Phase Stability Improvement of a γ-CsPbI3 Perovskite Solar Cell Utilizing a Barium Bis(trifluoromethanesulfonimide) Solution.

The cesium lead iodide (CsPbI3) perovskite solar cell possesses a wide band gap ranging from 1.65 to 1.75 eV, which is suitable for integration into a tandem structure along with a low-band-gap silicon solar cell. Moreover, CsPbI3 has received considerable attention as a potential solution for the prevalent issues of low thermal stability of organic-inorganic perovskite solar cells and phase segregation encountered in conventional mixed halide wide-band-gap perovskite solar cells. Through the implementation of volatile additives, CsPbI3 has demonstrated substantial advancements in efficiency, process temperature, and stability. This study introduces a novel approach for barium (Ba)-doping by spraying an antisolvent containing barium bis(trifluoromethanesulfonimide) during the spin-coating process. By incorporating Ba2+ through this spraying technique, the formation of the delta phase in CsPbI3 is significantly suppressed; thereby, a power conversion efficiency of 18.56% is achieved, and a remarkable 93% of the initial efficiency is maintained after 600 h.

Color balanced transparent luminescent solar concentrator based on a polydimethylsiloxane polymer waveguide with coexisting polar and non-polar fluorescent dyes.

Color balance is a critical concept in the application of functional transparent polymers from a customer's standpoint. In this study, multiple polar and non-polar fluorescent dyes are embedded simultaneously for the first time in a polydimethylsiloxane (PDMS) polymer matrix. Five dyes successfully coexist with the optimum blending ratio. Furthermore, simultaneous dispersing of polar and non-polar dyes in the polymer is achieved. Absorption and photoluminescence characteristics of multiple fluorescent dyes in PDMS medium are systemically deconvoluted and discussed. The competitive average visible transmittance and color balance of synthesized multi-fluorescent dye embedded PDMS is demonstrated by high color rendering index and CIE color space coordinates close to the white point. Additionally, the luminescent solar concentrator device demonstrates improved power conversion efficiency and light utilization efficiency than the pure PDMS waveguide-based device. Moreover, the long-term storage stability is demonstrated successfully. The findings, therefore, demonstrate the applicability of multi-fluorescent dye embedded PDMS to advanced transparent devices.

A new variant position of head-up CPR may be associated with improvement in the measurements of cranial near-infrared spectroscopy suggestive of an increase in cerebral blood flow in non-traumatic out-of-hospital cardiac arrest patients: A prospective interventional pilot study.

AIM OF THE STUDY: This study aimed to investigate the effect of the head-up position implemented during cardiopulmonary resuscitation (CPR) on cerebral blood flow (CBF) using near-infrared spectroscopy in out-of-hospital cardiac arrest patients. METHODS: Baseline characteristics (age, sex, cerebral performance category before cardiac arrest, witnessed cardiac arrest, bystander CPR, first monitored rhythm, no-flow time, prehospital low-flow time, CPR duration in the emergency department (ED), and reason for stopping CPR in the ED) were recorded. The changes of CBF were derived from the optical oscillation waveform measured by near-infrared spectroscopy in adult patients with out-of-hospital cardiac arrest by alternating head-up and supine positions at 4-minute intervals while performing CPR. The CBF velocity according to the head position was also evaluated using the time derivative of the oscillation waveform. RESULTS: During the study period, 28 patients were enrolled. The median increase in CBF in the prefrontal area in the head-up position was 14.6% (Interquartile range, 8.8-65.0), more than that in the supine position. An increase in CBF was observed in the head-up position compared with the supine position in 83.3% of the patients included in the analysis. CONCLUSION: CBF increased when the head-up position was used during CPR in non-traumatic out-of-hospital cardiac arrest patients.

Biomechanical forces enhance directed migration and activation of bone marrow-derived dendritic cells.

