Eur. Phys. J. Appl. Phys. (2014) 67: 30201
https://doi.org/10.1051/epjap/2014130545

The charge generation layer incorporating two p-doped hole transport layers for improving the performance of tandem organic light emitting diodes

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

^a e-mail: qindashan06@aliyun.com

Received: 30 November 2013
Revised: 30 March 2014
Accepted: 18 July 2014
Published online: 20 August 2014

Abstract

We report the charge generation layer (CGL) structure comprising of Li₂CO₃ doped bathocuproine (BCP:Li₂CO₃)/MoO₃ doped 4,4-N,N-bis [N-1-naphthyl-N-phenyl-amino]biphenyl (NPB:MoO₃)/MoO₃ doped 4,4′-N,N′-dicarbazole-biphenyl (CBP:MoO₃) for tandem organic light emitting diodes (TOLEDs). Compared to the TOLED using the conventional CGL structure of BCP:Li₂CO₃/20 nm CBP:MoO₃, the one using the CGL structure of BCP:Li₂CO₃/5 nm NPB:MoO₃/15 nm CBP:MoO₃ showed increased electrical and luminous properties, mostly because the introduction of the higher-conductivity NPB:MoO₃ relative to CBP:MoO₃ could improve the current conduction in the CGL structure. Whereas, the performance of the CGL structure of BCP:Li₂CO₃/x nm NPB:MoO₃/20- x nm CBP:MoO₃ decreased with x increasing, mostly due to the fact that the CBP:MoO₃ became depleted of mobile holes upon contacting p-doped NPB: the smaller thickness of CBP:MoO₃, the worse conductivity for it. We provide some in-depth insights on designing the high-performance CGLs for TOLEDs.