Heterogeneous Ti3C2Tx MXene-MWCNT@MoS2 Film for Enhanced Long-Term Electromagnetic Interference Shielding in the Moisture Environment.

MXene, as a novel two-dimensional (2D) material, has unique inherent features such as lightweight, flexibility, high electrical conductivity, customizable surface chemistry, and facile solution processability. However, utilizing MXene (Ti3C2Tx) films for long-term electromagnetic interference (EMI) shielding poses challenges, as they are susceptible to chemical deterioration through oxidation into TiO2. In this work, an ultrathin heterogeneous film of Ti3C2Tx MXene integrated with multiwalled carbon nanotubes supporting MoS2 clusters (MXene/MWCNT@MoS2) was developed. The heterogeneous film with 15 wt % of MWCNT@MoS2 clusters exhibited improved EMI shielding performance such as the highest EMI shielding effectiveness of 50 dB and the specific shielding effectiveness of 20,355 dB cm2 g -1, mainly attributed to the excellent electrical conductivity, distinctive porous structure, and multiple interfacial interactions. The heterogeneous films underwent extended exposure to a moisture environment (35 days), and their structural stability and EMI shielding performance were enhanced by the integration of MWCNT@MoS2 clusters. As a result, the engineered heterostructure of multilayered hybrid films holds promise as a viable option for improving the EMI shielding effectiveness and stability of Ti3C2Tx MXene.

2D MXenes for controlled releases of therapeutic proteins.

MXenes belong to a new class of two dimensional (2D) functional nanomaterials, mainly encompassing transition-metal carbides, nitrides and carbonitrides, with unique physical, chemical, electronic and mechanical properties for various emerging applications across different fields. To date, the potentials of MXenes for biomedical application such as drug delivery have not been thoroughly explored due to the lack of information on their biocompatibility, cytotoxicity and biomolecule-surface interaction. In this study, we developed novel drug delivery system from MXene for the controlled release of a model therapeutic protein. First, the structural, chemical and morphological properties of as synthesized MXenes were probed with electron microscopy and X-ray diffraction. Second, the potential cytotoxicity of MXene toward the proliferation and cell morphology of murine macrophages (RAW 264.7) were evaluated with MTT assays and electron microscopy, respectively. Moreover, the drug loading capacities and sustained release capabilities of MXene were assessed in conjunction with machine learning approaches. Our results demonstrated that MXene did not significantly induce cellular toxicity at any concentration below 1 mg/ml which is within the range for effective dose of drug delivery vehicle. Most importantly, MXene was efficiently loaded with FITC-catalase for subsequently achieving controlled release under different pHs. The release profiles of catalase from MXene showed higher initial rate under basic buffer (pH 9) compared to that in physiological (pH 7.4) and acidic buffers (pH 2). Taken together, the results of this study lead to a fundamental advancement toward the use of MXene as a nanocarrier for therapeutic proteins in drug delivery applications.

Dual nanozyme based on ultrathin 2D conductive MOF nanosheets intergraded with gold nanoparticles for electrochemical biosensing of H2O2 in cancer cells.

The development of facile, rapid and cost-effective strategies for sensitive detection of cancer biomarkers in human samples is of great significance for early diagnosis of malignant tumors related diseases. In this work, we develop a high-performance electrochemical biosensor based on highly active dual nanozyme amplified system, i.e., ultrathin two-dimension (2D) conductive metal-organic framework (C-MOF) nanosheets (NSs) decorated with high-density ultrafine gold nanoparticles (Au-NPs), and explore its application in sensitive detection of cancer biomarker H2O2 in live cells. The C-MOF NSs {i.e., Cu-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene)-NSs} provide large surface area and abundant active open metal sites (Cu-O4), which could improve the catalytic activity of Cu-HHTP-NSs towards H2O2. Moreover, abundant exposed O atoms also serve as anchor sites for the deposition of high-density ultrafine Au-NPs (∼3 nm) without agglomeration. Owing to the synergistic contributions of high catalytic activity of Cu-HHTP-NSs and Au-NPs as well as their unique structural and electrical properties, the as-prepared nanohybrid modified electrode exhibits good sensing performances to H2O2 with an extremely low detection limit of 5.6 nM (3σ rules) and a high sensitivity of 188.1 µA cm-2 mM-1. Furthermore, the proposed nanozymatic electrochemical biosensor has been applied in real-time tracking H2O2 released from different human colon cells to identify colon cancer cells from normal colon epithelial cell, which demonstrates its great prospect for early diagnosis and management of various cancer diseases.

