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

This study explores the impact of hypervalent KICl 2 passivation on the electronic properties and stability of MAPbI 3 perovskite slabs with PbI 2 vacancies using density functional theory (DFT). Adsorption energy calculations reveal that KICl 2 exhibits stronger binding energy (−4.73 eV) compared to O 2 (−3.32 eV) and H 2 O (−3.28 eV), indicating higher stability on the MAPbI 3 surface. However, due to the potential for KICl 2 to dissociate into KCl and ICl in solution, these compounds were also evaluated as alternative passivation agents. The surface free energy of the KICl 2 -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 KICl 2 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-3 p and I-5 p 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 KICl 2 -passivated surface shows stronger absorption in the 3–7 eV range. These findings suggest that KICl 2 passivation improves both the electronic properties and surface stability of MAPbI 3 , offering a promising strategy for enhancing perovskite solar cell efficiency.