Overcoming power efficiency limitation of white fluorescence light‐emitting diodes via multilevel‐hydrogen‐bond matrix

Abstract High power efficiency and low efficiency roll‐off at practical luminance are two requirements for new‐generation energy‐saving lighting technologies, which are still bottlenecks of thermally activated delayed fluorescence (TADF) white organic light‐emitting diodes (WOLED), despite the advantages of TADF materials and devices in low cost and high sustainability. Herein, we developed a spiro phosphine oxide host named SSOXSPO, which can form multiple and multidirectional intermolecular hydrogen bonds (IHB). The resulted multilevel IHB network integrates long‐range ordered and short‐range disordered alignments for suppressing triplet‐polaron quenching (TPQ) and triplet‐triplet annihilation (TTA). Electronic characteristics of SSOXSPO matrix are further regulated, leading to the optimal exciton allocation through balancing energy and charge transfer. As consequence, using SSOXSPO as host, the single‐emissive‐layer TADF WOLEDs realized the record performance, including ultralow operation voltage as ∼4.0 V, power efficiency beyond fluorescent tube (70.1 lm W−1) and negligible external quantum efficiency roll‐off (3%) at 1000 nits for indoor lighting. This work demonstrates that multiple interplays supported by host matrixes in TADF WOLEDs can facilitate the synergistic effects of TADF emitters on 100% exciton utilization