Revisiting the Exposed Surface Characteristics on the Stability and Photoelectric Properties of MAPbI3.

CH₃NH₃PbI₃ (MAPbI₃), as a promising candidate of photovoltaic materials, has attracted extensive interests due to its excellent photoelectric properties and low preparation cost. However, the relationship between synthesis parameter and performance is still unclear due to the overlook of exposed surface characteristics, limiting the mass-production and commercialization of MAPbI₃. Therefore, it is necessary to clarify the stability and photoelectric properties of different exposed surfaces of MAPbI₃ under humid environment. In this work, the stability and photoelectric properties of the MAI-terminated and PbI₂-terminated of MAPbI₃ (001) were thoroughly investigated using density functional theory calculation. To study the stability of exposed surface, adsorption energy of water molecules, ab initio molecular dynamics (AIMD), mean square displacement (MSD) and X-ray diffraction (XRD) were calculated. MSD of PbI₂-terminated surface is greater by two orders of magnitude compared to MAI-terminated surface. For the photoelectric properties of MAPbI₃, the bandgap, absorption coefficients, joint density of states (JDOS) and dielectric constants were investigated. The inhibitory effect of water on the photoelectric performance for PbI₂-terminated surface is more significant than that of MAI-terminated surface. Although the photoelectric properties of water molecules adsorption on MAI-terminated surface is basically unchanged, the diffusion of water molecules reduces the photoelectric properties of MAPbI₃. Overall, the stability and photoelectric properties of MAI-terminated surface are superior to PbI₂-terminated surface. Therefore, we strongly advocate paying attention to the exposed surface of MAPbI₃ during the thin film production process and adjusting synthesis parameters to prepare MAI-terminated surface dominated thin film, which should substantially improve the performance of MAPbI₃ in the application.