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Research on the chiral magneto-optical properties of inorganic nanomaterials has enabled novel applications in advanced optical and electronic devices. However, the corresponding chiral magneto-optical responses have only been studied under strong magnetic fields of ≥1 T, which limits the wider application of these novel materials. In this paper, we report on the enhanced chiral magneto-optical activity of supra-assembled Fe3O4 magnetite nanoparticles in the visible range at weak magnetic fields of 1.5 mT. The spherical supra-assembled particles with a diameter of ∼90 nm prepared by solvothermal synthesis had single-crystal-like structures, which resulted from the oriented attachment of nanograins. They exhibited superparamagnetic behavior even with a relatively large supraparticle diameter that exceeded the size limit for superparamagnetism. This can be attributed to the small size of nanograins with a diameter of ∼12 nm that constitute the suprastructured particles. Magnetic circular dichroism (MCD) measurements at magnetic fields of 1.5 mT showed distinct chiral magneto-optical activity from charge transfer transitions of magnetite in the visible range. For the supraparticles with lower crystallinity, the MCD peaks in the 250-550 nm range assigned as the ligand-to-metal charge transfer (LMCT) and the inter-sublattice charge transfer (ISCT) show increased intensities in comparison to those with higher crystallinity samples. On the contrary, the higher crystallinity sample shows higher MCD intensities near 600-700 nm for the intervalence charge transfer (IVCT) transition. The differences in MCD responses can be attributed to the crystallinity determined by the reaction time, lattice distortion near grain boundaries of the constituent nanocrystals, and dipolar interactions in the supra-assembled structures.

Chiral-structured nanoscale materials exhibit chiroptical properties with preferential absorptions of circularly polarized light. The distinctive optical responses of chiral materials have great potential for advanced optical and biomedical applications. However, the fabrication of three-dimensional structures with mirrored nanoscale geometry is still challenging. This study introduces chiral plasmonic nanopatterns in wavy shapes based on the unidirectional alignment of block copolymer thin films and their tilted transfer, combined with buckling processes. The cylindrical nanodomains of polystyrene-iblock/i-poly(2-vinylpyridine) thin films were unidirectionally aligned over a large area by the shear-rolling process. The aligned block copolymer thin films were transferred onto uniaxially prestrained polydimethylsiloxane films at certain angles relative to the stretching directions. The strain was then released to induce buckling. The aligned nanopatterns across the axis of the formed microwrinkles were selectively infiltrated with gold ions. After reduction by plasma treatment, chiral plasmonic nanowave patterns were fabricated with the presence of mirror-reflected circular dichroism spectra. This fabrication method does not require any lithography processing or innately chiral biomaterials, which can be advantageous over other conventional fabrication methods for artificial nanoscale chiral materials.

When various optically and/or electronically active materials, such as conjugated polymers, perovskites, metals, and metal oxides, are confined at the nanoscale, they can exhibit unique nano-confined behavior that significantly differs from the behavior observed at the macroscale. Although controlled nano-confinement of functional materials can allow modulation of their electronic properties without the aid of any synthetic methodologies or additional chemical treatments, limited assembly approaches for nano-confinement and insufficient analytical tools for electronic characterization remain critical challenges in the development of novel optoelectronic materials and the investigation of their modulated properties. This review describes how the nano-confined features of organic and inorganic materials are related to the control and improvement of their optoelectronic properties. In particular, we focus on various assembly approaches for effective nano-confinement as well as methods for nano-electronic characterization. Then, we briefly present challenges and perspectives on the direction of nano-confinement in terms of the preparation of optoelectronic materials with desired functionalities. Furthermore, we believe that this review can provide a basis for developing and designing next-generation optoelectronics through nano-confinement.

Highly conductive and porous current collectors that can provide favorable interfacial interaction with sulfur components play a critical role in the performance of lithium–sulfur (Li–S) batteries. Although three-dimensional (3D) porous textiles have emerged as promising current collector materials, most reported approaches have reached a limit in producing textiles with metal-like conductivity and do not effectively utilize the large surface area of textiles. Here, we introduce a Li–S copolymer cathode with high areal/specific capacity and good rate capability using a metallic cotton textile (CT)-based current collector that exhibits strong interfacial interaction with sulfur. To fabricate the metallic current collector, CT was first carbonized and subsequently electroplated with nickel (Ni). When a sulfur copolymer-based hybrid slurry and layer-by-layer-assembled conductive capping layer were deposited onto the Ni-electroplated CT, the resulting Li–S copolymer cathode displayed significantly enhanced areal capacity, specific capacity, and rate capability. These improvements were realized due to the full utilization of the large conductive surface area of Ni-electroplated CT as well as the effective chemical confinement of soluble lithium polysulfides by a conductive capping layer. The Li–S copolymer cathode prepared in this study outperforms previously reported sulfur copolymer-based cathodes and provides a basis for the development and design of future high-performance electrodes.

