Density functional theory investigation of hypervalent iodine KICl2 passivation at PbI2 vacancy sites on the MAPbI3 surface

Abstract

This study explores the impact of hypervalent KICl2 passivation on the electronic properties and stability of MAPbI3 perovskite slabs with PbI2 vacancies using density functional theory (DFT). Adsorption energy calculations reveal that KICl2 exhibits stronger binding energy (−4.73 eV) compared to O2 (−3.32 eV) and H2O (−3.28 eV), indicating higher stability on the MAPbI3 surface. However, due to the potential for KICl2 to dissociate into KCl and ICl in solution, these compounds were also evaluated as alternative passivation agents. The surface free energy of the KICl2-passivated slab is the lowest among the configurations studied, further confirming its enhanced surface stability. The projected density of states (PDOS) and band structure analyses show that KICl2 passivation introduces defect states near the conduction band minimum (CBM), reducing the bandgap from 1.89 eV (clean surface) to 1.81 eV. These defect states, contributed by Cl-3p and I-5p orbitals, enhance charge separation, potentially improving carrier collection. In contrast, the KCl-ICl passivated surface exhibits flat states near valence band edge, which could increase hole density and reduce hole mobility. Optical absorption calculations indicate that the KICl2-passivated surface shows stronger absorption in the 3–7 eV range. These findings suggest that KICl2 passivation improves both the electronic properties and surface stability of MAPbI3, offering a promising strategy for enhancing perovskite solar cell efficiency.