Iodide Vacancy Defects Clustering in Pairs Rather Than in Isolation in a Lead Iodide Perovskite: Identification, Origin, and Implications

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.