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The dynamic organic p–n junction

Abstract

Static p–n junctions in inorganic semiconductors are exploited in a wide range of today’s electronic appliances. Here, we demonstrate the in situ formation of a dynamic p–n junction structure within an organic semiconductor through electrochemistry. Specifically, we use scanning kelvin probe microscopy and optical probing on planar light-emitting electrochemical cells (LECs) with a mixture of a conjugated polymer and an electrolyte connecting two electrodes separated by 120 μm. We find that a significant portion of the potential drop between the electrodes coincides with the location of a thin and distinct light-emission zone positioned >30 μm away from the negative electrode. These results are relevant in the context of a long-standing scientific debate, as they prove that electrochemical doping can take place in LECs. Moreover, a study on the doping formation and dissipation kinetics provides interesting detail regarding the electronic structure and stability of the dynamic organic p–n junction, which may be useful in future dynamic p–n junction-based devices.

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Figure 1: Schematic diagram illustrating the probing of a planar LEC device with SKPM.
Figure 2: Light-emission and potential profiles in a planar LEC device during operation.
Figure 3: Experimental data illustrating the formation and reformation of an organic p–n junction.
Figure 4: Schematic diagrams illustrating the electrostatic profile and the electronic and ionic charge distribution within a p–n junction structure established at V =+5 V.

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Acknowledgements

L.E. and P.M. acknowledge the Swedish Research Council (VR) and Wenner-Gren stiftelserna for scientific financial support. L.E. is a ‘Royal Swedish Academy of Sciences Research Fellow’ supported by a grant from the Knut and Alice Wallenberg Foundation. N.D.R. acknowledges VR and Norrköpings Kommun for financial support of part of this work. The work of K.M. is made possible by a NanoNed grant (NanoNed is the Dutch nanotechnology initiative by the Ministry of Economic Affairs). The authors acknowledge A. Shchukarev at Umeå University for help with the X-ray photoemission spectroscopy measurements.

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P.M., K.M. and N.D.R. carried out the experiments. L.E., N.D.R. and M.K. wrote the manuscript. P.M., K.M., M.K., N.D.R. and L.E. contributed to data analysis and project planning.

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Correspondence to Ludvig Edman.

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Matyba, P., Maturova, K., Kemerink, M. et al. The dynamic organic p–n junction. Nature Mater 8, 672–676 (2009). https://doi.org/10.1038/nmat2478

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