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The combination of two p-doped layers for improving the hole current of organic light-emitting diodes

Authors

  • Lei Chen,

    1. Institute of Polymer Science and Engineering, School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, P. R. China
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  • Dashan Qin,

    Corresponding author
    • Institute of Polymer Science and Engineering, School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, P. R. China
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  • Yuhuan Chen,

    1. Institute of Polymer Science and Engineering, School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, P. R. China
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  • Guifang Li,

    1. Institute of Polymer Science and Engineering, School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, P. R. China
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  • Mingxia Wang,

    1. Institute of Polymer Science and Engineering, School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, P. R. China
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  • Dayan Ban

    1. Department of Electrical and Computer Engineering, University of Waterloo, 200 University Ave. West, Waterloo, ON, Canada
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Corresponding author: e-mail qindashan@yahoo.com.cn, Phone: 86 22 60204297, Fax: 86 22 60204297

e-mail dban@ecemail.uwaterloo.ca, Phone: 1 519 888 4567, Fax: 1 519 746 3077

Abstract

The combination of MoO3-doped 4,4-N,N-bis [N-1-naphthyl-N-phenyl-amino]biphenyl (NPB:MoO3) and 4,4′-N,N′-dicarbazole-biphenyl (CBP:MoO3) was used to enhance the hole conduction in organic light-emitting diodes (OLEDs). It is found that the OLED using NPB:MoO3 10 nm/CBP:MoO3 5 nm showed a much increased current density than the one using NPB:MoO3 5 nm/CBP:MoO3 5 nm at a given voltage larger than 4 V, mainly because the hole transport barrier across the p-doped heterojunction in the former device became smaller than that in the latter device with the driving voltage increasing, despite the fact that the 10-nm NPB:MoO3 in the former device caused more Ohmic loss than the 5-nm one in the latter device. As a result of the higher conductivity of NPB:MoO3 than that of CBP:MoO3, the OLED using the combination of 15-nm NPB:MoO3 and 5-nm CBP:MoO3 showed significantly increased performance than the one using the single 20-nm CBP:MoO3. We provide a useful way of advancing the OLEDs toward the practical applications in general lighting and flat-panel displays.

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