Preparation And Electrochromic Performance Of Tungsten Oxide And Nickel Oxide Thin Films And Devices

Electrochromism is a phenomenon that the optical properties of materials such as absorptivity and transmittance changes reversibly under the effect of applied electric field.The change of optical properties can be used to modulate thermal and light so that electrochromic materials can be applied to energy saving building and spacecraft thermal control.Therefore,the research of electrochromic materials and devices has attracted much attention.The electrochromic films of tungsten oxide and nickel oxide were prepared by electron beam evaporation.The effects of thickness and heat treatment temperature on the electrochromic properties were studied.The results shows that the regulation range of the transmittance of tungsten oxide and nickel oxide film increases with the increase of thickness.Besides,the regulation range of the transmittance of nickel oxide film after 500 cycles is increased.The regulation range of a 400 nm films increases from 26% to 43% after cycling.The effect of heat treatment on electrochromic films is also significant.The electrochromic performance of tungsten oxide films becomes poor after heat treatment.The transmittance of films is decrease and response time is slow,but when the heat treatment temperature exceeds 300℃,the regulation range of the transmittance of tungsten oxide is slightly increased.The infrared electrochromic performance of tungsten oxide film is mainly in the range of 2.5 ~ 10 μm.When the thickness is 250 nm,the emittance at 10 ~ 25μm band almost does not change with the voltage.With the increase of thickness,the emissivity is gradually increased.While the electrochromic performance of nickel oxide film is contrary to tungsten oxide,its transmittance range and response speed increase with the increase of temperature.But when the heat treatment temperature exceeds 350℃,the cyclic stability becomes worse,the variety of transmittance decreases and the response speed becomes slow.Nickel oxide thin films dose not exhibit electrochromic behavior in the infrared band,but the emissivity increases with the increase of thickness and heat treatment temperature.Subsequently,the preparation of the ITO layer was studied.It was found that the resistance of ITO electrode was very large and the transmittance was very low,only about 20%,while the resistance decreased after heat treatment,and the transmittance increased obviously,which up to about 80%.Electrochromic devices were deposited on ITO glass by evaporation,and the electrochemical and electrochromic properties were tested.The results showed that the device prepared at room temperature and 200℃ treated did not work,while after heat-treatment above 250℃,The electrochromic phenomenon can be observed and at the temperature of 300℃ and 350℃,the electrochromic devices owned the fastest response speed and the maximum spectrum modulation range,and both of them have good cyclic stability.