Preparation and Characterization of Nanostructured TiO2 Thin Films by Hydrothermal and Anodization Methods

Abstract

In recent years, metal oxide materials such as TiO2 and ZnO thin films have been extensively studied for various applications such as solar cells, gas sensors and protective coating [1-2]. Among them, TiO2 is a very suitable oxide material for dye-sensitized solar cell (DSC) appli‐ cations, because of its extraordinary oxidizing ability of photogenerated holes. TiO2 thin films are prepared by various preparation methods, but the efficiency of the DSC solar cell is strongly enhanced by the increased dye absorption capacity of the photoelectrode. The most important factors which strongly affect the device performance are series resistance, charge carrier-recombination, electron injection from a photoexcited dye into the conduction band of an oxide semiconductor and hole transportation to the counter. Adachi et al. [3] reported that the dye absorption capacity of TiO2 nanowires was about 4-5 times higher than that of P25 film, which is made of TiO2 nanoparticles. It means that the electron collection efficiency in P25 film is lower than that of TiO2 nanowires. The electron collection efficiency is deter‐ mined by trapping/detrapping events along the site of the electron traps (grain boundaries and defects). All these problems can be resolved using nanostructured TiO2 films such as nanoholes, nanotubes, nanorods and nanowires. Nanostructured TiO2 thin films have been prepared by sol-gel, anodization and hydrothermal methods [1, 4]. Very suitable methods to prepare the TiO2 nanorod and nanotube are hydrothermal and electrochemical anodization. In the present work, TiO2 nanowires, nanorods, nanoporous and nanotubes were prepared using hydrothermal and anodization methods. In this paper, we report the surface morpho‐ logical, optical, structural and electrical properties of TiO2 nanowires, nanorods, nanoporous and nanotubes. The fabrication procedure of dye-sensitized solar cells and the factors which affect the device performance will be discussed. Finally, photovoltaic parameters (Isc, Voc, FF