MIT Researchers Introduce Graphene Electrodes into Organic Solar Cells

The conventional solar cells usually employ highly purified silicon, which is expensive. To make solar cells inexpensive, compact and flexible, researchers have been using organic compounds.

However, they found it difficult to recognize suitable materials for making the electrodes, which would carry the current towards and from the cells, in particular materials for making the electrodes, which would match up to the organic cells’ transparency, flexibility and low cost. They had been using indium-tin-oxide or ITO as the electrode material, but with its rare nature making it very expensive; a replacement for ITO was required.

Currently researchers from MIT have found a substitute for ITO in carbon, which is available in plenty and inexpensive. The material used is graphene, which is one form of carbon where atoms are arranged in a flat sheet with a thickness of just one atom in a formation, similar to a chicken-wire design. The journal Nanotechnology has published an analysis of how graphene could be used as electrode in its December 17 issue.

Graphene being highly transparent does not block any incoming light and hence electrodes made from graphene could be applied to the transparent solar cells. Also being very flexible by nature, it could be included in the installations where the panels need to follow a patterned roof or the contours of a structure. In contrast, ITO was found to be brittle and stiff. But one major drawback is the inability of graphene to adhere to the panel. It repels water and hence typical procedures for production of an electrode on the surface by depositing the material from a solution would not be successful.

After having tried a variety of approaches to eliminate this problem the researchers finally hit upon doping the surface i.e. by introducing some impurities into the surface, changing its behavior and allowing graphene to bond tightly. An extra bonus to this procedure was that doping also enhanced the electrical conductivity of the material. Kong and her co-researchers after having replaced one electrode were also trying to replace the second electrode with graphene in the solar panel. However for commercializing this technique, first new ways of manufacturing graphene on a large scale need to be devised. Funding for the research was provided by an NSF research fellowship and by the Eni-MIT Alliance Solar Frontiers Center.