Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Observation of long-range exciton diffusion in highly ordered organic semiconductors


Excitons in polycrystalline and disordered films of organic semiconductors have been shown to diffuse over distances of 10–50 nm. Here, using polarization- and wavelength-dependent photoconductivity in the highly ordered organic semiconductor rubrene, we show that the diffusion of triplet excitons in this material occurs over macroscopic distances (2–8 μm), comparable to the light absorption length. Dissociation of these excitons at the surface of the crystal is found to be the main source of photoconductivity in rubrene. In addition, we observe strong photoluminescence quenching and a simultaneous enhancement of photoconductivity when the crystal surface is functionalized with exciton splitters. In combination with time-resolved measurements, these observations strongly suggest that long-lived triplet excitons are indeed generated in molecular crystals by fission of singlets, and these triplets provide a significant contribution to the surface photocurrent generated in organic materials. Our findings indicate that the exciton diffusion bottleneck is not an intrinsic limitation of organic semiconductors.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type



Prices may be subject to local taxes which are calculated during checkout

Figure 1: Polarization-resolved absorption coefficient and photoconductivity measured at the (ab) facet of rubrene.
Figure 2: Effect of surface functionalization on the photoconductivity of rubrene.
Figure 3: Modelling of the exciton diffusion length based on the experimental data and equations (1) and (2).
Figure 4: Photocurrent excitation spectra of rubrene.
Figure 5: PL quenching in rubrene single crystals.


  1. Kippelen, B. & Bredas, J-L. Organic photovoltaics. Energy Environ. Sci. 2, 251–261 (2009).

    Article  CAS  Google Scholar 

  2. Mori, T. & Kato, K. Photovoltaic properties of organic thin-film solar cell using various exciton-diffusion blocking materials. J. Photopolymer Sci. Technol. 20, 61–66 (2007).

    Article  CAS  Google Scholar 

  3. Peumans, P., Yakimov, A. & Forrest, S. R. Small molecular weight organic thin-film photodetectors and solar cells. J. Appl. Phys. 93, 3693–3723 (2004).

    Article  Google Scholar 

  4. Lunt, R. R., Giebink, N. C., Belak, A. A., Benziger, J. B. & Forrest, S. R. Exciton diffusion lengths of organic semiconductor thin films measured by spectrally resolved photoluminescence quenching. J. Appl. Phys. 105, 053711 (2009).

    Article  Google Scholar 

  5. Yang, L-G., Chen, H-Z. & Wang, M. Optimal film thickness for exciton diffusion length measurement by photocurrent response in organic heterostructures. Thin Solid Films 516, 7701–7707 (2008).

    Article  CAS  Google Scholar 

  6. Agranovich, V. M. & Bassani, G. F. (eds) Electronic Excitations in Organic Based Nanostructures 45–47 (Elsevier Academic, 2003).

  7. Bao, Z. & Locklin, J. (eds) Organic Field-Effect Transistors (Taylor & Francis, 2007).

  8. de Boer, R. W. I., Gershenson, M. E., Morpurgo, A. F. & Podzorov, V. Organic single-crystal field-effect transistors. Phys. Status Solidi 201, 1302–1331 (2004).

    Article  CAS  Google Scholar 

  9. Gershenson, M. E., Podzorov, V. & Morpurgo, A. F. Colloquium: Electronic transport in single-crystal organic transistors. Rev. Mod. Phys. 78, 973–989 (2006).

    Article  CAS  Google Scholar 

  10. Podzorov, V. et al. Intrinsic charge transport on the surface of organic semiconductors. Phys. Rev. Lett. 93, 086602 (2004).

    Article  CAS  Google Scholar 

  11. Ghosh, A. K. & Feng, T. Merocyanine organic solar cells. J. Appl. Phys. 49, 5982–5989 (1978).

    Article  CAS  Google Scholar 

  12. da Silva Filho, D. A., Kim, E-G. & Bredas, J-L. Transport properties in the rubrene crystal: Electronic coupling and vibrational reorganization energy. Adv. Mater. 17, 1072–1076 (2005).

