Skip to main content

Thank you for visiting nature.com. 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.

  • Article
  • Published:

Tuning magnetoresistance between positive and negative values in organic semiconductors

Nature Materials volume 6, pages 985–991 (2007)Cite this article

Abstract

Magnetic-field-dependent injection current, namely magnetoresistance, is readily observable in organic semiconductor devices. This provides a non-contact approach to tune organic optoelectronic properties by using a magnetic field. Here, we demonstrate that this magnetoresistance can be changed between positive and negative values by adjusting the dissociation and charge reaction in excited states through changing the bipolar charge injection in organic light-emitting diodes. This finding reveals that the magnetic-field-dependent generation of secondary charge carriers from the dissociation and charge reaction affects the injection current by forming further space charges at the organic–electrode interfaces and therefore accounts for the tunable magnetoresistance. Furthermore, the dissociation and charge reaction have opposite dependences on magnetic field in the generation of secondary charge carriers, consequently leading to negative and positive magnetoresistance, respectively. As a result, adjusting the dissociation and charge reaction in excited states provides a convenient pathway to tune the magnetoresistance in organic semiconductors.

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

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

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

Figure 1: Magnetoresistance characteristics and processes.
Figure 2: The energy levels for e–h pair and excitonic states in an external magnetic field.
Figure 3: Modification of bipolar charge injection by a PMMA charge-blocking layer in a double-layer ITO/polymer/PMMA/Au device.
Figure 4: Electroluminescence–current characteristics for double-layer ITO/MEHPPV(60 nm)/PMMA(x nm)/Au devices with different PMMA thicknesses.
Figure 5: Tuning of positive magnetoresistance by adjusting electron and hole injection in double-layer ITO/MEHPPV(60 nm)/PMMA(x nm)/Au OLEDs with different PMMA film thicknesses.
Figure 6: Tuning of negative magnetoresistance by adjusting electron and hole injection in double-layer PVK and Alq3 OLEDs with different PMMA film thicknesses.

Similar content being viewed by others

References

  1. Taliani, C. et al. Organic-inorganic hybrid spin-valve: A novel approach to spintronics. Phase Transit. 75, 1049–1058 (2002).

    Article  CAS  Google Scholar 

  2. Xiong, Z. H., Wu, D., Vardeny, Z. V. & Shi, J. Giant magnetoresistance in organic spin-valves. Nature 427, 821–824 (2004).

    Article  CAS  Google Scholar 

  3. Kalinowski, J., Cocchi, M., Virgili, D., Di Marco, P. & Fattori, V. Magnetic field effects on emission and current in Alq(3)-based electroluminescent diodes. Chem. Phys. Lett. 380, 710–715 (2003).

    Article  CAS  Google Scholar 

  4. Kalinowski, J., Cocchi, M., Virgili, D., Fattori, V. & Di Marco, P. Magnetic field effects on organic electrophosphorescence. Phys. Rev. B 70, 205303 (2004).

    Article  Google Scholar 

  5. Davis, A. H. & Bussmann, K. Large magnetic field effects in organic light emitting diodes based on tris(8-hydroxyquinoline aluminum) (Alq(3))/IN,N′-Di(naphthalen-1-yl)-N,N′diphenyl-benzidine (NPB) bilayers. J. Vac. Sci. Technol. A 22, 1885–1891 (2004).

    Article  CAS  Google Scholar 

  6. Francis, T. L., Mermer, Ö., Veeraraghavan, G. & Wohlgenannt, M. Large magnetoresistance at room temperature in semiconducting polymer sandwich devices. New J. Phys. 6, 185–192 (2004).

    Article  Google Scholar 

  7. Sheng, Y. et al. Hyperfine interaction and magnetoresistance in organic semiconductors. Phys. Rev. B 74, 045213 (2006).

    Article  Google Scholar 

  8. Wu, Y. & Hu, B. Metal electrode effects on spin–orbital coupling and magnetoresistance in organic semiconductor devices. Appl. Phys. Lett. 89, 203510 (2006).

    Article  Google Scholar 

  9. Desai, P. et al. Magnetoresistance and efficiency measurements of Alq3-based OLEDs. Phys. Rev. B 75, 094423 (2007).

    Article  Google Scholar 

  10. Wu, Y., Xu, Z., Hu, B. & Howe, J. Tuning magnetoresistance and magnetic field-dependent electroluminescence through mixing strong-spin–orbital-coupling molecule and weak-spin–orbital-coupling polymer. Phys. Rev. B 75, 035214 (2007).

    Article  Google Scholar 

  11. Fesser, K., Bishop, A. R. & Campbell, D. K. Optical absorption from polarons in a model of polyacetylene. Phys. Rev. B 27, 4804 (1983).

