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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. [ABSTRACT FROM AUTHOR]