Potential Applications In Wearable Electronics Research Articles

Self‐powered sensor based on compressible ionic gel electrolyte for simultaneous determination of temperature and pressure

AbstractThe simultaneous detection of multiple stimuli, such as pressure and temperature, has long been a persistent challenge for developing electronic skin (e‐skin) to emulate the functionality of human skin. Meanwhile, the demand for integrated power supply units is an additional pressing concern to achieve its lightweightness and flexibility. Herein, we propose a self‐powered dual temperature–pressure (SPDM) sensor, which utilizes a compressible ionic gel electrolyte driven by the potential difference between MXene and Al electrodes. The SPDM sensor exhibits a rapid and timely response to changes in pressure‐induced deformation, while exhibiting a slow and hysteretic response to temperature variations. These distinct response characteristics enable the differentiation of current signals generated by different stimuli through machine learning, resulting in an impressive accuracy rate of 99.1%. Furthermore, the developed SPDM sensor exhibits a wide pressure detection range of 0–800 kPa and a broad temperature detection range of 5–75°C, encompassing the environmental conditions encountered in daily human life. The dual‐mode coupled strategy by machine learning provides an effective approach for temperature and pressure detection and discrimination, showcasing its potential applications in wearable electronics, intelligent robots, human–machine interactions, and so on.

Highly reliable and stretchable OLEDs based on facile patterning method: toward stretchable organic optoelectronic devices

Stretchable displays attract significant attention because of their potential applications in wearable electronics, smart textiles, and human-conformable devices. This paper introduces an electrically stable, mechanically ultra-robust, and water-resistant stretchable OLED display (SOLED) mounted on a stress-relief pillar platform. The SOLED is fabricated on a thin, transparent polyethylene terephthalate (PET) film using conventional vacuum evaporation, organic-inorganic hybrid thin film encapsulation (TFE), and a nonselective laser patterning process. This simple and efficient process yields an OLED display with exceptional stretchability, reaching up to 95% strain and outstanding durability, enduring 100,000 stretch-release cycles at 50% strain. Operational lifetime and water-resistant storage lifetime measurements confirm that the TFE provides effective protection even after the nonselective laser patterning process. A 3 × 3 array SOLED display module mounted on a stress-relief pillar platform is successfully implemented, marking the first case of water-resistant display array operation in the field of SOLEDs. This work aims to develop practical stretchable displays by offering a reliable fabrication method and device design for creating mechanically robust and adaptable displays, potentially paving the way for future advances in human-conformable electronics and other innovative applications.

MXene bridging graphite nanoplatelets for electrically and thermally conductive nanofiber composites with high breathability

Electrically and thermally conductive polymer composites (CPCs) have promising applications in flexible and wearable electronics, and it remains difficult for the trade-off between the electrical and thermal properties and the breathability. We propose a “MXene bridging graphite nanoplatelets (GNPs)” strategy to prepare conductive membranes with high conductivity and excellent breathability. Rigid GNPs are randomly distributed inside polyurethane nanofibers and expand the network. MXene nanosheets are decorated onto the nanofibers and bridge GNPs to reduce the thermal and electrical contact resistance. The synergy of MXene and GNPs improves electrical and thermal conductivity without sacrificing their breathability. The electrical and thermal conductivity of the composites can reach 64.4 S/m and 4.9 W (m K)−1, respectively. In addition, the nanofiber composites with strong interfacial interactions and thus superior durability show outstanding photothermal conversion and heat dissipation capability. This study can provide inspiration for designing multi-functional, breathable CPCs with potential applications in wearable electronics.

