Binary room-temperature ionic liquids based electrolytes solidified with SiO_2 nanoparticles for dye-sensitized solar cells

摘要

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 BM1PF_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 BMIBF4 and BMIPF6, 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 100mW 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.