Rational Multidimensional Shielded Multiple Resonance Emitter Suppresses Concentration Quenching and Spectral Broadening for Solution-Processed Organic Light-Emitting Diodes

Thermally activated delayed fluorescence (TADF) emitters
based
on multiple resonance (MR) effects are promising for high-definition
organic light-emitting diodes (OLEDs) with narrowband emission and
high efficiency. However, they still face the challenges of aggregation-caused
quenching (ACQ) and spectral broadening. Solution-processable MR-TADF
emitters with an external quantum efficiency (EQE) of >20% and
a full
width at half-maximum (fwhm) of <30 nm have rarely been reported.
To construct ACQ-resistant emitters without sacrificing color purity,
the aggregation-induced MR-TADF material 6TBN with a
rigid B,N-containing polycyclic aromatic hydrocarbon core and four
carbazole substituents as well as 12 tert-butyl groups
on the periphery is designed. The multidimensional shielded effect
largely limits the ACQ, intermolecular interactions, and spectral
broadening. Consequently, solution-processed OLEDs based on 6TBN exhibit a maximum EQE of 23.0% and high color purity
with a fwhm of 25 nm. Furthermore, the nondoped device achieves a
high efficiency (12.3%) and merely a slight widening of the fwhm to
27 nm. This work provides a feasible strategy to achieve MR-TADF materials
with resistance to concentration quenching and high color purity.