π‐Extended Phenoxazine‐Based Asymmetric MR‐TADF Emitters for Narrow Emission Band Green OLEDs with a Power Efficiency of 150 lm W<sup>−1</sup>, an EQE of 27%, and an LT<sub>95</sub> of Over 3000 h at 1000 cdm<sup>−2</sup>
Haruki Nemma, Yuma Kori, Naoki Meguro, Ryunosuke Mimura, Yudai Chiba, Junji Kido, Hisahiro Sasabe
Abstract
Abstract Although multi‐resonance thermally activated delayed fluorescent (MR‐TADF) emitters simultaneously achieve high color purity and high efficiency in organic light‐emitting devices (OLEDs), MR‐TADF‐based OLEDs suffer from severe efficiency roll‐off and lifetime issues for practical application. To overcome these issues, a key solution is hyper OLED technology sensitized by TADF or phosphorescent emitters. In this study, a series of π‐extended phenoxazine‐based asymmetric MR‐TADF emitters for long lifetime, low‐power consumption, and narrow emission band green OLEDs is developed. As a sensitizer, a well‐known phosphorescent emitter is used, fac ‐tris(2‐phenylpyridinato‐C2,N)iridium(III) [Ir(ppy) 3 ]. Consequently, these MR‐TADF emitters achieve hyper OLEDs with a power efficiency of 150 lm W −1 , an external quantum efficiency of 27%, and a long lifetime LT 95 of over 3000 h at high brightness of 1000 cdm −2 . These performances are among the best in scientific literature.