Chiral Thermally Activated Delayed Fluorescence Materials Based on R/S-N2,N2′-Diphenyl-[1,1′-binaphthalene]-2,2′-diamine Donor with Narrow Emission Spectra for Highly Efficient Circularly Polarized Electroluminescence

In this study, two pairs of chiral thermally activated delayed fluorescence (TADF) materials enabling circularly polarized luminescence (CPL) named R/S-p- BAMCN (rod-shape) and R/S-o- BAMCN (helix-shape) are prepared based on a new pair of chiral donor (D*), R/S-N²,N²′-diphenyl-[1,1′-binaphthalene]-2,2′-diamine (R/S- BAM ), and two cyano (CN) acceptors. Due to the rigid molecular structure and special intramolecular arrangement, the chiral TADF materials show high photoluminescence quantum efficiency (up to 0.86) with narrow full-width at half-maximum (38 nm in cyclohexane, 51 nm in toluene) and photoluminescence dissymmetry factor (|g_PL|) up to 5.3 × 10⁻³. Particularly, the circularly polarized OLEDs (CP-OLEDs) with rod-shaped R/S-p- BAMCN as the emitter show high device performances with the maximum external quantum efficiency nearing 28%. Meanwhile, the semi-transparent CP-OLEDs based on helix-shaped R/S-o- BAMCN exhibit obvious circularly polarized electroluminescence (CPEL) properties with the electroluminescence |g_EL| factors around 4.6 × 10⁻³. The strategy of rigid D*-A-D* structure with special arrangement of chiral donor provides a direct way to obtain efficient CP-TADF materials with narrow emission spectra and promising CPL properties for better CPEL performance.     

Triptycene-derived TADF enantiomers displaying circularly polarized luminescence and high-efficiency electroluminescence

A pair of novel circularly polarized thermally activated delayed fluorescence (CP-TADF) enantiomers (+)-(S,S)-CTRI-Cz and (−)-(R,R)-CTRI-Cz based on chiral triptycene scaffold were designed and synthesized. The obtained triptycene-derived enantiomers displayed obvious TADF activities with small singlet-triplet energy gap value (ΔE_ST) of 0.20 eV and characteristic microsecond delayed lifetime of 15.4 μs. Moreover, the TADF enantiomers showed mirror-image circular dichroism (CD) and circularly polarized luminescence (CPL) activities, and their luminescence dissymmetry factors (g_lum) were about ±0.9 × 10⁻³. Finally, by using the TADF enantiomers as emitters, the optimized organic light-emitting diodes (OLEDs) achieved maximum external quantum efficiency (EQE_max), current efficiency (CE_max) and power efficiency (PE_max) of 15.0%, 48.8 cd/A and 46.9 lm/W, respectively.     

Semitransparent Circularly Polarized Phosphorescent Organic Light-Emitting Diodes with External Quantum Efficiency over 30% and Dissymmetry Factor Close to 10−2

To concurrently realize large electroluminescence dissymmetry factor and high device efficiency remains a formidable challenge in the development of circularly polarized organic light-emitting diode (CP-OLED). In this work, by introducing a famous chiral resource of R-camphor, two green chiral iridium(III) isomers of Λ/Δ-Ir-(R-camphor) containing dual stereogenic centers at iridium and ancillary ligand, are efficiently synthesized. Benefiting from their high phosphorescence quantum yields (≈93%) and obvious circularly polarized photoluminescence property with dissymmetry factors (|g_PL|) in the 10⁻³ order of magnitude, the circularly polarized phosphorescent organic light-emitting diodes using these chiral emitters show excellent performances with the maximum external quantum efficiency (EQE_max) of 30.6%, low efficiency roll-off, and intense circularly polarized electroluminescence signal with dissymmetry factor (g_EL) in the 10⁻⁴ order of magnitude. By the novel device engineering with semitransparent cathode, the resulting g_EL values are significantly boosted by one order of magnitude, up to 7.70 × 10⁻³, which is the highest among the CP-OLEDs with chiral iridium complexes. Noteworthy, the semitransparent devices deliver a record-high EQE_max of 18.8% among the semitransparent OLEDs. The combination of novel chiral Ir(III) complexes and the semitransparent devices sheds light on the development of high performance CP-OLEDs with simultaneously high efficiency and large dissymmetry factor.     

