Different-sized nanocrystalline-TiO2 particles have been used for the optimization of photovoltaic er effects of dye-sensitized solar cells (DSCs) using an ionic-liquid (IL) electrolyte. Ru dye (Z907) was used for the IL-DSC optimization. The TiO2 nanoparticle sizes and the thickness of nanocrystalline- TiO2 electrodes ranged from 13 nm to 81 nm and 2 mu m to 23 mu m, respectively. The particle size of the nanocrystalline TiO2 film greatly a r ected the photovoltaic characteristics, particularly for the IL electrolyte due to limitation of the photocurrent by I-/I-3(-)-diffusion. The optimized electrode for IL-DSC had a 15 mu m thickness using a 27 nm diameter of nanocrystallineTiO(2) particles. In order to characterize the e r ect of the TiO2 particle size on the photovoltaic e r ects of IL-DSCs, a scanning electron micrograph (surface and cross section of nanoparticles), BET specific surface area analysis, pore-size distribution analysis, photocurrent transient