Recent Advances in Fluorescence Recovery after Photobleaching for Decoupling Transport and Kinetics of Biomacromolecules in Cellular Physiology.

Among the new molecular tools available to scientists and engineers, some of the most useful include fluorescently tagged biomolecules. Tools, such as green fluorescence protein (GFP), have been applied to perform semi-quantitative studies on biological signal transduction and cellular structural dynamics involved in the physiology of healthy and disease states. Such studies focus on drug pharmacokinetics, receptor-mediated endocytosis, nuclear mechanobiology, viral infections, and cancer metastasis. In 1976, fluorescence recovery after photobleaching (FRAP), which involves the monitoring of fluorescence emission recovery within a photobleached spot, was developed. FRAP allowed investigators to probe two-dimensional (2D) diffusion of fluorescently-labelled biomolecules. Since then, FRAP has been refined through the advancements of optics, charged-coupled-device (CCD) cameras, confocal microscopes, and molecular probes. FRAP is now a highly quantitative tool used for transport and kinetic studies in the cytosol, organelles, and membrane of a cell. In this work, the authors intend to provide a review of recent advances in FRAP. The authors include epifluorescence spot FRAP, total internal reflection (TIR)/FRAP, and confocal microscope-based FRAP. The underlying mathematical models are also described. Finally, our understanding of coupled transport and kinetics as determined by FRAP will be discussed and the potential for future advances suggested.

Two-dimensional biphenylene: a promising anchoring material for lithium-sulfur batteries.

Trapping lithium polysulfides (LiPSs) on a material effectively suppresses the shuttle effect and enhances the cycling stability of Li-S batteries. For the first time, we advocate a recently synthesized two-dimensional material, biphenylene, as an anchoring material for the lithium-sulfur battery. The density functional theory calculations show that LiPSs bind with pristine biphenylene insubstantially with binding energy ranging from -0.21 eV to -1.22 eV. However, defect engineering through a single C atom vacancy significantly improves the binding strength (binding energy in the range -1.07 to -4.11 eV). The Bader analysis reveals that LiPSs and S8 clusters donate the charge (ranging from -0.05 e to -1.12 e) to the biphenylene sheet. The binding energy of LiPSs with electrolytes is smaller than those with the defective biphenylene sheet, which provides its potential as an anchoring material. Compared with other reported two-dimensional materials such as graphene, MXenes, and phosphorene, the biphenylene sheet exhibits higher binding energies with the polysulfides. Our study deepens the fundamental understanding and shows that the biphenylene sheet is an excellent anchoring material for lithium-sulfur batteries for suppressing the shuttle effect because of its superior conductivity, porosity, and strong anchoring ability.

Recent Trends in Synthesis and Applications of Porous MXene Assemblies: A Topical Review.

MXene possesses high conductivity, excellent hydrophilicity, rich surface chemistry, hence holds great potential in various applications. However, MXene materials have low surface area utilization due to the agglomeration of ultrathin nanosheets. Assembling 2D MXene nanosheets into 3D multi-level architectures is an effective way to circumvent this issue. Incorporation of MXene with other nanomaterials during the assembly process could rationally tune and tailor the specific surface area, porosity and surface chemistry of the MXene assemblies. The complementary and synergistic effect between MXene and nanomaterials could expand their advantages and make up for their disadvantages, thus boost the performance of 3D porous MXene composites. Herein, we summarize the recent progress in fabrication of porous MXene architectures from 2D to 3D, and also discuss the potential applications of MXene nanostructures in energy harvesting systems, sensing, electromagnetic interference shielding, water purification and photocatalysis.

