Metal-Perturbed Multiresonance TADF Emitter Enables High-Efficiency and Ultralow Efficiency Roll-Off Nonsensitized OLEDs with Pure Green Gamut.

Abstract

Multiresonance (MR)-induced thermally activated delayed fluorescence (TADF) emitters based on B- and N-embedded polycyclic aromatics are desirable for ultrahigh-definition organic light-emitting diodes (OLEDs) due to their high photoluminescence quantum yield (PLQY) and narrow bandwidth. But the reverse intersystem crossing (RISC) rates of MR-TADF emitters are usually small, resulting in severe device efficiency roll-off at high brightness. To solve this issue, a sensitizer for the MR-TADF emitter has been required. Herein, a new MR-TADF emitter is developed through coordination of Au with B/N-embedded polycyclic ligand. Benefitting from the Au perturbation, the RISC rate is dramatically accelerated to 2.3 × 10⁷ s^-1 , leading to delayed fluorescence lifetime as short as 4.3 µs. Meanwhile, the PLQY of 95% and full width at half maximum of 39 nm (0.18 eV) are essentially unchanged after metal coordination. Therefore, a high PLQY, short delayed fluorescence lifetime, and high color purity are concurrently realized in a single TADF emitter. Accordingly, vacuum-deposited OLEDs exhibit high-performance electroluminescence with a maximum external quantum efficiency (EQE) of 35.8% without sensitization. The EQE is maintained as high as 32.3% at 10 000 cd m^-2 . Furthermore, solution-processed OLED based on the emitter also achieves excellent performance with a maximum EQE of 25.7% and a small efficiency roll-off.