Investigations of Morphology and Carrier Transport Characteristics in High‐Performance PEDOT:PSS/Tellurium Binary Composite Fibers Produced via Continuous Wet‐Spinning

AbstractFiber‐based flexible thermoelectric (TE) generators are highly desirable due to their capability to convert thermal energy into electricity and their potential applications in wearable electronics. High‐performance poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/Tellurium (Te) composite TE fibers have been successfully developed via a continuous wet‐spinning approach followed by sulphuric acid treatment. With a simple pre‐modification to Te nanowires, the inorganic Te fillers form uniform distribution in PEDOT:PSS. At the optimal condition, the composite fibers exhibit a power factor of 233.5 µW m−1 K−2 and mechanical strength of 205 MPa, which are among the highest values reported so far for the PEDOT:PSS‐based TE fibers. From the viewpoint of TE property enhancement mechanism, understanding the morphology and carrier transport behavior in the 1D organic/inorganic composite fibers remains still challenging. On basis of a series of PEDOT:PSS/Te composite fibers with varying Te fractions, orientations of both the inorganic and organic constituents are quantitatively evaluated. Their electrical conductivities and Seebeck coefficients are also analyzed with modified series‐parallel models and energy filtering theory. This work may not only provide a universal approach to produce high‐performance organic/inorganic composite TE fibers for various wearable applications, but also help to understand the morphology and charge transport between heterogeneous phases in a 1D composite.

Dual Interface Modification Using Potassium Aspartic Acid to Realize Low Dark Current, High-Speed Nonfullerene Photodetectors.

Organic photodetectors (OPDs) have attracted tremendous interest due to their potential applications in wearable electronics. However, due to the nonideal contacts between the electrodes and organic semiconductors, OPDs still suffer from high dark current and slow frequency response. Herein, by inserting potassium aspartic acid (PAA) interlayers between ITO/metal oxides and the metal oxides/active layer, the shunts and hole injections are blocked and the energy levels of the electrodes are aligned. As a result, our dual-interface modified OPDs (ITO/PAA/ZnO/PAA/PTB7-Th:ITIC/MoO3/Ag) exhibit suppressed dark current 550 times lower than the reference device, corresponding to specific detectivity of 2.1 × 1012 Jones, broad linear dynamic range of 113 dB, and quick response time to the nanosecond level. PAA interlayers have also been demonstrated to improve the storage stability of OPDs, leading to 10 times slower degradation for the on/off ratio when compared with the reference and conventional polyethylenimine-modified OPDs.

Pressure-Driven Piezoelectric Sensors and Energy Harvesting in Biaxially Oriented Polyethylene Terephthalate Film.

This study reports the possibility of using biaxially oriented polyethylene terephthalate (BOPET) plastic packaging to convert mechanical energy into electrical energy. Electricity is generated due to the piezoelectricity of BOPET. Electricity generation depends on the mechanical deformation of the processing aids (inorganic crystals), which were found and identified by SEM and EDAX analyses as SiO2. BOPET, as an electron source, was assembled and tested as an energy conversion and self-powered mechanical stimuli sensor using potential applications in wearable electronics. When a pressure pulse after pendulum impact with a maximum stress of 926 kPa and an impact velocity of 2.1 m/s was applied, a voltage of 60 V was generated with short-circuit current and charge densities of 15 μAcm-2 and 138 nCm-2, respectively. Due to the orientation and stress-induced crystallization of polymer chains, BOPET films acquire very good mechanical properties, which are not lost during their primary usage as packaging materials and are beneficial for the durability of the sensors. The signals detected using BOPET sensors derived from pendulum impact and sieve analyses were also harvested for up to 80 cycles and up to 40 s with short-circuit voltages of 107 V and 95 V, respectively. In addition to their low price, the advantage of sensors made from BOPET plastic packaging waste lies in their chemical resistance and stability under exposure to oxygen, ultraviolet light, and moisture.

Screen-printed MXene-based all-solid-state textile supercapacitors

Textile-based supercapacitors (TSCs) have drawn increasing attention in recent years owing to their potential applications in wearable electronics. However, it remains a critical challenge to increase the energy density of TSCs. Herein, we develop a screen-printing strategy to scalable construct high-performance MXene-based all-solid-state textile supercapacitors, which exhibit excellent electrochemical performance, including high specific capacitance (4979.2 mF cm−2) and energy density (62.2 µWh cm−2). The electrochemical performance of assembled MXene-based TSCs is superior to the-state-of-the-art TSCs. This work provides a new strategy for fabricating high-performance flexible supercapacitors and paves the way for the development of wearable energy storage devices.

