Influence of secondary anodization voltage on free-standing crystallized TiO2 nanotube array membrane

Vertically aligned, free-standing crystallized TiO2 nanotube arrays with a length of 32 μm have been fabricated by a two-step anodization method. The TiO2 nanotube membrane can be detached from the Ti substrate through the secondary anodization process. The influence of the secondary anodization voltage on the morphology, crystalline phase and photovoltaic performance of the as-fabricated samples has been investigated. Results show that the side wall of TiO2 nanotubes becomes obviously thin as the secondary anodization voltage increases and leads to crack when the voltage reaches 25 V. The mass fraction of the anatase reduces by the increase of the voltage. Furthermore, the dye-sensitized solar cells (DSSCs) based on TiO2 nanotube arrays have been assembled. The energy conversion efficiency decreases with the increase of secondary anodization voltage, and a highest energy conversion efficiency of 10.6 % under UV illumination (368.1 nm) is obtained from the cell with TiO2 nanotube membrane re-anodizad at 15 V.