High-Efficiency Deep-Blue Narrowband Electroluminescence via Multi-Sensitization Using a D-meta-π-A Sensitizing Host

The strategic integration of thermally activated delayed fluorescence (TADF) sensitizers has emerged as a critical approach for triplet recycling in organic light-emitting diodes (OLEDs) with multiple resonance (MR) emitters. However, conventional single-sensitizer systems are frequently limited by slow exciton utilization and thus severe efficiency roll-off. This study develops a multi-sensitization strategy through the integrated design of a novel sensitizing host and parallel energy-transfer pathways to accelerate exciton utilization. The novel D-meta-π-A host exhibits a reverse intersystem crossing rate of 3.18 × 10⁶ s^-1 and a radiative decay rate of 1.94 × 10⁷ s^-1, together with balanced charge transport and blue-shifted photoluminescence in the neat film. Its photophysical behavior is consistent with contributions from both intra- and intermolecular charge-transfer (CT) states. The optimized device demonstrates remarkable electroluminescence performance with a maximum external quantum efficiency (EQE) of 37.1%, a record-high EQE of 32.4% at 5,000 cd m^-2, a turn-on voltage (at 1 cd m^-2) of 2.4 V, and a maximum power efficiency (PE) of 58.0 lm W^-1, exhibiting deep-blue emission, ultra-low power consumption, and suppressed efficiency roll-off. This work provides a viable design paradigm for high-performance MR-OLEDs through synergistic exciton management and sensitizer engineering.