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An electronic synapse (e-synapse) based on memristive switching is a promising electronic element that emulates a biological synapse to realize neuromorphic computing. However, the complex resistive switching process it relies on hampers the reproducibility of its performance. Thus, achievement of a reproducible electronic synapse with a high rate of finished products has become a significant challenge in the development of an artificial intelligent circuit. Here, we demonstrate an ultrathin e-synapse having high yield (>95%), minimal performance variation, and extremely low power consumption based on an Al2O3/graphene quantum dots/Al2O3 sandwich structure that was fabricated using atomic layer deposition. The e-synapse showed both high device-to-device and cycle-to-cycle reproducibility with high stability, endurance, and switching uniformity, because the essential synaptic behaviors could be observed. This implementation of an e-synapse with an Al2O3/graphene quantum dots/Al2O3 structure should intensify motivation for engineering e-synapses for neuromorphic computing. Circuits that emulate the actions of biological synapses can be fabricated from devices known as quantum tunnel junctions. Fushan Li from China’s Fuzhou University, Tae Whan Kim from Korea’s Hanyang University, and colleagues produced an ‘e-synapse’ where a thin insulating film prevents electrons from moving through a circuit, except for a small number that jump across the barrier through quantum tunneling. When the researchers embedded graphene quantum dots in the film, they found that these nanoparticles switched the device between low and high resistance states by either trapping or releasing tunneling electrons. This allows the circuit to mimic certain functions of the brain; the gradual accumulation of electrons and their spontaneous release, for example, occurred on timeframes similar as seen in short-term memory loss. The team’s manufacturing scheme yielded devices with high stability and reproducibility. This article demonstrates an ultrathin e-synapse having high yield, minimal performance variation, and extremely low power consumption based on a Al2O3/graphene quantum dots/Al2O3 sandwich structure that was fabricated by using atomic layer deposition. It showed both high device-to-device and cycle-to-cycle reproducibility with high stability, endurance, and switching uniformity, because of which the essential synaptic behaviors could be observed. This implementation of an e-synapse with an Al2O3/graphene quantum dots/Al2O3 structure should intensify motivation for engineering e-synapses for neuromorphic computing.

Harvesting walking energy to generate sustainable power is critical for the development of portable and wearable electronics. Here, we demonstrate that by ingeniously taking advantage of natural triboelectrification and static charges on the human body, electric energy can be generated from our walking without the use of a specially designed shoe/sole or triboelectric nanogenerator (TENG). The triboelectric system is composed of only Al electrodes, which makes it compatible with wearables due to its lightweight and flexibility. The electricity generated from every step during walking is sufficient to light up 100 commercial light-emitting diodes (LEDs) instantaneously. Furthermore, the simple system can act as a self-powered active sensor for monitoring our gait during walking, our health, and security. The triboelectric system is ultra-simple, lightweight, eco-friendly, and low-cost, which gives it potential for application in attachable electronics as a sustainable power source and a self-powered sensor.

Atomic force microscopy images showed that layers with a ZnO nanostructure were regularly formed on polyethylene naphthalate (PEN) substrates coated with indium tin oxide. The output voltage of triboelectric nanogenerators (TENGs) containing layers with the ZnO nanostructure and operating in the vertical contact-separation mode was approximately 20 V, which indicated that the power was enhanced by a factor of 2 compared to that of the TENG without such layers. Bending endurance tests on the TENGs demonstrated high stability under the stress caused by bending at an angle of 90°. The average open-circuit voltage of the TENGs operating in the ambient atmosphere was reduced by only 22% after 2000 bendings. This endurance of the TENGs under bending in air could be attributed to the presence of the layers with the ZnO nanostructure.

Large-size, organic light-emitting device (OLED) panels based on highly reliable gate driver circuits integrated using InGaZnO thin-film transistors (TFTs) were fabricated to achieve ultra-high image density (UHD). These large-size OLED panels were driven by using a novel gate driver circuit not only for displaying images but also for sensing TFT characteristics for external compensation. Regardless of the negative threshold voltage of the TFTs, the proposed gate driver circuit in OLED panels functioned precisely, resulting from a decrease in the leakage current. The falling time of the circuit is approximately $1.6~{{\mu }}\text{s}$ , which is fast enough to drive UHD OLED displays at 120 Hz. 120 Hz is most commonly used as the operating voltage because images consisting of 12 frames per second can be quickly shown on the display panel without any image sticking. The reliability tests showed that the lifetime of the proposed integrated gate driver is at least $1 \times 10^{5}$ h.

This paper reports a facile, cost effective method that uses an aqueous hydrothermal process for synthesizing two-dimensional molybdenum disulphide (MoS2) monolayer quantum dots (QDs) and their potential applications in flexible memristive devices. High-resolution transmission electron microscopy and atomic force microscopy images confirmed that the diameters of the synthesized MoS2 QDs with irregular shapes were in the range between 3 and 6 nm; their thicknesses were confirmed to lie between 1.0 and 0.8 nm, a clear indication that a monolayer of MoS2 QDs had been synthesized. Photoluminescence (PL) and time-resolved PL spectra of the MoS2 QDs revealed a strong emission in the blue region with a slower decay constant. Memristive devices fabricated by incorporating MoS2 QDs between poly(methylsilsesquioxane) ultrathin layers, which had been deposited on poly(ethylene terephthalate), demonstrated a high ON–OFF current ratio of ∼104, stable retention, and excellent endurance in the relaxed state; these devices were also demonstrated to function properly during bending and in a bent state. The flexible memristive devices demonstrated an OFF state with a very low current of 10−6 A. These results clearly show that ultrathin two-dimensional QDs have promising applications in high-performance flexible memristive devices.

