Phenomenally High Molar Extinction Coefficient Sensitizer with “Donor−Acceptor” Ligands for Dye-Sensitized Solar Cell Applications

A phenomenally high molar extinction coefficient heteroleptic ruthenium(II) complex [Ru(4,4′-carboxylic acid-2,2′-bipyridine)(4,4′-(4-{4-methyl-2,5-bis[3-methylbutoxy]styryl}-2,5-bis[3-methylbutoxy]-2,2′-bipyridine)(NCS)2] (DCSC13) was synthesized by incorporating donor−acceptor ligands. The absorption spectrum of the DCSC13 sensitizer is dominated by metal-to-ligand charge-transfer transitions (MLCT) in the visible region, with absorption maxima appearing at 442 and 554 nm. The lowest MLCT absorption bands are red-shifted, and the molar extinction coefficients of these bands are significantly higher at 72 100 and 30 600 M−1 cm−1, respectively, when compared to those of the analogous [Ru(4,4′-carboxylic acid-2,2′-bipyridine)(4,4′-dimethyl-2,2′-bipyridine)(NCS)2] (N820) sensitizer. The DCSC13 complex, when anchored on nanocrystalline TiO2 films, exhibited increased short-circuit photocurrent and consequent power-conversion efficiency when compared with the N820 sensitizer.