It’s kind of like a Swiss Army knife of windows or maybe a holy grail of photovoltaics, but earlier this week the National Renewable Energy Laboratory (NREL) announced that it has developed a glass that automatically tints when hit by sunlight and produces electricity.
Once hit by sunlight the thermochromic device begins converting sunlight into electricity at a conversion efficiency of 11.3 percent. While that’s far lower than the 20 percent efficiency rates of high-end solar panels from companies like Panasonic and SunPower, it’s a high rate for a device that could be integrated into windows on buildings or even vehicles while serving multiple purposes.
The proof of concept device, which uses perovskites and single-walled carbon nanotubes to perform its transformations, was developed by Lance Wheeler and Robert Tenent and their team at NREL. “There are thermochromic technologies out there but nothing that actually converts that energy into electricity,” Wheeler said of the device. He is lead author of “Switchable Photovoltaic Windows Enabled by Reversible Photothermal Complex Dissociation from Methylammonium Lead Iodide,” which was published in Nature Communications.
“There is a fundamental tradeoff between a good window and a good solar cell,” said Lance Wheeler said. “This technology bypasses that. We have a good solar cell when there’s lots of sunshine and we have a good window when there’s not.”
When not activated by sunlight, in what NREL called its “bleached state,” the window allowed an average of 68 percent of visible light to penetrate it. When activated by sunlight, only 3 percent of visible light could penetrate it. The automatic process took about 3 minutes, according to the lab.
The lab explained that the opacity change is occurs as solar energy heats the device. That drives out molecules of methylamine. When not hit by sunlight, the molecules are reabsorbed, making the window transparent again. The process can be watched in a short video here. Meanwhile the photovoltaic perovskite crystals in the material produce electricity when hit by light.
The device was tested under the illumination of one sun, NREL explained. However, its performance declined over 20 cycles as the switchable layer restructured itself. The team will now focus on improving cycle stability in the hopes of creating a commercially viable technology.
The idea for the technology came from the Energy I-Corps, launched last year. It paired researchers with industry mentors to better understand what consumers want and to develop ways to bring new technologies to the marketplace.Tweet