Development of soft actuators with higher performance and more versatile controllability has been strongly required for further innovative advancement of various soft applications. Among various soft actuators, electrochemical actuators have attracted much attention due to their lightweight, simple device configuration, and facile low-voltage control. However, the reported performances have not been satisfactory because their working mechanism depends on the limited electrode expansion by conventional electrochemical reactions. Herein, we report an electroosmosis-driven hydrogel actuator with a fully soft monolithic structure-based whole-body actuation mechanism using an amphiphilic interaction-induced layer-by-layer assembly. For this study, cracked electrodes with interconnected metal nanoparticles are prepared on hydrogels through layer-by-layer assembly and shape transformation of metal nanoparticles at hydrophobic/hydrophilic solvent interfaces. Electroosmotic pumping by cracked electrodes instantaneously induces hydrogel swelling through reversible and substantial hydraulic flow. The resultant actuator exhibits actuation strain of higher than 20% and energy density of 1.06 × 105 J m-3, allowing various geometries (e.g., curved-planar and square-pillared structures) and motions (e.g., slow-relaxation, spring-out, and two degree of freedom bending). In particular, the energy density of our actuators shows about 10-fold improvement than those of skeletal muscle, electrochemical actuators, and various stimuli-responsive hydrogel actuators reported to date.

A few critical issues in preparing transparent conductive electrodes (TCEs) based on solution-processable conductive nanomaterials are their low electrical conductivity and the unfavorable trade-off between electrical conductivity and optical transparency, which are closely related to the organic ligands bound to the nanomaterial surface. In particular, bulky/insulating organic ligands bound to the surface of conductive nanomaterials unavoidably act as high contact resistance sites at the interfaces between neighboring nanomaterials, which adversely affects the charge transfer kinetics of the resultant TCEs. This article reviews the latest research status of various interfacial control approaches for solution-processable TCEs. We describe how these approaches can be effectively applied to conductive nanomaterials and how interface-controlled conductive nanomaterials can be employed to improve the electrical and/or electrochemical performance of various transparent nanocomposite electrodes, including TCEs, energy storage electrodes, and electrochromic electrodes. Last, we provide perspectives on the development direction for next-generation transparent nanocomposite electrodes and breakthroughs for significantly mitigating the complex trade-off between their electrical/electrochemical performance and optical transparency.

Here, we report that metal nanoparticle (NP)-based paper/textile electrodes with bulk metallic conductivity can be prepared via organic linker-modulated ligand exchange reaction and in situ room-temperature metallic fusion without additional chemical or thermal treatments. For this study, amine-functionalized molecule linkers instead of bulky polymer linkers were layer-by-layer (LbL)-assembled with tetraoctylammonium bromide (TOABr)-stabilized Au NPs to form Au NP multilayered films. By conversion of the amine groups of the organic molecule linkers from -NH3+ to the -NH2 groups, as well as by a decrease in the size of the organic linkers, the LbL-assembled Au NPs became highly interconnected and fused during LbL deposition, resulting in Au NP multilayers with adjustable conductivity and transport behavior. These phenomena were also predicted by a density functional theory investigation for the model system. Particularly, LbL-assembled films composed of TOABr-Au NPs and diethylenetriamine ( Mw: ∼104) exhibited a remarkable electrical conductivity of 2.2 × 105 S·cm-1, which was higher than the electrical conductivity of the metal NP-based electrodes as well as the carbon material-based electrodes reported to date. Furthermore, based on our approach, a variety of insulating flexible papers and textiles were successfully converted into real metal-like paper and textile electrodes with high flexibility preserving their highly porous structure. This approach can provide a basis for further improving and controlling the electrical properties of flexible electrodes through the control of organic linkers.

Energy-harvesting devices such as piezoelectric and triboelectric nanogenerators (NGs), which can convert mechanical energy into electricity, are under development to be combined with various electronics. In particular, the rapid progress in microscale electronics such as nanorobotics or microelectromechanical devices has strongly increased the demand for ultrathin film devices. Therefore, the thickness, highly uniform structure, chemical composition, interfacial adhesion/interactions, and electrical performance of electrically active films should be carefully considered for high-performance ultrathin energy-harvesting devices. This review focuses on how layer-by-layer (LbL) assembly as a kind of thin film technology can be effectively applied to ultrathin piezoelectric and triboelectric films, and furthermore enhance device performance. First, we introduce the basics of various LbL assemblies using electrostatic, hydrogen-bonding, and covalent-bonding interactions. Then, the LbL-assembly-assisted piezoelectric and triboelectric NGs reported to date are reviewed. Finally, we briefly present perspectives on the direction of LbL assembly for the realization of various ultrathin piezoelectric and triboelectric NGs with high performance.

Biofuel cells, which can convert chemical energy into electricity have been considered as one of the most promising candidates for powering implantable and microscale biomedical devices. However, most biofuel cells generate a low power output, limiting their practical applications. Here, we introduce a high-performance biofuel cell based on gold nanoparticle-modified carbon nanotube hybrid fibers. These hybrid electrodes could be converted into anodes through additional enzyme deposition and used directly as cathodes, allowing notable oxygen reduction reaction activity as well as high electrical conductivity (∼6100 S cm−1). The formed hybrid biofuel cell, composed of an enzymatic anode and a gold nanoparticle-coated carbon fiber cathode, provides an outstanding stationary power output of 1.2 mW cm−2 under a fixed external resistance (cyclic voltammetry measurement ∼2.1 mW cm−2) at 300 mmol L−1 glucose. Furthermore, these one-dimensional hybrid electrodes with extremely high electrical conductivity can be widely applied in various wire-type electrochemical devices.

