Relying on advanced materials such as perovskites and single-walled carbon nano-tubes, a window technology was developed that responds to heat by transforming from transparent to tinted. As the window darkens, it generates electricity. The color change is driven by molecules (methylamine) that are reversibly absorbed into the device. When solar energy heats up the device, the molecules are driven out, and the device is darkened. When the Sun is not shining, the device is cooled back down, and the molecules re-absorb into the window device, which then appears transparent.

The switchable photovoltaic window dynamically transforms from transparent to tinted. (Photo by Dennis Schroeder/NREL)

The device allows an average of 68 percent of light in the visible portion of the solar spectrum to pass through when it is in a transparent, or bleached, state. When the window changes color — a process that took about three minutes of illumination during testing — only 3 percent is allowed through the window.

Existing solar window technologies are static, which means they are designed to harness a fraction of the sunlight without sacrificing too much visible light transmission needed for viewing, or for the comfort of building occupants. The proof-of-concept established a solar power conversion efficiency of 11.3 percent.

In testing under 1-sun illumination, the 1-square-centimeter demonstration device cycled through repeated transparent-tinted cycles, but the performance declined over the course of 20 cycles due to restructuring of the switchable layer. Ongoing research is focused on improving cycle stability.

The technology could be integrated into vehicles, buildings, and beyond. The electricity generated by the solar cell window could charge batteries to power smartphones or onboard electronics such as fans, rain sensors, and motors that would open or close the windows as programmed.

For more information, contact Heather Lammers at This email address is being protected from spambots. You need JavaScript enabled to view it.; 303-275-4084.


Tech Briefs Magazine

This article first appeared in the December, 2018 issue of Tech Briefs Magazine.

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