Mechanical forces are pervasive in the inflammatory site where dendritic cells (DCs) are activated to migrate into draining lymph nodes. For example, fluid shear stress modulates the movement patterns of DCs, including directness and forward migration indices (FMIs), without chemokine effects. However, little is known about the effects of biomechanical forces on the activation of DCs. Accordingly, here we fabricated a microfluidics system to assess how biomechanical forces affect the migration and activity of DCs during inflammation. Based on the structure of edema, we proposed and experimentally analyzed a novel concept for a microchip model that mimicked such vascular architecture. The intensity of shear stress generated in our engineered chip was found as 0.2-0.6 dyne/cm2 by computational simulation; this value corresponded to inflammation in tissues. In this platform, the directness and FMIs of DCs were significantly increased, whereas the migration velocity of DCs was not altered by shear stress, indicating that mechanical stimuli influenced DC migration. Moreover, DCs with shear stress showed increased expression of the DC activation markers MHC class I and CD86 compared with DCs under static conditions. Taken together, these data suggest that the biomechanical forces are important to regulate the migration and activity of DCs.

Leaf-inspired homeostatic cellulose biosensors.

An incompatibility between skin homeostasis and existing biosensor interfaces inhibits long-term electrophysiological signal measurement. Inspired by the leaf homeostasis system, we developed the first homeostatic cellulose biosensor with functions of protection, sensation, self-regulation, and biosafety. Moreover, we find that a mesoporous cellulose membrane transforms into homeostatic material with properties that include high ion conductivity, excellent flexibility and stability, appropriate adhesion force, and self-healing effects when swollen in a saline solution. The proposed biosensor is found to maintain a stable skin-sensor interface through homeostasis even when challenged by various stresses, such as a dynamic environment, severe detachment, dense hair, sweat, and long-term measurement. Last, we demonstrate the high usability of our homeostatic biosensor for continuous and stable measurement of electrophysiological signals and give a showcase application in the field of brain-computer interfacing where the biosensors and machine learning together help to control real-time applications beyond the laboratory at unprecedented versatility.

Self-Aggregation-Controlled Rapid Chemical Bath Deposition of SnO2 Layers and Stable Dark Depolarization Process for Highly Efficient Planar Perovskite Solar Cells.

Planar perovskite solar cells (PSCs) incorporating n-type SnO2 have attracted significant interest because of their excellent photovoltaic performance. However, the film fabrication of SnO2 is limited by self-aggregation and inhomogeneous growth of the intermediate phase, which produces poor morphology and properties. In this study, a self-controlled SnO2 layer is fabricated directly on a fluorine-doped tin oxide (FTO) surface through simple and rapid chemical bath deposition. The PSCs based on this hydrolyzed SnO2 layer exhibit an excellent power conversion efficiency of 20.21 % with negligible hysteresis. Analysis of the electrochemical impedance spectroscopy on the charge transport dynamics indicates that the bias voltage influences both interfacial charge transportation and the ionic double layer under illumination. The hydrolyzed SnO2 -based PSCs demonstrate a faster ionic charge response time of 2.5 ms in comparison with 100.5 ms for the hydrolyzed TiO2 -based hysteretic PSCs. The results of quasi-steady-state carrier transportation indicate that a dynamic hysteresis in the J-V curves can be explained by complex ionic-electronic kinetics owing to the slow ionic charge redistribution and hole accumulation caused by electrode polarization, which causes an increase in charge recombination. This study reveals that SnO2 -based PSCs lead to a stabilized dark depolarization process compared with TiO2 -based PSCs, which is relevant to the charge transport dynamics in the high-performing planar SnO2 -based PSCs.

Changes in the Photoluminescence of Monolayer and Bilayer Molybdenum Disulfide during Laser Irradiation.

Various postsynthesis processes for transition metal dichalcogenides have been attempted to control the layer number and defect concentration, on which electrical and optical properties strongly depend. In this work, we monitored changes in the photoluminescence (PL) of molybdenum disulfide (MoS2) until laser irradiation generated defects on the sample flake and completely etched it away. Higher laser power was required to etch bilayer MoS2 compared to monolayer MoS2. When the laser power was 270 µW with a full width at half-maximum of 1.8 µm on bilayer MoS2, the change in PL intensity over time showed a double maximum during laser irradiation due to a layer-by-layer etching of the flake. When the laser power was increased to 405 µW, however, both layers of bilayer MoS2 were etched all at once, which resulted in a single maximum in the change of PL intensity over time, as in the case of monolayer MoS2. The dependence of the etching pattern for bilayer MoS2 on laser power was also reflected in position changes of both exciton and trion PL peaks. The subtle changes in the PL spectra of MoS2 as a result of laser irradiation found here are discussed in terms of PL quantum efficiency, conversion between trions and excitons, mean interatomic spacing, and the screening of Coulomb interaction.

