Actualizing highly efficient solution‐processed thermally activated delayed fluorescent (TADF) organic light‐emitting diodes (OLEDs) at high brightness becomes significant to the popularization of purely organic electroluminescence. Herein, a highly soluble emitter benzene‐1,3,5‐triyltris((4‐(9,9‐dimethylacridin‐10(9H)‐yl)phenyl)methanone was developed, yielding high delayed fluorescence rate (kTADF > 105 s−1) ascribed to the multitransition channels and tiny singlet–triplet splitting energy (ΔEST ≈ 32.7 meV). The triplet locally excited state is 0.38 eV above the lowest triplet charge‐transfer state, assuring a solely thermal equilibrium route for reverse intersystem crossing. Condensed state solvation effect unveils a hidden “trade‐off”: the reverse upconversion and triplet concentration quenching processes can be promoted but with a reduced radiative rate from the increased dopant concentration and the more polarized surroundings. Striking a delicate balance, corresponding vacuum‐evaporated and solution‐processed TADF‐OLEDs realized maximum external quantum efficiencies (EQEs) of ≈26% and ≈22% with extremely suppressed efficiency roll‐off. Notably, the wet‐processed one achieves to date the highest EQEs of 20.7%, 18.5%, 17.1%, and 13.6%, among its counterparts at the luminance of 1000, 3000, 5000, and 10 000 cd m−2, respectively.
Thermally activated delayed fluorescent (TADF) materials generally suffer from severe concentration quenching. Efficient non‐doped TADF emitters are generally highly twisted aromatic amine‐based compounds with isolated chemical moieties. Herein we demonstrate that co‐facial packing and strong π–π intermolecular interactions give rise to bright TADF emissions in non‐doped film and crystalline states within the compound 2,4‐diphenyl‐6‐(thianthren‐1‐yl)‐1,3,5‐triazine (oTE‐DRZ). Quantum chemistry simulations indicate that a disperse outer orbital of sulfur atoms, a folded thianthrene plane (for a reduced donor–acceptor distance), and a triazine acceptor with n–π* character, generate a spatially conjugated transition with a small singlet–triplet splitting energy. In company with a highly emissive non‐doped film, the corresponding organic light‐emitting diode achieved a 20.6 % external quantum efficiency, verifying its potential for high‐performance optoelectronic applications. In a crystalline state, it was verified that intra‐ and intermolecular dual TADF assisted by a hidden room‐temperature phosphorescent state. This state could preserve the long‐lived excitons while suppressing non‐radiation, and it could serve as a “spring‐board” for cascade up‐conversion processes. The oTE‐DRZ crystal showed greenish‐blue emission with a very high photoluminescent quantum yield of approximately 87 %, which is the highest among all TADF crystals reported to date.
A fast radiative rate, highly suppressed nonradiation,
and a short
exciton lifetime are key elements for achieving efficient thermally
activated delayed fluorescence (TADF) organic light-emitting diodes
(OLEDs) with reduced efficiency roll-off at a high current density.
Herein, four representative TADF emitters are designed and synthesized
based on the combination of benzophenone (BP) or 3-benzoylpyridine
(BPy3) acceptors, with dendritic 3,3″,6,6″-tetra-tert-butyl-9′H-9,3′:6′,9″-tercarbazole
(CDTC) or 10H-spiro(acridine-9,9′-thioxanthene)
(TXDMAc) donors, respectively. Density functional theory simulation
and X-ray diffraction analysis validated the formation of CH···N
intramolecular hydrogen bonds regarding the BPy3-CDTC and BPy3-TXDMAc
compounds. Notably, the construction of intramolecular hydrogen bonding
within TADF emitters significantly enhances the intramolecular charge
transfer (ICT) strength while reducing the donor–acceptor (D-A)
dihedral angle, resulting in accelerated radiative and suppressed
nonradiative processes. With short TADF exciton lifetimes (τTADF) and high photoluminescence quantum yields (ϕPL), OLEDs employing BPy3-CDTC and BPy3-TXDMAc dopants realized
maximum external quantum efficiencies (EQEs) up to 18.9 and 25.6%,
respectively. Moreover, the nondoped device based on BPy3-TXDMAc exhibited
a maximum EQE of 18.7%, accompanied by an extremely small efficiency
loss of only 4.1% at the luminance of 1000 cd m–2. In particular, the operational lifetime of the sky-blue BPy3-CDTC-based
device was greatly extended by 10 times in contrast to the BP-CDTC-based
counterpart, verifying the idea that the in-built intramolecular hydrogen
bonding strategy was promising for the realization of efficient and
stable TADF-OLEDs.
Via employing a unique universal host, highly efficient full-color, white phosphorescent and TADF OLEDs were achieved with a simple and unified structure.
The effect of boronic ester substitution on the room-temperature phosphorescence of phenoxathiine-based derivatives was investigated to achieve an improved phosphorescence quantum efficiency of up to 20%.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.