High Photoluminescence Quantum Yield Research Articles

Four‐Membered Ring‐Embedded Cycloarene Enabling Anti‐Aromaticity and Ultra‐Narrowband Emission

AbstractThe synthesis of fully fused π‐conjugated cycloarenes embedded with nonbenzenoid aromatics is challenging. In this work, the first example of four‐membered ring‐embedded cycloarene (MF2) was designed and synthesized in single‐crystal form by macrocyclization and ring fusion strategies. For comparison, single bond‐linked chiral macrocycle MS2 without two fused four‐membered rings and its linear‐shaped polycyclic benzenoid monomer L1 were also synthesized. The pronounced anti‐aromaticity of four‐membered rings significantly adjusts the electronic structures and photophysical properties of cycloarene, resulting in an enhancement of the photoluminescence quantum yield (PLQY) from 10.66 % and 10.74 % for L1 and MS2, respectively, to 54.05 % for MF2, which is the highest PLQY among the reported cycloarenes. Notably, owing to the embedded anti‐aromatic four‐membered rings that reduce structural displacements, MF2 exhibits an ultra‐narrowband emission with a single‐digit full‐width at half‐maximum (FWHM) of only 7 nm (0.038 eV), which sets a new record among all reported organic narrowband luminescent molecules, and represents the first example of ultra‐narrowband emission in conventional polycyclic aromatic hydrocarbons (PAHs) devoid of heteroatoms.

Reversible Structural Phase Transitions in Zero-Dimensional Cu(I)-Based Metal Halides for Dynamically Tunable Emissions.

Exploring structural phase transitions and luminescence mechanisms in zero-dimensional (0D) metal halides poses significant challenges, that are crucial for unlocking the full potential of tunable optical properties and diversifying their functional capabilities. Herein, we have designed two inter-transformable 0D Cu(I)-based metal halides, namely (C19H18P)2CuI3 and (C19H18P)2Cu4I6, through distinct synthesis conditions utilizing identical reactants. Their optical properties and luminescence mechanisms were systematically elucidated by experiments combined with density functional theory calculations. The bright cyan-fluorescent (C19H18P)2CuI3 with high photoluminescence quantum yield (PLQY) of 77 % is attributed to the self-trapped exciton emission. Differently, the broad yellow-orange fluorescence of (C19H18P)2Cu4I6 displays a remarkable PLQY of 83 %. Its luminescence mechanism is mainly attributed to the combined effects of metal/halide-to-ligand charge transfer and cluster-centered charge transfer, which effects stem from the strong Cu-Cu bonding interactions in the (Cu4I6)2- clusters. Moreover, (C19H18P)2CuI3 and (C19H18P)2Cu4I6 exhibit reversible structural phase transitions. The elucidation of the phase transitions mechanism has paved the way for an unforgeable anti-counterfeiting system. This system dynamically shifts between cyan and yellow-orange fluorescence, triggered by the phase transitions, bolstering security and authenticity. This work enriches the luminescence theory of 0D metal halides, offering novel strategies for optical property modulation and fostering optical applications.

Dramatic Impact of Materials Combinations on the Chemical Organization of Core-Shell Nanocrystals: Boosting the Tm3+ Emission above 1600 nm.

This article represents the first foray into investigating the consequences of various material combinations on the short-wave infrared (SWIR, 1000-2000 nm) performance of Tm-based core-shell nanocrystals (NCs) above 1600 nm. In total, six different material combinations involving two different types of SWIR-emitting core NCs (α-NaTmF4 and LiTmF4) combined with three different protecting shell materials (α-NaYF4, CaF2, and LiYF4) have been synthesized. All corresponding homo- and heterostructured NCs have been meticulously characterized by powder X-ray diffraction and electron microscopy techniques. The latter revealed that out of the six investigated combinations, only one led to the formation of a true core-shell structure with well-segregated core and shell domains. The direct correlation between the downshifting performance and the spatial localization of Tm3+ ions within the final homo- and heterostructured NCs is established. Interestingly, to achieve the best SWIR performance, the formation of an abrupt interface is not a prerequisite, while the existence of a pure (even thin) protective shell is vital. Remarkably, although all homo- and heterostructured NCs have been synthesized under the exact same experimental conditions, Tm3+ SWIR emission is either fully quenched or highly efficient depending on the type of material combination. The most efficient combination (LiTmF4/LiYF4) achieved a high photoluminescence quantum yield of 39% for SWIR emission above 1600 nm (excitation power density in the range 0.5-3 W/cm2) despite significant intermixing. From now on, highly efficient SWIR-emitting probes with an emission above 1600 nm are within reach to unlock the full potential of in vivo SWIR imaging.

