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Electronic structures of interfacial states formed at polymeric semiconductor heterojunctions

Nature Materials volume 7, pages 483–489 (2008)Cite this article

Abstract

Heterojunctions between organic semiconductors are central to the operation of light-emitting and photovoltaic diodes, providing respectively for electron–hole capture and separation. However, relatively little is known about the character of electronic excitations stable at the heterojunction. We have developed molecular models to study such interfacial excited electronic excitations that form at the heterojunction between model polymer donor and polymer acceptor systems: poly(9,9-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine) (PFB) with poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), and poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) with F8BT. We find that for stable ground-state geometries the excited state has a strong charge-transfer character. Furthermore, when partly covalent, modelled radiative lifetimes (∼10−7 s) and off-chain axis polarization (30∘) match observed ‘exciplex’ emission. Additionally for the PFB:F8BT blend, geometries with fully ionic character are also found, thus accounting for the low electroluminescence efficiency of this system.

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Figure 1: Chemical/density functional theory (DFT) structures of investigated systems and their HOMO/LUMO orbitals.
Figure 2: Coulomb interaction energy and excited-state properties of representative PFB:F8BT structures.
Figure 3: Charge redistributions of the lowest excited states of representative configurations.
Figure 4: Polarization-resolved time-resolved photoluminescence of interface states.
Figure 5: Coulomb interaction energy and excited-state properties of representative TFB:F8BT structures.
Figure 6: Schematic diagram of the lowest electronic excitations in the PFB:F8BT and TFB:F8BT systems.

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References

  1. Morteani, A. C. et al. Barrier-free electron–hole capture in polymer blend heterojunction light-emitting diodes. Adv. Mater. 15, 1708–1712 (2003).

    Article  CAS  Google Scholar 

  2. Halls, J. J. M. et al. Efficient photodiodes from interpenetrating polymer networks. Nature 376, 498–500 (1995).

    Article  CAS  Google Scholar 

  3. Arias, A. C. et al. Photovoltaic performance and morphology of polyfluorene blends: A combined microscopic and photovoltaic investigation. Macromolecules 34, 6005–6013 (2001).

    Article  CAS  Google Scholar 

  4. Brabec, C. J., Sariciftci, N. S. & Hummelen, J. C. Plastic solar cells. Adv. Funct. Mater. 11, 15–26 (2001).

    Article  CAS  Google Scholar 

  5. Halls, J. J. M. et al. Charge- and energy-transfer processes at polymer/polymer interfaces: A joint experimental and theoretical study. Phys. Rev. B 60, 5721–5727 (1999).

    Article  CAS  Google Scholar 

  6. Cao, Y., Parker, I. D., Yu, G., Zhang, C. & Heeger, A. J. Improved quantum efficiency for electroluminescence in semiconducting polymers. Nature 397, 414–417 (1999).

    Article  CAS  Google Scholar 

  7. Palilis, L. C. et al. High performance blue light-emitting diodes based on conjugated polymer blends. Synth. Met. 121, 1729–1730 (2001).

    Article  CAS  Google Scholar 

  8. McNeill, C. R., Westenhoff, S., Groves, C., Friend, R. H. & Greenham, N. C. Influence of nanoscale phase separation on the charge generation dynamics and photovoltaic performance of conjugated polymer blends: Balancing charge generation and separation. J. Phys. Chem. C 111, 19153–19160 (2007).

    Article  CAS  Google Scholar 

  9. Morteani, A. C., Sreearunothai, P., Herz, L. M., Friend, R. H. & Silva, C. Exciton regeneration at polymeric semiconductor heterojunctions. Phys. Rev. Lett. 92, 247402 (2004).

    Article  Google Scholar 

  10. Morteani, A. C., Friend, R. H. & Silva, C. Endothermic exciplex–exciton energy-transfer in a blue-emitting polymeric heterojunction system. Chem. Phys. Lett. 391, 81–84 (2004).

    Article  CAS  Google Scholar 

  11. Sreearunothai, P. et al. Influence of copolymer interface orientation on the optical emission of polymeric semiconductor heterojunctions. Phys. Rev. Lett. 96, 117403 (2006).

    Article  CAS  Google Scholar 

  12. Bittner, E. R., Ramon, J. G. S. & Karabunarliev, S. Exciton dissociation dynamics in model donor–acceptor polymer heterojunctions. I. Energetics and spectra. J. Chem. Phys. 122, 214719 (2005).

    Article  Google Scholar 

  13. Ramon, J. G. S. & Bittner, E. R. Excited state calculations on fluorene-based polymer blends: Effect of stacking orientation and solvation. J. Chem. Phys. 126, 181101 (2007).

    Article  Google Scholar 

  14. Jenekhe, S. A. & Osaheni, J. A. Excimers and exciplexes of conjugated polymers. Science 265, 765–768 (1994).

    Article  CAS  Google Scholar 

  15. Granlund, T., Pettersson, L. A. A., Anderson, M. R. & Inganäs, O. Interference phenomenon determines the color in an organic light emitting diode. J. Appl. Phys. 81, 8097–8104 (1997).

    Article  CAS  Google Scholar 

  16. Gebler, D. D., Wang, Y. Z., Fu, D.-K., Swager, T. M. & Epstein, A. J. Exciplex emission from bilayers of poly(vinyl carbazole) and pyridine based conjugated copolymers. J. Chem. Phys. 108, 7842–7848 (1998).

