"In most materials, one absorbed photon generates one electron, but in the case of graphene, we have seen that one absorbed photon is able to produce many excited electrons, and therefore a greater electrical current" explained Frank Koppens, group leader at ICFO. This feature makes graphene an ideal building block for any device that relies on converting light into electricity. In particular, it enables efficient solar cells that can harvest light energy from the full solar spectrum with low loss.
The research carried out at the Institute of Photonic Science (ICFO) - an associate institute of the Universitat Politècnica de Catalunya • BarcelonaTech (UPC) - in collaboration with Massachusetts Institute of Technology, Cambridge (USA), Max Planck Institute for Polymer Research, Germany and Graphenea S.L. Donostia-San Sebastian, Spain, sent a known number of photons with different energies (different colors) onto a monolayer of graphene.
The researhers have seen that high energy photons (e.g. violet) are converted into a larger number of excited electrons than low energy photons (e.g. infrared). The linear scaling of the number of generated excited electrons with photon energy showed that graphene converts light into electricity with high efficiency. Even though it was already speculated that graphene holds potential for solar cells the research indicates that it is even more suitable than expected.
Although there are some issues for direct applications, such as graphene’s low absorption, graphene holds the potential to cause radical changes in many technologies that are currently based on conventional semiconductors.
"It was known that graphene is able to absorb a very large spectrum of light colors. However now we know that once the material has absorbed light, the energy conversion efficiency is very high. Our next challenge will be to find ways of extracting the electrical current and enhance the absorption of graphene. Then we will be able to design graphene devices that generate highly efficient solar power." concluded Koppens.
Visit ICFO at www.icfo.eu/graphene/index.htm