Physicists explore the key energy transport process underlying solar energy harvesting

Taking inspiration from spilled milk

Two Lehigh physicists have developed an imaging technique that makes it possible to directly observe light-emitting excitons as they diffuse in a new material that is being explored for its extraordinary electronic properties. Called rubrene, it is one of a new generation of single-crystal organic semiconductors.

Excitons, which are created by light, play a central role in the harvesting of solar energy using plastic solar cells. The achievement by Ivan Biaggio, professor of physics, and Pavel Irkhin, a Ph.D. candidate, represents the first time that an advanced imaging technique has been used to witness the long-range diffusion of energy-carrying excitons in an organic crystal.

One way to understand the mechanics of excitons, says Biaggio, is to pour a cup of milk on the floor. The milk spreads out in all directions from the point of impact. How far it goes depends on the type of surface on which it lands. Now imagine that the milk has been replaced with particle-like bundles of energy and the floor with an ordered arrangement of organic molecules.

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An article by Irkhin and Biaggio, titled “http://prl.aps.org/pdf/PRL/v107/i1/e017402">Direct Imaging of Anisotropic Exciton Diffusion and Triplet Diffusion Length in Rubrene Single Crystals,” was published July 1 by the journal Physical Review Letters.

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