Cascade Chirality Transfer Through Diastereomeric Interaction Enables Efficient Circularly Polarized Electroluminescence

Organic light-emitting diodes (OLEDs) with circularly polarized emission can bring a breakthrough innovation in display technologies. However, it remains challenging due to the difficulty in obtaining high efficiency and large dissymmetry factor simultaneously. Herein, it is demonstrated that robust circularly polarized (CP) electroluminescence can be induced by cascade chirality transfer within the emitting layer. Through spectroscopic data and theoretical analysis, the initiation of this chirality transfer process is assigned to diastereomeric interaction. Utilizing this interaction and excellent Förster resonance energy transfer ability to the well-known racemic emitter, CP-OLEDs with an electroluminescence dissymmetry factor (|g_EL|) up to 3.2 × 10⁻³ and high external quantum efficiency (EQE) of 32% are successfully fabricated. These devices also show ultra-low efficiency roll-off at high brightness, with EQE ≥ 20% at 128 000 cd m⁻². This study paves the way for the future development of CP-OLEDs through synergistic materials and device engineering.     

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.     

High Comprehensive Circularly Polarized Electroluminescence Performance Improved by Chiral Coassembled Host Materials

Circularly polarized organic light-emitting diodes are of great significance in 3D displays. However, achieving circularly polarized electroluminescence (CP-EL) simultaneously with a large dissymmetry factor (g_EL) and high efficiency still remains a formidable challenge. Herein, a facile and efficient strategy is developed for improving the performance of CP-EL devices using device emitting layers of chiral coassembled helix nanofiber host materials. Chiral coassembled helix nanofiber host materials ((S-/R-2Cz)_0.2-(PFpy)_0.8) could be smartly constructed through intermolecular π–π stacking interactions between the achiral conjugated pyridine-based polymer acceptor (PFpy) and the chiral binaphthyl-based donor (S-/R-2Cz). Significantly, the resulting chiral coassembled hosts (S-/R-2Cz)_0.2-(PFpy)_0.8 greatly promote a commercially available achiral phosphorescence emitter to achieve solution-processed red CP-EL device performances at 620 nm with a high external quantum efficiency of 4.1% and a large |g_EL| value of 0.014.     

Theoretical studying of basic photophysical processes in a thermally activated delayed fluorescence copper(I) complex: Determination of reverse intersystem crossing and radiative rate constants

The photophysical properties of a mononuclear Cu(dppb)(pz₂Bph₂) complex have been investigated by employing the thermal vibration correlation function (TVCF) approach. The harmonic oscillator model with origin displacement, distortion, and Duschinsky rotation effects for the potential energy surfaces are considered. Absorption spectrum obtained by the scalar relativistic density functional theory combined with restricted open-shell configuration interaction including spin-orbit coupling effects is in excellent agreement with the experimental data. We found that the intersystem crossing (ISC) from the first excited singlet state (S₁) to the triplet state (T₁) is forbidden by direct spin-orbit coupling at the first-order perturbation, but becomes allowed through combined with vibronic coupling. The reverse intersystem crossing (RISC) proceeds at a rate of K_RISC = 3.98 × 10⁸ s⁻¹ at room temperature 300 K, which is about 6 order of magnitude larger than the mean phosphorescence rate, K_{P, av} = 7.3 × 10² s⁻¹. At the same time, the ISC rate K_ISC = 3.06 × 10⁹ s⁻¹ is again about 3 order of magnitude larger than the fluorescence rate K_F = 6.47 × 10⁶ s⁻¹. This implies that the S₁ state can be populated from the T₁ state, TADF should be observed and TADF decay time is τ(300 K) = 2.32 μs by fitting calculation. But at 30 K, the situation will change. The RISC rate becomes very small, about K_RISC = 1.19 × 10¹ s⁻¹, while the ISC rate only decreases slightly from K_ISC = 3.06 × 10⁹ s⁻¹ to K_ISC = 1.93 × 10⁹ s⁻¹. As a consequence, the Cu(dppb)(pz₂Bph₂) complex is highly attractive candidates for applications of TADF.     

