A new rigid diindolocarbazole donor moiety for high quantum efficiency thermally activated delayed fluorescence emitterElectronic supplementary information (ESI) available: Material synthesis, material characterization, theoretical calculation data, photo-physical properties, device fabrication and performances. CCDC 1534408. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7tc04852a

In this communication, we report an excellent new highly conjugated and rigid electron donor (diindolocarbazole) for thermally activated delayed fluorescence (TADF) emitters. The donor-acceptor structure with diindolocarbazole donor induces high oscillator strength as well as high probability for the radiative transition, suitable frontier molecular overlap with proper intramolecular charge transfer and a large dihedral angle with out-of-plane structure between electron donor and acceptor; this results in high photoluminescence quantum yield, small singlet-triplet energy splitting, and extremely short delayed fluorescence exciton lifetime. The fabricated organic light emitting diode with new donor applied green emitter exhibits a remarkably high external quantum efficiency of 31.4% without any out-coupling technique. It also shows extremely low efficiency roll-off characteristics with the highest luminance of 71 160 cd m −2 as well as good operational device stability. We report a new electron donor moiety (diindolocarbazole) for high performances of thermally activated delayed fluorescence emitters.