High luminance bluish-green organic light-emitting diode based on Coumarin 6 doped into a blue emission layer

In this research, the interface barrier of the lowest unoccupied molecular orbital (LUMO) between LT-N421 and Alq₃ layers was reduced by inserting a DPVBi layer. Luminance was enhanced several folds when a DPVBi layer was inserted between LT-N421 and Alq₃ layers. Because DPVBi layer not only helped electrons injection into emission layer (EML) but it also blocked holes in the EML to increase the chance of holes and electrons recombination in EML and to improve the luminance of device. Another emphasis of this study was doping Coumarin 6 (C6) green dye in LT-N421, a new blue light-emitting layer. The performance of LT-N421 is better than that of DPVBi. The optimum doping concentration was 0.4 wt% of C6 doped in LT-N421, while the doping concentration of C6 was more than 0.5 wt%, it resulted in aggregation and led to self-quenching. The optimum structure of bluish-green organic light-emitting diode was successfully fabricated based on ITO/NPB (50 nm)/LT-N421:C6 (0.4 wt%, 32 nm)/DPVBi (8 nm)/Alq₃ (20 nm)/LiF (1 nm)/Al (200 nm). The CIE coordinate of the device was (0.22, 0.43) when the maximum luminance was 42400 cd/m² at 11 V. The current efficiency and power efficiency were 8.83 cd/A at 11 V and 3.96 lm/W at 6 V, respectively.