以昇陳

Potassium-sulfur batteries as a newly emerged energy storage system require systematic fundamental understandings regarding their mechanisms and challenges. In this review, efforts have been devoted to comprehensively summarize the recent progresses in each component of potassium-sulfur batteries, including cathodes, anodes, electrolytes, separators, and binders. Perspectives on potassium-sulfur batteries are also provided for future development and applications.

Abstract

The potassium–sulfur battery (K–S battery) as an innovative battery technology is a promising candidate for large-scale applications, due to its high energy density and the low cost of both K and S. The development of the K–S technology is, however, inhibited by its low reversible capacity and the safety issues related to the K metal anode. Here, the review starts by discussing the mechanism of the redox reactions for the K–S batteries and emphasizes the challenges for this battery system based on its current research status. Furthermore, the current improvement strategies for the K–S system in terms of the sulfur cathode, electrolyte, separator, and K metal anode are summarized. Finally, future perspectives on the development of the K–S system are proposed.

The current understanding of cathode performance and aging issues under fast charging conditions is summarized, mitigation strategies are discussed, and remaining challenges identified.

Abstract

Charging lithium-ion batteries (LiBs) in 10 to 15 min via extreme fast-charging (XFC) is important for the widespread adoption of electric vehicles (EVs). Lately, the battery research community has focused on identifying XFC bottlenecks and determining novel design solutions. Like other LiB components, cathodes can present XFC bottlenecks, especially when considering long-term battery life. Therefore, it is necessary to develop a comprehensive understanding of how XFC conditions degrade LiB cathodes. The present article reviews relevant cathode-focused studies and summarizes the current understanding regarding cathode performance and aging issues under XFC conditions. Dominant aging modes and mechanisms are identified at different length-scales with electrochemical correlations for LiNi _x Mn _y Co _z O₂ (NMC)-based cathodes. A range of electrochemical techniques and models provide key insights into cathode performance and life issues. A suite of multimodal and multiscale microscopy and X-ray techniques is surveyed to quantify chemical, structural, and crystallographic NMC-cathode degradation. Cathode cycle-life is scaled to equivalent EV miles to illustrate how cathode degradation translates to real-world scenarios and quantifies cathode-related bottlenecks that hinder XFC adoption. Finally, the article discusses several cathode cycle-life aging mitigation strategies with example case studies and identifies remaining challenges.

Nature Energy, Published online: 14 November 2022; doi:10.1038/s41560-022-01138-y

Organic solar cells with a bulk-heterojunction architecture suffer from photocurrent loss driven by triplet states. Now, Jiang et al. show that sequentially deposited donor–acceptor planar–mixed heterojunctions suppress triplet formation, enabling efficiencies over 19%.

Since an initial report in 2016, the thermopowers of ionic organics-based thermoelectrics have been enhanced by ≈4 times for p-type and >10 times for n-type electrolytes, whereas ionic conductivities of the ionic liquids (ILs)/polymers binary system are increased yet remain relatively lower than that of neat conducting polymers used in the early years.

Abstract

As the worldwide energy crisis is worsened, thermoelectric materials that can harvest low-grade waste heat and directly convert it into electricity provide promising alternative energy sources. Emerging ionic thermoelectrics (iTEs) have recently attracted widespread attention thanks to their impressively high thermopower that can reach hundreds of times more than conventional electronic thermoelectrics (eTEs). Based on the Soret effect, the performances of iTEs depend on the thermo-diffusion of mobile ions in electrolytes, resulting in electrical characteristics distinct from eTE materials and opening up additional potential applications of thermoelectrics. Among these materials, organics-based iTEs (i-OTEs) provide unique advantages such as low-cost, light-weight, and eco-friendliness, thereby offering more promising application scenarios that can utilize dissipated heat, for example, from human bodies or mobile devices. This concise review begins with the comparison of iTE and eTE, and then discusses their different mechanisms and applied devices in detail. Next, the recent advances of i-OTEs will be in-depth highlighted, including the merits and weaknesses of representative types of materials, effects of additives, and effective strategies for performance optimization. Finally, the state-of-the-art achievements of i-OTEs are summarized, and an overview is provided of the existing challenges and an outlook of prospective development and applications in future efforts.

Nature Chemistry, Published online: 27 October 2022; doi:10.1038/s41557-022-01070-4

Room-temperature phosphorescence in organic solids is attractive for practical applications but remains rare. Now, highly phosphorescent boroxine-linked covalent organic frameworks have been prepared by covalent doping with halogen atoms through the use of halogenated precursors. The resulting porous COFs exhibited oxygen-sensing capabilities with millisecond response time over a wide range of partial oxygen pressures.

