The dye-sensitized TiO2 nanocrystalline solar cell utilizing the iodide/triiodide redox mediator served as the system of reference for a theoretical characterization and computational simulation used to scrutinize its performance when viewed as an integral system incorporating a porous counter electrode and a porous spacer layer in between. The concentration profiles of the redox mediator of the thin-layer solar cell, as well as the concentration (mass-transfer) overpotential established on the counter electrode and the limiting current of the cell, are affected by the addition of a separation layer between the electrodes and by the geometric and structural properties of the counter electrode itself. Numerical solutions could be obtained from the mathematical model simulating the system that can explain the behavior observed in experimental cells. The feasibility of the porous counter electrode as an alternative is discussed through the model predictions and the experimental kinetic performance data of candidate materials.