Intelligent windows feature optically switchable coating

Researchers from the Winsmart project developed a vacuum insulating system which is one third the thickness of conventional double glazed windows. To make the frame suitably robust, a liquid tin alloy is injected around the edges of the cavity to form a seal. Due to the different surface tension between glass and liquid tin, a voltage is then applied to the tin for a short period of time to ensure it adheres to the glass and remains airtight after solidifying. To create the switchable glass, the team used vacuum sputtering to deposit 100 to 200nm thick layers of materials such as tungsten oxide on the glass panes. As this is done in a vacuum chamber, the materials are vaporised at high temperature and allowed to condensate onto the glass surface. This creates an electrically conducting layer, on top of which another layer of tungsten oxide is laid down. This functional device layer is therefore always enclosed between two electrically conducting layers when the window is put together. A power supply then lets current flow through the layered device and the tungsten oxide reacts to darken the glass. The researchers say that if the window could measure the amount of light falling on it, it could lighten or darken itself automatically. The researchers say that a number of different coatings could be laid on top of each other to make the glass water repellent or scratch resistant in addition to the optical switching functionality. The team is currently developing technologies that would enable efficient production of the technology. "In five to ten years the first Winsmart windows will be available on the market," said Empa researcher Matthias Koebel.