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.