High efficiency in blue TADF OLED using favorable horizontal oriented host

An appropriate host featuring a wide band gap (Eg) and high triplet energy (T1) is crucial for facilitating highly efficient blue-light emitting devices. In this study, 4Ac26CzBz, a new host comprising acridan and carbazole moieties linked to a benzimidazole core, has been synthesized and characterized. Notedly, 4Ac26CzBz exhibits a wide optical gap (Eg) and high triplet energy (T1) of 3.3 and 3.0 eV, respectively, and has been proven a suitable host for blue thermally activated delayed fluorescence (TADF) OLED. By adopting 4TCzBN as a blue-light dopant, a remarkably high device external quantum efficiency of 35.8 % (59.8 cd/A and 62.8 lm/W) and a low turn-on voltage (<3 eV) have been demonstrated, with significant suppression of the efficiency roll-off, maintaining a high efficiency of 29.7 % as luminance at 1000 cd/m2. This excellent performance is deduced from the host’s ambipolar carrier transporting properties, which refer to its ability to transport both electrons and holes effectively, high photoluminescence quantum yield (PLQY) of 98.6 %, and highly horizontal orientation of transition dipole, as determined through diverse analytical measurements. The good material properties of 4Ac26CzBz and the high OLED performance reveal its potential for the next generation’s advanced display and lighting applications.

Nanofiber Space-Confined Fabrication of High-Performance Perovskite Films for Flexible Conversion of Fluorescence Quantum Yields in LED Applications.

Perovskite is an advanced optoelectronic semiconductor material that has garnered significant attention in recent years. However, its drawback lies in its environmental instability, limiting its practical applications. To tackle this issue, this research delved into the idea of creating a space-confined structure and used electrospinning to produce a film of perovskite nanocomposite fibers. By effectively encapsulating perovskite nanocrystals into a polymer matrix, the perovskite could be shielded from water and oxygen in the environment, thereby reducing the likelihood of perovskite decomposition and enhancing the stability of its structure and properties. This study examined the influence of material composition and the spinning process on the nanofiber structure to create good spatial confinement. This strategy resulted in a high photoluminescence quantum yield of over 80% and a long-term environmental stability of as long as 1000 h over 90% of the original PLQY. By harnessing the flexibility of the composite fibers, this study demonstrated the potential applications and performance of this nanocomposite film in flexible quantum fluorescence conversion for LED applications.

Clar's Aromatic π-Sextet Rule for the Construction of Red Multiple Resonance Emitter.

Despite the proliferation of multiple resonance (MR) materials in the blue to green spectral ranges, red MR emitters remain scarce in the literature, an area that certainly warrants attention for future applications. Here, through a clever application of classic Clar's aromatic π-sextet rule, we triumphantly constructed the first red MR emitter by substituting the conventional benzene ring core with anthracene (fewer π-sextets). Theoretical studies indicate that the quantity of π-sextets ultimately determines the optical bandgap of a molecule, rather than the number of fused benzene rings. Benefiting from the high photoluminescence quantum yield of ~94% and horizontal dipole ratio of ~90%, the corresponding narrowband red (luminescence wavelength: 608 nm) organic light-emitting diode shows a high external quantum efficiency of 27.3%, with only a slight decrease of 3.7% at an elevated luminance level of 100,000 cd/m2.

