High Exciton Utilization Research Articles

A Highly Twisted Carbazole-Fused DABNA Derivative as an Orange-Red TADF Emitter for OLEDs with Nearly 40 % EQE.

Multiple resonance (MR) type thermally activated delayed fluorescence (TADF) material is currently a research hotspot in organic light-emitting diodes (OLEDs) due to their high color purity and high exciton utilization. However, there are only a handful of MR-TADF emitters with emissions beyond the blue-to-green region. The very limited emission colors for MR-TADF emitters are mainly caused by the fact that so far molecular modifications of MR-TADF do not offer much change in the emission colors. Here, we report a new approach to modifying a prototypical MR core of DABNA by fusing carbazoles to the MR framework. The carbazole-fused molecule (TCZ-F-DABNA) basically maintains the MR-dominated features of DABNA while red-shifting the emission. Its OLED achieves an external quantum efficiency of 39.2 % with a peak at 588 nm, which is a record-high efficiency for OLEDs with peaks beyond 560 nm. This work provides a new approach for significantly tunning emission colors of MR-TADF emitters.

A Highly Twisted Carbazole‐Fused DABNA Derivative as an Orange‐Red TADF Emitter for OLEDs with Nearly 40 % EQE

AbstractMultiple resonance (MR) type thermally activated delayed fluorescence (TADF) material is currently a research hotspot in organic light‐emitting diodes (OLEDs) due to their high color purity and high exciton utilization. However, there are only a handful of MR‐TADF emitters with emissions beyond the blue‐to‐green region. The very limited emission colors for MR‐TADF emitters are mainly caused by the fact that so far molecular modifications of MR‐TADF do not offer much change in the emission colors. Here, we report a new approach to modifying a prototypical MR core of DABNA by fusing carbazoles to the MR framework. The carbazole‐fused molecule (TCZ‐F‐DABNA) basically maintains the MR‐dominated features of DABNA while red‐shifting the emission. Its OLED achieves an external quantum efficiency of 39.2 % with a peak at 588 nm, which is a record‐high efficiency for OLEDs with peaks beyond 560 nm. This work provides a new approach for significantly tunning emission colors of MR‐TADF emitters.

High-performance circularly polarized electroluminescence from d-f transition europium(II) complexes

Circularly polarized organic light-emitting diodes (CP-OLEDs) have attracted increasing interest for their advantages in generating circularly polarized light directly and efficiently. To date, chiral luminescent materials with different emission mechanisms have been investigated as emitters in CP-OLEDs, but it is difficult to achieve a high luminescence dissymmetry factor (g) and high efficiency simultaneously. Herein, chiral luminescent europium(II) complexes with d-f transition characteristics are synthesized and used as emitters in CP-OLEDs. The europium(II) complexes show a maximum g value of 6.6 × 10−3 in doped films, and the corresponding CP-OLEDs show a maximum external quantum efficiency up to 15.6%. The performance is attributed to the unique europium(II) complex with a d-f transition mechanism, which results in a theoretically high magnetic transition dipole moment and high exciton utilization efficiency. This study focusing on chiral d-f transition-containing lanthanide complexes opens up an avenue to future exploration of high-performance chiroptical materials.

Dual Hybridized Local and Charge Transfer Characteristic Fluorophore as an Efficient Nondoped Emitter for Electroluminescent Device

Hybridized local and charge transfer (HLCT) is an attractive strategy for achieving efficient electroluminescence (EL) in electrofluorescent devices by the conversion of triplet‐state (T) to singlet‐state (S) excitons via a reverse intersystem crossing, giving rise to a high exciton utilization efficiency exceeding the spin statistical limit. Excellent device performance is reached using thermally evaporated emissive layers. However, for potential large‐scale commercialization, it is crucial to attain comparable device performances using low‐cost solution‐processing techniques. Herein, a new concept of dual HLCT characteristic fluorophore (BCBF) with a high solid‐state fluorescence as a nondoped emitter for a simple structured solution‐processed EL device is presented. BCBF is effectively formulated by π‐conjugation linking two HLCT fragments with a highly soluble hole‐transporting aromatic moiety. Its dual HLCT and photoluminescence (PL) properties are experimentally and theoretically probed by the solvatochromic effect and density functional theory (DFT) calculations. The molecule exhibits an intense yellow–green emission with a good solution‐processed film‐forming quality and a high solid‐state fluorescence quantum yield of 80%. BCBF is successfully utilized as a nondoped emissive layer in a solution‐processed double‐layered organic light‐emitting diode (OLED), which shows excellent EL performance (brightness of 47 580 cd m−2, current efficiency of 15.78 cd A−1, and external quantum efficiency of 7.20%).

