Uncovering the Veil of the Degradation in Perovskite CH₃NH₃PbI₃ upon Humidity Exposure: A First-Principles Study

Methylammonium lead iodide perovskite, CH₃NH₃PbI₃ (MAPbI₃), has made great progress in its efficiency as used in solid-state solar cells during recent years. Meanwhile, the degradation of its performance in moisture has attracted great attention, but the specific mechanism is not yet fully established. The water effects on the detailed structure and properties of the perovskite CH₃NH₃PbI₃ have been carefully explored based on first-principles calculations. The results reveal that the water adsorption energy on the CH₃NH₃PbI₃ (001) surface is ∼0.30 eV, while the water can easily penetrate into the surface in the form of molecular state owing to the huge interspace of CH₃NH₃PbI₃, which can further corrode down the whole structure gradually. More importantly, the deformation of the structure greatly affects the electronic structure, which decreases the optical absorption. Such work paves an important way to understand the initial degradation progress of the perovskite structure under the humidity condition, which should help to optimize the structure to prevent the penetration of water in the system.