LAUSR

Abstract Two fluorescent emitters, namely, phenylbis(4-(3,3″,6,6″-tetra- tert -butyl-9′H-[9,3′:6′,9″-tercarbazol]-9′-yl)phenyl)phosphineoxide (TPPOCz) and 9′,9‴′-(sulfonylbis(4,1-phenylene))bis(3,3″,6,6″-tetra- tert -butyl-9′H-9,3′:6′,9″- tercarbazole) (DBSOCz) are constructed. These compounds emit deep-blue and bluish-green signals and feature triphenylphosphine oxide/sulfonyldibenzene as electron acceptor core and carbazole dendrite as electron donor encapsulation groups. A simple construction strategy functionalizes these emitters to exhibit high thermal stability, suitable highest occupied molecular orbital/lowest unoccupied molecular orbital levels, relatively high photoluminescent quantum yields, and good film-forming capability. Emission spectrum and quantum computation were used to confirm that TPPOCz and DBSOCz possess small singlet–triplet energy splitting (0.22 and 0.10 eV). As a result, these fluorescent emitters exhibit significant thermally activated delayed fluorescence features with a short delayed fluorescence lifetime. Consequently, solution-processed OLEDs featuring DBSOCz as the non-doped emitter achieved a maximum current efficiency of 15.5 cd/A and external quantum efficiency of 7.65%. Surprisingly, the DBSOCz-based device exhibits an ultraslow current efficiency roll-off of 4.5% at a high luminance of 3000 cd/m 2 . The value represents almost the lowest attenuation of current efficiency in thermally activated delayed fluorescence-based OLEDs.