A New Process Increases Speed and Color Options of Switchable Windows Without Tungsten Oxide

YTO photo

Electrochromic glass windows on the market are able to change color tints when an electric voltage is applied, but don't offer very many color options. But according to New Atlas writer Darren Quick, that's about to change.

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 and provides different color shades to tinted windows. Here's how the whole thing works:

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.

YTO photo

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.

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