Exciplex Hosts for Constructing Green Multiple Resonance Delayed Fluorescence OLEDs with High Color Purity And Low Efficiency Roll‐Offs

Abstract A carbazole‐based hole‐transport‐type ( p ‐type) host, BPhCz, is developed using a nonsymmetrical connection strategy between two identical groups. Two benzimidazole–triazine‐based electron acceptor materials with superior electron transport abilities, namely SFX‐PIM‐TRZ and DSFX‐PIM‐TRZ, are designed to fabricate exciplex‐host systems combined with BPhCz. Exciplexes exhibit excellent carrier transport characteristics and appropriate energy levels and can serve as hosts for green multiple resonance‐induced thermally activated delayed fluorescence (MR‐TADF) devices. Efficient green MR‐TADF organic light‐emitting diodes with high color purity and low efficiency roll‐offs are successfully fabricated using the exciplexes prepared from BPhCz:SFX‐PIM‐TRZ and BPhCz:DSFX‐PIM‐TRZ as hosts, which show low driving voltages of 2.6 and 2.7 V, high maximum external quantum efficiencies (EQEs) of 35.7% and 35.5%, ultrapure green emission with Commission Internationale de L'Eclairage coordinates of (0.27, 0.69) and (0.28, 0.69), and high EQEs of 31% and 30.5% at 1000 cd m −2 , respectively.