The photoelectrochem. properties of colloidal film electrodes are compared with solid transparent thin films of TiO2. In particular the information that can be derived from anal. of the action spectra for front and back side illumination of the films is given. The mechanism of charge sepn. in the colloidal film is qual. discussed in terms of the kinetics at the electrode-electrolyte interface, and some effects of the presence of O2 in the electrolyte are demonstrated. The solar energy efficiency from measurements on dye-sensitized TiO2 film electrodes in solar cells is given.