Preparation of coaxial TiO2/ZnO nanotube arrays for high-efficiency photo-energy conversion applications

A novel type of coaxial TiO2/ZnO nanotube arrays has been prepared by electrochemical method. The TiO2/ZnO nanotube arrays can be applied as highly efficient photoanodes in dye-sensitized solar cells (DSSC). Such photoanode benefits from the capability of high sensitizer loading offered by the high specific surface, and the direct conduction path through the aligned nanotubes. Moreover, the heterojunction at the TiO2/ZnO interface favors charge separation and reduces the probability of charge recombination. With the coaxial TiO2/ZnO nanotubes as the photoanode, DSSC with an overall 2.8% energy-conversion efficiency was obtained, which was 40% higher than that using pure TiO2 nanotubes.

Research highlights
► Coaxial TiO2/ZnO nanotube arrays were prepared for the first time.
► The coaxial TiO2/ZnO nanotubes exhibited high photocatalytic activity.
► The coaxial TiO2/ZnO nanotubes displayed improved energy-conversion efficiency in DSSC.
► The energy band structure of the TiO2/ZnO nano-heterojunction enhances charge separation.