Researchers have successfully managed to create a “solar paint” made out of quantum dots, which exhibits similar properties to multifilm solar cell architectures. The later are sophisticated, expensive and require a lot of time to deploy; the paint can be easily applied to basically any surface, like a house’s roof, and prepare it to easily generate photocurrent.
By harvesting waste heat, researchers from the US Department of Energy’s National Renewable Energy Laboratory (NREL) have for the first time built a solar cell with an external quantum efficiency over 100 percent.
A cell's external quantum efficiency is the number of electrons flowing per second in its external circuit, divided by the number of photons per second entering it, and is different at different wavelengths.
The best result for the NREL solar cell was 114 percent. it means, says the team, that solar energy has a competitive future, making it possibly cheaper than energy from fossil or nuclear fuels.
The researchers, Mathew P. Genovese of the University of Waterloo in Canada, with Ian V. Lightcap and Prashant V. Kamat of the Radiation Laboratory and Department of Chemistry and Biochemistry at the University of Notre Dame in Indiana, will be publishing their study in an upcoming issue of ACS Nano.
The new solar paint, which the researchers humorously call “Sun Believable solar paint,” consists of a yellow or brown paste made of quantum dots. The small size of these tiny semiconductor nanocrystals makes it possible to capture nearly all incident visible sunlight with an extremely thin layer of dots. The researchers experimented with three types of quantum dots: CdS, CdSe, and TiO2, all of which are powder-like, with water and tert butanol as the solvent. As Kamat explained, all commercial paints are TiO2 nanoparticle-based suspensions. But instead of adding dye to give the paint a desired color, here the researchers added colored semiconductor nanocrystals to the solar paint to achieve the desired optical and electronic properties.