Lynn Loo: Self-powered smart windows

Thursday, Nov 8, 2018

A new transparent solar cell technology can turn ordinary windows into energy-efficient “smart” windows, regulating the transmission of sunlight and heat to save energy and improve occupant comfort.

Smart windows can darken on hot days to keep the sun out and rooms cool, or let heat in on cold days while reducing glare and protecting privacy. But these technologies require plugging the smart windows into an electricity source, adding to installation and operating costs.

The self-powered smart window demonstrated by Professor Yueh-Lin (Lynn) Loo, Princeton's Theodora D. ’78 and William H. Walton III ’74 Professor in Engineering and director of the Andlinger Center for Energy and the Environment, and her team includes two components: a solar cell that harvests near-ultraviolet light to produce electricity, and the technology to use that harvested electricity to change the window’s color. This color change with electricity, or “electrochromism,” regulates how much visible light and near-infrared heat enter the window.

Electrochromic windows are commercially available today for high-end new construction and luxury automobiles, where the installation cost and complexity of external wiring can be managed. With the new near-ultraviolet solar cells, external wires can be eliminated.

The fact that these solar cells selectively harness ultraviolet wavelengths differentiates them from existing solar cell technologies that absorb visible and/or infrared light. Solar cells that absorb visible light appear black, while those that absorb infrared light block much of the sun’s heat regardless of the season. Powering smart windows with near-ultraviolet solar cells allows for intelligent control of daytime lighting and solar heating throughout the year, which is particularly useful during winter days when occupants desire the warmth of the sun.

“It will be possible to control the sunlight passing into your home or office using an app on your phone or via a smart thermostat, thereby ensuring ideal comfort, privacy and energy efficiency at all times,” said Nicholas Davy, a graduate student who led the development of the near-ultraviolet solar cells as part of his Ph.D. work with Loo.

Beyond powering smart windows, the transparent solar cell technology can enable other wireless low-power consumer products, such as internet-of-things sensors, wearables and displays.

“We envision new smart windows that are self-powered to dynamically control the amount of natural light and heat that can come inside, reducing energy cost and making the space more comfortable.”

-Yueh-Lin (Lynn) Loo, Princeton's Theodora D. ’78 and William H. Walton III ’74 Professor in Engineering and Director of the Andlinger Center for Energy and the Environment, and Professor of Chemical and Biological Engineering

Team members: Jia Gao, former postdoctoral research associate; Amy Liu, Class of 2019; Melda Sezen-Edmonds, Ph.D. 2018
Collaborators: Antoine Kahn, vice dean of the School of Engineering and Applied Science and the Stephen C. Macaleer ’63 Professor in Engineering and Applied Science; Xin Lin, Ph.D. 2018; Nan Yao, senior research scholar at the Princeton Institute for the Science and Technology of Materials and director of the Imaging and Analysis Center
Development status: Loo and Davy have formed a new company, Andluca Technologies, to develop partnerships and products based on this technology.
Funding: National Science Foundation, Wilke Family Foundation

Contact: John Ritter, Director of Technology Licensing, jritter@princeton.edu or 609-258-1570