Cellular organization of three germ layer cells on different types of noncovalent functionalized graphene substrates.

Graphene and its derivatives have seen a rapid rise in interest as promising biomaterials especially in the field of tissue engineering, regenerative medicine, and cell biology of late. Despite its proven potential in numerous biological applications, information regarding the relationship between the different forms of graphene and cell lineages is still lacking partly due to its topical emergence in cellular studies. Herein, we explore the biocompatibility of four types of graphene substrates (chemical vapor deposition grown graphene, mechanically exfoliated graphene, chemically exfoliated graphene oxide, and reduced graphene oxide) with three types of somatic cells (keratinocytes, hepatocytes, endothelial cells) derived from the three germ layers in relation to cell adhesion, proliferation, morphology, and gene expression. The results revealed exceptional cell adhesion for all tested groups but enhanced proliferation and cytoskeletal interconnectivity in graphene oxide and reduced graphene oxide substrates. We were unable to detect any adverse effects in gene expression and survivability during a week of culture. We further show topographic changes to graphene substrates under fetal bovine serum adsorption to better illustrate the actual microenvironment of inhabitant cells. This study highlights the extraordinary synergy between graphene and somatic cells, suggesting the discretionary use of extracellular matrix components for in vitro cultivation.

Abnormal elastic modulus behavior in a crystalline-amorphous core-shell nanowire system.

We investigated the elastic modulus behavior of crystalline InAs/amorphous Al2O3 core-shell heterostructured nanowires with shell thicknesses varying between 10 and 90 nm by conducting in situ tensile tests inside a transmission electron microscope (TEM). Counterintuitively, the elastic modulus behaviors of InAs/Al2O3 core-shell nanowires differ greatly from those of bulk-scale composite materials, free from size effects. According to our results, the elastic modulus of InAs/Al2O3 core-shell nanowires increases, peaking at a shell thickness of 40 nm, and then decreases in the range of 50-90 nm. This abnormal behavior is attributed to the continuous decrease in the elastic modulus of the Al2O3 shell as the thickness increases, which is caused by changes in the atomic/electronic structure during the atomic layer deposition process and the relaxation of residual stress/strain in the shell transferred from the interfacial mismatch between the core and shell materials. A novel method for estimating the elastic modulus of the shell in a heterostructured core-shell system was suggested by considering these two effects, and the predictions from the suggested method coincided well with the experimental results. We also found that the former and latter effects account for 89% and 11% of the change in the elastic modulus of the shell. This study provides new insight by showing that the size dependency, which is caused by the inhomogeneity of the atomic/electronic structure and the residual stress/strain, must be considered to evaluate the mechanical properties of heterostructured nanowires.

Highly stretchable, mechanically stable, and weavable reduced graphene oxide yarn with high NO2 sensitivity for wearable gas sensors.

Stretchable gas sensors are important components of wearable electronic devices used for human safety and healthcare applications. However, the current low stretchability and poor stability of the materials limit their use. Here, we report a highly stretchable, stable, and sensitive NO2 gas sensor composed of reduced graphene oxide (RGO) sheets and highly elastic commercial yarns. To achieve high stretchability and good stability, the RGO sensors were fabricated using a pre-strain strategy (strain-release assembly). The fabricated stretchable RGO gas sensors showed high NO2 sensitivity (55% at 5.0 ppm) under 200% strain and outstanding mechanical stability (even up to 5000 cycles at 400% applied strain), making them ideal for wearable electronic applications. In addition, our elastic graphene gas sensors can also be woven into fabrics and clothes for the creation of smart textiles. Finally, we successfully fabricated wearable gas-sensing wrist-bands from superelastic graphene yarns and stretchable knits to demonstrate a wearable electronic device.

