Maximum External Quantum Efficiency Research Articles

Self‐Assembled Chiral Polymers Exhibiting Amplified Circularly Polarized Electroluminescence

Circularly polarized electroluminescence (CPEL) is highly promising in realm of 3D display and optical data storage. However, designing a groundbreaking chiral material with high comprehensive CPEL performance remains a formidable challenge. In this work, a pair of chiral polymers with self‐assembled behavior is designed by integrating a chiral BN‐moiety into polyfluorene backbone, named R‐PBN and S‐PBN, respectively. The chiral polymers show narrowband emission centered at 490 nm with full‐width half maximum (FWHM) of 29 nm and high photoluminescence quantum yield (PLQY) of 79%. After thermal annealing treatment, the chiral polymers undergo self‐assembly, exhibiting amplified circularly polarized luminescence (CPL) with asymmetry factor (|glum|) of up to 0.11. Moreover, the solution‐processed nondoped CP‐OLEDs based on the chiral polymers as emitting layers exhibit maximum external quantum efficiency (EQEmax) of 9.8%, intense CPEL activities with |gEL| of up to 0.07, and small FWHM of 36 nm, simultaneously. This represents the first case of self‐assembled chiral polymers that combines high EQE, large gEL value and narrowband emission.

Introducing steric groups to thermally activated delayed fluorescence emitter for constructing efficient non-doped solution-processed organic light-emitting diodes

Solution-processed organic light-emitting diodes (OLEDs) remain a reliable approach towards large-area and flexible display devices, but also hold higher requirement on luminescent materials. It is still challenge to develop emitting layers with great solution-processable property and excellent luminous behavior, and especially difficult for non-doped emitting materials. In this work, a TADF emitter, namely 2,3,5,6-tetrakis(4-([1,1':3′,1″-terphenyl]-5′-yl)-9H-carbazol-9-yl)benzonitrile (3Ph-4CzBN), was designed and synthesized by introducing the steric-hindrance triphenyl unit to 2,3,5,6-tetrakis(carbazol-9-yl) benzonitrile (4CzBN) which is usually applied to vacuum evaporation. The incorporation of triphenyl groups significantly increased the molecule weight, thereby rendering 3Ph-4CzBN suitable for solution-processed OLEDs. Meanwhile, 3Ph-4CzBN exhibited two-fold of photoluminescence quantum yield values in pure film than 4CzBN, indicating fluorescence quenching was relatively suppressed by steric groups. The solution-processed OLEDs employed 3Ph-4CzBN as non-doped emitting layer, achieved a maximum external quantum efficiency of 12.8 %, as well as current efficiency and power efficiency up to 34.2 cd A−1 and 23.9 lm W−1, respectively.

Tetra‐Donor Pyrazine Based Thermally Activated Delayed Fluorescence Emitters for Electroluminescence and Amplified Spontaneous Emission

AbstractThermally activated delayed fluorescence (TADF) materials are expected to address triplet‐related losses in electrically driven organic lasers, as the electrically generated triplets in the materials can be converted to radiative singlets through reverse intersystem crossing (RISC). This offers a way to bypass triplet absorption and annihilation in organic semiconductor lasers (OSLs). In this work, two versatile TADF emitters 4tCzPz and 4αCbPz for application in organic light‐emitting diodes (OLEDs) and OSLs are presented. Both emitters possess moderately high singlet‐triplet energy gap, ΔEST (≈0.30 eV) and show high photoluminescence quantum yields, ΦPL, in solution and solid‐state and prominent stimulated emission features in solution. Films of 4tCzPz and 4αCbPz doped in mCBP show an amplified spontaneous emission (ASE) threshold of 41.0 and 44.9 µJ/cm2, respectively. The OLEDs with 4tCzPz and 4αCbPz emit with peak wavelengths of 492 and 475 nm, respectively, and show corresponding maximum external quantum efficiencies, EQEmax, of 24.6 and 21.3%. The research shows that D‐A TADF materials hold significant potential not only as emitters for OLEDs but also in OSLs.

Photoluminescence Enhancement of 0D Organic-Inorganic Metal Halides via Aggregation-Induced Emission and Halide Substitution.

