Unraveling the Photogenerated Electron Localization on the Defect-Free CHNHPbI(001) Surfaces: Understanding and Implications from a First-Principles Study.

The localization of photogenerated electrons in photovoltaic and photocatalytic materials is crucial for reducing the electron-hole recombination rate. Here, the photogenerated electron localization is systematically investigated on the CHNHPbI (MAPbI) perovskite using first-principles calculations. It is found that under vacuum conditions, the photogenerated electron is delocalized in the MAPbI bulk as well as on the stochiometric MAPbI(001) surface with the CHNHI (MAI) termination, while it is trapped on the defect-free PbI-terminated surface. Our molecular dynamics simulations reveal that the introduction of solutions will prompt the formation of localized electronic states. The photogenerated electron is discovered to be localized on both the MAI- and PbI-terminated surfaces in the presence of solutions with different concentrations of HI, from pure water to the saturated solution. We demonstrate that the Pb-I bond weakening or breaking resulting in an unsaturated coordination of a Pb site is the prerequisite to trap the photogenerated electron.