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

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(R)(ISC)) is still a formidable challenge. Herein, a novel asymmetric MRTADF 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 pi-skeleton with peripheral protection can achieve a high PLQY of 96 % and a fast k(RISC) of above 1.0 x 10(5) s(-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(-2), representing the highest value for reported green MR-TADF materials at the same luminescence.

Automated summary

In this study, a novel asymmetric MRTADF emitter (2Cz-PTZ-BN) is designed with high PLQY and large k(RISC) values, enhancing the performance of pure green OLEDs. It maintains a high EQE even at high luminance, representing the highest value among reported green MR-TADF materials.