Preparation Of Amorphous WO₃ Films With In₂O₃:Sn Nanocrystals And Their Properties

The WO₃ thin films have visible light reflection characteristics, which show the important application value in the field of energy saving smart window. However, the present WO₃ electrochromic windows can only modulate the visible light band, lack in the ability to modulate independantly in near infrared spectrum, which is difficult to achieve the effects of both the lighting and thermal insulation, to a certain extent, limiting the widespread use of this kind of new type of glass windows in high-grade buildings. If introducing ITO nanometer crystal with NIR electrochromic properties into the amorphous WO₃ thin films, integrating electrochromic modulation band of ITO and WO₃, the new ITO-WO₃ system window is expected to achieve the controlledly partitioning ability in the visible&near-infrared light.Therefore, in this paper we firstly prepared the ITO nanocrystalline films which has near infrared electrochromic properties by the sol-gel method, to discuss the influencial factors of the electrochromic properties of the thin films, on the base of using in situ synthesis technology to prepare the amorphous WO₃ thin film which evenly distributed by ITO nanocrystalline, the effects of annealing temperature and the volume fraction of ITO nanocrystals on the microstructure of the composite films and the properties of visible near infrared （IR） partition controllable electrochromic properties were investigated, and the specific work are as follows:（1） The sol-gel method was adopted in the preparation of ITO nanocrystalline thin film on the glass substrate, to investigate the influence of the heat treatment temperature on the film’s microstructure and the near-infrared-electrochromic properties. Eventually, after the annealing treatment at 250℃, we could obtain the ITO nanocrystalline thin film with the grain size about 10 nm, which has good electrochromic properties in the near infrared band, with the colouring and fading contrast ratio as Δτ was 12.61%.（2） The sol-gel method was adopted in the preparation of amorphous WO₃ thin films distributed with nanocrystalline ITO on FTO substrates, to investigate the effects of the heat treatment temperature on the composite film’s microstructure and the electrochromic properties.The results showed that with the increase of annealing temperature, ITO crystalized at first.When the heat treatment temperature is 350, precipitated an ITO crystal particle with the grain size of about 8 nm in the home position of the amorphous WO₃ matrix, and the composite thin film had the visible near-infrared electrochromic properties. Continuing to rise of annealing temperature, the WO₃ substrate changed from amorphous to lath shaped polycrystalline, which the electrochromic properties of the composite films in the visible light band disappeared, and the near infrared electrochromic properties decreased.（3） Furthermore, with the In:W molar at the ratio with 0.1:1 in the controlled sol and the annealing treatment at 350 C, the ITO-WO₃ composite thin film showed the optimum electrochromic performance, which the near-infrared colouring and fading contrast ratio Δτwas 12.61% and the visible light colouring and fading contrast ratio Δτ’ was 42.12%. At the same time, the electrochromic mechanism of ITO-WO₃ thin films was also studied. It was based on the results of the combination of the local surface plasmon electrochromic and redox reactions.