Researchers at École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have observed and measured graphene converting a single photon into multiple electrons in a photovoltaic device. They say this shows that graphene might serve as a photovoltaic (PV) material with very high energy-conversion efficiencies.

Reported in IEEE Spectrum, the discovery builds on work conducted in 2014 by the Institute of Photonic Science (ICFO). ICFO scientists were able to indirectly show that graphene is capable of converting one photon into multiple electrons.

In this most recent work, researchers had to devise a way to measure the conversion process, which occurs on a femto-second scale (10^-15 seconds). That’s far faster than any conventional method for detecting electron movement, the researchers report.

The team turned to a new technique called ultrafast time- and angle-resolved photoemission spectroscopy (trARPES).

The graphene was placed in a vacuum chamber where the material was then hit with a “pump” pulse of laser light. In this heightened state, the graphene then was hit with a time-delayed “probe” pulse that serves to take a snapshot of the energy each electron has at that moment. By doing this numerous times, the researchers create a kind of stop-motion movie of the conversion process.

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