Tensile behaviors of Ti3C2Tx (MXene) films.

As the most representative member of a new emerging family of 2D material, titanium carbides or nitrides (MXenes), Ti3C2Tx and its 2D assembly format, Ti3C2Tx film, have displayed outstanding performance in a broad range of practical applications. However the mechanical behaviors of Ti3C2Tx films are rarely reported. We report a systematic study of the tensile behavior of Ti3C2Tx films. Ti3C2Tx films with various thicknesses (2-17 µm) were prepared by the vacuum filtration method. Quasi-static tension and cyclic tension tests were performed to investigate the deformation and fracture mechanism of Ti3C2Tx films. It was found that: (1) the relative sliding between Ti3C2Tx flakes is the dominant deformation mechanism of Ti3C2Tx films. Cyclic loading-releasing in tension suppresses the inter-layer sliding of Ti3C2Tx flakes effectively and thus the tensile strength of thicker Ti3C2Tx film (5 µm) film improves from 57 MPa to 67 MPa. (2) The mechanical properties of Ti3C2Tx films are found to be thickness dependent. When the film thickness increases from 2.3 to 17 µm, the tensile strength and elastic modulus drop from 61 to 36 MPa and from 17 to 8 GPa, respectively. This is interpreted as more structural defects presented in the through-the-thickness direction as film thickness is increased. (3) Moderate ultrasonication pretreatment (30 min) reduces the Ti3C2Tx flake size significantly while improving the compactness of the Ti3C2Tx film; and the resulting Ti3C2Tx film shows a linear stress-strain relationship without plastic-like deformation. As a result, the tensile strength of 5 µm thick Ti3C2Tx film is enhanced to 85 MPa; (4) Structural defects of the Ti3C2Tx film have significant effects on both the brittle-like fracture behavior and the distribution of tensile strength.

High-Performance Fiber-Film Hybrid-Structured Wearable Strain Sensor from a Highly Robust and Conductive Carbonized Bamboo Aerogel.

Bamboo, one of the most abundant biomaterials, has been used as a building material since ancient times; however, its application in functional materials has been rarely explored. Herein, a highly robust and conductive carbonized bamboo aerogel (CBA) is obtained from the natural bamboo through a simple three-step process of pulp oxidization, freeze-drying, and carbonization. The CBA obtained shows not only a low density of 0.02 g/cm3 but also a high conductivity of 6.42 S/m and remarkable elasticity with a maximum recoverable compressive strain of 60% due to its unique three-dimensional (3D) network randomly stacked with the hybrid structure of carbonized bamboo fibers and films. After encapsulation with silicone resin, the CBA/silicone composite prepared exhibits excellent flexibility and stretchability with a low Young's modulus (0.09 MPa) and a large failure strain (275%). Importantly, the CBA/silicone composite also offers remarkable strain-sensing performance with a maximum gauge factor of 30.6, a short responsive time of 50 ms, and a stable response to cyclic loading over 1000 cycles, which is comparable to those of the piezoresistive composites based on expensive nanomaterials. Moreover, the CBA/silicone composite demonstrates the capability as a wearable strain sensor for human motion recognition comprising finger bending, breathing, and throat movement. Considering the green and sustainable nature of bamboo as a raw material, combined with the excellent piezoresistive performance, low production cost, and simple preparation process, the flexible strain sensors with CBA/silicone composite as a sensing element are promising in wearable electronic devices, personalized healthcare, and artificial intelligence systems.

Nature-Inspired, Graphene-Wrapped 3D MoS2 Ultrathin Microflower Architecture as a High-Performance Anode Material for Sodium-Ion Batteries.

