Titania surface modification and photovoltaic characteristics with tungsten oxide

WO3-coated TiO2 film was prepared by depositing TiO2 suspension containing small amounts of ammonium tungstate solution. The morphology and structure of the samples were characterized with high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and photoluminescence (PL) emission spectrum. The results showed that WO3 formed a coating layer on surface of TiO2 and significantly reduced the surface traps of TiO2 nanoparticles. Transient photovoltage and electrochemical impedance measurements (EIS) were employed to study the charge separation/recombination process. The results revealed that the charge recombination was greatly retarded and the electron lifetime was increased due to the coating layer of WO3. These observations showed good correlation with current-voltage analyses of dye-sensitized solar cell fabricated from these films, with WO3 overlayer resulting in an increase in open-circuit voltage of up to 37 mV and 11% improvement in overall device efficiency.