A technique akin to spray painting could be used to create a new wave of solar cells. A team from the University of Toronto’s Department of Electrical and Computer Engineering and the IBM Canada Research and Development Center developed the method, called "sprayLD," which uses light-sensitive colloidal quantum dots (CQDs). The spraying method could be “integrated to large-area manufacturing processes and can be used to make solar cells on unconventional shapes,” the researchers wrote in a study published in Applied Physics Letters (doi: 10.1063/1.4898635). SprayLD works by blasting a liquid containing CQDs directly onto flexible surfaces. The material could be printed onto flexible film or plastic that would be used to coat a variety of surfaces, from the roofs of buildings and vehicles, to electronic devices and airplane wings. On a surface the size of an average car roof, the coated film or plastic could produce enough energy to power three 100-W light bulbs or 24 compact fluorescents, according to the researchers. </center> The coating method makes incorporating solar cells into existing manufacturing processes simpler. The sprayLD device would be less expensive to manufacture, too, as it is made from parts that are affordable and readily available — among them, spray nozzles and air brushes. “We were thrilled when this attractively manufacturable spray-coating process also led to superior-performance devices showing improved control and purity,” said professor Dr. Ted Sargent. In the study, the researchers tested the transferability of the sprayLD method to a roll-to-roll manufacturing process by spray-coating the CQD active layer onto six substrates mounted on a rapidly rotating drum, “yielding devices with an average power conversion efficiency of 6.7 percent.” By developing this CQD technique and implementing a fully automated process with near monolayer control, “an electronic defect is eliminated resulting in solar cell performance and statistical distribution superior to prior batch-processed methods,” the researchers wrote in another study published in Advanced Materials (doi: 10.1002/adma.201403281). “As quantum dot solar technology advances rapidly in performance, it’s important to determine how to scale them and make this new class of solar technologies manufacturable,” Sargent said. The work was funded by the IBM Canada Research and Development Center and King Abdullah University of Science and Technology. For more information, visit www.utoronto.ca.