Iodide and charge migration at defective surfaces of methylammonium lead triiodide perovskites: The role of hydrogen bonding

• Iodide migration induces reorientation and rotation of MA cations at the surfaces. • Activation barriers are connected with reorientation and rotation of MA cations. • Light-triggered carrier dynamics is largely affected by hydrogen bonding. • Photo-induced carrier dynamics at MAI- and PbI-terminated surfaces are different. • Inorganic lattice at the surfaces is stiffened by hydrogen bonding. Methylammonium lead triiodide perovskite (CH 3 NH 3 PbI 3 ) solar cells have exhibited impressive potential in photovoltaic applications, encouraging further work to improve operating stability. Ionic migration has been proposed to be a possible cause of the current-voltage hysteresis which is responsible for the instability of the CH 3 NH 3 PbI 3 solar cells. Motivated by the variation of the surface geometries of the CH 3 NH 3 PbI 3 material when going from the pristine to defective surfaces with the iodine vacancies, we adopt the density functional theory method to study the iodide migration along different paths at the defective surfaces followed by employing the time-dependent density functional theory method to calculate the light-induced electronic states along the paths. We find that the iodide movement is largely tuned by the reorientation and rotation of the organic cations with the disruption and formation of the hydrogen bonding during the iodide migration. Besides, the migration of the light-induced charge carriers varies along the paths with different orientations of the organic cations. We attribute the complicated dynamics of the mobile iodide ions and the associated trap states to the hydrogen bonding at the surfaces, providing crucial guidance for improving the stability and charge carrier lifetime in the CH 3 NH 3 PbI 3 and other metal halide perovskites.