Amphiphilic Polypyridyl Ruthenium Complexes with Substituted 2,2-Dipyridylamine Ligands for Nanocrystalline Dye-Sensitized Solar Cells

Two heteroleptic polypyridyl ruthenium complexes [Ru (dcbpy)(L)(NCS)2, where dcbpy is 4,4ʹ-dicarboxylic acid-2,2ʹ-bipyridine and L is N,N-di(2-pyridyl)dodecylamine or N,N-di(2-pyridyl)-tetradecylamine] have been synthesized and characterized by elemental analysis, voltammetry, 1H NMR, UV-vis, ATR-FTIR, and resonance Raman spectroscopies. Resonance Raman studies have revealed that the lowest unoccupied molecular orbital (LUMO) of the two sensitizers is localized on the dcbpy-ligand-bearing anchoring group. Nanosecond laser transient measurements have shown that dye regeneration by iodide in the electrolyte can efficiently compete with the recombination reaction of injected electrons trapped in the nanocrystalline TiO2 film with dye molecules in the oxidized state. Furthermore, these amphiphilic ruthenium complexes were successfully used as sensitizers for nanocrystalline dye-sensitized solar cells with efficiencies of 8.2% at the 100 mW cm-2 irradiance of air mass 1.5 solar light and 8.7% at lower light intensities.