how transparent solar panels + 'quantum dots' could harvest energy on an architectural scale

imagine a glass skyscraper that, instead of using energy, stands as source of power for the entire building. although this sounds like the city of the future, recent developments mean that it could soon be a reality — at least in part. the key lies in the creation of transparent solar cells which, when placed between the panes of double-glazed windows, inconspicuously harvest energy from the sun. however, a major challenge for scientists is maximizing the cell’s energy efficiency without compromising transparency.

image by robert coelius, michigan engineering communications & marketing (also main image)

in august 2020, a team led by university of michigan researchers set a new efficiency record for color-neutral, transparent solar cells. the team achieved 8.1% efficiency and 43.3% transparency with an organic, or carbon-based, design rather than conventional silicon. while the cells have a slight green tint, the team says that they are much more like the gray of sunglasses and car windows.

‘windows, which are on the face of every building, are an ideal location for organic solar cells because they offer something silicon can’t, which is a combination of very high efficiency and very high visible transparency,’ explains stephen forrest, the peter a. franken distinguished university professor of engineering and paul g. goebel professor of engineering. forrest led a team that includes researchers at north carolina state university, soochow university in china, and SLAC national accelerator laboratory.

image by robert coelius, michigan engineering communications & marketing

buildings with glass façades typically have a coating on them that reflects and absorbs some of the light, to reduce the brightness and heating inside the building. rather than discarding that energy away, transparent solar panels could use it to provide some of the building’s electricity needs. transparent solar cells are measured by their light utilization efficiency, which describes how much energy from the light hitting the window is available either as electricity or as transmitted light on the interior side. previous transparent solar cells have light utilization efficiencies of roughly 2-3%, putting the record 8.1% efficiency into context.

image courtesy of UbiQD

meanwhile, UbiQD, an advanced materials company based in new mexico, is continuing its development of transparent solar panels that are indistinguishable from regular glass. the company uses ‘quantum dots’ — microscopic particles that manipulate light — to harvest solar energy. these could also be integrated with windows. ‘we envision a world where sunlight harvesting is ubiquitous, a future where our cities are powered by quantum dot-tinted glass on skyscrapers,’ said hunter mcdaniel, founder and CEO of UbiQD, in 2017.

‘quantum dots (QDs) are vanishingly small ‘nano’ particles of material, so tiny that it would take roughly 100,000 of them to span your fingernail,’ explains the team at UbiQD. ‘owing to their small size, these materials are especially advantageous due to having remarkably high efficiency and size-tunable photoluminescence (PL, light emission) over a wide-range of colors.’

image courtesy of UbiQD

in may 2020, UbiQD partnered with nanosys, the manufacturer of the quantum dots, to develop luminescent greenhouse films. installed above plants in a greenhouse, ‘UbiGro’ is a layer of light that helps plants get more from the sun. the method uses fluorescence to create a more optimal light spectrum for crops, converting under-utilized portions of sunlight to more photosynthetically efficient orange light that plants crave.