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Tailored exciton diffusion in organic photovoltaic cells for enhanced power conversion efficiency

Nature Materials volume 12, pages 152–157 (2013)Cite this article

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Abstract

Photoconversion in planar-heterojunction organic photovoltaic cells (OPVs) is limited by a short exciton diffusion length (LD) that restricts migration to the dissociating electron donor/acceptor interface. Consequently, bulk heterojunctions are often used to realize high efficiency as these structures reduce the distance an exciton must travel to be dissociated. Here, we present an alternative approach that seeks to directly engineer LD by optimizing the intermolecular separation and consequently, the photophysical parameters responsible for excitonic energy transfer. By diluting the electron donor boron subphthalocyanine chloride into a wide-energy-gap host material, we optimize the degree of interaction between donor molecules and observe a ~50% increase in LD. Using this approach, we construct planar-heterojunction OPVs with a power conversion efficiency of (4.4 ± 0.3)%, > 30% larger than the case of optimized devices containing an undiluted donor layer. The underlying correlation between LD and the degree of molecular interaction has wide implications for the design of both OPV active materials and device architectures.

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Figure 1: Exciton diffusion in a dilute electron-donor film.
Figure 2: Performance of OPVs containing a dilute donor active layer.
Figure 3: Spectral response and internal efficiency.
Figure 4: Experimental prediction of self-Förster radius and exciton diffusion length.

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Acknowledgements

This work was supported primarily by the National Science Foundation (NSF) Program in Solid State and Materials Chemistry (DMR-1006566). Partial support was also received from the University of Minnesota NSF Materials Research Science and Engineering Center (DMR-0819885) and the University of Minnesota Initiative for Renewable Energy and the Environment. The authors wish to acknowledge helpful discussions with D. A. Blank.

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Authors and Affiliations

  1. Department of Chemical Engineering and Materials Science, University of Minnesota, 151 Amundson Hall, 421 Washington Avenue, S.E., Minnesota 55455, Minneapolis, USA

    S. Matthew Menke, Wade A. Luhman & Russell J. Holmes

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  1. S. Matthew Menke
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  2. Wade A. Luhman
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Contributions

S.M.M., W.A.L. and R.J.H. conceived the experiments. S.M.M. and W.A.L. fabricated the structures and carried out the measurements. S.M.M., W.A.L. and R.J.H. contributed to the analysis, and S.M.M. and R.J.H. wrote the manuscript.

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Correspondence to Russell J. Holmes.

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Menke, S., Luhman, W. & Holmes, R. Tailored exciton diffusion in organic photovoltaic cells for enhanced power conversion efficiency. Nature Mater 12, 152–157 (2013). https://doi.org/10.1038/nmat3467

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