Electrical conductivity, mechanical flexibility, and large electroactive surface areas are the most important factors in determining the performance of various flexible electrodes in energy storage devices. Herein, a layer-by-layer (LbL) assembly-induced metal electrodeposition approach is introduced to prepare a variety of highly porous 3D-current collectors with high flexibility, metallic conductivity, and large surface area. In this study, a few metal nanoparticle (NP) layers are LbL-assembled onto insulating paper for the preparation of conductive paper. Subsequent Ni electroplating of the metal NP-coated substrates reduces the sheet resistance from ≈103 to

A luminescent solar concentrator-based photovoltaic system (LSC-PVs) is highly transparent because it harvests solar light via the LSC, a transparent panel containing only fluorophores, and is, therefore, promising as a PV window. However, for the practical use of LSC-PV, achieving high efficiency remains a challenge. Here, we demonstrate an LSC-PV, which is based on the combination of an upconversion (UC)-assisted dual band harvesting LSC and perovskite solar cells (PSCs). We prepare a dual LSC panel consisting of a downshift (DS) LSC that absorbs violet light and an LSC that upconverts the red light. We apply a highly efficient mixed halide PSC with an efficiency of 17.22%. We control the thickness of the LSC panel as well as the dye concentration to maximize the emission from dual LSCs. The dual LSCs coupled with a PSC exhibit a high average-visible-transmittance of 82% and achieve a maximum efficiency of 7.53% at 1 sun (AM 1.5G) illumination. The dual LSC–PSC exhibits a constant efficiency even under oblique solar light illumination and a stable operation with an efficiency retention of 80%.

Organic-ligand-based solution processes of metal and transition metal oxide (TMO) nanoparticles (NPs) have been widely studied for the preparation of electrode materials with desired electrical and electrochemical properties for various energy devices. However, the ligands adsorbed on NPs have a significant effect on the intrinsic properties of materials, thus influencing the performance of bulk electrodes assembled by NPs for energy devices. To resolve these critical drawbacks, numerous approaches have focused on developing unique surface chemistry that can exchange bulky ligands with small ligands or remove bulky ligands from NPs after NP deposition. In particular, recent studies have reported that the ligand-exchange-induced layer-by-layer (LE-LbL) assembly of NPs enables controlled assembly of NPs with the desired interparticle distance, and interfaces, dramatically improving the electrical/electrochemical performance of electrodes. This emerging approach also demonstrates that efficient surface ligand engineering can exploit the unique electrochemical properties of individual NPs and maximize the electrochemical performance of the resultant NP-assembled electrodes through improved charge transfer efficiency. This report focuses on how LE-LbL assembly can be effectively applied to NP-based energy storage/conversion electrodes. First, the basic principles of the LE-LbL approach are introduced and then recent progress on NP-based energy electrodes prepared via the LE-LbL approach is reviewed.

Nanocomposites with aligned nanofillers have received significant attention because of their excellent mechanical properties. However, because of the difficulty in identifying interfacial interactions in mechanical responses, the anisotropic dynamic mechanical properties of aligned nanocomposites, especially those with high reinforcement contents, are not fully understood. In this study, aligned aramid nanofiber/poly(vinyl alcohol) (ANF/PVA) nanocomposites with a nanofiller volume fraction of 48% are fabricated by using the swelling-assisted stretching method. This method enabled high degree of alignment of the ANF nanofibers with a sheath of PVA matrix. Enhancement of mechanical strength and stiffness is attributed to improvements of interfacial interactions between aligned ANFs and PVA via effective stress transfer. The damping properties are varied by activation of different dissipation modes, such as the stick–slip and reversible matrix-tearing at the interfaces, that are dependent to the loading angle relative to the nanofiber alignment direction. Resultant viscoelastic properties evaluated by the weight-adjusted viscoelastic figure of merits, the combination of stiffness and damping properties, exceed the conventional limit line up to three folds in magnitude. Deepening the understanding of anisotropic dynamic mechanical responses is required for designing aligned nanocomposite materials for mechanical and electronic applications.

We investigate the operational instability of quantum dot (QD)-based light-emitting diodes (QLEDs). Spectroscopic analysis on the QD emissive layer within devices in chorus with the optoelectronic and electrical characteristics of devices discloses that the device efficiency of QLEDs under operation is indeed deteriorated by two main mechanisms. The first is the luminance efficiency drop of the QD emissive layer in the running devices owing to the accumulation of excess electrons in the QDs, which escalates the possibility of nonradiative Auger recombination processes in the QDs. The other is the electron leakage toward hole transport layers (HTLs) that accompanies irreversible physical damage to the HTL by creating nonradiative recombination centers. These processes are distinguishable in terms of the time scale and the reversibility, but both stem from a single origin, the discrepancy between electron versus hole injection rates into QDs. Based on experimental and calculation results, we propose mechanistic models for the operation of QLEDs in individual quantum dot levels and their degradation during operation and offer rational guidelines that promise the realization of high-performance QLEDs with proven operational stability.

We demonstrate a direct-write patternable water-based poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) composite ink which is capable of providing highly stretchable and washing-resistant electrodes on a fabric substrate for electronic textile applications. An aqueous composite ink consisting of PEDOT:PSS, graphene oxide nanosheets and anionic polyurethane does readily not permeated into hygroscopic fabric, which facilitate direct drawing of fine PEDOT electrode on the fabric without undesired blur effect. This limited permeation of aqueous PEDOT composite ink on the hygroscopic fabric is mainly originated from the intermolecular interactions of anionic polyurethane including hydrogen bonding with water molecules, and charge balancing interactions with PEDOT chains. Furthermore, addition of the graphene oxide nanosheets contributes to enhance the electrical conductivity of the composite by improving crystallization of PEDOT molecules. The PEDOT composite film shows unique structure of the PEDOT nanofibril network embedded by the polyurethane matrix, which resulted in an enough electrical pathway for charge carriers even though only 2.9 wt% of PEDOT:PSS existed in the composite film. The PEDOT composite film exhibited electrical conductivity of 4.6 S/cm, extremely high stretchability of 375% rupture strain, and high durability for repeated washing process with strong bleaching agent. Light emitting diode incorporated on the stretchable spandex with interconnects of the PEDOT composite pattern showed that LED light intensity was almost maintained even with stretching of PEDOT interconnects to 290%.

