TiO<sub>2</sub> Hole Transport Layer Incorporated\nin a Thermally Evaporated Sb<sub>2</sub>Se<sub>3</sub> Photoelectrode\nExhibiting Low Onset Potential for Photoelectrochemical Applications

Developing\ncost-effective photoelectrodes with a low band gap in\nthe NIR-visible regions remains a challenge to achieve effective hydrogen\nproduction. We report the details of superstrate-configured photocathodes,\nconsisting of antimony selenide (Sb<sub>2</sub>Se<sub>3</sub>) light\nabsorbing layers with titanium dioxide (TiO<sub>2</sub>) as a hole\ntransport layer, exhibiting the capability for hydrogen evolution\nwith broad range light absorption enabled by the low band gap value\nof ∼1.2 eV of Sb<sub>2</sub>Se<sub>3.</sub> Strong anisotropy\nis a significant characteristic property of Sb<sub>2</sub>Se<sub>3</sub>, allowing superior electrical transportation along the [<i>hkl</i>] crystallographic orientation, which is obtained via\nclose space evaporation of presynthesized bulk material at a growth\ntemperature of 250 °C, over the solution-processed TiO<sub>2</sub> film on a fluorine-doped tin oxide (FTO) substrate. The superstrate-configured\nFTO/TiO<sub>2</sub>/Sb<sub>2</sub>Se<sub>3</sub> photocathode exhibited\na photocurrent density of 100 μA cm<sup>–2</sup> at −0.3\nV vs RHE in 0.5 M H<sub>2</sub>SO<sub>4</sub> under 1 sun illumination.\nTo further improve photocurrent density, Pt as a cocatalyst was deposited\nover Sb<sub>2</sub>Se<sub>3</sub> that led to enhanced photocurrent\nto 3 mA cm<sup>–2</sup> at −0.3 V vs RHE in 0.5 M H<sub>2</sub>SO<sub>4</sub> under 1 sun illumination. Despite the relatively\nlower photocurrent observed, which resulted due to a large conduction\nband offset (Δ<i>E</i><sub>CB</sub> = 0.99 eV) of\nthe TiO<sub>2</sub>/Sb<sub>2</sub>Se<sub>3</sub> interface in a superstrate\nconfiguration, a significantly lower onset potential of −0.1\nV vs RHE was observed. The results are encouraging due to the low\nband gap of Sb<sub>2</sub>Se<sub>3</sub>, photocorrosion stability,\nand straightforward fabrication, which is expected to assist for significant\noutcomes.