Carbon, and its many forms, has been waging a war, of sorts, on silicon, that ubiquitous semiconductor, as it challenges silicon's dominance by bringing its own properties to the table. Carbon can be a considerably stronger and more flexibly material than silicon, while also being cheaper to work with, but there is still a great deal of work to do before it can compete for the throne. Researchers at Stanford University have done some of that work by creating the first all-carbon solar cell.
Carbon has been used in cells before, but what makes this cell special is every component is made of carbon, instead of just the active layer that converts the light to electricity. This is very important because typically those other components, including the electrodes, are made of expensive materials like indium tin oxide (ITO). Indium is a rare element and ITO has so many uses that it is quite expensive. In this new solar cell, the electrodes are made of a combination of graphene and carbon nanotubes, which are transparent, like ITO, but are also flexible and relatively cheap to make.
One issue with this design, that the researchers hope to remedy soon, is a rather low efficiency of 1%. This is partly because carbon primarily reacts to near-infrared light, instead of more abundant visible light. However, as this solar cell is a thin film design, it does have the advantage of being paintable, so instead of having rigid, flat, silicon solar cells, a surface could be painted on, to create a solar cell of any shape.