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

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.