Effects of Position of Exciton-Blocking Layer on Characteristics of Blue Phosphorescent Organic Light-Emitting Diodes

Abstract

In this study, we systematically examined the effects of the position of the exciton- blocking layer (EBL) in blue phosphorescent organic light-emitting diodes. The EBL was located either in the front and/or the rear of the emission layer (EML), and its effects to the device performances and electroluminescence spectra were investigated. The width and location of the recombination zone related to the triplet exciton quenching occurred in the devices with/without a front- or rear-EBL resulted in an optical micro-cavity effect in the EL spectrum at approximately 500 nm. The EBLs provided the direct, extra path of charge carriers from the hole transport layer (HTL)/electron transport layer (ETL) to the ETL/HTL through EML, resulting that the device operating voltage did not increase. The device with both front- and rear-placed EBLs exhibited the highest device performance, as triplet exciton quenching did not occur in it at the interface between the HTL/ETL and the EML.