Manipulation of the sterically hindering effect to realize AIE and TADF for high-performing nondoped solution-processed OLEDs with extremely low efficiency roll-off†
Robust luminogens with thermally activated delayed fluorescence (TADF) and aggregation-induced emission (AIE) characteristics are desirable for high efficiency, low efficiency roll-off and low-cost organic light-emitting diodes (OLEDs). Derived from the 2,4,5,6-tetra(carbazol-9-yl)-1,3-dicyanobenzene (4CzIPN) framework, two TADF-characterized luminogens, 4CzIPN-MO and 4CzPhIPN-MO, are presented in this paper. Encouragingly, along with the carbazole fragment modification of 4CzIPN by using methoxy groups, an unexpected AIE behavior can be observed as for 4CzPhIPN-MO with the insertion of phenyl-bridges between the carbazole moieties and the central benzene ring. The advantages of the novel designed 4CzPhIPN-MO structure are found to be capable to reduce the injection barrier, suppress nonradiative decay, and increase the solid-state photoluminescence (PL) efficiency. Consequently, the nondoped OLED performs outstandingly with a maximum EQE of 14.5%, and extremely low efficiency roll-off of 3.8% and 3.9%, respectively, at a luminance of 100 and 1000 cd m−2, which is among the best EQE roll-off performance of nondoped solution-processed TADF OLEDs reported so far. This work demonstrates that the manipulation of the molecular topologies is a promising and practical strategy for achieving efficient and stable solution-processed OLEDs.