Enhancement of electroluminescent properties of organic light-emitting device by using exciton adjusting layer

Organic light-emitting devices (OLEDs) with stable white light emitting were fabricated by using exciton adjusting layer (EAL) inserted between dual emitting layers (EMLs). Three charge transport materials with different characteristics were chosen as EAL, including 4,7-diphenyl-1,1′-phenanthroline (Bphen), N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) and N,N′-dicarbazolyl-3,5-benzene (mCP). Device structure was given as: ITO/NPB (30 nm)/mCP: (t-bt)2Ir(acac) (2 nm, 4 wt.%)/EALs/ mCP: Firpic (12 nm, 10 wt.%)/Bphen (35 nm)/Mg: Ag (100 nm). The results showed that, compared with device without EAL, the devices employed EAL yielded high device performance as well as favorable luminescence property and stable white emission. For the device with mCP EAL, the maximum brightness of 24700cd/m2 and current efficiency of 14.5 cd/A were obtained, while the CIE coordinates of device changed from (0.33, 0.35) to (0.35, 0.36) with the bias voltage increasing from 5 V to 12 V. It was suggested that by incorporating EAL in OLEDs, the charge carrier recombination zone was broadened, and the balance of electron-hole was improved between EMLs.