Electrochromic films of tungsten oxyfluoride and electron bombarded tungsten oxide

Reactive DC magnetron sputtering of W was performed in a plasma of Ar + O-2 with and without CF4 addition and a positive substrate bias. The durability under extended Li+ intercalation/deintercalation was excellent for electron bombarded oxide films and poor for oxyfluoride films, while the electrochromic colour/bleach dynamics was slow for the electron bombarded oxide but fast for the oxyfluoride. The range of optical modulation was large. Tandem films, with a thin protective layer of electron bombarded oxide covering a thicker oxyfluoride layer, were able to combine rapid dynamics with good durability.