Design strategy of yellow thermally activated delayed fluorescent dendrimers and their highly efficient non-doped solution-processed OLEDs with low driving voltage

We designed and synthesized two dendrimers TA-Cz and TA-3Cz with TADF characteristics by using non-conjugated aliphatic chains carbazole/tricarbazole as peripheral dendrons. Both dendrimers possess excellent thermal and morphological stabilities. Introduced the phenyl bridge to increase the distance of the emission core TA between donor (D) and acceptor (A) is a promising route to simultaneously achieve small singlet–triplet energy splitting (ΔE_ST) and enhanced PL quantum yields (PLQYs). Furthermore, non-conjugated aliphatic chains carbazole/tricarbazole dendrons were conveniently introduced to the TADF core, which can effective encapsulate the emission core to restrain the concentration quenching effect and make the fluorescence of the core independent. By utilizing TA-3Cz emitter as the non-doped solution-processed emissive layers, the resulting yellow OLED achieved low driving voltage of 2.4 V and superior external quantum efficiency of 11.8%. Thus, our results here provide a facile strategy to obtain highly efficient non-doped solution-processed OLEDs by employing the reasonable molecular design of the TADF core and the utilization of flexible alkyl chain.     

Highly efficient near-infrared thermally activated delayed fluorescence material based on a spirobifluorene decorated donor

The development of red/near-infrared (NIR) thermally activated delayed fluorescence (TADF) emitters are relatively lagging due to the spin statistics and energy gap law. Herein, we designed and synthesized a new NIR TADF emitter, 3-(4-(9,9′-spirobi[fluorene]-3-yl(phenyl)amino)phenyl)acenaphtho[1,2-b]pyrazine-8,9-dicarboni-trile (SDPA-APDC), by incorporating a spiro-type electron-donating moiety N,N-diphenyl-9,9′-spirobi[fluorene]-2-amine (SDPA) to an electron-withdrawing unit acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile (APDC). The photophysical, electrochemical and thermal properties of SDPA-APDC have been systematically explored. Consequently, the emitter was found high photoluminescence quantum yield (PLQY), narrow bandgap, small singlet-triplet energy gap (ΔE_ST) and excellent thermal stability. Furthermore, SDPA-APDC was developed for electroluminescence devices. The doped devices of SDPA-APDC achieved a red emission peak at 696 nm with a maximum external quantum efficiency (EQE) of 10.75%. And the non-doped device exhibited a NIR emission peak at 782 nm with a maximum EQE of 2.55%     

Highly Efficient Green‐Emitting Phosphorescent Iridium Dendrimers Based on Carbazole Dendrons

Green‐emitting iridium dendrimers with rigid hole‐transporting carbazole dendrons are designed, synthesized, and investigated. With second‐generation dendrons, the photoluminescence quantum yield of the dendrimers is up to 87 % in solution and 45 % in a film. High‐quality films of the dendrimers are fabricated by spin‐coating, producing highly efficient, non‐doped electrophosphorescent organic light‐emitting diodes (OLEDs). With a device structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonic acid)/neat dendrimer/1,3,5‐tris(2‐N‐phenylbenzimidazolyl)benzene/LiF/Al, a maximum external quantum efficiency (EQE) of 10.3 % and a maximum luminous efficiency of 34.7 cd A^–1 are realized. By doping the dendrimers into a carbazole‐based host, the maximum EQE can be further increased to 16.6 %. The integration of rigid hole‐transporting dendrons and phosphorescent complexes provides a new route to design highly efficient solution‐processable dendrimers for OLED applications.     

Aggregation-induced emission type thermally activated delayed fluorescent materials for high efficiency in non-doped organic light-emitting diodes

Aggregation-induced emission (AIE) type thermally activated delayed fluorescent (TADF) emitters were developed by asymmetric substitution of donor moieties to a diphenylsulfone acceptor. The AIE properties of the TADF emitters increased the quantum efficiency of the non-doped TADF devices and asymmetric substitution was more effective than symmetric substitution to enhance the quantum efficiency of the non-doped devices.     

