Efficient Host Material Research Articles

High‐Efficiency Deep Red Electroluminescence via a Spiro‐Based Pure Hydrogen Carbon Host

AbstractDeep‐red and near‐infrared emitters with twisted donor–acceptor (D–A) structures often exhibit suboptimal performance in organic light‐emitting diodes (OLEDs) due to constraints imposed by the energy gap law. In this work, a pure hydrogen carbon (PHC) host material named SBF‐DTP is purposefully tailored for deep‐red OLEDs. The excellent capacity of SBF‐DTP to support D–A type DR emitters effectively arises from its distinctive attributes: localized excitation states, 3D configuration, and low polarity. When employing SBF‐DTP as the host for the fluorescence emitter DCPA‐TPA and the thermally activated delayed fluorescence emitter APDC‐DTPA, doped films exhibit substantially enhanced photoluminescence quantum yields. This improvement leads to high‐efficiency OLEDs with external quantum efficiencies of 5.47% for DCPA‐TPA and 20.03% for APDC‐DTPA, respectively, which is about twice as high as the initial reports. This findings underscore the paramount significance of developing efficient host materials in the pursuit of high‐performance deep red and even near‐infrared OLEDs.

Theoretical evaluation of newly predicted VC4 monolayer for Li-ion batteries

Carbon-rich materials could increase the capacity and improve stability by decreasing the Li+-metal repulsive interactions. Herein, a new two-dimensional (2D) vanadium tetra carbide (VC4) was predicted using the first-principles calculations. The electrical characteristics, Li-anodic applications, and structural stability of VC4 were evaluated. With a comparatively less band gap, the bare VC4 displayed a semiconductor, while the Li+-loaded VC4 possessed a metallic nature. Using a multilayer Li top/bottom adsorption technique, a high Li storage capacity of 1353 mA h g−1 was observed in the VC4 monolayer. Notably, Bader's charge scheme confirmed a favorable and reversible electrochemical reaction between Li5VC4 and VC4. Significantly, VC4 serves as a host for high-performance lithium-ion batteries (LIBs), featuring a low barrier energy of 0.18 eV and an average open circuit voltage (OCV) of 0.52 V. Impressively, the variations of the structural parameters are within 10 % for a maximum Li+ intercalation, indicating high structural stability. These enthralling findings indicate that the monolayer VC4 sheet can be realized as an efficient Li host material for rechargeable LIBs.

An exploratory investigation of the high pressure β-V2O5 polymorph as 3 V cathode material for potassium-ion battery

Electrochemical potassium-ion insertion in high pressure /high temperature (HP/HT) β-V2O5 polymorph is examined for the first time. Monoclinic HP/HT β-V2O5 delivers a high reversible capacity of 120 mAh g−1 at C/20 rate corresponding to the K0.8V2O5 composition, at an average discharge potential of 3.2 V vs. K+/K. A good cycling performance is achieved over at least 175 cycles at C/5 rate at room temperature, confirming HP/HT β-V2O5 is an efficient host material for K+ insertion-extraction reaction. First insight into the reversibility of the structural changes upon potassiation is given.

Efficient Host Materials for Lithium-Sulfur Batteries: Ultrafine CoP Nanoparticles in Black Phosphorus-Carbon Composite.

The pursuit of efficient host materials to address the sluggish redox kinetics of sulfur species has been a longstanding challenge in advancing the practical application of lithium-sulfur batteries. In this study, amorphous carbon layer loaded with ultrafine CoP nanoparticles prepared by a one-step in situ carbonization/phosphating method to enhance the inhibition of 2D black phosphorus (BP) on LiPSs shuttle. The carbon coating layer facilitates accelerated electron/ion transport, enabling the active involvement of BP in the conversion of soluble lithium polysulfides (LiPSs). Concurrently, the ultra-fine CoP nanoparticles enhance the chemical anchoring ability and introduce additional catalytic sites. As a result, S@BP@C-CoP electrodes demonstrate exemplary cycling stability (with a minimal capacity decay of 0.054 % over 500 cycles at 1 C) and superior rate performance (607.1 mAh g-1 at 5 C). Moreover, at a sulfur loading of 5.5 mg cm-2, the electrode maintains an impressive reversible areal capacity of 5.45 mAh cm-2 after 50 cycles at 0.1 C. This research establishes a promising approach, leveraging black phosphorus-based materials, for developing high-efficiency Li-S batteries.

