Electrochromic switching of tungsten oxide films grown by reactive ion-beam sputter deposition

Abstract

AbstractChromogenic thin films are crucial building blocks in smart windows to modulate the flux of visible light and heat radiation into buildings. Electrochromic materials such as tungsten oxide are well established in those devices. Sputter deposition offers a well-suited method for the production of such layers, which can also be used on an industrial scale. Tungsten oxide films were prepared by means of reactive ion-beam sputter deposition. The choice of distinct gas mixtures as well as the growth temperature during the sputtering process allows to tune the properties of the resulting layers. Especially, the variation in the growth temperatures was found to have an impact on the structure of the resulting samples and, as a consequence, on their optical and electrochemical properties. By specific choice of the reactive gas, the deposition of colorless transparent as well as blue films of different composition is possible. The optical transmittance in the visible spectral range was up to 75% for as-deposited oxygen-rich layers. Additionally, hydrogen-doped tungsten oxide samples were grown. Superior electrochromic switching was observed for H$$^{+}$$ + -doped layers, probably by some kind of preconditioning. This resulted in a value for the standardized optical coloration efficiency of 26.5 cm$$^{2}$$ 2 /C.