The Study Of The WO₃ Electrochromic Thin Films

Tungsten oxide is one type of transition metal oxides, having broad application prospects in gas sensor, photocatalyst and electrochromic devices, et al. Due to its high transmission rate changes, excellent coloration efficiency, good reversibility, relatively low cost, longer durability and non- toxicity, it is first adopted and the most widely used as electrochromic material. It can be used as smart window of architecture and automobile glazing to save energy and modulate the transmission of light and solar radiation.This study will research tungsten oxide. The objective of this study is to investigate the effects of sputtering conditions on the composition microstructure, electrochromic properties of tungsten oxide films prepared by DC reactive magnetron sputtering. The achievements and innovation points are as follows:(1) WO₃ electrochromic films are successfully prepared by DC reactive magnetron sputtering in different process parameters, and XRD, SEM analysis was used to study the effects of different process parameters on the film-forming properties. The tungsten oxide films we prepared have a good performance, having high transmission rate when not colored, the maximum value is about 95%.When Colored, at the 550nm, visible light transmission rate changes can reach 64.5%, reach advanced level in our country's similar research. After repeated experiments, considering the performance of the films and film-forming rate, we consider that it is appropriate to prepare tungsten oxide films under target-substrate distance of 13cm, argon oxygen ratio of 1:1 (the argon is 0.4Pa, the oxygen is 0.4Pa).(2) We research the effects of Heat Treatment to tungsten oxide films. Heat Treatment can involve non-crystal to crystal transformation. XRD measurements show that: tungsten oxide films prepared by DC reactive magnetron sputtering are all non-crystal films. The films after annealing show crystal characteristics. Because tungsten oxide films of non-crystal structure have better electrochromic properties, so annealing can't improve electrochromic properties of tungsten oxide films.(3) We research the effects of different voltage to WO₃ electrochromic films. During electrochemical reaction, only voltage reach a certain value, WO₃ films coloration will occur. When the voltage increases to a excessive value(such as 9V), we found that WO₃ films can't naturally bleach completely. It is due to excessive voltage, ion implantation is too deep to lead to WO₆ unit excessive structural distortion, films structure can not be restored, resulting films can not naturally bleach completely.(4) Target-substrate distance change has a significant impact on the surface morphology and electrochromic properties of tungsten oxide films. The transmission rate change show a downward trend with target-substrate distance decrease. The tungsten oxide films we prepared have a good performance, having high transmission rate when not colored, the maximum value is about 95%.When Colored, at the 550nm, visible light transmission rate changes can reach 64.5%, using Beer-Lambert law, the optical density is 0.54. At 800 nm, the light transmission rate changes can reach 85%, the optical density is 1.02.Electrochromic performance is very good.