Patching sulfur vacancies: A versatile approach for achieving ultrasensitive gas sensors based on transition metal dichalcogenides.

Transition metal dichalcogenides (TMDCs) garner significant attention for their potential to create high-performance gas sensors. Despite their favorable properties such as tunable bandgap, high carrier mobility, and large surface-to-volume ratio, the performance of TMDCs devices is compromised by sulfur vacancies, which reduce carrier mobility. To mitigate this issue, we propose a simple and universal approach for patching sulfur vacancies, wherein thiol groups are inserted to repair sulfur vacancies. The sulfur vacancy patching (SVP) approach is applied to fabricate a MoS2-based gas sensor using mechanical exfoliation and all-dry transfer methods, and the resulting 4-nitrothiophenol (4NTP) repaired molybdenum disulfide (4NTP-MoS2) is prepared via a sample solution process. Our results show that 4NTP-MoS2 exhibits higher response (increased by 200 %) to ppb-level NO2 with shorter response/recovery times (61/82 s) and better selectivity at 25 °C compared to pristine MoS2. Notably, the limit of detection (LOD) toward NO2 of 4NTP-MoS2 is 10 ppb. Kelvin probe force microscopy (KPFM) and density functional theory (DFT) reveal that the improved gas sensing performance is mainly attributed to the 4NTP-induced n-doping effect on MoS2 and the corresponding increment of surface absorption energy to NO2. Additionally, our 4NTP-induced SVP approach is universal for enhancing gas sensing properties of other TMDCs, such as MoSe2, WS2, and WSe2.

Co-Solvent Engineering Contributing to Achieve High-Performance Perovskite Solar Cells and Modules Based on Anti-Solvent Free Technology.

The pinhole-free and defect-less perovskite film is crucial for achieving high efficiency and stable perovskite solar cells (PSCs), which can be prepared by widely used anti-solvent crystallization strategies. However, the involvement of anti-solvent requires precise control and inevitably brings toxicity in fabrication procedures, which limits its large-scale industrial application. In this work, a facile and effective co-solvent engineering strategy is introduced to obtain high- quality perovskite film while avoiding the usage of anti-solvent. The uniform and compact perovskite polycrystalline films have been fabricated through the addition of co-solvent that owns strong coordination capacity with perovskite components , meanwhile possessing the weaker interaction with main solvent . With those strategies, a champion power conversion efficiency (PCE) of 22% has been achieved with the optimal co-solvent, N-methylpyrrolidone (NMP) and without usage of anti-solvent. Subsequently, PSCs based on NMP show high repeatability and good shelf stability (80% PCE remains after storing in ambient condition for 30 days). Finally, the perovskite solar module (5 × 5 cm) with 7 subcells connects in series yielding champion PCE of 16.54%. This strategy provides a general guidance of co-solvent selection for PSCs based on anti-solvent free technology and promotes commercial application of PSCs.

Constructing molecular bridge for high-efficiency and stable perovskite solar cells based on P3HT.

Poly (3-hexylthiophene) (P3HT) is one of the most attractive hole transport materials (HTMs) for the pursuit of stable, low-cost, and high-efficiency perovskite solar cells (PSCs). However, the poor contact and the severe recombination at P3HT/perovskite interface lead to a low power conversion efficiency (PCE). Thus, we construct a molecular bridge, 2-((7-(4-(bis(4-methoxyphenyl)amino)phenyl)-10-(2-(2-ethoxyethoxy)ethyl)-10H-phenoxazin-3-yl)methylene)malononitrile (MDN), whose malononitrile group can anchor the perovskite surface while the triphenylamine group can form π-π stacking with P3HT, to form a charge transport channel. In addition, MDN is also found effectively passivate the defects and reduce the recombination to a large extent. Finally, a PCE of 22.87% has been achieved with MDN-doped P3HT (M-P3HT) as HTM, much higher than the efficiency of PSCs with pristine P3HT. Furthermore, MDN gives the un-encapsulated device enhanced long-term stability that 92% of its initial efficiency maintain even after two months of aging at 75% relative humidity (RH) follow by one month of aging at 85% RH in the atmosphere, and the PCE does not change after operating at the maximum power point (MPP) under 1 sun illumination (~45 oC in N2) over 500 hours.

Achieving Highly Reversible Zinc Anodes via N, N-Dimethylacetamide Enabled Zn-Ion Solvation Regulation.

