Wearable Electronic Devices Research Articles

Toward Flexible and Stretchable Organic Solar Cells: A Comprehensive Review of Transparent Conductive Electrodes, Photoactive Materials, and Device Performance

AbstractFlexible and stretchable organic solar cells (FOSCs and SOSCs) hold immense potential due to their versatility and applicability in emerging areas such as wearable electronics, foldable devices, and biointegrated systems. Despite these promising applications, several challenges remain, primarily related to the mechanical durability, material performance, and scalability required for commercialization. This review comprehensively highlights recent advancements in the design and fabrication of FOSCs and SOSCs, with a particular emphasis on key functional layers, including transparent conductive electrodes, interfacial layers, photoactive materials, and top electrodes. Innovations in material design, such as active layers and transparent conductive electrodes with improved flexibility, are discussed alongside developments in device processes to achieve power conversion efficiencies exceeding 19%. Furthermore, the review addresses remaining challenges, including the need for scalable manufacturing techniques and enhanced mechanical robustness under strain. Finally, the prospects of FOSCs and SOSCs are analyzed, providing insights into how these technologies can contribute to the development of sustainable, high‐performance power sources for wearable electronic devices and other flexible electronics. This review offers valuable insights, bringing the commercialization of wearable, high‐performance FOSCs and SOSCs closer to reality.

Nanocellulose‐reinforced, anti‐freezing, highly conductive ionic organic hydrogels for flexible electronic devices

AbstractCurrently, flexible electronic devices based on ionic conductive hydrogels are receiving widespread attention in the field of human health detection. In this paper, a facile one‐pot method is proposed for the preparation of ionic organic hydrogels, in which polyvinyl alcohol (PVA), cellulose nanofiber (CNF), and graphene oxide (GO) are dissolved in dimethyl sulfoxide‐water (DMSO/H2O), and the organic hydrogel is obtained by a freezing–thawing process. The ionic organic hydrogel with excellent properties is then prepared by soaking the hydrogel in a calcium chloride (CaCl2) solution using a salting‐out strategy. The ionic organic hydrogel possesses good tensile (283%) and strength (0.3 MPa), super electrical conductivity (7.72 S/m), and high strain sensitivity [gauge factor (GF) up to 5.22]. Meanwhile, it has excellent anti‐freezing and moisturizing properties. In addition, the ionic organic hydrogels can be used in flexible strain sensors and triboelectric nanogenerators to realize real‐time monitoring of human motion, traceless writing, and energy conversion. It is foreseen that the prepared ionic organic hydrogels provide a feasible method for realizing the long‐term use of wearable electronic devices in extreme environments and daily life.

High-Performance Triboelectric Nanogenerator Based on Silk Fibroin-MXene Composite Film for Diagnosing Insomnia Symptoms.

In this study, we developed a flexible, biocompatible, and high-output electrical performance triboelectric nanogenerator (TENG) employing a silk fibroin (SF)-MXene composite film (SF-MXene-F) and a PDMS film as the friction layer. The inclusion of MXene in the SF film increased its surface charge density, presenting a practical approach to designing high-performance SF composite film-based TENGs. At a MXene content of 40%, our SF-MXene composite film-based TENG (SF-MXene-FTENG) achieved optimal output electrical performance, featuring a maximum open-circuit voltage (Voc) of 418 V, a maximum short-circuit current (Isc) of 11.6 μA, and a maximum output power density of 9.92 W/m2. The Voc and power densities of the SF-MXene-FTENG surpassed previously reported optimal values for SF-based TENGs by 1.6 and 3.8 times, respectively. Furthermore, leveraging the exceptional biocompatibility and light shading performance of TENGs, we designed a wearable smart TENG eye mask capable of diagnosing insomnia symptoms and monitoring sleep quality in real time. The SF-MXene-FTENG holds promising application potential as a wearable electronic device for diagnosing sleep-related diseases.

