Low-voltage top-emitting organic light-emitting devices with an organic double-heterojunction structure

We demonstrate low-voltage top-emitting organic light-emitting devices with a narrow recombination zone confined by an organic double-heterojunction structure. The devices had a configuration of Al/Glass/ ITO/m-MTDATA/NPB/Alq(3)/TPBI/Alq(3)/LiF/Al/Ag. In these devices, 4,4',4 ''-tris(3-methylphenylphenylamino)-triphenylamine (m-MTDATA), N,N'-bis-(I-naphthyl)-N,N'-diphenyl-1,1'-biph-enyl-4,4'-diamine (NPB), 2,2',2 ''-(1,3,5-phenylene)tris(1-phenyl-1H-benzimidazole) (TPBI) and tris (8-hydroxyquinoline) aluminium (Alq(3)) were used as the hole injection, hole transporting, hole blocking and emission/electron-transporting layers, respectively. They exhibit low driving voltages, for instance, similar to 200 cd m(-2) at the voltage of 4 V. The maximum efficiency and luminance of the device are 1.628 cd A(-1) and 9573 cd m(-2).