Photoelectrochemical Characterization of Semitransparent WO3 Films

Tungsten trioxide films on transparent substrates (glass and F:SnO2 or indium-tin oxide coated glass) were prepared by various methods like doctor-blading, dip-coating, layer-by-layer painting, and spin-coating. Films of up to 10 X 10 cm were grown and characterized by X-ray diffraction, scanning electron microscopy, optical reflectance and transmittance, and photoelectrochemical measurements. Well-crystallized WO3 with monoclinic structure prevails on all substrates after annealing at or above 550DGC. Films grown via layer-by-layer painting and spin-coating using organic precursors consist of WO3 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 HClO4 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/cm2 (front-side illumination) and 0.67 mA/cm2 (back-side illumination) were drawn.