Atomic theory of point defect assisted carrier recombination in Rb₃Sb₂I₉

Rubidium Antimony Iodide (Rb₃Sb₂I₉) is on the frontier of perovskite-inspired halide semiconductor research, with its lead-free nature and optoelectronic properties pointing to its significant potential for various energy harvesting and sensing applications. However, the performance bottlenecks that have emerged from Rb₃Sb₂I₉ device studies to date highlight the importance of identifying its defect states that act as recombination centers. Here we examine the structure, energetics and electronic properties of intrinsic point defects using ab initio density functional methods. Rubidium vacancies and interstitials are found to be common defects, but they have very shallow gap states and may not enhance recombination significantly beyond that of bulk effects. In contrast, iodine vacancies are also common but are deep defects whose recombination behavior may be important in many circumstances. Our energy calculations for iodine vacancies quantitatively match several experiments. Strategies are suggested for ameliorating these defects in order to move Rb₃Sb₂I₉ toward realizing its full potential.