The purpose of this study is to compare and analyze the kinematic characteristics of the upper limb segments during the archery shooting of Paralympic Wheelchair Class archers (ARW2—second wheelchair class—paraplegia or comparable disability) and Paralympic Standing Class archers (ARST—standing archery class—loss of 25 points in the upper limbs or lower limbs), where archers are classified according to their disability grade among elite disabled archers. The participants of this study were selected as seven elite athletes with disabilities by the ARW2 (n = 4) and ARST (n = 3). The analysis variables were (1) the time required for each phase, (2) the angle of inclination of the body center, (3) the change of trajectory of body center, and (4) the change of the movement trajectory of the bow center by phase when performing six shots in total. The ARW2 group (drawing phase, M = 2.228 s, p &lt, 0.05, holding phase, M = 4.414 s, p &lt, 0.05) showed a longer time than the ARST group (drawing phase, M = 0.985 s, holding phase, M = 3.042 s), and the angle of the body did not show a significant difference between the two groups. Additionally, in the direction of the anteroposterior axis in the drawing phase, the change in the movement trajectory of the body center showed a more significant amount of change in the ARW2 group than in the ARST group, and the change in the movement trajectory of the bow center did not show a significant difference between the two groups.

The development of artificial skin, such as electronic skin, is critical to emerging artificial intelligence systems. Electronic skins reported to date are mechanically flexible, and can detect various stimuli, but lack the ability to regulate themselves and learn information from the outside world. The integration of bio-inspired multifunction in a single electronic platform is critical to the development of e-skin systems. Here, we demonstrate a self-powered, light-stimulated, smart e-skin based on a photosensitive perovskite material. The electronic skin implements the functions of both tactile sensing and photoelectric neural computing. The strategy for developing such a material system and architecture of the electronic skin meets the requirement of multifunctional smart human-machine interfaces and has promising potential for application in future artificial intelligence systems.

A novel nanocomposite-based non-volatile resistance switching random access memory device introducing single-walled carbon nanotube (SWCNT)@TiO2 core–shell wires was proposed for flexible electronics. The SWCNT was de-bundled by ultrasonication with sodium dodecylbenzene sulfonate (SDBS), and then the TiO2 skin layer on the SWCNT surface was successfully introduced by adding benzyl alcohol as a weak surfactant. The nanocomposite resistance switching layer was composed of the SWCNT@TiO2 core–shell wires and poly(vinyl alcohol) (PVA) matrix by a simple spin-coating method. The device exhibited reproducible resistance switching performance with a remarkably narrow distribution of operating parameters (VSET and VRESET were 2.63 ± 0.16 and 0.95 ± 0.11 V, respectively) with a large RON/ROFF ratio of 105 for 200 consecutive switching cycles. Furthermore, the excellent resistance switching behavior in our device was maintained against mechanical stress up to 105 bending test. We believe that the nanocomposite memory device with SWCNT@TiO2 core–shell wires would be a critical asset to realize practical application for a flexible non-volatile memory field.

Biosynaptic devices based on chicken egg albumen (CEA):graphene quantum dot (GQD) hybrid nanocomposites were fabricated to achieve stable synaptic behaviors. Current-voltage (I-V) curves for the biosynaptic devices under consecutive negative and positive voltage sweeps showed clockwise pinched hysteresis, which is a critical feature of a biological synapse. The effect of the GQD concentration in the CEA layer on the device performance was studied. The retention time of the biosynaptic devices was relatively constant, maintaining a value above 104 s under ambient conditions. The carrier transport mechanisms of the biosynaptic devices were described and analyzed on the basis of the slopes of the I-V curves and their fittings.

Perovskite materials have been utilized as promising active materials for memristive devices due to their excellent properties. However, most reported perovskite-based memristive devices exhibit relatively low current ON/OFF ratios, which limits their practical applications in memory devices. In this work, memristive devices with a large memory margin were fabricated utilizing a CH3NH3PbBr3 (MAPbBr3) perovskite layer. The nanocrystalline MAPbBr3 perovskite thin films were successfully formed at low temperature by using a chlorobenzene dripping method. The MAPbBr3 perovskite layer was employed as a resistive switching layer in memristive devices with a structure of indium-tin-oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/MAPbBr3/Al. The maximum ON/OFF ratio of the memristive devices based on the MAPbBr3 perovskite was as large as 3.6ｘ106. The memristive devices showed high device-to-device reproducibility with set-voltage distributions between −0.5 and −0.8 V, as well as good endurances of at least 120 cycles and retention times longer than 1ｘ104 s. The carrier transport mechanisms of the memristive devices were described on the basis of the I-V curves, and their operating mechanisms were explained via the formation and rupture of filaments in the MAPbBr3 perovskite.

