A hypothesis of the charge separation mechanism was proposed to elucidate the PEC performance enhancement in the Sb2Se3-H photoelectrode. Derived from the Tauc plots, the optical band gaps for both Sb2Se3 films were determined to be the same (1.17 eV, Figure ). The Fermi level (EF) position of both Sb2Se3 films can be determined by the flat band potential. The EF position with respect to the valence band maximum (i.e., the doping level)