Phosphine Oxide Linkage Manipulating Trinuclear Iridium(III) Complex for High‐Efficiency Bilayer Nondoped Organic Light‐Emitting Diodes

Developing high‐efficiency nondoped phosphorescence (PH) organic light‐emitting diodes (OLEDs) by solution processing is still a big challenge, due to high demand on quenching suppression ability of phosphors. Here, phosphine oxide (PO) linkage is incorporated between Ir 3+ complexed cores of a trinuclear phosphorescent emitter named [Ir(PBI) 2 ] 3 TPBIPO. The emission spectra of single‐molecular [Ir(PBI) 2 ] 3 TPBIPO is identical to its mononuclear congeners, but its frontier molecular orbitals (FMO) and triplet state location are separated by electron‐withdrawing effect of P=O. Furthermore, by virtue of tetrahedral configuration of sp 3 ‐hybrid PO linker, steric hindrance of [Ir(PBI) 2 ] 3 TPBIPO is enhanced by locking the spatial orientations of the cores and vanishing packing freedom, giving rise to the effectively suppressed triplet quenching. As a consequence, neat [Ir(PBI) 2 ] 3 TPBIPO film achieves a photoluminescence quantum yield of ≈90%, and a state‐of‐the‐art external quantum efficiency of 23.2% at 1000 nits from its spin‐coated bilayer non‐doped OLEDs.