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

Abstract

Yellow organic light-emitting devices (YOLEDs) with a novel structure of ITO/MoO 3 (5 nm)/NPB(40 nm)/ TCTA(15 nm)/CBP:(tbt) 2 Ir(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 ](picolinate) iridium (III) (FIrpic) layer is regarded as a highperformance modification layer. By adjusting the thickness of FIrpic and the concentration of (tbt) 2 Ir(acac), a YOLED achieves a high luminance of 41618 cd/m 2 , 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.

Recent progress on organic light-emitting diodes with phosphorescent ultrathin (<1nm) light-emitting layers

“…Considering blue phosphors easily suffer chemical degradation during device operation and there are still no ideal blue phosphorescent emitters in terms of lifetime and color stability, the development of all phosphorescent blue and white OLEDs is greatly restricted ( Zhu et al., 2017 ; Yin et al., 2014 ). Instead, hybrid white OLEDs, structured by using blue fluorophores and complementary long wavelength phosphors, have drawn considerable attention because of their advantages of simultaneously combining the excellent stability of blue fluorophors and the high efficiency of long wavelength phosphors.…”

Tetraalkyl-substituted zinc phthalocyanines used as anode buffer layers for organic light-emitting diodes*

“…[4,9] Therefore, insertion of a hole injection layer (HIL) between the ITO anode and the organic hole transport layer (HTL) has become a popular strategy for provision of favorable band alignment in OLEDs. [10][11][12][13] The metal oxides such as WO 3 , [14] V 2 O 5 , [15] MoO 3 , [3,13,[16][17][18] ReO 3 , [19] and NiO x [20] are important HIL materials and have been used widely to enhance the hole injection because they offer appropriate energy levels, good thermal stability, and excellent charge carrier mobility. [8] However, these inorganic HILs are usually prepared by annealing a precursor layer at relatively high temperatures, which thus limits the application of these materials in flexible electronic products.…”

Efficient Trilayer Phosphorescent Organic Light-Emitting Devices Without Electrode Modification Layer and Its Working Mechanism

“…For example, deoxyribonucleic acid-cetyltrimetylammonium complex can act as hole-transporting layers (HTL) because of high hole mobility, meanwhile the low lowest unoccupied molecular orbital (LUMO) energy level makes it suit for the EBL [ 4 ]. 4,4′,4″-Tris (carbazol-9-yl)-triphenylamine (TCTA) is usually used to be HTL; besides, it can also serve as the host in emitting layer (EML) because of its high triplet energy [ 5 , 6 ]. Hence, it is possible to simplify the structure without sacrificing the device performance by choosing appropriate material.…”