The phase transformation and structures of Titania (TiO2) nanotubes arrays prepared by anodization method for energy conversion

The films of TiO2 nanotube arrays were fabricated bu the anodization of Ti metal sheets for dye-sensitized solar cell (DSSCs). The anodization was carried out under the electrolyte of 0.3 wt% NH4F and 3 V% ethylene glycol in deionized-water. DC power supply was used at a constant voltage of 70 Volts. The TiO2 nanotubes were annealed at different temperatures from 300 C to 700 C. The morphology of the nanotube arrays was characterized by scanning electron microscopy (SEM). The phase and structure of the TiO2 nanotube array films were determined by X-ray diffraction (XRD). The phase of the nanotubes is transformed from anatase to rutile when annealing temperature is changed from 450 C to 500 C or higher. When annealing temperatures at 700 C or higher, the phase of the nanotubes become completely rutile and the nanotubes changed to nanacrystalline. The efficiency of dye-sensitized solar cells which annealed at 450 C was 0.530%