Optimization of Thermoelectric Performance of Ag2Te Films via a Co-Sputtering Method.

Providing self-powered energy for wearable electronic devices is currently an important research direction in the field of thermoelectric (TE) thin films. In this study, a simple dual-source magnetron sputtering method was used to prepare Ag2Te thin films, which exhibit good TE properties at room temperature, and the growth temperature and subsequent annealing process were optimized to obtain high-quality films. The experimental results show that films grown at a substrate temperature of 280 °C exhibit a high power factor (PF) of ~3.95 μW/cm·K2 at room temperature, which is further improved to 4.79 μW/cm·K2 after optimal annealing treatment, and a highest PF of ~7.85 μW/cm·K2 was observed at 200 °C. Appropriate annealing temperature effectively increases the carrier mobility of the Ag2Te films and adjusts the Ag/Te ratio to make the composition closer to the stoichiometric ratio, thus promoting the enhancement of electrical transport properties. A TE device with five legs was assembled using as-fabricated Ag2Te thin films. With a temperature difference of 40 K, the device was able to generate an output voltage of approximately 14.43 mV and a corresponding power of about 50.52 nW. This work not only prepared a high-performance Ag2Te film but also demonstrated its application prospects in the field of self-powered electronic devices.

Humidity Sensing Using Polymers: A Critical Review of Current Technologies and Emerging Trends

In the post-pandemic era, human demand for a healthy lifestyle and a smart society has surged, leading to vibrant growth in the field of flexible electronic sensor technology for health monitoring. Flexible polymer humidity sensors are not only capable of the real-time monitoring of human respiration and skin moisture information but also serve as a non-contact human–machine interaction method. In addition, the development of moist-electric generation technology is expected to break free from the traditional reliance of flexible electronic devices on power equipment, which is of significant importance for the miniaturization, reliability, and environmentally friendly development of flexible devices. Currently, flexible polymer humidity sensors are playing a significant role in the field of wearable electronic devices and thus have attracted considerable attention. This review begins by introducing the structural types and working principles of various humidity sensors, including the types of capacitive, impedance/resistive, frequency-based, fiber optic, and voltage-based sensors. It mainly focuses on the latest research advancements in flexible polymer humidity sensors, particularly in the modification of humidity-sensitive materials, sensor fabrication, and hygrosensitivity mechanisms. Studies on material composites including different types of polymers, polymers combined with porous nanostructured materials, polymers combined with metal oxides, and two-dimensional materials are reviewed, along with a comparative summary of the fabrication and performance mechanisms of related devices. This paper concludes with a discussion on the current challenges and opportunities faced by flexible polymer humidity sensors, providing new research perspectives for their future development.

High volumetric-energy-density flexible supercapacitors based on PEDOT:PSS incorporated with carbon quantum dots hybrid electrodes

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is a highly successful conductive polymer utilized as an electrode material in energy storage units for portable and wearable electronic devices. Nevertheless, employing PEDOT:PSS in supercapacitors (SC) in its pristine state presents challenges due to its suboptimal electrochemical performance and operational instability. To surmount these limitations, PEDOT:PSS has been integrated with carbon-based materials to form flexible electrodes, which exhibit physical and chemical stability during SC operation. We developed a streamlined fabrication process for high-performance SC electrodes composed of PEDOT:PSS and carbon quantum dots (CQDs). The CQDs were synthesized under microwave irradiation, yielding green- and red-light emissions. Through optimizing the ratios of CQDs to PEDOT:PSS, the SC electrodes were prepared using a spray-coating technique, marking a significant improvement in device performance with a high volumetric capacitance (104.10 F cm−3), impressive energy density (19.68 Wh cm−3), and excellent cyclic stability, retaining ∼85% of its original volumetric capacitance after 15,000 repeated GCD cycles. Moreover, the SCs, when utilized as a flexible substrate, demonstrated the ability to maintain up to ∼85% of their electrochemical performance even after 3,000 bending cycles (at a bending angle of 60°). These attributes render this hybrid composite an ideal candidate for a lightweight smart energy storage component in portable and wearable electronic technologies.

