High performance dye-sensitized solar cells using ionic liquids as their electrolytes

Room temperature ionic liquids have been used as electrolytes to investigate the performance and the characteristics in dye-sensitized solar cells (DSSCs). The ionic liquids used are 1-ethyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide(EMImTFSI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF(4)), 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF(6)), 1-ethyl-3-methylimidazolium dicyanamide (EMImDCA), and 1-butylpyridinium bis(trifluoromethanesulfonyl)imide (BPTFSI), in which 1-ethyl-3-methylimidazolium iodide (EMImI) and I-2 are dissolved as a redox. couple. The structure and the property greatly influence the DSSC performances. Especially, the photocurrents are affected by the ionic conductivity (viscosity) and charge transport by the exchange reaction between the iodide/tri-iodide redox couple. EMImDCA is specific in terms of enhancement of the open-circuit voltages. The photo-energy conversion efficiency of DSSCs with EMImDCA under 100 mW cm(-2) can be optimized up to 5.5%, when [I-] + [I-3(-)] = 2M and [I-]:[I-2] = 10:1 with the addition of 4-t-butylpyridine and LiI. (C) 2004 Elsevier B.V. All rights reserved.