Chromogenic 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.

The capabilities of ion-beam techniques for thin-film processing, i.e., for materials deposition by ion-beam sputtering and surface treatment, are reviewed. The basic interaction mechanisms between ions and solids are summarized and related to materials processing by ion sources. Typical geometries of ion sources, targets, and samples are discussed for corresponding experimental apparatus. The versatility of ion-beam techniques in the preparation of thin films and multilayer structures is illustrated by several examples: ion-beam sputter-deposition of various binary oxide materials (including crystalline MgO, NiO, ZnO, SnxOy, and CuxOy) as well as combinatorial growth of materials libraries of amorphous ternary oxides. Furthermore, controlled ion-beam etching of surfaces is discussed.

Smart windows are an important technology in terms of energy saving potential in the building sector due to their ability to control visible light and thermal radiation. The essential component of this type of window glazing is an electrochromic thin film. In addition to the widely established tungsten oxide as the optically active material, in particular the counter electrode offers significant potential for improving the overall device performance. In this study, tantalum vanadium oxide films are prepared by reactive radio-frequency sputtering on fluorine-doped tin oxide substrates and optimized in terms of their spectro-electrochemical properties as ion storage layer. We show that an oxide-based tantalum-vanadium alloy is a promising approach to address the open challenges of pure vanadium pentoxide. The coatings exhibit color neutrality in combination with a high transmittance of up to 80% in the as-prepared state and suitable optical transmittance switching. Additionally, we find both a sufficient stability upon cycling and a suitable charge density of about 35 mC cm−2. Thus, the presented oxide-based alloy offers a beneficial performance as an ion storage layer in electrochromic devices.

In this study, radio-frequency sputtered tantalum vanadium oxide (TaVO x ) films are investigated as a promising material for the ion storage layer in an electrochromic device. Using spectroelectrochemical measurements by cyclic voltammetry, the electrochromic switching properties of the material are presented. The intercalation and deintercalation mechanisms of Li+ ions into TaVO x thin films have been studied by X-ray photoelectron spectroscopy. To obtain information about the composition and electronic structure of the material, films with different degrees of intercalation levels of Li+ ions are studied. The results clarify which species are involved in the electrochromic mechanism. In order to be able to evaluate the stability of electrochemically treated samples, films in the final deintercalated state are also analyzed. It is shown that only vanadium is actively involved in the investigated redox reaction. Finally, TaVO x is integrated with the solid-state electrolyte lithium phosphorus sulfuric oxynitride into a model electrochromic switching cell. Chronoamperometry shows a stable charge transfer of about 27 mC cm–2 combined with suitable values for optical transmittance of more than 70% (at 550 nm). Based on the high stability in terms of charge density and suitable color neutrality, we confirm the general suitability of this material combination for use in electrochromic applications.

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/admi.202202422.