Beginning with photocathodes based on Sb2Se3, which is an emerging light absorbing semiconductor for PEC water splitting and solar cells, it is successfully shown that each functional layer and interface in the multi-layered photocathodes can be investigated under operando conditions depending on the frequency domain at which the photophysical /electrochemical processes occur. The carefully verified model allows us to obtain in-depth information about the TiO2 layer as well as the Sb2Se3 layer (e.g. depletion layer thickness, carrier densities, charge carrier lifetimes under different light intensities and applied potentials) and to compare it with those data obtained by the EIS analysis of Cu2O and Si photocathodes.