Fluorophore-Bridge-Fluorophore Architecture for Efficient Narrowband Pure Green Electroluminescence

Abstract

Developing narrowband multiple resonance thermally activated delayed fluorescence (MR-TADF) materials for concentration-independent organic light-emitting diodes (OLEDs) with high efficiency and color purity is still a challenge. Herein, a fluorophore-bridge-fluorophore architecture is developed, resulting in two MR-TADF materials (BNCz-n-POABNCz and POABNCz-n-POABNCz) by “face-to-face” arrangement of BNCz (based on carbazole unit) and POABNCz (based on carbazole and phenoxazine groups) cores sterically on the naphthalene bridge. Two materials show green emissions peaking at 501/516 nm with full-width at half-maximum values of 30/33 nm in toluene and photoluminescence quantum yields of 94%/87% in doped films, respectively. Remarkably, the POABNCz-n-POABNCz exhibits high color purity with Commission Internationale de L'Eclairage coordinates of (0.19, 0.71), reaching the National Television System Committee standard for pure green emission. Furthermore, the OLEDs D1 and D2 composing BNCz-n-POABNCz and POABNCz-n-POABNCz illustrate maximum external quantum efficiencies (EQE_max) of 32.0% and 33.6%, respectively. Even at a doping ratio of 20 wt%, D2 still remains an EQE_max ≈28.5%.