The complex defect chemistry of antimony selenide

Abstract

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.