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Beating the thermodynamic limit with photo-activation of n-doping in organic semiconductors

A Corrigendum to this article was published on 23 January 2018

This article has been updated

Abstract

Chemical doping of organic semiconductors using molecular dopants plays a key role in the fabrication of efficient organic electronic devices. Although a variety of stable molecular p-dopants have been developed and successfully deployed in devices in the past decade, air-stable molecular n-dopants suitable for materials with low electron affinity are still elusive. Here we demonstrate that photo-activation of a cleavable air-stable dimeric dopant can result in kinetically stable and efficient n-doping of host semiconductors, whose reduction potentials are beyond the thermodynamic reach of the dimer’s effective reducing strength. Electron-transport layers doped in this manner are used to fabricate high-efficiency organic light-emitting diodes. Our strategy thus enables a new paradigm for using air-stable molecular dopants to improve conductivity in, and provide ohmic contacts to, organic semiconductors with very low electron affinity.

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Figure 1: Molecular structure and electrochemical redox potentials of the host and the dopant, and optical absorption spectra of UV-activated doped film.
Figure 2: Evolution of work function and conductivity of doped POPy2 films under photo-activation.
Figure 3: Dominant paths for the photo-assisted doping for the dimer/host system.
Figure 4: Evolution of charge-transfer state in doped POPy2 films observed via EQEPV measurements.
Figure 5: Structure, energy diagram and characterization of a high-efficiency OLED.

Change history

  • 15 December 2017

    In the version of this Article originally published, the source of 'ZADN' stated in the Methods should have read 'obtained as free research samples from Guangzhou ChinaRay Optoelectronic Materials' instead of 'China-Ray'. This has now been corrected in the online versions of the Article.

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Acknowledgements

A.K., X.L. and F.Z. acknowledge funding for this work from the National Science Foundation under grants DMR-1506097. Work in Berlin was supported by the Sfb951 (DFG) and the Helmholtz Energy-Alliance ‘Hybrid Photovoltaics’. B.P.R., M.A.F., and K.M.L. acknowledge funding for this work from the Department of Energy EERE SSL Program under Award #DE-EE0006672 and the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award #DE-SC0012458. Work at the Georgia Institute of Technology was supported by the National Science Foundation under grants DMR-1305247. We thank E. Longhi for synthetic assistance, E. List-Kratochvil for stimulating discussions about optical interference phenomena during UV/Vis measurements, G. Ligorio for performing PL measurements in Berlin, and A. Zykov, P. Schäfer and S. Kowarik for performing XRD measurements.

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X.L., B.W., K.M., A.K., N.K., S.R.M. and S.B. initialized this series of experiments. K.M., S.B. and S.R.M. synthesized the dopant molecules. X.L., B.W., A.K. and N.K. designed the work function and conductivity experiments, prepared the films, and carried out Kelvin probe, IV, AFM, UPS, XPS and IPES measurements. B.W. and N.K. conducted optical absorption spectroscopy. K.M.L. and B.P.R. performed part of the PL experiments in Princeton. X.L., K.M.L., M.A.F., B.P.R. and A.K. designed and performed EQEPV and OLED measurements. F.Z., K.M.L., X.L. and A.K. designed and fabricated samples for SIMS and RBS. All authors discussed the results and contributed to the manuscript.

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Correspondence to Antoine Kahn.

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Lin, X., Wegner, B., Lee, K. et al. Beating the thermodynamic limit with photo-activation of n-doping in organic semiconductors. Nature Mater 16, 1209–1215 (2017). https://doi.org/10.1038/nmat5027

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