Highly Efficient Asymmetric Multiple Resonance Thermally Activated Delayed Fluorescence Emitter with EQE of 32.8 % and Extremely Low Efficiency Roll‐Off

Abstract

Multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters show great potentials for high color purity organic light-emitting diodes (OLEDs). However, the simultaneous realization of high photoluminescence quantum yield (PLQY) and high reverse intersystem crossing rate (k RISC ) is still a formidable challenge. Herein, a novel asymmetric MR-TADF emitter (2Cz-PTZ-BN) is designed that fully inherits the high PLQY and large k RISC values of the properly selected parent molecules. The resonating extended π-skeleton with peripheral protection can achieve a high PLQY of 96 % and a fast k RISC of above 1.0 × 10 5 s À 1 , and boost the performance of corresponding pure green devices with an outstanding external quantum efficiency (EQE) of up to 32.8 % without utilizing any sensitizing hosts. Remarkably, the device sufficiently maintains a high EQE exceeding 23 % at a high luminance of 1000 cd m À 2 , representing the highest value for reported green MR-TADF materials at the same luminescence.

Narrowband emission: organic thermally-activated delayed fluorescence materials and underlying mechanisms

“…Following this, based on the parent BCz-BN and 2PTZBN , Yang and coworkers have designed two asymmetric MR-TADF emitters, Cz-PTZ-BN and 2Cz-PTZ-BN , via an asymmetrically peripheral protection strategy. 65 Both emitters show pure green emission at 510 and 505 nm, with high Φ PL of 84 and 87% in toluene, respectively. Furthermore, the introduced peripheral donor carbazole substitute provides 2Cz-PTZ-BN with a balance of a high Φ PL of 96% in 3 wt% doped films and clearly improved k risc of 1.0 × 10 5 s −1 , together with the suppression of undesired bimolecular interactions.…”

“…Based on the heavy-atom effect, the introduction of heavy atoms, such as S and Se, is effective for increasing the SOC effect and hence the improvement of the k risc . [62][63][64][65][66][67][68][69] Furthermore, incorporating S and Se atoms into the MR skeleton is a proven strategy for achieving MR-TADF-based devices with suppressed roll-off at high luminance intensity. 67,70,71 In this section, MR skeletons with incorporated O, S, or Se heteroatoms are summarized with a focus on the molecular design strategy for producing faster k risc .…”