Electrochemical characterization and photovoltaic performance of the binary ionic liquid electrolyte of 1-methyl-3-propylimidazolium iodide and 1-ethyl-3-methylimidazolium tetrafluoroborate for dye-sensitized solar cells

Determination of triiodide diffusion coefficient, charge-transfer resistance and photovoltaic performance of the binary ionic liquid electrolyte of 1-methyl-3-propylimidazolium iodide (MPII) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) for dye-sensitized solar cells (DSSCs) were performed at varying volume ratios of MPII/EMIMBF4. Compared to pure MPII ionic liquid, the addition of EMIMBF4 not only increased triiodide diffusion coefficient, but also decreased charge-transfer resistance at Pt/electrolyte interface, leading to the notably improved photovoltaic performance of DSSC. The highest photoelectric conversion efficiency of 4.99% was obtained under light intensity of 100 mW/cm2 for the DSSC with the binary MPII/EMIMBF4 ionic liquid electrolyte when the volume ratio of MPII/EMIMBF4 was 50/50, which was much higher than that of pure MPII ionic liquid electrolyte (2.6%).