High Exciton Utilization of 1D Molecular Column with High Packing Energy Formed by Folded π-Molecules.

π-Molecules play important roles in many applications such as organic light-emitting devices, photocatalysis, photovoltaics, biosensors, and medicine. Very often, π-conjugated molecules with high utilization of excited states in the solid state are of great research interest. However, owing to the gap between molecular structure and effective molecular packing, there are very few designs toward π molecules with very high exciton utilization in the solid state. Herein, we report a new π skeleton, folded π, to achieve high exciton utilization in the solid state. Based on a "folded π" formula, 12 compounds with two or three folding π planes were designed and synthesized. We found that folded π molecules tend to form well-aligned 1D molecular columns of patterns ("box", "braid", or "stair") with high packing energy, which is mainly contributed by numerous weak π interactions. As a result of effective suppression of molecular motion, all the compounds show very high exciton utilization in solids.

New-Fashioned Universal and Functional Host-Material from a Near-Ultraviolet Organic Emitter for High-Efficiency Organic Light-Emitting Diodes with Low Efficiency Roll-Offs.

In this work, a near-ultraviolet (NUV) emitter, 2MCz-CNMCz, with hot-exciton property is designed based on a "long-short axis" strategy, which exhibits good thermal stability, bipolar carrier transport ability, and high T1 energy level. Its nondoped NUV organic light-emitting diode (OLED) achieves a record maximum external quantum efficiency (ηext ) of 7.76%, with a peak at 404nm and CIE coordinates of (0.158, 0.039). The corresponding high exciton utilization efficiency (ηr ) in the electroluminescence process reveals its potential as a functional sensitizing host. As expected, the TBPe-based blue fluorescent OLED with 2MCz-CNMCz as the host material shows better efficiency and lower efficiency roll-off than that with traditional host material mCP. Meanwhile, the Ir complexes-based green/yellow/red phosphorescent OLEDs with 2MCz-CNMCz host are also fabricated, reaching high ηext values of 26.1%, 30.4%, and 20.4%, respectively, and displaying negligible efficiency roll-offs at 1000cdm-2 , which are among the best OLED performances based on the same emitters. To the authors' best knowledge, this is the first report on the design of high-quality universal and functional host material, and may bring new inspiration to the preparation of high-efficiency, low roll-off, full-color OLEDs.

Molecular engineering of blue diphenylsulfone-based emitter with aggregation-enhanced emission and thermally activated delayed fluorescence characteristics: impairing intermolecular electron-exchange interactions using steric hindrance

Thermally activated delayed fluorescence (TADF) emitters with aggregation-enhanced emission (AEE) characteristics are in high demand in organic light-emitting diodes (OLEDs) because of their strong fluorescence and high exciton utilization under electrical excitation. In this work, an AEE-active TADF emitter, 10,10′-(5-((9-phenyl-9H-carbazol-3-yl)sulfonyl)-1,3-phenylene)bis(9,9-dimethyl-9,10-dihydroacridine) (CZ-DPS-BAD), adopting diphenylsulfone skeleton as electron-accepting segment and 9-phenylcarbazole and 9,9-dimethyl-9,10-dihydroacridine as electron donors is developed. The small singlet-triplet splitting (0.13 eV) and high photoluminescence quantum yield (82 %) of CZ-DPS-BAD can attribute to the formation of large dihedral angles between electron donor-acceptors and weak electron-exchange interaction that suppress concentration quenching and exciton annihilation. The assigned characteristics result in reverse intersystem crossing rate of up to 5.0 × 105 s−1 and a delayed fluorescence lifetime of 5.3 μs. Notably, CZ-DPS-BAD behaves excellent non-doped OLED performance with the emission peak of 486 nm, the maximum current efficiency of 47.4 cd/A, the maximum power efficiency of 46.1 lm W−1, the maximum external quantum efficiency of 20.3 %, and the exciton utilizin efficiency of 83 %. It was also found that the short delayed fluorescence lifetime impair the triplet exciton annihilation resulting small efficiency roll-off in OLED. This work provides a general approach to explore new efficient and stable emitters by rationally regulating intermolecular interactions and integrating AEE and TADF, which facilitates their applications in optoelectronics.