0D organic-inorganic metal halides (OIMHs) provide unprecedented versatility in structures and photoluminescence properties. Here, a series of bluish-white emissive 0D OIMHs, (TPE-TPP)2Sb2BrxCl8-x (x = 1.16 to 8), are prepared by assembling the 1-triphenylphosphonium-4-(1,2,2-triphenylethenyl)benzene cation (TPE-TPP)+ with antimony halides anions. Based on experimental characterizations and theoretical calculations, the emission of the 0D OIMHs are attributed to the fluorescence of the organic cations with aggregation-induced emission (AIE) properties. The 0D structure minimized the molecular motion and intermolecular interactions between (TPE-TPP)+ cations, effectively suppressing the non-radiative recombination processes. Consequently, the photoluminescence quantum efficiency (PLQE) of (TPE-TPP)2Sb2Br1.16Cl6.84 is significantly enhanced to 55.4% as compared to the organic salt (TPE-TPP)Br (20.5%). The PLQE of (TPE-TPP)2Sb2BrxCl8-x can also be readily manipulated by halide substitution, due to the competitive processes between non-radiative recombination on the inorganic moiety and the energy transfer from inorganic to organic. In addition, electrically driven light-emitting diodes (LEDs) are fabricated based on (TPE-TPP)2Sb2Br1.16Cl6.84 emitter, which exhibited bluish-white emission with a maximum external quantum efficiency (EQE) of 1.1% and luminance of 335cdm-2. This is the first report of electrically driven LED based on 0D OIMH with bluish-white emission.

High-n Phase Suppression for Efficient and Stable Blue Perovskite Light-Emitting Diodes.

Quasi-2D perovskites light-emitting diodes (PeLEDs) have achieved significant progress due to their superior optical and electronic properties. However, the blue PeLEDs still exist inefficient energy transfer and electroluminescence performance caused by mixed multidimensional phase distribution. In this work, transition metal salt (zinc bromide, ZnBr2) is introduced to modulate phase distributions by suppressing the nucleation of high n phase perovskites, which effectively shortens the energy transfer path for blue emission. Moreover, ZnBr2 also facilitates energy level matching and reduces non-radiative recombination, thus improving electroluminescence (EL) efficiency. Benefiting from these combined improvements, an efficient blue PeLEDs is obtained with a maximum external quantum efficiency (EQE) of 16.2% peaking located at 486nm. This work provides a promising approach to tune phase distribution of quasi-2D perovskites and achieving highly efficient blue PeLEDs.

Decoding the Impact of Molecular Configuration on High‐Efficiency Blue Hot Exciton Emitters

AbstractRealizing highly efficient organic light‐emitting diodes (OLEDs) based on “hot exciton” emitters is crucial for the widespread use of purely organic electroluminescence. Herein, it is demonstrated that the radiative decay rate, modulated by molecular configuration, plays a vital role in determining the optoelectronic properties of hot exciton materials. The proof‐of‐concept isomers, TPA‐1IPCN and TPA‐3IPCN, and TPA‐1IANCN and TPA‐3IANCN are intentionally designed and successfully synthesized. By employing a novel donor–acceptor–acceptor (D–A'–A) molecular architecture, implementing a molecular isomerization strategy, incorporating diverse steric hindrance moieties, and strategically manipulating the positioning of functional groups, precise modulation of the molecular configuration can be achieved to enable accurate regulation of the radiative decay rate. Consequently, various optoelectronic properties, including photoluminescent wavelength, photoluminescence quantum yield, fluorescence lifetime, packing mode in aggregated state, and molecular horizontal dipole ratios in films, undergo significant modifications. As a result, non‐doped blue OLED based on TPA‐1IPCN exhibits outstanding maximum external quantum efficiency (EQE) of 10.3% with minimal efficiency roll‐off—one of the highest reported values for blue OLEDs based on hot exciton materials.

Chemical Reaction Modulated Low-Dimensional Phase Toward Highly Efficient Sky-Blue Perovskite Light-Emitting Diodes.

Blue perovskite light-emitting diodes (PeLEDs) are crucial avenues for achieving full-color displays and lighting based on perovskite materials. However, the relatively low external quantum efficiency (EQE) has hindered their progression towards commercial applications. Quasi-two-dimensional (quasi-2D) perovskites stand out as promising candidates for blue PeLEDs, with optimized control over low-dimensional phases contributing to enhanced radiative properties of excitons. Herein, the impact of organic molecular dopants on the crystallization of various n-phase structures in quasi-2D perovskite films. The results reveal that the highly reactive bis(4-(trifluoromethyl)phenyl)phosphine oxide (BTF-PPO) molecule could effectively restrain the formation of organic spacer cation-ordered layered perovskite phases through chemical reactions, simultaneously passivate those uncoordinated Pb2+ defects. Consequently, the prepared PeLEDs exhibited a maximum EQE of 16.6 % (@ 490 nm). The finding provides a new route to design dopant molecules for phase modulation in quasi-2D PeLEDs.

