Mesoporous NiO electrodes were used in photoelectrochem. cells using iodide/triiodide-based redox electrolytes. Cathodic photocurrents were found upon visible light excitation. These photocurrents were enhanced when Coumarin 343 dye was adsorbed at the NiO surface or when a un-anchored dye (Coumarin 337) was added to the electrolyte. The proposed reaction for photocurrent generation is as follows: in the absence of dyes, excitation of triiodide gives diiodide radicals, which subsequently accept electrons from the NiO electrode. Enhanced photocurrent generation in the presence of dyes is possibly due to energy transfer from excited dye mols. to triiodide. Charge transport studies of C343-sensitized NiO suggest that hole transport in mesoporous NiO is due to hopping of pos. charge between Ni-surface atoms.