Highly efficient and nearly roll-off-free electrofluorescent devices via multiple sensitizations.

The efficiency roll-off at high luminance has hindered the wide application of organic light-emitting diodes (OLEDs) for decades. To circumvent this issue, both high exciton utilization and short exciton residence should be satisfied, which, however, faces formidable challenges. Here, we propose an advanced approach of phosphor-assisted thermally activated delayed fluorophor (TADF)–sensitized fluorescence, abbreviated as TPSF. It is proved to be a rational strategy that can realize high quantum efficiency and elaborately accelerated radiative exciton consumption simultaneously by breaking singlet-triplet spin-flip cycles on a TADF host via multiple sensitizations. On the basis of a TADF molecule exhibiting anti–accumulation-caused quenching character, a proof-of-concept device exhibits a maximum external quantum efficiency (EQEmax) of 24.2% with an ultrahigh L90% (the luminance at which EQE drops to 90% of its maximum value) of 190,500 cd m−2 and a greatly improved operational stability, unlocking the full potential of OLEDs for ultrahigh-luminance applications.

Intramolecular exciplex-typed molecule based on a stereoscopic V-shaped aromatic macrocycle and investigation of host-dependence of exciton utilization

Through-space charge transfer (TSCT) has been increasingly utilized for the design of efficient thermally activated delayed fluorescence (TADF) emitters. TSCT molecular skeletons with spatially and electronically confined D/A subunits can provide a small ΔEST, and also ease for fine control of CT properties within a single molecule. However so far TSCT-TADF molecules have not been fully investigated. Herein, we report a new ortho-position molecular pattern for TSCT-TADF design, using a stereoscopic V-shaped aromatic macrocycle of electron-deficient oxacalix[2]arene[2]triazine to “clip” the electron-rich triphenylamine unit. The new emitter OC2A2T-TPA exhibits a small ΔEST of 18 meV, and the OLED device that uses high-energy-level host DPEPO realizes the first-time electroluminescence application of OC2A2T-type macrocyclic compounds by achieving an impressive external quantum efficiency (EQE) of 14.6 %. Further host-dependence investigation reveals that OC2A2T-TPA actually behaves like an intramolecular exciplex, exhibiting high exciton utilization once its high-lying locally excited (LE) states on D/A could be sensitized first in the case of DPEPO host, otherwise low exciton utilization in the case of lower-energy-level mCP host. This work opens a way to enrich TSCT-TADF design and clarifies the importance to involve the high-lying LE states in the energy transfer routes for high-efficiency intramolecular-exciplex molecules.

Y‐Shaped Pyrene‐Based Aggregation‐Induced Emission Blue Emitters for High‐Performance OLED Devices

AbstractThe proposed concept of aggregation‐induced emission (AIE) has offered an efficient strategy to design high‐performance luminescent materials. Herein, three blue emitters containing a pyrene core decorated with either triphenylamine or tetraphenylethylene units are presented. The designed compoundsPy‐TPAandPy‐2TPEare AIE or active materials with blue emission from 464 to 478 nm in the solid state, whereasPy‐2TPAis not. Moreover, the enhanced thermal stability of compoundsPy‐TPAandPy‐2TPEallows for their utilization as emitter layers for the fabrication of blue organic light‐emitting diode (OLED) devices. The devices exhibit excellent electroluminescence emission with maximum λmax emin the range 456–482 nm with a maximum external quantum efficiency of 7.27%, high exciton utilization efficiency (77.3%), and low turn‐on voltage (≤3.1 V), as well as low‐efficiency roll‐off. Theoretical calculations reveal that the high exciton utilization efficiency (ƞr) originates from the triplet excitons at T2to the lowest single excited (S1) state via a reverse intersystem crossing process following the principle of the “hot exciton” mechanism. This article not only provides powerful evidence revealing the advantages of pyrene‐based AIEgens for OLED applications, but also offers a new approach for designing pyrene‐based “hot exciton” materials for next‐generation OLEDs.