Construction of high strength PVA/cellulose conductive hydrogels based on sodium citrate/aluminium chloride dual ions regulation

Hydrogels used for flexible sensing usually require a good balance between mechanical strength and conductivity. In this study, polyvinyl alcohol/carboxymethyl cellulose/cellulose nanofibers (PVA/CMC/CNF) hydrogels with multi-hierarchical structures were firstly prepared by adjusting the CNF content. Then, PVA/CMC/CNF-xM with excellent mechanical properties and conductivity were prepared by cyclic freezing-thawing and sodium citrate/aluminium chloride (Na3Cit/AlCl3) dual ions salt equilibrium methods. Results showed that at an ion concentration of 3 mol/L, PVA/CMC/CNF-3 M hydrogel exhibited a tensile strength, elongation at break and conductivity of 3.41 MPa, 1271 % and 0.35 S/m, respectively. The structural evolution of PVA/CMC/CNF-xM conductive hydrogels were studied, and the results indicated that Cit3− formed numerous intermolecular hydrogen bonds, while Al3+ could strongly coordinate with carboxyl and hydroxyl groups between the polysaccharide chains. Meanwhile, PVA/CMC/CNF-3 M possessed a low strain detection limit of 1 %, making it not only can be used for human motion monitoring, but also information encoding and transmission. This work may provide a facile approach for preparing high-strength and conductive hydrogels, which can be applied in flexible wearable electronic devices and information transmission.

A diode-like integrated hydrogel for piezoionic generators and sensors

Wearable sensing electronic devices based on hydrogel are gradually developing towards multifunction and portability, however, efficiently harvesting energy from the surrounding environment to power traditional hydrogel-based wearable electronic devices is a major challenge. The assembly of multilayer heterogeneous hydrogels is a potential strategy to address this challenge. Herein, inspired by the structure of diodes, a diode-like integrated hydrogel composed of a three-tier structure of anionic polyelectrolyte hydrogel, polyacrylamide hydrogel and cationic polyelectrolyte hydrogel is developed. By the connection of polyacrylamide hydrogel, the composite hydrogel exhibits excellent structural stability and mechanical properties. Notably, due to the introduction of MXene ion-conducting microchannels, the directional transport of free cations and anions ionized by anionic and cationic polyelectrolytes is achieved, thereby improving the conductivity (74.58 mS/cm), sensing (gauge factor = 7.47) and piezoionic output performance of the composite hydrogel. The composite hydrogel-based sensor can sense tiny facial movements and recognize the direction of human movement, and the composite hydrogel-based piezoionic generator exhibit more efficient mechanical-electric conversion performance, which can output the maximum voltage of 1410mV, current of 28 μA, and power density of 2.9mW/m2 for a composite hydrogel of 5×5 cm2. The integration of multilayer heterogeneous hydrogels proposes a versatile strategy for the development of high-performance hydrogel-based self-powered sensing electronic devices, expanding the application of hydrogels in artificial intelligence and human-computer interaction.

Van der Waals GeSe with Strain- and Gate-Tunable Linear Dichroism for Wearable Electronics.

The direct detection of light polarization poses a crucial challenge in the field of optoelectronics and photonics. Herein, the tunable linear dichroism (LD) in GeSe-based polarized photodetectors is presented through electronic and structural asymmetry modulation, and demonstrate their application prospects in wearable electronics. An improvement in the dichroic ratio up to 34% is achieved under a gate voltage of 20V, and the improvement reaches 44% by applying a tensile strain along the zigzag direction. Theoretical calculations reveal that the gate regulation of barrier height between GeSe and Au electrodes is responsible for the electrical-tunable LD, while the anisotropic optical absorption in response to strains leads to the strain-tunable LD. Moreover, flexible GeSe transistors are developed for wearable applications including motion sensors and glucose monitors. This study offers viable approaches for modulating the optical anisotropy of low-dimensional materials and emphasizes the versatility of van der Waals materials for practical applications in wearable electronic devices.