We introduce high-performance supercapacitor electrodes with ternary components prepared from consecutive amphiphilic ligand-exchange-based layer-by-layer (LbL) assembly among amine-functionalized multi-walled carbon nanotubes (NH2-MWCNTs) in alcohol, oleic acid-stabilized Fe3O4 nanoparticles (OA-Fe3O4 NPs) in toluene, and semiconducting polymers (PEDOT:PSS) in water. The periodic insertion of semiconducting polymers within the (OA-Fe3O4 NP/NH2-MWCNT)n multilayer-coated indium tin oxide (ITO) electrode enhanced the volumetric and areal capacitances up to 408 ± 4 F cm−3 and 8.79 ± 0.06 mF cm−2 at 5 mV s−1, respectively, allowing excellent cycling stability (98.8% of the initial capacitance after 5000 cycles) and good rate capability. These values were higher than those of the OA-Fe3O4 NP/NH2-MWCNT multilayered electrode without semiconducting polymer linkers (volumetric capacitance ∼241 ± 4 F cm−3 and areal capacitance ∼1.95 ± 0.03 mF cm−2) at the same scan rate. Furthermore, when the asymmetric supercapacitor cells (ASCs) were prepared using OA-Fe3O4 NP- and OA-MnO NP-based ternary component electrodes, they displayed high volumetric energy (0.36 mW h cm−3) and power densities (820 mW cm−3).

We introduce a layer-by-layer (LbL) assembly-induced triboelectric nanogenerator (TENG) with a high and stable electric output under a wide range of humidity conditions. In this study, highly porous (cationic poly(allylamine hydrochloride) (PAH)/anionic poly(acrylic acid) (PAA))n multilayer films were prepared via a pH-controlled electrostatic LbL assembly with a subsequent acid treatment and were used as a mold for the triboelectric poly(dimethylsiloxane) (PDMS) replica. The electrical output of the TENGs composed of a protuberant PDMS plate and Al electrodes significantly increased based on the evolution of the nano-/micro-structured PDMS bumps. Particularly, the protuberant PDMS film molded from the porous (1.5 mg mL−1 PAH/0.5 mg mL−1 PAA)20 multilayers displayed a high open-circuit voltage output of 242 V and a short-circuit current density of 16.2 μA cm−2 under a compressive force of 90 N in a relative humidity (RH) of 20%. When this hierarchical PDMS surface was additionally modified by fluorine self-assembled monolayer, the voltage output and current density of the resultant TENG at the same experimental conditions were increased up to approximately 288 V and 17 μA cm−2, respectively, exhibiting a remarkably high humidity-resistant electrical performance (16% loss of the initial voltage at 80% RH).

Herein, we introduce a high-performance and highly flexible asymmetric supercapacitor that is prepared from metallic cotton threads coated with pseudocapacitive nanoparticles without the aid of carbon-based conductive materials. In this study, Au nanoparticles are layer-by-layer assembled on highly porous cotton threads using amine-functionalized molecular linkers in organic media for the preparation of metallic cotton threads that can store a large amount of pseudocapacitive nanoparticles. The highly porous metallic cotton threads exhibit exceptional electrical conductivity (∼2.1 × 104 S cm−1, resistance of ∼0.1 Ω cm−1) and yet maintain the intrinsic flexibility of cotton. Using the same assembly method, Fe3O4 and MnO nanoparticles are deposited onto the metallic cotton threads to prepare the anode and the cathode, respectively, of the asymmetric supercapacitors, and furthermore, Au nanoparticles are periodically inserted between the pseudocapacitive multilayers to facilitate charge transport. The assembled all solid-state asymmetric supercapacitors with a unique structural design deliver a notable areal energy density of 80.7 μW h cm−2 (at 172.5 μW cm−2) and a power density of 3450.1 μW cm−2 (at 53.7 μW h cm−2), exceeding the performance of conventional thread-type asymmetric supercapacitors. We also emphasize that this energy performance can be further enhanced by increasing the number of metal and/or pseudocapacitive nanoparticle layers deposited.

Synthesis of various earth-abundant electroactive materials in gram-scale via simple methods with excellent efficiency can effectively reduce the cost. In this context, we have demonstrated a gram-scale synthesis of α-Fe2O3@rGO core@shell nanocubes via a direct solution route. By the concept of charge-charge interactions, we have successfully wrapped the reduced graphene oxide (rGO) over the surface of α-Fe2O3 nanocubes resulting in the formation of α-Fe2O3@rGO core@shell nanocubes in a gram-scale. The synthesized α-Fe2O3@rGO core@shell nanocubes were characterized by a group of analytical methods and finally explored as an effective anode material for sodium-ion batteries (SIBs). The α-Fe2O3@rGO-10 wt% core@shell nanocubes sample displays an exceptional specific capacity of 970.2 mAh g−1 at 0.1 C-rate with a better rate capability of 77.8 mAh g−1 at 5.0 C-rate. Moreover, the α-Fe2O3@rGO-10 wt% sample also demonstrates a better specific capacity of about 586.9 mAh g−1 after 100 cycles at 0.1 C-rate. The current approach can enable the synthesis of various electroactive materials on a gram-scale using a cost-effective strategy with better electrochemical performance for practical energy storage devices.

