Effects of the electrolyte of DSCs on impedance spectra were evaluated by changing concentration of redox couple, viscosity, and additives to electrolyte. The relation with current–voltage characteristics ( I– V characteristics) was investigated. In many cases, the impedance component attributed to charge transfer at TiO 2|electrolyte interface demonstrated strong relation with the I– V characteristics. The recombination of electrons in TiO 2 with I 3 − in electrolyte was a key factor in determining performance of DSCs. To evaluate the effect of I 3 −, diffusion-limiting current in the electrolyte for various viscosities was evaluated by cyclic voltammetry. When the short circuit current (SCC) was almost equal to the diffusion-limiting current, strong influence of the diffusion coefficient on the impedance spectra was observed: impedance arcs were enlarged as the diffusion coefficient was decreased. On the other hand, when the diffusion-limiting current was larger than the SCC, photo-excitation and electron injection processes became dominating factors in the DSCs performance. The SCC was regulated by the charge recombination process at TiO 2|electrolyte interface, and thus the impedance component ω 3 was related to the performance in such condition.