Solution-processed multiple exciplexes via spirofluorene and S-triazine moieties for red thermally activated delayed fluorescence emissive layer OLEDs

A series of novel binary and ternary components of the exciplexes as the cohosts for a red thermally activated delayed fluorescence (TADF) dopant were investigated in the solution-processed OLEDs, where 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl] phenylene (OXD-7) as a conventional acceptor, and 1,3-bis(carbazol-9-yl)benzene (mCP) as a conventional donor were respectively mixed with two molecules containing spirofluorene and s-triazine moieties (TDP-TRZ or DTDP-TRZ) with excellent thermal stability and high electron mobility as the second acceptors. Particularly, the power efficiencies of the devices with the exciplexes are generally enhanced via this strategy of host engineering. The designed devices could achieve a percentage increase of 179% in the power efficiency, compared with the reference device with single-component host, mainly owing to the synergistic effects of electron block, balanced injection of charge carriers and efficient exciton harvesting. The working mechanism of energy transfer in binary and ternary components of the exciplexes hosted red TADF OLEDs is studied. This work provides a novel device design philosophy with the multiple exciplexes cohosts for solution-processed TADF OLEDs, which would help to simplify the fabrication processing, lower the cost, and popularize OLED technology.     

Management of Host–Guest Triplet Exciton Distribution for Stable,High-Efficiency,Low Roll-Off Solution-Processed Blue Organic Light-Emitting Diodes by Employing Triplet-Energy-Mediated Hosts

High-quality hosts are indispensable for simultaneously realizing stable, high efficiency, and low roll-off blue solution-processed organic light-emitting diodes (OLEDs). Herein, three solution processable bipolar hosts with successively reduced triplet energies approaching the T₁ state of thermally activated delayed fluorescence (TADF) emitter are developed and evaluated for high-performance blue OLED devices. The smaller T₁ energy gap between host and guest allows the quenching of long-lived triplet excitons to reduce exciton concentration inside the device, and thus suppresses singlet-triplet and triplet-triplet annihilations. Triplet-energy-mediated hosts with high enough T₁ and better charge balance in device facilitate high exciton utilization efficiency and uniform triplet exciton distribution among host and TADF guest. Benefited from these synergetic factors, a high maximum external quantum efficiency (EQE_max) of 20.8%, long operational lifetime (T₅₀ of 398.3 h @ 500 cd m⁻²), and negligible efficiency roll-off (EQE of 20.1% @ 1000 cd m⁻²) are achieved for bluish-green TADF OLEDs. Additionally introducing a narrowband emission multiple-resonance TADF material as terminal emitter to accelerate exciton dynamic and improve exciton utilization, a higher EQE_max of 23.1%, suppressed roll-off and extended lifetime of 456.3 h are achieved for the sky-blue sensitized OLEDs at the same brightness.     

Simple-structure organic light emitting diodes: Exploring the use of thermally activated delayed fluorescence host and guest materials

We investigate the dependence of the performance of non-doped blue light emitting devices with thermally activated delayed fluorescence (TADF) material bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) emission layer on hole and electron transport layers as well as emission layer thickness and study the underlying device physics. On this basis, efficient green and orange devices using DMAC-DPS as host material and TADF material (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) or 2,3,5,6-tetrakis(3,6-diphenylcarbazol-9-yl)-1,4-dicyanobenzene (4CzTPN-Ph) as emitting dopant are reported. In addition, white devices using single DMAC-DPS: 4CzTPN-Ph emission layer show the maximum external quantum efficiency of 13.4%, maximum power efficiency of 38.3 lm W⁻¹ and current-insensitive Commission Internationale de I'Eclairage (CIE) coordinates of (0.29, 0.39). Compared to the approach of combining TADF host and fluorescent dopant, the present devices enable the utilization of all excitons for light emission and the adoption of broad dopant concentration without significantly affecting device efficiency, which is important for the realization of the desired colour purity for display applications, while maintaining the advantages of simple-structure and low-cost.     

