In an effort to improve the energy efficiency of building, researchers have sought to develop windows that change transparency to let more light – and therefore heat – through when it's cold, and less when it's hot. Unfortunately, these methods tend to impede the passage of visible light, some by tinting panes and others by complete obscuration. But a team at the Cockrell School of Engineering at The University of Texas at Austin has developed a "smart window" technology that allows the passage of light while blocking heat, or vice versa.

Two years ago, Delia Milliron and her team produced a "smart" glass coating that could block visible light, near-infrared light (NIR), or both. By embedding indium tin oxide (ITO) nanocrystals in glass imbued with niobium oxide, the research team created an electrochromic material that's able to transmit or block light depending on the electric potential applied.

The team's advancements on their previous research have led to the creation of electrochromic materials that can selectively permit the passage of light, while blocking heat (cool mode) and, conversely, block light while allowing the transfer of heat (warm mode). These new materials allows control of up to 90 percent of NIR and 80 percent of visible light. And since switching between modes takes mere minutes instead of hours, as was the case with the previously-reported material, commercialized products may be closer at hand.

In order to make this new electrochromic material practical, the researchers structured the components into a single, porous, interpenetrating network. This design provides channels for electronic and ionic change, thereby enabling selective blocking of light and/or NIR through different applied voltages. Milliron and her team demonstrated a proof-of-concept that achieves optical control properties from a single-component film. They are now working toward methods suitable for low-cost manufacturing.

Illustration of different possible modes for this latest "smart window" technology(Credit: Cockrell School of Engineering)

"These two advancements show that sophisticated dynamic control of sunlight is possible," Milliron said. "We believe our deliberately crafted nanocrystal-based materials could meet the performance and cost targets needed to progress toward commercialization of smart windows."

The research was published in the Journal of the American Chemical Society.

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