Highly Efficient Multiple Resonance TADF Emitters by Hybridizing Long-Range and Short-Range Charger Transfer to Enable Narrowband and Low Roll-Off OLEDs

Abstract

Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials show great potential for ultrahigh-definition organic light-emitting diodes (OLEDs) owing to their exceptional luminescence efficiencies and narrow emission spectra. Nevertheless, the device performances of MR-TADF emitters typically suffer from significant efficiency loss under high current densities due to the slow reverse intersystem crossing (RISC) rates. Here, we propose a straightforward yet effective strategy to introduce three typical spiral electron acceptor fragments to the MR framework featuring hybridized short-range charge transfer (SRCT) and long-rang charge transfer (LRCT) characteristics. Comprehensive photophysical and computational properties of these MR-TADF materials demonstrate that the electron-withdrawing difference between the three acceptor units of MR frameworks has a significant influence on the emission color, full-width at half-maximum (FWHM) and RISC rates. Remarkably, the sensitizer-free OLED based on BNAP demonstrated the best device performance, with electroluminescent peak at 512 nm, FWHM of 36 nm, the CIE coordinates of (0.17, 0.68), and the maximum external quantum efficiency (EQE) of 36.1%. The EQE values at 100 cd m-² and 1000 cd m-² were 32.8% and 16.1%, respectively, revealing that the introduction of LRCT feature can effectively modulate the energy level and harness high-energy triplet excitons to suppress efficiency roll-off.