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Direct measurement of the electric-field distribution in a light-emitting electrochemical cell

Nature Materials volume 6, pages 894–899 (2007)Cite this article

Abstract

The interplay between ionic and electronic charge carriers in mixed conductors offers rich physics and unique device potential. In light-emitting electrochemical cells (LEECs), for example, the redistribution of ions assists the injection of electronic carriers and leads to efficient light emission. The mechanism of operation of LEECs has been controversial, as there is no consensus regarding the distribution of electric field in these devices. Here, we probe the operation of LEECs using electric force microscopy on planar devices. We show that obtaining the appropriate boundary conditions is essential for capturing the underlying device physics. A patterning scheme that avoids overlap between the mixed-conductor layer and the metal electrodes enabled the accurate in situ measurement of the electric-field distribution. The results show that accumulation and depletion of mobile ions near the electrodes create high interfacial electric fields that enhance the injection of electronic carriers.

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Figure 1: Time dependence of the in situ potential and electric-field profiles for Au/[Ru(bpy)3]2+(PF6−)2/Au devices under 5 V operation, in which the [Ru(bpy)3]2+(PF6−)2 is unpatterned.
Figure 2: Schematic diagram of the ionic space-charge effects in unpatterned and patterned Au/[Ru(bpy)3]2+(PF6−)2/Au devices (not to scale).
Figure 3: Patterning [Ru(bpy)3]2+(PF6−)2 with parylene.
Figure 4: Time dependence of the in situ potential and electric-field profiles for Au/[Ru(bpy)3]2+(PF6−)2/Au devices under 5 V operation, in which the [Ru(bpy)3]2+(PF6−)2 layer has been patterned to be restricted between the electrodes.
Figure 5: Simulation results for carrier and electric-field distributions in an LEEC.
Figure 6: Voltage dependence of potential and electric-field distributions and spatial profile of light emission.

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Acknowledgements

This work was supported by the National Science Foundation, the Center for NanoScale Systems and the New York State Office of Science, Technology and Academic Research (NYSTAR), and made possible by the use of the Cornell NanoScale Facility. J.D.S. was supported by a National Science Foundation Graduate Research Fellowship. Thanks are due to J. Blakely and D. Cahen for fruitful discussions.

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  1. Jason D. Slinker, John A. DeFranco and Michael J. Jaquith: These authors contributed equally to this work

Authors and Affiliations

  1. Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853-1501, USA

    Jason D. Slinker, John A. DeFranco & George G. Malliaras

  2. Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301, USA

    Michael J. Jaquith, William R. Silveira, Yu-Wu Zhong, Héctor D. Abruña & John A. Marohn

  3. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14843-3501, USA

    Jose M. Moran-Mirabal & Harold G. Craighead

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Correspondence to George G. Malliaras.

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Slinker, J., DeFranco, J., Jaquith, M. et al. Direct measurement of the electric-field distribution in a light-emitting electrochemical cell. Nature Mater 6, 894–899 (2007). https://doi.org/10.1038/nmat2021

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