Suppressing shuttle effect of polysulfides by yttrium hydroxide nanoarchitecture for stable lithium‑sulfur batteries

Rechargeable lithium–sulfur (Li–S) batteries reveal promising prospect as high energy storage systems because of the extraordinary theoretical specific energy density. However, the shuttle effect and sluggish reaction kinetics of polysulfides hamper the commercialization applications of high energy density Li-S batteries. Herein, a novel and efficient sulfur host material of yttrium hydroxide (Y(OH)3) has rationally been achieved for Li–S batteries. Y(OH)3 host not only suppress shuttle effect of polysulfides by physical confinement and chemisorption, but also decline Li2S nucleation and deposition reaction barriers and expedite chemical reaction kinetics. Consequently, the prepared Y(OH)3/S cathodes achieve a high initial specific capacity of 1295 mAh g−1 at 0.1 C and improved cycling stability with a low capacity decay rate of 0.019% per cycle over 1000 cycles at 2.0 C. The enhanced performances confirm a potential host material for facilitating practical implementation of Li–S batteries.

Carbon nanofibers implanted porous catalytic metal oxide design as efficient bifunctional electrode host material for lithium-sulfur battery

The shuttling effect of lithium polysulfides (LiPSs) and uncontrolled dendrite formation of metal lithium anode are the two critical obstacles hindering the commercial application of lithium-sulfur (Li-S) batteries. Herein, a bifunctional electrode host design consists of carbon nanofibers implanted ordered porous Co-decorated Al2O3 supported on carbon nanotube film (CNTF) is proposed to address these problems. As cathode sulfur host material, benefiting from the synergistic effect of porous Co-Al2O3 and the embedded CNFs, the CNFs/Co-Al2O3@CNTF exhibits excellent conductivity, efficient LiPSs confinement and catalytic conversion performance. It shows a high initial capacity of 1165 mAh g−1 at 0.2 C, and holds a capacity of 594 mAh g−1 even up to 3 C. When serves as anode, the CNFs/Co-Al2O3@CNTF electrode exhibits excellent Li+ diffusion performance and uniform lithium growth behavior, achieving a dendrite-free lithium electrode. The anode also shows good cycle stability during an ultra-long cycle time of 1000 h. A flexible pack cell assembled from CNFs/Co-Al2O3@CNTF electrodes delivers a specific capacity of 972 mAh g−1 with capacity retention rate of 86.4% at 0.1 C.

Synthesis, characterization and enhanced photoluminescence and temperature dependence of ZrO2:Dy3+ phosphors upon incorporation of K+ ions

This study reports the successful synthesis and comprehensive characterization of ZrO2:Dy3+ phosphors with the incorporation of K+ ions. The introduction of Dy3+ and K+ in the ZrO2 lattice as lanthanide activators demonstrates its potential as an efficient host material. The structural integrity of ZrO2 remains unaltered following the doping process. Fourier-transform infrared spectroscopy (FTIR) analysis confirms the presence of Zr-O and O-H stretching, along with H2O bending modes in the phosphor sample. The wide luminescence band seen at 460 nm is attributed to luminescence defects in the ZrO2 induced by oxygen, and the presence of water molecules. Photoluminescence (PL) spectra analysis reveals pronounced emission peaks at 491 and 578 nm, corresponding to 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions, respectively, upon excitation at 349 nm. Optimizing the Dy3+ doping concentration to 0.4 wt% and achieving a critical distance of 31.82 Å resulted in efficient energy transfer. Notably, co-doping K+ as a charge compensator significantly enhances the luminescence intensity. Moreover, at lower temperatures, direct excitation of Dy3+ ions through our pump wavelength, coupled with exciton-mediated energy transfer, leads to a remarkable increase in PL intensity. Tailoring the doping concentrations effectively shifts the emission spectrum of the phosphor mixture, aligning with the standard white light illumination coordinates (0.333, 0.333). This property positions the material as a promising candidate for applications in white light-emitting diodes (WLEDs) and various high-quality lighting applications. The enhanced photoluminescence and temperature dependence observed in ZrO2:Dy3+ phosphors upon the incorporation of K+ ions pave the way for their potential utilization in advanced luminescent devices.

