Nondoped-type red organic electroluminescent devices based on a 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran ultrathin layer

摘要

Nondoped-type red organic electroluminescent devices based on a 4-(dicyanomethylene) -2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) ultrathin layer have been fabricated. When the ultrathin DCJTB layer is inserted between N, N'-bis-(1-naphthyl)-N, N'-diphenyl-1,1'-biph-enyl-4,4'-diamine (NPB) and tri-(8-hydroxyquinoline) aluminium (Alq_3) (type A device), the emission from Alq_3 is mixed with the emission from DCJTB and the colour purity of the device becomes poor. When utilizing the Alq_3 (5 nm)/TPBI (45 nm) (TPBI: 2,2',2-(1,3,5-phenylene)tris (1-phenyl-1 H-benzimidazole)) bilayer as a hole/exciton blocking and electron transporting layer (type B device), the emission from Alq_3 disappears. We attribute it to the excitons confinement effect by the Alq_3 (5 nm)/TPBI (45 nm) bilayer. The type B device with 0.2 nm DCJTB has a maximum efficiency of 2.20 cd A~(-1) and a luminance of 280 cd m~(-2) is achieved at 20 mA cm~(-2) with an EL efficiency of 1.41 cd A~(-1), and the CIE coordinates are (0.628, 0.369).