In this study, binary ionic liquids (bi-IL) of imidazolium salts containing cations with different carbon side chain lengths (C = 2, 4, 6, 8) and anions such as iodide (I −), tetrafluoroborate (BF 4 −), hexafluorophosphate (PF 6 −) and trifluoromethansulfonate (SO 3CF 3 −) were used as electrolytes in dye-sensitized solar cells (DSSCs). On increasing the side chain length of imidazolinium salts, the diffusion coefficients of I 3 − and the cell conversion efficiencies decreased; however, the electron lifetimes in TiO 2 electrode increased. As for different anions, the cell which contains 1-butyl-3-methyl imidazolium trifluoromethansulfonate (BMISO 3CF 3) electrolyte has better performance than those containing BMIBF 4 and BMIPF 6. From the impedance measurement, the cell containing BMISO 3CF 3 electrolyte has a small charge transfer resistance ( R ct2 ) at the TiO 2/dye/electrolyte interface. Moreover, the characteristic frequency peak for TiO 2 in the cell based on BMISO 3CF 3 is less than that of BMIBF 4 and BMIPF 6, indicating the cell with bi-IL electrolyte based on BMISO 3CF 3 has higher electron lifetime in TiO 2 electrode. Finally, the solid-state composite was introduced to form solid-state electrolytes for highly efficient DSSCs with a conversion efficiency of 4.83% under illumination of 100 mW cm −2. The long-term stability of DSSCs with a solidified bi-IL electrolyte containing SiO 2 nanoparticles, which is superior to that of a bi-IL electrolyte alone, was also presented.