Fabrication of Double-Layered TiO2 Films with Nanosphere Light Scatterers by One-Step Soaking Method

Nanostructured TiO2 films with a double-layered structure are prepared by a lacile one-step soaking method. We have investigated the morphology of nanostructured TiO2 films according to the reaction time, concentration of the reactant, and reaction temperature of the soaking reaction, which all have a significant effect on the thickness and layered-structure of the nanostructured TiO2 films. The TiO2 films prepared by this soaking method have a unique double-layered structure, which is composed of a dense TiO2 bottom layer and stacked TiO2 nanospheres on the top layer. The growth of TiO2 nanospheres on the top of the double-layered TiO2 films shows stepwise behavior, which means there are two different growth mechanisms resulting in the dense TiO2 bottom layer and the spherical TiO2 top layer. There is an optimum reactant concentration and reaction temperature for achieving double-layered TiO2 films, which can be explained by the theory of nanoparticle synthesis. The stacked TiO2 nanospheres of double-layered TiO2 films contribute to the light scattering effects of TiO2 films, which could be used for the performance improvement of TiO2 photoelectrodes for sensitized solar cells.