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Efficiency enhancement in low-bandgap polymer solar cells by processing with alkane dithiols


High charge-separation efficiency combined with the reduced fabrication costs associated with solution processing and the potential for implementation on flexible substrates make ‘plastic’ solar cells a compelling option for tomorrow’s photovoltaics1. Attempts to control the donor/acceptor morphology in bulk heterojunction materials as required for achieving high power-conversion efficiency have, however, met with limited success2,3,4. By incorporating a few volume per cent of alkanedithiols in the solution used to spin-cast films comprising a low-bandgap polymer and a fullerene derivative, the power-conversion efficiency of photovoltaic cells (air-mass 1.5 global conditions) is increased from 2.8% to 5.5% through altering the bulk heterojunction morphology5. This discovery can potentially enable morphological control in bulk heterojunction materials where thermal annealing is either undesirable or ineffective.

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Figure 1: Ultraviolet–visible absorption.
Figure 2: Device IV characteristics.
Figure 3: IPCE.
Figure 4: Morphology characterization.


  1. Scharber, M. C. et al. Design rules for donors in bulk-heterojunction solar cells—Towards 10% energy-conversion efficiency. Adv. Mater. 18, 789–794 (2006).

    CAS  Article  Google Scholar 

  2. Hoppe, H. & Sariciftci, N. S. Morphology of polymer/fullerene bulk heterojunction solar cells. J. Mater. Chem. 16, 45–61 (2006).

    CAS  Article  Google Scholar 

  3. Ma, W. L., Yang, C. Y., Gong, X., Lee, K. & Heeger, A. J. Thermally stable, efficient polymer solar cells with nanoscale control of the interpenetrating network morphology. Adv. Funct. Mater. 15, 1617–1622 (2005).

    CAS  Article  Google Scholar 

  4. Muhlbacher, D. et al. High photovoltaic performance of a low-bandgap polymer. Adv. Mater. 18, 2884–2889 (2006).

    Article  Google Scholar 

  5. Peet, J. et al. Method for increasing the photoconductive response in conjugated polymer/fullerene composites. Appl. Phys. Lett. 89, 252105 (2006).

    Article  Google Scholar 

  6. Yu, G. & Heeger, A. J. Charge separation and photovoltaic conversion in polymer composites with internal donor/acceptor heterojunctions. J. Appl. Phys. 78, 4510–4515 (1995).

    CAS  Article  Google Scholar 

  7. Yu, G., Gao, J., Hummelen, J. C., Wudl, F. & Heeger, A. J. Polymer photovoltaic cells: Enhanced efficiencies via a network of internal donor-acceptor hetrojunctions. Science 270, 1789–1791 (1995).

    CAS  Article  Google Scholar 

  8. Halls, J. J. M., Pichler, K., Friend, R. H., Moratti, S. C. & Holmes, A. B. Exciton diffusion and dissociation in a poly(p-phenylenevinylene)/C-60 heterojunction photovoltaic cell. Appl. Phys. Lett. 68, 3120–3122 (1996).

    CAS  Article  Google Scholar 

  9. Kraabel, B., McBranch, D., Sariciftci, N. S., Moses, D. & Heeger, A. J. Ultrafast spectroscopic studies of photoinduced electron transfer from semiconducting polymers to C60 . Phys. Rev. B 50, 18543–18552 (1994).

    CAS  Article  Google Scholar 

  10. Kraabel, B. et al. Subpicosecond photoinduced electron transfer from conjugated polymers to functionalized fullerenes. J. Chem. Phys. 104, 4267–4273 (1996).

    CAS  Article  Google Scholar 

  11. Brabec, C. J. et al. Tracing photoinduced electron transfer process in conjugated polymer/fullerene bulk heterojunctions in real time. Chem. Phys. Lett. 340, 232–236 (2001).

    CAS  Article  Google Scholar 

  12. Sievers, D. W., Shrotriya, V. & Yang, Y. Modeling optical effects and thickness dependent current in polymer bulk-heterojunction solar cells. J. Appl. Phys. 100, 114509 (2006).

    Article  Google Scholar 

  13. Dennler, G. et al. Charge carrier mobility and lifetime versus composition of conjugated polymer/fullerene bulk-heterojunction solar cells. Org. Electron. 7, 229–234 (2006).

    CAS  Article  Google Scholar 

  14. Li, G. et al. High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends. Nature Mater. 4, 864–868 (2005).

    CAS  Article  Google Scholar 

  15. Reyes-Reyes, M., Kim, K. & Carroll, D. L. High-efficiency photovoltaic devices based on annealed poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C-61 blends. Appl. Phys. Lett. 87, 083506 (2005).

    Article  Google Scholar 

  16. Kim, Y. 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).

    CAS  Article  Google Scholar 

  17. ASTM G-173-03. Terrestrial Reference Spectra for Photovoltaic Performance Evaluation (American Society for Testing Materials (ASTM) International, West Conshohocken).

  18. Soci, C. et al. Photoconductivity of a low-bandgap conjugated polymer. Adv. Funct. Mater. 200600267 (2007).

  19. Wienk, M. M. et al. Efficient methano[70]fullerene/MDMO-PPV bulk heterojunction photovoltaic cells. Angew. Chem. Int. Edn 42, 3371–3375 (2003).

    CAS  Article  Google Scholar 

  20. Lee, C. H. et al. Sensitization of the photoconductivity of conducting polymers by C-60-photoinduced electron-transfer. Phys. Rev. B 48, 15425–15433 (1993).

    CAS  Article  Google Scholar 

  21. Auston, D. H. Impulse-response of photoconductors in transmission-lines. IEEE J. Quantum Electron. 19, 639–648 (1983).

    Article  Google Scholar 

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The research was financially supported by grants from the Department of Energy (DE-FC26-04NT42277) (G.C.B.), the Office of Naval Research (N0014-0411) (G.C.B.), the Department of Energy (DE-FG02-06ER46324)(A.J.H.), Konarka Technologies (A.J.H.) and by the Ministry of Science & Technology of Korea under the International Cooperation Research Program Global Research Laboratory Program. J.P. thanks the NDSEG fellowship for support. The authors thank J. Yuen for thin-film transistor substrate preparation and Tom Mates for assistance with XPS measurement and analysis. We thank C. J. Brabec, Z. Zou, D. Waller and R. Gaudiana at Konarka Technologies for making the PCPDTBT available for our use. We thank C. Waldauf for important discussions.

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Authors and Affiliations



Devices were fabricated by J.P. and J.Y.K. Photoconductivity work was done by N.E.C. Transmission electron microscopy measurements were taken by W.L.M. AFM, FET, XPS, wide-angle X-ray diffraction, ultraviolet–visible, FTIR and Raman spectroscopy measurements were taken by J.P. D.M., A.J.H. and G.C.B. contributed to project planning, experimental design and manuscript preparation.

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Correspondence to A. J. Heeger or G. C. Bazan.

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Competing interests

A. J. Heeger is a member of the board of directors of Konarka Technologies, and serves as chief scientist. The work reported here was carried out at UCSB; the University of California is seeking intellectual property rights on this discovery.

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Peet, J., Kim, J., Coates, N. et al. Efficiency enhancement in low-bandgap polymer solar cells by processing with alkane dithiols. Nature Mater 6, 497–500 (2007).

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