Photovoltage dependence on film thickness and type of illumination in nanoporous thin film electrodes according to a simple diffusion model

A simple model predicting the value of the open-circuit voltage at semiconductor nanostructured electrodes under steady-state conditions is presented. The model assumes that diffusion is the main driving force for electron transport. Analytical expressions are derived showing that the electron concentration near the back contact not only depends on the illumination intensity, light absorption coefficient, electron lifetime and diffusion coefficient for electrons, but also on the film thickness and type of illumination, either through the electrolyte or through the substrate. The behavior predicted by the model is contrasted with literature experimental results concerning TiO2 dye-sensitized solar cells.