The structure–property–electrochemical performance relationship of the elastomeric electrolyte system is established to demonstrate the importance of balancing Li-ion transport and mechanical properties for achieving high energy Li metal batteries.

Abstract

Solid-state lithium (Li)-metal batteries (LMBs) are garnering attention as a next-generation battery technology that can surpass conventional Li-ion batteries in terms of energy density and operational safety under the condition that the issue of uncontrolled Li dendrite is resolved. In this study, various plastic crystal-embedded elastomer electrolytes (PCEEs) are investigated with different phase-separated structures, prepared by systematically adjusting the volume ratio of the phases, to elucidate the structure-property-electrochemical performance relationship of the PCEE in the LMBs. At an optimal volume ratio of elastomer phase to plastic-crystal phase (i.e., 1:1), bicontinuous-structured PCEE, consisting of efficient ion-conducting, plastic-crystal pathways with long-range connectivity within a crosslinked elastomer matrix, exhibits exceptionally high ionic conductivity (≈10⁻³ S cm⁻¹) at 20 °C and excellent mechanical resilience (elongation at break ≈ 300%). A full cell featuring this optimized PCEE, a 35 µm thick Li anode, and a high loading LiNi_0.83Mn_0.06Co_0.11O₂ (NMC-83) cathode delivers a high energy density of 437 Wh kg_{anode+cathode+electrolyte} ⁻¹. The established structure–property–electrochemical performance relationship of the PCEE for solid-state LMBs is expected to inform the development of the elastomeric electrolytes for various electrochemical energy systems.

Nature Energy, Published online: 10 November 2022; doi:10.1038/s41560-022-01155-x

Achieving both high efficiency and stability in organic solar cells is challenging. Now, Liang et al. show that oligomer acceptors improve the molecular packing and morphology of the active layer, affording a 15% efficiency and enhanced stability.

An organic molecule PO-T2T is investigated as an electron transport layer (ETL) material for InP green quantum-dot light-emitting diodes (QLEDs). By replacing ZnMgO with PO-T2T, exciton quenching is suppressed and charge balance is improved, and thus the resultant QLEDs exhibit a maximum external quantum efficiency of 15.0% and a luminance of 10 010 cd m⁻², corresponding to 211% and 237% enhancements, respectively, compared to 7.1% and 4207 cd m⁻² of the devices with ZnMgO ETL.

Abstract

ZnMgO thin film is commonly used as an electron transport layer (ETL) in quantum-dot light-emitting diodes (QLEDs); however, it often induces the problems of interface exciton quenching and electron over-injection in the devices. Herein, an organic molecule 2,4,6-tris(3-(diphenylphosphoryl)phenyl)-1,3,5-triazine (PO-T2T) is investigated as a ETL material for InP green QLEDs. Due to the high injection barrier and moderate electron mobility, the PO-T2T can prevent electron over-injection and accumulation in the InP QLEDs. Besides, with the organic ETL, the interfacial exciton quenching is effectively suppressed. By depositing the PO-T2T using a solution-assisted evaporation method, efficient InP green QLEDs are achieved, which exhibit a maximum external quantum efficiency of 15.0% and a luminance of 10 010 cd m⁻², corresponding to 211% and 237% enhancements, respectively, compared to 7.1% and 4207 cd m⁻² of the devices with ZnMgO ETL.

A deep-blue multiple-resonance-type thermally activated delayed fluorescence (MR-TADF) compound (3tPAB) is selected as sensitizer for both blue traditional fluorescence and MR-TADF organic light-emitting diodes. TADF-sensitized fluorescent (TSF) and TADF-sensitized TADF (TST) device using 3tPAB as sensitizer presents maximum external quantum efficiency (EQE_max) of 14.4% and 33.9%, respectively. Compared with the device without sensitizer, the efficiency is increased ≈2.4 and 1.25 times, respectively.

