Tungsten oxide thin films for electrochromic applications: Pulse width‐controlled deposition by high‐power impulse magnetron sputtering (HiPIMS)

Metal oxide thin films have been of prime interest among electrochromic materials because of their chemical stability, strong adherence to various substrates, and high coloration efficiency. Compared to other transition metal oxides, such as V 2 O 5 , MoO 3 , and TiO 2 , tungsten oxide (WO 3 ) exhibits superior electrochromic properties, including long‐term durability and excellent contrast ratio. High‐power impulse magnetron sputtering (HiPIMS) holds great potential in fabricating durable WO 3 ‐based electrochromic layers. However, the tungsten target‐plasma interactions in reactive‐HiPIMS deposition of WO 3 and their role in modulating the electrochromic function of the resulting WO 3 coatings are yet to be understood. Here, we provide evidence that by controlling the HiPIMS pulse length, the stoichiometry of tungsten oxide structures can be tuned to optimize the transparency and electrochromic function of the coatings. X‐ray photoelectron spectroscopy (XPS) data showed that at pulse lengths shorter than 85 μs, the concentration of suboxide compounds is less than that of tungsten trioxide, while for pulse lengths longer than 100 μs, this balance is reversed. The average optical transparency of the coatings in the range of visible light was higher than 80%. The optical transmittance modulation (ΔT) of 38.1, 36.2 and 34.3% and coloration efficiency of 41.3, 38.4, and 35.9 cm 2 C −1 were measured for the WO x samples deposited at pulse lengths of 70, 85 and 100 μs, respectively. Tuning the HiPIMS pulse characteristics is a simple strategy to deposit tungsten oxide films with tuned electrochromic properties for an array of applications, from smart windows to wearable displays. This article is protected by copyright. All rights reserved.