Enhancing the efficiency of blue organic light-emitting diodes by using a dual emitting layer structure

Abstract

Blue, as one of the three primary colors, plays a crucial role in the advancement of high-efficiency organic light-emitting diodes (OLEDs). However, achieving high-performance blue OLEDs remains a significant challenge in flat-panel display technology. In this study, we developed highly efficient blue phosphorescent OLEDs (PhOLEDs) by employing a dual emitting layer (EML) structure. Two fabrication methods were explored to optimize device performance. In the first approach, bis(3,5-difluoro-2-(2-pyridyl)phenyl)(2-carboxypyridyl)iridium(III) (FIrpic) was doped into two host materials—1,3-bis(carbazol-9-yl)benzene (mCP) and 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T). By precisely tuning the doping concentration and the thickness of the emitting layers, we achieved a maximum external quantum efficiency (EQE) of 17.49% and a peak brightness of 13 580 cd m⁻². In the second approach, an ultra-thin layer of 2,2′,2′′-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) was inserted as a hole blocking layer (HBL) between the mCP:FIrpic emitting layers. This modification further enhanced device performance, facilitating an EQE of 18.99% and a peak brightness of 15 890 cd m⁻². These results suggest that the superior performance of our devices is attributed to enhanced multi-channel energy transfer between the host materials and the luminescent guest, effectively expanding the exciton formation region and optimizing the carrier balance. Our findings demonstrate the potential of the dual emitting layer strategy in the design of high-performance blue PhOLEDs, paving the way for future advancements in OLED technology.