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A strong regioregularity effect in self-organizing conjugated polymer films and high-efficiency polythiophene:fullerene solar cells

Nature Materials volume 5, pages 197–203 (2006)Cite this article

Abstract

Low-cost photovoltaic energy conversion using conjugated molecular materials has become increasingly feasible through the development of organic ‘bulk heterojunction (BHJ)’ structures1,2,3,4,5,6,7, where efficient light-induced charge separation is enabled by a large-area donor–acceptor interface2,3. The highest efficiencies have been achieved using blends of poly(3-hexylthiophene) (P3HT) and a fullerene derivative8,9,10,11,12, but performance depends critically on the material properties and processing conditions. This variability is believed to be influenced by the self-organizing properties of P3HT, which means that both optical13,14 and electronic15,16 properties are sensitive to the molecular packing. However, the relationship between molecular nanostructure, optoelectronic properties of the blend material and device performance has not yet been demonstrated. Here we focus on the influence of polymer regioregularity (RR) on the molecular nanostructure, and hence on the resulting material properties and device performance. We find a strong influence of RR on solar-cell performance, which can be attributed to enhanced optical absorption and transport resulting from the organization of P3HT chains and domains. Further optimization of devices using the highest RR material resulted in a power conversion efficiency of 4.4%, even without optimization of electrodes7.

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Figure 1: Schematic structure of polymer solar cells and energy-minimized structure of P3HTs.
Figure 2: Optical spectra of pristine and blend films.
Figure 3: GIXRD setup and results for pristine and blend films.
Figure 4: Electrical properties and polaron dynamics of pristine and/or blend films.
Figure 5: Best performance of polymer solar cells made in this work.

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Acknowledgements

The authors thank Merck Chemicals for supplying the P3HT polymer and British Petroleum International for financial support through the OSCER project. Y.K. thanks G. Y. Heo (Postech, Korea), J. W. Park and H. J. Kim (PNU, Korea) for their help with the GIXRD and SEM measurements.

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Authors and Affiliations

  1. Department of Physics, Blackett Laboratory, Imperial College London, London, SW7 2BW, UK

    Youngkyoo Kim, Sachetan M. Tuladhar, Stelios A. Choulis, Jenny Nelson & Donal D. C. Bradley

  2. Department of Chemistry, Imperial College London, London, SW7 2AZ, UK

    Steffan Cook & James R. Durrant

  3. Merck Chemicals, Chilworth Science Park, Southampton, SO16 7QD, UK

    Mark Giles & Iain McCulloch

  4. Department of Polymer Science and Engineering, Pusan National University, Pusan, 609-735, South Korea

    Chang-Sik Ha

  5. Department of Chemistry & Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang, 790-784, South Korea

    Moonhor Ree

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  1. Youngkyoo Kim
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Correspondence to Youngkyoo Kim, Jenny Nelson or Donal D. C. Bradley.

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Kim, Y., Cook, S., Tuladhar, S. et al. A strong regioregularity effect in self-organizing conjugated polymer films and high-efficiency polythiophene:fullerene solar cells. Nature Mater 5, 197–203 (2006). https://doi.org/10.1038/nmat1574

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