Tandem organic light-emitting diodes with an effective nondoped charge-generation unit

Authors

  • Bo Jiao,

    1. Key Laboratory of Photonics Technology for Information, School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an, Shannxi, P.R. China
    2. Key Laboratory for Physical Electronics and Devices of the Ministry of Education, School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an, Shannxi, P.R. China
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  • Zhaoxin Wu,

    Corresponding author
    1. Key Laboratory of Photonics Technology for Information, School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an, Shannxi, P.R. China
    2. Key Laboratory for Physical Electronics and Devices of the Ministry of Education, School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an, Shannxi, P.R. China
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  • Zhiyuan Yang,

    1. School of Information Science and Technology, Northwest University, Xi'an, Shannxi, P.R. China
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  • Xun Hou

    1. Key Laboratory of Photonics Technology for Information, School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an, Shannxi, P.R. China
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Abstract

An undoped charge-generation unit (CGU) with the structure of lithium fluoride (LiF)/aluminum/molybdenum trioxide (MoO3) was demonstrated in tandem organic light-emitting diodes (OLEDs). Tandem OLEDs with two identical emissive units consisting of 4,4′-bis-(1-naphthyl-N-phenylamino)-biphenyl (NPB)/tris(8-hydroxyquinoline) aluminum (Alq3) exhibited superior performance over a corresponding single-unit device. Under a driving current of 650 A m−2, the current efficiency of the tandem OLEDs was about 6.95 cd A−1, almost double that of the single-unit OLEDs. The operational stability of the tandem OLEDs was also enhanced compared with that of the single-unit OLEDs. It was demonstrated that the MoO3 plays a critical role of charge generation in this undoped CGU. The LiF/Al layers were used to enhance the electron injection from MoO3 layer to the adjacent Alq3 layer. Furthermore, fabrication of this CGU involves no sputtering or doping process, which can render tandem OLEDs processing more feasible.

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