Asymmetric intramolecular charge transfer enables highly efficient red thermally activated delayed fluorescent emitters

•“Asymmetric D-A-wA” strategy is demonstrated for high-efficiency red TADF emitters.•Diphenylphosphine oxide as the second acceptor markedly improves TADF properties.•Strong red emission peaked at 645 nm with a high PLQY of 94.7 % is realized.•The maxima of 19360 cd m−2 for luminance and 11.4 % for EQE at 632 nm are achieved.