Enhanced Electrical Conductivity and Mechanical Properties of Stretchable Thermoelectric Generators Formed by Doped Semiconducting Polymer/Elastomer Blends.

Recent research efforts have concentrated on the development of flexible and stretchable thermoelectric (TE) materials. However, significant challenges have emerged, including increased resistance and reduced electrical conductivity when subjected to strain. To address these issues, rigid semiconducting polymers and elastic insulating polymers have been incorporated and nanoconfinement effects have been exploited to enhance the charge mobility. Herein, a feasible approach is presented for fabricating stretchable TE materials by using a doped semiconducting polymer blend consisting of either poly(3-hexylthiophene) (P3HT) or poly(3,6-dithiophen-2-yl-2,5-di(2-decyltetradecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-thienylenevinylene-2,5-yl) (PDVT-10) as the rigid polymer with styrene-ethylene-butylene-styrene (SEBS) as the elastic polymer. In particular, the blend composition is optimized to achieve a continuous network structure with SEBS, thereby improving the stretchability. The optimized polymer films exhibit well-ordered microstructural aggregates, indicative of good miscibility with FeCl3 and enhanced doping efficiency. Notably, a lower activation energy and higher charge-carrier concentration contribute to an improved electrical conductivity under high tensile strain, with a maximum output power of 1.39 nW at a ΔT of 22.4 K. These findings offer valuable insights and serve as guidelines for the development of stretchable p-n junction thermoelectric generators based on doped semiconducting polymer blends with potential applications in wearable electronics and energy harvesting.

Dual-porous structured dielectric layer for soft capacitive pressure sensor with high sensitivity

Highly sensitive, soft pressure sensors are urgently required in wearable electronics and robotics applications. In this study, we fabricated a dual-porous structured elastomer using a simple and cost-effective method, in which yeast and sugar particles were introduced into Ecoflex solution. The combination of yeast fermentation and sugar particle dissolution resulted in a dual-porous elastomer consisting of both large closed pores and small open pores. The dual-porous elastomer was employed as the dielectric layer in a soft capacitive pressure sensor. The pressure sensor exhibited a sensitivity over six times higher than that of the sensor with a mono-porous elastomer-based dielectric layer in the pressure range of 1–10 kPa. The finite element simulation demonstrated that the sensitivity enhancement can be attributed to the significantly low stiffness and buckling load resulting from the presence of large closed pores. Finger-attached sensors and motion-monitoring systems demonstrated a wide range of potential applications in wearable electronics.

High mass loading of polypyrrole in conductive hydrogels for stretchable all-in-one supercapacitors and self-powered strain sensing system

Developing high mass loading of conducting polymers in hydrogels for flexible supercapacitors remains an enormous challenge. Herein, we demonstrate an effective and facile strategy for incorporating high mass-loading of polypyrrole (PPy) nanoparticles into an open porous polydopamine/polyacrylamide (PDA/PAAM) hydrogel substrate. The as-prepared PDA/PAAM/PPy hydrogels exhibit great stretchability and desirable self-healing properties. Taking advantage of the sandwiched configuration and high mass of electroactive PPy (up to 11.13 mg/cm2), the PDA/PAAM/PPy hydrogels could be directly used as all-in-one supercapacitors, which can deliver a superior specific capacitance of 860 mF/cm2 at 1.0 mA/cm2, an excellent energy density of 76.44 μWh/cm2, a maximum power density of 4 mW/cm2, and excellent capacitance retention of 85 % after 5000 cycles. What’s more, the PDA/PAAM/PPy hydrogels show significant strain-sensitive behavior. A self-powered sensing system integrating the supercapacitor and strain sensor is achieved to monitor various human motions. Therefore, the resultant hydrogels have potential applications in wearable electronics.

Washable All-in-One Self-Charging Power Unit Based on a Triboelectric Nanogenerator and Supercapacitor for Smart Textiles.

