Transition from Anodic Titania Nanotubes to Nanowires: Arising from Nanotube Growth to Application in Dye-Sensitized Solar Cells

Anodic formation of titania nanowires has been interpreted using a bamboo-splitting model; however, a number of phenomena are difficult to explain with this model. Herein, transition from nanotubes to nanowires is investigated by varying the anodizing conditions. The results indicate that the transition requires a large number of hydrogen ions to reduce the passivated area of tube walls, and therefore can be observed only in an intermediate chemical dissolution environment. Accordingly, a model in terms of stretching and splitting is proposed to interpret the transition process. The model provides a basis to suppress the nanowires with surface treatments before anodization and to clear the nanowires with an ultrasonication process after anodization. The nanotubenanowire transition also arises when the tubes are directly used in dye-sensitized solar cells. Treatment with titanium tetrachloride solution for about 10 h is found to be effective in suppressing the nanowires, and thus improving the photovoltaic properties of the solar cells.