Within today’s global challenge to capture and utilize solar energy for a sustainable development on a grand scale, dye-sensitized solar cells (DSCs) represent a particularly promising approach to the direct conversion of light into electrical energy at low cost and with high effi ciency [13.1-13.6]. In these devices, a dye sensitizer absorbs the solar radiation and transfers the photoexcited electron to a wide band-gap semiconductor electrode consisting of a mesoporous oxide layer based on nanometer-sized particles. The concomitant hole is transferred to the redox electrolyte [13.7], typically iodide/triiodide in solution or a hole-transporting material in the solid state.