Lightweight, portability, and sustainability have become key factors of the power source for the rapid development of multifunctional wearable electronic devices. In this work, a washable, wearable, and durable self-charging system for human motion energy harvesting and storage based on asymmetric supercapacitors (ASCs) and triboelectric nanogenerators (TENGs) is investigated. The all-solid-state flexible ASC is composed of a cobalt-nickel layered double hydroxide grown on a carbon cloth (CoNi-LDH@CC) as the positive electrode and activated carbon cloth (ACC) as the negative electrode and exhibits the performance of small size, high flexibility, and superior stability. The device was able to provide a capacity of 345 mF cm-2 and a cycle retention rate of 83% after 5000 cycles, which shows great potential as an energy storage unit. Additionally, flexible silicon rubber-coated carbon cloth (CC) is waterproof and soft and can be used as a TENG textile to gain energy for stable charging of an ASC, which presents an open-circuit voltage and short-circuit current of 280 V and 4 μA, respectively. The ASC and TENG can be assembled to continuously collect and store energy, which provides an all-in-one self-charging system qualified with washable and durable for potential applications in wearable electronics.

Flexible and Stretchable Poly(styrene-butadiene-styrene)/MXene Nanosheet Composite and Coaxial Fibers for Wearable Strain Sensors

Fiber-based strain sensors have become a vital part for wearable electronics owing to their lightweight, flexibility, and easy processing. A poly(styrene-butadiene-styrene) (SBS)/MXene composite and coaxial fiber-based strain sensors were produced through a continuous, facile, and scalable wet-spinning approach, which exhibited both high stretchability and sensitivity. Electromechanical properties displayed that SBS/MXene composite fibers showed extremely high sensitivity (1.63 × 104), low strain detection (0.5%), and outstanding durability and reliability, which laid a foundation for detecting human motion including subtle activities, such as breathing and wrist pulse, and large-scale activities, such as bending of limb joints. The strain-sensing performance was further investigated by SBS/MXene coaxial fibers with SBS/MXene as sheath and SBS as core, presenting high sensitivity (4.69 × 103) and repeatability. SBS/MXene composite and coaxial fiber sensors demonstrated the potential application in wearable electronics with human motion detection.

A Flexible and Highly Sensitive Pressure Sense Electrode Based on Cotton Pulp for Wearable Electronics.

Flexible pressure sensors with high sensitivity have great potential applications in wearable electronics. However, it is still a great challenge to prepare sense electrodes with high flexibility, high sensitivity, and high electrochemical performance. Here, we propose a novel and simple method for carbonizing cotton fibers as excellent electrically conductive materials. Moreover, carbonized cotton fiber (CCF) and polydimethylsiloxane (PDMS) were assembled into a flexible sense electrode. The CCF/PDMS electrode shows a high sensitivity of 10.8 kPa-1, a wide response frequency from 0.2-2.0 Hz, and durability over 900 cycles. The combined CCF/PDMS sensors can monitor human movement and pulse vibration, showing the enormous potential for use in wearable device technology. Additionally, the CCF/PDMS can be used as electrodes with a specific capacitance of 332.5 mF cm-2 at a current density of 5 mA cm-2, thanks to their high electrical conductivity and hydrophilicity, demonstrating the promising prospect of flexible supercapacitors.

Achieving Synergetic Anion‐Cation Redox Chemistry in Freestanding Amorphous Vanadium Oxysulfide Cathodes toward Ultrafast and Stable Aqueous Zinc‐Ion Batteries

