Sunrise to sunset, new window coating blocks heat -- not view

Windows welcome light into interi or spaces, but they also bring in unwanted heat. A new window coating blocks heat-generating ultraviolet and infrared light and lets through visible light, regardless of the sun's angle. The coating can be inc or p or ated onto exist ing windows or automobiles and can reduce air-conditioning cooling costs by m or e than one-third in hot climates.

"The angle between the sunshine and your window is always changing," said Tengfei Luo, the D or ini Family Profess or f or Energy Studies at the University of Notre Dame and the lead of the study. "Our coating maintains functionality and efficiency whatever the sun's position in the sky."

Window coatings used in many recent studies are optimized f or light that enters a room at a 90-degree angle. Yet at noon, often the hottest time of the day, the sun's rays enter vertically installed windows at oblique angles.

Luo and his postdoct or al associate Seongmin Kim previously fabricated a transparent window coating by stacking ultra-thin layers of silica, alumina and titanium oxide on a glass base. A micrometer-thick silicon polymer was added to enhance the structure's cooling power by reflecting thermal radiation through the atmospheric window and  into outer space.

Additional optimization of the or der of the layers was necessary to ensure the coating would accommodate multiple angles of solar light. However, a trial-and-err or approach was not practical, given the immense number of possible combinations, Luo said.

To shuffle the layers into an optimal configuration -- one that maximized the transmission of visible light while minimizing the passage of heat-producing wavelengths -- the team used quantum computing, or m or e specifically, quantum annealing, and validated their result s experimentally.

Their model produced a coating that both maintained transparency and reduced temperature by 5.4 to 7.2 degrees Celsius in a model room, even when light was transmitted in a broad range of angles. The lab's result s were recently published in Cell Rep or ts Physical Science.

"Like polarized sunglasses, our coating lessens the intensity of incoming light, but, unlike sunglasses, our coating remains clear and effective even when you tilt it at different angles," Luo said.

The active learning and quantum computing scheme developed to create this coating can be used to design of a broad range of materials with complex properties.