The performance of dye-sensitized solar cells (DSSC), made of highly ordered anodic titanium oxide (ATO) nanotube (NT) arrays produced directly on Ti foil, depends on the length of these arrays. We controlled these lengths L from 4 to 41 µm while varying the concentration (0.1, 0.25, 0.5, and 0.8 wt %) of the electrolyte (NH 4 F) in ethylene glycol in the presence of H 2 O (2 vol %) with anodization for various periods (t ) 0.5-8 h). The compact and bundle layers introduced during anodization were effectively removed upon simple ultrasonic cleaning in deionized water containing submicrometer particles of Al 2 O 3 in a small proportion. The photovoltaic performance of the NT-DSSC devices (NH 4 F at 0.5 wt %) made of ATO films, as prepared, increased from 3.0% to 5.2% as L was increased from 6 µm (t ) 0.5 h) to 30 µm (t ) 8 h). After treatment of the ATO films with TiCl 4 in a two-step annealing process, the optimized NT-DSSC device attained an overall efficiency of 7.0% power conversion.

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Highly ordered and vertically aligned straight nanotubes can be fabricated using an electrochemical anodization method on the valve metal surfaces, and a variety of nanostructures can be derived from these nanotubes. These nanomaterials have found a wide range of applications, especially in the fields of renewable energy generation and storage. This review provides step-by-step guidelines about the fabrication details and parameters of these nanomaterials, focusing on the systems originated from the metals of Al, Ti and Zr. Based on the fabrication of these nanotubes, different methods were developed to produce uniform metal nanowires using electrodeposition and mechanical injection, nanospheres and nanowhiskers on the top surfaces of the nanotubes, and dye-sensitized solar cells using anodic Ti oxide. These nanostructures and their phase transitions were characterized in detail by X-ray diffraction and electron microscopy techniques. Finally, towards the commercial applications of the nanotube related materials, fabrication of large-scale porous films was proposed.