Sb2S3/TiO2 Heterojunction Photocathodes: Band Alignment and Water Splitting Properties

Antimony sulfide (Sb₂S₃) is a promising light absorbing semiconductor for photovoltaic applications, though it remains vastly unexplored for photoelectrochemical water splitting. Sb₂S₃ was synthesized by a simple sulfurization of electrodeposited antimony metal at relatively low temperatures (240-300°C) with elemental sulfur. Using a TiO₂ buffer layer and a platinum co-catalyst, photocurrent densities up to ~ 9 mA cm^-2 were achieved at -0.4 V vs. RHE in 1 M H₂SO₄ under one sun illumination. Using XPS band alignment studies and potential dependent IPCE measurements, a conduction band offset of 0.7 eV was obtained for the Sb₂S₃/TiO₂ junction as well as an unfavorable band bending at the heterointerface, which explains the low photovoltage that was observed (~ 0.1 V). Upon inserting an In₂S₃ buffer layer, which offers a better band alignment, a 0.15 V increase in photovoltage was obtained. The excellent PEC performance and the identification of the origin of the low photovoltage of the Sb₂S₃ photocathodes in this work pave the way for the further development of this promising earth abundant light absorbing semiconductor for solar fuels generation.