    Article  CAS  Google Scholar 

  12. Bassler, H. Injection, transport and recombination of charge carriers in organic light-emitting diodes. Polym. Adv. Technol. 9, 402–418 (1998).

    Article  CAS  Google Scholar 

  13. Kalinowski, J. Electroluminescence in organics. J. Phys. D 32, R179–R250 (1999).

    Article  CAS  Google Scholar 

  14. Kalinowski, J., Szmytkowski, J. & Stampor, W. Magnetic hyperfine modulation of charge photogeneration in solid films of Alq3 . Chem. Phys. Lett. 378, 380–387 (2003).

    Article  CAS  Google Scholar 

  15. Wilkinson, J., Davis, A. H., Bussmann, K. & Long, J. P. Evidence for charge-carrier mediated magnetic-field modulation of electroluminescence in organic light-emitting diodes. Appl. Phys. Lett. 86, 111109 (2005).

    Article  Google Scholar 

  16. Köhler, A. et al. UV photocurrent spectroscopy in poly(p-phenylene vinylene) and derivatives. Synth. Met. 84, 675–676 (1997).

    Article  Google Scholar 

  17. Muller, J. G. et al. Ultrafast dynamics of charge carrier photogeneration and geminate recombination in conjugated polymer: Fullerene solar cells. Phys. Rev. B 72, 195208 (2005).

    Article  Google Scholar 

  18. Szmytkowski, J., Stampor, W., Kalinowski, J. & Kafafi, Z. H. Electric field-assisted dissociation of singlet excitons in tris-(8-hydroxyquinolinato) aluminum (III). Appl. Phys. Lett. 80, 1465 (2002).

    Article  CAS  Google Scholar 

  19. Kalinowski, J. et al. Coexistence of dissociation and annihilation of excitons on charge carriers in organic phosphorescent emitters. Phys. Rev. B 74, 085316 (2006).

    Article  Google Scholar 

  20. Pope, M. & Swenberg, C. E. Electronic Processes in Organic Crystals 2nd edn (Oxford Univ. Press, Oxford, 1999).

    Google Scholar 

  21. Wittmer, M. & Zschokke-Gränacher, I. Exciton-charge carrier interactions in the electroluminescence of crystalline anthracence. J. Chem. Phys. 63, 4187–4194 (1975).

    Article  CAS  Google Scholar 

  22. Ern, V. & Merrifield, R. E. Magnetic field effect on triplet exciton quenching in organic crystals. Phys. Rev. Lett. 21, 609–611 (1968).

    Article  CAS  Google Scholar 

  23. Tolstov, I. V. et al. On the role of magnetic field spin effect in photoconductivity of composite films of MEH-PPV and nanosized particles of PbS. J. Lumin. 112, 368–371 (2005).

    Article  CAS  Google Scholar 

  24. Kalinowski, J. & Signerski, R. Exciton-enhanced double injection current in tetracene crystals. Phys. Status Solidi B 118, K147–K150 (1983).

    Article  CAS  Google Scholar 

  25. Kalinowski, J. & Godlewski, J. Magnetic field effects on recombination radiation in tetracene crystal. Chem. Phys. Lett. 36, 345 (1975).

    Article  CAS  Google Scholar 

  26. Birks, J. B. Organic Molecular Photophysics (Wiley, London, 1975).

    Google Scholar 

  27. Frenkel, J. On pre-breakdown phenomena in insulators and electronic semiconductors. Phys. Rev. 54, 647–648 (1938).

    Article  Google Scholar 

  28. Onsager, L. Initial recombination of ions. Phys. Rev. 54, 554–557 (1938).

    Article  CAS  Google Scholar 

  29. Doubleday, C. Jr, Turro, N. J. & Wang, J. F. Dynamics of flexible triplet biradicals. Acc. Chem. Res. 22, 199–205 (1989).

    Article  CAS  Google Scholar 

  30. Hu, B., Wu, Y., Zhang, Z., Dai, S. & Shen, J. Effects of ferromagnetic nanowires on singlet and triplet exciton fractions in fluorescent and phosphorescent organic semiconductors. Appl. Phys. Lett. 88, 022114 (2006).

    Article  Google Scholar 

  31. Wu, Y., Hu, B., Howe, J., Li, A-P. & Shen, J. Spin injection from ferromagnetic nanoclusters into organic semiconducting polymers. Phys. Rev. B 75, 075413 (2007).

    Article  Google Scholar 

  32. Ito, F., Ikoma, T., Akiyama, K., Watanabe, A. & Tero-Kubota, S. Carrier generation process on photoconductive polymer films as studied by magnetic field effects on the charge-transfer fluorescence and photocurrent. J. Phys. Chem. B 109, 8707–8717 (2005).

