Photoelectron spectroscopy is used to measure the electronic d. of states in the band gap region of a nanostructured TiO2 film. Such nanostructured films are used in dye-sensitized solar cells, and a plain TiO2 film as well as a dye-sensitized film were examd. To simulate the electrolyte effect on the energy levels at the oxide/dye/electrolyte interface in a solar cell, the d. of states in the band gap region for an electrochem. prepd. TiO2 film inserted with Li+ was measured. The distribution and chem. nature of electron trap states in the band gap and the energy matching between the LUMO level of the adsorbed dye, cis-bis(4,4'-dicarboxy-2,2'-bipyridine)-bis(isothiocyanato)ruthenium(II), and the TiO2 conduction band edge are discussed.