NOVELTY - Nanostructured photo-water splitting cell for producing hydrogen, comprises: a photoanode comprising a support and a nanostructured metal oxide film disposed on at least one surface of the support, where: the film comprises continuous individual columnar structures oriented approximately normal to the support; the columnar structures have an average width (w) and a grain size criterion (Xs); and (w/10) is greater than (Xs), and a cathode comprising a counter electrode, where the nanostructured photo-water splitting cell has a sunlight to hydrogen conversion efficiency of 10-15%.    USE - The nanostructured photo-water splitting cell is useful for producing hydrogen. The solar cells are useful for the conversion of photons into electric energy. The nanostructured films are useful for the preparation of high efficiency photo-water splitting cells for the preparation of hydrogen gas and for the preparation of high efficiency dye-sensitized solar cells and p/n junction oxide solar cells.    ADVANTAGE - The method is a low cost method for the preparation of nanostructured films having high surface area and having tailored morphological characteristics suitable for applications in catalytic reactors and photovoltaic films. The method is a single step and controlled process for the preparation of photoactive films using a flame aerosol reactor. The photovoltaic films have high efficiency for the conversion of ultraviolet light into electrical current by the photocatalyst, and hydrogen by water splitting.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a nanostructured dye-sensitized solar cell comprising an electron conducting layer comprising a support and the nanostructured metal oxide film, a light absorbing layer and a hole-conducting layer, where the nanostructured dye-sensitized solar cell has a sunlight to electricity conversion efficiency of 1-20%;    (2) a nanostructured positive(p)/negative(n) junction solar cell comprising an n-type oxide semiconductor layer comprising a support and the nanostructured metal oxide film and a p-type oxide semiconductor layer comprising a support and the nanostructured metal oxide film, where the nanostructured p/n junction solar cell has a sunlight to electricity conversion of 10-20%; and    (3) the preparation of a metal species based nanostructured film in a flame aerosol reactor comprising introducing a vaporized metal precursor stream, introducing a vaporized fuel stream, introducing a vaporized oxidizer stream, combusting the metal precursor stream, the fuel stream and the oxidizer stream in a flame to form metal species based nanoparticles in the flame region, depositing the metal species-based nanoparticles on a support surface, where the temperature of the surface is controlled, and sintering the metal species-based nanoparticles to form the metal species-based nanostructured film.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic illustration of a flame aerosol reactor.    Metal precursor source (1)    Metal precursor (2)    Metal precursor feed line (3)    Fuel source (5)    Oxidizer source. (10)