    Article  CAS  Google Scholar 

  33. Kalinowski, J. et al. Quenching effects in organic electrophosphorescence. Phys. Rev. B 66, 235321 (2002).

    Article  Google Scholar 

  34. Graupner, W., Partee, J., Shinar, J., Leising, G. & Scherf, U. Dynamics of long-lived polarons in poly(para-phyenylene)-type ladder polymers. Phys. Rev. Lett. 77, 2033–2036 (1996).

    Article  CAS  Google Scholar 

  35. Stampor, W. Electromodulation of fluorescence in hole-transporting materials (TPD, TAPC) for organic light-emitting diodes. Chem. Phys. 256, 351–362 (2000).

    Article  CAS  Google Scholar 

  36. Xu, Z., Wu, Y. & Hu, B. Dissociation processes of singlet and triplet excitons in organic photovoltaic cells. Appl. Phys. Lett. 89, 131116 (2006).

    Article  Google Scholar 

  37. Köhler, A., Wittmann, H. F., Friend, R. H., Khan, M. S. & Lewis, J. Enhanced photocurrent response in photocells made with platinum-poly-yne/C60 blends by photoinduced electron transfer. Synth. Met. 77, 147–150 (1996).

    Article  Google Scholar 

  38. Sariciftci, N. S., Smilowitz, L., Heeger, A. J. & Wudl, F. Photoinduced electron-transfer from a conducting polymer to buckminsterfullerene. Science 258, 1474–1476 (1992).

    Article  CAS  Google Scholar 

  39. Wohlgenannt, M. & Vardeny, Z. V. Spin-dependent exciton formation rates in π-conjugated materials. J. Phys. Condens. Matter 15, R83–R107 (2003).

    Article  CAS  Google Scholar 

  40. Finkenzeller, W. J. & Yersin, H. Emission of Ir(ppy)(3). Temperature dependence, decay dynamics, and magnetic field properties. Chem. Phys. Lett. 377, 299–305 (2003).

    Article  CAS  Google Scholar 

  41. Salis, G., Alvarado, S. F., Tschudy, M., Brunschwiler, T. & Allenspach, R. Hysteretic electroluminescence in organic light-emitting diodes for spin injection. Phys. Rev. B 70, 085203 (2004).

    Article  Google Scholar 

  42. Geacintov, N. E., Pope, M. & Fox, S. Magnetic field effects on photo-enhanced currents in organic crystals. J. Phys. Chem. Solids 31, 1375–1379 (1970).

    Article  CAS  Google Scholar 

  43. Levinson, J., Weisz, S. Z., Cobas, A. & Rolon, A. Determination of the triplet exciton-trapped electron reaction rate constant in Anthracene crystals. J. Chem. Phys. 52, 2794–2795 (1970).

    Article  CAS  Google Scholar 

  44. Helfrich, W. Destruction of triplet excitons in Anthracene by injected electrons. Phys. Rev. Lett. 16, 401–403 (1966).

    Article  CAS  Google Scholar 

  45. 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).

    Article  CAS  Google Scholar 

  46. Steiner, U. E. & Ulrich, T. Magnetic field effects in chemical kinetics and related phenomena. Chem. Phys. 89, 51–147 (1999).

    Google Scholar 

  47. Ganzorig, C. & Iizumi, Y. A possible mechanism for enhanced electrofluorescence emission through triplet-triplet annihilation in organic electroluminescent devices. Appl. Phys. Lett. 81, 3137–3139 (2002).

    Article  CAS  Google Scholar 

  48. Prigodin, V. N., Bergeson, J. D., Lincoln, D. M. & Epstein, A. J. Anomalous room temperature magnetoresistance in organic semiconductors. Synth. Met. 156, 757–761 (2006).

    Article  CAS  Google Scholar 

  49. Parker, I. D. Carrier tunneling and device characteristics in polymer light-emitting diodes. J. Appl. Phys. 75, 1656–1666 (1994).

    Article  CAS  Google Scholar 

  50. Eastman, D. E. Photoelectric workfunctions of transition, rare-earth, and nobel metals. Phys. Rev. B 2, 1–2 (1970).

    Article  Google Scholar 

Download references

Acknowledgements

This research was supported by the Airforce Office of Scientific Office (FA9550-06-10070) and the National Science Foundation Career Award (ECCS-0644945). Partial support from the Center for Materials Processing and Joint Institute of Advanced Materials Laboratory at the University of Tennessee is also acknowledged.

Author information

Authors and Affiliations

  1. Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA

    Bin Hu & Yue Wu

Authors
  1. Bin Hu
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Yue Wu
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Bin Hu.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Hu, B., Wu, Y. Tuning magnetoresistance between positive and negative values in organic semiconductors. Nature Mater 6, 985–991 (2007). https://doi.org/10.1038/nmat2034

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nmat2034

This article is cited by

Search

Advanced search

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