Highly conductive and environmentally stable gold/graphene yarns for flexible and wearable electronics.

Here, we fabricated high-performance gold/graphene yarns through a facile method by the electroless deposition of gold nanoparticles onto the surface of graphene yarns. The gold/graphene yarns are fabricated using a completely solution-based process that can be scaled up for practical applications. They possess high electrical conductivity (2.86 × 102 S cm-1) and good gravimetric specific conductivity (6.81 × 102 S cm2 g-1) as well as good reliability under 1000 bending tests with a maximum bending angle of 170° and 10 washing tests with laundry detergents. These stable conducting yarns could also be integrated into textiles and clothes in various forms to create smart fabrics and wearable devices. In addition, this facile approach is easily applicable to various graphene films and devices on soft substrates that are presently used in flexible/wearable electronics.

A PbI2-xClx seed layer for obtaining efficient planar-heterojunction perovskite solar cells via an interdiffusion process.

Despite the previous reports on the fabrication of CH3NH3PbI3-xClx films via sequential deposition, the positioning and formation of PbI2 in MAPbI3-xClx perovskite films made from the seed layer containing PbI2 and PbCl2 in different ratios have not yet been addressed. In this study, the PbI2 content in a perovskite absorber layer is controlled by changing the PbCl2 ratio in a PbI2-xClx seed layer. The addition of PbCl2 in the seed layer facilitates PbI2 generation and affects the morphology of the perovskite film. By integrating a perovskite absorber via the PbI2-xClx seed-layer into a solar cell, we investigated the effects of the correlation between the chlorine and PbI2 contents on the device performance through intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy. Elemental depth profiling analyses confirm that not only was the formed PbI2 preferentially located near the metal-oxide layer, but residual chlorine was adsorbed at the TiO2 layer. Our findings demonstrate that the geometric features of the formed PbI2 affected the perovskite solar cells according to the chlorine content, likely because of the elemental gradient induced by annealing. The PbI2-xClx-derived planar-heterojunction perovskite solar cells exhibited maximum power-conversion efficiencies of 17.56% at reverse scan and 17.21% at forward scan, suppressed current density-voltage hysteresis, and good performance distributions.

Ultrasensitive and highly selective graphene-based single yarn for use in wearable gas sensor.

Electric components based on fibers or textiles have been investigated owing to their potential applications in wearable devices. High performance on response to gas, drape-ability and washing durability are of important for gas sensors based on fiber substrates. In this report, we demonstrate the bendable and washable electronic textile (e-textile) gas sensors composed of reduced graphene oxides (RGOs) using commercially available yarn and molecular glue through an electrostatic self-assembly. The e-textile gas sensor possesses chemical durability to several detergent washing treatments and mechanical stability under 1,000 bending tests at an extreme bending radius of 1 mm as well as a high response to NO2 gas at room temperature with selectivity to other gases such as acetone, ethanol, ethylene, and CO2.

A 3D scaffold for ultra-sensitive reduced graphene oxide gas sensors.

An ultra-sensitive gas sensor based on a reduced graphene oxide nanofiber mat was successfully fabricated using a combination of an electrospinning method and graphene oxide wrapping through an electrostatic self-assembly, followed by a low-temperature chemical reduction. The sensor showed excellent sensitivity to NO2 gas.

Preparation and characterization of graphene oxide encapsulated gold nanoparticles.

We present a simple approach for the fabrication of graphene oxide-encapsulated gold nanoparticles using graphene oxide sheet-wrapping via electrostatic self-assembly. By mixing bovine serum albumin molecule-functionalized gold nanoparticles with graphene oxide dispersion, positively charged bovine serum albumin/gold nanoparticles easily assembled with negatively charged graphene oxide sheets through electrostatic interaction. Transmittance electron microscopy, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy were used to confirm the encapsulation of graphene oxide on gold nanoparticles. Interestingly, graphene oxide sheets wrapping mainly occurs along the main body of single or a few gold nanoparticles. Additionally, by measuring the ultraviolet-visible spectroscopy spectrum, we found that the surface plasmon resonances band of the graphene oxide-encapsulated gold nanoparticles was found to become red-shifted compared to that of pristine gold nanoparticles, whereas similar to that of bovine serum albumin-coated gold nanoparticles. These results indicating that most of graphene oxide-encapsulated gold nanoparticles have good monodispersity and spherical shape. These resulting materials may potentially serve as a platform for plasmon resonance electron transfer spectroscopy or a probe for low level biosensing.