Enabling Record-high Deep-Red/Near-Infrared Electroluminescence Through Subtly Managing Intermolecular Interactions of a Thermally Activated Delayed Fluorescence Emitter

Deep-red/near-infrared (DR/NIR) organic light-emitting diodes (OLEDs) are promising for applications such as night-vision readable marking, bioimaging, and photodynamic therapy. To tune emission spectra into the DR/NIR region, red emitters generally require assistance from intermolecular interactions. But such interactions generally lead to sharp efficiency declines resulting from unwanted quenching events. To overcome this challenge, herein, an advanced method via strategically managing the intermolecular interactions of thermally activated delayed fluorescence (TADF) emitters is proposed. The proof-of-concept molecule called DCN-SPTPA exhibits impressive resistance to quenching while delivering controllable aggregation behavior for redshifting the emission by installing an end-spiro group. Consequently, two emitters demonstrate similar photophysical properties and device performance at very low doping levels; while DCN-SPTPA -based OLEDs demonstrate a 1.3–1.4-fold enhancement of the external quantum efficiencies (EQEs) with respect to the control molecule at 5–20 wt.% doping ratios, affording DR/NIR emission at 656, 688, 696, and 716 nm with record-breaking EQEs of 36.1%, 29.3%, 28.2%, and 24.0%, respectively. Moreover, DCN-SPTPA -based nondoped NIR device also retains a state-of-the-art EQE of 2.61% peaked at 800 nm. This work first demonstrates instructive guidance for accurately manipulating the intermolecular interactions of red TADF emitters, which will spur future developments in high-performance DR/NIR OLEDs.     

Solution‐Processible Red Iridium Dendrimers based on Oligocarbazole Host Dendrons: Synthesis,Properties, and their Applications in Organic Light‐Emitting Diodes

A series of novel red‐emitting iridium dendrimers functionalized with oligocarbazole host dendrons up to the third generation ( red‐G3 ) have been synthesized by a convergent method, and their photophysical, electrochemical, and electroluminescent properties have been investigated. In addition to controlling the intermolecular interactions, oligocarbazole‐based dendrons could also participate in the electrochemical and charge‐transporting process. As a result, highly efficient electrophosphorescent devices can be fabricated by spin‐coating from chlorobenzene solution in different device configurations. The maximum external quantum efficiency (EQE) based on the non‐doped device configuration increases monotonically with increasing dendron generation. An EQE as high as 6.3% was obtained as for the third generation dendrimer red‐G3 , which is about 30 times higher than that of the prototype red‐G0 . Further optimization of the device configuration gave an EQE of 11.8% (13.0 cd A^?1, 7.2 lm W^?1) at 100 cd m^?2 with CIE coordinates of (0.65, 0.35). The state‐of‐the‐art performance indicated the potential of these oligocarbazole‐based red iridium dendrimers as solution processible emissive materials for organic light‐emitting diode applications.     

Effect of dendron generation on properties of self-host heteroleptic green light-emitting iridium dendrimers

A series of self-host heteroleptic green light-emitting iridium (Ir) dendrimers G1 and G2 have been synthesized under mild conditions with high yields, and their photophysical, electrochemical and electroluminescent properties are investigated in detail. Compared with the model compound G0, both G1 and G2 exhibit similar photophysical and electrochemical properties, indicating that the incorporation of carbazole dendrons via a flexible non-conjugated spacer can retain the independence of the emissive Ir core. However, the device performance gradually increases with the increasing dendron generation due to the reduced intermolecular interactions. As a result, a peak luminous efficiency of 17.2 cd/A has been obtained for the G2-based non-doped device, which is about 6 times that of G0. Further dispersing the dendrimer G2 into a host matrix, the efficiency can be improved to 29.2 cd/A.     

Color stable and highly efficient hybrid white organic light-emitting devices using heavily doped thermally activated delayed fluorescence and ultrathin non-doped phosphorescence layers

Blue/orange complementary fluorescence/phosphorescence hybrid white organic light-emitting devices with excellent color stability and high efficiency have been fabricated, which are based on an easily fabricated multiple emissive layer (EML) configuration with an ultrathin non-doped orange phosphorescence EML selectively inserted between heavily doped blue thermally activated delayed fluorescence (TADF) EMLs. Through systematic investigation and improvement on luminance-dependent color shift and efficiency deterioration, a slight Commission Internationale de 1′Eclairage coordinates shift of (0.008, 0.003) at a practical luminance range from 1000 to 10000 cd/m², a maximum power efficiency of 45.8 lm/W, a maximum external quantum efficiency (EQE) of 15.7% and an EQE above 12% at 1000 cd/m² have been achieved. The heavily doped blue TADF emitters which act as the main charge transport channels and recombination sites in the host with high-lying lowest triplet excited state, take advantage of the bipolar transport ability to broaden the major charge recombination region, which alleviates triplet energy loss. The selectively inserted ultrathin non-doped orange EML makes its emission mechanism dominated by Förster energy transfer, which is effective to keep color stable under different drive voltages.     