We present a highly sensitive and selective NO2 sensor based on Bi2O3 branched SnO2 nanowires (NWs). SnO2 NWs were first synthesized by a vapor-liquid-solid method, were coated with an Au layer, and Bi2O3 branches were grown on their stems by the same procedure used for pure Bi powders. The fabricated sensor showed a high response (Rg/Ra) of 56.92 to 2 ppm of NO2 gas at an optimal temperature. Furthermore, its response to other interfering gases such as ethanol, acetone, toluene, and benzene, was less than 1.55, which demonstrated excellent selectivity of the sensor towards NO2 gas. For comparison and to better understand the sensing mechanism, a pristine SnO2 NWs sensor was also tested. The superior sensing properties of the branched NW sensor relative to the pristine sensor were mainly attributed to the high surface area of the sensor resulting from Bi2O3 branching, as well as the formation of homo-and heterojunctions (Bi2O3-SnO2). In addition, several factors including the presence of Au contributed to the excellent selectivity to NO2 gas. Based on the results obtained in this work, we believe that the present sensor with an easy fabrication method, along with its high sensitivity and selectivity towards NO2, can be used for the detection of NO2 gas in real applications.

The technology of triboelectric nanogenerators (TENGs) has made great progress as a promising approach to generating electricity from ambient vibration energy. However, finding a way to generate enough electrical output efficiently from vibrations with a broadband of amplitudes is crucial when the relatively low current output of existing TENGs and the existence of natural vibrations with diverse amplitudes are considered. In this work, a freestanding and lightweight triboelectric nanogenerator with a capsule structure (namely, a capsule TENG) is demonstrated with an aim toward optional 3D integration and the efficient harvesting of energy from vibrations with a broadband of amplitudes. The capsule TENGs can be easily integrated to form 1D, 2D, and 3D structures to realize high electrical output. Under ideal conditions, the total output power of an integrated capsule-TENG pack can be approximately estimated as p × n2, where p is the peak output power per capsule TENG and n is the number of capsule TENGs. When capsule TENGs with hybrid structures, such as different lengths of the capsule tube and different numbers of paired electrodes, are assembled, energy can be more efficiently harvested from vibrations with a broadband of amplitudes. A total of three parameters (the active area-to-volume ratio, the power-to-volume ratio, and the power-to-weight ratio), which are important parameters for 3D-integrated TENGs, are proposed. The results of this research show that capsule TENGs are versatile devices that can potentially be used for the efficient harvesting of ambient vibration energy.

This paper presents the analytical electric potentials of vertical flash memory with a macaroni structure derived by solving a one-dimensional Pöisson equation for vertical flash memory. The solution provides the cross-sectional electric potentials between the surface and the inner oxide layer of the polysilicon channel in flash memory. The band bending and the charge density were obtained on the basis of the electric potential of the device, which is an important factor in flash memory operation. Additional parameters for the electric potentials in flash memory with a macaroni structure are described.

The development of portable power banks by using triboelectric nanogenerator-based technology has been a subject of great interest. However, when the potential wide range of future applications of such devices is considered, their heavy use of nanomaterials, polymers, and micro/nano fabrication technologies will increase the cost of and the energy consumed during production; moreover, their improper disposal may harm the environment. Here, we demonstrate portable card-type triboelectric nanogenerators (Card-TENGs) assembled by using less problematic, readily available materials through a top-down approach. The Card-TENGs are fabricated mainly from paper, including card paper and printer paper, which can greatly reduce the fabrication cost and the risk to the environment. Electricity can be generated simply by shaking the Card-TENGs, and Card-TENGs can be combined to form single and multilayer structures, which will enhance their electrical output. Furthermore, the as-fabricated Card-TENGs can be easily integrated into packs to increase the total output for lighting LEDs arrays and powering calculators.

One diode and one resistor (1D–1R) memristive devices based on inorganic Schottky diodes and poly(methylsilsesquioxane) (PMSSQ):graphene quantum dot (GQD) hybrid nanocomposites were fabricated to achieve stable memory characteristics. Current-voltage (I-V) curves for the Al/PMSSQ:GQDs/Al/p-Si/Al devices at room temperature exhibited write-once, read-many-times memory (WORM) characteristics with an ON/OFF ratio of as large as 104 resulting from the formation of a 1D–1R structure. I-V characteristics of the WORM 1D–1R device demonstrated that the memory and the diode behaviors of the 1D–1R device functioned simultaneously. The retention time of the WORM 1D–1R devices could be maintained at a value larger than 104 s under ambient conditions. The operating mechanisms of the devices were analyzed on the basis of the I–V results and with the aid of the energy band diagram.

Flexible memristive devices with a structure of Al/polyimide:mica/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate/indium-tin-oxide/polyethylene glycol naphthalate showed electrical bistability characteristics. The maximum current margin of the devices with mica nanosheets was much larger than that of the devices without mica nanosheets. For these devices, the current vs. time curves showed nonvolatile characteristics with a retention time of more than 1 × 104 s, and the current vs. number-of-cycles curves demonstrated an endurance for high resistance state/low resistance state switchings of 1 × 102 cycles. As to the operation performance, the “reset” voltage was distributed between 2.5 and 3 V, and the “set” voltage was distributed between −0.7 and −0.5 V, indicative of high uniformity. The electrical characteristics of the devices after full bendings with various radii of curvature were similar to those before bending, which was indicative of devices having ultra-flexibility. The carrier transport and the operation mechanisms of the devices were explained based on the current vs. voltage curves and the energy band diagrams.

