A New Ionic Liquid Electrolyte Enhances the Conversion Efficiency of Dye-Sensitized Solar Cells

An ionic liquid electrolyte composed of 1-methyl-3-propylimidazolium iodide, 1-methyl-3-ethylimidazolium dicyanamide, and lithium iodide (LiI) was combined with an amphiphilic polypyridyl ruthenium sensitizer to obtain a solar cell based on a solvent-free electrolyte that had an efficiency of 6.6% at an irradiance of air mass 1.5 (AM 1.5, 100 mW cm-2) and >7.1% at lower light intensities. This is the first time such a high efficiency was obtained for dye-sensitized solar cells with pure ionic liquid electrolytes. A thin-layer electrochemical cell was used to determine the redox potential of sensitizers anchored on TiO2 nanocrystalline film by square-wave voltammetry. Laser transient absorbance measurements revealed that a significant enhancement of the device efficiency, after adding LiI to the ionic liquid electrolyte, could be ascribed to an increase in the electron injection yield and dye regeneration rate.