High-efficiency organic light-emitting diodes based on ultrathin blue phosphorescent modification layer

Yellow organic light-emitting devices (YOLEDs) with a novel structure of ITO/MoO₃(5 nm)/NPB(40 nm)/TCTA(15 nm)/CBP:(tbt)₂Ir(acac)(x%)(25 nm)/FIrpic(y nm)/TPBi(35 nm)/Mg:Ag are fabricated. The ultrathin blue phosphorescent bis(4,6-difluorophenyl)-pyridi-nato-N,C2\prime ](picolinate) iridium (III) (FIrpic) layer is regarded as a high-performance modification layer. By adjusting the thickness of FIrpic and the concentration of (tbt)₂Ir(acac), a YOLED achieves a high luminance of 41618 cd/m², power efficiency of 49.7 lm/W, current efficiency of 67.3 cd/A, external quantum efficiency (EQE) of 18%, and a low efficiency roll-off at high luminance. The results show that phosphorescent material of FIrpic plays a significant role in improving YOLED performance. The ultrathin FIrpic modification layer blocks excitons in EML. In the meantime, the high triplet energy of FIrpic (2.75 eV) alleviates the exciton energy transport from EML to FIrpic.