Article

Intrinsic non-radiative voltage losses in fullerene-based organic solar cells

  • Nature Energy 2, Article number: 17053 (2017)
  • doi:10.1038/nenergy.2017.53
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Abstract

Organic solar cells demonstrate external quantum efficiencies and fill factors approaching those of conventional photovoltaic technologies. However, as compared with the optical gap of the absorber materials, their open-circuit voltage is much lower, largely due to the presence of significant non-radiative recombination. Here, we study a large data set of published and new material combinations and find that non-radiative voltage losses decrease with increasing charge-transfer-state energies. This observation is explained by considering non-radiative charge-transfer-state decay as electron transfer in the Marcus inverted regime, being facilitated by a common skeletal molecular vibrational mode. Our results suggest an intrinsic link between non-radiative voltage losses and electron-vibration coupling, indicating that these losses are unavoidable. Accordingly, the theoretical upper limit for the power conversion efficiency of single-junction organic solar cells would be reduced to about 25.5% and the optimal optical gap increases to 1.45–1.65 eV, that is, 0.2–0.3 eV higher than for technologies with minimized non-radiative voltage losses.

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Acknowledgements

This work was supported by the German Federal Ministry for Education and Research (BMBF) through the InnoProfille project ‘Organische p-i-n Bauelemente 2.2’. K.T. acknowledges the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme FP7 under the REA grant agreement PIEF-GA-2012-327199. F.P. and D.N. acknowledge funding by the German Research Foundation (DFG) via the SFB 951 ‘HIOS’. The work of Georgia Tech was supported by the Department of the Navy, Office of Naval Research Award No. N00014-14-1-0580 (CAOP MURI), and through a State-Sponsored Scholarship for Graduate Students to Y.F. from the China Scholarship Council. M.T. thanks the Christ Church Oxford for financial support with a Junior Research Fellowship. M.K.R. acknowledges the UK Engineering and Physical Science Research Council (EPSRC) through grant EP/L026066/1. Additionally, we thank for the supply of the donor molecules: P. Bäuerle from University of Ulm for DH4T, DH6T and several DCV2-nT, M. Hummert for P4-Ph4-DIP and BP-Bodipy, and B. Beyer for ZnF4Pc. Furthermore, we acknowledge F. Holzmueller, C. Koerner, M. Saalfrank and R. Meerheim for providing OSC devices for this study.

Author information

Author notes

    • Yeli Fan

    Present address: School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, Jiangsu, China.

Affiliations

  1. Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany

    • Johannes Benduhn
    • , Sascha Ullbrich
    • , Olaf Zeika
    • , Donato Spoltore
    •  & Koen Vandewal
  2. Experimental Physics VI, Julius-Maximilian University of Würzburg, 97074 Würzburg, Germany

    • Kristofer Tvingstedt
  3. Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24–25, 14476 Potsdam, Germany

    • Fortunato Piersimoni
    •  & Dieter Neher
  4. Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA

    • Yeli Fan
    • , Stephen Barlow
    •  & Seth R. Marder
  5. Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK

    • Manuel Tropiano
  6. Department of Chemistry, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis 55455, USA

    • Kathryn A. McGarry
    •  & Christopher J. Douglas
  7. Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, UK

    • Moritz K. Riede

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Contributions

J.B., K.T., D.S. and K.V. designed the experiments, prepared photovoltaic devices and optimized their processing parameters for photovoltaic performance. J.B. measured the sensitive EQEPV spectra, K.T. measured the EQEEL, and F.P. measured the corresponding EL spectra. D.S., J.B. and S.U. performed the standard characterization of the solar cells. M.T., Y.F. and O.Z. synthesized donor molecules for low-ECT systems, important for this study. K.A.M. synthesized deuterated rubrene. D.N., S.B., S.R.M., M.K.R. and C.J.D. supervised their team members involved in the project. K.V. supervised the overall project. All authors contributed to analysis and writing.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Johannes Benduhn or Kristofer Tvingstedt or Koen Vandewal.

Supplementary information

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    Supplementary Information

    Supplementary Notes 1–3, Supplementary Tables 1–6, Supplementary Figures 1–7 and Supplementary References.