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

Journal name:
Nature Photonics
Volume:
6,
Pages:
115–120
Year published:
DOI:
doi:10.1038/nphoton.2011.317
Received
Accepted
Published online

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.

At a glance

Figures

  1. Effect of light soaking on device performance for inverted solar cells with an as-prepared ZnO-PVP nanocomposite ETL.
    Figure 1: Effect of light soaking on device performance for inverted solar cells with an as-prepared ZnO–PVP nanocomposite ETL.

    Photo J–V characteristics for inverted PDTG–TPD:PC71BM solar cells, highlighting the effect of prolonged light soaking on device performance under AM 1.5G solar illumination at 100 mW cm−2.

  2. Enhanced device performance in inverted PDTG-TPD:PC71BM solar cells by UV-ozone treatment of the 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.

    a, Photo J–V curves of inverted PDTG–TPD:PC71BM solar cells with UV-ozone treated ZnO–PVP nanocomposite films as ETLs for various treatment times (5, 10, 20 and 30 min) under initial AM 1.5G solar illumination at 100 mW cm−2. b, Corresponding EQE for devices with 10 min UV-ozone treated ZnO–PVP nanocomposite films. The EQE spectrum for devices with as-prepared composite films is shown for comparison.

  3. Certified I-V characteristics for an inverted PDTG-TPD:PC71BM solar cell with 10 min UV-ozone treated ZnO-PVP nanocomposite ETL.
    Figure 3: Certified IV characteristics for an inverted PDTG–TPD:PC71BM solar cell with 10 min UV-ozone treated ZnO–PVP nanocomposite ETL.

    The device was certified by NEWPORT Corporation. A light mask with an area of 0.0304 cm2 was used to define the device area.

  4. Tapping-mode AFM images for ZnO-PVP nanocomposite films used in device fabrication (optimized conditions).
    Figure 4: Tapping-mode AFM images for ZnO–PVP nanocomposite films used in device fabrication (optimized conditions).

    Appropriate scales are shown on the right. a,b, Three-dimensional topography images for the as-prepared and 10 min UV-ozone treated ZnO–PVP nanocomposite films show the change in surface roughness upon UV-ozone treatment. c, Phase image for the as-prepared nanocomposite film, showing a PVP-rich surface on which no ZnO nanoclusters can be seen. d, Phase image for the UV-ozone treated nanocomposite film, showing a ZnO nanocluster-rich surface, with more ZnO nanoclusters exposed on the surface. e,f, Schematic images of the as-prepared and UV-ozone treated ZnO–PVP nanocomposite films, emphasizing the PVP-rich and ZnO-rich surfaces before and after UV-ozone treatment.

  5. XPS data for the as-prepared and 10 min UV-ozone treated ZnO-PVP nanocomposite films.
    Figure 5: XPS data for the as-prepared and 10 min UV-ozone treated ZnO–PVP nanocomposite films.

    a,b, O 1s (a) and Zn 2p (b) XPS spectra for the as-prepared and 10 min UV-ozone treated ZnO–PVP nanocomposite films. c, Atomic concentrations of carbon, zinc and oxygen before and after UV-ozone treatment based on the corresponding XPS spectra.

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Author information

  1. These authors contributed equally to this work

    • Cephas E. Small &
    • Song Chen

Affiliations

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

    • Cephas E. Small,
    • Song Chen,
    • Jegadesan Subbiah,
    • Sai-Wing Tsang,
    • Tzung-Han Lai &
    • Franky So
  2. The George and Josephine Butler Polymer Research Laboratory, Department of Chemistry, Center for Macromolecular Science and Engineering, University of Florida, Box 117200, Gainesville, Florida 32611, USA

    • Chad M. Amb &
    • John R. Reynolds

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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The authors declare no competing financial interests.

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