Tris(dibenzoylmethane)(monophenanthroline)europium(III) based red emitting organic light emitting diodes

Abstract

The concept of a blue light emitting diode containing a hole blocking layer (HBL) is generalized to efficiently excite dye molecules introduced in the form of an emission layer on the hole transporting side. The concept allows the excitation of an emitting molecule even if the molecule does not act primarily as a recombination center. On the basis of this concept pure red emitting organic light emitting diodes were produced utilizing tris(dibenzoylmethane)(monophenanthroline)europium(III) [Eu(dbm)3phen] as the emitting layer in an Al/LiF/Aluminum tris(8-hydroxyquinoline) (Alq3)/HBL/Eu(dbm) 3phen/N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (α-NPD)/copper-phthalocyanine (CuPc)/indium tin oxide structure. Additionally, the luminance output of such a device was improved by partially adding a hole transport material to the emitting layer in order to increase the penetration of holes into the emission region. A maximum luminance output of 200 cd/m2 at 15 V was achieved without optimizing the layer thickness. Furthermore, the effect of saturation of the Eu3+ emission is studied and discussed. The basic device architecture presented here is expected to work with other transport and emitting materials also. © 2001 American Institute of Physics.