Efficient hybrid white organic light-emitting diodes with superior color stability and slow efficiency roll-off based on ultrathin emitting layer structures

In this work, high-performance hybrid white organic light-emitting diodes (WOLEDs) with high efficiencies, slow roll-off and excellent color stability were realized by strategically inserting ultrathin red phosphorescent emitter film into bluish-green thermally activated delayed fluorescent (TADF) light-emitting layer (EML). Experimental results demonstrated that the introduction of ultrathin phosphor film helps to harvest superfluous triplet excitons within bluish-green EML and relieve local exciton accumulation-induced quenching, thereby guaranteeing high exciton utilization probability. Besides, the strong holes' trapping of ultrathin layer leads to improved carriers balance, thus realizing stable recombination zone. Finally, the optimal hybrid WOLED obtained the maximum current efficiency (ηc), power efficiency (ηp) and external quantum efficiency (EQE) of 63.84 cd A−1, 66.06 lm W−1 and 28.16%, respectively. At the brightness of 1000 cd m−2, ηc, ηp and EQE as high as 57.14 cd A−1, 49.88 lm W−1 and 25.23%, respectively, can still be remained by the same device, manifesting slow efficiency roll-off. In addition, the resulting WOLED displayed excellent color stability with slightly shifted Commission Internationale de l’Eclairage coordinates (CIEx,y) from (0.43, 0.44) at 1000 cd m−2 to (0.41, 0.43) at 10000 cd m−2.

Tetracoordinate Boron-Based Multifunctional Chiral Thermally Activated Delayed Fluorescence Emitters.

Purely organic emitters have shown great potential but still suffer from low efficiency in near-infrared organic light-emitting diodes (NIR-OLEDs) due to the intensive non-radiative recombination. In this contribution, two pairs of thermally activated delayed fluorescence (TADF) enantiomers (R/S-DOBP and R/S-HDOBP) with tetracoordinate boron geometries were designed and synthesized. The TADF emitters simultaneously showed aggregation-induced emission, circularly polarized luminescence, high-contrast mechanochromism, and piezochromism behaviors. More importantly, R/S-DOBP and R/S-HDOBP revealed high photoluminescence quantum yields and efficient reverse intersystem crossing in neat films. The nondoped solution-processed OLEDs based on these unique emitters revealed the NIR emission (peaking at 716 nm) with a maximum external quantum efficiency of 1.9 % and high exciton utilization efficiency of 86 %, which represent one of the best solution-processed nondoped NIR-OLEDs.

Tetracoordinate Boron‐Based Multifunctional Chiral Thermally Activated Delayed Fluorescence Emitters

AbstractPurely organic emitters have shown great potential but still suffer from low efficiency in near‐infrared organic light‐emitting diodes (NIR‐OLEDs) due to the intensive non‐radiative recombination. In this contribution, two pairs of thermally activated delayed fluorescence (TADF) enantiomers (R/S‐DOBP and R/S‐HDOBP) with tetracoordinate boron geometries were designed and synthesized. The TADF emitters simultaneously showed aggregation‐induced emission, circularly polarized luminescence, high‐contrast mechanochromism, and piezochromism behaviors. More importantly, R/S‐DOBP and R/S‐HDOBP revealed high photoluminescence quantum yields and efficient reverse intersystem crossing in neat films. The nondoped solution‐processed OLEDs based on these unique emitters revealed the NIR emission (peaking at 716 nm) with a maximum external quantum efficiency of 1.9 % and high exciton utilization efficiency of 86 %, which represent one of the best solution‐processed nondoped NIR‐OLEDs.

Structurally modified [1,2,4]triazolo[1,5‑a]pyridine derivatives as promising materials for highly efficient blue fluorescent organic light-emitting diodes

Here, we designed and synthesized three donor–acceptor (D-A) emitters, 1-phenyl-2-(4-(2-phenyl-[1,2,4]triazolo[1,5-a]pyridin-6-yl)phenyl)-1H-phenanthro[9,10-d]imidazole (m-PPI-TP), 1-phenyl-2-(4-(2-phenyl-[1,2,4]triazolo[1,5-a]pyridin-7-yl)phenyl)-1H-phenanthro[9,10-d]imidazole (p-PPI-TP) and 1-phenyl-2-(4-(2-phenyl-[1,2,4]triazolo[1,5-a]pyridin-8-yl)phenyl)-1H-phenanthro[9,10-d]imidazole (o'-PPI-TP), based on [1,2,4]triazolo[1,5-a]pyridine (TP) as electron-transporting unit and 1,2-diphenyl-1H-phenanthro[9,10-d]imidazole (PPI) as hole-transporting moiety serving as emitting block concurrently. All three compounds were demonstrated to be thermally stable with decomposition temperatures (Td) in the range of 454–476 °C and high photoluminescence quantum yields over 86%. Besides, high exciton utilization efficiency (EUE) via “hot exciton” process was proved according to photophysical experiments and theoretical calculations analysis. What’s more, the structure–property relationships between different substituted sites of the TP building block and PPI unit were also unveiled. Finally, the non-doped blue and doped deep-blue OLEDs were fabricated with high external quantum efficiency (EQE) approaching 8%. The yellow and red phosphorescent OLEDs (PHOLEDs) based on m-PPI-TP as the host material achieved the best EL performance with EQE of 26.55% and 20.35%, respectively.