    Article  CAS  Google Scholar 

  17. Offermans, T., van Hal, P. A., Meskers, S. C. J., Koetse, M. M. & Janssen, R. A. J. Exciplex dynamics in a blend of π-conjugated polymers with electron donating and accepting properties: MDMO-PPV and PCNEPV. Phys. Rev. B 72, 045213 (2005).

    Article  Google Scholar 

  18. Weller, A. The Exciplex 23–38 (Academic, New York, 1975).

    Book  Google Scholar 

  19. Xia, Y. & Friend, R. H. Controlled phase separation of polyfluorene blends via inkjet printing. Macromolecules 38, 6466–6471 (2005).

    Article  CAS  Google Scholar 

  20. Gould, I. R., Young, R. H., Mueller, L. J., Albrecht, A. C. & Farid, S. Electronic structure of exciplexes and excited charge-transfer complexes. J. Am. Chem. Soc. 116, 8188–8199 (1994).

    Article  CAS  Google Scholar 

  21. Valeur, B. Molecular Fluorescence Ch. 5 (Wiley-VCH Verlag GmbH, Weinheim, 2002).

    Google Scholar 

  22. Mihailetchi, V. D., Koster, L. J. A., Hummelen, J. C. & Blom, P. W. M. Photocurrent generation in polymer–fullerene bulk heterojunctions. Phys. Rev. Lett. 93, 216601 (2004).

    Article  CAS  Google Scholar 

  23. Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 98, 5648–5652 (1993).

    Article  CAS  Google Scholar 

  24. Lee, C., Yang, W. & Parr, R. G. Development of the Colle–Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 37, 785–789 (1988).

    Article  CAS  Google Scholar 

  25. Cornil, J. et al. Electronic and optical properties of polyfluorene and fluorene-based copolymers: A quantum-chemical characterization. J. Chem. Phys. 118, 6615–6623 (2003).

    Article  CAS  Google Scholar 

  26. Accelrys, Inc. Cerius2 and Discover (programs) and Discover User Guide (Molecular Simulations, Inc., San Diego, 1996).

  27. Ridley, J. & Zerner, M. C. An intermediate neglect of differential overlap technique for spectroscopy: Pyrrole and the azines. Theor. Chim. Acta 32, 111–134 (1973).

    Article  CAS  Google Scholar 

  28. Mataga, N. & Nishimoto, K. Electronic structure and spectra of nitrogen heterocycles. Z. Phys. Chem. Neue. Folge. 13, 140–157 (1957).

    Article  CAS  Google Scholar 

  29. Chandross, M. & Mazumdar, S. Coulomb interactions and linear, nonlinear, and triplet absorption in poly(para-phenylenevinylene). Phys. Rev. B 55, 1497–1504 (1997).

    Article  CAS  Google Scholar 

  30. Westenhoff, S. et al. Supramolecular electronic coupling in chiral oligothiophene nanostructures. Adv. Mater. 18, 1281–1285 (2006).

    Article  CAS  Google Scholar 

  31. Silva, C. et al. Exciton and polaron dynamics in a step-ladder polymeric semiconductor: The influence of interchain order. J. Phys. Condens. Matter 14, 9803–9824 (2002).

    Article  CAS  Google Scholar 

Download references

Acknowledgements

We thank J. S. Kim and W. J. D. Beenken for discussions. This work was supported by the Engineering and Physical Science Research Council, and by the EU Integrated Project NAIMO (No NMP4-CT-2004-500355). The work in Mons was partly supported by the Belgian Federal Government ‘Interuniversity Attraction Pole in Supramolecular Chemistry and Catalysis, PAI 5/3’, the Belgian National Fund for Scientific Research (FNRS/FRFC) and the European STREP project MODECOM (NMP-CT-2006-016434). D.B. is a research director of FNRS.

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Author notes

  1. Sebastian Westenhoff

    Present address: Present address: Department of Chemistry, Biochemistry and Biophysics, Gothenburg University, 40530 Gothenburg, Sweden,

  2. Paiboon Sreearunothai

    Present address: Present address: Chemistry Department, Building 555A, Brookhaven National Lab, Upton, New York 11973-5000, USA,

Authors and Affiliations

  1. Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge, CB3 0HE, UK

    Ya-shih Huang, Sebastian Westenhoff, Paiboon Sreearunothai, Justin M. Hodgkiss & Richard H. Friend

  2. Laboratory for Chemistry of Novel Materials, University of Mons-Hainaut, Place du Parc 20, B-7000 Mons, Belgium

    Ya-shih Huang, Igor Avilov, Caroline Deleener & David Beljonne

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Contributions

Y.-S.H., I.A., P.S. and C.D. carried out the modelling. S.W. and J.M.H. measured the photoluminescence anisotropy. Y.-S.H., S.W., R.H.F. and D.B. analysed data, interpreted results and wrote the paper. All authors provided comments on the manuscript. R.H.F. contributed to the interpretation of the combined modelling and experimental work. D.B. and R.H.F. directed the research.

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Correspondence to Richard H. Friend or David Beljonne.

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Huang, Ys., Westenhoff, S., Avilov, I. et al. Electronic structures of interfacial states formed at polymeric semiconductor heterojunctions. Nature Mater 7, 483–489 (2008). https://doi.org/10.1038/nmat2182

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