Chemical Reaction Modulated Low‐Dimensional Phase Toward Highly Efficient Sky‐Blue Perovskite Light‐Emitting Diodes

Blue perovskite light‐emitting diodes (PeLEDs) are crucial avenues for achieving full‐color displays and lighting based on perovskite materials. However, the relatively low external quantum efficiency (EQE) has hindered their progression towards commercial applications. Quasi‐two‐dimensional (quasi‐2D) perovskites stand out as promising candidates for blue PeLEDs, with optimized control over low‐dimensional phases contributing to enhanced radiative properties of excitons. Herein, the impact of organic molecular dopants on the crystallization of various n‐phase structures in quasi‐2D perovskite films. The results reveal that the highly reactive bis(4‐(trifluoromethyl)phenyl)phosphine oxide (BTF‐PPO) molecule could effectively restrain the formation of organic spacer cation‐ordered layered perovskite phases through chemical reactions, simultaneously passivate those uncoordinated Pb2+ defects. Consequently, the prepared PeLEDs exhibited a maximum EQE of 16.6% (@ 490 nm). The finding provides a new route to design dopant molecules for phase modulation in quasi‐2D PeLEDs.

Monoammonium Modified Dion-Jacobson Quasi-2D Perovskite for High Efficiency Pure-Blue Light Emitting Diodes.

Quasi-2D perovskites exhibit impressive optoelectronic properties and hold significant promise for future light-emitting devices. However, the efficiency of perovskite light-emitting diodes (PeLEDs) is seriously limited by defect-induced nonradiative recombination and imbalanced charge injection. Here, the defect states are passivated and charge injection balance is effectively improved by introducing the additive cyclohexanemethylammonium (CHMA) to bromide-based Dion-Jacobson (D-J) structure quasi-2D perovskite emission layer. CHMA participates in the crystallization of perovskite, leading to high quality film composed of compact and well-contacted grains with enhanced hole transportation and less defects. As a result, the corresponding PeLEDs exhibit stable pure blue emission at 466nm with a maximum external quantum efficiency (EQE) of 9.22%. According to current knowledge, this represents the highest EQE reported for pure-blue PeLEDs based on quasi-2D bromide perovskite thin films. These findings underscore the potential of quasi-2D perovskites for advanced light-emitting devices and pave the way for further advancements in PeLEDs.

Highly Efficient Hybrid White Organic Light‐Emitting Diodes with External Quantum Efficiency Exceeding 30% by Integrating Electron‐Trapping Sensitized Structure and Gradient‐Doping System

AbstractIn this work, efficient two‐color (blue and yellow) hybrid white organic light‐emitting diodes (WOLEDs) with high efficiencies are constructed by introducing iridium(III) bis(4,6‐(difluorophenyl) pyridinato‐N,C2’)picolinate (FIrpic) as electron sensitizer. Experimental results demonstrate that FIrpic with the deep lowest unoccupied molecular orbital (LUMO) level enables preferential electron trapping to collect excessive electrons, thus realizing carrier's balance and high recombination probability. The obtained cool WOLED exhibits the maximum external quantum efficiency (EQE), current efficiency (ηc), and power efficiency (ηp) of 31.05%, 76.36 cd A−1 and 69.92 lm W−1, respectively. Moreover, by gradient doping FIrpic into yellow EML, the generated forward built‐in electric field originating from gradient electrons distribution reduces carriers transport resistance and improves the transport of holes; the diffusion effect of gradient electrons distribution promotes electrons’ transport, thus enhancing the utilization probabilities of carriers and excitons. Besides, FIrpic acts also as an energy transfer ladder to facilitate the energy transfer from host to yellow emitter. Consequently, warm WOLED with enhanced yellow emission achieves the maximum EQE, ηc, and ηp of 33.27%, 75.66 cd A−1 and 88.04 lm W−1, respectively.

Enhanced Thermally Activated Delayed Fluorescence by Sole Coordination: From an Organic Molecule to Its Zinc Complex.