Triboelectric nanogenerators (TENGs) based on solution-processed zinc-oxide (ZnO) nanoripples acting as a triboelectric layer were fabricated to enhance their output voltage. Scanning electron microscopy images showed that ZnO nanoripples were uniformly formed on glass substrates coated with indium-tin oxide. The TENG containing ZnO nanoripples and operating in the vertical contact-separation mode exhibited an output voltage of 68 V, which was almost 3 times larger than that of the TENGs with ZnO nanorods. The open-circuit output voltages of TENGs were found to depend significantly on the condition of the ZnO nanoripple precursors. The friction force on the ZnO nanoripple matrix increased with increasing density of ZnO nanoripples due to an increase in the contact area between the ZnO nanoripples and the PI layer, resulting in an enhancement of the output voltage of the TENGs based on nanoripples.

The development of electronic-skin (e-skin) with artificial tactile-perception is crucial for emerging artificial-intelligence systems. However, considering the relatively simple function of existing e-skins, their performances still have much room for improvement. Here, a cuttable, transparent, stretchable, and lightweight e-skin that functions on the basis of the triboelectric effect is demonstrated. Well-designed micro-gaps are introduced to make the e-skin respond sensitively to various mechanical stimulations, including pressing, stretching, folding, and twisting. Ag nanowires coated with graphene quantum dots are employed as the electrode, as well as the friction layer, to increase the sensitivity to external mechanical stimulations. Self-powered, smart, artificial fingers with tactile sensation to monitor the actions of the fingers were fabricated to demonstrate the potential application of our newly developed e-skin. The architecture and the material system of the device demonstrated in this work will promote the development of human-machine interfaces and intelligent machines.

Triboelectric nanogenerator (TENG) as a powerful mechanical energy harvesting technology has major applications as micro/nano-power source, for self-powered sensors and even large-scale blue energy, which would impact the world likely development for the future. In this work, a theoretical model for the sliding-mode TENG with considering the external force applied onto the TENG was presented. Through approximate analytical equations derivation, the output characteristics of TENG with arbitrary load resistance were calculated, including the output power and energy. Based on the relationships between the output characteristics and load resistance or sliding velocity, the force applied on the sliding component of TENG and the friction force were investigated for two cases, i.e., without load resistor and with load resistor. Also, the influences of the resistance and sliding velocity on the forces were investigated. Furthermore, the corresponding experiments were carried out to measure the force applied on the TENG as well as the output performance of the fabricated sliding-mode TENG. The experimental results are in good agreement with the theoretical predictions, which can effectively reveal the principle of applied force on the TENG and facilitate the understanding of the relationship between the power, energy and applied force.

The electrical characteristics of flexible memristive devices utilizing a graphene oxide (GO):polyvinylpyrrolidone (PVP) nanocomposite charge-trapping layer with a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)-modified layer fabricated on an indium-tin-oxide (ITO)-coated polyethylene glycol naphthalate (PEN) substrate were investigated. Current-voltage (I-V) curves for the Al/GO:PVP/PEDOT:PSS/ITO/PEN devices showed remarkable hysteresis behaviors before and after bending. The maximum memory margins of the devices before and after 100 bending cycles were approximately 7.69 × 103 and 5.16 × 102, respectively. The devices showed nonvolatile memory effect with a retention time of more than 1 × 104 s. The “Reset” voltages were distributed between 2.3 and 3.5 V, and the “Set” voltages were dispersed between −0.7 and −0.2 V, indicative of excellent, uniform electrical performance. The endurance number of ON/OFF-switching and bending cycles for the devices was 1 × 102, respectively. The bipolar resistive switching behavior was explained on the basis of I-V results. In particular, the bipolar resistive switching behaviors of the LRS and the HRS for the devices are dominated by the Ohmic and space charge current mechanisms, respectively.

Organic light-emitting devices (OLEDs) with a poly(N,N′-bis-4-butylphenyl-N,N′-bisphenyl)benzidine (poly-TPD):octadecylamine (ODA)-graphene quantum dots (GQDs) hole transport layer (HTL) were fabricated to enhance their efficiency. Photoluminescence (PL) and PL excitation spectra showed that the optical energy bandgap of the ODA-GQDs was 2.7 eV, and ultraviolet photoelectron spectroscopy spectra demonstrated that the edge of the highest occupied molecular orbital of the ODA-GQDs was 5.3 eV below the Fermi level. While the operating voltage of the OLEDs with a PVK:ODA-GQD (9.77 V, 0.25 wt%) HTL at 10 mA/cm2 was 0.8 V lower than that of the OLEDs with a poly-TPD HTL (10.57 V), their current efficiency was larger by more than 20% than that of the OLEDs with poly-TPD (32.88 cd/A) due to an increase in the number of holes injected from the ITO to the HTL. The number of injected holes was increased due to a reduction of the energy barrier and an increase in the conductivity.

