A new thiocyanate-free cyclometallated ruthenium complex for dye-sensitized solar cells: Beneficial effects of substitution on the cyclometallated ligand

A new thiocyanate-free cyclometallated 2-phenylpyridine Ru(II) complex, [Ru(dFppyCF3)(dcbpy)2]+PF6− (dFppyCF3 = 2-(2,4-difluorophenyl)-5-trifluoromethyilpyridine; dcbpy = 2,2′-bipyridine-4,4′-dicarboxylic acid), containing an electronwithdrawing trifluoromethyl group on the pyridine ring of the cyclometallated ligand, was synthesized and used as photosensitizer in DSSC devices. Its optical and electrochemical properties and stability behaviour towards ligand exchange with the common solar cell additive 4-tert-butylpyridine was compared to that of benchmark DSSC dye N719 and of the reference complex [Ru(dFppy)(dcbpy)2]+PF6−. Substitution of the pyridine ring by the CF3 group afforded enhanced optical properties and a larger overall power conversion efficiency of the corresponding DSSC (3.7%), with a significant improvement compared to the reference cyclometallated complex under the same fabrication conditions.