New Family of Ruthenium‐Dye‐ Sensitized Nanocrystalline TiO2 Solar Cells with a High Solar‐Energy‐Conversion Efficiency

A new type of ruthenium complexes 6-8 with tridentate bipyridine-pyrazolate ancillary ligands has been synthesized in an attempt to elongate the π-conjugated system as well as to increase the optical extinction coefficient, possible dye uptake on TiO2, and photostability. Structural characterization, photophysical studies, and corresponding theoretical approaches have been made to ensure their fundamental basis. As for dye-sensitized solar cell applications, it was found that 6-8 possess a larger dye uptake of 2.4 x 10 -7 mol cm -2 , 1.5 x10 -7 mol cm -2 , and 1.3 x 10 -7 mol cm -2 , respectively, on TiO2 than that of the commercial N3 dye (1.1 x10 -7 mol cm -2 ). Compound 8 works as a highly efficient photosensitizer for the dye-sensitized nanocrystalline TiO 2 solar cell, producing a 5.65 % solar-light-to-electricity conversion efficiency (compare with 6.01 % for N3 in this study), a short-circuit current density of 15.6 mA cm -2 , an open-circuit photovoltage of 0.64 V, and a fill factor of 0.57 under standard AM 1.5 irradiation (100 mW cm -2 ). These, in combination with its superior thermal and light-soaking stability, lead to the conclusion that the concomitant tridentate binding properties offered by the bipyridine-pyrazolate ligand render a more stable complexation, such that extended life spans of DSSCs may be expected.