The effective implantation of conductive and charge storage materials into flexible frames has been strongly demanded for the development of flexible supercapacitors. Here, we introduce metallic cellulose paper-based supercapacitor electrodes with excellent energy storage performance by minimizing the contact resistance between neighboring metal and/or metal oxide nanoparticles using an assembly approach, called ligand-mediated layer-by-layer assembly. This approach can convert the insulating paper to the highly porous metallic paper with large surface areas that can function as current collectors and nanoparticle reservoirs for supercapacitor electrodes. Moreover, we demonstrate that the alternating structure design of the metal and pseudocapacitive nanoparticles on the metallic papers can remarkably increase the areal capacitance and rate capability with a notable decrease in the internal resistance. The maximum power and energy density of the metallic paper-based supercapacitors are estimated to be 15.1 mW cm−2 and 267.3 μWh cm−2, respectively, substantially outperforming the performance of conventional paper or textile-type supercapacitors., With ligand-mediated layer-by-layer assembly between metal nanoparticles and small organic molecules, the authors prepare metallic paper electrodes for supercapacitors with high power and energy densities. This approach could be extended to various electrodes for portable/wearable electronics.

We report the instantaneous pulsed-light cross-linking of polymer gate dielectrics on a flexible substrate by using intensely pulsed white light (IPWL) irradiation. Irradiation with IPWL for only 1.8 s of a poly(4-vinylphenol) (PVP) thin film with the cross-linking agent poly(melamine-co-formaldehyde) (PMF) deposited on a plastic substrate was found to yield fully cross-linked PVP films. It was confirmed that the IPWL-cross-linked PVP films have smooth pinhole-free surfaces and exhibit a low leakage current density, organic solvent resistance, and good compatibility with organic semiconductor, and that they can be used as replacements for typical PVP dielectrics that are cross-linked with time and energy intensive thermal heating processes. The synchronization of the IPWL irradiation with substrate transfer was found to enable the preparation of cross-linked PVP films on large area substrates with a highly uniform capacitance. Flexible OTFT based on IPWL-cross-linked PVP dielectrics were found to exhibit good electrical performance that is comparable to that of devices with thermally cross-linked PVP dielectric, as well as excellent deformation stability even at a bending radius of 3 mm.

One of the most critical issues in electrochromic (EC) films based on transition metal oxides such as tungsten oxides (WOx) is their poor charge transfer property, which is closely related to EC performance. Herein, high-performance EC films with enhanced charge transport are prepared using small-molecule linkers and transparent/conductive nanoparticles (NPs). In this work, oleylamine (OAm)-stabilized WO2.72 nanorods (NRs) and OAm-stabilized indium tin oxide (ITO) NPs are layer-by-layer (LbL)-assembled with small-molecule linkers (tris(2-aminoethyl)amine, TREN) using a ligand-exchange reaction between bulky/insulating OAm ligands and TREN molecules. In this case, there is only one TREN layer between neighboring inorganic components (WO2.72 NRs and/or ITO NPs), resulting in a dramatic decrease in the separation distance. This minimized separation distance as well as the periodic insertion of transparent/conductive ITO NPs can significantly reduce the charge transfer resistance within WO2.72 NR-based EC films, which remarkably improves their EC performance. Compared to EC films without ITO NPs, the formed EC films with ITO NPs exhibit faster switching responses (4.1 times in coloration time and 3.5 times in bleaching time) and a maximum optical modulation of approximately 55.8%. These results suggest that electrochemical performance, including EC performance, can be significantly improved through structural/interfacial designing of nanocomposites.

SnO2 Free-standing anodes are regarded as a potential negative electrode for high energy lithium ion batteries (LIBs). However, they suffer from poor rate capability and reversibility because of very low electric conductivity of SnO2. In this study, in order to endow electrical conductivity to the surface of SnO2 particles, a novel and facile method using a plasma are employed to dope nitrogen into the lattice of SnO2. The SnO2 free-standing anode was fabricated by carbonizing an electro-spun fiber sheet followed by depositing SnO2 particles on the surface of carbon nanofibers (CNF) comprising the sheet through a hydrothermal process. The best N-doped SnO2 anode obtained under an optimized condition exhibits a 23 times higher specific capacity of 767 mAh g−1 than that of a pristine SnO2 anode (

Despite considerable interest in textile-based battery electrodes with large surface areas and mechanical flexibility, issues have restricted further advances in the energy performance of textile electrodes. These issues include the ineffective incorporation of conductive and/or active components into textile frameworks, the poor charge transfer between energy materials, and the formation of numerous unstable interfaces within textile electrodes. Herein, we introduce an aluminum textile-based lithium-ion battery cathode with remarkable areal capacity, high rate performance, and good cycling stability. Ligand exchange reaction-induced layer-by-layer (LbL) assembly of metal nanoparticles and small molecule linkers, with subsequent metal electroplating, perfectly converted polyester textiles to 3D-porous aluminum textiles that can be used as current collectors and high-energy reservoirs. The consecutive LbL assembly of high-energy LiFePO4 and conductive indium tin oxide nanoparticles onto the aluminum textiles using small organic linkers significantly increased the areal capacity and cycling stability (at least 580 cycles) of the resultant cathode, allowing facile charge transfer within the textile electrodes. Furthermore, the areal capacity of these textile electrodes increased from 1.07 to 3.28 mA h cm−2, with an increase in the folding number from 0 to 2.