Rare Earth Complexes with 5d-4f Transition: New Emitters in Organic Light-Emitting Diodes.

Organic light-emitting diodes (OLEDs) are considered as next-generation displays and lighting technologies. During the past three decades, various luminescent materials such as fluorescence, phosphorescence, and thermally activated delayed fluorescence materials have been subsequently investigated as emitters. To date, blue OLEDs are still the bottleneck as compared to red and green ones because of the lack of efficient emitters with simultaneous high exciton utilization efficiency and long-term stability. Recently, d-f transition rare earth complexes have been reported as new emitters in OLEDs with potential high efficiency and stability. In this Perspective, we present a brief introduction to OLEDs and an overview of the previous electroluminescence study on d-f transition rare earth complexes. This is followed by our recent developments in cerium(III) complex- and europium(II) complex-based OLEDs. We finally discuss the challenges and opportunities for OLED study based on d-f transition rare earth complexes.

Efficient exciton regulation for high-performance hybrid white organic light-emitting diodes with superior efficiency/CRI/color stability based on blue aggregation-induced emission fluorophor

Fluorescent/phosphorescent hybrid white organic light-emitting diodes (WOLEDs) combining blue aggregation-induced emission (AIE) fluorophors with efficient yellow (or green/red) phosphors have attracted more attention in applications of full-color display and solid-state lighting. However, it is still a major challenge for hybrid WOLEDs based on AIE-active fluorophors to simultaneously realize high efficiency, high color rendering index (CRI), good color stability and low efficiency roll-off. Here, a sky-blue AIE fluorophor as the neat emitter has been successfully applied to high-performance blue OLED and two-/three-color hybrid WOLEDs. The blue device with a high exciton utilization efficiency of 47.4%–71.1% realizes the external quantum efficiencies (EQEs) of 6.3 and 5.5% at 1000 and 5000 cd m −2 . By accurately managing the arrangement of emissive layers, Three-color WOLED without the damage of deep-blue light not only realizes high efficiencies of 41.6 cd A −1 and 46.6 lm W −1 , but also shows a high CRI over 80 and good color stability with the Commission Internationale de L'Eclairage (CIE) coordinates changing from (0.432, 0.480) to (0.418, 0.488) when the driving voltage increases from 4 to 7 V, meeting the requirement for energy-saving and healthy lighting source. Such excellent EL performance is really rare in the no deep-blue light damage, high CRI and good color stability hybrid WOLEDs based on AIE-active fluorophor. High efficiency hybrid WOLEDs with no deep-blue light damage, good color stability, and high CRI over 80 have been achieved based on blue aggregation-induced emission fluorophor. • A blue AIE-active fluorophor realizes theEQEs of 6.3 and 5.5% at 1000 and 5000 cd m −2 . • The WOLED with no deep-blue light damage, high CRI over 80, and color stability is realized. • The WOLED shows the -forward-viewing current efficiency of 41.6 cd A −1 , and remains as high as 38.7 and 36.8 cd A −1 at 100 and 1000 cd m −2 .

The Second Excited Triplet‐State Facilitates TADF and Triplet–Triplet Annihilation Photon Upconversion via a Thermally Activated Reverse Internal Conversion

AbstractRecent years have seen a surge in organic emitters that exhibit thermally activated delayed fluorescence (TADF) behavior owing to their high exciton utilization efficiency, low biological toxicity, etc. However, the existing TADF channel is insufficiently well developed as to design high‐performance materials especially in the high‐lying triplet state mediated reverse intersystem crossing process. A thermally activated reverse internal conversion (TARIC) pathway is reported here, which can achieve effective population transfer from T1 to T2 states via conical intersection point with the barrier of 3.81 kcal mol−1. On this basis, the mediated T2 state facilitates the TADF and triplet–triplet annihilation photon upconversion (TTA–UC) channel. Furthermore, benefited from the TARIC pathway, the designed 2′,7′‐dichlorofluorescein (DCF) derivative DCF−MPYM−Me photosensitizer presents an excellent upconversion efficiency of 13.6%. The high upconversion efficiency is the best performance in purely organic TADF photosensitizers without heavy atoms in TTA−UC systems.