A BPAPTPyC organic molecule containing a sandwich structural chromophore is designed and synthesized to produce blue thermally activated delayed fluorescence (TADF). The chromophore is composed of two di(4-tert-butylphenyl)amino donors and one inserted terpyridyl acceptor hitched at positions 1, 8, and 9 of a single carbazole via the p-phenylene group, in which the multiple space π-π interactions between the donor and acceptor enable the molecule to possess the TADF feature with a high energy emission at 470 nm but a low photoluminescence quantum yield (PLQY) and a small proportion of the delayed component. In contrast, the corresponding Zn(BPAPTPyC)Cl2 complex has a high PLQY and a short lifetime with a red-shifted emission due to the enhanced rigidity and electron accepting ability of the terpyridyl group from coordination. A solution-processed organic light-emitting diode (OLED) based on the complex achieves a maximum external quantum efficiency (EQE) of 17.9% with an emission peak at 585 nm, while an OLED of the organic molecule produces blue emission with a maximum EQE of 2.7%.

Rational design of red iridophosphors based on 1-(6-methoxynaphthalene-2-yl)isoquinoline ligand for solution‐processed OLEDs

Phosphorescent metal complexes find widespread application in organic light-emitting diodes (OLEDs), with iridium(III) complexes being particularly favored for their superior performance. Owing to the flexible modifications of both main and auxiliary ligands, the photophysical properties of iridium(III) complexes can be finely tuned. In this study, two red neutral iridium(III) complexes, designated as Ir1 and Ir2, are successfully synthesized and characterized. Various auxiliary ligands including acetylacetone and 2-picolinic acid are employed in combination with 1-(6-methoxynaphthalene-2-yl)isoquinoline as the cyclometalating ligand. Both complexes exhibit red emission, with Ir1 emitting at 631 nm and Ir2 at 615 nm. Furthermore, they demonstrated good solubility in common organic solvents, facilitating device fabrication via solution methods. Electroluminescent (EL) devices based on complexes Ir1 and Ir2 are further prepared using spin-coating method, achieving maximum external quantum efficiencies (EQEs) of 3.30 % and 4.52 %, respectively, and both devices exhibited bright red EL with CIE coordinates of (0.68, 0.32) and (0.66, 0.34), which were very close to the standard red coordinates of (0.67, 0.33).

Improving efficiency in RGB phosphorescent and white organic light emitting diodes via donor-spiro-boron acceptor host materials

The universal host material with boron acceptor core structure is exceptionally sparse to be designed for red, green, and blue in efficient phosphorescent organic light emitting diodes (PhOLEDs) accompanying white OLEDs, possessing indistinguishable device feature. Herein, two boron acceptors spiro-host materials namely 1'-(4-(dimesitylboranyl)phenyl)-10-phenyl-10H-spiro[acridine-9,9′-fluorene] (TPA-PBM) and 1-(4-(dimesitylboranyl)phenyl)-3′,6′-dimethylspiro[fluorene-9,8′-indolo[3,2,1-de]acridine] (2MeCz-PBM) were designed and synthesized. The designed rigid donor strategy exhibited good device performance among the reported boron donor-spiro-acceptor (D-spiro-A) skeleton for organic light emitting diodes (OLEDs). In particular, we fabricate RGB three-color phosphorescent OLEDs based on TPA-PBM and 2MeCz-PBM. The red devices exhibit a maximum external quantum efficiency (EQE) of nearly 28 % (26.8 % for TPA-PBM and 27.5 % for 2MeCz-PBM), with an electroluminescence spectrum at 608 nm. The green/blue devices obtain maximum EQEs of 21.2 %/15.3 % and 21.8 % 17.3 %, for TPA-PBM and 2MeCz-PBM, respectively. Furthermore, green devices display an extremely low efficiency roll-off with decreasing 1 % and 3 % at luminance of 5000 cd m−2. Additionally, the two-color white OLED using 2MeCz-PBM exhibits EQEmax and PEmax are 24.5 % and 62.9 lm W−1 respectively, the EQE remain 23.8 % at commercial lighting brightness of 1000 cd m−2. The WOLED also shows a stable white spectrum with CIE varying range of (0.41, 0.47) to (0.39, 0.46) at 100 cd m−2 to 15000 cd m−2. All obtained results confirmed that our targeted molecules have advantage of carrier balance and efficient charge recombination, which might replace many other commercial host materials.

