An improved process for the preparation of nanostructured metal species-based films in a flame aerosol reactor is provided. The process comprises combusting vaporized metal precursor, vaporized fuel and vaporized oxidizer streams to form metal species-based nanoparticles in a flame that are deposited onto a temperature controlled support surface and sintered to form the metal species-based nanostructured film. Improved nanostructured photo-watersplitting cells having a sunlight to hydrogen conversion efficiency of from about 10% to about 15%, dye sensitized solar cells having a sunlight to electricity conversion efficiency of from about 10% to about 20%, and nanostructured p/n junction solar cells having a sunlight to electricity conversion of from about 10% to about 20% are provided. Each cell type comprises a nanostructured metal oxide film having continuous individual columnar structures having an average width (w) and grain size criterion (X3) wherein w/10 is greater than X3.
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