Solution-processed aggregation-induced delayed fluorescence (AIDF) emitters based on strong π-accepting triazine cores for highly efficient nondoped OLEDs with low efficiency roll-off.

Abstract Currently, aggregation-induced delayed fluorescence (AIDF) is the most potential method that overcomes the limitations of thermally activated delayed fluorescence (TADF) emitters. Herein, to develop high efficient AIDF emitters, a novel strategy of introducing carbazole dendrites to a strengthen electron acceptor to construct D−π−A structure has been presented. Two emitters, namely diphenyl(4-(4-phenyl-6-(4-(3,3″,6,6″-tetra- tert -butyl-9′H-[9,3':6′,9″-tercarbazol]-9′-yl)phen yl)-1,3,5-triazin-2-yl)phenyl) phosphine oxide (CzTAZPO) and diphenyl(4-(4-phenyl-6-(4-(3,3″,6,6″-tetra- tert -butyl-9′H-[9,3':6′,9″-tercarbazol]-9′-yl)phenyl)-1,3,5-triazin-2-yl)phenyl)phosphine oxide (sCzTAZPO) with a twisted carbazole dendrites structure are synthesized and investigated theoretically and experimentally. Both compounds show aggregation-induced emission, a prominent TADF and bipolar properties. The reasonable molecular design strategy allows CzTAZPO to exhibit high oscillator strengths (f) and small singlet–triplet energy gap (Δ E ST) at the same time, which signifcantly increase the rate of reverse intersystem crossing process and fluorescence quantum efficiency. High-performance nondoped OLEDs are fabricated with CzTAZPO neat films as the emission layers, providing excellent maximum current efficiency (CE max) and maximum external quantum efficiency (EQE max) of 29.1 cd A−1 and 12.8%, respectively. More importantly, nondoped OLEDs provided negligible EQE roll-off of 1.6% from the maximum values to those at 1000 cd m−2. The AIDF emitters with small Δ E ST , high photoluminescence quantum yields (Φ PL), bipolar charge transport and high rate constant of reverse intersystem crossing process are promising candidates for OLEDs that are roll-off-free and possess high efficiency. Graphical abstract Image 1 Highlights • A strategy to construct solution-processed AIDF was proposed. • Two solution-processed AIDF emitters were designed and synthesized. • CzTAZPO exhibit high oscillator strengths and small singlet–triplet energy gap. • CzTAZPO based nondoped OLED shown high efficiencies (EQE>12%) and low roll-off (<1.6%). • This strategy would be a promising method for efficient and stable OLEDs. [ABSTRACT FROM AUTHOR]