New‐Fashioned Universal and Functional Host‐Material from a Near‐Ultraviolet Organic Emitter for High‐Efficiency Organic Light‐Emitting Diodes with Low Efficiency Roll‐Offs

In this work, a near-ultraviolet (NUV) emitter, 2MCz-CNMCz, with hot-exciton property is designed based on a "long-short axis" strategy, which exhibits good thermal stability, bipolar carrier transport ability, and high T₁ energy level. Its nondoped NUV organic light-emitting diode (OLED) achieves a record maximum external quantum efficiency (η_ext ) of 7.76%, with a peak at 404 nm and CIE coordinates of (0.158, 0.039). The corresponding high exciton utilization efficiency (η_r ) in the electroluminescence process reveals its potential as a functional sensitizing host. As expected, the TBPe-based blue fluorescent OLED with 2MCz-CNMCz as the host material shows better efficiency and lower efficiency roll-off than that with traditional host material mCP. Meanwhile, the Ir complexes-based green/yellow/red phosphorescent OLEDs with 2MCz-CNMCz host are also fabricated, reaching high η_ext values of 26.1%, 30.4%, and 20.4%, respectively, and displaying negligible efficiency roll-offs at 1000 cd m^-2 , which are among the best OLED performances based on the same emitters. To the authors' best knowledge, this is the first report on the design of high-quality universal and functional host material, and may bring new inspiration to the preparation of high-efficiency, low roll-off, full-color OLEDs.