Construction of Efficient Deep-Red/Near-Infrared Emitter Based on a Large π-Conjugated Acceptor and Delayed Fluorescence OLEDs with External Quantum Efficiency of over 20%

Organic light-emitting materials with thermally activated delayed fluorescence (TADF) are promising for promoting the efficiency of organic light-emitting diodes (OLEDs) without any precious metals. However, the device performance of the deep-red/near-infrared (DR/NIR) TADF-OLEDs remains backward compared with that of blue, green, and orange-red TADF-OLEDs. In this contribution, a donor–acceptor type TADF emitter, 2-(tert-butyl)-6-(4-(diphenylamino)phenyl)phenanthro[4,5-abc]phenazine-11,12-dicarbonitrile, namely, TPA-PPDCN, containing a large rigid phenanthro[4,5-abc]phenazine-11,12-dicarbonitrile as an acceptor unit and a triphenylamine (TPA) as a donor moiety, is designed and synthesized. The compound exhibits excellent thermal stability, small singlet–triplet energy split and a strong DR/NIR emission with the photoluminescence quantum yields of 73–87% in doped thin films. More importantly, highly efficient DR and NIR OLEDs with emission peaks at 664 and 692 nm and the maximum external quantum efficiencies of 20.2 and 16.4%, respectively, have been achieved, which represent the highest device performance among the reported DR/NIR TADF OLEDs.