shows low efficiency roll-off of 16% with EQE of 20.2% at 1000 cd m -2 , which is better than that of SP-OLED with tBuCz2m2pTRZ where at 500 cd/m2 the efficiency roll-off was 14% (EQE500 of 22.7%). Although the device with tBuCzCO2HDCzB can also show narrowband green emission with a λEL at 498 nm and CIE coordinates of (0.15, 0.56), the EQEmax decreased significantly to 12.5% at 433 cd m -2 and the EQE1000 was only 9.5%. The EQE of the nondoped device employing 2GtBuCzCO2HDCzB as the emitter, at 1000 cd m -2 , is one of the best among the green SP-OLEDs, and the best amongst the green solution-processed MR-TADF OLEDs (Figure ). Despite both emitters having only moderate kRISC, the enhanced