Abstract

Due to the limitation of donor and acceptor group selection, the efficient thermally activated delayed fluorescence (TADF) type sensitizer used for blue organic light-emitting diodes (OLEDs) is rare. Multiple resonance (MR) type TADF emitters can easily achieve efficient blue emission. And the compounds exhibit small Stokes shift and lower absorption energy under the same emission color compared with traditional TADF, mitigating the damage of high-energy absorption of sensitizer on material stability. However, their characteristics as sensitizers have not been explored. In this work, a deep-blue MR-TADF compound (3tPAB) is selected as a sensitizer for both blue traditional fluorescence and MR-TADF OLED. Given the improved photoluminescence quantum yield and the utilization of triplet excitons, the TADF-sensitized fluorescent device using 3tPAB as sensitizer presents a maximum external quantum efficiency (EQE_max) of 14.4%, showing ≈2.4 times increase compared with the device without sensitizer. More impressively, TADF-sensitized TADF (TST) device using 3tPAB as sensitizer and MR-TADF compound PhDMAC-BN as emitter exhibits EQE_max of 33.9%. And in TST device, efficient Förster energy transfer is demonstrated, thus, the device can maintain high color purity. The work first demonstrates the feasibility of MR-TADF as a sensitizer and provides a new strategy for developing high-performance blue OLED with high color purity.

The recombination and accumulation of polarons are investigated by the numerical model for transient electroluminescence. These are induced by the different recombination coefficients and degradation mechanisms. As a result, it is demonstrated that the longer device lifetime is attributed to the suppression of the exciton–polaron interaction via fast polaron recombination.

Abstract

The device performance of phosphorescent organic light-emitting diodes (PHOLEDs) is improved by using the exciplex-forming cohost with the thermally activated delayed fluorescence (TADF) property. This work comprehensively investigates the excitons and polarons management of exciplex host and dopant to understand the device degradation of PHOLEDs with various host materials. The recombination and accumulation of polarons is newly integrated in the numerical model for understanding transient electroluminescence in order to theoretically characterize a diversity of the polaron dynamics. Based on the unique excitons kinetics, polarons kinetics, and recombination coefficients coming from the exciplex host materials, the device degradation is examined. As a result, it is revealed that the longer device lifetime is attributed to the suppression of the exciton–polaron interaction by minimizing the steady-state polarons via fast polaron recombination. The combination of the exciton–polaron coupled kinetics model and the device degradation model show that the recombination coefficient should be considered a key parameter of the host materials to design long-lived PHOLEDs.

A rational molecular design strategy for developing efficient thermally-activated delayed fluorescence materials is presented through the additional introduction of donor (D) or acceptor (A) units in D-A framework, enabling the corresponding organic light-emitting diodes with external quantum efficiency enhanced from 8.5% to 11.6% and up to 27.5%, respectively, due to improved photophysical and horizontal dipole ratio properties.

Abstract

Thermally-activated delayed fluorescence (TADF) emitters are usually constructed with twisted donor-acceptor (D-A) frameworks, while studies on the relationship between diverse D-A structures are still in high demand to achieve high-performance emitters. Herein, by adopting triphenylamine as electron donor and dibenzo[a,c]phenazine as electron acceptor, three TADF molecules are reported with different frameworks of D-A (TPZ), D-A-D (DPZ) and D-A-A (APZ). Theoretical and experimental results demonstrate that different D-A frameworks play significant effects on photophysical, horizontal dipole ratio, and electroluminescence properties of the TADF molecules. In comparison, the APZ-OLED device achieves the best performance with a maximum external quantum efficiency of 27.5%, resulting from its low energy gap between the singlet and triplet, effective reverse intersystem crossing, high photoluminescence quantum yield, and horizontal dipole ratio. This work provides an insight into the relationship between efficient TADF emitters and rational molecular design engineering.

A red thermally activated delayed fluorescence emitter with cruciform structure is developed by rational molecular isomer engineering, exhibiting a high photoluminescence efficiency of 95%, a small singlet–triplet energy split of 0.24 eV, and a large horizontal emitting dipole ratio of 86% simultaneously. An external quantum efficiency up to 34.3% with a peak wavelength of 610 nm is achieved.

Abstract

The development of red organic emissive materials with high-efficiency and low-cost is of great significance but formidable challenge for organic light-emitting diodes (OLEDs). Herein, through isomer engineering, a pair of red thermally activated delayed fluorescence (TADF) isomers with Y-shape and cruciform structures, namely TPA-APQDCN-Y and TPA-APQDCN-C, are developed by integrating two triphenylamine (TPA) donor moieties into different positions of rigid planar acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile (APQDCN) acceptor core. Compared to common Y-shape structure, the unique cruciform structure can result in the formation of intramolecular H-bonding, the limited molecular packing, the balance of the contradiction between the small spatial overlap of frontier molecular orbitals, and high oscillator strength, contributing to a higher photoluminescence quantum yield of 95%, a smaller singlet–triplet energy split of 0.24 eV and a larger horizontal emitting dipole ratio of 86%. An external quantum efficiency of 34.3% with an emission peak at 610 nm is achieved for TPA-APQDCN-C based red electroluminescent device, which is the highest value for red TADF-OLEDs with emission maximum beyond 600 nm ever reported.