In response to the increasing concern for energy management, molybdenum disulfide (MoS2) has been extensively researched as an attractive anode material for sodium-ion batteries (SIBs). The proficient cycling durability and good rate performance of SIBs are the two key parameters that determine their potential for practical use. In this study, nature-inspired three-dimensional (3D) MoS2 ultrathin marigold flower-like microstructures were prepared by a controlled hydrothermal method. These microscale flowers are constructed by arbitrarily arranged but closely interconnected two-dimensional ultrathin MoS2 nanosheets. The as-prepared MoS2 microflowers (MFs) have then been chemically wrapped by layered graphene sheets to form the bonded 3D hybrid MoS2-G networks. TEM, SEM, XRD, XPS, and Raman characterizations were used to study the morphology, crystallization, chemical compositions, and wrapping contact between MoS2 and graphene. The ultrathin nature of MoS2 in 3D MFs and graphene wrapping provide strong electrical conductive channels and conductive networks in an electrode. Benefitting from the 2 nm ultrathin crystalline MoS2 sheets, chemically bonded graphene, defect-induced sodium storage active sites, and 3D interstitial spaces, the prepared electrode exhibited an outstanding specific capacity (606 mA h g-1 at 200 mA g-1), remarkable rate performance (345 mA h g-1 at 1600 mA g-1), and long cycle life (over 100 cycles with tremendous Coulombic efficiencies beyond 100%). The proposed synthesis strategy and 3D design developed in the present study reveal a unique way to fabricate promising anode materials for SIBs.

Impact of Terminal End-Group of Acceptor-Donor-Acceptor-type Small Molecules on Molecular Packing and Photovoltaic Properties.

In this study, we synthesized two acceptor-donor-acceptor (A-D-A)-type small molecules (SMs) (P3T4-VCN and P3T4-INCN) with different terminal end-groups (dicyanovinyl (VCN) and 2-methylene-3-(1,1-dicyanomethylene)indanone (INCN)) based on the 1,4-bis(thiophenylphenylthiophene)-2,5-difluorophenylene (P3T4) core that possesses high coplanarity because of intrachain noncovalent Coulombic interactions. We investigated the influence of terminal end-groups on intermolecular packing and the resulting electrical and photovoltaic characteristics. A small change in the end-group structure of the SMs induces a significant variation in the torsional structures, molecular packing, and pristine/blend film morphology. It is noteworthy that the less crystalline P3T4-INCN with tilted conformation is highly sensitive to post-treatments (i.e., additives and annealing) such that it permits facile morphological modulation. However, the highly planar and crystalline P3T4-VCN exhibits a strong tolerance toward processing treatments. After morphology optimization, the fullerene-based bulk-heterojunction solar cell of tilted P3T4-INCN exhibits a power conversion efficiency (PCE) of 5.68%, which is significantly superior to that of P3T4-VCN:PC71BM (PCE = 1.29%). Our results demonstrate the importance of the terminal end-group for the design of A-D-A-type SMs and their sensitivity toward the postprocessing treatments in optimizing their performance.

Facile Synthesis of Composition-Controlled Graphene-Supported PtPd Alloy Nanocatalysts and Their Applications in Methanol Electro-Oxidation and Lithium-Oxygen Batteries.

A new and simple approach is reported for the synthesis of uniformly dispersed PtPd alloy nanocatalysts supported on graphene nanoplatelets (GNPs) (PtPd-GNPs) through the introduction of bifunctional materials, which can modify the GNP surface and simultaneously reduce metal ions. With the use of poly(4-styrenesulfonic acid), poly(vinyl pyrrolidone), poly(diallyldimethylammonium chloride), and poly(vinyl alcohol) as bifunctional materials, PtPd-GNPs can be produced through a procedure that is far simpler than previously reported methods. The as-prepared nanocrystals on GNPs clearly exhibit uniform PtPd alloy structures of around 2 nm in size, which are strongly anchored and well distributed on the GNP sheets. The Pt/Pd atomic ratio and loading density of the nanocrystals on the GNPs are controlled easily by changing the metal precursor feed ratio and the mass ratio of GNP to the metal precursor, respectively. As a result of the synergism between Pt and Pd, the as-prepared PtPd-GNPs exhibit markedly enhanced electrocatalytic performance during methanol electro-oxidation compared with monometallic Pt-GNP or commercially available Pt/C. Furthermore, the PtPd-GNP nanocatalysts also show greatly enhanced catalytic activity toward the oxygen reduction/evolution reaction in a lithium-oxygen (Li-O2 ) process, resulting in greatly improved cycling stability of a Li-O2 battery.

Progress in Integrative Biomaterial Systems to Approach Three-Dimensional Cell Mechanotransduction.

Mechanotransduction between cells and the extracellular matrix regulates major cellular functions in physiological and pathological situations. The effect of mechanical cues on biochemical signaling triggered by cell-matrix and cell-cell interactions on model biomimetic surfaces has been extensively investigated by a combination of fabrication, biophysical, and biological methods. To simulate the in vivo physiological microenvironment in vitro, three dimensional (3D) microstructures with tailored bio-functionality have been fabricated on substrates of various materials. However, less attention has been paid to the design of 3D biomaterial systems with geometric variances, such as the possession of precise micro-features and/or bio-sensing elements for probing the mechanical responses of cells to the external microenvironment. Such precisely engineered 3D model experimental platforms pave the way for studying the mechanotransduction of multicellular aggregates under controlled geometric and mechanical parameters. Concurrently with the progress in 3D biomaterial fabrication, cell traction force microscopy (CTFM) developed in the field of cell biophysics has emerged as a highly sensitive technique for probing the mechanical stresses exerted by cells onto the opposing deformable surface. In the current work, we first review the recent advances in the fabrication of 3D micropatterned biomaterials which enable the seamless integration with experimental cell mechanics in a controlled 3D microenvironment. Then, we discuss the role of collective cell-cell interactions in the mechanotransduction of engineered tissue equivalents determined by such integrative biomaterial systems under simulated physiological conditions.

Solution-Assembled Blends of Regioregularity-Controlled Polythiophenes for Coexistence of Mechanical Resilience and Electronic Performance.

Considering all the potential applications of organic electronics in portable, wearable, and implantable devices, it is of great importance to develop electroactive materials that possess mechanical reliability along with excellent electronic performance. The coexistence of these two attributes, however, is very difficult to achieve because there is an inverse relationship between the electrical properties and the mechanical flexibility, both of which are associated with the conjugation length and intermolecular ordering of the polymers. Herein, we demonstrate a simple and robust approach based on solution assembly of two different poly(3-hexylthiophene)s (P3HTs) with regioregularity (RR) contents of 97% and 66% to impart both electrical and mechanical properties to films for organic electronic applications. The 97% RR P3HT exhibits high electronic performance but poor mechanical resilience, and vice versa for the 66% RR P3HT. Selective crystallization of high RR P3HT induced by solution assembly allows the use of a one-step process to construct percolated networks of high RR P3HT nanowires (NWs) in a low RR P3HT matrix. Only 5 wt % of high RR P3HT NWs in a 95 wt % low RR P3HT matrix was required to produce hole mobilities comparable to that of pure high RR P3HT, and this blend film exhibited improvements by factors of 20 and 60 in elongation at break and toughness, respectively. Selective self-assembly of RR-controlled polymers allowed us to overcome the fragile nature of highly crystalline conjugated polymer films without sacrificing their electronic properties.

Flexible wire-shaped strain sensor from cotton thread for human health and motion detection.