Realizing Stable Luminescence in Antimony Doped Hybrid Tin(IV) Chloride toward Full Spectrum WLED and Anticounterfeiting Applications.

The outstanding optical properties empower Sb3+-doped zero-dimensional hybrid metal halides as cutting-edge luminescent materials. In this research, we present an efficient hybrid tin chloride, TEA2SnCl6:Sb3+ (TEA = tetraethylammonium), with broad dual emission bands peaking in the blue and orange regions that arise from the singlet and triplet state emissions of [SbCl5]2-, respectively. TEA2SnCl6:Sb3+ demonstrates a high photoluminescence quantum yield (PLQY) of 83.5% under 328 nm excitation, while 358 nm light induces an orange emission with a PLQY of 92.5% and a low thermal quenching behavior (73.9% at 423 K). Benefiting from the appealing luminescence properties of TEA2SnCl6:Sb3+, a full spectrum white light-emitting diode (WLED) device and an anticounterfeiting model were constructed, affirming the potential use of Sb3+-doped TEA2SnCl6 hybrid metal halide in versatile application fields.

Narrowband Emission in Pt(II) Complexes via Ligand Engineering for Blue Phosphorescent Organic Light‐Emitting Diodes

AbstractIn this study, three stable tetradentate Pt(II) complexes are synthesized and characterized, namely, Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu, tailored for blue phosphorescent organic light‐emitting diodes to realize high‐efficiency and narrowband emissions via ligand engineering. Biphenyl (Pt‐biPh) or tert‐butyl‐modified biphenyl (Pt‐biPh5tBu and Pt‐biPh4tBu) is introduced into the carbene unit of the ligand to control the intermolecular interactions between the Pt(II) phosphors. Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu exhibit high photoluminescence quantum yields of 74%, 84%, and 92% with exciton lifetimes of 2.2, 2.3, and 2.5 µs, respectively, demonstrating rapid and efficient light emission. Furthermore, Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu show maximum external quantum efficiency (EQE) values of 18.1%, 19.0%, and 21.8%, respectively. Pt‐biPh5tBu and Pt‐biPh4tBu exhibit narrowband emission with a full width at half maximum of 21 nm owing to the small vibrational emission because of their sterically hindered and bulky ligand structures. Moreover, phosphor‐sensitized thermally activated delayed fluorescence devices employing a Pt‐biPh4tBu sensitizer achieve a high EQE of 28.6%. In particular, Pt‐biPh4tBu performs better than the state‐of‐the‐art phosphor as the sensitizer of the blue phosphor‐sensitized thermally activated delayed fluorescence devices in terms of the EQE.

Top-Down Synthesis of N-Type PbS Quantum Dots with High Photoluminescence Quantum Yield from Microsized Pb(OH)Cl.

Synthesis of PbS quantum dots (QDs) with uniform and controllable size is of great importance in realizing functionality manipulation, as well as building advanced devices, and these QDs have been normally synthesized via "bottom-up" colloidal chemistry. However, the problems of complicated techniques and the relative high cost of the "bottom-up" methods still need to be overcome. Herein, we present a facile and cost-effective "top-down" strategy for the production of PbS QDs with controllable sizes and narrow dispersions (4.8% < σ < 7%) based on the sulfuration reaction of highly active lead oxide and oxychloride intermediates. We investigated the two-step reaction mechanism of the QD synthesis. Initially, Pb(OH)Cl undergoes a reaction with oleic acid in the presence of oleylamine as an activator, leading to the formation of active lead oxide/oxychloride intermediates. Notably, this distinctive reaction induces the creation of numerous cracks within the intermediates, thereby augmenting the active sites available for the subsequent sulfuration reactions. In that, the sulfur precursor reacts with the intermediates, resulting in the rapid generation of a substantial number of PbS fragments. Over time, these small fragments undergo "ripening" until reaching the "critical" size threshold. Different from the ones obtained by the traditional "bottom-up" method, our synthesized colloidal QDs exhibit a S-rich surface and are confirmed to be N-type. In addition, size-tunable near-infrared photoluminescence renders these QDs a promising material for various applications.