Via incorporating bandgap modulation and zwitterionic functionalization, the second near-infrared (NIR-II) excitation donor–acceptor–donor-based small molecule with high QY (0.65%) and great photothermal property (η = 30.8%) is successfully developed, which can be intercalated within liposomes and retain its excellent optical properties in an aqueous environment, realizing precise in vivo 1064 nm single-photon NIR-II fluorescence imaging/photothermal therapy.

Abstract

Conjugated small-molecule (CSM) phototheranostic agents that operate in the second near-infrared (NIR-II) region have garnered significant attention in the field of biomedicine. However, a lack of fluorescence-emitting ability hinders their use in precise fluorescence imaging (FI)-guided photothermal therapy (PTT). Herein, a two-pronged fluorescence intensification strategy—molecular engineering for rational bandgap modulation and lipid-intercalation to combat fluorescence quenching—is used to develop NIR-II-excited ultrabright donor–acceptor–donor-based (D–A–D)-based zwitterionic CSM nanoagent for tumor phototheranostics. The molecular engineering strategy produces the NIR-II-excited D–A–D-based zwitterionic fluorophore (BTFQ) that exhibits a high NIR-II fluorescence quantum yield (QY = 0.65%) in dichloromethane. More importantly, BTFQ complexed with liposome (DMPC) to form the zwitterion–liposome nanoagent (BTFQ/DMPC) shows a negligible loss of QY (0.63%) in aqueous media. Moreover, because BTFQ/DMPC possesses excellent photothermal conversion efficiency (PCE = 30.8%) performance, it can be used to realize efficient in vivo 1064 nm single-photon high-resolution NIR-II FI guided NIR-II PTT. This study introduces a new avenue for the development of NIR-II-excited NIR-II FI/PTT agents for precise and effective tumor treatment.

Organic planar heterojunctions are fabricated by matching the thickness of a non-fullerene acceptor to its exciton diffusion length. Additional hole transfer mediated by the exciton diffusion generates a photocurrent over 10 mA cm⁻² in the planar heterojunction. Well-defined planar interfaces reduce the dark leakage current, resulting in 83 times higher photodetector detectivity than the corresponding bulk heterojunction device.

Abstract

While non-fullerene acceptors (NFAs) have recently been demonstrated to exhibit long-range exciton diffusion, most organic photovoltaic and photodetector studies still focus on blended polymer: NFA systems. Herein, a 40 nm exciton diffusion length for IT4F excitons is determined, and it is demonstrated that sharp interface, planar heterojunction (PHJ) IT4F/PM6 devices with the IT4F layer thickness matched to this diffusion length yield optimized photovoltaic and photodetector performance. The PHJ devices yield an enhanced device open-circuit voltage relative to bulk heterojunction (BHJ) devices, associated with suppressed bimolecular recombination losses. The PHJ architecture also results in a ≈100-fold increase in electroluminescence (EL) quantum efficiency relative to the BHJ device, correlated with a shift from charge transfer state EL for the BHJ to IT4F exciton dominated EL for the PHJ, attributed to significant hole injection from PM6 into IT4F. Of particular note, the PHJ architecture is shown to suppress dark leakage current, resulting in 83 times higher photodetector detectivity at −2 V bias than the equivalent BHJ device.

This is a review on the design of purely organic small molecules to overcome the energy gap law and achieve highly efficient near-infrared light emission. Representative deep-red to near-infrared molecules reported over the past 5 years are introduced and analyzed. Promising molecular design strategies to achieve higher quantum efficiencies are also reviewed.

Abstract

Organic light-emitting materials in the near-infrared (NIR) region are important to realize next-generation lightweight and wearable applications in bioimaging, photodynamic therapy, and telecommunications. Inorganic and organometallic light-emitting materials are expensive and toxic; thus, the development of purely organic light-emitting materials is essential. However, the development of highly efficient NIR light-emitting materials made of organic materials is still in its infancy. Therefore, this review outlines molecular design strategies for developing organic small-molecule NIR light-emitting materials with high emission efficiency that can overcome the energy-gap law to be applied to next-generation wearable devices. After briefly reviewing the basic knowledge required for the NIR emission of organic molecules, representative high-efficiency molecules reported over the past 5 years are classified according to their core moieties, and their molecular design, physical properties, and luminescence characteristics are analyzed. Further, the perspective and outlook regarding the development of next-generation high-efficiency NIR organic light-emitting materials are provided.

