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High-efficiency inverted dithienogermole–thienopyrrolodione-based polymer solar cells

Nature Photonics volume 6, pages 115–120 (2012)Cite this article

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Abstract

Inverted polymer bulk heterojunction solar cells have received a great deal of attention because of their compatibility with large-scale roll-to-roll processing. The inverted cell geometry has the following structure: substrate (rigid or flexible)/indium tin oxide/electron-transporting layer/photoactive layer/hole-transporting layer/top anode. Solution-processed metal-oxide films, based on materials such as ZnO and TiO2, are typically used as the electron-transporting layers. Here, we demonstrate enhanced charge collection in inverted polymer solar cells using a surface-modified ZnO–polymer nanocomposite electron-transporting layer. Using this approach, we demonstrate inverted polymer solar cells based on a low-bandgap polymer with an alternating dithienogermole–thienopyrrolodione repeat unit (PDTG–TPD) with certified power conversion efficiencies of 7.4%. To our knowledge, this is the highest efficiency reported to date for polymer solar cells with a device architecture compatible with the roll-to-roll process.

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Figure 1: Effect of light soaking on device performance for inverted solar cells with an as-prepared ZnO–PVP nanocomposite ETL.
Figure 2: Enhanced device performance in inverted PDTG–TPD:PC71BM solar cells by UV-ozone treatment of the ZnO–PVP nanocomposite ETL.
Figure 3: Certified I–V characteristics for an inverted PDTG–TPD:PC71BM solar cell with 10 min UV-ozone treated ZnO–PVP nanocomposite ETL.
Figure 4: Tapping-mode AFM images for ZnO–PVP nanocomposite films used in device fabrication (optimized conditions).
Figure 5: XPS data for the as-prepared and 10 min UV-ozone treated ZnO–PVP nanocomposite films.

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Acknowledgements

The authors acknowledge support from the Office of Naval Research (contract no. N000141110245) for the fabrication and characterization of polymer solar cells. F.S. acknowledges support from the Department of Energy Basic Energy Sciences (contract no. DE-FG0207ER46464) for the synthesis and characterization of ZnO composite films. J.R.R. acknowledges the support of the Air Force Office of Scientific Research (contract no. FA9550-09-1-0320) for the synthesis of the PDTG and PDTS polymers. The authors would also like to thank the Major Analytical Instrumentation Center (MAIC) and the Dr Andrew Rinzler research group at the University of Florida for their assistance in characterizing the ZnO composite films.

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  1. Cephas E. Small and Song Chen: These authors contributed equally to this work

Authors and Affiliations

  1. Department of Materials Science and Engineering, University of Florida, Box 117200, Gainesville, 32611, Florida, USA

    Cephas E. Small, Song Chen, Jegadesan Subbiah, Sai-Wing Tsang, Tzung-Han Lai & Franky So

  2. Department of Chemistry, The George and Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science and Engineering, University of Florida, Box 117200, Gainesville, 32611, Florida, USA

    Chad M. Amb & John R. Reynolds

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  1. Cephas E. Small
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Contributions

C.E.S. performed polymer solar cell fabrication, characterization and data analysis, as well as characterization of the ZnO–polymer films by AFM and XPS. S.C. contributed to data analysis, establishing a model to explain the ETL effects, and fabrication of the certified solar cells. J.S. contributed to the early process optimization of the PDTG–TPD and PDTS–TPD BHJ solar cells. T-H.L. conceived the idea for modification of the ZnO–polymer composite ETL by UV-ozone treatment and conducted optical transmission measurements. C.A. synthesized the polymers used in this work. S-W.T. assisted in planning and interpreting the data. F.S. and J.R.R. initiated and directed the research project. All authors discussed the results and commented on the manuscript.

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Correspondence to John R. Reynolds or Franky So.

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The authors declare no competing financial interests.

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Small, C., Chen, S., Subbiah, J. et al. High-efficiency inverted dithienogermole–thienopyrrolodione-based polymer solar cells. Nature Photon 6, 115–120 (2012). https://doi.org/10.1038/nphoton.2011.317

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