Dual‐Core Engineering for Efficient Deep‐Blue Multiple Resonance Thermally Activated Delayed Fluorescent Materials

AbstractDeveloping narrowband blue multiple resonance (MR) organic emitters with Commission Internationale de L'Eclairage (CIE) y coordinates &lt;0.1 is essential for advanced display technologies. This study proposes a deep‐blue thermally activated delayed fluorescence (TADF) emitter, named 2BNO, which integrates two independent MR cores. Unlike many TADF materials with single‐bonded dual emitting cores, 2BNO utilizes a steric hindrance‐assisted fluorene bridge to achieve an orthorhombic molecular structure. The dual‐core MR‐TADF emitter shows enhanced light absorption and a high photoluminescence quantum yield. Notably, the emission of 2BNO is not significantly redshifted compared to single‐core compounds and maintains a narrow full width at half‐maximum (FWHM) of 24 nm with CIE coordinates of (0.147, 0.041) in 2Me‐THF solution, nearing the BT.2020 blue standard. Organic light‐emitting diodes (OLEDs) incorporating 2BNO as the emitter exhibit deep‐blue emission at 460 nm with a narrow FWHM of 29 nm and CIE coordinates of (0.14, 0.09). The dual emitting core design significantly improves device efficiency, achieving a high external quantum efficiency (EQE) of 19.8%. The dual‐core molecular design strategy in this work is demonstrated to be effective in promoting the efficiency of the TADF emitters while preserving deep‐blue color purity.

Room-temperature efficient and tunable interlayer exciton emissions in WS2/WSe2 heterobilayers at high generation rates.

Transition metal dichalcogenide (TMDC) heterobilayers (HBs) have been intensively investigated lately because they offer novel platforms for the exploration of interlayer excitons (IXs). However, the potentials of IXs in TMDC HBs have not been fully studied as efficient and tunable emitters for both photoluminescence (PL) and electroluminescence (EL) at room temperature (RT). Also, the efficiencies of the PL and EL of IXs have not been carefully quantified. In this work, we demonstrate that IX in WS2/WSe2 HBs could serve as promising emitters at high generation rates due to its immunity to efficiency roll-off. Furthermore, by applying gate voltages to balance the electron and hole concentrations and to reinforce the built-in electric fields, high PL quantum yield (QY) and EL external quantum efficiency (EQE) of ∼0.48% and ∼0.11% were achieved at RT, respectively, with generation rates exceeding 1021 cm-2·s-1, which confirms the capabilities of IXs as efficient NIR light emitters by surpassing most of the intralayer emissions from TMDCs.

Rare earth Nd3+-doped organic-inorganic hybrid perovskite quantum dots for white LED

Lead halide perovskite quantum dots (QDs) have garnered significant attention due to their tunable band gaps, unique quantum confinement effects, and high photoluminescence quantum yields (PLQYs). Among them, Organic-inorganic QDs make them promising candidates for optoelectronic devices such as quantum dot light-emitting diodes (QLEDs), solar cells, lasers, and photodetectors. However, the toxicity of lead (Pb) has raised environmental and health concerns, hindering their industrial application. To alleviate concerns about heavy metals Pb, extensive research has been conducted on B-site doping and the development of lead-free perovskites. Herein, we firstly developed B-site doping strategy on organic-inorganic hybrid perovskite QDs via rare-earth elements. Neodymium (III) (Nd3+) doped FAPbBr3 QDs were prepared through the ligand-assisted reprecipitation method at room temperature. The B-site doping strategy could alleviate the heavy metal problem of Pb and modulate the band gap of FAPbBr3 QDs facilely. The results demonstrated that increasing the concentration of Nd³⁺ can change the emission of FAPbBr₃ QDs from pure green to deep blue. Specifically, we achieved highly pure blue emission (∼438 nm) with a full width at half maximum (FWHM) of 13 nm for Nd³⁺-doped FAPbBr₃ QDs. Time-resolved photoluminescence (TRPL) spectroscopy revealed a decrease in the lifetime of FAPbBr₃ QDs from 22.86 to 15.46 ns as the doping concentration increased. Additionally, we fabricated a white LED (WLED) utilizing blue-emitting Nd³⁺-doped FAPbBr₃, green-emitting FAPbBr₃ QDs, and red QDs, achieving a white emission color coordinate of (0.33, 0.36). This study pioneers the application of B-site rare-earth doping in organic-inorganic hybrid perovskite QDs, demonstrating that B-site composition engineering is a reliable strategy to further exploit the perovskite family for wider optoelectronic applications.

