UV light shines through a sample of transparent material containing quantum dots, tiny nanoparticles that can be used to harness solar energy for electricity. | Photo courtesy of LANL.
Researchers in the Center for Advanced Solar Photophysics at Los Alamos National Laboratory are seeking to transform everyday windows into solar collectors by harnessing the unique properties of quantum dots.
The advantages of solar power as a source of clean, renewable energy seem obvious. Sunlight is abundant, free and, for all practical purposes, eternal. While the price of solar photovoltaic cells recently has plummeted and their efficiency has gone up, challenges remain around siting vast arrays of solar-electric panels and finding ways to integrate them into buildings and other applications.
These challenges prompted a joint research team from Los Alamos National Laboratory and the University of Milano-Bicocca in Italy to try a fresh approach to solar power. Working with quantum dots, the team achieved a breakthrough in solar-concentrating technology that can turn windows into electric generators and revolutionize the way we think about where and how we generate energy.
Think about it: If windows can generate electricity for use on site, the consumer would gain the advantages of free, non-polluting power and at least partial grid independence. The grid would reduce its reliance on fossil fuels, gain resilience and get relief from peak-use demands, which would slash greenhouse gas emissions. Solar windows would also be practically unnoticeable, meaning you could reap the benefits of solar power at home with a minimum of impact on you or the community around you.
If this technology replaced all the glazing on the One World Trade Center building in New York City, the windows could power more than 350 apartments.
Quantum dots fashioned from a light-emitting material make it work. As nanocrystals roughly one-billionth of a meter across, or just 10 to 50 atoms wide, quantum dots obey quantum-mechanics laws. That trait gives them properties that can be manipulated in the laboratory. Quantum dots can absorb light at one wavelength, efficiently convert it and re-emit it at another wavelength. A bigger quantum dot emits on the red end of the spectrum, a smaller dot on the green-blue end. By adjusting the dots’ size, we can precisely tune those wavelengths to suit our purposes. A luminescent solar concentrator consists of quantum dots dispersed in a clear plastic material, which forms a waveguide. The quantum dots absorb sunlight and convert it to a wavelength best suited for the PV cells. Then the waveguide directs light toward the solar cells installed at its edges, which make electricity.
That sounds fine in theory, but the team had to fix a few deal-breaking problems that plagued earlier, proof-of-concept demonstrations of related solar-concentrating technologies, including the use of materials containing environmentally harmful metals. The team solved these problems by creating quantum dots of copper, indium, selenium and sulfur, a composition without any toxic metals. A new industrial method developed by the University of Milan embeds the dots in a transparent material, where the dots absorb uniformly across the solar spectrum. The team’s quantum dots re-emit infrared light, which is ideal for the most common silicon solar cells, yet invisible to the human eye: Occupants in the room will notice only a slight, neutral-colored tinting effect, much like the filtering of conventional “low-E” windows that saves on cooling bills.
Turning windows into solar collectors is the kind of disruptive technology that can revolutionize energy generation and consumption and contribute to a low-carbon energy future. Someday, buildings ranging from your own house to urban skyscrapers might generate much of their own electricity through innocuous luminescent solar concentrating windows. If this technology replaced all the glazing on the One World Trade Center building in New York City, the windows could power more than 350 apartments. How’s that for megascale impact from nanotechnology?