Graphene is a one-atom thick material with high electrical conductivity, but as a zero bandgap semiconductor, it acts like a metal. This means that transistors made of the material cannot be easily turned on and off.
However black phosphorus can also be separated into one-atom thick layers known as phosphorene and it does not have the switching problems.
This means that the energy needed to power transistors would be incredibly low.
Thomas Szkopek wrote in Nature that transistors work more efficiently when they are thin, with electrons moving in only two dimensions. Nothing gets thinner than a single layer of atoms.
Of course black phosphorous is not ideal. It is damaged by light, which spells trouble for the creation of single layer transistors.
But the experiments at the highest-powered magnet laboratory in the world, the National High Magnetic Field Laboratory in Florida, the research team discovered that even in thicker sheets of black phosphorous, the electrons still move only in two dimensions.
This is surprising as the electrons are able to be pulled into a sheet of charge which is two-dimensional, even though they occupy a volume that is several atomic layers in thickness. Finding that the 2D electronic structure of black phosphorous was not dependent on the thickness means that it could be manufactured on a large scale.
Of course all that is a few years off, while graphene is closer to production.