The Effect of Core Delocalization on Intermolecular Interactions in Conjugated Dendrimers

Four generations of conjugated dendrimers that contain 1,3,5‐tris(distyrylbenzenyl)benzene cores, stilbene dendrons, and t‐butyl surface groups have been synthesized. The dendrimers were synthesized by coupling benzylphosphonate‐focused dendrons with 1,3,5‐tris(4‐formylstilbenyl)benzene to give the dendrimers in yields in the range 60–82 %. We have probed the optoelectronic properties of the dendrimers by electrochemistry, photoluminescence, and in light‐emitting device structures. We have found that the degree of aggregation is strongly generation dependent. We compared the properties of these benzene‐centered dendrimers with an equivalent family of dendrimers that differs only in having a nitrogen atom as the central unit. We found that the aggregation of dendrimers was strongly dependent on the degree of delocalization across the central unit. The dendrimers with the benzene central unit, which have three localized distyrylbenzene chromophores, were found to aggregate more strongly in the solid state than those with nitrogen as the central unit. In the latter case the electroactive component is comprised of all three distyrylbenzene units and the nitrogen atom.     

Molecular engineering of “A-D-D-A” dual-emitting-cores emitters with thermally activated delayed fluorescence and aggregation-induced emission characteristics

Endowing thermally activated delayed fluorescence (TADF) emitter with aggregation-induced emission (AIE) peculiarity is of great significance for realizing more promising commercial applications. Herein, two new dual-emitting-cores emitters with a structure of acceptor-donor-donor-acceptor (A-D-D-A), namely 2DBT-BZ-2Cz and 2DFT-BZ-2Cz, were designed and synthesized to explore their luminescence trait. The emitters, adopting dual carbazole as donor segments and dual phenyl ketone in peripheral skeleton as electron acceptor units, were featured with small singlet (S₁)–triplet (T₁) splitting energy (ΔE_ST) of 0.02 eV and 0.01 eV. The efficient thermally activated delayed fluorescence (TADF) characteristics and aggregation-induced emission property make them suitable for nondoped OLED devices. The solution-processed green OLEDs based on 2DBT-BZ-2Cz demonstrated greater device performance with current efficiency of 20.7 cd A⁻¹ and maximum luminescence of 10,000 cd m⁻². This work thus provides the direction to explore luminogens of dual-emitting-cores with TADF and AIE features as promising candidates in solid state lighting.     

Ultra-Deep-Blue Aggregation-Induced Delayed Fluorescence Emitters: Achieving Nearly 16% EQE in Solution-Processed Nondoped and Doped OLEDs with CIEy < 0.1

Ultra-deep-blue aggregation-induced delayed fluorescence (AIDF) emitters (TB-tCz and TB-tPCz) bearing organoboron-based cores as acceptors and 3,6-substituted carbazoles as donors are presented. The thermally activated delayed fluorescence (TADF) properties of the two emitters are confirmed by theoretical calculations and time-resolved photoluminescence experiments. TB-tCz and TB-tPCz exhibit fast reverse intersystem crossing rate constants owing to efficient spin–orbit coupling between the singlet and triplet states. When applied in solution-processed organic light-emitting diodes (OLEDs), the TB-tCz- and TB-tPCz-based nondoped devices exhibit ultra-deep-blue emissions of 416–428 nm and high color purity owing to their narrow bandwidths of 42.2–44.4 nm, corresponding to the Commission International de l´Eclairage color coordinates of (x = 0.16–0.17, y = 0.05–0.06). They show a maximum external quantum efficiency (EQE_max) of 8.21% and 15.8%, respectively, exhibiting an unprecedented high performance in solution-processed deep-blue TADF-OLEDs. Furthermore, both emitters exhibit excellent device performances (EQE_max = 14.1–15.9%) and color purity in solution-processed doped OLEDs. The current study provides an AIDF emitter design strategy to implement high-efficiency deep-blue OLEDs in the future.     

