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Nat Mater. 2014 Jan;13(1):63-8. doi: 10.1038/nmat3807. Epub 2013 Nov 17.

Efficient charge generation by relaxed charge-transfer states at organic interfaces.

Author information

1
Department of Materials Science and Engineering, Stanford University, 476 Lomita Mall, Stanford, California 94305, USA.
2
Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Straße 24-25, 14476 Potsdam, Germany.
3
1] Department of Materials Science and Engineering, Stanford University, 476 Lomita Mall, Stanford, California 94305, USA [2] King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
4
Institut für Angewandte Photophysik TU Dresden, George-Bähr-Strasse 1, 01062, Dresden, Germany.
5
Department of Chemistry, University of California, 727 Latimer Hall, Berkeley, California 94720, USA.
6
1] Department of Materials Science and Engineering, Stanford University, 476 Lomita Mall, Stanford, California 94305, USA [2].
7
1] King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia [2] Department of Chemistry, University of California, 727 Latimer Hall, Berkeley, California 94720, USA.
8
King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
9
1] Institut für Angewandte Photophysik TU Dresden, George-Bähr-Strasse 1, 01062, Dresden, Germany [2].

Abstract

Interfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold via weakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer:fullerene, small-molecule:C60 and polymer:polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy.

PMID:
24240240
DOI:
10.1038/nmat3807

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