Case of the Bromine Vacancy in Cs4PbBr6

Typically defect tolerance is equated with a lack of deleterious defects or with abundant defects creating only shallow levels. Here, we address the idea that deep defects, when unavoidable, do not guarantee harmful consequences. Using halogen vacancy as a common defect among halides, we explore its behavior in Cs4PbBr6. It is a large gap material (band gap of similar to 4 eV) known for its green emission at similar to 520 nm. We show that its Br-vacancy is indeed a deep defect as obtained from hybrid density functional calculations. An analysis of the configuration coordinate diagram corresponding to the defect's charge transition levels enables us to conclude that the nonradiative recombination cycle will be hampered by an extremely slow hole capture process. Therefore, Br-vacancy will not suppress light emission in Cs4PbBr6. Although this finding does not signal that all deep defects will behave similarly, it indicates that defect tolerance may be achievable despite their occurrence.