A universal thermally activated delayed fluorescence (TADF) host, 4'-diphenylphosphinoylspiro[fluorene-9,9'-xanthene] (SFXSPO), is constructed with a highly distorted and asymmetric configuration and disordered molecular packing in its solid state. SFXSPO successfully endows its full-color TADF diodes with state-of-the-art performance, e.g., the record external quantum efficiency of 22.5% and 19.1% and internal quantum efficiency of ≈100% for its yellow TADF diodes and single-host full-TADF nearly-white-emitting devices, respectively.

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.

Blue thermally activated delayed fluorescence (TADF) dyes are basically combinations of strong acceptors and weak donors. In this work, a weak acceptor PO group was employed to construct a series of weak acceptor− strong donor (WASD)-type emitters with a phenoxazine donor, namely 10-(4-(diphenylphosphoryl)phenyl)-10H-phenoxazine (SPXZPO), 10,10′-(4,4′-(phenylphosphoryl)bis(4,1-phenylene))bis(10H-phenoxazine) (DPXZPO), and 10,10′,10″-(4,4′,4″-phosphoryltris(benzene-4,1-diyl))tris(10H-phenoxazine) (TPXZPO). Owing to the insulating effect of PO on conjugation extension and intramolecular electronic communications, the photoluminescence spectra of these molecules are almost identical, manifesting the superiority of WASD structure in emission color preservation. Simultaneously, the multi-dipolar characteristics of TPXZPO enhance the intramolecular charge transfer (ICT), facilitating reverse intersystem crossing for higher TADF efficiency and shorter lifetime. As a consequence, TPXZPO realized the desired pure-blue electroluminescence peak at 464 nm, accompanied by a favorable external quantum efficiency (η ext ) up to 15.3%, 100% exciton utilization, and reduced efficiency roll-offs. Its complementary full-TADF white organic light-emitting diodes also achieved η ext as high as 16.3%, among the best results reported so far for white TADF devices. The success of TPXZPO, the first example of a PO-based WASD-type blue TADF dye, is attributed to the comprehensive and harmonized effects of the PO joint on controlling conjugation and intramolecular electronic communication and the multi-dipolar structure on enhancing ICT.

Because of the sensitivity of blue thermally activated delayed fluorescence (TADF) emitters to host-dopant interactions, ambipolar host materials are absent in blue TADF diodes, partially inducing low luminance and serious efficiency roll-off. Herein, on the basis of donor-s-acceptor structure, the excited-state dipole moment of ambipolar host materials is dramatically reduced to 2 Debye, thereby restraining the host-dopant dipole-dipole interaction and related nonradiative transitions. State-of-the-art external quantum efficiency beyond 20% from the blue TADF devices, as well as record-low roll-off, is achieved.

Despite their merits of environmental friendliness, low cost, and large‐scale production, thermally activated delayed fluorescence (TADF) based white organic light‐emitting diodes (WOLEDs) for daily lighting applications still face the formidable challenges of structural simplification and controllable exciton allocation. Here, the state‐of‐the‐art full‐TADF WOLEDs with features of the single‐doped single emissive layers (EMLs) and ultrasimple trilayer structure are demonstrated. The EMLs are binary systems as yellow TADF emitter (4CzTPNBu) doped blue TADF matrix (ptBCzPO2TPTZ) with the large steric hindrance and mismatched frontier molecular orbital energy levels to effectively restrain excessive blue‐to‐yellow triplet exciton transfer and host‐dopant interaction induced triplet quenching. Simultaneously, Förster resonance energy transfer is utilized to optimize exciton allocation for the balance of blue and yellow emissions, giving rise to the photoluminescence quantum yield beyond 90%. Consequently, these single‐doped EMLs endow their cool white, pure white, and warm white diodes with the high‐quality and ultrastable white light and the 100% exciton utilization efficiencies through the extremely simple structures, making them competent for the diverse daily lighting applications.