As Sb2Se3 is a p-type semiconductor, one would expect the p-type absorber to go from accumulation to the flat band potential, and then to the depletion regime with increasing negative bias. This also implies that one can perform a Mott-Schottky analysis when one is able to determine the depletion layer capacitance (Cdep after the photocurrent onset, Figure ). Drawing a Mott-Schottky plot with the presumable Cdep yields a doping density for the Sb2Se3 semiconductor of 8.07×10 17 cm -3 , which is in close agreement with literature values, verifying our interpretation. We also performed EIS measurements on the multilayer photocathode in the dark to obtain the flat band potentials of Sb2Se3 and TiO2 (see Figure in the Supporting Information) showing the actual doping density (~2×10 17 cm -3 ) without a contribution from light generated charges. Interestingly, the flat band potential deviates in the dark (~0.45 VRHE) and under illumination (~0.15 VRHE). The discrepancy might originate from several different effects. One effect is originating from the actual overpotential of the RuOx for hydrogen evolution. The second effect probably originates from the additional photogenerated charge carriers, as also explained in the literature. Normally, one would expect under illumination that the slope in the Mott-Schottky plots show a higher "doping" due to the additional photogenerated charges, but that near the actual flat band potential the slope of dark and light Mott-Schottky plot should nearly overlap as the photogenerated charge carriers will recombine under weak band bending.