High Molar Extinction Coefficient Ruthenium Sensitizers for Thin Film Dye-Sensitized Solar Cells

We present two sensitizers, Ru(4,4′-dicarboxyvinyl)-2,2′-bipyridine)(4,4′-dinonyl-2,2′-bipyridine)(NCS) 2 (K9) and Ru(4,4′-dicarboxy(phenylethenyl)-2,2′-bipyridine)(4,4′-dinonyl-2,2′-bipyridine)(NCS) 2 (K23), which were synthesized and characterized by analytical, spectroscopic, and electrochemical impedance measurements. The two sensitizers that contain hydrophobic alkyl chains and an extended π-conjugation bridge between carboxylic acid groups and the ruthenium chromophore center exhibit enhanced red response and higher molar extinction coefficients when compared to the Ru(4,4′-dicarboxy-2,2′-bipyridine)(4,4′-dinonyl-2,2′-bipyridine)(NCS) 2 (Z907) sensitizer. The performances of the K9, K23, and Z907 sensitizers in nanocrystalline TiO 2 -based thin film solar cells were studied using transparent 2.6-μm-thick mesoporous layers, which show short-circuit photocurrent densities ( J sc ) of 7.80, 8.31, and 7.16 mA/cm 2, corresponding to overall conversion efficiencies of 4.14, 4.41, and 4.06%, respectively. The increase in the J sc of the cells with K9 and K23 with respect to that with Z907 is due to the enhanced molar extinction coefficient of the new sensitizers. The incident monochromatic photon-to-current conversion efficiency for the K23 is plotted as a function of excitation wavelength show in the plateau region 79% and even at 700 nm 69%.