Systematical Investigation of Ultrathin Doped Emissive Layer Structure: Achieving Highly Efficient and Long‐Lifetime Orange Organic Light‐Emitting Diodes

Abstract

Phosphorescent organic light‐emitting diodes (PhOLEDs) with ultrathin emissive layer (UEML) structure have great potential in solid‐state lighting and display applications due to their relatively simple fabrication process. In this paper, the effect of doped UEML architecture on the performance of orange PhOLEDs is systematically investigated and highly efficient and long‐lifetime devices with the doped UEML structures are successfully constructed. Through strategic exciton management, the probability of exciton recombination is significantly enhanced, while simultaneously that of exciton annihilation is greatly suppressed, along with excellent charge balance. The resulting orange PhOLEDs based on tris[2‐(2‐pyridyl) imidazole] gallium(III):bis (2‐phenylbenzothiazolato) (acetylacetonate) iridium as emitter exhibit a maximum current efficiency of 60.8 cd A−1, power efficiency of 65.8 lm W−1, and external quantum efficiency of 23.4%, respectively. In addition, the doped UEML architecture greatly extends the device operational stability with a nearly fourfold lifetime improvement (time to reduce to 50% of the initial luminance at 2300 cd m−2) over the conventional phosphorescent device with doped bulk emitting layer. This should be the best results reported so far for orange PhOLEDs, indicating the use of doped UEML structure displays great potential value in designing highly efficient and long‐lifetime PhOLEDs.

Progress in Research on White Organic Light-Emitting Diodes Based on Ultrathin Emitting Layers

“…The selection of materials and the rationality of device structures play crucial roles in the performance of WOLEDs based on UEMLs [13]. Considering that the main mechanism of WOLEDs based on UEMLs is typically energy transfer between host and guest molecules, the efficiency of devices can be enhanced by effectively managing excitons through rational adjustments in the thickness and positioning of UEMLs, thereby broadening the exciton recombination zone and reducing triplet-triplet annihilation (TTA) [14]. For device stability, continual innovation in multifunctional emitting materials and rational device structure design is essential [15].…”

Organic Light-Emitting Diodes with Ultrathin Emitting Nanolayers

“…To discover more emission mechanisms related to UEN-based OLEDs, in 2019, Zhao et al developed high-performance orange OLEDs with UEN structures [62]. The characteristics and structure of the device with doping-free UENs are shown in Figure 2.…”

Use of Hybrid PEDOT:PSS/Metal Sulfide Quantum Dots for a Hole Injection Layer in Highly Efficient Green Phosphorescent Organic Light-Emitting Diodes

“…One of the most important issue for the OLEDs application in industry is the device efficiency. The effective charge injection and transportation, and exciton confinement in the emitting layer are the key parameters to achieve highly efficient OLEDs ( Lee et al, 1999 ; Wang et al, 2008 ; Song et al, 2018 ; Zhao et al, 2020 ). To date, many research groups have used the solution processed hole injection layer (HIL) to improve the device performance and to decrease the fabrication costs ( Li et al, 2018 ; Hu et al, 2020 ; Wang et al, 2020 ).…”