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Tungsten trioxide films on transparent substrates ͑glass and F:SnO 2 or indium-tin oxide coated glass͒ were prepared by various methods like doctor-blading, dip-coating, layer-by-layer painting, and spin-coating. Films of up to 10 ϫ 10 cm were grown and characterized by X-ray diffraction, scanning electron microscopy, optical reflectance and transmittance, and photoelectrochemical measurements. Well-crystallized WO 3 with monoclinic structure prevails on all substrates after annealing at or above 550°C. Films grown via layer-by-layer painting and spin-coating using organic precursors consist of WO 3 particulates of around 50 nm. Such films are specular and highly transparent outside the bandgap. Their photoactivity extends up to 470 nm and junctions with 0.1 M HClO 4 yield incident photon to current conversion efficiencies values above 0.9 at 313 nm and 0.1 at 436 nm. Under solar illumination, photocurrents of up to 0.91 mA/cm 2 ͑front-side illumination͒ and 0.67 mA/cm 2 ͑back-side illumination͒ were drawn.

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