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 × 10^-7 mol cm^-2,1.5 × 10^-7 mol cm^-2, and 1.3 × 10^-7 mol cm ^-2, respectively, on TiO₂ than that of the commercial N3 dye (1.1×10^-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 mAcm^-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.