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.

Regulating the Nature of Triplet Excited States of Thermally Activated Delayed Fluorescence Emitters

“…On the other hand, for catering to the various molecular systems, new controlling mechanisms of triplet properties should be further explored. Similar to halogenation, incorporating electronwithdrawing phosphine oxide groups 48 or metal perturbation 49 into TADF emitters is a possibly feasible pathway. Utilizing the characteristics of triplet valleys of spirofluorene or spirofluorene xanthene instead of fluorene as the confined skeleton is also a promising strategy for regulating the triplet nature.…”

Recent advances and prospects for organoboron-based thermally activated delayed fluorescence emitters

“…The EQE max of the 177 device was 35.8% and EQE remained at 32.3% at 10 000 cd m −2 . 101 Heavy-atom integration into the TADF molecule could significantly promote the RISC process. Subsequently, they further reported a pure green multi-resonance TADF molecule 178 and 179 by introducing a peripheral heavy atom selenium onto the parent BN-Cz molecule.…”

Spirofluorene-locked carbazole based multiple resonance thermally activated delayed fluorescence emitters for efficient solution-processed narrowband green OLEDs

“…Yang et al also reported green MR-TADF emitters through coordination of Au with B, N-doped PAH cores, which exhibit high RISC rate constants (2.3 × 10 7 s −1 ) and small device efficiency roll-off at high luminance. 37 However, it should be noted that the majority of present MR-TADF-based OLEDs were fabricated by vacuum deposition, while the development of solution-processed MR-TADF emitters suitable for the fabrication of low-cost and large-area OLEDs has lagged behind and is still to be addressed. 38–43…”