Cobalt-loaded three-dimensional ordered Ta/N-doped TiO2 framework as conductive multi-functional host for lithium-sulfur battery

The low electrical conductivity of sulfur and severe shuttling effect of lithium polysulfides (LiPSs) have hindered the practical application of lithium-sulfur (Li-S) batteries. In this work, a conductive Ta/N co-doped TiO2 framework featured with three-dimensional ordered macroporous (3DOM) structure embedded with ZIF-67 derived Co-anchored N-doped carbon (Co-NC) is synthesized as efficient sulfur host material in Li-S batteries. The 3DOM Ta/N-TiO2 backbone has good structural stability, which benefits the electrolyte penetration and sulfur accommodation. Meanwhile, the Ta/N co-doping not only improves the conductivity of TiO2, but also strengthens the adsorption of LiPSs. In addition, the embedded Co-NC increases the active site of 3DOM skeleton towards LiPSs conversion, facilitates the diffusion of Li+ ion, and at the same time provides additional microspores for sulfur confinement. Attributed to these features, the sulfur electrode based on 3DOM Ta/N-TiO2@Co-NC achieves excellent electrochemical performance. The S/3DOM Ta/N-TiO2@Co-NC cell maintains a discharge capacity of 789.2 mAh g−1 after 500 cycles at 1C with a low decay rate of 0.06 % per cycle. Additionally, an initial area capacity of 5.67 mAh cm−2 is obtained under areal sulfur loading of 6.55 mg cm−2. This multistage porous sulfur cathode design has the potential to expedite the development of feasible Li-S battery.

Spiroborate-Based Host Materials with High Triplet Energies and Ambipolar Charge-Transport Properties.

Organic light-emitting diodes (OLEDs) receive considerable attention because of their commercial use in flat panel displays. Herein, highly efficient spiroborate-based host materials are reported for use in blue OLEDs. Our designed spiroborates (SBOX) were simple to synthesize and exhibited high triplet excitation energies, narrow S-T gaps, and balanced charge carrier mobilities. A blue OLED containing one of the designed spiroborates, SBON, as a host exhibited a high external quantum efficiency (27.6 %) and low turn-on voltage (3.7 V) compared to those observed using 3,3'-di(9H-carbazol-9-yl)-1,1'-biphenyl (17.6 % and 4.5 V, respectively), indicating their potential as host materials in OLEDs.

Enhanced catalytic activity of Co-CoO via VC0.75 heterostructure enables fast redox kinetics of polysulfides in Lithium-Sulfur batteries

The shuttle effect and sluggish redox kinetics of lithium polysulfides lead to a short lifespan and poor rate capability of lithium-sulfur (Li-S) batteries. Introducing electrocatalysts into sulfur host materials has been deemed a promising strategy to overcome these issues in Li-S batteries. Herein, an efficient catalytic sulfur host material (i.e., VC0.75/Co-CoO) has been fabricated by simply pyrolyzing the electrospun vanadium and cobalt salt-based polymer fibers. Electrochemical measurements demonstrated that the as-formed heterostructure of Co-CoO with VC0.75 evidently strengthens the redox kinetics of polysulfides due to the enhanced adsorption ability to polysulfides and adjusts the electronic structure of heterostructure via the introduction of VC0.75. Further theoretical computation discloses that Co-CoO mainly plays the role in stretching the SS bond in polysulfides to facilitate the reduction of polysulfide, extending the Li-S bond in Li2S and reducing energy barriers of Li2S decomposition to promote the oxidation process of Li2S. Accordingly, the collaboration of Co-CoO and VC0.75 synergetically facilitates the redox kinetics of polysulfides, prolonging the lifespan of Li-S batteries. Impressively, VC0.75/Co-CoO composites endow Li-S batteries with a discharge capacity decay rate as low as 0.02 % per cycle at the current density of 0.2 C. The specific capacity reaches 626 mAh/g at the high current density of 1.0 C even after 450 cycles. This work sheds light on a facile methodology for improving the catalytic activity of sulfur host materials in Li-S batteries.

