The as-deposited metallic Sb-H film, exposing planes with higher surface energies, preferentially reacts with Se atoms to lower their surface energy, forming a thermodynamically stable phase. Therefore, a faster rate of nucleation is expected for the Sb-H thin film, giving rise to more nanorods that are relatively thinner and longer compared to the case with a lower rate of nucleation, where the Sb2Se3 has more time to grow laterally (i.e., become thicker) before encountering a neighboring rod. X-ray photoelectron spectroscopy (XPS) measurements were further carried out to characterize the chemical state of both Sb2Se3 thin films. Figure shows XPS spectra of the Sb 3d core levels for the Sb2Se3-L and Sb2Se3-H surfaces, exhibiting identical results. The binding energies of 529.1 and 538.5 eV associated with Sb5/2 and Sb3/2 peaks were indexed to the oxidation state of Sb 3+ in Sb2Se3, confirming the formation of Sb2Se3. Peaks located at 529.7 and 539.1 eV were attributed to Sb5/2 and Sb3/2 of Sb2O3. A small oxygen peak at 532.2 eV belonging to O 1s further confirmed the existence of Sb2O3, which originated from the selenization process due to residual O2 in the tube. The formation of Sb2O3 is more favorable in the presence of O2 because of the large Gibbs free energy (-605 kJ/mol) and standard molar reaction enthalpy (-718 kJ/mol). Considering that no distinguishable peak from Sb2O3 can be observed in the XRD pattern, we assumed that Sb2O3 only existed on the film's surface, in accordance with previous literature. To evaluate the PEC performance of the Sb2Se3 photocathodes at the device level, an n-type TiO2 layer was coated on the surface of the Sb2Se3 via atomic layer deposition (ALD), which served as an electron selective contact. A nominal 2 nm Pt layer, acting as a hydrogen evolution catalyst, was deposited by sputtering. The device structure of FTO/Au/Sb2Se3/TiO2/Pt is depicted in Figure , and the cross-sectional SEM image of the complete device is shown in Figure . Figure reveals a thin TiO2 (∼ 50 nm) layer uniformly covering both nanostructured Sb2Se3 samples, regardless of their nanostructured morphology. The PEC performance of the Sb2Se3-L and Sb2Se3-H photoelectrodes was measured in a 1 M H2SO4 electrolyte (pH 0) under AM 1.5 G simulated illumination (100 mW cm -2 ), as seen in Figure . The Sb2Se3-L photocathode exhibited a photocurrent density of -15.2 mA cm -2 at 0 VRHE and an onset potential of 0.21 VRHE. In contrast, the Sb2Se3-H photocathode demonstrated a significant enhancement, with a photocurrent density of -22.1 mA cm -2 at 0 VRHE and an onset potential shift to 0.31 VRHE. The Sb2Se3-L photocathode exhibited a dark current at negative potentials (< -0.05 VRHE), suggesting the presence of pinholes in the film, whereas no dark current was observed in the Sb2Se3-H photocathode. This observation implies that a compact and pinhole-free Sb2Se3 film was synthesized by optimizing the metallic Sb film deposition conditions. Additionally, the stability of the Sb2Se3-H device was recorded in a 1 M H2SO4 solution at 0.2 VRHE shown in Figure . The photocurrent density remained at -10 mA cm -2 over 2 h and gradually decreased to -8 mA cm -2 after running 5 h, retaining 80% of its initial value.