Synthesis of mesoporous anatase TiO ₂ nanotubes by a hydrothermal treatment and their use in solid-state dye-sensitized solar cells

Mesoporous anatase TiO ₂ nanotubes (NTs) with the diameter of about 7∼12 nm and the length of several hundred nanometers were synthesized by a hydrothermal method on commercial TiO ₂ particles in NaOH followed by HCl washing. The samples were characterized by X-ray diffraction (XRD), transmitting electron microscopy (TEM), and Brunauer-Emmet-Teller (BET) measurements. The hydrothermal treatment temperature at 130 °C was shown to affect not only the extent of particle-to-sheet conversion, and thus the resulting structures of the NTs, but also the anatase-torutile transformation. The surface area of the NTs was ∼200 m ²g ^-1. This value was much higher in comparison to TiO ₂ nanoparticles of ∼50 m ²g ^-1. It was also found that the NT photoelectrodes had a pronounced impact on the performance of solar cells as compared to nanoparticle ones. This was probably due to lead to a significantly higher specific dye loading and, for certain hydrothermal treatments, resulting in a doubling of the solar cell efficiency (in our case from 2.84% to 4.03% of AM 1.5 conditions).