Spiral donor-based host materials for highly efficient blue thermally activated delayed fluorescence OLEDs

Spiral donor units have attracted extensive research focuses in designing highly emissive thermally activated delayed fluorescence (TADF) emitters. Herein, to reveal the significance of spiral donor units for constructing highly efficient host materials, several spiral donor-based host materials are developed. With the incorporation of spiral donor, increased intermolecular distance is achieved to reduce the concentration quenching effect of dopant. Moreover, the high triplet energy level of spiral donor can provide an additional energy transfer channel to further improve the device performance. Noteworthy, by connecting spiral donors or conventional carbazole unit with different electron-withdrawing units phenoxathiine 10,10-dioxide (PX) or phenoxathiine (PA), these hosts are given different photophysical properties of TADF, room-temperature phosphorescence (RTP) and conventional fluorescence (CF). The strong electron-withdrawing ability of PX is beneficial to the TADF character of spiral donor-based molecules, while the weak electron-withdrawing ability of PA is beneficial to the RTP property. Consequently, the blue OLEDs with DspiroAc-TRZ as a dopant emitter based on the hosts with TADF characters exhibit higher performance than those with RTP and CF properties, and excellent external quantum efficiency (EQE) of 36.1 % and current efficiency of 84.6 cd/A are achieved in a simple device structure. Furthermore, peak EQEs of 34.0 % and 33.0 % are achieved, when DspiroS-PX and DspiroS-PA hosted DspiroAc-TRZ are used to sensitize blue multi-resonance TADF emitter v-DABNA. Our work may shed new light on designing highly efficient host materials for TADF emitters.

High‐Efficiency Dual‐Mode Polychromatic Emission of Rare‐Earth‐Based Double Perovskite with Low Phonon Energy toward High‐Level Anti‐Counterfeiting and Information Encryption

AbstractThe development of rare‐earth‐doped luminescent materials with single component, multicolor, and multimode still remains a challenge. Here, rare‐earth‐based double perovskite single crystals (Cs2NaYbCl6 DPSCs) are fabricated with low phonon energy of 134 cm−1, which offers great potential to serve as highly efficient luminescent host materials. Subsequently, Er3+, Tm3+, and Ho3+ are successfully incorporated into Cs2NaYbCl6 host to form Cs2NaLnxYb1−xCl6 (Ln = Er, Tm, and Ho) DPSCs, realizing efficient dual‐mode polychromatic emission. Under 980 nm laser excitation, Cs2NaLnxYb1−xCl6 DPSCs show high upconversion (UC) efficiencies of 12.9%, 7.2%, and 3.1% for Cs2NaEr0.3Yb0.7Cl6, Cs2NaTm0.02Yb0.98Cl6, and Cs2NaHo0.3Yb0.7Cl6, respectively. Meanwhile, Cs2NaErxYb1−xCl6 DPSCs exhibit the adjustable size (0.5–10 mm) and tunable UC or down‐shifting emission colors from yellow, green to red upon 980, 1540, or 380 nm excitation. Moreover, the DPSCs demonstrate weak concentration and thermal quenching effect, and excellent resistance against oxygen, heat and humidity. Finally, the anti‐counterfeiting and information encryption applications based on multicolor emitting DPSCs are designed and realized.

