Monday, March 4, 2013

New Graphene Photovoltaic Cell Could Achieve 60% Efficiency

Graphene is a substance composed of pure carbon, with atoms arranged in a regular hexagonal pattern similar to graphite, but in a one-atom thick sheet. It is very light, with a 1-square-meter sheet weighing only 0.77 milligrams. Several potential applications for graphene are under development, and many more have been proposed. These include display screens, electric circuits, various medical, chemical, and industrial processes enhanced or enabled by the use of new graphene materials.

Recently, researchers have applied graphene to photovoltaic cells. They showed that it is highly efficient at generating electrons when light was shined.

When light strikes silicon and gallium arsenide, single electron was generated for each photon absorbed. Since a photon contains more energy than one electron can carry, much of the energy contained in the incoming light is lost as heat. Now, new research reveals that when graphene absorbs a photon it generates multiple electrons. This means that graphene could be more efficient than the devices commonly used today.

Previous theoretical work had inspired hope that graphene had this property, says Frank Koppens, a group leader at the Institute of Photonic Sciences in Spain, who led the research. Although the work only hints at possible solar applications, it shows that graphene could be considered a candidate for use in so-called third-generation solar cells. Today’s silicon cells have a theoretical efficiency limit of around 30%. Graphene could improve the theoretical limit to over 60%.

Graphene was already exciting as a photovoltaic material because of its unique optical properties which covers a very broad spectrum of the sunlight. It is also flexible, robust, relatively cheap, and easily integrated with other materials.

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