Although aqueous zinc-ion batteries (ZIBs) are promising for scalable energy storage application, the actual performance of ZIBs is hampered by the irreversibility. Optimization of electrolyte composition is a relatively practical and facile way to improve coulombic efficiency (CE) and Zn plating/stripping reversibility of ZIBs. N,N-Dimethylacetamide (DMA) has a higher Gutmann donor number (DN) than that of H2 O, abundant polar groups, and economic price. Herein, a mixture electrolyte containing 10 vol% DMA and ZnSO4 , which has an enhanced Zn reversibility almost fourfold higher than that of pure ZnSO4 electrolyte, is demonstrated. The density functional theory (DFT) calculation and spectroscopic analysis reveal DMA has the ability to reconstruct the solvation structure of Zn2+ and capture free water molecules via forming Hbonds. The inhibited dendrite growth on Zn anode is further clarified by an in situ characterization. This work provides a feasible way for the development of long-lifespan ZIBs.

Additive Engineering in Antisolvent for Widening the Processing Window and Promoting Perovskite Seed Formation in Perovskite Solar Cells.

The chlorobenzene (CB) antisolvent is widely used to fabricate high-efficiency perovskite solar cells (PSCs). However, the narrow processing window and the strict volume ratio of a binary mixed solvent limit the fabrication of large-area and high-quality perovskite films. In this work, by systematic investigation of additives with the CB antisolvent, a universal guideline is achieved wherein a small amount of additive with a donor number between 9.0 and 27.0 kcal/mol can significantly widen the antisolvent treating time slot from 2 to 40 s while simultaneously enlarging the processor binary mixed solvent (dimethylformamide/dimethyl sulfoxide) from 7:3 to 0:10. Moreover, this process facilitates the formation of perovskite seeds as templates for perovskite crystal growth, effectively reducing the bulk defects in perovskite films. Finally, the obtained PSCs show remarkable power conversion efficiencies (PCEs) of 22.22 and 19.74% for rigid and flexible devices, respectively.

CarbonIron Electron Transport Channels in Porphyrin-Graphene Complex for ppb-Level Room Temperature NO Gas Sensing.

It is a great challenge to develop efficient room-temperature sensing materials and sensors for nitric oxide (NO) gas, which is a biomarker molecule used in the monitoring of inflammatory respiratory diseases. Herein, Hemin (Fe (III)-protoporphyrin IX) is introduced into the nitrogen-doped reduced graphene oxide (N-rGO) to obtain a novel sensing material HNG-ethanol. Detailed XPS spectra and DFT calculations confirm the formation of carbon-iron bonds in HNG-ethanol during synthesis process, which act as electron transport channels from graphene to Hemin. Owing to this unique chemical structure, HNG-ethanol exhibits superior gas sensing properties toward NO gas (Ra /Rg  = 3.05, 20 ppm) with a practical limit of detection (LOD) of 500 ppb and reliable repeatability (over 5 cycles). The HNG-ethanol sensor also possesses high selectivity against other exhaled gases, high humidity resistance, and stability (less than 3% decrease over 30 days). In addition, a deep understanding of the gas sensing mechanisms is proposed for the first time in this work, which is instructive to the community for fabricating sensing materials based on graphene-iron derivatives in the future.

Binary Supramolecular Chirality "1/0" Switched by Hierarchical Photoisomerization of a Flower-Like Compound with a Binaphthol Core and Alkyl-Functionalized Azobenzene Side Chains.

Chiral supramolecular assemblies are abundant in nature, but controlling the chirality of artificial systems still remains a challenge. In this work, we developed a system where supramolecular chirality can be controlled between chiral and achiral states, namely a chiral "1/0" switch using a flower-like azobenzene compound with a binaphthol core. Upon photoisomerization by ultraviolet irradiation, the terminal alkyl tails envelop the chiral "centre" with a reduction in the dihedral angle of the binaphthol moiety from 76.1° to 61.4°, like "closing petals". In the doped liquid crystal E7 matrix, this hierarchical conformational transition prevents the transfer of chirality to the host liquid crystal, resulting in a degradation from cholesteric phase (HTP value: 13.84 µm-1 ) to an achiral nematic phase.

Li-Ion Cooperative Migration and Oxy-Sulfide Synergistic Effect in Li14 P2 Ge2 S16-6 x Ox Solid-State-Electrolyte Enables Extraordinary Conductivity and High Stability.