C-H-activated Csp2-Csp3 diastereoselective gridization enables ultraviolet-emitting stereo-molecular nanohydrocarbons with mulitple H···H interactions

Gridization is an emerging molecular integration technology that enables the creation of multifunctional organic semiconductors through precise linkages. While Friedel-Crafts gridization of fluorenols is potent, direct linkage among fluorene molecules poses a challenge. Herein, we report an achiral Pd-PPh3-cataylized diastereoselective (>99:1 d.r.) gridization based on the C-H-activation of fluorene to give dimeric and trimeric windmill-type nanogrids (DWGs and TWGs). These non-conjugated stereo-nanogrids showcase intramolecular multiple H…H interactions with a low field shift to 8.51 ppm and circularly polarized luminescence with high luminescent dissymmetry factors (|gPL | = 0.012). Significantly, the nondoped organic light-emitting diodes (OLEDs) utilizing cis-trans-TWG1 emitter present an ultraviolet electroluminescent peak at ~386 nm (CIE: 0.17, 0.04) with a maximum external quantum efficiency of 4.17%, marking the highest record among nondoped ultraviolet OLEDs based on hydrocarbon compounds and the pioneering ultraviolet OLEDs based on macrocycles. These nanohydrocarbon offer potential nanoscafflolds for ultraviolet light-emitting optoelectronic applications.

Highly Horizontal Oriented Tricomponent Exciplex Host with Multiple Reverse Intersystem Crossing Channels for High-Performance Narrowband Electroluminescence and Eye-Protection White Organic Light-Emitting Diodes.

Despite multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters with small full-width at half maximum are attractive for wide color-gamut display and eye-protection lighting applications, their inefficient reverse intersystem crossing (RISC) process and long exciton lifetime induce serious efficiency roll-off, which significantly limits their development. Herein, a novel device concept of building highly efficient tricomponent exciplex with multiple RISC channels is proposed to realize reduced exciton quenching and enhanced upconversion of nonradiative triplet excitons, and subsequently used as a host for high-performance MR-TADF organic light-emitting diodes (OLEDs). Compared with traditional binary exciplex, the tricomponent exciplex exhibits obviously improved photoluminescence quantum yield, emitting dipole orientation and RISC rate constant, and a record-breaking external quantum efficiency (EQE) of 30.4% is achieved for tricomponent exciplex p-PhBCzPh: PO-T2T: DspiroAc-TRZ (50: 20: 30) based OLED. Remarkably, maximum EQEs of 36.2% and 40.3% and ultralow efficiency roll-off with EQEs of 26.1% and 30.0% at 1000cd m-2 are respectively achieved for its sky-blue and pure-green MR-TADF doped OLEDs. Additionally, the blue emission unit hosted by tricomponent exciplex is combined with an orange-red TADF emission unit to achieve a double-emission-layer blue-hazard-free warm white OLED with an EQEmax of 30.3% and stable electroluminescence spectra over a wide brightness range.

Synergistic Effect of Zn2+ Cation Doping and Te2− Anion Passivation on CsPbBrxI3‐x Nanocrystals for Efficient Perovskite Light‐Emitting Diodes

AbstractThe challenges of instability and surface defects in CsPbBrxI3‐x nanocrystals (NCs) pose significant limitations on their potential application in high‐performance pure‐red perovskite light‐emitting diodes (PeLEDs). Herein, a synergistic strategy of divalent cation (Zn2+) doping and anion (Te2−) passivation is proposed to solve these issues. Density functional theory analysis reveals that the synergistic effect can not only reduce the formation energy of CsPbBrxI3‐x NCs but also increase theiodide vacancy defect formation energy of CsPbBrxI3‐x NCs. Consequently, the optimized Zn2+/Te2− co‐modified CsPbBrxI3‐x NCs exhibit significantly enhanced stability with a near‐unity photoluminescence efficiency. Pure‐red PeLEDs based on these CsPbBrxI3‐x NCs possess outstanding spectral stability with a maximum external quantum efficiency and luminance of 16.1% and 1397.2 cd m−2, respectively. This synergistic strategy provides a new approach for enhancing the performance of mixed halide perovskite NCs and the corresponding optoelectronic devices.

