Efficient White Electroluminescent Device with Stable Emission Spectrum

In this work, we report a novel white organic light-emitting device (WOLED) with stable emission spectrum. Red emitter 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) was selected and doped into N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-diphenyl-4,4'-diamine (NPB) layer as hole transport layer and the first light-emitting layer (EML1), which provides blue and red emissions. The widely used green material tris(8-hydroxyquinoline) aluminum (AlQ) was selected as sensitizer of electron injection and doped into NPB layer as the second light-emitting layer (EML2), which provides blue and green emissions. The doping concentrations of DCJTB and AlQ were optimized to be 0.4% and 0.14%, respectively, while the thickness of EML2 was optimized to be 3 nm. Finally, we obtained the pure white organic light-emitting device, which possesses 3.1 V turn-on voltage, 32749 cd/m(2) maximum brightness, 8.67 cd/A maximum current efficiency, and 8.78 lm/W maximum power efficiency. More importantly, the use of hole-type host material help to confine the recombination zone of holes and electrons, thus improving the stability of electroluminescent spectrum. With increasing current density, the Commission Internationale de l'Eclairage (CIE) coordinates of this device change from (0.343, 0.342) to (0.328, 0.336)