Memristive devices based on cesium-lead-chlorine (CsPbCl3) perovskite quantum dots (PQDs) embedded in a poly(methyl methacrylate) (PMMA) layer were fabricated to enhance their memory stability. Current-voltage (I-V) measurements on Al/PQDs embedded in PMMA layer/indium-tin-oxide devices at 300 K showed nonvolatile rewritable memristive behaviors. The maximum ON/OFF ratio of the current bistability for the devices was as large as 2 × 104. The retention time for the devices was above 1 × 104 s, indicative of high stability of the device. The operating mechanisms of the devices related to the interaction between the PQDs and the PMMA matrix could be explained by adjusting the thickness of the active layer. Furthermore, the carrier transport mechanisms of the devices are described on the basis of the I-V results with the aid of the energy-band diagram. The carrier transport could be attributed to the space-charge-limited-current mechanism in the high resistance state and to Ohmic conduction in the low resistance state.

The effects of the ZnS shell layer on the memory performances of flexible memristive devices based on quantum dots (QDs) with an InP/ZnSe/ZnS core–multishell structure embedded in a poly(methylmethacrylate) layer were investigated. The on/off ratios of the devices based on QDs with an InP/ZnSe core–shell structure and with an InP/ZnSe/ZnS core–multishell structure were approximately 4.2 × 102 and 8.5 × 103, respectively, indicative of enhanced charge storage capability in the latter. After bending, the memory characteristics of the memristive devices based on QDs with the InP/ZnSe/ZnS structure were similar to those before bending. In addition, those devices maintained the same on/off ratios for retention time of 1 × 104 s, and the number of endurance cycles was above 1 × 102. The reset voltages ranged from −2.3 to −3.1 V, and the set voltages ranged from 1.3 to 2.1 V, indicative of reliable electrical characteristics. Furthermore, the possible operating mechanisms of the devices are presented on the basi...

Transparent and flexible photodetectors (PDs) based on CH3NH3PbI3 perovskite nanoparticles (NPs) were fabricated by using co-evaporation of methyl ammonium iodide and lead iodide. X-ray diffraction patterns and high-resolution transmission electron microscopy images demonstrated the formation of perovskite NPs. The optical transmittance of the perovskite NPs/glass was above 80% over the entire range of visible wavelengths, indicative of high transparency. The PDs based on CH3NH3PbI3 perovskite NPs were sensitive to a broad range of visible light from 450 to 650 nm. The currents in the PDs under exposure to red, green, and blue light-emitting diodes were enhanced to 5, 10, and 20 times that of the PD in the dark, respectively. The rise and the decay times of the PDs were 50 and 120 μs. The current in the perovskite NP PD on a polyethylene terephthalate substrate was enhanced by approximately 69% when the NP PD was exposed to a blue LED emitting at a wavelength of 459 nm. Despite multiple bending, the transparent and flexible PDs based on methyl ammonium iodide and lead iodide NPs showed reproducibility and high stability in performance.

Organic bistable devices (OBDs) with exfoliated mica nanoparticles (NPs) embedded into an insulating poly(methylmethacrylate) (PMMA) layer were fabricated by using a spin-coating method. Current–voltage (I–V) curves for the Al/PMMA/exfoliated mica NP/PMMA/indium-tin-oxide/glass devices at 300 K showed a clockwise current hysteresis behavior due to the existence of the exfoliated muscovite-type mica NPs, which is an essential feature for bistable devices. Write-read-erase-read data showed that the OBDs had rewritable nonvolatile memories and an endurance number of ON/OFF switching for the OBDs of 102 cycles. An ON/OFF ratio of 1 × 103 was maintained for retention times larger than 1 × 104 s. The memory mechanisms of the fabricated OBDs were described by using the trapping and the tunneling processes within a PMMA active layer containing exfoliated muscovite-type mica NPs on the basis of the energy band diagram and the I–V curves.

The current-voltage results for nonvolatile memristive devices based on hexagonal boron-nitride nanosheets:polymethyl methacrylate nanocomposites exhibit the characteristics of write-once-read-many-times in the voltage range from −3 to 3 V. The electrical characteristics remain unchanged even the devices are under highly bended states. After the devices had finished the “writing” process, they could be read more than 500 times under both flat and bending conditions. Both the high and the low resistance states could be maintained at almost constant levels for more than 1.5 × 104 s, and the ON/OFF ratio of the devices remained about 103. After more than 2 × 103 bendings, the electrical properties of the devices remained almost the same.

The ability to combine the color-tunability capability of natural organisms with a memory function in a single device is highly desired and holds promise for potential applications such as intelligent artificial skin and human-machine interfaces. In this work, we propose a universal strategy to realize color-tunable skin with the compound function of memory by ingeniously integrating a memristor interface into a flexible quantum-dot light-emitting device. The devices developed using this strategy have multiple responses to electrical and light stimulations and can easily change their color over a wide range from red to green. Moreover, these color-tunable devices can mimic the unique function of “once bitten, twice shy” to enhance self-protection, and their color tunability is consistent with the memory-forgetting curve proposed by psychologists.

