Abstract
Despite the rapid development of thermally activated delayed fluorescent (TADF) materials, developing organic light-emitting diodes (OLEDs) with small efficiency roll-off remains a formidable challenge. Herein, we have designed a TADF molecule (mClSFO) based on the spiro fluorene skeleton. The highly twisted structure and multiple charge-transfer channels effectively suppress aggregation-caused quenching (ACQ) and endow mClSFO with excellent exciton dynamic properties to reduce efficiency roll-off. Fast radiative rate (kr) and rapid reverse intersystem crossing (RISC) rate (kRISC) of 1.6 × 107 s-1 and 1.07 × 106 s-1, respectively, are obtained in mClSFO. As a result, OLEDs based on mClSFO obtain impressive maximum external quantum efficiency (EQEmax) exceeding 20% across a wide doping concentration range of 10-60 wt%. 30 wt% doped OLED exhibits an EQEmax of 23.1% with a small efficiency roll-off, maintaining an EQE of 18.6% at 1000 cd m-2. The small efficiency roll-off and low concentration dependence observed in the TADF emitter underscore its significant potential.
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