Firstly, the time-dependent diffusion of minority carriers occurring in picosecond-nanosecond windows and, secondly, recombination losses occurring in microsecond-millisecond windows were modeled with differential equations. The latter were incorporated as properties of active sources that were embedded into an equivalent circuit that had been tested previously. The shape and magnitude of the electrical response created by illuminating the photo-electrochemical cell were measured in the external circuit and were fitted quantitatively to the minority carrier diffusion model and to the recombination loss model operative in the respective time windows.