Discovering New Type of Lead-Free Cluster-Based Hybrid Double Perovskite Derivatives with Chiral Optical Activities and Low X-Ray Detection Limit

2D chiral hybrid perovskites have recently emerged as outstanding semiconductor materials. However, most of the reported 2D chiral perovskites have limited structural types and contain high levels of toxic lead, which severely hinders their further applications. Herein, by using a mixed-cation strategy, an unprecedented type of lead-free cluster-based 2D chiral hybrid double perovskite derivatives are successfully obtained, [(R/S-PPA)₄(IPA)₆Ag₂Bi₄I₂₄]·2H₂O ( 1-R and 1-S ), and [(R/S-PPA)₄(n-BA)₆Ag₂Bi₄I₂₄]·2H₂O ( 2-R and 2-S ) (R/S-PPA=R/S–1-phenylpropylamine; IPA=isopentylamine; n-BA=n-butylamine). Their inorganic skeletons are linked by binuclear {Bi₂I₁₀} and infinite chain {Ag₂Bi₂I₁₄}_∞, in which bismuth clusters and multiple coordination modes (e.g., tetrahedral AgI₄ and octahedral AgI₆) are introduced into the double perovskite system for the first time. This introduction induces distortion of the inorganic layer, which may facilitate the transfer of chirality from the chiral cations into achiral double perovskite skeletons. Further, circular dichroism measurements and circularly polarized light detection confirm their inherent chiral optical activities. In addition, 1-S exhibits an ultralow X-ray detection limit of 129.5 nGy s⁻¹, which is 42-fold lower than that of demands in regular medical diagnosis (5.5 µGy s⁻¹). This study provides a pathway to construct novel type of lead-free cluster-based double perovskite derivatives.     

Multilevel Structure Engineered Lead-Free Piezoceramics Enabling Breakthrough in Energy Harvesting Performance for Bioelectronics

The prevalence of wearable/implantable medical electronics together with the rapid development of the Internet of Medicine Things call for the advancement of biocompatible, reliable, and high-efficiency energy harvesters. However, most current harvesters are based on toxic lead-based piezoelectric materials, raising biological safety concerns. What hinders the application of lead-free piezoelectric energy harvesters (PEHs) is the low power output, where the key challenge lies in obtaining a high piezoelectric voltage constant (g₃₃) and harvesting figure of merit (d₃₃ × g₃₃). Here, micron pores are introduced into phased boundary engineered high-performance (K, Na)NbO₃-based ceramic matrix, resulting in the state-of-the-art g₃₃ and the highest d₃₃ × g₃₃ values of 57.3 × 10⁻³ Vm N⁻¹ and 20887 × 10⁻¹⁵ m² N⁻¹ in lead-free piezoceramics, respectively. Concomitantly, ultrahigh energy harvesting performances are obtained in porous ceramic PEHs, with output voltage and power density of 200 V and 11.6 mW cm⁻² under instantaneous force impact and an average charging rate of 14.1 µW under high-frequency (1 MHz) ultrasound excitation, far outperforming previously reported PEHs. Porous ceramic PEHs are further developed into wearable and bio-implantable devices for human motion sensing and percutaneous ultrasound power transmission, opening avenues for the design of next-generation eco-friendly WIMEs.     

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.     

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.     

Organic Molecular Intercalated V3O7·H2O with High Operating Voltage for Long Cycle Life Aqueous Zn-Ion Batteries

V₃O₇·H₂O (VO) is an attractive cathode material for high-capacity aqueous Zn-ion batteries (AZIBs), but it is limited by slow ion mobility and low working platform voltage. Here, a 1,3-propane diamine (DP)-intercalated VO with nanoribbon-assembled thorn flower-like structure is fabricated by a facile hydrothermal method, noted as VO-DP. The study shows that the zinc ion diffusion coefficient in VO-DP (3.1 × 10⁻⁸ cm⁻² s⁻¹) is five orders of magnitude higher than that of a pure VO counterpart. Auxiliary density functional theory simulation shows that the embedded energy of zinc ions in VO-DP significantly decreases from 0.24 to −2.5 eV, thus leading to excellent diffusion kinetics and superior rate performance. Benefiting from these unique properties, AZIBs composed of VO-DP cathodes exhibit high operating voltage (0.89 V), remarkable capacities of 473 mA h g⁻¹ at 0.05 A g⁻¹, excellent rate capability (144 mA h g⁻¹ at 10 A g⁻¹) and long-term cycling performance (73% capacity retention over 15 000 cycles at 10 A g⁻¹).     

