Isotype Heterojunction Solar Cells Using n‑Type Sb₂Se₃ Thin Films

The carrier-type of the emerging photovoltaic Sb₂Se₃ was evaluated for both thin films and bulk crystals via a range of complementary techniques. X-ray photoelectron spectroscopy (XPS), hot probe, Hall effect, and surface photovoltage spectroscopy showed films and crystals synthesized from the Sb₂Se₃ granulate material to be n-type with chlorine identified as an unintentional n-type dopant via secondary ion mass spectrometry analysis. The validity of chlorine as a dopant was confirmed by the synthesis of intrinsic crystals from metallic precursors and subsequent deliberate n-type doping by the addition of MgCl₂. Chlorine was also shown to be a substitutional n-type shallow dopant by density functional theory calculations. TiO₂/Sb₂Se₃ n–n isotype heterojunction solar cells with 7.3% efficiency are subsequently demonstrated, with band alignment analyzed via XPS.