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 +/-Delta(x,y) = (0.001, 0.008) for the device with THBL structure during the applied voltage of 6-9V. 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.