Ruthenium dyes with heteroleptic tridentate 2,6-bis(benzimidazol-2-yl)-pyridine for dye-sensitized solar cells: Enhancement in performance through structural modifications

Three heteroleptic pyridine/benzimidazole-based ruthenium sensitizers, [Ru(L1)(dcbpyH2)NCS](SCN) (Y1, L1 = 2,6-bis(1-benzylbenzimidazol-2-yl)-pyridine, dcbpyH2 = 4,4′-dicarboxylic acid-2,2′-bipyridine), [Ru(L2)(dcbpyH2)NCS](SCN) (Y2, L2 = 2,6-bis(1-ethylbenzimidazol-2-yl)-pyridine), and [Ru(L3)(dcbpyH2)NCS](SCN) (Y3, L3 = 2,6-bis(1-hexylbenzimidazol-2-yl)-pyridine) are synthesized and applied to dye-sensitized solar cells (DSSCs). The power-conversion efficiency of dye Y3 is higher than those of dyes Y1 and Y2, due to the modification of the auxochromic ligand with a hexyl moiety. The origins of the performance diversity in these devices have been studied with respect to power-conversion efficiency by UV–Vis absorption and emission spectra, cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent spectroscopy (IMPS), intensity modulated photovoltage spectroscopy (IMVS), and density functional theory (DFT) studies. The better solar-cell performance of Y3 compared to Y1 and Y2 was believed to derive from the enhanced electron lifetimes.

Three heteroleptic pyridine/benzimidazole-based ruthenium sensitizers have been synthesized and the influence of the benzimidazole substituents on the device performance in dye-sensitized solar has been studied. We found that the hexyl-substituted Y3 had a higher power conversion efficiency than those on phenyl-substituted Y1 and ethyl-substituted Y2, because the hexyl-substituted dye gave higher electron collection efficiency and availably retarded charge recombination.Figure optionsDownload as PowerPoint slideHighlights
► Three novel heteroleptic pyridine/benzimidazole-based ruthenium sensitizers.
► The benzimidazole substituents influence the device performance in DSSCs.
► The performance differences of three dyes are analyzed by electrochemical data.