Enhanced life time and suppressed efficiency roll-off in phosphorescent organic light-emitting diodes with multiple quantum well structures

Ja-Ryong Koo,Kum Hee Lee,Seok Jae Lee,Dong Whan Im,Gun Woo Hyung,Seung Soo Yoon,Jung-Hwan Park,Young Kwan Kim,Han Sung Yu,Woo Young Kim

doi:10.1063/1.3679428

Abstract

We demonstrate red phosphorescent organic light-emitting diodes (OLEDs) with multiple quantum well structures which confine triplet exciton inside an emitting layer (EML) region. Five types of OLEDs, from a single to five quantum wells, are fabricated with charge control layers to produce high efficiencies, and the performance of the devices is investigated. The improved quantum efficiency and lifetime of the OLED with four quantum wells, and its suppressed quantum efficiency roll-off of 17.6%, can be described by the increased electron–hole charge balance owing to the bipolar property as well as the efficient triplet exciton confinement within each EML, and by prevention of serious triplet–triplet and/or triplet–polaron annihilation as well as the Förster self-quenching due to charge control layers.

Highlights

Phosphorescent organic light-emitting diodes (PHOLEDs) have aroused much interest on account of their highly efficient light emission in comparison with conventional fluorescent OLEDs
High performance PHOLEDs commonly consist of a host-dopant system to enhance energy transfer and prevent triplet–triplet annihilation (TTA) and/or triplet–polaron annihilation (TPA).[1,2,3]
High efficiency in typical OLED structures can be obtained by means of a charge balance inside emitting layer (EML), and the EL efficiency in case of a QW structure is enhanced by using exciton confinement inside the EML

Summary

INTRODUCTION

Phosphorescent OLEDs with MQW structure, which can confine triplet exciton inside the EML, was investigated to enhance the several efficiencies of red PHOLEDs. Five types of triplet MQW OLEDs, from a single to five quantum wells, were fabricated with CCLs to produce high efficiencies, and their performances were compared with each other. MQW PHOLEDs with four QWs showed both an improved quantum efficiency and lifetime Their reduced luminous efficiency roll-off can be clarified by the increased balance between electron–hole charges and efficient confinement of triplet exciton, as well as the bipolar property of the EML

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSION