Composite Active Layer Research Articles

Modulation of Ionically Generated Space Charge Effects at Hybrid Perovskite and Oxide Interfaces via Surface Modification

AbstractInterfacial space charges significantly influence transport and recombination of charge carriers in optoelectronic devices. Due to the mixed ionic‐electronic conducting properties of halide perovskites, not only electronic effects, but also ionic interactions at their interfaces need to be considered in the analysis of space charges. Understanding of these interactions and their control is currently missing. This study elucidates the ionic effects on space charge formation at the interface between methylammonium lead iodide (MAPI) and alumina, and its modulation through surface modification using organic molecules. Embedding insulating alumina nanoparticles within MAPI films leads to enhancement of the electronic conductivity. This effect is consistent with the formation of an interfacial inversion layer in MAPI and can only be explained on the basis of ionic interactions. Such an effect is attenuated by surface modification of the oxide via the chemisorption of organic molecules. Finally, the same trend is observed in solar cells, where reducing the potential of the distributed space charges within the composite active layer improves device performance. These findings emphasize the necessity of taking into account ionic interactions to control the space charge formation at interfaces involving mixed ionic‐electronic conductors, an essential aspect in the performance optimization of halide perovskite‐based devices.

Soft composite actuators of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene)-based nanofibers and polydimethylsiloxane: Fabrication, electromechanical characterization, and dynamic modeling

Nanofibrous unimorph cantilever beam soft actuators offer remarkable advantages, such as rapid viscoelastic relaxation, low power consumption, and high weight-specific properties. However, the presence of high porosity in the nanofibrous active layer poses a challenge due to its low breakdown voltage, limiting the practical applications of this class of soft actuators. This study proposes an innovative solution to enhance the relative permittivity of the nanofibrous layer by redesigning it as a composite layer. By integrating electrospun aligned nanofibers of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) into a polydimethylsiloxane elastomeric matrix, the composite active layer achieves a notable increase in relative permittivity (10.5 at 100 Hz), surpassing the individual materials' values (2.5 and 2.7 at 100 Hz for the nanofibers and polydimethylsiloxane, respectively). To realize novel soft actuators, the composite active layer is placed between carbon black electrodes, with Kapton® serving as the passive layer. Remarkably, aligning the nanofibers in the transversal direction of the actuator enhances its actuation capabilities significantly. When subjected to a 25 MVm−1 electric field, the tip deflection and blocking force exhibit a ∼400% improvement compared to polydimethylsiloxane-based actuators. To support these findings, a physics-based dynamic model is derived and validated through experimental tests in both static and transient time simulations.

Two-dimensional model of ion transport in composite membranes active layers with TEM-scanned morphology

Ion rejection by composite membranes for RO/NF is performed by an ultrathin polyamide active layer (AL) with non-uniform thickness. Current models explain the solute and water fluxes by concentration and potential in AL of uniform properties, there are studies showing the effects of its topology on permeability. We developed a two-dimensional extension of the solution-friction model, coupling ion and water transport in irregularly-shaped charged AL, with geometry extracted from TEM images. Simulations indicated that AL with pronounced roughness lead to highly non-uniform distribution of ionic fluxes and lead to NaCl permeability greater than obtained by uniform layers. The transmembrane pressure and membrane charge can shift the relative dominance of ion transport mechanisms. In weakly charged membranes diffusion dominates, even at high water fluxes. Electromigration can counteract the convective flux in highly charged membranes. The model revealed the possibility of circular ionic currents within/around the AL. The response of the 2D model to variations in flux and salinity can be identical to the response of a 1D model, providing that the 1D model uses an appropriate equivalent membrane thickness. We provided a method to convert the detailed 2D geometry into a single number that can be computed from images' active layers.

High-performance Ta2O5-based resistive random-access memory with embedded graphene quantum dots and Pt–Ag composite active layer

Resistive random-access memory (RRAM) has garnered significant interest in developing nonvolatile memory systems due to its ability to provide external field tunable resistive states with fast speed and low power consumption. This tunable resistive state primarily results from the formation and breakage of conductive pathways triggered by active ion migration. However, due to the stochastic nature of ion migration, the stability of the switching process is a long-standing bottleneck. Here, we investigate the impact of device kinetic parameters on the stability of resistive switching behavior and propose a high-performance RRAM with a Pt–Ag/Ta2O5/GQDs/Pt structure. Incorporating quantum dots can regulate the direction of Ag ion migration, while the Pt–Ag composite electrode can manipulate the oxidation rate of Ag atoms. Compared to the Ag/Ta2O5/GQDs/Pt device, the Pt–Ag/Ta2O5/GQDs/Pt device exhibited a 15-fold reduction in operating voltage, a 10-fold increase in on/off ratio, and superior endurance and uniformity. These findings demonstrate that tuning kinetic parameters has the potential to enhance resistive switching performance, which offers an effective pathway for designing high-performance memory systems.

Modulus Estimation of Composites with High Porosity, High Particle Volume Fraction, and Particle Eigenstrain: Application to the LIB Active Layer with a Bridged-Particle Mesostructure

Due to the complex mesostructure and components of composite active layers in lithium-ion battery (LIB) electrodes, coupled with the concentration-dependent material properties and eigenstrains, efficiently estimating the effective modulus of the active layers remains a great challenge. In this work, the classic Mori–Tanaka method is found to be unable to estimate the modulus of the active layer. By realizing the importance of the mesostructure feature, a rod-rod model is proposed. The resulting modulus is expressed analytically. It is shown that the rod-rod model can accurately estimate the modulus evolution of the active layer if the material properties of the components and the evolution of volume fractions are known in advance. Moreover, a simplified rod-rod model is also developed to reduce the complexity of the proposed method. By knowing the volume fractions at two arbitrary states of charge and subsequently determining two constants, the simplified model can estimate the modulus efficiently. Considering both its accuracy and its simplicity, the simplified rod-rod model is the most suitable for the estimation. Thus, the methods developed in this work provide a new perspective for analyzing the material properties of composite active layers in LIB electrodes.

High-performance nanofiltration membranes with a polyamide-polyester composite layer and a polydopamine surface layer for desalination and dye pollutant removal

Due to water shortages, people have to use wastewater, seawater and brackish groundwater. People prefer to use membrane-based technologies to produce high-quality water, because they are environmentally friendly and have higher energy efficiencies than traditional thermal methods. The desalination nanofiltration (NF) membranes developed demonstrate a trade-off between water permeabilities and selectivities. Researchers are devoted to develop desalination NF membranes with both high water permeabilities and high selectivities. Using novel strategies, we successfully constructed double-high-performance NF membranes with a polyamide-polyester composite layer and a surface layer via a facile additional two-step approach. We used both triethanolamine (TEOA) and piperazine (PIP) to react with trimesoyl chloride (TMC) to form a composite active layer and coated the self-assembled polydopamine (PDA) on the surface of the composite active layer. To our knowledge, their performances are among the topmost of developed NF membranes for desalination and dye pollutant removal. We used scanning electron microscope (SEM), atomic force microscope (AFM) and water contact angle gauge (WCA) to investigate the membrane surface characteristics. The membrane obtained via the two-step approach has a water permeability of up to 21.3 LMH/bar, while that of the control polyamide NF membrane is as low as 8.2 LMH/bar. The developed membrane owes apparently improved water permeability in addition to maintaining high selectivities. Furthermore, the coating of the self-assembled PDA can alleviate membrane fouling. We also performed molecular dynamics (MD) simulations to study why the use of TEOA in addition to PIP to react with TMC improves membrane performances and give guidances and inspirations to future researches.

An Improved Experiment for Measuring Lithium Concentration-Dependent Material Properties of Graphite Composite Electrodes.

The in situ curvature measurement of bilayer beam electrodes is widely used to measure the lithium concentration-dependent material properties of lithium-ion battery electrodes, and further understand the mechano-electrochemical coupling behaviors during electrochemical cycling. The application of this method relies on the basic assumption that lithium is uniformly distributed along the length and thickness of the curved active composite layer. However, when the electrode undergoes large bending deformation, the distribution of lithium concentration in the electrolyte and active composite layer challenges the reliability of the experimental measurements. In this paper, an improved experiment for simultaneously measuring the partial molar volume and the elastic modulus of the graphite composite electrode is proposed. The distance between the two electrodes in the optical electrochemical cell is designed and graphite composite electrodes with four different thickness ratios are measured. The quantitative experimental data indicate that the improved experiment can better satisfy the basic assumptions. The partial molar volume and the elastic modulus of the graphite composite electrode evolve nonlinearly with the increase of lithium concentration, which are related to the phase transition of graphite and also affected by the other components in the composite active layer. This improved experiment is valuable for the reliable characterization of the Li concentration-dependent material properties in commercial electrodes, and developing next-generation lithium batteries with more stable structures and longer lifetimes.

Investigation of 3D and 2D/3D heterojunction perovskite-based phototransistors

3D organic–inorganic hybrid perovskites have been widely used in applications associated with the photovoltaic effect owing to their favorable optoelectronic characteristics. However, the interaction of the perovskite in conventional perovskite-based electronic devices with moisture in air typically leads to a low environmental stability of these devices. Therefore, in this study, we fabricated mixed dimensional 2D/3D perovskite composite active layers to enhance the environmental stability of perovskite-based phototransistors without compromising their photoelectric properties. The photoresponsivity of the optimized 2D/3D perovskite-based phototransistor (5.27 × 10−2 A/W) was observed to be 2.08 times greater than that of the 3D perovskite-based phototransistor (2.61 × 10−2 A/W). Furthermore, the 2D/3D perovskite-based phototransistor retained 90.2% and 82.3% of its photocurrent generation and photoresponsivity, respectively, after being subjected to air with 40% humidity for 14 days. These results suggest that the 2D/3D perovskite films could effectively enhance the photoelectric performance and environmental stability of perovskite-based phototransistors.

The effects of Ti3C2 MXene additive on lithiation induced stress in silicon/graphite-based electrodes for lithium ion batteries

The lithiation induced stress in multilayer silicon/graphite-based electrodes for lithium ion batteries is evaluated analytically. Firstly, the silicon/graphite-based composite active layer is reinforced by Ti3C2 MXene, and the effects of Ti3C2 MXene additive on elastic modulus of the active layer are discussed based on the Halpin–Tsai empirical equation. Secondly, biaxial stresses in both bilayer and symmetric trilayer silicon/graphite-based electrodes are estimated by a mechano-electrochemical model, which is derived by imitating thermal expansion stress in layered structural components. And the effects of Ti3C2 MXene’s parameters, including additive amount, number of layers and length–width ratio, on the stress in multilayer silicon/graphite-based electrodes are also be discussed in detail. Finally, based on the numerical analysis, some design strategies for Ti3C2 MXene reinforced composite active layer are proposed from mechanical views.

Functional Materials Based on Nanoparticle Modified Polypropylene Fibers

Background: The formation and modification of the surface of polypropylene fibers provide a versatile material for a variety of applications. Objective: This research examines the production of new materials by pneumatic spraying of a polypropylene melt jet, on the surface of which metal and metal oxide nanoparticles are prepared using the sol-gel technique and photoreduction followed by ultra-high frequency processing. We used the obtained materials to remove Bisphenol A in the photoreactor. Method: Based on an analysis of the obtained values of the numerical characteristics in the spray zone and the physical essence of the criteria under consideration, a mechanism for the destruction of the melt jet from the formation of a fiber-forming system is proposed. Analysis of the degradation of Bisphenol A was carried out by electron spectroscopy and fluorescence. Results: A composite active layer, “polymer – inorganic nanoparticles”, on the surface of polypropylene fibers has been demonstrated to create new photocatalytic materials. Bisphenol A in water was examined as a toxicant. Conclusion: Based on the analysis of the obtained values of the numerical characteristics in the spray zone and the physical essence of the considered criteria, it was found that the pressure drop in the nozzle, the nozzle critical section area, and the rheological properties of the melt are dominating factors in the influence on the morphology and size of the ultra-fine fibers obtained by pneumatic spraying. It was determined that materials based on a polypropylene carrier with the largest diameter of 6.71 μm have the best sorption capacity for Bisphenol A. A decrease in the concentration of bisphenol A in water by more than two times in 30 minutes of UV irradiation in the presence of polypropylene was achieved without additional injection of oxidants.

Ferroelectric Based Multi-Type Energy-Harvesting Device to Power a Mobile Medical Telemetry System

We have presented a multi-type energy-harvesting device for converting lighting, heating, and deformation to electricity using a composite material based on Sn2P2S6 ferroelectric semiconductor to power the mobile medical telemetry equipment. To convert vibrations and motion, a second transducer layer is used, which is based on the triboelectric effect. It also uses Sn2P2S6 powder as an active substance. Ferroelectric powder allows us to accumulate charge due to both the triboelectric and piezoelectric effect which significantly increases the efficiency of the converter. We have determined the pyroelectric, piezoelectric and photoelectric parameters of the composite active layer and triboelectric response amplitude and effectivity of triboelectric stage.

Bipolar Resistive Switching Behavior of PVP-GQD/HfOx/ITO/Graphene Hybrid Flexible Resistive Random Access Memory.

We have investigated highly flexible memristive devices using reduced graphene oxide (RGO) nanosheet nanocomposites with an embedded GQD Layer. Resistive switching behavior of poly (4-vinylphenol):graphene quantum dot (PVP:GQD) composite and HfOx hybrid bilayer was explored for developing flexible resistive random access memory (RRAM) devices. A composite active layer was designed based on graphene quantum dots, which is a low-dimensional structure, and a heterogeneous active layer of graphene quantum dots was applied to the interfacial defect structure to overcome the limitations. Increasing to 0.3–0.6 wt % PVP-GQD, Vf changed from 2.27–2.74 V. When negative deflection is applied to the lower electrode, electrons travel through the HfOx/ITO interface. In addition, as the PVP-GQD concentration increased, the depth of the interfacial defect decreased, and confirmed the repetition of appropriate electrical properties through Al and HfOx/ITO. The low interfacial defects help electrophoresis of Al+ ions to the PVP GQD layer and the HfOx thin film. A local electric field increase occurred, resulting in the breakage of the conductive filament in the defect.

Separation of green solvent dimethyl carbonate/methanol azeotropic mixture by pervaporation with polydimethylsiloxane/polyhedral oligomeric silsesquioxane composite membrane

<p>A composite active layer was prepared by cage type polyhedral oligomeric silsesquioxane (POSS) and polydimethylsiloxane (PDMS) and was combined with polyacrylonitrile (PAN) porous support layer to form pervaporation (PV) membrane, which was used in the PV membrane separation of dimethyl carbonate (DMC)/methanol(MeOH) azeotrope. The active layer of PDMS/POSS was characterized by using X-ray diffraction, thermogravimetry, and swelling test, and the PV membrane was characterized by using scanning electron microscope and contact angle measurement. The permeability flux, separation factor and swelling/diffusion selectivity of the composite membrane were evaluated by PV test. Results show that POSS interferes with the ordered structure of PDMS, reduces the contact angle of the membrane, and is conducive to the preferential penetration of DMC. The separation flux of DMC was greatly increased in the PV process of DMC/MeOH azeotropic mixture. Moreover, the excellent swelling selectivity of PDMS/POSS active layer kept the separation factor at a high level. The novelty of this research is that POSS nanoparticles modified PV composite membranes, which can be used to separate DMC/MeOH azeotropic mixtures with good results. The maximum permeation flux of composite membrane M-3 was 4.9 kg/m2h at the operating temperature of 50 ℃, and the separation factor was 2.31, which was higher than data reported in literature.</p>

From gradual change to abrupt change in Ni-Al layered double hydroxide memristor by adsorbed small molecule oxadiazole

The memristor based on Ni-Al layered double hydroxide (Ni-Al LDHs) was investigated. The memristor be composed of oxadiazole-adsorbing Ni-Al LDHs composite active layer was researched. Experimental results show that memristors characteristic could be modulated by adsorbing oxadiazole with Ni-Al LDHs in active layer from gradual change to abrupt changes in resistive switching. While, Ni-Al LDHs devices show gradual current changes, and its synaptic plasticity and spike-time-dependent plasticity in Hebbian learning has been investigated; the device with adsorbed oxadiazole small molecules undergoes abrupt changes. This study shows the potential of nanocomposites that adsorb electrically active small molecules to modify the resistive switching characteristics of memristors and paves the way for the design of nanocomposite memristors for use in advanced devices.

High Flux and Antifouling Thin-Film Nanocomposite Forward Osmosis Membrane with Ingrained Silica Nanoparticles

A novel high flux and antifouling thin-film nanocomposite (TFnC) forward osmosis (FO) membrane containing silica (SiO2) nanoparticles was fabricated using a facile electrospinning technique followed by interfacial polymerization on the surface of an electrospun nanofiber mat. Both the electrospun nylon-6 (N6) substrate and the polyamide (PA) active layer contained superhydrophilic SiO2 nanoparticles enhancing the hydrophilicity of the fabricated FO membrane. The electrospun N6/SiO2-supported TFnC FO membrane with a PA/SiO2 composite active layer was robust (tensile strength of 24.1 MPa) with a water contact angle of 14°. The membrane exhibited a high water flux (27.1 LMH) with a low specific reverse salt flux (5.9 × 10–3 mol L–1) at draw solution concentration of 1 M NaCl at 24 °C. The fabricated membrane also showed antifouling propensities for model foulants of sodium alginate and calcium sulfate. After fouling and cleaning operations, the flux recoveries were 98% and 94% (of the initial water flux) for the membranes fouled with sodium alginate and calcium sulfate, respectively. Moreover, a strong interaction between the active layer and the substrate highlighted the structural stability of the fabricated TFnC membrane.

Analog and Digital Bipolar Resistive Switching in Co-Al-Layered Double Hydroxide Memristor.

We demonstrate a nonvolatile memristor based on Co–Al-layered double hydroxide (Co–Al LDH). We also introduce a memristor that has a hexazinone-adsorbing Co–Al LDH composite active layer. Memristor characteristics could be modulated by adsorbing hexazinone with Co–Al LDHs in the active layer. While different, Co–Al LDH-based memory devices show gradual current changes, and the memory device with small molecules of adsorbed hexazinone undergo abrupt changes. Both devices demonstrate programmable memory peculiarities. In particular, both memristors show rewritable resistive switching with electrical bistability (>105 s). This research manifests the promising potential of 2D nanocomposite materials for adsorbing electroactive small molecules and rectifying resistive switching properties for memristors, paving a way for design of promising 2D nanocomposite memristors for advanced device applications.

