Management of Multi-Energy-Transfer Channels and Exciton Harvesting for Power-Efficient White Thermally Activated Delayed Fluorescence Diodes

White organic light-emitting diodes (WOLEDs) based on thermally activated delayed fluorescence (TADF) emitters attract considerable attention owing to the advantages of full exciton harvesting, low cost, and environmental sustainability. However, compared to phosphorescent counterparts, the power efficiencies of TADF-based WOLEDs lag behind. Herein, a newly synthesized TADF emitter named DPPZ-DMAC featuring near-zero singlet−triplet splitting and high photoluminescence quantum yield (91.6%) is utilized as an ideal orange-yellow dopant for realizing a power-efficient WOLED with a mixed system consisting of a blue TADF sensitizer and a conventional fluorescent host. The balanced carrier transport, modulated energy transfer and exciton harvesting, and less exciton quenching can be realized simultaneously. Eventually, a warm WOLED is achieved with an external quantum efficiency of ≈30%, power efficiency of >80 lm W^-1, turn-on voltage of 2.5 V, and correlated color temperature of 3600 K. Moreover, the color coordinate of the resulting white emission is close to the standard blackbody radiation and can be precisely tuned inside the specific quadrangles given by the American National Standard Institute (ANSI), revealing a large prospect for indoor health lightings.