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-(1-naphthyl)- N , N '-diphenyl-1,1'-biph-enyl-4,4'-diamine (NPB), 2,2',2''-(1,3,5-phenylene)tris(1-phenyl-1 H -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, ∼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 .