Design and Characterization of Heteroleptic Ruthenium Complexes Containing Benzimidazole Ligands for Dye-Sensitized Solar Cells: The Effect of Fluorine Substituents on Photovoltaic Performance

Abstract

"We designed heteroleptic ruthenium complexes (RD12-RD15) containing fluoro-substituted benzimidazole ligands for dye-sensitized solar cells (DSSCs). These dyes were synthesized according to a typical one-pot procedure with the corresponding ancillary ligands produced in two simple steps; they were prepared into DSSC devices according to the same conditions of fabrication. The eventual devices show a systematic trend of increasing V-OC and decreasing J(SC) with fluorine atoms of increasing number substituted on the ligand. The charge extraction results show that upward shifts of the TiO2 potential occurred when the fluoro-substituted dyes were sensitized on TiO2 with a systematic trend of shift N719 > RD15 (with 5 F) > RD12 (with 2 F) > RD5 (no F); the intensity modulated photovoltage spectra indicate that those fluoro substituents retard charge recombination with the electron lifetimes (tau(R)) in the order RD15 > RD12 > RD5 > N719, consistent with the variation of V-OC for the systems."