Polycyclic phenazine-derived rigid donors construct thermally activated delayed fluorescence emitters for highly efficient orange OLEDs with extremely low roll-off

Two new thermally activated delayed fluorescence (TADF) molecules, tBuInPz-BO and InPz-BO, are constructed via connecting novel rigid polycyclic phenazine-derived donors with oxygen-bridged boron acceptor. Both emitters exhibit fast reverse intersystem crossing rates and high photoluminescence quantum yields, owing to the high molecular structural rigidity. As a result, the orange organic light-emitting diode (OLED) fabricated with tBuInPz-BO shows a maximum external quantum efficiency (EQEmax) of 22.0% with the electroluminescence peak at 585 nm. Moreover, the device displays extremely low efficiency roll-off. At high luminance of 1000 and 10000 cd/m2, the EQE values still maintain a high level of 20.2% and 14.8%, respectively, achieving state-of-the-art electroluminescence performance among TADF-based orange OLEDs. This work reveals the great potential of the new phenazine-derived donors for constructing highly efficient TADF emitters.