Preparation And Properties Of Inorganic Flexible Reflective Electrochromic Films And Devices

Electrochromism refers to a phenomenon that the optical properties of materials can change stably and reversibly when voltages are applied.Absorptivity,reflectance and transmittance can change in the visible region,and emissivit y changes in the infrared region.Therefore,electrochromic materials can be used in military camouflage and spacecraft thermal control.Electrochromic camouflage mainly includes color camouflage and infrared thermal camouflage.Color camouflage achieves the same goal by changing its own color and background fusion.Thermal camouflage realizes camouflage by changing the emissivity of the material surface.Therefore,the research of electrochromic films and devices in military camouflage has attracted much attention.In this paper,the electrochromic films of tungsten oxide?WO₃?and nickel oxide?Ni O?were prepared by vacuum electron beam evaporation.The results show that the reflectance range of WO₃ and Ni O films increases with the increase of thickness.When the thickness of WO₃ reaches 600 nm,the apparent color of the films changes from dark green to earthy yellow reversibly.At the voltage of 1 V,the reflectance at the wavelength of 1000 nm reaches the maximum value,which is 48%.At the voltage of 1 V,the coloring time is 1.69 s,and the fading time is 2.95 s.When the thickness of Ni O is 500 nm,the apparent color of the film changes from dark red to earthy yellow.When the voltage is 1.3 V,the reflectivity regulation at the wavelength of 1000 nm reaches the maximum of 38%.When the voltage is 1.3 V,the coloring time of the film is 1.39 s,and the fading time is 0.64 s.The coloring time and fading time of the two kinds of electrochromic films increased with the increase of thickness,and the fading time also increased with the increase of voltage.Finally,the color of WO₃ based and Ni O based electrochromic devices under different voltage is studied.For two kinds of electrochromic devices,the apparent color of the device gradually darkens with the increase of voltage.The cyclic voltammetric curve of the device is central symmetrical on the whole,and the color change of the device is relatively stable.Among them,WO₃ based devices can achieve the transformation from emerald green to earthy yellow in the apparent state,and its color transformation is consistent with that of emerald green leaves and withered yellow leaves.With the increase of thickness,the coloring time and fading time are longer,and the maximum reflectivity adjustment under 1.5 V voltage is 43%.With the increase of film thickness,the coloring time and fading time of the assembled device are both longer,and the reflectivity can be adjusted to 38% at 1.8 V.