Preparationand Characterization of Rutile-anatase Hybrid TiO2Thin Film by Hydrothermal Synthesis

Nanoporous TiO2 films are commonly used as working electrodes in dye-sensitized solar cells (DSSCs). So far, there have been attempts to synthesize films with various TiO2 nanostructures to increase the power-conversion efficiency. In this work, vertically aligned rutile TiO2 nanorods were grown on fluorinated tin oxide (FTO) glass by hydrothermal synthesis, followed by deposition of an anatase TiO2 film. This new method of anatase TiO2 growth avoided the use of a seed layer that is usually required in hydrothermal synthesis of TiO2 electrodes. The dense anatase TiO2 layer was designed to behave as the electron-generating layer, while the less dense rutile nanorods acted as electron-transfer pathwaysto the FTO glass. In order to facilitate the electron transfer, the rutile phase nanorods were treated with a TiCl4 solution so that the nanorods were coated with the anatase TiO2 film after heat treatment. Compared to the electrode consisting of only rutile TiO2, the power-conversion efficiency of the rutile-anatase hybrid TiO2 electrode was found to be much higher. The total thickness of the rutile-anatase hybrid TiO2 structures were around 4.5-5.0 µm, and the highest power efficiency of the cell assembled with the structured TiO2 electrode was around 3.94%.