Precise Molecular Design of TADF Sensitizer With Balanced Exciton Dynamics for High‐Performance Narrowband Hyperfluorescence OLEDs

ABSTRACT Hyperfluorescence (HF) organic light‐emitting diodes (OLEDs) hold great promise for next‐generation displays for the simultaneously high color‐purity, high efficiency, and long operational stability. However, the development of purely organic thermally activated delayed fluorescence (TADF) sensitizers remains challenging because efficient exciton harvesting, spin conversion, and energy transfer require a delicate balance among multiple competing excited‐state processes. Here, we report a molecular design strategy that enables balanced exciton dynamics through the concurrent optimization of reverse intersystem crossing (RISC), intersystem crossing, radiative decay, and nonradiative loss. By integrating a trifluoromethyl‐functionalized multi‐resonance acceptor with a rigid donor featuring enhanced spin‐orbit coupling characteristics as well as an optimized donor–acceptor geometry, the resulting heavy‐atom‐free TADF sensitizers exhibit near‐unity photoluminescence quantum yields, suppressed nonradiative decay, rapid RISC rate, well‐regulated spin‐conversion and radiative processes. This balanced kinetic profile minimizes exciton accumulation on the sensitizer while promoting efficient exciton transfer to the terminal emitter. Consequently, narrowband green hyperfluorescence OLEDs achieve a maximum external quantum efficiency of 36.1% and retain high efficiencies of 30.6% and 25.4% at ultra‐high brightness of 10 000 and 100 000 cd m − 2 , respectively. These results establish balanced exciton dynamics as an effective design principle for high‐performance TADF sensitizers and hyperfluorescence OLEDs.