The purpose of this study was to develop and apply a team building program for a curling team through needs assessment. The participants in this study were 69 high-school, college, professional, and national curling athletes for the needs assessment, 4 sport psychologists and 2 curling experts for verifying the validity of the program, and 5 curling athletes of professional curling teams for the application of the team building program. The needs assessment data were analyzed by inductive content analysis. The team building program was developed based on the results of needs assessment, goal setting of the team building program, and a selection of activities for the team building program. The team building program was applied to five curling players for 7 sessions. Team cohesion, team efficacy, and effective communication were measured two times (i.e., pre and post) to examine the effects of team building intervention. The results of needs assessment indicated interpersonal relationship, communication, and performance were necessary factors for team building. Consequently, goals of the team building program were to improve communication and interpersonal relationships. Team building activities were selected through team building literature review and expert meetings. Secondly, the team building intervention had a positive influence on team cohesion, team efficacy, and communication. These results indicated that team building would positively contribute to team factors and team performance.

The properties of nonvolatile memristive devices (NMD) fabricated utilizing organic/inorganic hybrid nanocomposites were investigated due to their superior advantages such as mechanical flexibility, low cost, low-power consumption, simple technological process in fabrication and high reproducibility. The current-voltage (I-V) curves for the Al/polyvinylpyrrolidone (PVP): graphene quantum-dot (GQD)/indium-tin-oxide (ITO) memristive devices showed current bistability characteristics at 300 K. The window margins corresponding to the high-conductivity (ON) state and the low-conductivity (OFF) state of the devices increased with increasing concentration of the GQDs. The ON/OFF ratio of the optimized device was 1 × 104, which was the largest memory margin among the devices fabricated in this research. The endurance number of ON/OFF switching was above 1 × 102 cycles, and the retention time was relatively constant, maintaining a value above 104 s. The devices showed high reproducibility with the writing voltage being distributed between −0.5 and −1.5 V and the erasing voltage being distributed between 2 and 3 V. The ON state currents remained between 0.02 and 0.03 A, and the OFF state currents stayed between 10−6 and 10−4 A. The carrier transport mechanisms are illustrated by using both the results obtained by fitting the I-V curves and the energy band diagrams of the devices.

Composite-based memristive devices have attracted tremendous attention as promising applications in futuristic information technologies due to their synergetic effects between the solid filler and the polymer matrix for enabling versatile information processing. Here, we demonstrate the digital data storing and the analog data processing capabilities of artificial synapses consisting of zeolitic imidazolate framework-8 (ZIF 8):polyvinylpyrrolidone (PVP) hybrid nanocomposites. The composite-based devices exhibited excellent resistive switching behaviors with reliable operating voltage (1.24 ± 0.12 and −2.75 ± 0.33 V) and a large RON/ROFF ratio (7.8 × 103) for 500 repeated resistance switching cycles. The fundamental synaptic behaviors in neuromorphic systems, such as potentiation/depression, transitions from short-term to long-term memory, and the biological learning rules of spiking time-dependent plasticity, were imitated. Finally, via structural and theoretical analyses, we demonstrated that the excellent memristive behaviors were due to the ion trapping effect of the ZIF-8 nanoparticles in the ZIF-8:PVP hybrid composite film.

Wearable displays that can be applied to smart clothing systems are attracting attention as a core technology in terms of the communication between machines and humans. However, currently available displays still lack durability under random deformations of clothes. Here, we report a self-healable organic light-emitting devices (OLEDs) for smart clothing system, which can recover from the various physical deformations of clothing. The reduced luminance of damaged OLEDs can be recovered again, and the structure variation caused by repetitive motions of the OLEDs can be restored to the original shape. In addition, the operating voltage of the self-healable OLEDs is 2.9 V, which is the lowest among those reported for light-emitting devices with self-healing materials. The electroluminescence intensity at 514 nm of a damaged OLEDs is only about 14.2% of its initial value due to the formations of leakage currents around internal and external cracks. However, the electroluminescence intensity at 514 nm of a damaged device recovers to 95.3% of its initial value due to the self-healing property of the polyvinyl alcohol:Agar nanocomposite and the shape-memory property of the cross-linked polyurethane. Furthermore, we demonstrate that our newly developed self-healable OLEDs represents a new core technology for future smart clothing systems because it can self-recover from damage.

Repetitious mechanical stress or external mechanical impact can damage wearable electronic devices, leading to serious degradations in their electrical performances, which limits their applications. Because self-healing would be an excellent solution to the above-mentioned issue, this paper presents a self-healable memory device based on a novel nanocomposite layer consisting of a polyvinyl alcohol matrix and imidazole-modified graphene quantum dots. The device exhibits reliable electrical performance over 600 cycles, and the electrical properties of the device are maintained without any failure under this bending stress. Further, it is confirmed that the damaged device can recover its original electric characteristics after the self-healing process. It is believed that such outstanding results will lead the way to the realization of future wearable electronic systems.

Mimicking synaptic plasticity is a key to harnessing the power of the brain. In the present work, manganese oxide (MnO2) thin films were developed by using the simple, low-cost hydrothermal method, and the hydrothermal deposition-time-dependent resistive switching property of MnO2 thin films was investigated. The current-voltage and the charge-magnetic flux characteristics suggested that the developed devices could be placed into the category of memristive devices. The bio-synaptic properties, such as synaptic weight, potentiation depression, and symmetric Hebbian learning of these devices were demonstrated. The developed devices were able to switch between two distinctly separable resistance states and to retain the resistive switching states for 103 s without any significant degradation. In addition, their non-zero current-voltage crossing property suggests that parasitic meminductance coexists with memristive behavior. For these devices, Schottky conduction mechanisms were found to be responsible for the resistive switching effect. The results of the present investigation should be very useful for neuromorphic computing applications.

