The Defect Tolerance of Chalcogenide Perovskites BaZrS₃ and Ba₃Zr₂S₇

Chalcogenide perovskites (CPs), such as BaZrS₃, have been proposed as defect-tolerant materials, which maintain the electronic properties of their pristine form even in the presence of defects, with desirable characteristics such as large absorption coefficients, and long recombination lifetime for application as solar cells and optoelectronic devices. A systematic investigation of the defect tolerance of such perovskites is critical to develop a full understanding of their potential. We have used BaZrS₃ and Ba₃Zr₂S₇ as prototypical CPs and investigated their defect tolerance to intrinsic point defects using a combination of density-functional-theory calculations, spectroscopic and transport measurements. Our calculation indicates that most defects lead to shallow levels. However, we find that the sulfur vacancies have low formation energy and lead to a deep transition level that is spatially localized to act as non-radiative recombination center in BaZrS₃. Our work demonstrates that control over the chalcogen stoichiometry is critical to improve the performance of CPs. We also find that sulfur vacancies act as shallow-level defects in Ba₃Zr₂S₇, a derivative of BaZrS₃ with layered structure, making Ba₃Zr₂S₇ a promising alternative for semiconducting applications.