The Investigation on Color Purity of Blue Organic Light-Emitting Diodes (BOLED) by Hole-Blocking Layer

Organic light-emitting diodes (OLEDs) with triple hole-blocking layer (THBL) structure, which consist of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,4′-bis(2,2′diphenyl vinil)-1,1′-biphenyl (DPVBi), and (4,4′-N,N′-dicarbazole)biphenyl (CBP), have been fabricated. Regardless of applied voltage variation, the luminous efficiency of the OLEDs with THBL structure was increased by 41% as compared with the dual hole-blocking layer (DHBL) structure. The CIE coordinates of (0.157, 0.111) of device with THBL structure are close to pure blue emission than that of other devices of DHBL. There is a coordinate with the slight shift of = (0.001, 0.008) for the device with THBL structure during the applied voltage of 6–9 V. The results indicate that the excitons can be effectively confined in the emitting layer of device, leading to an enhancement of luminance efficiency and more stable coordinate.