Improved efficiency of blue phosphorescence organic light-emitting diodes with irregular stepwise-doping emitting layers

Abstract

We demonstrate highly efficient blue phosphorescence organic light-emitting diodes (PHOLED) with irregular stepwise-doping emitting layers (EMLs). High efficiency is realized by inserting a high-doping EML between two relatively low-doping EMLs. Peak luminous efficiency and power efficiency of 19.2 cd A -1 and 18.0 lm W-1 are achieved, while those of a continuous stepwise-doping device are 9.8 cd A-1 and 8.6 lm W -1. The dramatic efficiency enhancement is mainly attributed to the high hole-electron recombination probability and suppressed triplet excitons quenching by fine tuning the doping concentrations in the EMLs. A stepwise doping emitting layer is considered as an effective way to control the charge transport and recombination in organic light-emitting diodes (OLEDs). It has been demonstrated that the irregular stepwise doping profile in the emitting layer can deliver better charge carrier balance and tune the recombination zone away from the low triplet energy electron transporting layer to avoid possible quenching. Both effects improve the efficiency significantly. It is anticipated that this method can also be applied to other emitting systems to realize better performance. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.