Highly sensitive hydrogen gas sensor based on a MoS2-Pt nanoparticle composite

A highly sensitive hydrogen gas sensor composed of an MoS2-Pt nanoparticle thin film as the active layer is introduced. The sensor achieved ultra-fast response and recovery rates of 4 s and 19 s, respectively, for 100 ppm of H2. The MoS2-Pt composite film exhibits a high sensor response (R1/R2) of 10 when exposed to 100 ppm of H2 gas, which outperforms the existing metal sulfide- based sensors. The stability of the device over a period of 70 days and the selectivity of the device is outstanding. A plausible mechanism for the MoS2-Pt based H2 gas sensor is discussed. Furthermore, the sensitivity, response and recovery rates for various concentrations of H2 gas are studied. The sensor response is exceptionally promising. This sensor with metal sulfide-platinum composite active layers can be applied in the sensor field to amplify the sensing performance.

Biosensor based on the directly enzyme immobilization into a gold nanotriangles/conductive polymer biocompatible coat for electrochemical detection of Chlorpyrifos in water

AbstractOrganic conductive polymers have been widely used as active layers in bioelectronic devices. In this work, a novel approach to entrap enzymes directly into the conductive active layer is described, using a polysaccharide as a surfactant. The surfactant allowed the electropolymerization from a micellar media and it acted as a doping agent in the conductive polymer. Gold nanotriangles were added to the matrix in order to enhance the enzymatic product quantification. The composition and oxidation state of the biocompatible conductive layer were confirmed by infrared spectrophotometric and Raman studies. Meanwhile, the gold nanotriangles presence, distribution and electrochemical activity were studied by transmission electron microscopy, atomic force microscopy, dynamic light scattering and cyclic voltammetry techniques. The inhibition of the enzyme, due to the presence of pesticides, was used to electrochemically quantify their concentration in real water samples. The concentration was confirmed by gas and liquid chromatography. Therefore, this novel composite active layer allows building a biosensor with suitable performance for an early warning in environmental control, especially in countries highly impacted by agricultural activities.

Effects of technology parameters on stress in silicon-graphite based multilayer electrodes for lithium ion batteries

Stress in a multilayer electrode for a lithium ion battery (LIB) generated by the insertion of lithium ions results in the mechanical degradation and failure of the electrode, as well as the deterioration of the electrochemical properties of the battery. In this paper, the effective deformation of a composite active layer caused by the distortion of active material in the electrochemical process was predicted as a function of state of charge (SOC). A general analytical solution of in-plane stress in a multilayer electrode for a LIB was derived with respect to the geometry parameters, material properties, and SOC. The effects produced by the thickness ratio of the current collector to the composite active layer, porosity of the composite active layer, and mass ratio of silicon to graphite on the variation and distribution of in-plane stress in both two-layered and symmetric three-layered silicon-graphite (SG) based electrodes were appraised and discussed. Based on the stress analysis, some optimized design strategies for SG based multilayer LIB electrodes are suggested.

Highly sensitive BEHP-co-MEH:PPV + Poly(acrylic acid) partial sodium salt based relative humidity sensor

A high performance humidity sensor for environmental and health monitoring has been fabricated using a composite of BEHP-co-MEH:PPV co-polymer and super hydrophilic Poly(acrylic acid) partial sodium salt (PAASS) as the sensing layer. The device was fabricated using all printing methods. Reverse offset printing was used to fabricate silver electrodes on LiNbO3 piezoelectric substrate while spin coating was used to deposit the composite active layer. Four samples with different concentrations of PAASS were fabricated to find out the effect of super hydrophilic material concentration on the performance of the sensors. Physical, chemical, and electrical characterizations were performed for the sensors and their response was recorded for varying humidity levels. The results showed that the response of sensors towards humidity change is very sensitive, quite stable, and can effectively measure low humidity levels with reasonable response and recovery times. The capacitance of the sensors was measured between 0% RH and 80% RH at 1kHz and 10kHz test frequencies. The maximum absolute change in capacitance was ∼2750pF (34pF per%RH sensitivity) for the sample with maximum concentration of PAAPSS recorded at 1kHz test frequency. Different composition ratios resulted in different performance parameters, with some of them improved, and the others compromised. The concentrations can be optimized with application specific requirements.