Flexible 2D Boron Imidazolate Framework for Polysulfide Adsorption in Lithium–Sulfur Batteries

The “polysulfide shuttle,” a process initiated by the dissolution of polysulfides, is recognized to be one of the major failure mechanisms of lithium–sulfur (Li–S) batteries. Much research effort has been dedicated toward efficient cathode additives and host materials to suppress the leaching of polysulfide species. Herein, we report a new 2D metal–organic framework constituted by a tritopic ligand, boron imidazolate ([BH(Im)3]−, Im = imidazole), and Co2+ ions for lithium polysulfide adsorption. The cobalt imidazolate framework (CoN6-BIF) contains octahedrally coordinated Co centers that form two-dimensional layers in the a,b plane. Composite cathodes containing CoN6-BIF exhibited high sulfur utilization and capacity retention, resulting in improved specific capacity and cycle life compared to sulfur/carbon controls. Density functional theory (DFT) calculations suggest that CoN6-BIF linkers are rotationally flexible, allowing the framework to accommodate polysulfide in the expanded pores. This unusual property of BIFs opens up new avenues for exploring flexible metal–organic frameworks (MOFs) and their applications to energy storage.

The Optimization of a Carbon Paper/MnO2 Composite Current Collector for Manufacturing a High-Performance Li–S Battery Cathode

High theoretical energy density endows lithium–sulfur batteries to be a promising candidate of the secondary batteries. Numerous studies have been implemented relying on exploring efficient host materials or separator modifying layers to solve the problematic shuttling and insufficient conversion of soluble polysulfides, whereas few studies have focused on the modification of the cathode collector. Herein, a high-performance sulfur cathode is manufactured with carbon paper/MnO2 as the cathode collector and liquid lithium polysulfides as the electrode material. The interface of carbon paper/MnO2 is proposed to afford fast electronic transport, strong chemical adsorption, and effective electrocatalysis to confine the diffusion of lithium polysulfides and facilitate their conversion during the charge/discharge process. More importantly, with no conductive additives and binders assisting, the gravimetric energy density of the sulfur cathode could be largely improved. Specifically, lithium–sulfur batteries using carbon paper/MnO2 as a cathode collector could stably circulate for 200 cycles at 0.2 C with a capacity of 664 mAh g−1, which is higher than that of carbon paper as a cathode collector (486 mAh g−1). This work may provide a new perspective to enhance the electrochemical performance of lithium–sulfur batteries by optimizing the cathode collector.

Novel carbazole host materials for solution processed TADF Organic Light Emitting Diodes

Several functional and internal layers have been used to improve the performance of solution-processed Organic Light Emitting Diodes (OLED) devices. In the case of thermally activated delayed fluorescence (TADF) OLEDs, a large number of emitter materials have already been reported, but the design and development of potential host materials are overlooked. Efficient solution processable host materials for TADF OLEDs can reduce the complexity in the device architecture and production cost. In this work, we utilized a series of carbazole-based solution-processable host materials (ME4, ME5, ME9, ME10, and ME13) to fabricate the 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) based green TADF OLEDs. Among them, the ME9 composing device showed the best performance. The resultant device exhibited a maximum power efficacy of 40.0 lm/W, current efficacy of 44.7 cd/A, and external quantum efficiency of 14.1% with a maximum luminance of 16,220 cd/m2. The excellent performance may attribute to the low singlet-triplet energy gap (ΔEST), high photoluminescence quantum yield (PLQY), high thermal stability, and unique porous morphology of the ME9.

Implanting MoS2 quantum dots on MgB2 nanosheets for lithium–sulfur batteries

AbstractAs a new generation of high‐efficiency energy storage devices, lithium–sulfur (Li–S) battery attract increasing attention. However, slow conversion kinetics of lithium polysulfides (LiPSs) and severe shuttle effect are bottlenecks. Developing efficient sulfur host materials to suppress the shuttling of LiPSs and accelerate their conversion kinetics is a general strategy to enhance the performance of Li–S batteries. Herein, MoS2 quantum dots (QDs)@MgB2 nanosheet was synthesized using a simple liquid‐phase mixing method. The MoS2 QDs not only inhibit the stacking of MgB2 nanosheets but also expose more unsaturated metal active sites, which can effectively improve the adsorption of LiPSs, accelerate its catalytic conversion and suppress its shuttle effect. Moreover, MgB2 nanosheets can be used as polypropylene (PP) separator modifier. The battery using MoS2 QDs@MgB2 as the sulfur host material and MgB2@PP as the separator has high rate capability and excellent stability. In addition, the discharge‐specific capacity shows a good application prospect.image