Modifying Electronic Structure of Cation-Exchanged Bimetallic Sulfide/Metal Oxide Heterostructure through In Situ Inclusion of Silver (Ag) Nanoparticles for Extrinsic Pseudocapacitor

The inferior electrical conductivity of conventional electrodes and their slow charge transport impose limitations on the electrochemical performance of supercapacitors (SCs) using those electrodes, necessitating strategies to overcome the limitations. An in situ Ag ion-incorporated cation-exchanged bimetallic sulfide/metal oxide heterostructure (Ag-Co_9-xFe_xS₈@α-Fe_xO_y) is synthesized using a two-step hydrothermal method. The coordination bond formation and Ag nanoparticle (NP) incorporation improve the electrical conductivity and adhesion of the heterostructure and reduce its interface resistance and volume expansion throughout the charge/discharge cycles. Density functional theory investigations indicate that the remarkable interlayer and interparticle conductivities of the heterostructure resulting from Ag doping have changed its electronic states, leading to an enhanced electrical conductivity. The optimized electrode has an excellent specific capacity (213.6 mA h g⁻¹ at 1 A g⁻¹) and can maintain 93.2% capacity retention with excellent Coulombic efficiency over 20 000 charge/discharge cycles. A flexible solid-state extrinsic pseudocapacitor (EPSC) is fabricated using Ag-Co_9-xFe_xS₈@α-Fe_xO_y and Ti₃C₂T_X electrodes. The EPSC has specific and volumetric capacitances of 259 F g⁻¹ and 2.7 F cm⁻³ at 0.7 A g⁻¹, respectively, an energy density of 80.9 Wh kg⁻¹ at 525 W kg⁻¹, and a capacity retention of 92.8% over 5000 charge/discharge cycles.     

Aggregation induced intermolecular charge transfer in simple nonconjugated donor–acceptor system

The exploration of exciplex for organic light-emitting diodes (OLEDs) has been fleetly developed. However, many of them confront with the problems like phase separation and poor solubility, hampering their utilization in solution process. Hence, a series of soluble exciplex luminophores with the simple architecture of D-spacer-A (mCP-6C-TRZ, phCz-6C-TRZ and 2phCz-6C-TRZ) are synthesized and characterized, in which, the alkyl chain as ample spacer breaks the molecular backbone conjugation, induces intermolecular charge transfer process instead of intramolecular charge transfer in solid state. These materials are endowed with narrowed singlet−triplet splitting energy (ΔE_ST), efficient reverse intersystem crossing (RISC) process, and distinct thermally activated delayed fluorescence (TADF) characteristics. In view of their high triplet energy level (E_T) and bipolar carrier transport ability, where efficient exciplexes are applied as the host, the solution-processed phosphorescence devices realize a low efficiency roll-off of 7.0% at 1000 cd m⁻², high luminance, current efficiency (CE) and external quantum efficiency (EQE) of 25,990 cd m⁻², 20.0 cd A⁻¹ and 6.7%, respectively. These results offer a promising tactic to the establishment of exciplex with TADF feature as host for fabricating efficient solution processed OLEDs.     

Controllable thin-film morphology and structure for 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8BTBT) based organic field-effect transistors