Organic‐Inorganic Hybrid Cuprous‐Based Metal Halides with Unique Two‐Dimensional Crystal Structure for White Light‐Emitting Diodes

AbstractTernary cuprous (Cu+)‐based metal halides, represented by cesium copper iodide (e.g., CsCu2I3 and Cs3Cu2I5), are garnering increasing interest for light‐emitting applications owing to their intrinsically high photoluminescence quantum yield and direct band gap. Toward electrically driven light‐emitting diodes (LEDs), it is highly desirable for the light emitters to have a high structural dimensionality as it may favor efficient electrical injection. However, unlike lead‐based halide perovskites whose light‐emitting units can be facilely arranged in three‐dimensional (3D) ways, to date, nearly all ternary Cu+‐based metal halides crystallize into 0D or 1D networks of Cu−X (X=Cl, Br, I) polyhedra, whereas 3D and even 2D structures remain mostly uncharted. Here, by employing a fluorinated organic cation, we report a new kind of ternary Cu+‐based metal halides, (DFPD)CuX2 (DFPD+=4,4‐difluoropiperidinium), which exhibits unique 2D layered crystal structure. Theoretical calculations reveal a highly dispersive conduction band of (DFPD)CuBr2, which is beneficial for charge carrier injection. It is also of particular significance to find that the 2D (DFPD)CuBr2 crystals show appealing properties, including improved ambient stability and an efficient warm white‐light emission, making it a promising candidate for single‐component lighting and display applications.

Multiple Enol-Keto Isomerization and Excited-State Unidirectional Intramolecular Proton Transfer Generate Intense, Narrowband Red OLEDs.

A novel series of excited-state intramolecular proton transfer (ESIPT) emitters, namely, DPNA, DPNA-F, and DPNA-tBu, endowed with dual intramolecular hydrogen bonds, were designed and synthesized. In the condensed phase, DPNAs exhibit unmatched absorption and emission spectral features, where the minor 0-0 absorption peak becomes a major one in the emission. Detailed spectroscopic and dynamic approaches conclude fast ground-state equilibrium among enol-enol (EE), enol-keto (EK), and keto-keto (KK) isomers. The equilibrium ratio can be fine-tuned by varying the substitutions in DPNAs. Independent of isomers and excitation wavelength, ultrafast ESIPT takes place for all DPNAs, giving solely KK tautomer emission maximized at >650 nm. The spectral temporal evolution of ESIPT was resolved by a state-of-the-art technique, namely, the transient grating photoluminescence (TGPL), where the rate of EK* → KK* is measured to be (157 fs)-1 for DPNA-tBu, while a stepwise process is resolved for EE* → EK* → KK*, with a rate of EE* → EK* of (72 fs)-1. For all DPNAs, the KK tautomer emission shows a narrowband emission with high photoluminescence quantum yields (PLQY, ∼62% for DPNA in toluene) in the red, offering advantages to fabricate deep-red organic light-emitting diodes (OLED). The resulting OLEDs give high external quantum efficiency with a spectral full width at half-maximum (FWHM) as narrow as ∼40 nm centered at 666-670 nm for DPNAs, fully satisfying the BT. 2020 standard. The unique ESIPT properties and highly intense tautomer emission with a small fwhm thus establish a benchmark for reaching red narrowband organic electroluminescence.

Aggregation Induced Emission-Based Covalent Organic Frameworks for High-Performance Optical Wireless Communication.

