White organic light-emitting diodes from three emitter layers

Three-wavelength white organic light-emitting diodes (WOLEDs) were fabricated using two doped layers, which were obtained by separating the recombination zones into three emitter layers. A sky blue emission originated from the 4,4′-bis(2,2′-diphenylethen-1-yl)biphenyl (DPVBi) layer. A green emission originated from a tris(8-quinolinolato)aluminum (III) (Alq 3) host doped with a green fluorescent 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano [6,7,8-ij]-quinolizin-11-one (C545T) dye. An orange emission was obtained from the N, N′-bis(1-naphthyl)- N, N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) host doped with a red fluorescent dye, 4-(dicyanomethylene)-2- tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB). A white light resulted from the partial excitations of these three emitter layers by controlling the layer thickness and concentration of the fluorescent dyes in each emissive layer simultaneously. The electroluminescent spectrum of the device was not sensitive to the driving voltage of the device. The white light device showed a maximum luminance of approximately 53,000 cd/m 2. The external quantum and power efficiency at a luminance of approximately 100 cd/m 2 were 2.62% and 3.04 lm/W, respectively.