Organic field-effect transistors (OFETs) based on organic semiconductor material 2,7-dioctyl[1]benzothieno[3,2-b] benzothiophene (C8BTBT) as the active layer were fabricated by using organic molecular beam deposition (OMBD) and solution-processed methods, in which the C8BTBT thin-film morphology could be well controlled. In OMBD method, C8BTBT thin-film morphology could be controlled by the thickness of organic semiconductor layer and the deposition rate, of which the high-quality C8BTBT thin film was obtained at a thickness of about 20 nm and at a deposition rate of 1.2 nm/min, resulting in an obvious mobility improvement from 2.8 × 10⁻³ cm² V⁻¹ s⁻¹ to 1.20 cm² V⁻¹ s⁻¹. While in the solution-processing, C8BTBT thin-film morphology and thickness are related to the spin-coating speed and the substrate position in spin coater, i.e., in-centre and off-centre position. The off-centre spin-coating with an optimized speed produced large-size domain C8BTBT thin film and accordingly resulted in a mobility of 1.47 cm² V⁻¹ s⁻¹. Furthermore, an additive polystyrene (PS) was added into C8BTBT solution could further improve the thin-film morphology with more metal-stable phase as well as improve the interface contact with the substrate SiO₂, resulting in the highest mobility up to 3.56 cm² V⁻¹ s⁻¹. The research suggested that C8BTBT-based OFETs with the mobility over 1.20 cm² V⁻¹ s⁻¹ could be fabricated by using both OMBD and solution-processed methods through the thin-film morphology and structure optimization, which shows the potential applications in high-performance flexible and printed electronics.     

Organic-Carbon Core–Shell Structure Promotes Cathode Performance for Na-Ion Batteries

The organic-carbon core-shell structure is constructed for the cathode material of [N,N'-bis(2-anthraquinone)]-perylene-3,4,9,10-tetracarboxydiimide (PTCDI-DAQ, 200 mAh g⁻¹) through an interesting strategy called the surface self-carbonization. As expected, the organic-carbon core–shell structure (PTCDI-DAQ@C) can endow PTCDI-DAQ the outstanding cathode performance in Na-ion batteries. In half cells using 1 m NaPF₆/DME, PTCDI-DAQ@C can maintain 173 mAh g⁻¹ for nearly one year, while PTCDI-DAQ quickly decreases from 203 to 121 mAh g⁻¹ only after 100 cycles. Meanwhile, the constructed Na-ion full cells with the Na-intercalated hard carbon anode can deliver the peak discharge capacity of 195 mAh g⁻¹_cathode and the high median voltage of 1.7 V in 0.9–3.2 V, corresponding to the peak energy densities of 332 Wh kg⁻¹_cathode and 184 Wh kg⁻¹_{total mass}, respectively. Notably, the electrode materials only include the very cheap elements of C, H, O, N, and Na. Furthermore, the Na-ion full cells can also show the very impressive high-temperature (197 mAh g⁻¹_cathode at 50 °C) and subzero (185/90 mAh g⁻¹_cathode at −10/−40 °C) performances, respectively. To the best of the authors’ knowledge, the comprehensive properties of the Na-ion full cells are the best results based on organic cathodes.     

Tailoring Rational Crystal Orientation and Tunable Sulfur Vacancy on Metal-Sulfides toward Advanced Ultrafast Ion-Storage Capability

Attracted by high energy density and power density, metal-sulfides anodes have promising application prospects in fast charging batteries. However, they still suffer from low electrical conductivity and sluggish electrochemical kinetics, resulting in poor fast charging capacity. Herein, spindle-like antimony sulfide (Sb₂S₃) is rationally tailored with favorable (hk1) crystal orientation and rich S-vacancies using a simple hydrothermal method, which improve electric conductivity significantly. Triggered by S-vacancies lattice defects, Sb O C interfacial bonds and S-doped carbon layer are built successfully. Under their multiple-controlling synergistic effects, electrochemical kinetics and reaction reversibility are promoted effectively. As expected, Sb₂S₃/HTAB@C show high average initial coulombic efficiency of 86.12%, and deliver 624.5 and 428.4 mAh g⁻¹ after cycling 100 cycles at 10.0 and 30.0 A g⁻¹ respectively in Li-ion batteries (LIBs). Electrochemical kinetic analysis and theoretical calculations indicate that superior ultrafast charging capacity originates from quickened interfacial electron/ions transferring and alleviates electrochemical polarization. Ex situ technologies powerfully prove good stability of (hk1) orientation, Sb O C bonds and S-doped carbon layer. Notably, full LIBs of SS/H@C versus LiFePO₄@C display 500.9 and 398.3 mAh g⁻¹ at 5.0 and 10.0 A g⁻¹, respectively. This study is anticipated to open avenue to develop advanced metal-sulfides anodes for fast charging batteries.     

