Optimization of Optical Modulation in Amorphous WO3 Thin Films

WO₃ thin films were prepared on indium-tin oxide (ITO) glass substrates at different substrate temperature by radio frequency magnetron sputtering. Then the films were soaked in five organic solvents of acetone, ethanol, cyclohexane, acetonitrile and ethyl acetate for 48 h, respectively. The changes in the microstructure, surface morphology and electrochromic (EC) properties of WO₃ thin films before and after the immersion treatment were systematically studied. It was found that after soaking in ethanol, the optical modulation of amorphous WO₃ thin films deposited at room temperature increased from 50 to 85%, showing excellent EC performance. Moreover, the immersion treatment in ethanol is also helpful for improving the EC properties of amorphous WO₃ thin films prepared at elevated substrate temperature. However, after immersion in the other organic solvents, the optical modulation of WO₃ thin films increased less (for acetone: 77%) or even decreased significantly (for cyclohexane, acetonitrile and ethyl acetate: 31%, 30% and 35%, respectively). In addition, the immersion treatment in ethanol cannot improve the optical modulation of crystalline WO₃ thin films prepared at 600 °C, which dropped from 58 to 40%. The authors believe that this is mainly related to the different dredging effects of various organic solvents on the transport channels of Li-ions and electrons in WO₃ thin films. Therefore, this work provides a new approach for the optimization of EC performance of amorphous WO₃ thin films.