New 'smart' windows go from clear to dark in one minute

Scientists have developed dynamic windows that can switch from transparent to opaque or back again in under a minute and do not degrade over time.
The prototypes created by researchers at Stanford University in the US are plates of conductive glass outlined with metal ions that spread out over the surface, blocking light, in response to electrical current.
Dynamic windows have the potential to transform our homes, businesses, cars, and more, reducing heating and cooling costs or the need for blinds, researchers said.
Smart windows already being sold, such as those used on airlines, are made of materials, such as tungsten oxide, that change colour when charged with electricity, they said.

However, these materials tend to be expensive, have a blue tint, can take over 20 minutes to dim, and become less opaque over time.
"We did not tweak what was out there, we came up with a completely different solution," said Michael McGehee, a professor at Stanford University.

"We have had a lot of moments where we have thought, 'how is it even possible that we have made something that works so well, so quickly,' and we are now running the technology by glass and other kinds of companies," said McGehee, senior author of the research published in the journal Joule.

The new prototypes block light through the movement of copper and another metal in a solution over a sheet of transparent indium tin oxide modified by platinum nanoparticles.
When transparent, the windows are clear and allow about 80 per cent of surrounding natural light through, and when dark, transmission drops to under five per cent.
The researchers switched the windows on and off at least 5,500 times and saw no change in the transmission of light, indicating that the design is durable.