Investigation On Preparation And Properties Of TiO₂ Nanotube Array Thin Films For Flexible DSSC

For the large specific surface, stable chemical properties and low cost, TiO2 nanotube array has been applied in new material field as the photoanode in the dye-sensitized solar cells. However, the photoelectric conversion was inefficient. The structure and constitute would influence the conversion efficiency and long-term stability. In this paper, anodic oxidation method was used to prepare orderly arranged and shape-controlled TiO2 nanotube array, and the technological conditions about controlling the nanotube morphology was investigated. On the basis of this, the optimal structures and constitute to enhance the efficiency was investigated. In addition, the preparation and photoelectric properties of non-substrate TiO2 nanotube array thin films were also investigated tentatively.(1) TiO2 nanotube array was prepared on the surface of Ti foils by anodization. The influence of anodization process (including concentration of NH4F and H2O, anodizing voltage, anodizing time and the temperature) on the morphology of TiO2 nanotube array films was investigated, in order to achieve the precisely control of the morphology. And further explain the growth mechanism of TiO2 nanotube arrays. The experimental results show a faster growing speed in proper electrolyte in higher temperature. In addition, the average tube diameter and tube wall thickness are related to anodization temperature. Conducted heat treatment between the two-step anodization will get rid of lodging of the nanotube preparing the nanotube array with big tube diameter and thin wall thickness.(2) Based on the results of the former work, "self-striping" method was tentatively adopted to prepare non-substrate TiO2 nanotube array. A large area of TiO2 nanotube array films was peeled off the Ti foil surface when combine heat treatment with anodization. The different morphologies of TiO2 nanotube array films could be obtained by changing the temperature of heat treatment. It indicates that with the temperature of heat treatment in 300℃, the nanotubes are partly end-opened; in 400℃ the bottom is completely closed.(3) The photoelectron performance of the TiO2 nanotube array films with different morphology and substrate was investigated.Use the nanotube whose substrate is Ti as photo-anode material to package solar cells and measure its photoelectron performance. The conversion efficiency of the solar cells versus the tube diameter and tube length are in direct ratio, the reasonable explanation of this phenomenon is that the tube with longer length bigger diameter may absorb more dye, so increase the amount of photoproduction electron. The conversion efficiency is the highest reaching 3.23% when the tube length is 8.3μm. As for the cells whose substrate is FTO, the photoelectric conversion efficiency is 3.45% when the heat treatment temperature is 200℃. And the photoelectron performance of backside illuminated DSSC and front-side illuminated DSSC was discussed, the photoelectric conversion efficiency of the front-side illuminated DSSC is 17.5% higher than the backside illuminated DSSC, reaching 4.01%.