Highly Efficient Deep-Red Non-Doped Diodes Based on a T-Shape Thermally Activated Delayed Fluorescence Emitter.

Device simplification is of practical significance for organic light emitting diodes (OLEDs), and remains the great challenge for deep-red emitters. Herein, a deep-red thermally activated delayed fluorescence molecule (pTPA-DPPZ) is reported which features a T shaped structure containing two triphenylamine (TPA) donors, one either side of a planar dipyridophenazine (DPPZ) acceptor. The rational spatial arrangement of the functional groups leads to limited but sufficient molecular packing for effective carrier transport. The neat pTPA-DPPZ film achieves an around 90-fold improved radiation rate constant of 107  s-1 and the nearly unitary reverse intersystem crossing (RISC) efficiency, as well as accelerated emission decays for quenching suppression. The high radiation and RISC result in a photoluminescence quantum yield of 87 %. The bilayer OLED based on the pTPA-DPPZ emissive layer achieved the record external quantum efficiencies of 12.3 % for maximum and 10.4 % at 1000 nits, accompanied by the deep-red electroluminescence with the excellent color purity.