Red OLED with efficiency of 25.6% at 10,000 cd m(-2) based on selenium embedding multiple resonance framework.

Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials featuring narrowband emission and high luminescence efficiency hold great promise for ultra-high-definition displays. However, red MR emitter-based organic light-emitting diodes (OLEDs) commonly suffer from pronounced efficiency roll-off due to intrinsically slow reverse intersystem crossing (RISC), which severely hinders their practical application. Herein, we present efficient OLEDs based on a selenium-embedded red MR framework featuring fast RISC, which not only serves as a high-performance emitter but also functions as a sensitizer. The emitter (tFSeBN) shows red emission at 607 nm and achieves a record-high RISC rate of 7.5 × 10 s. The corresponding OLED delivers a maximum external quantum efficiency (EQE) of 34.7% and maintains high EQE values of 31.0% and 25.6% at luminance levels of 1000 and 10,000 cd m, highlighting its ultra-low efficiency roll-off. Owing to its high tolerance to doping concentration and accelerated RISC, tFSeBN further serves as an efficient sensitizer in hyperfluorescent OLEDs, enabling pure-red emission with CIE coordinates of (0.70, 0.30), high EQE and suppressed efficiency roll-off. This work provides a viable pathway to address the long-standing efficiency roll-off issue in red MR-OLEDs, serving as an alternative to conventional noble-metal-sensitized architectures for the red OLED industry.