In this paper, we studied the influence of different cations on redox behavior of I− and I3 − by cyclic voltammetry and electrochemical impedance spectroscopy. It was demonstrated that increasing cation size tends to give rise to higher reductive activity of I− and lower diffusion coefficient of I3 − in these cations, alkylimidazolium, [Na⊂15-C-5]+ and [K⊂18-C-6]+. Moreover, we measured the performance of dye-sensitized solar cells (DSCs) with electrolyte containing [K⊂18-C-6]I or 1,2-dimethyl-3-propylimidazolium iodide (DMPII). It was found that dye-sensitized solar cells (DSCs) with [K⊂18-C-6]I give a little higher short-circuit photocurrent density and a little lower fill factor than DSCs with DMPII.