A manufacturing technique can produce electrochromic glass (glass that darkens in response to sunlight) that darkens to colors other than blue, which until now has been the only choice. And the new glass also switches color nearly 10 times as fast.

The standard technique for electrochromic glass manufacturing is to coat two panes of glass with a film of translucent indium tin oxide or the less-expensive fluorine-doped tin oxide. One of the panes gets an additional coating of electrochromic tungsten oxide.

Electrochromic glass.The two panes are sandwiched together, coated sides facing, with a gel-like electrolyte between them. Applying voltage to the glass causes the panes to darken. Reversing polarization returns the glass to its previous state. Changing states can take 15 to 20 minutes for large (3-square-meter) glass panes.

Researchers at Fraunhofer Institute for Applied Polymer Research (IAP) are developing a technology based on a resin mixed with organic monomers. Rather than add a second coating to one glass pane, the researchers sandwiched the panes as before with the resin mixture between them. After curing the resin, application of direct current ensures bonding between monomers and an electrode to form an electrochromic polymer.

Using monomers yields two advantages. Varying the choice of monomer changes the color of the glass when it darkens. In addition, monomers react more quickly to light stimulation, darkening a 1.2-square-meter pane in 20-30 seconds.

The new glass panes are stronger than conventional electrochromic glass. When tested against the German (DIN) standard, two panes provide enough strength for overhead glazing or flooring. This increased strength would cut construction costs.