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 pi-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 TiO2-based thin film solar cells were studied using transparent 2.6-mu m-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 die K23 is plotted as a function of excitation wavelength show in the plateau region 79% and even at 700 nm 69%.