New process increases speed and color options of switchable windows
Those in the market for some windows made from electrochromic glass that switches from translucent to transparent and vice versa when a voltage is applied can currently choose any color tint, as long as it's blue. But that's set to change with the development of a new manufacturing technique that increases the color options on offer, while also speeding up the switching process by almost 10 times.
Most electrochromic glass windows on the market are produced by coating two panes of glass in a thin film of translucent indium tin oxide or fluorine-doped tin oxide to make the glass electrically conductive. Then one of the panes is coated in electrochromic tungsten oxide and the two panes are brought together with the coatings facing each other and a gel-like electrolyte separating them.
When a voltage is applied, the tungsten oxide coating darkens, and when the polarity of the voltage is reversed, the coating lightens. The lightening and darkening process doesn't happen instantly, with windows measuring around 2.5 square meters (27 sq ft) potentially taking up to 20 minutes for the process to complete.
Now researchers at the Fraunhofer Institute for Applied Polymer Research (IAP), working with Tilse Formglas GmbH have turned to a different technology that speeds up the switching process considerably, while also enabling various different colors.
The new process still starts with coating two panes with tin oxide, but the tungsten oxide coating is skipped. Instead, the two panes are again brought together, but with a specially developed resin containing electrochromic organic monomers sandwiched between them. Heat or UV radiation is then used to cure the resin before a direct current is applied to ensure that the monomers on an electrode bond to form an electrochromic polymer.
The end result is a pane that can be switched much faster and at a much lower voltage. According to Dr. Volker Eberhardt, a scientist at Fraunhofer IAP, a pane measuring 1.2 sq m (13 sq ft) in size will darken in 20 to 30 seconds, compared to over 10 minutes for standard tungsten-oxide-based panes. Additionally, the researchers say that using other monomers will allow the creation of panes with red or purple tints in the future.
The new technique also results in sturdier panes. Whereas with the current technology multiple layers are required to produce panes that are strong enough to walk on or be used for overhead glazing, just two layers of the new electrochromic resin glazing is suitable for such applications. These panes are also suitable for use on ships, the team says.
The researchers have produced a prototype of the new electrochromic glazing that switches to blue, but they plan to branch out into other colors such as red next.