TiO<sub>2</sub> Hole Transport Layer Incorporated in a Thermally Evaporated Sb<sub>2</sub>Se<sub>3</sub> Photoelectrode Exhibiting Low Onset Potential for Photoelectrochemical Applications
Thatheyus Peter Xavier, P. Malar, Chih‐Yu Kuo, Mani Govindasamy
Abstract
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 (Sb 2 Se 3 ) light absorbing layers with titanium dioxide (TiO 2 ) 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 Sb 2 Se 3. Strong anisotropy is a significant characteristic property of Sb 2 Se 3, 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 TiO 2 film on a fluorine-doped tin oxide (FTO) substrate. The superstrate-configured FTO/TiO 2 /Sb 2 Se 3 photocathode exhibited a photocurrent density of 100 μA cm –2 at −0.3 V vs RHE in 0.5 M H 2 SO 4 under 1 sun illumination. To further improve photocurrent density, Pt as a cocatalyst was deposited over Sb 2 Se 3 that led to enhanced photocurrent to 3 mA cm –2 at −0.3 V vs RHE in 0.5 M H 2 SO 4 under 1 sun illumination. Despite the relatively lower photocurrent observed, which resulted due to a large conduction band offset (Δ E CB = 0.99 eV) of the TiO 2 /Sb 2 Se 3 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 Sb 2 Se 3, photocorrosion stability, and straightforward fabrication, which is expected to assist for significant outcomes.