In this work, a wire-shaped flexible strain sensor was fabricated by encapsulating conductive carbon thread (CT) with polydimethylsiloxane (PDMS) elastomer. The key strain sensitive material, CT, was prepared by pyrolysing cotton thread in N2 atmosphere. The CT/PDMS composite wire shows a typical piezo-resistive behavior with high strain sensitivity. The gauge factors (GF) calculated at low strain of 0-4% and high strain of 8-10% are 8.7 and 18.5, respectively, which are much higher than that of the traditional metallic strain sensor (GF around 2). The wire-shaped CT/PDMS composite sensor shows excellent response to cyclic tensile loading within the strain range of 0-10%, the frequency range of 0.01-10 Hz, to up to 2000 cycles. The potential of the wire senor as wearable strain sensor is demonstrated by the finger motion and blood pulse monitoring. Featured by the low costs of cotton wire and PDMS resin, the simple structure and fabrication technique, as well as high performance with miniaturized size, the wire-shaped sensor based on CT/PDMS composite is believed to have a great potential for application in wearable electronics for human health and motion monitoring.

Enhanced Sensitivity of Patterned Graphene Strain Sensors Used for Monitoring Subtle Human Body Motions.

With the growth of the wearable electronics industry, structural modifications of sensing materials have been widely attempted to improve the sensitivity of sensors. Herein, we demonstrate patterned graphene strain sensors, which can monitor small-scale motions by using the simple, scalable, and solution-processable method. The electrical properties of the sensors are easily tuned via repetition of the layer-by-layer assembly, leading to increment of thickness of the conducting layers. In contrast to nonpatterned sensors, the patterned sensors show enhanced sensitivity and the ability to distinguish subtle motions, such as similar phonations and 81 beats per minute of pulse rate.

Multifunctional Wearable Device Based on Flexible and Conductive Carbon Sponge/Polydimethylsiloxane Composite.

Wearable devices that can be used to monitor personal health, track human motions, and provide thermotherapy, etc., are highly desired in personalized healthcare. In this work, a multifunctional wearable "wrist band" which works as both heater for thermotherapy and sensor for personal health and motion monitoring is fabricated from a flexible and conductive carbon sponge/polydimethylsiloxane (CS/PDMS) composite. The key functional material of the wrist band, namely, the conductive CS, is synthesized from waste paper by a freeze-drying and high-temperature pyrolysis process. When the wrist band works as a heater under 15 V, a stable temperature difference of 20 °C is achieved between the wrist band and the ambient. When the wrist band serves as a wearable strain sensor, the wrist band exhibits fast and repeatable response and excellent durability within the strain range of 0-20% and the working frequency of 0.01-10 Hz. Finally, the typical applications of the multifunctional wearable wrist band, as a heater for thermotherapy and a sensor for blood pulse, breathe, and walk monitoring, are demonstrated. Due to its low cost, high flexibility, moderate conductivity, and excellent strain sensibility, the as-prepared wearable device based on the CS/PDMS composite is promising to be applied for the provision of personal healthcare.

How Sensitive Is the Elasticity of Hydroxyapatite-Nanoparticle-Reinforced Chitosan Composite to Changes in Particle Concentration and Crystallization Temperature?

Hydroxyapatite (HA) nanoparticle-reinforced chitosan composites are biocompatible and biodegradable structural materials that are used as biomaterials in tissue engineering. However, in order for these materials to function effectively as intended, e.g., to provide adequate structural support for repairing damaged tissues, it is necessary to analyse and optimise the material processing parameters that affect the relevant mechanical properties. Here we are concerned with the strength, stiffness and toughness of wet-spun HA-reinforced chitosan fibres. Unlike previous studies which have addressed each of these parameters as singly applied treatments, we have carried out an experiment designed using a two-factor analysis of variance to study the main effects of two key material processing parameters, namely HA concentration and crystallization temperature, and their interactions on the respective mechanical properties of the composite fibres. The analysis reveals that significant interaction occurs between the crystallization temperature and HA concentration. Starting at a low HA concentration level, the magnitude of the respective mechanical properties decreases significantly with increasing HA concentration until a critical HA concentration is reached, at around 0.20-0.30 (HA mass fraction), beyond which the magnitude of the mechanical properties increases significantly with HA concentration. The sensitivity of the mechanical properties to crystallization temperature is masked by the interaction between the two parameters-further analysis reveals that the dependence on crystallization temperature is significant in at least some levels of HA concentration. The magnitude of the mechanical properties of the chitosan composite fibre corresponding to 40 °C is higher than that at 100 °C at low HA concentration; the reverse applies at high HA concentration. In conclusion, the elasticity of the HA nanoparticle-reinforced chitosan composite fibre is sensitive to HA concentration and crystallization temperature, and there exists a critical concentration level whereby the magnitude of the mechanical property is a minimum.

