Multiple resonance delayed fluorescence emitter with C3 symmetry for high-performance solution-processed OLEDs

Abstract

Solution-processed organic materials that exhibit both high emission efficiency and narrowband emission characteristics are rare, and the performance of corresponding solution-processed organic light-emitting diodes (sOLEDs) remains inadequate for practical applications. This study proposes a proof-of-concept design aimed at enhancing both solution processing capability and emission efficiency in multiple-resonance induced thermally activated delayed fluorescence (MR-TADF) materials through the integration of multiple emitting units. A unique emitter named TriBNCz is synthesized and characterized, incorporating three MR-building blocks onto a single phenyl ring, resulting in sky-blue emission with a peak at 490 nm and a small full width at half maximum (FWHM) of 25 nm. Significant improvements in solution processing attributes, including solubility and film-forming properties, are achieved. Moreover, except for the MR effect of the excited states, long-range charge transfer properties of excited states are also obtained. The multiple charge transfer channels contribute to higher rate of reverse intersystem crossing (kRISC). The optimized sOLED device exhibits a maximum external quantum efficiency (EQEmax) of 17.8 %. Furthermore, by employing 5TCzBN as a sensitizer, the sensitized sOLED achieves an EQEmax of 28.8 % and a high-level EQE of 26.1 % at 1000 cd m−2, with an FWHM of 30 nm and Commission Internationale de I’Éclairage (CIE) coordinates of (0.103, 0.497), representing one of the best results among narrowband emission sOLEDs. This research opens a new avenue to develop high-performance solution-processed organic materials and sOLED devices.