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

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. Two pairs of exciplexes are developed as hosts for constructing green organic light-emitting diodes (OLEDs) with high efficiency and color purity. The OLEDs achieve ultrapure green emission with a peak wavelength of 532 nm, full-width at half-maximum of 36 nm, high external quantum efficiency (EQE) of 35.7%, and reduced efficiency roll-off with EQE of 31.0% at 1000 cd m-2.image