Molecular core–shell structure design: Facilitating delayed fluorescence in aggregates toward highly efficient solution‐processed OLEDs

AbstractLight has been sought and explored by human since ancient times. As the most important form of light, fluorescence is significant to applications in bioimaging and optoelectronic devices. However, fluorescence quenching problem constitutes a serious bottleneck in materials creation. Inspired from the core–shell structure in nature, we report an effective strategy to overcome this long‐standing problem by utilizing a molecular core–shell structure. With an emissive core and multifunctional shell fragments, these compounds show aggregation‐induced delayed fluorescence (AIDF) properties by restricting singlet oxygen (1O2) generation and suppressing the triplet–triplet annihilation (TTA). Protected by the functional shell, the aggregation‐induced emission luminogens (AIEgens) exhibit strong emission with high photoluminescent quantum yield and exciton utilization. Furthermore, because the shell materials can form exciplex with electron‐transport materials, the fully solution‐processed organic light‐emitting diodes (OLEDs) based on these core–shell materials show low turn‐on voltages, excellent device performance with current efficiency of 61.4 cd A–1 and power efficiency of 42.8 lm W–1, which is a record‐breaking efficiency based on all‐solution processed organic multilayer systems among the AIE‐OLEDs so far. This simple visualization strategy based on molecular core–shell structure provides a promising platform for AIEgens used in the fully wet‐processed optoelectronic field.

A Bipolar Delayed Fluorescence Luminogen with Fast Reverse Intersystem Crossing and High Horizontal Dipole Orientation for High‐Performance Sky‐Blue and White OLEDs

AbstractThe development of robust luminescent materials plays a key role for organic light‐emitting diodes (OLEDs). Herein, a tailor‐made sky‐blue delayed fluorescence luminogen (DCPC‐BP‐SFAC) containing a carbonyl acceptor and spiro[acridine‐9,9″‐fluorene] and 9,9″‐(cyclohexane‐1,1‐diylbis(4,1‐phenylene))bis(9H‐carbazole) donors is explored, which holds merits of excellent thermal stability, strong photoluminescence, balanced carrier transport, and horizontal dipole orientation. Owing to a charge‐transfer dominated singlet state and a charge‐transfer and local‐excitation hybrid triplet state, DCPC‐BP‐SFAC has a small energy gap between singlet and triplet as well as a large spin–orbit coupling constant, which result in a fast reverse intersystem crossing process and thus efficient delayed fluorescence. High‐performance sky‐blue OLEDs with outstanding external quantum efficiencies (ηext) reaching 32.6% are achieved based on DCPC‐BP‐SFAC, benefiting from high exciton utilization and large light out‐coupling efficiency. Moreover, using DCPC‐BP‐SFAC as blue emitter and host material simultaneously, efficient all‐fluorescence out‐of‐phase sensitizing white OLEDs without interlayer are fabricated, providing high ηext of up to 21.6% and stable warm‐white light with a high color rendering index of 84. The outstanding electroluminescence performances demonstrate the great potentials of DCPC‐BP‐SFAC in practical display and lighting devices.

Nearly 100% exciton utilization in highly efficient red OLEDs based on dibenzothioxanthone acceptor

Improving the utilization of excitons has always been an important topic for the development of electroluminescence devices. In this work, we designed and synthesized three red TADF emitters TPA-DBT12, TPA-DBT3 and DTPA-DBT by employing dibenzothioxanthone (DBT) acceptor framework to stabilize the locally excited triplet state to participate in the reverse intersystem crossing (RISC) process. The fast RISC process and singlet radiation decay process gave rise to evidently enhanced exciton utilization. All of the red OLEDs based on these materials showed maximum EQE over 11% and high exciton utilization close to 100%. This work not only extend the acceptor framework for red materials but also provide a new perspective for the design of highly efficient red TADF materials with 100% exciton utilization by managing locally excited triplet state.