Fabrication And Post-treatment Of TiO 2 Nanotube Arrays As Photoelectrode In DSSC

TiO₂ was proved to be the optimum material for photoelectrode applied in dye sensitized solar cells(DSSCs), due to its proper band gap, excellent photoelectric effect and chemical stability. Compared with the traditional TiO₂ nanoparticle films, TiO₂ nanotube arrays, benefiting from its higher specific area and more efficient electron transfer path, are expected to exhibit improved photoelectrical property. Thus, the systematical studies on the fabrication, post-treatment and application of TiO₂ nanotube arrays have both scientific and engineering significances.Highly ordered nanotube arrays, fabricated from pure Ti foils by anodic oxidation, were characterized by field emission scanning electron microscopy(FESEM) and X-ray diffraction (XRD). Then, dye adsorption and photoelectrochemistry properties of the nanotubes were measured with the aid of UV-vis spectrum and CHI660C Electrochemical Workstation, respectively. Finally, nanotube arrays were used as photoelectrodes to build DSSCs and their photo-to-electricity performance were measured by simulated sunlight.The results showed that nanotubes with the length from 2μm to 50μm could be achieved in NH4F/ethylene glycol containing 1% water. Bundle layers on the top of nanotubes brought about negative effect on the photoelectric property of the photoelectrode and could be removed by sonicleaning. After annealed at 450℃, nanotube arrays with the length of 27μm displayed the best photo-to-electricity performance, indicating that the anatase TiO₂ is preferred crystalline phase in DSSCs. Although nanotubes assembled together into bundles after quenching, every single one maintained tubelike shape. Quenching treatment improved the electron transportation and dye adsorption of TiO₂ nanotube arrays, leading to better photoelectric properties of DSSCs. When the nanotube arrays were quenched in ethanol at -100℃, the prepared DSSC obtained an photo-to-electricity efficiency 20% higher than samples by annealing. After TiCl₄ post-treatment, the percentage of anatase in nanotube arrays and the amount of dye adsorption apparently increased, and the photo-to-electricity efficiency of DSSC could be raised by 34%. To obtain nanotube arrays with best photovoltaic properties, the optimized post-treatment process was immersing samples in 0.10M TiCl₄ aqueous containing 0.05M HCl for 90min.