The TiO2 layer was deposited on the Sb2Se3 thin film using a thermal ALD system (PICOSUN, R-200). The deposition chamber temperature was 120 ºC with tetrakis(dimethylamino)titanium (TDMAT, Aldrich, 99.99%) and H2O as the precursors for Ti and O, respectively. The cylinder temperature was held at 85 ºC and room temperature for TDMAT and H2O, respectively. For the Sb2Se3 photocathodes, 930 deposition cycles were used to obtain approximately 50 nm TiO2 layers. A galvanostatic photo-deposition technique was used for RuOx HER catalyst deposition. The prepared electrode (FTO/Au/Sb2Se3/TiO2) was immersed in a 1.3 mM potassium perruthenate (KRuO4, Alfa Aesar) solution at a current density of -28.3 μA cm -2 for 15 min under simulated 1 sun illumination.