Publication date: December 2022

Source: Materials Today Energy, Volume 30

Author(s): Devendrasinh Darbar, Thomas Malkowski, Ethan C. Self, Indranil Bhattacharya, Mogalahalli Venkatesh Venkatashamy Reddy, Jagjit Nanda

Nature Energy, Published online: 27 October 2022; doi:10.1038/s41560-022-01144-0

It is a challenging task to understand the reversibility of lithium-metal anodes in batteries. Here the authors identify the lithium electrode potential as a critical factor that affects the anode reversibility and subsequently propose an electrolyte design to improve the cycling performance.

Nature Photonics, Published online: 27 October 2022; doi:10.1038/s41566-022-01092-x

Heavy atoms like Cl, Br and I introduced into thermally activated delayed fluorescence chromophores can increase the X-ray absorption cross-section. Light yield of ~20,000 photons MeV–1, detection limit of 45.5 nGy s−1 and imaging resolution of >18.0 line pairs per millimetre is demonstrated.

MPhS-C2 with shortened terminal alkyl chain, features thermal annealing (TA)-insensitive aggregation and condense packing, leading to suppressed upshifts of highest occupied molecular orbital energy level during TA, and efficient charge transport at small phase separation in BTP-eC9 blended devices, obtaining the highest PCE of 17.11% with ΔV _nr of 0.192 V in ASM-OSCs.

Abstract

A critical bottleneck for further efficiency breakthroughs in organic solar cells (OSCs) is to minimize the non-radiative energy loss (eΔV _nr) while maximizing the charge generation. With the development of highly emissive low-bandgap non-fullerene acceptors, the design of high-performance donors becomes critical to enable the blend with the electroluminescence quantum efficiency to approach or surpass the pristine acceptor. Herein, by shortening the end-capped alkyl chains of the small-molecular donors from hexyl (MPhS-C6) to ethyl (MPhS-C2), the material obtained aggregation that was insensitive to thermal annealing (TA) along with condensed packing simultaneously. The former leads to small phase separation and suppressed upshifts of the highest occupied molecular orbital energy level during TA, and the latter facilitates its efficient charge-transport at aggregation-less packing. Hence, the ΔV _nr decreases from 0.242 to 0.182 V, from MPhS-C6 to MPhS-C2 based OSCs. An excellent PCE of 17.11% is obtained by 1,8-diiodoctane addition due to almost unchanged high J _sc (26.6 mA cm⁻²) and V _oc (0.888 V) with improved fill factor, which is the record efficiency with the smallest energy loss (0.497 eV) and ΔV _nr (0.192 V) in all-small-molecule OSCs. These results emphasize the potential material design direction of obtaining concurrent TA-insensitive aggregation and condensed packing to maximize the device performances with a super low ΔV _nr.

Regulation of the configurations of the non-conjugated polymer acceptors enables green solvent-processed large-area binary all-polymer solar cells to achieve record efficiency and robustness. This study not only provides a series of reliable novel conductive materials with excellent performance for flexible wearable solar cells but also elucidates a concept to evaluate the comprehensive performance of organic solar cells.

Abstract

With the great potential of the all-polymer solar cells for large-area wearable devices, both large-area device efficiency and mechanical flexibility are very critical but attract limited attention. In this work, from the perspective of the polymer configurations, two types of terpolymer acceptors PYTX-A and PYTX-B (X = Cl or H) are developed. The configuration difference caused by the replacement of non-conjugated units results in distinct photovoltaic performance and mechanical flexibility. Benefiting from a good match between the intrinsically slow film-forming of the active materials and the technically slow film-forming of the blade-coating process, the toluene-processed large-area (1.21 cm²) binary device achieves a record efficiency of 14.70%. More importantly, a new parameter of efficiency stretchability factor (ESF) is proposed for the first time to comprehensively evaluate the overall device performance. PM6:PYTCl-A and PM6:PYTCl-B yield significantly higher ESF than PM6:PY-IT. Further blending with non-conjugated polymer donor PM6-A, the best ESF of 3.12% is achieved for PM6-A:PYTCl-A, which is among the highest comprehensive performances.

