Sequential surface passivation for enhanced stability of vapor-deposited methylammonium lead iodide thin films

Understanding the correlation between surface passivation and degradation kinetics in vapor-deposited organic-inorganic hybrid perovskite thin films is crucial for developing strategies to enhance their structural integrity for long-term operational stability. Here, we demonstrate that the sequential introduction of vapor-phase phenethylammonium iodide (PEAI) and methylammonium (MAI) into methylammonium lead iodide (MAPbI(3)) thin films, which is obtained from PbI2, suppresses their degradation and enhances the ambient stability. Compared with the simultaneous PEAI introduction during the conversion of PbI2 to MAPbI(3), the MAPbI(3) films with sequential treatment exhibited higher PEAI surface coverage, which imparts superior resistance to degradation. Combined analyses of the exposure-time-dependent crystal structure evolution, photoemission profiles, and photocurrent generation characteristics of the films reveal that conformal PEAI passivation suppresses the volatile release of methylammonium (MA) species and the inclusion of O-2/H2O molecules. This study highlights the importance of developing a vapor-phase passivation strategy for innate polycrystalline perovskite thin films and their optoelectronic applications with long-term stability.