Roll-to-roll pulsed dc magnetron sputtering deposition of WO3 for electrochromic windows

Abstract This paper reports on the deposition conditions and properties of WO 3 films used as electrochromic layer in a monolithic device on a plastic substrate. The deposition technique employed was roll-to-roll pulsed dc magnetron sputtering. The oxide was deposited at room temperature in an argon and oxygen plasma on a transparent conducting ITO layer previously coated on a PET film. The influence of deposition parameters such as pulse mode, total pressure and oxygen partial pressure has been investigated, in order to obtain the best compromise between a high deposition rate and adequate electro-optical properties. As expected, the deposition rate increases with decreasing total pressure and oxygen partial pressure. To control the coloring/bleaching behavior, lithium ions from an aprotic electrolyte have been intercalated in films. Films with thickness around 400 nm exhibit a contrast ratio of 9:1. The optical efficiency increases slightly with increasing total pressure and lies between 30–40 cm 2 C −1 . Further, the coloring and bleaching time decreases with increasing total pressure, coloring being faster than bleaching. This is consistent with UV–Vis ellipsometric measurements which reveal that the refractive index decreases with increasing total pressure. TEM investigations also confirm that films deposited at low total pressure exhibit a dense structure whereas those deposited at high-pressure exhibit a columnar structure.