CsPbBr3 quantum dots (QDs)-NOA63 nanocomposites (NCs) are fabricated by using a UV-initiated thiol−ene “click” reaction, and the hydrophobic CsPbBr3 QDs are successfully embedded in the NOA63 matrix without chemical decomposition. The CsPbBr3 QDs-NOA63 NCs are utilized as a piezoelectric layer for piezoelectric nanogenerators (PENGs), which are compared with PENGs based on NOA63 and on CsPbBr3 QDs. The average output voltages of the PENGs based on the CsPbBr3 QDs-NOA63 NCs is significantly larger than that of the PENGs with CsPbBr3 QDs alone by a factor of 5.55. The significantly higher output voltages of the PENGs based on the CsPbBr3 QDs-NOA63 NCs is attributed to the very large piezoelectric coupling efficiency due to the utilization of NOA63. Moreover, such PENGs are found to have advantages such as an effective stress transfer, a morphology passivation effect and an enhanced piezoelectric response, and chemical compatibility with CsPbBr3 QDs.

In the current era of busy and eventful daily routines, the need for self-driven, robust, and low maintenance healthcare systems emerges significantly more than in earlier times. The nanogenerator (NG) technology provides a new pathway by utilizing nanostructured and eco-friendly materials toward biomedical systems by harvesting biomechanical energy. Triboelectric NGs (TENGs) have been well-developed to cater all these matters, giving self-powered, sustainable, environment-friendly, and low footprint devices. TENG comes up with great potential, therefore, we have summarized various dimensions of its applications in healthcare management, including prevention, detection, diagnosis, and treatment. We have reviewed different aspects of TENG healthcare systems that provide wearable, minimally invasive, and simple solutions while harvesting human motion as the power source. Here, recent advancements of triboelectric devices are compiled while discussing their significance, structure, capabilities, performance, and future potential. Meanwhile, the impact of TENG on protecting and treating various internal and external human organs, such as the heart, neural tissues, skin, and hair, has been described in detail. Moreover, TENG-based solutions have also included minimizing the effects of contemporary and lingering challenges such as air pollution and viral infectious diseases on human health. In the very end, we have concluded with the opportunities and possible solutions for anticipated challenges.

Organic bistable light-emitting devices (OBLEDs) with an aluminum (Al)-nanoparticle-embedded tris(8-hydroxyquinoline)aluminum (Alq3) layer and double emitting layers (EMLs) were fabricated to investigate their color switching behaviors. Scanning electron microscopy images showed that Al nanoparticles were formed on the Alq3 layer. The Al nanoparticles in the Alq3 layer improved the storage margin of the organic bistable devices (OBDs), and the double EMLs changed the emission color of the organic light-emitting devices (OLEDs) according to the variations of the ON and the OFF states of the OBDs. The variations of the ON and the OFF states of the OBDs could be clearly distinguished by the color switching of the OLED. The luminances of the OBLEDs with double EMLs in the ON and the OFF states were 641.80 and 22.25 cd/m2, respectively, and their CIE coordinates at 20 V were (0.42, 0.46) and (0.51, 0.47), respectively, which corresponded to the ON and the OFF states of the OBLEDs.

The effects of taper angle of the string and the number of layers on the electrical characteristics of vertical NAND flash memories are investigated. Simulation results show that the transconductance and the threshold voltage distribution over the position of the cell along the string depend on taper angle and the number of layers. There is a taper angle that minimizes the spread of threshold voltage, and hence, the impact of the random telegraph noise and this angle depends on the number of layers. These results will be helpful in designing the vertical NAND flash memories.

As one of their major goals, researchers attempting to harvest mechanical energy efficiently have continuously sought ways to integrate mature technologies with cutting-edge designs to enhance the performances of triboelectric nanogenerators (TENGs). In this research, we introduced monolayer molybdenum-disulfide (MoS2) into the friction layer of a TENG as the triboelectric electron-acceptor layer in an attempt to dramatically enhance its output performance. As a proof of the concept, we fabricated a vertical contact-separation mode TENG containing monolayer MoS2 as an electron-acceptor layer and found that the TENG exhibited a peak power density as large as 25.7 W/m2, which is 120 times larger than that of the device without monolayer MoS2. The mechanisms behind the performance enhancement, which are related to the highly efficient capture of triboelectric electrons in monolayer MoS2, are discussed in detail. This study indicates that monolayer MoS2 can be used as a functional material for efficient energ...

