Structural Optimizing Carrier Recombination for Efficient Blue Phosphorescence Organic Light-Emitting Diode With Ambipolar Host

A high-efficiency blue phosphorescence organic light-emitting diode (OLED) with a new ambipolar organic compound, 9-(2-(4,5-diphenyl-4H-1,2,4-triazol-3-yl) phenyl)-9H-carbazole (CbzTAZ) as the host, structurally engineered the emitting layer (EML) and electron-transporting layer (ETL) to achieve the great carrier balance in the EML. The chemical structure of Cbz-TAZcontains an electron-transporting 1,2,4-triazole segment and a hole-transporting carbazole ring. By scanning the composite ratio between the CbzTAZ host and the blue emitter iridium(III) bis[4,6-(di-fluorophenyl)-pyridinato-N,C2'] picolinate to be an efficient EML, and then by fine-tuning the layer thicknesses of the ETL and EML, a highly efficient blue PhOLED was obtained because of the improved electron-hole balance and broad recombination zone coverage in the EML. The blue PhOLED exhibited a maximum-current efficiency (eta(C)) of 48 cd/A, a power efficiency (eta(P)) of 42.2 lm/W, and an external quantum efficiency (eta(EQE)) of 22.9%. In addition, the device demonstrated a satisfactory efficiency roll-off (eta(C) of 41.1 cd/A, eta(P) of 18.1 lm/W, and eta(EQE) of 19.8%) at a high brightness value of 1000 cd/m(2).