Synthesis of long TiO2 nanotube arrays with a small diameter for efficient dye-sensitized solar cells

The surface/volume ratio of TiO2 nanotube arrays determines their electrical, optical and chemical properties for various applications. For dye-sensitized solar cells (DSSCs), it is very important to fabricate long TiO2 nanotube arrays with a larger surface area in order to have more dye loading and achieve higher conversion efficiencies accordingly. In this paper, a convenient anodization method is introduced to synthesize high aspect ratio TiO2 nanotubes at a low voltage and a high temperature. With a high reaction temperature, the diffusion rate of ions in the anodization process was enhanced. At the optimum temperature, nanotubes longer than 16 mu m with outside diameters as small as 75 nm could be obtained at a voltage of 20 V. Significantly, using these resulting TiO2 nanotube arrays to fabricate front-side illuminated DSSCs, a conversion efficiency as high as 5.98% could be achieved due to the large surface area and the enhanced attachment of the dye.