Energy-efficient window tinting goes dark at the flick of a switch

MIT's electrochromic material is able to switch from light to dark at the flick of a switch(Credit: Khalid Abdulaziz Kaabi and Dennis Sheberla)

Current electrochromic window tinting techniques are effective to a point, but there are limitations to the technology. They're generally slow to change state, struggle to achieve high levels of darkness, and rely on a constant current to maintain their tint. A team at MIT has developed an energy-efficient thin film material that overcomes these shortcomings and is capable of going dark at the flick of a switch.

With its ability to let sunlight in on cold days and block it when hot, electrochromic tinting can cut heating and cooling costs. But one of the biggest issues with existing materials is the time it takes them to become tinted. The change is kicked off by an electric current, which runs through the material to give it a negative charge. Positive ions then flow in to balance the material, making it darker in the process. Although the end result is a tinted window, because the ions don't match the speed of the electrons, the change doesn't happen instantly.

The team at MIT says its system is faster than existing electrochromic tinting systems because of its use of metal-organic frameworks (MOFs. Although these MOFs are most commonly used to store gases, researchers say their ability to quickly conduct both ions and electrons make them useful in optical applications as well. By instantly changing from clear to dark, researchers say their system boast a clear advantage over current technologies.

The material, which takes the form of a thin film, is made up of two chemical compounds, an organic material and a salt, and once it's gone dark, it doesn't require a constant current to maintain its tint, boosting its energy efficiency credentials.

As well as working faster than current systems, MIT's electrochromic material is darker. In the Boeing 787 the windows turn green when a current is run through them, limiting their ability to block the sunlight. By using a unique mix of green and red, the research team has produced a material able to go from transparent to almost completely black.

"It's this combination of these two, of a relatively fast switching time and a nearly black color, that has really got people excited," says MIT professor of chemistry Mircea Dinc─â. "These could lead to pretty significant energy savings. You could just flip a switch when the sun shines through the window and turn it dark."

Having performed initial testing on the material's properties, researchers are planning to create a 1-inch sample to demonstrate it on a wider scale. There are also plans to investigate manufacturing costs.

The results of the MIT research are published in the online journal Chem.

Source: MIT

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