Hybrid CdSe/TiO2nanowire photoelectrodes: Fabrication and photoelectric performance

Abstract

Well-aligned TiO₂ nanowire arrays are fabricated through a simple hydrothermal method and sensitized with electrodeposited CdSe nanoparticles. Annealing treatments at various temperatures (350 °C, 380 °C, 400 °C and 450 °C) are used to improve the performance of the as-deposited photoelectrode and the effects of various annealing atmospheres (air, O₂, N₂, Ar and vacuum) are further investigated. Although the film is only 2μm thick, a significant photocurrent density of 8.83 mA cm⁻² is observed under 100 mW cm⁻² illumination (AM 1.5 G) for the sample annealed at 400 °C in air, which is 5.69 times higher than that of the as-deposited sample and much better compared with that of the samples annealed in other environments. Careful investigation on the annealing effect is performed with a range of analytical techniques, such as SEM, TEM, HRTEM, EDX, UV-vis absorption spectra, and XRD. In particular, HRTEM observation affords a further insight into the exact change in CdSe crystalline structure annealed at different temperature. The results indicate that the crystal structure of CdSe nanoparticles and the interface between TiO₂ and CdSe are improved with appropriate annealing below 400 °C, leading to an enhancement of performance. On the other hand, over-annealing at 450 °C results in severe migration and oxidation of CdSe, and leads to a poor photoelectric performance. A better understanding of the influence of the annealing environment is obtained through the adoption of different annealing atmospheres at 400 °C. It is found that both O₂ and N₂ have a more positive effect on the annealing process compared with Ar and vacuum, while air is found to be the favorite environment for annealing treatment.