The characteristic time constant (τ) for a given R-C element can be calculated by multiplying the resistance with the associated capacitance. Therefore, the charge transfer time τCT of an electron to the electrolyte (associated with the lowest frequency semi-circle) can be calculated by τCT=RCTCcat, see Figure in the Supporting information). The time constant, representing the effective time until the photo-generated electrons are transferred to the electrolyte, decreases drastically from ~1 s (just before the onset) to several ms after the photocurrent onset. This indicates that the RuOx catalyst becomes active at negative potentials and that as the band banding in the Sb2Se3 increases, electrons can accumulate at the catalystelectrolyte interface and be transferred within a shorter time. These values and the decreasing trend of the time constant are in good agreement with those obtained by transient photocurrent (TPC) decay (see Figure in the Supporting information). In the TPC experiments, a green light pulse (5 % sun intensity) was illuminated on a Sb2Se3 photocathode under 10 % sun white LED at different potentials. When the colored light pulse was initiated, a sharp cathodic photocurrent spike was observed, which decayed until the photocurrent reached the steady state.