Preparation and performances of all-solid-state variable infrared emittance devices based on amorphous and crystalline WO3 electrochromic thin films

In this study, two all-solid-state electrochromic devices (ECDs), composed of amorphous WO3 (a-WO3) and crystalline WO3 (c-WO3) as the electrochromic layers, have been prepared using radio frequency magnetron sputtering. The devices have five-layered structures consisting of LiTaO3 as the solid electrolyte layer, NiOx as the ion storage layer, and ITO as the electrode layer. The a-WO3 and c-WO3 films are prepared by adjusting the sputtering power, thus not affecting the phase composition of the other layers. The infrared (IR) emittance of both devices is studied in detail. The results show that the crystallinity of the WO3 layer greatly influences the IR emittance of the devices. The IR emittance of the a-WO3 ECD in the range of 2.5–25 μm increases greatly after lithium ion insertion, whereas the IR emittance of the c-WO3 ECD decreases. This difference can be explained by the absorption of IR vibrations and the reflection of the pseudo-metallic behavior of WO3. a-WO3 ECD exhibits a greater regulating capacity for thermal radiation, and its emittance modulation range is about 0.37 in the spectral range 8–14 μm and 0.30 in the spectral range 2.5–25 μm. The electrochromic technique is an ideal thermal control method for future space technology.