Structural and photovoltaic properties of binary TiO2–ZrO2 oxides system prepared by sol–gel method

Sole component of titania, zirconia and binary TiO2–ZrO2 oxides with various molar ratio of zirconia content were prepared by sol–gel methods of surfactant assisted mechanism. The samples were calcined at different temperatures and characterized by nitrogen adsorption porosimetry, XRD, TG–DTA, SEM and diffuse reflectance UV–vis spectra. At 500 °C, the crystalline phase of pure titania is an anatase phase and pure zirconia is a tetragonal. The binary oxides show the anatase-type of titania at the molar ratio up to 40 mol% of ZrO2 added while the same molar concentration of TiO2–ZrO2 (50 mol% ZrO2) shows the amorphous phase. At the low concentration of doped ZrO2 (5 mol%) the phase transformation from the anatase phase to the rutile phase arose at the calcination temperature around 900 °C. The binary oxides possessed larger surface area than the sole components. The diffuse reflectance UV–vis spectra of the binary oxides are shift to the shorter wavelength (blue-shift) with increasing ZrO2 molar ratio. The pure TiO2 and 5 mol% TiO2–ZrO2 binary oxide samples were used as semiconductors for electrodes of dye-sensitized solar cells. The binary oxide electrode gave higher short-circuit current density (Jsc) and open-circuit voltage (Voc) due to the higher surface area and the larger band gap respectively. Consequently, the higher of Jsc and Voc enhanced the solar energy conversion efficiency of the DSC fabricated by binary oxide electrode when compared to the cell that fabricated by the pure TiO2 electrode.