High Quantum Yield Sensitization of Nanocrystalline Titanium Dioxide Photoelectrodes with cis-Dicyanobis(4,4‘-dicarboxy-2,2‘-bipyridine)osmium(II) or Tris(4,4‘-dicarboxy-2,2‘-bipyridine)osmium(II) Complexes

Osmium polypyridyl complexes were used as sensitizers in solar cells that utilize nanocrystalline titanium dioxide photoelectrodes. Exposure of TiO_2 electrodes to sources of Os^(II)(H_2L‘)_2(CN)_2 (where L‘ is 4,4‘-dicarboxylato-2,2‘-bipyridine) or Os^(II)(H_2L‘)_3^(2+) extended the light absorption and spectral response of the cell to longer wavelengths than did exposure of TiO_2 to Ru(H_2L‘)_2(NCS)_2. The Os complexes also provided very high external quantum yields for photocurrent flow and produced open-circuit voltages similar to those of the Ru complex. The Os-based systems therefore offer promise in developing efficient dye-sensitized nanocrystalline TiO_2-based photoelectrochemical cells.