Here, we report the first utilization of covalent organic frameworks (COFs) in optical wireless communication (OWC) applications. In the solid form, aggregation-induced emission (AIE) luminogen often shows promising emissive characteristics that augment radiative decays and improve fluorescence. We have synthesized an AIE-COF through the Knoevenagel condensation reaction by taking advantage of the ability to carefully design and alter the COF structure by integrating an AIE luminogen with linear building blocks. The synthesized AIE-COF exhibited a high solid-state photoluminescence quantum yield (∼39%) and a short photoluminescence lifetime (∼1 ns), crucial for achieving modulation bandwidth for high-speed OWC applications. For comparison, we constructed an aggregation-caused quenching based COF, showing a similar lifetime but almost insignificant quantum yield. The orthogonal frequency-division multiplexing modulation strategy employed by the AIE-COF demonstrates remarkable high-rate data transmission, with a wide -3 dB modulation bandwidth of nearly 200 MHz and achieving high net data rates of 825 Mb/s, outperforming traditional materials. These results open new avenues for the ability to design and finetune new COF materials for their utilization as color converters in developing cutting-edge OWC components, enabling faster and more efficient data transfer.

High‐Efficiency Deep Red Fluorescent Material with Aggregation Induced Emission and the Application in Organic Light‐Emitting Diodes

AbstractThe development of highly efficient deep red materials with emission wavelength beyond 650 nm remains a big challenge due to the constraints imposed by the energy gap rule. In this work, a donor‐acceptor‐donor type emitter, 4,7‐bis (10‐(4‐(tert‐butyl) phenyl)‐10H‐phenothiazin‐3‐yl) benzo[c][1,2,5] thiadiazole (TBPPTZ) is designed and synthesized. Resulting from the slight twist angle between the donor and acceptor units, TBPPTZ exhibits nearly planar conformation and an extended conjugated structure. TBPPTZ shows a deep red emission peak at 687 nm and aggregation induced emission property with a high photoluminescence quantum yield of 45 % in neat thin film. The optimized organic light‐emitting diode (OLEDs) utilizing TBPPTZ as the non‐doped emissive layer obtains a high external quantum efficiency (EQE) up to 2.51 % with an electroluminescence (EL) peak at 676 nm, aligning with the Commission Internationale de L'Eclairage (CIE) coordinates (0.68, 0.31), which shows a small EQE roll‐off of only 5.6 % at 100 cd m−2. Additionally, the doped OLED achieves an EQE up to 5.09 %, with an EL peak at 656 nm and CIE coordinates of (0.65, 0.34). The findings of this research not only contribute to achieve highly efficient deep red OLEDs but also offer a novel and effective deep red molecular strategy to realize high‐quality OLEDs.

Incorporating Sb (III) and Bi (III) ions into Cs2AgNaInCl6 perovskite toward efficient white-light emission with high color rendering index

Single phosphor with efficient and high quality white-light emission is necessary for lighting applications. In this work, we report a double perovskite, Cs2AgNaInCl6 with Bi3+ and Sb3+ incorporation, which demonstrates excellent white-light properties including tunable emission component and correlated colour temperature (CCT). Using the broad-band emission of self-trapped excitons (STEs) associated with Bi3+ and Sb3+ in the Cs2AgNaInCl6 host, the blue and orange dual-band STEs emission located at 460 and 565 nm covers the entire visible range to achieve high-quality white light emission. The relative intensity of the dual emission components can be adjusted flexibly by modulating the doping ratio of Bi3+ and Sb3+. The dual STEs emission shares the same optimal excitation wavelength at 340 nm. The optimal sample of Bi3+ (1 %) and Sb3+ (10 %) codoped Cs2Ag0.1Na0.9InCl6 exhibits high color rendering index (CRI) of up to 93, and high photo-luminescence quantum yield (PLQY) of 76 %. This codoping in double perovskite approach represents a promising method for achieving high-quality white lighting application within a single phosphor.

Controllable p- and n-type behaviours in emissive perovskite semiconductors.

