Sb2S3/TiO2 Heterojunction Photocathodes: Band Alignment and Water Splitting Properties
<p>Antimony sulfide (Sb<sub>2</sub>S<sub>3</sub>) is a promising light absorbing semiconductor for photovoltaic applications, though it remains vastly unexplored for photoelectrochemical water splitting. Sb<sub>2</sub>S<sub>3</sub> was synthesized by a simple sulfurization of electrodeposited antimony metal at relatively low temperatures (240-300°C) with elemental sulfur. Using a TiO<sub>2</sub> buffer layer and a platinum co-catalyst, photocurrent densities up to ~ 9 mA cm<sup>-2</sup> were achieved at -0.4 V vs. RHE in 1 M H<sub>2</sub>SO<sub>4</sub> 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 Sb<sub>2</sub>S<sub>3</sub>/TiO<sub>2 </sub>junction as well as an unfavorable band bending at the heterointerface, which explains the low photovoltage that was observed (~ 0.1 V).<sub> </sub>Upon inserting an In<sub>2</sub>S<sub>3</sub> 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 Sb<sub>2</sub>S<sub>3</sub> photocathodes in this work pave the way for the further development of this promising earth abundant light absorbing semiconductor for solar fuels generation.</p>