Smarter window materials to control light and energy

Researchers are a step closer to delivering smart windows with a new level of energy efficiency, engineering materials that allow windows to reveal light without transferring heat, at the same time blocking light while allowing heat transmission.

The new materials could significantly reduce costs for heating and cooling buildings by allowing occupants to more precisely control the energy and sunlight passing through a window according to recent research.

In 2013 in the Milliron Research Group at the McKetta Department of Chemical Engineering became the first to develop dual-band electrochromic materials that blend two materials with distinct optical properties for selective control of visible and heat-producing near-infrared light (NIR). In a 2013 issue of Nature, the group demonstrated how, using a small jolt of electricity, a nanocrystal material could be switched back and forth, enabling independent control of light and energy.

The team headed by Delia Milliron now has engineered two new advancements in electrochromic materials — a highly selective cool mode and a warm mode, not thought possible several years ago.

The cool mode material is a major step toward a commercialized product because it enables control of 90 percent of NIR and 80 percent of the visible light from the sun and takes only minutes to switch between modes. The previously reported material could require hours.

To achieve this high performance, the team has developed a new nanostructured architecture for electrochromic materials that allows for a cool mode to block near-infrared light while allowing the visible light to shine through. This could help reduce energy costs for cooling buildings and homes during the summer. “We believe our new architected nanocomposite could be seen as a model material, establishing the ideal design for a dual-band electrochromic material,” Milliron said. “This material could be ideal for application as a smart electrochromic window for buildings.”

In the paper, the team demonstrates how the new material can strongly and selectively modulate visible light and NIR by applying a small voltage. In a second research paper the team reported a proof-of-concept demonstrating how they can achieve optical control properties in windows from a well-crafted, single-component film. The concept includes a simple coating that creates a new warm mode, in which visible light can be blocked, while near-infrared light can enter. This new setting could be most useful on a sunny winter day, allowing infrared radiation to pass into a building for warmth, while reducing the glare from sunlight.

“We believe our deliberately crafted nanocrystal-based materials could meet the performance and cost targets needed to progress toward commercialization of smart windows.”