Researchers at the Institute of Photonic Science (ICFO), in collaboration with Massachusetts Institute of Technology, USA, Max Planck Institute for Polymer Research, Germany, and Graphenea S.L. Donostia-San Sebastian, Spain have demonstrated graphene is able to convert a single photon such that when it’s absorbed it releases multiple freed electrons.
This is a very promising discovery. Graphene could become an important alternative material for light detection like camera cells and photovoltaic solar harvesting technologies.
Now the conventional semiconductors like silicon cut loose one electron for each photon.
Frank Koppens, group leader at ICFO said, “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 generate larger electrical signals.” The new discovery suggests graphene would be an ideal building block for any device that relies on converting light into electricity. In particular, it enables efficient light detectors and potentially also solar cells that can harvest light energy from the full solar spectrum with lower loss.
The experiment consisted in sending a known number of photons with different energies (different colors) onto a monolayer of graphene. Link to the Cornell Library pdf download.
Klaas-JanTielrooij a researcher at ICFO explains, “We 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 observed relation between the photon energy and the number of generated excited electrons shows that graphene converts light into electricity with very high efficiency. Even though it was already speculated that graphene holds potential for light-to-electricity conversion, it now turns out that it is even more suitable than expected!”
The discovery isn’t fully worked out for the next steps for commercial applications because there are some issues for direct applications, such as graphene’s low light absorption. The balance between the low light absorption rate and the multiplied result isn’t discussed.
Koppes isn’t deterred in seeing graphene holds the potential to cause radical changes in many technologies that are currently based on conventional semiconductors. He said, “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 detect light more efficiently and could potentially even lead to more efficient solar cells.”
The internationally collaborating team’s paper, “Photoexcitation cascade and multiple hot-carrier generation in graphene” by K.J. Tielrooij, J.C.W. Song, S.A. Jensen, A. Centeno, A. Pesquera, A. Zurutuza Elorza, M. Bonn, L.S. Levitov and F.H.L. Koppens has been published in Nature Physics.
The team’s result is quite encouraging. Two generations ago the suggestion was plastics were the wave of the future and that idea has very much come to pass.
Today plastics are virtually everywhere in almost every application. Plastics can be seen as the key material that revolutionized technology over the past one-half century.
There is widespread optimism in the scientific community that graphene will provide similar paradigm shifting advances in the decades to come. Mobile phones that fold, transparent and flexible solar panels, extra thin computers, and now photo collection devices add to the endless list of potential applications.
Europe’s scientists, industries and the European Commission are so convinced of the potential of graphene to revolutionize the world economy that they promise an injection of €1.000 million euros in graphene research even in the midst of an economic slowdown.
In the 1960s the future was talked up at cocktail parties, now it’s on the blogs. Pass the news around.