Four-electron negative- U vacancy defects in antimony selenide

Abstract

The phenomenon of negative-U behavior, where a defect traps a second charge carrier more strongly than the first, has been established in many host crystals. Here, we report the case of four-carrier transitions for both vacancy defects in Sb2Se3. A global structure searching strategy is employed to explore the defect energy landscape from first principles, revealing large atomic reconfigurations which facilitate a major charge redistribution. A thermodynamic analysis of the accessible charge states reveals a four-electron negative-U transition (Δq=4) for both VSe and VSb which, combined with previous calculations for antisites and interstitials, now demonstrates amphoteric behavior for all intrinsic point defects in Sb2Se3, with an impact on its usage in solar cells. The unusual behavior is facilitated by valence alternation, a reconfiguration of the local bonding environments, characteristic of both Se and Sb. © 2023 authors. Published by the American Physical Society.