Critical to the development of all-solid-state lithium-ion batteries technology are novel solid-state electrolytes with high ionic conductivity and robust stability under inorganic solid-electrolyte operating conditions. Herein, by using density functional theory and molecular dynamics, a mixed oxygen-sulfur-based Li-superionic conductor is screened out from the local chemical structure of ß-Li3 PS4 to discover novel Li14 P2 Ge2 S8 O8 (LPGSO) with high ionic conductivity and high stability under thermal, moist, and electrochemical conditions, which causes oxygenation at specific sites to improve the stability and selective sulfuration to provide an O-S mixed path by Li-S/O structure units with coordination number between 3 and 4 for fast Li-cooperative conduction. Furthermore, LPGSO exhibits a quasi-isotropic 3D Li-ion cooperative diffusion with a lesser migration barrier (≈0.19 eV) compared to its sulfide-analog Li14 P2 Ge2 S16 . The theoretical ionic conductivity of this conductor at room temperature is as high as ≈30.0 mS cm-1 , which is among the best in current solid-state electrolytes. Such an oxy-sulfide synergistic effect and Li-ion cooperative migration mechanism would enable the engineering of next-generation electrolyte materials with desirable safety and high ionic conductivity, for possible application in the near future.

Building a smart surface with converse temperature-dependent wettability based on poly(acrylamide-co-acrylonitrile).

A smart surface with converse temperature-dependent (CTD) wettability was fabricated from an upper critical solution temperature-type (UCST-type) poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)) copolymer. The obtained surface exhibits a remarkable and reversible hydrophobic-hydrophilic transition depending on temperature with a high response rate. The static water contact angle of the surface decreases from 103° ± 2° to 60° ± 1° as the temperature increases from 30 °C to 80 °C. Further, the wettability of the UCST-type surface shows a positive linear relationship between wettability and temperature. This study for the first time provides an UCST-type smart surface with wettability that decreases by over 35° as the temperature increases by only 20 °C.

Configuration-Controllable Polymeric Nanovehicles Self-Assembled in Pixel Grids under an Electric Field.

Polymeric nanovehicles have been widely applied in many fields, but during the process of preparation, it is still hard to reach the balance between precise structure control and mass production. In the present work, using industrial pixel grids as the macroscopic template, we applied dual effects of confinement and dielectric difference to speed up the self-assembly of polymeric nanovehicles, even to regulate the generated mesostructures and cargo loading. Within 2 min, a poly(ethylene glycol)-block-poly(d,l-lactide acid) (PEG-b-PDLLA) amphiphilic block copolymer layer was rapidly pushed off and broken down into uniform nanoparticles at 40 V. Hereinto, increasing volume of the outer aqueous phase in pixel grids favored the architectonic transformation of the generated nanovehicles from solid micelles with a diameter of 95 nm to hollow vesicles with a diameter of 232 nm. In particular, all the elements from the confinement cells to the preparation process can be completed via wet printing. Electric-field-induced pixel template technology is facile, cheap, controllable, and recyclable, and it is anticipated to promote continuous and bulk production of polymeric nanovehicles.

Transition of interfacial capacitors in electrowetting on a graphite surface by ion intercalation.

The low voltage electrowetting response of a LiCl aqueous solution on a freshly cleaved surface of highly oriented pyrolytic graphite (HOPG) is presented. For applied voltages below 1 V, the energy stored in the electrical double layer (EDL) is insufficient to drive the spreading of the drop due to the pinning of the three phase contact line at the step edges. Electrochemical impedance spectroscopy shows a dramatic increase in capacitance above 1 V, which provides a sufficient electrowetting force for depinning the contact line, resulting in a subsequent decrease of the contact angle. The transition of the interfacial capacitance from the EDL to the many-fold high capacitance of the pseudocapacitor drives the electrowetting transition on the HOPG surface. The observed changes in the capacitances above 1 V are correlated with the cyclic voltammetry and atomic force microscopy results, which show that the Cl- ions intercalate into the graphite galleries upon acquiring sufficient energy to overcome the van der Waals attraction between the graphene layers through the side of the step edge of the basal planes. To the best of our knowledge, this is the first study on the voltage dependent intercalation mediated transition of interfacial capacitance driving the spreading of an aqueous electrolyte drop on the HOPG surface, which provides a fundamental understanding of the mechanism and opens up potential applications in microfluidics and charge storage technologies.

One-step formation of infrared reflection microsheets via local photo-induced in situ polymerization.

