Synthesis and characterization of urea-containing imidazolium iodide electrolyte for dye-sensitized solar cells

Novel gel-type ionic salts based on aminopropyl imidazolium iodide (APII) functionalized with urea were synthesized and used as the electrolyte in dye-sensitized solar cells (DSSCs). The synthesized APIIs were in a viscous gel state. The electrolytes exhibited the characteristics of an intra- or inter-molecular hydrogen bonding interaction through their urea bonds. The two synthesized electrolytes that contained two urea groups and two imidazolium salts simultaneously (APII-HM2, APII-HP2) were highly viscous and showed relative thermal stability compared to a commercial ionic liquid (IL) of DMII (methylmethylimidazolium iodide; DMII). These new electrolytes were examined by 1H NMR spectroscopy and their ionic conductivities and diffusion coefficients were measured. Among the six APIIs, the single urea-containing electrolyte (APII-HP1) exhibited a maximum solar photo-conversion efficiency of 7.31%, which was slightly higher than that of the reference (DMII, 6.59%).