The complex defect chemistry of antimony selenide

Antimony selenide, Sb2Se3, is a highly promising solar absorber material with excellent optoelectronic properties; solar cell efficiencies are now poised to exceed 10%, after a rapid rise over the past few years. However, the open-circuit voltage ( V-oc) of most cells remains low, and such a high V-oc deficit, along with defect spectroscopy studies, suggest that recombination via deep trap states may be a limiting factor. A comprehensive study of all the intrinsic defects in Sb2Se3 is warranted - in this article, we calculate the formation energies and transition levels of these defects using hybrid Density Functional Theory. Our results demonstrate that cation-anion antisite defects have low formation energies, and possess multiple mid-gap transition levels, making them the most likely candidates for previously observed trap states, and possible recombination centres. Suppressing these dominant defects will be crucial for future cell development - thus we also present potential methods to counteract their detrimental effects and allow further improvement in efficiencies.