Graphene highly efficient at converting light to electricity
BARCELONA, Spain – Graphene is even more efficient at converting light to electricity than was previously known, making it an ideal building block for any device that relies on such conversions, a new international study has found.
Researchers at the Institute of Photonic Science (ICFO), in collaboration with MIT in the US, Max Planck Institute for Polymer Research in Germany and Graphenea SL of Donostia-San Sebastian in Spain, have demonstrated that graphene can convert a single photon of light into multiple electrons able to drive electric current. The discovery is an important one for next-generation light detectors and solar cells, and for other light-detecting and light-harvesting technologies that currently rely on conventional semiconductors such as silicon.
“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,” said ICFO group leader Frank Koppens.
In their experiment, the investigators sent a known number of photons with different energies (different colors) onto a monolayer of graphene.
“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),” said ICFO researcher K.J. Tielrooij. “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.”
There are still some issues for direct applications, such as graphene’s low absorption, but it holds the potential to cause radical changes in many technologies that are currently based on conventional semiconductors. And, because of its potential, the European Commission has promised an injection of €1 billion (about $1.3 billion) in graphene research over 10 years.
“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,” Koppens said. “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 study appeared in Nature Physics (doi: 10.1038/nphys2564).
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