Efficient Dual‐Functional Quantum Dot Light‐Emitting Diodes with UV‐Vis‐NIR Broad‐Spectrum Photosensitivity

AbstractPhotosensitive quantum dot light‐emitting diodes (PSQLEDs) possess the dual capabilities of generating and detecting light signals, which is of significant importance for the development of miniaturized and integrated optoelectronic devices. However, the state‐of‐the‐art PSQLEDs can only detect light signals within a certain wavelength range, and require switching between the two functions under different bias voltage directions. In this work, The use of a ZnO/quantum dots (QDs)/ZnO multilayer (ZQZ ML) architecture as both the electron transport layer and the photosensitive layer is pioneered. The QDs in this structure are composed of narrow‐bandgap lead sulfide QDs and wide‐bandgap cadmium selenide QDs, successfully realizing a unique PSQLED device with C photosensitive characteristics. As a result, the as‐fabricated device can respond to illumination from 365 to 1300 nm, and the device achieves a photoresponse rate of 20.9 mA W−1 in self‐powered mode to UV light. After UV light irradiation, the maximum external quantum efficiency and maximum luminance of device reached 11.8% and 64,549 cd m−2, respectively. The device shows a record‐high luminance ON/OFF ratio of 5500%, which is beneficial for high contrast and accurate information display.

Boosting External Quantum Efficiency to 12.0 % of an Ultraviolet OLED by Engineering the Horizontal Dipole Orientation of a Hot Exciton Emitter

AbstractCurrently, much research effort has been devoted to improving the exciton utilization efficiency and narrowing the emission spectra of ultraviolet (UV) fluorophores for organic light‐emitting diode (OLED) applications, while almost no attention has been paid to optimizing their light out‐coupling efficiency. Here, we developed a linear donor‐acceptor‐donor (D–A–D) triad, namely CDFDB, which possesses high‐lying reverse intersystem crossing (hRISC) property. Thanks to its integrated narrowband UV photoluminescence (PL) (λPL: 397 nm; FWHM: 48 nm), moderate PL quantum yield (ϕPL: 72 %, Tol), good triplet hot exciton (HE) conversion capability, and large horizontal dipole ratio (Θ//: 92 %), the OLEDs based on CDFDB not only can emit UV electroluminescence with relatively good color purity (λEL: 398 nm; CIEx,y: 0.161, 0.040), but also show a record maximum external quantum efficiency (EQEmax) of 12.0 %. This study highlights the important role of horizontal dipole orientation engineering in the molecular design of HE UV‐OLED fluorophores.

Manipulating the photophysical properties of multi-donor molecules for fast reverse intersystem crossing in solution-processed OLED devices

The slow reverse intersystem crossing (RISC) rate in thermally activated delayed fluorescence (TADF) emitters result in extended exciton lifetime and pronounced efficiency loss at high luminance level. To address this limitation, we have developed and characterized a series of novel compounds featuring triazine cores substituted with tert-butyl carbazole moieties at various positions and quantities. The objective here is to fine-tune the charge transfer properties, thereby enhancing the efficiency of the RISC process. Our studies reveal that through-space charge transfer is more effective than long-range through-bond charge transfer in minimizing the singlet-triplet energy gap and accelerating RISC. The optimized compound, 4tCzTrz, exhibits an exceptionally fast RISC rate of 1.02 × 107 s−1 and a high photoluminescence quantum yield of up to 100 %. Solution-processed organic light-emitting diodes (OLEDs) incorporating this molecule have achieved outstanding maximum external quantum efficiencies of around 20 %, whether used as an emitter directly or as a sensitizer to boost overall emission efficiency.

Boosting External Quantum Efficiency to 12.0 % of an Ultraviolet OLED by Engineering the Horizontal Dipole Orientation of a Hot Exciton Emitter.

Currently, much research effort has been devoted to improving the exciton utilization efficiency and narrowing the emission spectra of ultraviolet (UV) fluorophores for organic light-emitting diode (OLED) applications, while almost no attention has been paid to optimizing their light out-coupling efficiency. Here, we developed a linear donor-acceptor-donor (D-A-D) triad, namely CDFDB, which possesses high-lying reverse intersystem crossing (hRISC) property. Thanks to its integrated narrowband UV photoluminescence (PL) (λPL: 397 nm; FWHM: 48 nm), moderate PL quantum yield (ϕPL: 72 %, Tol), good triplet hot exciton (HE) conversion capability, and large horizontal dipole ratio (Θ//: 92 %), the OLEDs based on CDFDB not only can emit UV electroluminescence with relatively good color purity (λEL: 398 nm; CIEx,y: 0.161, 0.040), but also show a record maximum external quantum efficiency (EQEmax) of 12.0 %. This study highlights the important role of horizontal dipole orientation engineering in the molecular design of HE UV-OLED fluorophores.