Liquid crystal (LC) smart windows with adjustable reflectivity have been gradually applied in green and intelligent building materials for energy saving needs, but their applications are limited by their fundamental defects. In this study, we developed local photo-induced in situ polymerization to rapidly fabricate the infrared reflection microsheets of a cholesteric LC polymer as functional units. With the exception of the LC formula, the photo mask, liquid crystal cell, polymerization inhibitor, and the preparation conditions were specifically managed to control the extent of in situ polymerization, namely the microsheet morphology. The circular, triangular and oval-shaped microsheets were precisely obtained and were slightly bigger than the light hole. This easy, controllable, continuous and recyclable technology is expected to promote the industrialization of a high quality LC smart window with an adjustable reflection band and state.

Protonation-induced molecular permeation at the oil/water interface in an electric field.

As a common physicochemical phenomenon, protonation can cause molecules, atoms or ions with lone-pair electrons to become charged, and can further cause some changes in their physical and chemical properties. Our study first focused on the molecular protonation process and accompanying transitions of the oil/water interface properties in an electric field. The relationship between the protonation degree increment and applied voltage was proposed as a guide for controlling the protonation via applying an electric field. Besides the protonation degree, the water solubility of the oily target molecule obviously increased at 30 V for 600 s along with electric field-driven protonation. At the same time, the electrical conductivity and the underwater interface wettability of oil phase transitioned. These property transitions are anticipated to guide the further improvement and updating of promising protonation functions.

Magnetic polymeric nanoassemblies for magnetic resonance imaging-combined cancer theranostics.

Cancer has become one of the primary causes of death worldwide. Current cancer-therapy schemes are progressing relatively slowly in terms of reducing mortality, prolonging survival, time and enhancing cure rate, owing to the enormous obstacles of cancer pathophysiology. Therefore, specific diagnosis and therapy for malignant tumors are becoming more and more crucial and urgent, especially for early cancer diagnosis and cancer-targeted therapy. Derived theranostics that combine several functions into one "package" could further overcome undesirable differences in biodistribution and selectivity between distinct imaging and therapeutic agents. In this article, we discuss a chief clinical diagnosis tool - MRI - focusing on recent progress in magnetic agents or systems in multifunctional polymer nanoassemblies for combing cancer theranostics. We describe abundant polymeric MRI-contrast agents integrated with chemotherapy, gene therapy, thermotherapy, and radiotherapy, as well as other developing directions.

Insight into fast ion migration kinetics of a new hybrid single Li-ion conductor based on aluminate complexes for solid-state Li-ion batteries.

A novel hybrid single Li-ion conductor (SLIC) for a Li-ion solid electrolyte was prepared by mixing aluminate complexes-polyethylene glycol (LiAl-PEG) and polyethylene oxide (PEO) for solid-state Li-ion batteries. The LiAl-PEG/PEO blend possesses high thermal stability and electrochemical stability with an oxidation decomposition voltage up to 4.8 V. Notably, this hybrid SLIC exhibits not only excellent Li-ion migration kinetics, but also good ionic conductivity as high as 4.0 × 10-5 and 2.6 × 10-4 S cm-1 at 30 and 100 °C, respectively, which is much higher than previously reported SLICs. Importantly, by the combination of molecular dynamics simulations and experiment measurements, the mechanisms of Li-ion migration across the SLIC (LiAl-PEG), the salt-in-polymer (LiClO4/PEO) and the optimized SLIC (LiAl-PEG/PEO) were systematically investigated for the first time. The new hopping transport mechanism was verified for the SLIC system at the nanoscale. As for the hybrid SLIC, PEO chains enhance the segmental mobility of the ether-chains bonded with Al atoms, improve the ionicity, and provide extra ionic paths for Li transfer, resulting in the optimized Li-ion migration kinetics of LiAl-PEG/PEO.

Quartz Microcrystal-Hybridized Organosilicone Encapsulant with Enhanced Optical and Thermal Performances.

Encapsulant is one determining factor underpinning the device lifetimes of organic optoelectronics. However, encapsulant seriously needs improvement in optical, thermal, and mechanical properties, especially to develop organic light emitting diodes. In this study, we prepared an in situ crosslinked organosilane composite containing benzyloxy and glycidyl-modified quartz microcrystal (mQMC) as high performance encapsulant. In the present work, methylphenylsilanediol (MPSD) was introduced as a novel crosslinker to impart appropriate structural strength. Along with increasing mQMC fillers, this organosilane system shows improved properties, such as refractive index, thermal stability, and storage modulus. Specifically, these hybridized mQMCs in the organosilane framework may facilitate an approximate two-fold increase (0.238 W/(m·K)) in overall thermal conductivity at the determined concentration.

