TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Process: (I) is a layer of an oxide of a Group Ib - VIIb or VIII metal, specifically an oxide of titanium, cerium, vanadium, iron, copper, zinc, zirconium, niobium, molybdenum, ruthenium, tantalum, tungsten or praseodymium. (I) is especially of titanium dioxide (TiO2), particularly in anatase form. The colloid dispersion is a colloidal suspension, preferably having an average particle size of less than 50 (especially ca. 7) nm. The thickness of the layer (I) is less than 100 (especially less than 10) nm. The colloid dispersion especially contains particles of TiO2 or its organometallic precursor; in particular the TiO2 particles are obtained by polymerization of titanium alkoxides, preferably by hydrolysis and polymerization of titanium isopropoxide in propanol. Thermal spraying is carried out by plasma spraying, preferably under atmospheric conditions. The substrate is of glass (preferably float glass), plastics or fiber-reinforced plastics. EXAMPLE - A titanium dioxide (TiO2) colloidal dispersion, containing 5 wt. % TiO2 of average particle size 7 nm, was prepared by controlled hydrolysis and polymerization of titanium isopropoxide in anhydrous propanol using acetylacetone as protectant and caproic acid as catalyst. A working electrode was prepared by coating a fluorine-doped tin oxide (FTO) electrode with the dispersion using a water-cooled injection system attached to a direct current plasma torch, operated using an argon-helium mixture at 280 A, ca. 20 kW and 1 bar. The final coating was obtained in 20 spraying cycles, the substrate temperature not exceeding 175degreesC. A solar cell (sensitization cell) comprised: (i) the transparent coated substrate with a nanocrystalline TiO2 layer produced as above (thickness 40 microns) as working electrode; (ii) a solution with methoxy-propionitrile as solvent and iodine-iodide as redox electrode, infiltrated into the TiO2 layer; and (iii) a counter-electrode consisting of a conductive, transparent glass catalytic substrate, coated with a thin conductive platinum film on the electrolyte side.