Hydrothermal synthesis of rutile-anatase TiO₂ nanobranched arrays for efficient dye-sensitized solar cells

Rutile-anatase TiO₂ nanobranched arrays were prepared in two sequential hydrothermal-synthesis steps. The morphologies and crystalline nanostructures of the samples were investigated by controlling growth time and the concentration of the titanium precursor. All samples were characterized by field-emission scanning electron microscopy and X-ray diffraction analysis. It was found that treating the surfaces of rutile TiO₂ nanorods with aqueous TiCl₄ solutions allows the anatase TiO₂ nanobranches to grow perpendicular to the main rutile TiO₂ nanorods attached to the FTO glass. Irregularly shaped, dense TiO₂ structures formed in the absence of TiCl₄ treatment. A light-to-electricity conversion efficiency of 3.45% was achieved using 2.3 μm tall TiO₂ nanobranched arrays in a dye-sensitized solar cell. This value is significantly higher than that observed for pure rutile TiO₂ nanorods.