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.