Controllable Preparation Of Titania Nanotubes And Their Application In Solar Cells

One dimension(1D) titania nanostructure, especially nanotubes, are important inorganic functional materials. Due to their superior physical and electrochemical properties, such as the excellent electron percolation pathways, large inner surface area, low cost, chemical inertness and strong optical absorption, they has been widely used in photocatalytic degradation of pollutants, photolysis hydrogen production, sensors and solar cells. There are many methods to prepare TiO2 nanotubes, such as anodic oxidation, hydrothermal and template method. However, the TiO2 nanotubes prepared by hydrothermal method seems to be unordered, meanwhile the TiO2 nanotubes prepared via template method have template size limits, it may also damage the morphology of TiO2 nanotubes when removing the template.Therefore, researchers always fabricate TiO2 nanotubes through anodic oxidation. TiO2 exhibits a wide band gap(3.0 eV for the rutile and 3.2 eV for the anatase phase) which can be induced only by the ultraviolet(UV) light with the wavelength below 390 nm of the solar spectrum and thus leading to a low utilization ratio of solar power. Simultaneously, the high electron-hole recombination rate also reduces the photoelectric conversion efficiency. In order to reduce the band gap of TiO2 and improve the utilization rate of light, the current research mainly focuses on the modification of TiO2 nanotubes, such as nonmetal doping, transition metal doping and surface sensitization. In addition, coupling TiO2 nanotubes with narrow band gap semiconductors to form heterojunction has great potential application in the all-solid-state and inorganic solar cells.In this article, we prepared the controllable length and diameter of TiO2 nanotubes via controlling the voltage and time of anodic oxidation, studied their dynamic relationships. In addition, the optimized TiO2 nanotubes(length of ~7.7 ?m, diameter of ~75 nm) were filled up with ZnS nanoparticles by successive ionic layer adsorption and reaction. Subsequently, the ZnS nanoparticles were converted to CuS entirely during the ion exchange procedure, thus leading to the CuS/TiO2 nanocomposite fim. Finally, the p-Cu S/n-TiO2 heterojunction was used for the designing of a new all-solid-state and inorganic solar cell. Its photoelectric properties were studied.Results show that the length of titanium dioxide nanotubes increased with the increase of voltage. However, the diameter of titanium dioxide nanotubes firstly increased and then decreased. The best parameter of voltage was 50 V. Moreover, keeping the voltage unchanged, the length and diameter of titanium dioxide nanotubes were increased along with the increase of oxidation time. In the modification process, the TiO2 NTs were firstly filled with ZnS nanoparticles by successive ionic layer adsorption and reaction. Subsequently, the ZnS nanoparticles were converted to the Cu S little by little following the ion exchange process due to much smaller solubility product(Ksp) of Cu S in contrast to Zn S(6.3?10-36 vs. 1.6?10-24 for Cu S vs. ZnS), thus leading to Cu S/TiO2 heterojunction. Finally, a new all-solid-state and inorganic solar cell was assembled with the framework of FTO/TiO2(blocking layer)/TiO2 NTs/CuS/graphite/FTO based on the p-CuS/n-TiO2 heterojunction and its ? was 0.25 %. This two-step method is simple and eco-friendly. It can be used to modify the TiO2 nanotubes with other sulfide, such as PbS?Cd S?Ag2S?CoS etc. Meanwhile, their photoelectric properties were studied.