Switchable windows with tungsten oxide

Tungsten oxide can change its colour reversibly upon electron injection. It can be produced by sputtering, evaporation, chemical vapour deposition or other processes. In addition to its high colouration efficiency and fast reaction kinetics, the redox potential of the electron injection is low enough to allow various switchable systems, such as electrochromic, gasochromic, photoelectrochromic or photochromic glazing. In this paper, electrochromic devices with a redox electrolyte are introduced. This is related to the photoelectrochromic device, which is an electrochromic device with redox electrolyte and an additional dye-sensitised layer of TiO2, which generates the energy for the colouration of the device by sunlight. The photochromic device is in principal a photoelectrochromic device, where the catalytic layer for the reaction of the redox electrolyte is in direct contact with the electrochromic layer. In gasochromic devices, tungsten oxide reacts with diluted hydrogen and oxygen gases. This paper aims to give an overview of these different approaches.