In-situ controlled oxidation of sputtered WS2 nano-walls for high-performance WO3 electrochromic devices

It is crucial to obtain repeatable, large-area, functional nanostructured material of WO3, especially for electrochromic device (ECD) applications. Although radio frequency magnetron sputtering (RFMS) has been one of the main methods to grow WO3, it lacks obtaining high surface/volume ratio nanostructured films. In the current study, the nano-wall structure of WO3 thin films has been obtained by novel in-situ controlled thermal oxidation of nano-wall WS2 thin films grown by RFMS. In-situ optical and electrical measurements have been utilized to preserve the surface morphology during the conversion. The oxidation has been indicated to occur from the surface toward to depth of the sample by depth profile x-ray photoelectron spectroscopy measurements. The optical modulation (OM), colouring efficiency (CE) and colouration response time of the 520 nm WO3 thin film has been determined to be 77.2%, 69.3 cm2C-1 and 13.4 s, respectively, at 700 nm wavelength under -0.4 V applied voltage. 1000 cycles of the measurements have been shown to keep the 77.2% of the first value of the OM. The ECD of the same thickness of the WO3 thin film was fabricated in the configuration of ITO/WO3/1 M LiClO4 (PC)/NiO/ITO, and almost similar EC characteristics were achieved.