Flexible nonvolatile memory (NVM) devices fabricated utilizing Au nanoparticles (AuNPs) embedded in a poly(methylmethacrylate) (PMMA) layer were fabricated on a silver nanowire (AgNW) or a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/AgNW coated on poly(ethylene terephthalate) (PET) substrates. The transmittance and the sheet resistance of the PEDOT:PSS/AgNW hybrid layer were approximately 89% and 50 Ω/sq, respectively, which were comparable to the values for commercial indium-tin-oxide (ITO) electrodes. Current-voltage curves for the Al/PMMA:AuNP/PEDOT:PSS/AgNW/PET devices at 300 K showed clockwise current hysteresis behaviors due to the existence of the AuNPs. The endurance number of ON/OFF switching for the NVM devices was above 30 cycles. An ON/OFF ratio of 1 × 103 was maintained for retention times longer than 1 × 104 s. The maximum memory margins of the NVM devices before and after bending were approximately 3.4 × 103 and 1.4 × 103, respectively. The retention times of the devices before and after bending remained same 1 × 104 s. The memory margin and the stability of flexible NVMs fabricated on AgNW electrodes were enhanced due to the embedded PEDOT:PSS buffer layer.

Au-WO3 nanocomposites (NCs) were used as a hole transport layer (HTL) to enhance the power conversion efficiency (PCE) of organic photovoltaic (OPV) cells. The photon absorption of the active layer in the OPV cells was increased due to the plasmonic effect caused by the Au-WO3 NCs, resulting in an enhanced short-circuit current density for the OPV cells with the Au-WO3 NC HTL. The value of the root-mean-square roughness of the Au-WO3 NC film was smaller than that of the WO3 NP film, resulting in a more efficient transport of holes from the active layer. The PCE of the OPV cell with an Au-WO3 NCs HTL with an Au NP concentration of 10 wt% was improved by 60.37% in comparison with that with WO3 nanoparticles. The enhancement of the PCE was attributed to both an increase in the efficiency of the hole transport at an Au-WO3 NCs HTL with an Au NP concentration of 10 wt%/active layer heterointerface and an enhanced photon absorption due to the localized surface plasmon resonance effect of the Au-WO3 NCs.

Hybrid perovskite CH3NH3PbI3 has attracted extensive research interests in optoelectronic devices in recent years. Herein an inkjet printing method has been employed to deposit a perovskite CH3NH3PbI3 layer. By choosing the proper solvent and controlling the crystal growth rate, hybrid perovskite CH3NH3PbI3 nanowires, microwires, a network, and islands were synthesized by means of inkjet printing. Electrode–gap–electrode lateral-structured photodetectors were fabricated with these different crystals, of which a hybrid perovskite microwire-based photodetector would balance the uniformity and low defects to obtain a switching ratio of 16000%, responsivity of 1.2 A/W, and normalized detectivity of 2.39 × 1012 Jones at a light power density of 0.1 mW/cm2. Furthermore, the hybrid perovskite microwire-based photodetector arrays were fabricated and applied in an imaging sensor, from which the clear mapping of the light source signal was successfully obtained. This work paves the way for the realization of low-co...

The science and technology of organic electronics have made consistent progress. However, the long-term stability of organic devices is a critical issue that remains to be resolved. Encapsulation is a straightforward and practical means to protect organic materials from oxygen or moisture and thus improve air stability. Here, we report a high-performance flexible inorganic SiNx/SiOxNy hybrid barrier film for application in organic solar cells (OSCs). This hybrid barrier film shows average transmittance of 85.5% and a water-vapor transmission rate of 7.1×10–5 g m−2 day−1. In OSCs comprising poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-bA]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]-thiophenediyl] (PTB7) and [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM), which were encapsulated by the SiNx/SiOxNy hybrid barrier film, the power-conversion efficiency remained above 86% of the initial value even after 2000 h of storage in air, which is comparable to that obtained for a device encapsulated by a glass lid.

Graphene quantum dots (GQDs) have currently emerged as excellent candidates for applications in GQD-based LEDs because of their potential applications in next-generation multifunctional systems. However, the numerous oxygenous functional groups and defects existing in the GQDs restrict their florescence quantum yield, resulting in a decrease in the brightness of light-emitting devices (LEDs) based on GQDs. Here, we report on solution-processed and highly-efficient LEDs that have been developed based on octadecylamine (ODA)-GQDs. In contrast with the GQDs, the number of oxygen components in the ODA-GQDs is lower due to nucleophilic substitution between the amine and the epoxy functional groups. The current and the external quantum efficiency of an LED with ODA-GQDs are 6.51 cd/A and 2.67%, respectively, this current efficiency of 6.51 cd/A being the highest among the efficiencies reported for LEDs based on GQDs. The efficiency enhancement in the LEDs with ODA-GQDs is attributed to significant improvements in the optical properties of the ODA-GQDs. The successful demonstration of this efficiency enhancement for LEDs based on ODA-GQDs indicates a potential for applications of GQD-based LEDs as next-generation real optical sources.

Wearable solar textiles have currently emerged as excellent candidates for potential applications in next-generation wearable functional clothing. Here, we report a wearable ultra-lightweight polymer solar textile based on transparent electronic fabrics (e-fabrics). The transparent e-fabrics with a structure of polyester/Ag nanowires/graphene core-shell have been used as anodes, as well as transparent substrates, for solar textiles. The anode buffer layer and the bulk heterojunction layer were deposited by blade-coating them onto the e-fabrics. The fabricated solar textiles show a power conversion efficiency of 2.27%, a low areal density of 5.0 mg/cm 2 , good endurance against mechanical deformations, and high compatibility with clothing. These results indicate that these novel solar textiles hold potential applications in the field of wearable self-powered portable electronics.