Water Infiltration in Methylammonium Lead Iodide Perovskite: Fast and Inconspicuous

While the susceptibility of CH₃NH₃PbI₃ to water is well-documented, the influence of water on device performance is not well-understood. Herein, we use infrared spectroscopy to show that water infiltration into CH₃NH₃PbI₃ occurs much faster and at a humidity much lower than previously thought. We propose a molecular model in which water molecules have a strong effect on the hydrogen bonding between the methylammonium cations and the Pb–I cage. Furthermore, the exposure of CH₃NH₃PbI₃ to the ambient environment increases the photocurrent of films in lateral devices by more than 1 order of magnitude. The observed slow component in the photocurrent buildup indicates that the effect is associated with enhanced proton conduction when light is combined with water and oxygen exposure