Novel graphene foam composite with adjustable sensitivity for sensor applications.

In this study, free-standing graphene foam (GF) was developed by a three-step method: (1) vacuum-assisted dip-coating of nickel foam (Ni-F) with graphene oxide (GO), (2) reduction of GO to reduced graphene oxide (rGO), and then (3) etching out the nickel scaffold. Pure GF samples were tested for their morphology, chemistry, and mechanical integrity. GF mimics the microstructure of Ni-F while individual bones of GF were hollow, because of the complete removal of nickel. The GF-PDMS composites were tested for their ability to sense both compressive and bending strains in the form of change in electrical resistance. The composite showed different sensitivity to bending and compression. Upon applying a 30% compressive strain on the GF-PDMS composite, its resistance increased to ∼120% of its original value. Similarly, bending a sample to a radius of 1 mm caused the composite to change its resistance to ∼52% of its original resistance value. The relative change in resistance of the composite by an applied pressure/strain can be tuned to considerably different values by heat-treating the GF at different temperatures prior to infusing PDMS into its scaffold. Upon heat treating the GF at 800 °C prior to PDMS infusion, the GF-PDMS demonstrated ∼10 times better sensitivity than the untreated sample for a compressive strain of 20%. The composite was also tested for its ability to retain a change in electrical resistance when a brief load/strain is applied. The GF-PDMS composite was tested for at least 500 cycles under compressive cyclic loading and showed good electromechanical durability. Finally, it was demonstrated that the composite can be used to measure human blood pressure when attached to human skin.

Enhancing mechanical properties of highly efficient polymer solar cells using size-tuned polymer nanoparticles.

The low mechanical durability of polymer solar cells (PSCs) has been considered as one of the critical hurdles for their commercialization. We described a facile and powerful strategy for enhancing the mechanical properties of PSCs while maintaining their high power conversion efficiency (PCE) by using monodispersed polystyrene nanoparticles (PS NPs). We prepared highly monodispersed, size-controlled PS NPs (60, 80, and 100 nm), and used them to modify the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) anode buffer layer (ABL). The PS NPs played two important roles; i.e., they served as (1) binders in the PEDOT:PSS films, and (2) interfacial modifiers between ABL and the active layer, resulting in remarkable improvement of the mechanical integrity of the PSCs. The addition of PS NPs enhanced the inherent mechanical toughness of the PEDOT:PSS ABL due to their elastic properties, allowing the modified ABL to tolerate higher mechanical deformations. In addition, the adhesion energy (Gc) between the active layer and the modified PEDOT:PSS layer was enhanced significantly, i.e., by a factor of more than 1.5. The Gc value has a strong relationship with the sizes of the PS NP, showing the greatest enhancement when the largest size PS NPs (100 nm) were used. In addition, PS NPs significantly improve the air-stability of the PSCs by suppressing moisture adsorption and corrosion of the electrodes. Thus, the modification of ABL with PS NPs effectively enhances both the mechanical and the long-term stabilities of the PSCs without sacrificing their PCE values, demonstrating their great potential as applications in flexible organic electronics.

Graphene foam developed with a novel two-step technique for low and high strains and pressure-sensing applications.

Freestanding, mechanically stable, and highly electrically conductive graphene foam (GF) is formed with a two-step facile, adaptable, and scalable technique. This work also demonstrates the formation of graphene foam with tunable densities and its use as strain/pressure sensor for both high and low strains and pressures.