TiO₂ Hole Transport Layer Incorporated in a Thermally Evaporated Sb₂Se₃ Photoelectrode Exhibiting Low Onset Potential for Photoelectrochemical Applications

Developing cost-effective photoelectrodes with a low band gap in the NIR-visible regions remains a challenge to achieve effective hydrogen production. We report the details of superstrate-configured photocathodes, consisting of antimony selenide (Sb2Se3) light absorbing layers with titanium dioxide (TiO2) as a hole transport layer, exhibiting the capability for hydrogen evolution with broad range light absorption enabled by the low band gap value of ∼1.2 eV of Sb2Se3. Strong anisotropy is a significant characteristic property of Sb2Se3, allowing superior electrical transportation along the [hkl] crystallographic orientation, which is obtained via close space evaporation of presynthesized bulk material at a growth temperature of 250 °C, over the solution-processed TiO2 film on a fluorine-doped tin oxide (FTO) substrate. The superstrate-configured FTO/TiO2/Sb2Se3 photocathode exhibited a photocurrent density of 100 μA cm–2 at −0.3 V vs RHE in 0.5 M H2SO4 under 1 sun illumination. To further improve photocurrent density, Pt as a cocatalyst was deposited over Sb2Se3 that led to enhanced photocurrent to 3 mA cm–2 at −0.3 V vs RHE in 0.5 M H2SO4 under 1 sun illumination. Despite the relatively lower photocurrent observed, which resulted due to a large conduction band offset (ΔECB = 0.99 eV) of the TiO2/Sb2Se3 interface in a superstrate configuration, a significantly lower onset potential of −0.1 V vs RHE was observed. The results are encouraging due to the low band gap of Sb2Se3, photocorrosion stability, and straightforward fabrication, which is expected to assist for significant outcomes.