Novel D-D′-A structure thermally activated delayed fluorescence emitters realizing over 20% external quantum efficiencies in both evaporation- and solution-processed organic light-emitting diodes

Thermally activated delayed fluorescence (TADF) emitters have only realized limited performance in solution-processed organic light-emitting diodes (OLEDs) comparing to in evaporation-processed OLEDs. To address this issue, a novel D-D′-A structure, where A is the electron-accepting group, D is the primary electron-donating group and D′ is the secondary electron-donating group, was proposed to develop efficient solution-processable TADF emitters in this work. As the intermediate D′ spacer weakens the direct intramolecular interaction between D and A groups, D-D′-A structure molecules simultaneously possess intramolecular and intermolecular charge-transfer transition channels, suppressing the aggregation-caused quenching induced by solution process. Accordingly, a novel TADF emitter 2-(3,6-bis(9,9-dimethylacridin-10(9H)-yl)-9H-carbazol-9-yl)thianthrene 5,5,10,10-tetraoxide (DMAC-Cz-TTR) was designed and synthesized. In the optimized evaporation- and solution-processed OLEDs, DMAC-Cz-TTR successfully realized similar maximum external quantum efficiencies (EQEs) of 21.1% and 20.6%, respectively. To the best of our knowledge, this is the first TADF emitter realizing nearly equal performance in both evaporation- and solution-processed OLEDs with over 20% EQEs. The outstanding performance of DMAC-Cz-TTR successfully demonstrates the feasibility of the D-D′-A structure to develop efficient solution-processable TADF emitters.     

Simultaneously enhancement of quantum efficiency and color purity by molecular design in star-shaped solution-processed blue emitters

A series of fluorene-free bipolar star-shaped molecules, Sn-Cz-OXD (n = 1–5), with increasing conjugated length in branches were synthesized as high efficient blue emitters for OLEDs. With the extension of conjugated branches, the solid PL quantum efficiency and external quantum efficiency of Sn-Cz-OXD significantly increased with longer spacer, while the emission spectrum of these materials exhibited a blue-shift with enhanced color purity due to the unique molecular design. All materials maintained exceptionally high thermal stability after prolonged heat treatment at 150 °C in air. The photophysical, electrochemical, thermal properties of these emitters were studied in relation to the molecular structure. Nondoped device based on S4-Cz-OXD with structure ITO/PEDOT:PSS/EML/TPBI/LiF/Al emitted stable pure blue light with CIE coordinates of (0.157, 0.146). It exhibited high current efficiency and external quantum efficiency of 4.96 cd A⁻¹ and 4.20%, respectively. These values are among the best results for solution-processed non-doped blue device based on fluorene-free materials, indicating its potential for commercial applications.     

Copper(I) Complex as Sensitizer Enables High-Performance Organic Light-Emitting Diodes with Very Low Efficiency Roll-Off

Organic light-emitting diodes (OLEDs) utilizing purely organic thermally activated delayed fluorescence (TADF) sensitizers have recently achieved high efficiencies and narrow-band emissions. However, these devices still face intractable challenges of severe efficiency roll-off at practical luminance and finite operational lifetime. Herein, a carbene-Cu(I)-amide complex, (MAC*)Cu(Cz), is demonstrated as a TADF sensitizer for both fluorescent and TADF OLEDs. The (MAC*)Cu(Cz)-sensitized fluorescent OLED not only achieves a high external quantum efficiency (EQE) of 14.6% with an extremely low efficiency roll-off of 12% at the high luminance of 10 000 nits, but also delivers a 15 times longer operational lifetime than that of the non-sensitized reference device. More importantly, utilizing the (MAC*)Cu(Cz) sensitizer in the multi-resonance (MR) TADF OLED results in a record-high EQE of 26.5% together with a full-width at half maximum of 46 nm and an emission peak at 566 nm. This value is the state-of-the-art efficiency for yellow-emitting MR-TADF OLEDs. The photophysical analysis proved that the fast reverse intersystem crossing process of (MAC*)Cu(Cz) is the key factor to suppress triplet exciton involved quenching at high luminance. This finding firstly demonstrates the use of Cu(I) complex as an efficient TADF sensitizer and paves the way for practical applications of TADF sensitized OLEDs.     

