Acceleration of reverse intersystem crossing in multi-resonance TADF emitter

The cutting-edge organic light-emitting diode (OLED) applications require high device efficiency operating at high brightness, placing high demand on the device efficiency roll-off. The rapid reverse intersystem crossing rate (kRISC) of the thermally activated delayed fluorescence (TADF) emitter is crucial for achieving high-performance OLEDs with low efficiency roll-off. Herein, we demonstrate an effective approach to accelerate the kRISC of multi-resonance TADF emitters by the synergetic long-range charge transfer and heavy-atom effect. The proof-of-concept emitter shows a rapid kRISC of 2.2 × 106 s−1 and a radiative decay rate (kr) of 4.9 × 107 s−1 together with a near-unity photoluminescence quantum yield. Leveraging these exceptional properties, the corresponding OLED devices achieve a maximum external quantum efficiency (EQE) of nearly 30% with minimal efficiency roll-off, maintaining an EQE of 25.1% even at the brightness of 10,000 cd m−2. This study offers a fresh and impactful approach to tackle the efficiency roll-off concern in OLEDs.