Enhancing color purity and stable efficiency of white organic light diodes by using hole-blocking layer

The organic light-emitting diodes with triple hole-blocking layer (THBL) formation sandwich structure which generate white emission were fabricated. The 5,6,11,12-tetraphenylnapthacene (Rubrene), (4,4′-N, N′-dicarbazole)biphenyl (CBP), and 4,4′- bis(2,2′ diphenylvinil)-1,1′-biphenyl (DPVBi) were used as emitting materials in the device.The function of CBP layer is not only an emitting layer but also a hole-blocking layer (HBL), and the Rubrene was doped into the CBP. The optimal configuration structure was indium tin oxide (ITO)/Molybdenum trioxide (MoO3) (5 nm)/[4,4-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) (35 nm)/CBP (HBL1) (5 nm)/DPVBi (I) (10 nm)/CBP (HBL2) : Rubrene (4 : 1) (3 nm)/DPVBi (II) (30 nm)/CBP (HBL3) (2 nm)/4,7-diphenyl-1,10-phenanthroline (BPhen) (10 nm)/Lithium fluoride (LiF)/aluminum (Al). The result showed that the device with Rubrene doped in CBP (HBL2) exhibited a stable white emission with the color coordinates of (0.322, 0.368), and the coordinate with the slight shift of ±Δx,y = (0.001, 0.011) for applied voltage of 8-12V was observed.