Multiple Charge Transfer Processes Enable Blue Emitter for Highly Efficient OLEDs

Abstract Solely through‐space charge transfer (TSCT)‐type thermally activated delayed fluorescent (TADF) emitters exhibit low radiative decay rates (), while solely through‐bond charge transfer (TBCT) type TADF emitters generally suffer from low reverse intersystem crossing (RISC) rates ( k RISC ). Here, PhCzSpiroS‐TRZ with versatile spiro‐heterocyclic architecture and an extra donor of 9‐phenyl‐9H‐carbazole are developed as emitter and ideal host for TADF‐ and TADF‐sensitized fluorescence (TSF) organic light‐emitting diodes (OLEDs) in detail. Abandoning solely TSCT or TBCT process, PhCzSpiroS‐TRZ with multiple charge transfer characteristic exhibits photoluminescence quantum yield of 96.3% and of 2.2 × 10 7 s −1 , which is considerably higher among all the reported TSCT‐TADF molecules. Noticeably, state‐of‐the‐art blue OLEDs using PhCzSpiroS‐TRZ as emitter and sensitizer show maximum external quantum efficiencies (EQEs) of 33.6% and 32.8%, ranking among TADF materials for achieving EQEs >30% in both TADF‐ and TSF‐OLEDs.