Ultralong, Small-Diameter TiO2 Nanotubes Achieved by an Optimized Two-Step Anodization for Efficient Dye-Sensitized Solar Cells

An optimized two-step anodization is developed to fabricate ultralong, small-diameter TiO2 nanotubes, that is, with tube length of up to 31 mu m and pore diameter of about 35 nm in this work. This overcomes the length limitation of small diameter tubes that usually presents in conventional one-step anodization. The small tubes with lengths of 23 mu m yield a conversion efficiency of 5.02% in dye-sensitized solar cells under nonoptimized conditions.