Diphenylimidazole Based Fluorophores for Explosive Chemosensors and as Efficient Host Materials for Green Phosphorescent Organic Light Emitting Diodes

Diphenylimidazole Based Fluorophores for Explosive Chemosensors and as Efficient Host Materials for Green Phosphorescent Organic Light Emitting Diodes

Bipolar tetraphenylsilane-based host molecules for blue phosphorescence

A class of bipolar host molecules with the linkage of hole-transporting groups (diphenylamine and N-phenylcarbazole) and electron-transporting units (pyridine and carboline) to tetraphenylsilane (TPSi) core were designed for blue phosphorescence by means of quantum-chemical calculations. The geometrical and electronic structures, triplet energies, and charge injection and transport properties of the designed host molecules were analyzed in details. The calculated results indicate that the designed molecules possess the triplet energies larger than 2.80 eV and might be the potential host materials for blue phosphorescence. The positions of N atom in pyridine and carboline have significant effects on molecular geometry, dipole moment, LUMO level, triplet energy, and electron reorganization energy. This work provides an in-depth understanding of the structure-property relationship of the TPSi-based host molecules, and offers the guideline for the screening of the efficient bipolar host materials for blue phosphorescence.

A simple bipolar host material based on triphenylamine and pyridine featuring σ-linkage for efficient solution-processed phosphorescent organic light-emitting diodes

Solution-processable host materials play an important role in achieving highly efficient and cost-effective phosphorescent organic light-emitting diodes (PhOLEDs). This paper designed and prepared a simple solution-processable host material of TPA-PyF2 based on triphenylamine and pyridine to fabricate efficient solution-processed PhOLEDs. TPA-PyF2 featured an σ-linkage between the electron donor and acceptor units, which not only served to limit the conjugation length of the molecule and maintain a high triplet energy level, but also endowed the host molecule with a three-dimensional structure to enable high film morphological stability for solution processing. As a result, TPA-PyF2 exhibited a high triplet energy level (2.82 eV), high thermal stability, bipolar charge transfer, and excellent film morphology. Blue solution-processed OLED with a simple double-layer structure based on TPA-PyF2 host achieved a maximum current efficiency, power efficiency, and luminance of 17.2 cd/A, 7.1 lm/W, and 11519 cd/m2, respectively, with a small efficiency roll-off of only 9.1% at the practical luminance of 1000 cd/m2. This work reveals that the σ-linkage strategy is promising in designing efficient solution-processable host materials for high-efficiency PhOLEDs.

A Universal Spinning-Coordinating Strategy to Construct Continuous Metal-Nitrogen-Carbon Heterointerface with Boosted Lithium Polysulfides Immobilization for 3D-Printed LiS Batteries.

Constructing intimate coupling between transition metal and carbon nanomaterials is an effective means to achieve strong immobilization of lithium polysulfides (LiPSs) in the applications of lithium–sulfur (Li—S) batteries. Herein, a universal spinning‐coordinating strategy of constructing continuous metal–nitrogen–carbon (M—N—C, M = Co, Fe, Ni) heterointerface is reported to covalently bond metal nanoparticles with nitrogen‐doped porous carbon fibers (denoted as M/M—N@NPCF). Guided by theoretical simulations, the Co/Co—N@NPCF hybrid is synthesized as a proof of concept and used as an efficient sulfur host material. The polarized Co—N—C bridging bonds can induce rapid electron transfer from Co nanoparticles to the NPCF skeleton, promoting the chemical anchoring of LiPSs to improve sulfur utilization. Hence, the as‐assembled Li—S battery presents a remarkable capacity of 781 mAh g−1 at 2.0 C and a prominent cycling lifespan with a low decay rate of only 0.032% per cycle. Additionally, a well‐designed Co/Co—N@NPCF‐S electrode with a high sulfur loading of 7.1 mg cm−2 is further achieved by 3D printing technique, which demonstrates an excellent areal capacity of 6.4 mAh cm−2 at 0.2 C under a lean‐electrolyte condition. The acquired insights into strongly coupled continuous heterointerface in this work pave the way for rational designs of host materials in Li—S systems.