of methylammonium lead iodide (MAPbI 3 ) thin‐film transistors can be achieved by solution processing of the MAPbI 3 film in ambient air via solvent engineering. N , N ‐dimethylformamide (DMF), mixed with dimethyl sulfoxide (DMSO) and hydroiodic acid (HI), is found to be the most suitable solvent for one‐step deposition in ambient air. While the HI promotes homogeneous nucleation, the low boiling point of DMF and the high vapor pressure and strong Lewis base property of DMSO lead to fast crystallization and consequent large grain size. The oxygen in air passivates grain boundary defects, thereby improving lateral conduction and minimizing grain boundary defect‐mediated ion migration. This approach paves the way for the simple fabrication of hybrid perovskites by eliminating the need for well‐controlled inert environments and provides a solution for the problem of ambient air stability in perovskite devices.