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, have announced the solar paint.
The new material 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.
As Kamat explains, solar paint has advantages in simplicity, economics, and stability compared to multifilm solar cell architectures. While preparing a quantum dot film as a solar cell usually requires multiple time-intensive steps, solar cells in paint form can simply be brushed on to a surface in one step.
The researchers experimented with several different combinations and ratios of the quantum dots to make different paint mixtures. They found that a composite of mixed CdS/TiO2 and CdSe/TiO2 nanoparticles achieve the best performance, particularly when the CdS and CdSe are deposited directly on the TiO2 nanoparticles as a coating. When coated on a glass electrode, the paint has an overall power conversion efficiency exceeding 1%. Although some multifilm quantum dot solar cells have efficiencies greater than 5%, the researchers think that using different quantum dots and further optimization could significantly increase the efficiency of the paint.
The new solar paint is the first step toward developing a solar technology that could potentially have wide-ranging applications. Some uses could include painting electronic devices such as cell phones and computers, in addition to rooftops, windows, and cars. Large-scale applications could be used to build solar farms in deserts.