We report on a new technique that incorporates silver nanoparticles (AgNPs) onto polyamide (PA) thin film composite (TFC) reverse osmosis membranes via arc plasma deposition (APD) to impart antibacterial properties and simultaneously improve membrane performance. APD allows the direct deposition of AgNPs under vacuum dry condition, overcoming the drawbacks of the conventional wet-chemical methods. AgNPs (~7.6 nm in diameter) were uniformly distributed without aggregation throughout the PA selective layer with some partially implanted into the PA matrix. Ag loading could be tuned by simply adjusting the number of APD purse shots. The deposited AgNPs exhibited good leaching stability, presumably due to the strong Ag-PA chemical interaction and partially buried AgNP morphology. The resulting Ag-incorporated TFC (Ag-TFC) membrane showed the strong and long-lasting antibacterial properties for both gram-negative and -positive bacteria. Simultaneously, the Ag-TFC membrane exhibited an enhancement in water flux of approximately 40% without deterioration in NaCl rejection. These performance changes were tentatively attributed to the partial destruction of the PA layer under the high energetic APD condition along with the increased membrane hydrophilicity. Hence, the APD process provides a simple and effective route to modify membranes with functional NPs.

Organo-lead halide perovskite solar cells (PSCs) have received great attention because of their optimized optical and electrical properties for solar cell applications. Recently, a dramatic increase in the photovoltaic performance of PSCs with organic hole transport materials (HTMs) has been reported. However, as of now, future commercialization can be hampered because the stability of PSCs with organic HTM has not been guaranteed for long periods under conventional working conditions, including moist conditions. Furthermore, conventional organic HTMs are normally expensive because material synthesis and purification are complicated. It is herein reported, for the first time, octadecylamine-capped pyrite nanoparticles (ODA-FeS2 NPs) as a bi-functional layer (charge extraction layer and moisture-proof layer) for organo-lead halide PSCs. FeS2 is a promising candidate for the HTM of PSCs because of its high conductivity and suitable energy levels for hole extraction. A bi-functional layer based on ODA-FeS2 NPs shows excellent hole transport ability and moisture-proof performance. Through this approach, the best-performing device with ODA-FeS2 NPs-based bi-functional layer shows a power conversion efficiency of 12.6% and maintains stable photovoltaic performance in 50% relative humidity for 1000 h. As a result, this study has the potential to break through the barriers for the commercialization of PSCs.

Control of crystallization of a solution-processed perovskite layer is of prime importance for high performance solar cells. In spite of the negative effect of water on perovskite solar energy conversion in several previous works, we observed that humidity plays a critical role to develop a thin uniform, dense perovskite film with preferred crystals, in particular, in a device with architecture of ITO/PEDOT:PSS/CH3NH3PbI3/ PC71BM/LiF/Al fabricated by two-step sequential spin-coating process. Humidity controlled spin-coating of CH3NH3I on the pre-formed PbI2 layer was the most influential process and systematic structural investigation as a function of humidity revealed that grains of CH3NH3PbI3 perovskite crystals increase in size with their preferred orientation while film surface becomes roughened as the humidity increases. The performance of a device was closely related to the humidity dependent film morphology and in 40% relative humidity, the device exhibited the maximum power conversion efficiency of approximately 12% more than 10 times greater than that of a device fabricated at 20% humidity. The results suggest that our process with controlled humidity can be another efficient route for high performance and reliable perovskite solar cells. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Resistive switching behavior-based memory devices are considered promising candidates for next-generation data storage because of their simple structure configuration, low power consumption, and rapid operating speed. Here, the resistive switching nonvolatile memory properties of Fe 2 O 3 nanocomposite (NC) films prepared from the thermal calcination of layer-by-layer (LbL) assembled ferritin multilayers were successfully investigated. For this study, negatively charged ferritin nanoparticles were alternately deposited onto the Pt-coated Si substrate with positively charged poly(allylamine hydrochloride) (PAH) by solution-based electrostatic LbL assembly, and the formed multilayers were thermally calcinated to obtain a homogeneous transition metal oxide NC film through the elimination of organic components, including the protein shell of ferritin. The formed memory device exhibits a stable ON/OFF current ratio of approximately 10 3 , with nanosecond switching times under an applied external bias. In addition, these reversible switching properties were kept stable during the repeated cycling tests of above 200 cycles and a test period of approximately 10 5 s under atmosphere. These solution-based approaches can provide a basis for large-area inorganic nanoparticle-based electric devices through the design of bio-nanomaterials at the molecular level.

