A new structure that combines atomic-layered semiconductor materials could pave the way to more efficient solar cells. Researchers from the Vienna University of Technology created the new structure, which merges together two semiconductor materials in ultra-thin layers. Graphene was added, making them extremely light weight and very flexible. Both of the new semiconductor layers are each comprised of three atomic layers, and they may have the capacity to handle photovoltaic energy conversion, according to the researchers. A new semiconductor structure, consisting of two ultra-thin layers, could lead to development of new and more efficient types of solar cells. Courtesy of Vienna University of Technology. Recently, the researchers produced an ultra-thin semiconductor layer of crystal tungsten diselenide. When coupled with a layer of molybdenum disulphide, it resulted in development of the new semiconductor structure, which the researchers said could be used for lower-cost, extremely thin, semi-transparent, flexible solar cells, as well as potentially a new type of solar cell technology altogether. “Quite often, two-dimensional crystals have electronic properties that are completely different from those of thicker layers of the same material,” said researcher Dr. Thomas Mueller, an associate professor at TU Vienna. “We had already been able to show that tungsten diselenide can be used to turn light into electric energy and vice versa.” He noted that solar cells made only of tungsten diselenide require numerous tiny metal electrodes. However, combining that material with molybdenium disulphide obviates that requirement and the structure can be used to build large-area solar cells. “One of the greatest challenges was to stack the two materials, creating an atomically flat structure,” Mueller said. “If there are any molecules between the two layers, so that there is no direct contact, the solar cell will not work.” In the study, contact was accomplished by heating both layers in a vacuum and stacking them in an ambient atmosphere. The researchers removed the water between the two layers by heating the structure a second time. The researchers are now looking at the possibility of a semiconductor structure that has more than two layers, which they said should reduce transparency while also increasing electrical power. The research was published in Nano Letters (doi: 10.1021/nl501962c). For more information, visit www.tuwien.ac.at.