    Article  CAS  Google Scholar 

  13. Reese, C. & Bao, Z. High angular resolution measurement of the anisotropy of charge transport in single crystals. Adv. Mater. 19, 4535–4538 (2007).

    Article  CAS  Google Scholar 

  14. Podzorov, V., Pudalov, V. M. & Gershenson, M. E. Light-induced switching in back-gated organic transistors with built-in conduction channel. Appl. Phys. Lett. 85, 6039–6041 (2004).

    Article  CAS  Google Scholar 

  15. Podzorov, V., Pudalov, V. M. & Gershenson, M. E. Interaction of organic surfaces with active species in the high-vacuum environment. Appl. Phys. Lett. 87, 093505 (2005).

    Article  Google Scholar 

  16. Hulea, I. N. et al. Tunable Fröhlich polarons in organic single-crystal transistors. Nature Mater. 5, 982–986 (2006).

    Article  CAS  Google Scholar 

  17. Cahen, D., Kahn, A. & Umbach, E. Energetics of interfaces between molecules and conductors. Mater. Today 8, 32–41 (July/August, 2005).

    Article  CAS  Google Scholar 

  18. Wakabayashi, Y., Takeya, J. & Kimura, T. Sub-Å resolution electron density analysis of the surface of organic rubrene crystal. Phys. Rev. Lett. 104, 066103 (2010).

    Article  Google Scholar 

  19. Nozue, Y. & Goto, T. Picosecond studies of excitonic luminescenceand reabsorption effect in anthracene crystals. J. Phys. Soc. Jpn 58, 1831–1837 (1989).

    Article  CAS  Google Scholar 

  20. Sai, N., Tiago, M. L., Chelikowsky, J. R. & Reboredo, F. A. Optical spectra and exchange–correlation effects in molecular crystals. Phys. Rev. B 77, 161306 (2008).

    Article  Google Scholar 

  21. Müller, A. S., Avlasevich, Y. S., Müllen, K. & Bardeen, C. J. Evidence for exciton fission and fusion in a covalently linked tetracene dimer. Chem. Phys. Lett. 421, 518–522 (2006).

    Article  Google Scholar 

  22. Najafov, H., Biaggio, I., Podzorov, V., Calhoun, M. F. & Gershenson, M. E. Primary photoexcitations and the origin of the photocurrent in rubrene single crystals. Phys. Rev. Lett. 96, 056604 (2006).

    Article  Google Scholar 

  23. SudhaDevi, L. et al. Triplet energy transfer in conjugated polymers: Experimental investigation of a weakly disordered compounds. Phys. Rev. B 78, 045210 (2008).

    Article  Google Scholar 

  24. Markov, D. E., Tanase, C., Blom, P. W. M. & Wildeman, J. Simultaneous enhancement of charge transport and exciton diffusion in poly(p-phenylene vinylene) derivatives. Phys. Rev. B 72, 045217 (2005).

    Article  Google Scholar 

  25. Yoo, S., Domercq, B. & Kippelen, B. Efficient thin-film organic solar cells based on pentacene/C60 heterojunctions. Appl. Phys. Lett. 85, 5427–5429 (2004).

    Article  CAS  Google Scholar 

Download references


This work has been financially supported by NSF-DMR-0843985 and the Industrial Technology Research Grant Program 09E51007d (NEDO). We are very grateful to A. Zakhidov, V. M. Agranovich and E. Garfunkel for helpful discussions, and especially grateful to I. Biaggio for fruitful discussions and for access to the time-resolved PL set-up.

Author information

Authors and Affiliations



H.N. and V.P. designed and carried out experiment and performed data analysis; B.L. and Q.Z. fabricated samples; L.C.F. provided important input on data analysis and presentation, and V.P. wrote the paper.

Corresponding author

Correspondence to V. Podzorov.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Information (PDF 204 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Najafov, H., Lee, B., Zhou, Q. et al. Observation of long-range exciton diffusion in highly ordered organic semiconductors. Nature Mater 9, 938–943 (2010).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing