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Endohedral fullerenes for organic photovoltaic devices

Nature Materials volume 8, pages 208–212 (2009)Cite this article

Abstract

So far, one of the fundamental limitations of organic photovoltaic (OPV) device power conversion efficiencies (PCEs) has been the low voltage output caused by a molecular orbital mismatch between the donor polymer and acceptor molecules. Here, we present a means of addressing the low voltage output by introducing novel trimetallic nitride endohedral fullerenes (TNEFs) as acceptor materials for use in photovoltaic devices. TNEFs were discovered in 1999 by Stevenson et al. 1; for the first time derivatives of the TNEF acceptor, Lu3N@C80, are synthesized and integrated into OPV devices. The reduced energy offset of the molecular orbitals of Lu3N@C80 to the donor, poly(3-hexyl)thiophene (P3HT), reduces energy losses in the charge transfer process and increases the open circuit voltage (Voc) to 260 mV above reference devices made with [6,6]-phenyl-C61-butyric methyl ester (C60-PCBM) acceptor. PCEs >4% have been observed using P3HT as the donor material. This work clears a path towards higher PCEs in OPV devices by demonstrating that high-yield charge separation can occur with OPV systems that have a reduced donor/acceptor lowest unoccupied molecular orbital energy offset.

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Figure 1: TNEF electrochemical properties to establish LUMO levels.
Figure 2
Figure 3: Absorption spectra of Lu3N@C80 and its methano derivatives.
Figure 4: Time-resolved TNEF photophysics.
Figure 5: Blend-film electronic and optical properties.

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Acknowledgements

This material is based on work supported by the Air Force Office of Scientific Research under Contract No. FA9550-06-C-0010. Any opinion, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the Air Force Office of Scientific Research. This material is also based on work supported by the National Science Foundation under Grant No. 0348955 and Grant No. IIP-0740454. Additional thanks to The Cluster of Excellence ‘Engineering of Advanced Materials’ and the Alexander von Humboldt Foundation for generous support (S.G.S.).

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Authors and Affiliations

  1. Georgetown University, 37th and O st. NW, Washington, District of Columbia 20057, USA

    Russel B. Ross & Edward Van Keuren

  2. Luna Innovations Incorporated, 521 Bridge Street, Danville, Virginia 24541, USA

    Claudia M. Cardona, Brian C. Holloway & Martin Drees

  3. Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander- Universität Erlangen-Nürnberg, Egerlandstr. 3, 91058 Erlangen, Germany

    Dirk M. Guldi & Shankara Gayathri Sankaranarayanan

  4. National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, Colorado 80401, USA

    Matthew O. Reese & Nikos Kopidakis

  5. Center for Polymer and Organic Solids, University of California, Santa Barbara, California 93106, USA

    Jeff Peet & Guillermo C. Bazan

  6. Department of Chemistry and Biochemistry (or Center for Polymers and Organic Solids) University of California at Santa Barbara, Santa Barbara, California 93117, USA

    Bright Walker

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Corresponding author

Correspondence to Martin Drees.

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Competing interests

R.B.R., E.V.K. and D.M.G. all work, or have worked, under contract for Luna Innovations, which has a financial interest in the successful application of TNEF in OPVs.

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Ross, R., Cardona, C., Guldi, D. et al. Endohedral fullerenes for organic photovoltaic devices. Nature Mater 8, 208–212 (2009). https://doi.org/10.1038/nmat2379

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