Synthesis and Electrochemical Properties of 2,6-Bis(quinoline-2-yl)pyridyl Ruthenium Complexes as Near-Infrared Sensitizers for Dye-Sensitized Solar Cells

New ruthenium(II)--polypyridyl complexes 1a -- 1d ( 1a : $\text{X}= \text{Y}= \text{H}$, 1b : $\text{X}= \text{H}$, $\text{Y}= \text{Cl}$, 1c : $\text{X}= \text{H}$, $\text{Y}= \text{Me}$, 1d : $\text{X}= \text{COOH}$, $\text{Y}= \text{H}$) having 2,6-bis(4-carboxyquinolin-2-yl)pyridine derivatives as ligands were synthesized as sensitizers for dye-sensitized solar cells (DSCs) and their photophysical and photochemical properties were characterized. The photovoltaic performance of DSCs sensitized with 1a -- 1d was found to be different. The DSC sensitized with 1a exhibits higher efficiency and IPCE value than those sensitized with 1b -- 1d . The APCE value of the DSC sensitized with 1a was almost 80% in the 500--800 nm range. Therefore, the performance of the DSC sensitized with 1a might improve if the adsorption of 1a on the TiO 2 surface could be appropriately controlled by investigation of dye immersion condition or introduction of bulky substituents on the ligand in order to suppress dye aggregation.