Multiphosphine‐Oxide Hosts for Ultralow‐Voltage‐Driven True‐Blue Thermally Activated Delayed Fluorescence Diodes with External Quantum Efficiency beyond 20%

Highly efficient low-voltage-driven -true-blue thermally activated -delayed fluorescence diodes are realized through employing a tri-phosphine oxide host (2,2',4-tris(di(phenyl) -phosphoryl)-diphenylether (DPETPO)) with a record external quantum efficiency of 23.0% and the lowest onset voltage of 2.8 V to date.