We introduce a novel, robust, cost-effective, and scalable approach for the preparation of a large-area force-assembled triboelectric nanogenerator (FTENG), which allows a stable and high electric output under a wide range of humidity conditions through its dual-sized morphology (i.e., microstructures and nanostructures). In this study, hexagonally packed colloidal arrays prepared by a force assembly approach rather than by conventional self-assembly were used as a mold for a triboelectric poly(dimethylsiloxane) (PDMS) replica with desired pattern shapes (intaglio and embossed structures) and sizes. The morphological size of the PDMS films was determined by the diameter of the force-assembled colloids. The electrical output performance of FTENGs composed of electrodes and a PDMS film increased substantially as the size of the micropores (for intaglio-structured PDMS) or embossed features (for embossed-structured PDMS) decreased. Furthermore, the triboelectric PDMS film with micro-/nanosized features (i.e., dual-embossed PDMS) displayed a remarkable electrical output of 207 V (open-circuit voltage under a compressive force of 90 N in relative humidity (RH) of 20%) and high hydrophobicity compared to that of PDMS films with flat, intaglio or embossed structures. This device maintained a high electric output even in a high-humidity environment (i.e., open-circuit output voltage ~175 V in RH 80%). Our approach using force-assembly and hierarchical surface morphology will provide a novel and effective framework for developing strong power sources in various self-powered electronics.

We present a new strategy to strongly and effectively immobilize silver nanoparticles (AgNPs) on polyamide thin film composite membranes to endow antibacterial activity. This method relies on the immobilization of relatively large silica particles (SiO 2 , ~400 nm in diameter), where AgNPs of ~30 nm in diameter are tightly and densely bound (AgNP@SiO 2 ), on the membrane surface using cysteamine as a covalent linker. The formation of multiple Ag–S chemical bonds between a “bumpy” AgNP@SiO 2 and the rough membrane surface provides a great leaching stability of AgNPs and AgNP@SiO 2 . AgNP@SiO 2 particles were well distributed over the entire membrane surface without severe aggregation. The surface coverage of the membrane by AgNP@SiO 2 was tuned by adjusting the deposition time and AgNP@SiO 2 particle concentration. The AgNP@SiO 2 -immobilized membrane showed excellent antibacterial properties against Escherichia coli , Pseudomonas aeruginosa and Staphylococcus aureus, even with a relatively low particle coverage. Importantly, the separation performance (water flux and salt rejection) of the membrane was not impaired by particle immobilization. These beneficial effects are attributed mainly to the sparse and good distribution of AgNP@SiO 2 , which can reinforce the antibacterial activity of AgNPs while having a negligible impact on the hydraulic resistance.

We introduce high-performance ultrathin electrochemical electrodes based on multi-stacking of high-energy multiwall carbon nanotube (MWCNT) hybrids and conductive MWCNTs. The MWCNT hybrids coated with oleic acid-stabilized pseudocapacitive nanoparticles (i.e., OA-PC–MWCNTs) were assembled via a sequential covalent-bonded layer-by-layer (LbL) approach with amine-functionalized MWCNTs (NH2–MWCNT) in organic media, generating a highly porous structure and allowing for precise nanoscale control of the electrode thickness. The resultant NH2–MWCNT/OA-PC–MWCNT multilayer electrodes exhibited a high energy capacity and remarkable operational stability, considerably higher than the capacity and stability of conventional blended nanocomposite or electrostatic LbL-assembled electrodes. The volumetric capacitances of the (NH2–MWCNT/OA–Fe3O4–MWCNT)20 and (NH2–MWCNT/OA–MnO–MWCNT)20 were approximately 394 ± 10, and 674 ± 13 F cm−3 at 1 A cm−3, respectively. Additionally, these electrodes maintained their high volumetric capacitances without loss of initial capacitance even after 10 000 cycles; this cycling stability stemmed from the formation of chemically stable covalent bonds between the MWCNT hybrids and NH2–MWCNTs and between the PC NPs and NH2–MWCNTs. Given that a variety of PC NPs can be used to prepare MWCNT hybrids and that this approach can be further expanded to nanocomposite films including LbL-assembled multilayers, our approach may provide a promising platform for designing electrodes for use as thin film-type energy storage devices.

Current energy production habits deplete fossil fuels and accumulate atmospheric CO 2 , which contribute to the global climate change. Electrochemical fuel production via CO 2 reduction reaction is an idealistic yet an achievable process that mitigates CO 2 emissions and simultaneously satisfies energy demands. Here, the enhancement of CO 2 reduction activity and stability on size-controlled particulate Ag electrocatalysts derived from a simple, one-step cyclic voltammetry (CV) process by changing scan rates (1–200 mV/s) was demonstrated. Interestingly, larger nanoparticles prepared by slower scan rates (1–5 mV/s) have exhibited the most degree of enhancement for CO 2 reduction to CO product. Compared to untreated Ag foil, nanostructured Ag electrode has shown an anodic shift of approximately 200 mV in the onset potential of CO partial current density ( j CO ), 160 mV reduction of overpotential at j CO = 10 mA/cm 2 , and increased Faradaic efficiency (F.E.) for CO production especially at lower biased potentials (−0.89 to −1.19 V vs. RHE). Stability tests have demonstrated a drastic improvement in maintaining CO F.E. X-ray photoelectron spectroscopy suggests that the enhancement is associated with stable oxygen species incorporated on the nanoparticle Ag surfaces during the CV fabrication process.

