Once the glass is switched from clear to dark, or vice versa, the system requires little to no power to maintain its new state; only needing electricity when it’s time to switch back again.
Existing electrochromic materials have found only niche applications. The windows can be darkened by turning on the voltage, Mircea Dincă, MIT professor of chemistry, said, but: “when you flip the switch, it actually takes a few minutes for the window to turn dark. Obviously, you want that to be faster.”
The reason for the slowness is that the changes within the material rely on a movement of electrons that gives the window a negative charge. Positive ions then move through the material to restore the electrical balance, creating the colour-changing effect. But while electrons flow rapidly through materials, ions move more slowly, limiting the overall reaction speed.
The MIT team overcame this by using metal-organic frameworks, which are said to conduct both electrons and ions at high speeds.
They have also produced a coating that can go all the way from perfectly clear to nearly black (achieved by blending two complementary colours, green and red). The material is made by combining two chemical compounds, an organic material and a metal salt. Once mixed, these self-assemble into a thin film of the switchable material.
“It’s the combination of the two – a relatively fast switching time and a nearly black colour – that has really got people excited,” Dincă said.
According to Dincă, the material could also be used for low-power displays, similar to displays like electronic ink.
