Abstract: A hierarchical configuration of TiO₂ nanoarray film, comprising a nestlike TiO₂ nanoarray layer integrated with a nanosheet network overlayer, was constructed. The hierarchical TiO₂ film was obtained by the post-hydrothermal treatment with NaOH solution on hydrothermally synthesized TiO₂-derived nanostructured arrays grown on fluorine-doped tin oxide substrate (FTO). The TiO₂ films were characterized by field-emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy, and absorbance spectroscopy. FE-SEM shows that the hierarchical TiO₂ film with a thickness of 1.5 μm is composed of a nanosheet overlayer (~0.2 μm height) and the nestlike nanoarray layer (~1.3 μm height). XRD patterns display that the TiO₂ films have pure anatase phase structure. UV-Vis spectra reveal enhanced light scattering and dye adsorption ability of the hierarchical TiO₂ film. For the dye-sensitized solar cell (DSSC) based on the nanosheet/nestlike nanoarray hierarchical TiO₂ film, a short-circuit current (J_sc) of 7.79 mA·cm^-2, open-circuit voltage (V_oc) of 0.80 V, fill factor (FF) of 0.40, and photoelectric conversion efficiency (η) of 2.48% are achieved. Within the dye-sensitized solar cell, the photoelectric conversion efficiency of the hierarchical TiO₂ film was nearly ten times higher than that of nanostructured array film.

Key words: TiO₂, Nanosheet/nestlike nanoarray, Hydrothermal synthesis, Dye-sensitized solar cell, Photoelectric conversion