Encapsulated multi-resonance TADF dendrimer with AIEE property for efficient solution-processed narrowband deep-blue OLEDs

The utilization of multiple resonances (MR) thermally activated delayed fluorescence (TADF) materials for solution-processed organic light-emitting diodes (OLEDs) faced notable challenges in severe aggregation-caused quenching (ACQ) issues. Here, we successfully developed a narrow-band deep blue MR-TADF dendrimer (2CzphQAO) for solution-processed OLEDs by introducing three flexible carbazole branches around carbonyl/N emissive core as encapsulated unit. The branches connected by alkyl chains can not only effectively avoid the severe aggregation quenching of narrowband emission, but also improve its solubility in conventional organic solvents. In addition, 2CzphQAO also exhibits clear aggregation-induced emission enhancement (AIEE) properties in the molecular packaging state, which can effectively promote exciton utilization without causing spectral broadening. The resultant encapsulated MR-TADF dendrimer was able to show bright deep-blue emission peaked at 438 nm with a full width at half maximum (FWHM) of 47 nm. The solution-processed OLEDs based on the dendrimer achieved a maximum external quantum efficiency (EQE max) of 12.1 % with Commission Internationale de l’Eclairage (CIE) coordinate of (0.13,0.14), which is among the promising device efficiency of solution-processed narrowband deep blue OLEDs. This study demonstrates that the encapsulation of rigid MR-TADF molecule will be a feasible strategy for design efficient solution-processable OLEDs with high color purity.