Imidazolium functionalized cobalt tris(bipyridyl) complex redox shuttles for high efficiency ionic liquid electrolyte dye-sensitized solar cells

Abstract

Co^II/III redox couples and their derivatives have been extensively studied and applied as redox mediators for high efficiency organic solvent DSSCs. However, Co^II/III complex redox mediator-based ionic liquid electrolyte DSSCs have not been studied so far due to the poor solubility of most Co^II/III complexes in ionic liquid electrolytes. Herein, an imidazolium functionalized cobalt tris(bipyridyl) complex redox mediator ([Co((MeIm-Bpy)PF₆)₃]^2+/3+) (((MeIm-Bpy)PF₆)₃ = 3,3′-(2,2′-bipyridine-4,4′-diyl-bis(methylene))bis(1-methyl-1H-imidazol-3-ium)hexafluorohosphate) with high redox potential and good solubility in ionic liquid electrolyte has been synthesized and applied in ionic liquid electrolyte DSSCs. Using the dye N719 as the photosensitizer, overall power conversion efficiencies of 7.37% and 8.29% are achieved in binary ionic liquid-based electrolyte under 1.5 solar spectrum illumination at 100 and 50 mW cm⁻², respectively. Both values are considerably higher than those of the I⁻/I₃⁻ redox couple-based ionic liquid electrolyte.