Highly efficient terbium(III)-based organic light-emitting diodes obtained by exciton confinement

We present highly efficient Tb(III)-based organic light-emitting diodes optimized by the subtle choice of bipolar hosts, adjacent layers and double emitting structures. By introducing di(9H-carbazol-9-yl)(phenyl) phosphine oxide (DCPPO) as the host for the first emitting layer, and 9-(4-tert-butylphenyl)-3,6-bis(diphenylphosphine oxide)-carbazole (DPPOC) for the second emitting layer for Tb(PMIP)(3) (PMIP stands for 1-phenyl-3-methyl-4-isobutyryl-pyrazol-5-one), the excitons can be well confined within the double-emitting layer. When 4,4',4 ''-tris(N-carbazolyl) triphenylamine (TCTA) and tris-[3-(3-pyridyl)mesityl] borane (3TPYMB) with high triplet energy levels are used as a hole transporting layer (HTL) and an electron transporting layer (ETL), respectively, the optimized device reaches a maximum efficiency of 52 lm W-1, 57 cd A(-1), i.e. a maximum external quantum efficiency (EQE) of 15%. At a practical brightness of 100 cd m(-2) (4.6 V) the efficiency remains at around 20 lm W-1, 30 cd A(-1).