Impact of compound doping on hole and electron balance in p-i-n organic light-emitting diodes

Xin-Xin Wang,Xiao-Hong Zhang,Jing Xiao,Sui-Dong Wang,Xu Gao

doi:10.1063/1.4826982

Abstract

The fluorescent and phosphorescent p-i-n organic light-emitting diodes (OLEDs) with well controllable compound doping have been systematically investigated, where MoO3 and LiF are the effective p-type and n-type dopants, respectively. For both the bulk and interfacial doping, the hole and electron balance in the devices is found to be strongly dependent on the doping configuration, which could either facilitate or compromise the device power efficiency. The impact of the compound doping on the charge balance is further confirmed by the change of the emission region with different doping configuration. The modulation of p-type and n-type doping densities and position is thus essential for optimizing hole and electron balance in p-i-n OLEDs.

Highlights

Organic light-emitting diodes (OLEDs) based on small molecules have progressed remarkably since 1987,1–3 and are currently entering the market of flat-panel displays and solid-state lighting
Note that the n-doping organic light-emitting diodes (OLEDs) show better performance compared with the corresponding undoped devices using conventional Al/lithium fluoride (LiF) cathode.[19,20]
Doping in p-i-n OLEDs can significantly reduce operation voltage, it would be compromised by doping induced charge imbalance

Summary

INTRODUCTION

Organic light-emitting diodes (OLEDs) based on small molecules have progressed remarkably since 1987,1–3 and are currently entering the market of flat-panel displays and solid-state lighting. According to ηP ∼ ηL/V, ideal doping in OLEDs should simultaneously reduce operation voltage and facilitate charge balance, this is not always the case as demonstrated in the present report Due to their high stability and excellent doping controllability, appropriate compound dopants have been utilized to improve OLED performance.[12,19,20,21,22] acceptor-like molybdenum trioxide (MoO3)[12,17,18] and donor-like lithium fluoride (LiF)[19,20] are employed as the p-type and n-type compound dopants, respectively. The bulk and interfacial effects of the compound doping are compared as well

EXPERIMENTAL

RESULTS AND DISCUSSION

SUMMARY