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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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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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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DOI: https://doi.org/10.1038/nmat2379
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