Formation mechanism of bound rubber in elastomer nanocomposites: a molecular dynamics simulation study.

Bound rubber plays a key role in the mechanical reinforcement of elastomer nanocomposites. In the present work, we reveal the formation mechanism of bound rubber in elastomer nanocomposites, using the coarse-grained molecular dynamics simulations. For the polymer-nanoparticle system, the "chain bridge" connected with neighboring nanoparticles forms, once the gap between two neighboring nanoparticles is less than the polymer size. The polymer-nanoparticle-solvent systems, mimicking the oil-swollen rubber in the experiment, are simulated with three models. From the analysis of the potential energy, the static structure and dynamic diffusing processes, all the models indicate that the increase of the volume fraction of the nanoparticles and the polymer-nanoparticle interaction strength could promote the formation of the bound rubber. The existence of solvent disrupts the bound rubber, and eventually deteriorates the mechanical properties. These simulations could provide some theoretical guidance for a better understanding of the formation mechanism of the bound rubber, which is helpful for designing the elastomer materials with excellent mechanical properties.

Multiscale Interface Effect on Homogeneous Dielectric Structure of ZrO2/Teflon Nanocomposite for Electrowetting Application.

Electrowetting-on-dielectric is a preferred option in practical applications of the electrowetting phenomenon but limited by dielectric and breakdown performances of the dielectric layer. In the present work, a ceramic/polymer nanocomposite as a novel dielectric layer is developed to intensify the overall electrowetting performances by multiscale interface effect. Hereinto, surface fluoro-modified ZrO2 nanoparticles (mZrO2) are dispersed well in AF 1600 matrix to form a mZrO2@AF 1600 nanocomposite. The small addition of mZrO2 improves the dielectric constant of the nanocomposite, and the experimental value is larger than the theoretical value calculated by Maxwell⁻Garnett model, but fits well with the Rahaman⁻Khastgir model. The molecular dynamics simulations with the explicit model further verify the interfacial effect. Meanwhile, double contact angle modulation and higher breakdown field strength (Eb) are obtained. For the three-layer sandwich structure, both the top and bottom AF 1600 layer decrease the surface roughness for better electrowetting reproducibility and wider wettability modulation. The Forlani⁻Minnaja theory related to the empirical relationship between Eb and thickness of dielectric layer fit well with the monolayer structure, but cannot be applied in multi-layer structures. A new relationship is proposed to guide the design of dielectric multi-layers with high breakdown field strength.

Nanocrystals generated under tensile stress in metallic glasses with phase selectivity.

Revealing the mechanism of phase selectivity can provide guidance for controlling crystals with certain phases for special properties. In the present work, nanocrystals of about 2-4 nm diameters with a B2 structure (thermodynamic metastable phase) are generated from CuZr glassy fiber by applying tensile stress at ambient temperature. By combining the ab initio calculations with the molecular dynamics simulations, the stabilities of B2 austenite and B19' martensitic phases under applied tensile stress are compared, and the phase transformation mechanism is revealed. The results show that the B2 structure has a bigger attractive basin, and the phase transition could occur with a larger applied stress during the deformation. Therefore, insights into the higher symmetric B2 nanocrystal with selective nucleation driven under directional stress are provided.

Electrowetting Performances of Novel Fluorinated Polymer Dielectric Layer Based on Poly(1H,1H,2H,2H-perfluoroctylmethacrylate) Nanoemulsion.

In electrowetting devices, hydrophobic insulating layer, namely dielectric layer, is capable of reversibly switching surface wettability through applied electric field. It is critically important but limited by material defects in dielectricity, reversibility, film forming, adhesiveness, price and so on. To solve this key problem, we introduced a novel fluorinated polyacrylate-poly(1H,1H,2H,2H-perfluoroctylmethacrylate (PFMA) to construct micron/submicron-scale dielectric layer via facile spray coating of nanoemulsion for replacing the most common Teflon AF series. All the results illustrated that, continuous and dense PFMA film with surface relief less than 20 nm was one-step fabricated at 110 °C, and exhibited much higher static water contact angle of 124°, contact angle variation of 42°, dielectric constant of about 2.6, and breakdown voltage of 210 V than Teflon AF 1600. Particularly, soft and highly compatible polyacrylate mainchain assigned five times much better adhesiveness than common adhesive tape, to PFMA layer. As a promising option, PFMA dielectric layer may further facilitate tremendous development of electrowetting performances and applications.