Abstract

The defect properties at surfaces or grain boundaries of metal halide perovskites are largely unexplored due to the complexity of surface structures stirred by the rotational A-site cations with varied dipole moments. Using a combination of density functional theory (DFT) and time-dependent DFT methods, we study the nature of iodine vacancies at the surfaces of lead iodide perovskites (APbI3) with A-site cations including methylammonium (MA = CH3NH3+), formamidinium, and cesium. It is found that the light-induced charge distributions are sensitively dependent on MA orientation at the MAI-terminated surfaces with vacancies at the apical position while the electronic excitation is marginally affected by A-site species at both the AI- and PbI-terminated surfaces with vacancies at the equatorial site. Such variations of electronic excitation are rationalized by analyzing the electrostatic interactions between the A-site cations and charged defects as well as the projected p orbitals of Pb atoms at the bottom of the conduction band.

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