AbstractFlexible aqueous zinc‐ion batteries (AZIBs) with high safety and low cost hold great promise for potential applications in wearable electronics, but the strong electrostatic interaction between Zn2+ and crystalline structures, and the traditional cathodes with single cationic redox center remain stumbling blocks to developing high‐performance AZIBs. Herein, freestanding amorphous vanadium oxysulfide (AVSO) cathodes with abundant defects and auxiliary anionic redox centers are developed via in situ anodic oxidation strategy. The well‐designed amorphous AVSO cathodes demonstrate numerous Zn2+ isotropic pathways and rapid reaction kinetics, performing a high reversible capacity of 538.7 mAhg‐1 and high‐rate capability (237.8 mAhg‐1@40Ag‐1). Experimental results and theoretical simulations reveal that vanadium cations serve as the main redox centers while sulfur anions in AVSO cathode as the supporting redox centers to compensate local electron‐transfer ability of active sites. Significantly, the amorphous structure with sulfur chemistry can tolerate volumetric change upon Zn2+/H+ insertion and weaken electrostatic interaction between Zn2+ and host materials. Consequently, the AVSO composites display alleviated structural degradation and exceptional long‐term cyclability (89.8% retention after 20 000 cycles at 40 Ag‐1). This work can be generally extended to various freestanding amorphous cathode materials of multiple redox reactions, inspiring development of designing ultrafast and long‐life wearable AZIBs.

Room-temperature self-healing and recyclable polyurethane elastomers with high strength and superior robustness based on dynamic double-crosslinked structure

Mechanically robust elastomers with the functionalities of room-temperature self-healing ability and even recyclability provide new opportunities to revolutionize next-generation flexible electronics. However, it remains a great challenge to synthesize such materials due to the conflicting requirements of the self-healing ability and mechanical robustness for the dynamicity of crosslinks. Herein, a room-temperature self-healing and recyclable polyurethane (PU) elastomer with ultrahigh mechanical performance is constructed by synergistically incorporating dynamic disulfide bonds and multiple hydrogen bonds (H-bonds) into a PU chain. The introduction of diazolidinyl urea (DU) motifs forms strong H-bonds and branching crosslinking points, improving the robustness of the crosslinked structure, and the fast metathesis of the aromatic disulfide bonds mainly contributes to the dynamicity of the crosslinked network. The resulting PU elastomers exhibit high tensile strength (14.08 MPa), toughness (64.6 MJ m−3), superior elastic restorability, outstanding self-healing capability (∼81% at room temperature), and multiple recyclability. Furthermore, a wearable sensor based on this elastomer is constructed to monitor different human motions, demonstrating the potential application in wearable electronics.

Proposal and Design of Flexible All-Polymer/CIGS Tandem Solar Cell.

Tandem solar cells (TSCs) have attracted prodigious attention for their high efficiency, which can surmount the Shockley-Queisser limit for single-junction solar cells. Flexible TSCs are lightweight and cost-effective, and are considered a promising approach for a wide range of applications. In this paper, a numerical model, based on TCAD simulation, is presented to assess the performance of a novel two-terminal (2T) all-polymer/CIGS TSC. To confirm the model, the obtained simulation results were compared with standalone fabricated all-polymer and CIGS single solar cells. Common properties of the polymer and CIGS complementary candidates are their non-toxicity and flexibility. The initial top all-polymer solar cell had a photoactive blend layer (PM7:PIDT), the optical bandgap of which was 1.76 eV, and the initial bottom cell had a photoactive CIGS layer, with a bandgap of 1.15 eV. The simulation was then carried out on the initially connected cells, revealing a power conversion efficiency (PCE) of 16.77%. Next, some optimization techniques were applied to enhance the tandem performance. Upon treating the band alignment, the PCE became 18.57%, while the optimization of polymer and CIGS thicknesses showed the best performance, reflected by a PCE of 22.73%. Moreover, it was found that the condition of current matching did not necessarily meet the maximum PCE condition, signifying the essential role of full optoelectronic simulations. All TCAD simulations were performed via an Atlas device simulator, where the light illumination was AM1.5G. The current study can offer design strategies and effective suggestions for flexible thin-film TSCs for potential applications in wearable electronics.

Superelastic Conductive Fibers with Fractal Helices for Flexible Electronic Applications (Adv. Mater. Technol. 8/2023)

Fractal Helices In article number 2201951, Bin Sheng and co-workers present a simple method, including winding and thermoplastic molding, to prepare fractal helix fiber (FHF). By keeping silver wire working in elastic region, the FHF can be drastically and repeatedly stretched with a nearly infinite service life, which has potential applications in wearable electronics.

