Characteristics of Low-Temperature Annealed TiO2 Films Deposited by Precipitation from Hydrolyzed TiCl4 Solutions

The effect of annealing temperature on the properties of TiO2 films prepared from hydrolyzed TiCl4 solutions was characterized by X-ray diffraction (XRD) and photoelectrochemical measurements. It is found that the amount of rutile in the TiO2 films increases from room temperature to 250 °C. Above 250 °C, the amount of crystalline rutile material did not change. Analysis of XRD data suggests that a noncrystalline phase is converted to the rutile phase of TiO2 by heat treatment of the films. Furthermore, the analysis indicates that the size of the rutile crystallites increases with temperature from about 100 to 400 °C. The photocurrent and conversion efficiency of the cells improved substantially with annealing temperature. The higher photocurrent appears to correlate with the increased crystallinity of the film. The TiO2 material displayed a photochromic effect.