Importantly, besides the high EQEmax of 17.4% and high maximum luminance (Lmax) of 4707 cd m -2 , device 3 showed an improved efficiency roll-off of 32.2% at 100 cd/m 2 compared to devices 1 (34.5%) and 2 (38.9%). To further optimize the device, the doping concentration was increased to 3 wt% to improve the bipolar carrier balance (device 4). Despite a slightly reduced EQEmax of 16.5%, which was attributed to the decreased FPL of 82%, device 4 showed higher a Lmax of 5574 cd m -2 and better roll-off (24.8%) at 100 cd/m 2 . Device 4 arguably represent the best performing OLED of the reported carbonyl-based pure blue (CIEx+CIEy < 0.3) MR-TADF OLEDs (Table and Figure ).