Most existing solar-powered smart windows are designed to respond automatically to changing conditions, such as light or heat—becoming darker to filter out the sun’s rays on bright days, while turning clear on cloudy days to let more light in.

This feature can help control indoor temperatures and offers a degree of privacy without resorting to aids such as mini-blinds.

However, this arrangement means that on cool or cloudy days, consumers can’t flip a switch and tint the windows for privacy. Also, these devices often operate on a mere fraction of the light energy to which they are exposed, while the rest is absorbed by the windows. This has the effect of heating them up, which can add warmth to a room that the windows are supposed to help keep cool.

Existing solar-powered smart windows are designed to respond automatically to changing conditions. Image credit: PixabayNow, scientists led by Jeremy Munday, assistant professor of electrical and computer engineering at the University of Maryland, report a development in this niche: solar smart windows that can turn opaque on demand and even power other devices.

The researchers have created a smart window by sandwiching a polymer matrix containing microdroplets of liquid crystal materials and an amorphous silicon layer—the type often used in solar cells—between two glass panes.

When the window is turned “on” by the user, the silicon layer absorbs the light and provides the low power needed to align the crystals so light can pass through and make the window transparent. When the window is “off,” the liquid crystals scatter light, making the glass opaque.

The extra energy that doesn’t go toward operating the window is harvested and can be redirected to power other devices, such as lights, TVs or smartphones, the researchers say.