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Isotope effect in spin response of π-conjugated polymer films and devices

Nature Materials volume 9, pages 345–352 (2010)Cite this article

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Abstract

Recent advances in organic spin response include long polaron spin-coherence times measured by optically detected magnetic resonance (ODMR), substantive room-temperature magnetoelectroluminescence and magnetoconductance obtained in organic light-emitting diodes (OLEDs) and spin-polarized carrier injection from ferromagnetic electrodes in organic spin valves (OSVs). Although the hyperfine interaction (HFI) has been foreseen to have an important role in organic spin response, no clear experimental evidence has been reported so far. Using the chemical versatility advantage of the organics, we studied and compared spin responses in films, OLED and OSV devices based on π-conjugated polymers made of protonated, H-, and deuterated, D-hydrogen having a weaker HFI strength. We demonstrate that the HFI does indeed have a crucial role in all three spin responses. OLED films based on the D-polymers show substantially narrower magneto-electroluminescence and ODMR responses, and as a result of the longer spin diffusion obtained, OSV devices based on D-polymers show a substantially larger magnetoresistance.

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Figure 1: D- and H-polymer structures and their basic optical properties.
Figure 2: Isotope dependence of the spin-1/2 ODMR response in DOO-PPV polymers.
Figure 3: Isotope dependence of the MEL response in OLEDs based on DOO-PPV polymers.
Figure 4: Isotope dependence of the magnetoresistance response in OSVs based on DOO-PPV polymers.

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Acknowledgements

We thank R. Polson for the Raman scattering measurements of the two polymers, and M. Wohlgenannt for useful discussions. This work was supported in part by the Department of Energy (Grant No. 04-ER46109; Z.V.V.), the NSFC and National Basic Research Program of China (Grant 2009CB929502; X-G.L.) and the Israel Science Foundation (ISF 745/08; E.E.). Z.V.V. wishes to thank the Lady Davis foundation for helping his stay at the Technion during spring 2009, where part of the present work was conceived.

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Authors and Affiliations

  1. Department of Physics and Astronomy, University of Utah, 115 South 1400 East, Salt Lake City, Utah 84112, USA

    Tho D. Nguyen, Golda Hukic-Markosian, Fujian Wang, Leonard Wojcik & Z. Valy Vardeny

  2. Department of Physics, Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei 230026, China

    Xiao-Guang Li

  3. Physics Department and Solid State Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel

    Eitan Ehrenfreund

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Contributions

T.D.N. was responsible for the OLED and OSV device fabrication and measurements; G.H-M. was responsible for the ODMR measurements; F.W. was responsible for the MFE and OSV system apparatus and magneto-optic Kerr effect measurements; L.W. was responsible for the synthesis of the D- and H- polymers; X-G.L. was responsible for growing the LSMO substrates; E.E. was responsible for the ODMR and MEL analysis and model fittings; Z.V.V. was responsible for project planning, group managing and first draft writing.

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Correspondence to Z. Valy Vardeny.

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Nguyen, T., Hukic-Markosian, G., Wang, F. et al. Isotope effect in spin response of π-conjugated polymer films and devices. Nature Mater 9, 345–352 (2010). https://doi.org/10.1038/nmat2633

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