Deepening Insights into Aggregation Effect of Intermolecular Charge-Transfer Aggregates for Highly Efficient Near-Infrared Non-Doped Organic Light-Emitting Diodes over 780 nm

Though urgently needed, high-efficiency near-infrared (NIR) organic light-emitting diode (OLED) is still rare due to the energy-gap law. Formation of intermolecular charge-transfer aggregates (CTA) with nonadiabatic coupling suppression can decelerate non-radiative decay rates for high-efficiency NIR-OLEDs. However, the aggregation effect of CTA is still not fully understood, which limits the rational design of CTA. Herein, two CTA molecules with a same π-framework but different terminal substituents are developed to unveil the aggregation effect. In highly ordered crystalline states, the terminal substituents substantially affect the molecular packing motifs and intermolecular charge-transfer states, thus leading to distinct photophysical properties. In comparison, in amorphous states, these two CTA demonstrate similar photophysical behaviors and properties due to their similar molecular packing and intermolecular interactions as evidenced by molecular dynamics simulations. Importantly, the formations of amorphous CTA trigger multifunction improvements such as aggregation-induced NIR emission, aggregation-induced thermally activated delayed fluorescence, self-doping and self-host features. The non-doped OLEDs demonstrate NIR emissions centered at 788 and 803 nm, and high maximum external quantum efficiencies of 2.6% and 1.5% with small efficiency roll-off, respectively. This study provides deeper insight into the aggregation effect of CTA and lays a foundation for the development of high-efficiency NIR non-doped OLEDs.     

Achieving Narrow FWHM and High EQE Over 38% in Blue OLEDs Using Rigid Heteroatom-Based Deep Blue TADF Sensitized Host

Simultaneously obtaining high efficiency and deep blue emission in organic light emitting diodes (OLEDs) remains a challenge. To overcome the demands associated with deep blue thermally activated delayed fluorescence (TADF) emitters, two deep blue TADF materials namely, DBA–BFICz and DBA–BTICz, are designed and synthesized by incorporating oxygen-bridged boron (DBA) acceptor with heteroatoms, oxygen and sulphur-based donors, BFICz and BTICz, respectively. Both TADF materials show deep blue photoluminescence emissions below 450 nm by enhancing the optical band gap over 2.8 eV through deeper highest occupied molecular orbital (HOMO) level of heteroatom based donor moieties. At the same time, the photoluminescence quantum yields (PLQYs) of both TADF materials remain over 94%. The TADF device with DBA–BFICz as an emitter exhibits a good external quantum efficiency (EQE) of 33.2%. Since both new TADF materials show deep blue emissions and high efficiencies, hyperfluorescence (HF) OLED devices are fabricated using ν-DABNA as a fluorescence dopant. DBA–BFICz as a TADF sensitized host in HF–OLED reveals an outstanding EQE of 38.8% along with narrow full width at half maximum of 19 nm in the bottom emission pure blue OLEDs. This study provides an approach to develop deep blue TADF emitters for highly efficient OLEDs.     

A Multiple Resonance Emitter Integrating Para-B-π-B′/Meta-N-π-N Pattern via an Unembedded Organoboron Decoration for Both High-Efficiency Solution- and Vacuum-Processed OLEDs

Multiple resonance (MR)-type thermally activated delayed fluorescence (TADF) emitters have promising prospects for high-color-purity organic light-emitting diodes (OLEDs), but they are seldom attempted in the fabrication of solution-processed devices. In addition, another issue with MR-TADF emitters is that their heteroatom patterns are very limited, hampering their diversity. Herein, a novel double boron (B)-containing MR-TADF paradigm that merges an unembedded organoboron unit and a B-embedded π-fused MR framework into one system, furnishing a unique para-B-π-B′/meta-N (nitrogen)-π-N molecular pattern is proposed. Based on this, a proof-of-concept molecule, BNB ′ -1 , is developed, simultaneously achieving a bright sharp emission peaking at 540 nm with a full width at half maximum (FWHM) of only 24.5 nm/98 meV, a nearly unity photoluminescence quantum yield and excellent organic solubility. A solution-processed OLED using BNB′-1 emitter delivers an impressive external quantum efficiency (EQE) as high as 36.2% with an emissive FWHM of only 30.0 nm/0.13 eV at ≈540 nm; both parameters set new records among the ever-reported solution-processed MR-OLEDs. Moreover, BNB′-1 also obtains a superhigh EQE of 40.3% in vacuum-processed OLEDs, surpassing all MR-OLEDs in the similar emission region. This work provides an interesting solution to develop high-performance solution-processable MR-TADF emitters with diverse heteroatom patterns.