x 10 5 s -1 , which is amongst the fastest kRISC for deep-blue MR-TADF emitters with CIEy ≤ 0.10 (Table ). ). By contrast, Device I only showed a poor EQEmax of 1.3%, which is in part due to the fact that only singlet excitons can be utilized. Additionally, the poor carrier transporting properties in device I, in which a high turn-on voltage was obtained, may contribute to the lower EQE than the theoretical value (5%).