Carbazole-dendrite-encapsulated electron acceptor core for constructing thermally activated delayed fluorescence emitters used in nondoped solution-processed organic light-emitting diodes

摘要

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 func-tionalizes 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.