Twisted Structure and Multiple Charge‐Transfer Channels Endow Thermally Activated Delayed Fluorescence Devices with Small Efficiency Roll‐Off and Low Concentration Dependence

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. A twisted TADF molecule, mClSFO, is synthesized to reduce efficiency roll‐off and concentration dependence in OLEDs. 30 wt % doped OLED exhibits best performance with an EQEmax of 23.1 % with small efficiency roll‐off, maintaining an EQE of 18.6 % at 1000 cd m−2.