Highly Efficient Circularly Polarized Electroluminescence from Aggregation‐Induced Emission Luminogens with Amplified Chirality and Delayed Fluorescence

Development of highly efficient circularly polarized organic light‐emitting diodes (CPOLEDs) has gained increasing interest as they show improved luminous efficiency and high contract 3D images in OLED displays. In this work, a series of binaphthalene‐containing luminogenic enantiomers with aggregation‐induced emission (AIE) and delayed fluorescence properties is designed and synthesized. These molecules can emit from green to red light depending on the solvent polarity due to the twisted intramolecular charge transfer effect. However, their solid powders show bright light emissions, demonstrating a phenomenon of AIE. All the molecules exhibit Cotton effects and circularly polarized luminescence in toluene solution and films. Multilayer CPOLEDs using the doped and neat films of the molecules as emitting layers are fabricated, which exhibit high external quantum efficiency of up to 9.3% and 3.5% and electroluminescence dissymmetry factor (g_EL) of up to +0.026/?0.021 and +0.06/?0.06, respectively. Compared with doped CPOLEDs, the nondoped ones show higher g_EL and much smaller current efficiency roll‐off due to the stronger AIE effect. By altering the donor unit, the electroluminescence maximum of the doped film can vary from 493 to 571 nm. As far as it is known, this is the first example of efficient CPOLEDs based on small chiral organic molecules.     

AlGaN/GaN Schottky barrier diodes on silicon substrates with various Fe doping concentrations in the buffer layers

This study demonstrated AlGaN/GaN Schottky barrier diodes (SBDs) for use in high-frequency, high-power, and high-temperature electronics applications. Four structures with various Fe doping concentrations in the buffer layers were investigated to suppress the leakage current and improve the breakdown voltage. The fabricated SBD with an Fe-doped AlGaN buffer layer of 8 × 10¹⁷ cm^− 3 realized the highest on-resistance (R_ON) and turn-on voltage (V_ON) because of the memory effect of Fe diffusion. The optimal device was the SBD with an Fe-doped buffer layer of 7 × 10¹⁷ cm^− 3, which exhibited a R_ON of 31.6 mΩ-cm², a V_ON of 1.2 V, a breakdown voltage of 803 V, and a buffer breakdown voltage of 758 V. Additionally, the low-frequency noise decreased when the Fe doping concentration in the buffer layer was increased. This was because the electron density in the channel exhibited the same trend as that of the Fe doping concentration in the buffer layer.     

Hierarchical Design of Cross-Linked NiCo2S4 Nanowires Bridged NiCo-Hydrocarbonate Polyhedrons for High-Performance Asymmetric Supercapacitor

Engineering core-shell materials with rationally designed architectures and components is an effective strategy to fulfill the high-performance requirements of supercapacitors. Herein, hierarchical candied-haws-like NiCo₂S₄@NiCo(HCO₃)₂ core-shell heterostructure (NiCo₂S₄@HCs) is designed with NiCo(HCO₃)₂ polyhedrons being tightly strung by cross-linked NiCo₂S₄ nanowires. This rational design not only creates more electroactive sites but also suppresses the volume expansion during the charge–discharge processes. Meanwhile, density functional theory calculations ascertain that the formation of NiCo₂S₄@HCs heterostructure simultaneously facilitates OH⁻ adsorption/desorption and accelerates electron transfer within the electrode, boosting fast and efficient redox reactions. Ex situ X-ray diffraction and Raman measurements reveal that gradual phase transformations from NiCo(HCO₃)₂ to NiCo(OH)₂CO₃ and then to highly-active NiCoOOH take place during the cycles. Therefore, NiCo₂S₄@HCs demonstrates an ultrahigh capacitance of 3178.2 F g⁻¹ at 1 A g⁻¹ and a remarkable rate capability of 2179.3 F g⁻¹ at 30 A g⁻¹. In addition, the asymmetric supercapacitor NiCo₂S₄@HCs//AC exhibits a high energy density of 69.6 W h kg⁻¹ at the power density of 847 W kg⁻¹ and excellent cycling stability with 90.2% retained capacitance after 10 000 cycles. Therefore, this novel structural design has effectively manipulated the interface charge states and guaranteed the structural integrity of electrode materials to achieve superior electrochemical performances.