Thermally activated delayed fluorescence exciplex sensitizers with fast reverse intersystem crossing for improving efficiency stability of organic light-emitting diodes based on multi-resonance emitters

Abstract

Organic luminescent materials often show novel optical properties that are different from those in the isolated state when forming aggregates, which have attracted increasing attention due to the potential applications in diverse research frontiers. In this work, two planar and rigid polycyclic aromatic hydrocarbons (QOPTZ and QOAD) embedded with carbonyl and sulfone groups are synthesized. They show normal fluorescence in toluene solutions but delayed fluorescence when doped in 3,3′-di-(9H-carbazol-9-yl)-1,1′-biphenyl (mCBP) host. Experimental and theoretical results reveal that the electron-deficient QOPTZ and QOAD can form exciplexes with electron-rich mCBP, and the strong intermolecular donor-acceptor interactions result in orbital degeneracy and narrowed singlet-triplet energy splitting, opening effective reverse intersystem crossing channels for the occurrence of delayed fluorescence. The organic light-emitting diodes (OLEDs) based on the exciplexes achieve high maximum external quantum efficiencies (EQE_maxs) of up to 24.8%. Moreover, efficient green hyperfluorescence OLEDs are fabricated by employing these exciplexes as sensitizers for multi-resonance emitters, realizing the improved EQE_maxs of 32.7% with greatly reduced efficiency roll-offs. These results are conducive to the development of efficient and stable exciplex-based OLEDs.