Reliable control of the conductivity and its polarity in semiconductors is at the heart of modern electronics1-7,and has led to key inventions including diodes, transistors, solar cells, photodetectors, light-emitting diodes and semiconductor lasers. For archetypal semiconductors such as Si and GaN, positive (p)- and negative (n)-type conductivities are achieved through the doping of electron-accepting and electron-donating elements into the crystal lattices, respectively1-6. For halide perovskites, which are an emerging class of semiconductors, mechanisms for reliably controlling charge conduction behaviours while maintaining high optoelectronic qualities are yet to be discovered. Here we report that the p- and n-type characteristics in a wide-bandgap perovskite semiconductor can be adjusted by incorporating a phosphonic acid molecular dopant with strong electron-withdrawing abilities. The resultant carrier concentrations were more than 1013 cm-3 for the p- and n-type samples, with Hall coefficients ranging from -0.5 m3 C-1 (n-type) to 0.6 m3 C-1 (p-type). A shift of the Fermi level across the bandgapwas observed. Importantly, the transition from n- to p-type conductivity was achieved while retaining high photoluminescence quantum yields of 70-85%. The controllable doping in the emissive perovskite semiconductor enabled the demonstration of ultrahigh brightness (more than 1.1 × 106 cd m-2) and exceptional external quantum efficiency (28.4%) in perovskite light-emitting diodes with a simple architecture.

Control of Hybrid Exciton Lifetime in MoSe2/WS2 Moiré Heterostructures.

Hybrid excitons, characterized by their strong oscillation strength and long lifetimes, hold great potential as information carriers in semiconductors. They offer promising applications in exciton-based devices and circuits. MoSe2/WS2 heterostructures represent an ideal platform for studying hybrid excitons, but how to regulate the exciton lifetime has not yet been explored. In this study, layer hybridization is modulated by applying electric fields parallel or antiparallel to the dipole moment, enabling us to regulate the exciton lifetime from 1.36 to 4.60ns. Furthermore, the time-resolved photoluminescence decay traces are measured at different excitation power. A hybrid exciton annihilation rate of 8.9 × 10-4cm2s-1 is obtained by fitting. This work reveals the effects of electric fields and excitation power on the lifetime of hybrid excitons in MoSe2/WS2 1.5° moiré heterostructures, which play important roles in high photoluminescence quantum yield optoelectronic devices based on transition-metal dichalcogenides heterostructures.

Design and performance of sulfur and selenium-substituted triarylboron D3-A TADF emitters for OLED applications

This study presents the design, synthesis, and comprehensive theoretical and photophysical analysis of two new D3-A type thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diode (OLED) applications. Utilizing a triarylboron core as the electron-accepting group and phenothiazine (PTZ) or phenoselenazine (PSZ) as electron-donating units, the molecules BTP-S and BTP-Se were developed. The D3-A structure supports the separation of frontier molecular orbitals (FMOs), leading to minimized singlet-triplet energy gaps (ΔEST), which are crucial for the TADF mechanism. Density functional theory (DFT) calculations presented that BTP-S and BTP-Se exhibit band gaps (Eg) of 2.52 and 3.23 eV, respectively, with BTP-S showing an ΔEST value as low as 0.007 eV for the S1-T1 transition at the lowest energy conformation. Photophysical studies revealed high photoluminescence quantum yields (PLQYs) for both compounds, with BTP-S achieving up to 85 % in mCP films and BTP-Se up to 59 %. In vacuum-processed OLEDs, BTP-S achieved a maximum external quantum efficiency (EQE) of 25.3 %, a current efficiency (ηc) of 195.8 cd/A, and a maximum luminance (Lmax) of 17356 cd/m2, while BTP-Se reached an EQE of 7.5 %, an ηc of 132.19 cd/A, and an Lmax of 16826 cd/m2 likely limited by the contributions of a folded-donor conformer enabled by the Se substitution. These findings underscore the impact of donor unit selection and conformation on the TADF characteristics, and provide valuable insights for designing high-performance OLED materials.