Electrical communication between an enzyme and an electrode is one of the most important factors in determining the performance of biofuel cells. Here, we introduce a glucose oxidase-coated metallic cotton fiber-based hybrid biofuel cell with efficient electrical communication between the anodic enzyme and the conductive support. Gold nanoparticles are layer-by-layer assembled with small organic linkers onto cotton fibers to form metallic cotton fibers with extremely high conductivity (>2.1×104 S cm−1), and are used as an enzyme-free cathode as well as a conductive support for the enzymatic anode. For preparation of the anode, the glucose oxidase is sequentially layer-by-layer-assembled with the same linkers onto the metallic cotton fibers. The resulting biofuel cells exhibit a remarkable power density of 3.7 mW cm−2, significantly outperforming conventional biofuel cells. Our strategy to promote charge transfer through electrodes can provide an important tool to improve the performance of biofuel cells., Biofuel cells offer biocompatibility and operation at mild conditions, but application is limited by relatively low output power. Here the authors use layer-by-layer assembly for glucose oxidase-coated metallic cotton fibers for use as electrodes in a hybrid biofuel cell to achieve high output power.

For the development of wearable electronics, the replacement of rigid, metallic components with fully elastomeric materials is crucial. However, current elastomeric electrodes suffer from low electrical conductivity and poor electrical stability. Herein, a metal-like conductive elastomer with exceptional electrical performance and stability is presented, which is used to fabricate fully elastomeric electronics. The key feature of this material is its wrinkled structure, which is induced by in situ cooperation of solvent swelling and densely packed nanoparticle assembly. Specifically, layer-by-layer assembly of metal nanoparticles and small-molecule linkers on elastomers generates the hierarchical wrinkled elastomer. The elastomer demonstrates remarkable electrical conductivity (170 000 and 11 000 S cm-1 at 0% and 100% strain, respectively), outperforming previously reported elastomeric electrodes based on nanomaterials. Furthermore, a fully elastomeric triboelectric nanogenerator based on wrinkled elastomeric electrode exhibits excellent electric power generation performance due to the compressible, large contact area of the wrinkled surface during periodic contact and separation.

We present ligand-asymmetric Janus quantum dots (QDs) to improve the device performance of quantum dot light-emitting diodes (QLEDs). Specifically, we devise blue QLEDs incorporating blue QDs with asymmetrically modified ligands, in which the bottom ligand of QDs in contact with ZnO electron-transport layer serves as a robust adhesive layer and an effective electron-blocking layer and the top ligand ensures uniform deposition of organic hole transport layers with enhanced hole injection properties. Suppressed electron overflow by the bottom ligand and stimulated hole injection enabled by the top ligand contribute synergistically to boost the balance of charge injection in blue QDs and therefore the device performance of blue QLEDs. As an ultimate achievement, the blue QLED adopting ligand-asymmetric QDs displays 2-fold enhancement in peak external quantum efficiency (EQE = 3.23%) compared to the case of QDs with native ligands (oleic acid) (peak EQE = 1.49%). The present study demonstrates an integrated strategy to control over the charge injection properties into QDs via ligand engineering that enables enhancement of the device performance of blue QLEDs and thus promises successful realization of white light-emitting devices using QDs.

We introduce high-performance ultrathin supercapacitor electrodes obtained through the direct covalent-bonding layer-by-layer (LbL) assembly (or ligand-exchange LbL assembly) of amine-functionalized multiwalled carbon nanotubes (CNTs) and transition metal oxide nanoparticles (TMO NPs). The main characteristic of our approach is that the internal interfacial resistance of the electrodes can be minimized through the direct covalent-bonding adsorption of densely packed, high-quality TMO NPs onto CNTs without the aid of nonactive binders or insulating NP ligands, and the resulting volumetric capacitance and cycling stability of the electrodes can be significantly enhanced. For this study, well-defined oleic acid-stabilized pseudocapacitive metal oxide nanoparticles (i.e., OA–Fe 3 O 4 and OA–MnO NPs) prepared in toluene were densely adsorbed onto the CNT layer due to the high affinity between the surface of the TMO NPs and the NH 2 moieties of the CNTs. The (CNT/OA–Fe 3 O 4 NP) 20 multilayer electrode exhibited a high volumetric capacitance of 248±15 F cm −3 (128±7 F g −1 ) at 5 mV s −1 despite the intrinsically low specific capacitance of the Fe 3 O 4 NPs. Additionally, these film electrodes exhibited high performance stability, maintaining 99.2% of their initial capacitance after 1000 cycles. Furthermore, upon the insertion of OA–MnO NPs with high crystallinity and a high theoretical pseudocapacitance value within multilayers instead of OA–Fe 3 O 4 NPs, the formed electrodes (i.e., (CNT/OA–MnO NP) 20 multilayers) exhibited a higher volumetric capacitance of 305±10 F cm −3 (183±5 F g −1 ) (at a scan rate of 5 mV s −1 ) than other conventional ultrathin supercapacitor electrodes, including manganese oxide or iron oxide NPs.

New highly birefringent reactive liquid crystal materials based on the 2-methylhydroquinone core were designed and synthesised. Rod-type liquid crystal compounds bearing photo-crosslinkable reactive group of acryloyl, methacryloyl, cinnamoyl, furylacryloyl group were synthesised by introducing acetylene groups via Sonogashira coupling to obtain high birefringence, and lateral groups such as fluoro and methyl to adjust the temperature of the liquid crystal phase. The synthesised compounds were characterised using nuclear magnetic resonance spectroscopy, mass spectrometry and elemental analysis. In addition, their thermal behaviour was investigated using differential scanning calorimetry and polarised optical microscopy. After aligning the synthesised compounds, liquid crystal films were prepared by photo-irradiation. Photo-elastic modulator results showed that the obtained liquid crystal films had high birefringence (Δn) values of 0.32–0.40.