Iodide Vacancy Defects Clustering in Pairs Rather Than in Isolation in a Lead Iodide Perovskite: Identification,...

Iodide (I^-) vacancy defects are strongly related to the stability of perovskite optoelectronic devices. The I^- vacancy in lead iodide perovskites is normally considered to exist in the form of a single isolated defect. However, we determined that the I^- vacancies cluster in pairs in specific ways in the typical perovskite of tetragonal CsPbI₃. This I^- vacancy-vacancy dimer is energetically more favorable than two isolated I^- monovacancies. It breaks the symmetry of the Pb-I octahedron, resulting in lattice distortion. Its origin lies in the special lattice distortion effect caused by the electron orbital interaction of the perovskite material. Furthermore, the I^- vacancy-vacancy dimer and the associated lattice distortion increase the carrier lifetime by 1.3 times compared to that of the system with two isolated I^- monovacancies, but they also compromise its structural stability. This new insight into the I^- vacancy defect will enhance our understanding of perovskite optoelectronic devices.