We have investigated the influence of electrolyte composition on the photovoltaic performance of a dye-sensitized nanocrystalline TiO2 solar cell (DSSC) based on a Ru(II) terpyridyl complex photosensitizer (the black dye). We have also spectroscopically investigated the interaction between the electrolyte components and the adsorbed dye, The absorption peaks attributed to the metal-to-ligand charge transfer transitions of the black dye in solution and adsorbed on a TiO2 film, were red-shifted in the presence of Li cations, which led to an expansion of the spectral response of the solar cell toward the near-IR region. The photovoltaic performance of the DSSC based on the black dye depended remarkably on the electrolyte composition. We developed a novel efficient organic liquid electrolyte containing an imidazolium iodide such as 1,2-dimethyl-3-n-propylimidazolium iodide or 1-ethyl-3-methylimidazolium iodide (EMImI) for a DSSC based on the black dye. A high solar energy-to-electricity conversion efficiency of 9.2% (J(sc) = 19.0 mA cm(-2), V-oc = 0.67V, and FF = 0.72) was attained under AM 1.5 irradiation (100 mWcm(2)) using a novel electrolyte consisting of 1.5 M EMImI, 0.05 M iodine, and acetonitrile as a solvent with an antireflection film. (C) 2004 Elsevier B.V. All rights reserved.