A novel method for applying reduced graphene oxide directly to electronic textiles from yarns to fabrics.

Conductive, flexible, and durable reduced RGO textiles with a facile preparation method are presented. BSA proteins serve as universal adhesives for improving the adsorption of GO onto any textile, irrespective of the materials and the surface conditions. Using this method, we successfully prepared various RGO textiles based on nylon-6 yarns, cotton yarns, polyester yarns, and nonwoven fabrics.

Fabrication of Ag nanoparticles embedded in TiO2 nanotubes: using electrospun nanofibers for controlling plasmonic effects.

Composites of electrospun poly(ethylene oxide) (PEO) fibers and silver nanoparticles (Ag NPs) were used as a soft template for coating with TiO2 by atomic layer deposition (ALD). Whereas the as-deposited TiO2 layers on PEO fibers and Ag NPs were completely amorphous, the TiO2 layers were transformed into polycrystalline TiO2 nanotubes (NTs) with embedded Ag NPs after calcination. Their plasmonic effect can be controlled by varying the thickness of the dielectric Al2 O3 spacer between Ag NPs and dye molecules by means of the ALD process. Electronic and spectroscopic analyses demonstrated enhanced photocurrent generation and solar-cell performance due to the intense electromagnetic field of the dye resulting from the surface plasmon effect of the Ag NPs.

Production of large-scale, freestanding vanadium pentoxide nanobelt porous structures.

Large-scale, freestanding, porous structures of vanadium pentoxide nanobelts (VPNs) were successfully prepared using the template-free freeze-drying method. The porous and multi-layered VPN macrostructures are composed of randomly oriented long nanobelts (over 100 µm) and their side length can be controlled up to a few tens of centimetres. Also, the bulk density and surface area of these macrostructures are 3-5 mg cm(-3) and 40-80 m(2) g(-1), respectively, which are similar to those of the excellent adsorbents. In addition, the removal efficiency measurements of ammonia molecules revealed that the VPN porous structures can adsorb the ammonia molecules with the combinations of van der Waals forces and strong chemical bonding by functional groups on the VPN surface.

Electrical quadruple hysteresis in Pd-doped vanadium pentoxide nanowires due to water adsorption.

Humidity-dependent current-voltage (I-V) characteristics of Pd-doped vanadium pentoxide nanowires (Pd-VONs) were investigated. Electrical quadruple hysteresis (QH) was observed and attributed to the large amount of water molecules adsorbed on the nanowires. Using QH in Pd-VONs, the reaction of water with PdO was interpreted as the water molecules are desorbed and then dissociated with increasing bias voltage. Owing to the dissociated H+ and OH- ions, PdO is reduced and oxidized. As a result, water molecules recombine as the bias voltage is decreased.

Formation of (111)-oriented nickel nanocrystals by thermal annealing of nickel thin films.

We have produced Ni nanocrystals with face centered cubic structure by thermally annealing Ni films deposited on SiO2-covered Si(001) substrates in a flow of mixed hydrogen and argon gas. Ni films thicker than 5 nm self-assemble into highly (111)-oriented Ni nanocrystals on a flat and continuous SiO2 interlayer during the thermal annealing, while Ni films of 5 nm thickness aggregate to the irregularly shaped nanoparticles. The lateral width of the nanocrystals ranges from tens of nanometers to hundreds of nanometers, and the crystal height is under 100 nm. The nanocrystals have wide (111) top facets of hexagonal shape and narrow (100) sidewalls of truncated pyramidal shape, as a result of each crystal minimizing its total surface energy. Our results demonstrate that the formation of nanocrystals during thermal annealing is strongly affected by the morphology of the SiO2 interlayer, the Ni film thickness, the annealing temperature, and the partial pressure of hydrogen gas.