Bright White Organic Light-Emitting Diode Mixed Blue and Green Emission

Double-layer and triple-layer organic light-emitting diodes (OLEDs) were fabricated using a novel star-shaped hexafluorenylbenzene organic material, 1,2,3,4,5,6-hexakis(9,9-diethyl-9H-fluoren-2-yl)benzene (HKEthFLYPh) as an energy transfer layer, N, N′-bis-(1-naphthyl)-N, N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) as a hole-transport layer (HTL) and blue emissive layer (EML), and tris(8-hydroxyquinoline)aluminum (Alq3) as an electron-transport layer (ETL) and green light-emitting layer. Bright white light was obtained with a triple-layer device structure of indium-tin-oxide (ITO)/NPB (40 nm)/HKEthFLYPh (10 nm)/Alq3 (50 nm)/Mg:Ag (200 nm). A maximum luminance of 8523 cd·m−2 at 15 V and a power efficiency of 1.0 lm·W−1 at 5.5 V were achieved. The Commissions Internationale de L′Eclairage (CIE) coordinates of the device were (0.29, 0.34) at 9 V, which located in white light region. With increasing film thickness of HKEthFLYPh, light emission intensity from NPB increased compared to that of Alq3.