Nature Photonics, Published online: 24 October 2022; doi:10.1038/s41566-022-01088-7

A Fourier-transform waveguide spectrometer is demonstrated by using HgTe-quantum-dot-based photoconductors with a spectral response up to a wavelength of 2 μm. The spectral resolution is 50 cm–1. The total active spectrometer volume is below 100 μm × 100 μm × 100 μm.

Nature Photonics, Published online: 24 October 2022; doi:10.1038/s41566-022-01084-x

One-micrometre-thick OLEDs with low operating voltages of 5.11 V, 3.55 V and 6.88 V at 1,000 cd cm–2 for red, green and blue devices, respectively, and long lifetimes (55,000 h, 18,000 h and 1,600 h, respectively) are realized.

Nature Photonics, Published online: 13 October 2022; doi:10.1038/s41566-022-01083-y

Green OLEDs based on BNSeSe offer high operational efficiency and reduced efficiency roll-off.

Nature Photonics, Published online: 10 October 2022; doi:10.1038/s41566-022-01079-8

A new series of self-assembled Pt(II) complexes with high emission quantum yields enables OLEDs with a maximum emission wavelength of 995 nm and an external quantum efficiency of 4.3%.

Exciton–polaron quenching induced by spontaneous orientation polarization (SOP) is generally quantified and modeled in organic light-emitting devices (OLEDs). Quenching is probed using photoluminescence and engineered by varying electron transport layer SOP through materials selection and dilution with a nonpolar material. This work underscores the significance of SOP-induced quenching in limiting OLED efficiency and provides a means to tune its severity.

Abstract

Many electron transport layer (ETL) materials employed in organic light-emitting devices (OLEDs) show a preferred orientation of the molecular permanent dipole moments. This phenomenon is known as spontaneous orientation polarization (SOP) and results in the formation of bound polarization charge. In an OLED, this leads to the accumulation of polarons (typically holes) at the ETL/emissive layer interface to balance this charge. Previous work on phosphorescent OLEDs has found that exciton–polaron quenching due to SOP-induced hole accumulation can reduce peak efficiency by ≈20%. In this work, the generality of this phenomenon is systematically established by probing polaron accumulation and quenching in phosphorescent OLEDs with varying degrees of SOP. Exciton quenching is quantified by optically probing the photoluminescence of the device emissive layer during operation. It is found that the degree of SOP-induced luminescence quenching and reduction in device efficiency scale directly with ETL SOP. It is further demonstrated that the degree of polarization and amount of quenching can be tuned by mixing the polar ETL with a nonpolar host (dipolar doping). This work establishes a ubiquitous role for SOP in determining OLED efficiency and demonstrates dipolar doping as a means to tune the underlying exciton–polaron quenching.

Nature Photonics, Published online: 13 October 2022; doi:10.1038/s41566-022-01083-y

Green OLEDs based on BNSeSe offer high operational efficiency and reduced efficiency roll-off.

A multi-resonance thermally activated delayed fluorescence (MR-TADF) emitter exhibiting deep-blue emission with Commission Internationale de L'Eclairage coordinates of (0.132, 0.092), narrow full width at half maximum of 22 nm, and high external quantum efficiency of 23.4% is developed by introducing bulky biphenyls and N-biphenyl-N-ortho-dimethylphenylamine that create dense local triplet states and suppress intramolecular aggregation.

Abstract

Multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules based on boron and nitrogen atoms are emerging as next-generation blue emitters for organic light-emitting diodes (OLEDs) due to their narrow emission spectra and triplet harvesting properties. However, intermolecular aggregation stemming from the planar structure of typical MR-TADF molecules that leads to concentration quenching and broadened spectra limits the utilization of the full potential of MR-TADF emitters. Herein, a deep-blue MR-TADF emitter, pBP-DABNA-Me, is developed to suppress intermolecular interactions effectively. Furthermore, photophysical investigation and theoretical calculations reveal that adding biphenyl moieties to the core body creates dense local triplet states in the vicinity of S₁ and T₁ energetically, letting the emitter harvest excitons efficiently. OLEDs based on pBP-DABNA-Me show a high external quantum efficiency (EQE) of 23.4% and a pure-blue emission with a Commission Internationale de L'Eclairage (CIE) coordinate of (0.132, 0.092), which are maintained even at a high doping concentration of 100 wt%. Furthermore, by incorporating a conventional TADF sensitizer, deep-blue OLEDs with a CIE value of (0.133, 0.109) and an extremely high EQE of 30.1% are realized. These findings provide insight into design strategies for developing efficient deep-blue MR-TADF emitters with fast triplet upconversion and suppressed self-aggregation.