Effect of surface polarization and structural deformation on the formation and stabilization of polarons in two-dimensional Ruddlesden-Popper metal halide perovskites

First-principles density-functional theory calculations were performed to reveal the effect of surface polarization and structural deformation on the formation and stabilization of the polaron in two-dimensional Ruddlesden-Popper perovskites. Our results revealed that the orientational distribution of organic cations induces surface polarization. The surface dipole moment can be well featured by the c axis distances between N and the nearest I atoms. Structural deformation and surface dipole moments result in separate real-space distributions of hole and electron polarons. Our results also reveal that the structural deformation of the [PbI6] sublattices and surface polarization are closely related to the reorientation of organic cations and can be effectively modulated by it. This reorientation significantly impacts the stabilization of polarons. Our understandings provide insight into the nature of polarons in two-dimensional Ruddlesden-Popper perovskites and general guidance for the proper selection of organic cations in two-dimensional perovskites for suitable applications in photovoltaic and optoelectronic devices.