Superflexible Inorganic Ag2Te0.6S0.4 Fiber with High Thermoelectric Performance

Fiber-based inorganic thermoelectric (TE) devices, owing to the small size, light-weight, flexibility, and high TE performance, are promising for applications in flexible thermoelectrics. Unfortunately, current inorganic TE fibers are strictly constrained by limited mechanical freedom because of the undesirable tensile strain, typically limited to a value of 1.5%, posing a strong obstacle for further application in large-scale wearable systems. Here, a superflexible Ag2 Te0.6 S0.4 inorganic TE fiber is demonstrated that provides a record tensile strain of 21.2%, such that it enables various complex deformations. Importantly, the TE performance of the fiber shows high stability after ≈1000 cycles of bending and releasing processes with a small bending radius of 5mm. This allows for the integration of the inorganic TE fiber into 3D wearable fabric, yielding a normalized power density of 0.4µWm-1 K-2 under the temperature difference of 20 K, which is approaching the high-performance Bi2 Te3 -based inorganic TE fabric and is nearly two orders of magnitude higher than the organic TE fabrics. These results highlight that the inorganic TE fiber with both superior shape-conformable ability and high TE performance may find potential applications in wearable electronics.

Multifunctional Electronic Textiles by Direct 3D Printing of Stretchable Conductive Fibers

AbstractThe integration of functional fibers into wearable devices by traditional methods is commonly completed in weaving. A new post‐weaving method of integrating fiber devices into textiles is needed to address the challenge of incorporating functional fiber into ready‐made garments without tearing down the clothing and re‐weaving. A 3D printing method to simultaneously fabricate and integrate highly stretchable conductive fiber into ready‐made garments with designed patterns is presented. The fabricated sheath–core fiber consists of a styrene–ethylene–butylene–styrene (SEBS) shell and a Ga–In–Sn alloy liquid metal core. The SEBS shell guarantees the high stretchability (up to 600%) and flexibility, while the liquid metal core offers a high conductivity maintained at large deformation. It is shown that sophisticated patterns, which have millimeter‐level‐resolution that are difficult to be integrated into textiles by weaving, and even more laborious to be incorporated into ready‐made garments, can now be easily modified and implemented into both textiles and ready‐made garments by a time‐saving and low‐cost 3D printing method. Utilizing the electrical characteristics of the fiber in pre‐designed patterns, on‐clothing soft electronics can be printed directly. A printed on‐clothing strain sensor, bending sensor, wireless charging coil, and a touch‐sensing network are demonstrated to show the potential applications in wearable electronics.

Graphene Film with a Controllable Microstructure for Efficient Electrochemical Energy Storage.

The agglomeration of graphene sheets and undesired pore size distribution usually lead to unsatisfactory electrochemical properties of reduced graphene oxide (RGO) film electrodes. Herein, crumpled exfoliated graphene (EG) sheets are adopted as the microstructure-regulating agent to tune the morphology and micro-/mesopore amounts with the aim of increasing active surface sites and ion transportation paths in electrodes. With the optimum ratio between EG and GO, the resulting 75%-EG/RGO shows significantly improved specific gravimetric capacitance (Cs) and rate capability when compared with pure RGO electrodes in a symmetrical supercapacitor system. Moreover, when coupling the 75%-EG/RGO cathode with a Zn anode to form a Zn ion hybrid supercapacitor (ZHS), the 75%-EG/RGO exhibits a much higher Cs of 327.39 F g-1 at 0.1 A g-1 and can maintain 91.7% capacitance after 8000 cycles. Systematic ex situ X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) measurements reveal that the charge storage mechanism is based on both reversible physical adsorption and dual ion uptake. Furthermore, the quasi-solid-state flexible ZHS also presents high capacitive performance and can maintain ∼100% capacitance under various bending states, demonstrating potential application in wearable electronics. This strategy opens up a new path for constructing high-performance graphene film electrodes.