3D-Printed Multi-Axis Alignment Airgap Dielectric Layer for Flexible Capacitive Pressure Sensor

Flexible pressure sensors are increasingly recognized for their potential use in wearable electronic devices, attributed to their sensitivity and broad pressure response range. Introducing surface microstructures can notably enhance sensitivity; however, the pressure response range remains constrained by the limited volume of the compressible structure. To overcome this limitation, this study implements an aligned airgap structure fabricated using 3D printing technology. This structure, designed with a precisely aligned triaxial airgap configuration, offers high deformability under pressure, substantially broadening the pressure response range and improving sensitivity. This study analyzes the key structural parameters—the number of axes and pore size—that influence the compressibility and stability of the dielectric material. The results indicate that the capacitive pressure sensor with an aligned airgap structure, manufactured via 3D printing, exhibits a wide operating pressure range (50 Pa to 500 kPa), rapid response time (100 ms), wide limit of detection (50 Pa), and approximately 21 times enhancement in sensitivity (~0.019 kPa−1 within 100 kPa) compared with conventional bulk structures. Furthermore, foot pressure monitoring trials for wearable sensor applications demonstrated exceptional performance, indicating the sensor’s suitability as a wearable device for detecting plantar pressure. These findings advocate for the potential of 3D printing technology to supplant traditional sensor manufacturing processes.

Innovative Wearable Electronics: Next-Generation Nitrogen-Doped Lutetium-Carbon Microspheres Composites for Robust Energy Harvesting.

In the quest to advance wearable electronics, this study presents a novel method using nitrogen-doped lutetium-carbon microspheres (N, Lu-CMS) for high-performance piezoelectric energy harvesting. The synthesis of N, Lu-CMS begins with the polymerization of sucrose, followed by the preparation of N, Lu-CMS metal complexes through the incorporation of lutetium (III) nitrate hydrate and thiourea, yielding a black powder product. The wearable electronic device is designed with a silicon rubber (SR) matrix, reinforced with 0D fillers such as N, Lu-CMS, or molybdenum disulfide (MoS₂). Mechanical testing revealed a significant improvement in compressive modulus, reaching 3.7MPa (N, Lu-CMS) at a concentration of 3 parts per hundred rubber (phr). Electromechanical assessments demonstrated efficient energy conversion, while biomechanical analysis, including thumb pressing tests, showed a notable increase in output voltage, peaking at ≈285mV (N, Lu-CMS) at 3 phr. This research provides a foundation for future engineering applications, particularly in electronic packaging for wearable electronics and smart devices, underscoring the significant impact of N, Lu-CMS in this emerging field. The surface power density achieved is 0.026 nWcm- 2 (N, Lu-CMS) and 0.0056 nWcm- 2 (Hybrid). Lastly, the conversion efficiency is 6.26% for N, Lu-CMS, and 1.05% for the hybrid system.

Hierarchical MoO2@MoS2 heterojunction nanosheets anchored with metal-organic framework-derived CoFe alloy as bifunctional catalysts for flexible zinc-air batteries

Crafting a robust, high-performance, non-precious metal-based flexible air electrode is crucial for realizing flexible zinc-air batteries (ZABs). Herein, hierarchical MoO2 and MoS2 heterojunction nanosheets grown on carbon cloth (CC) are prepared through a simple hydrothermal reaction followed by calcination. Afterward, through self-assembly and high-temperature carbonization of zeolitic imidazolate framework-67 (ZIF-67) and Materials of Institute Lavoisier-101 (MIL-101) on the heterojunction nanosheets, a hierarchical structure of nitrogen-doped carbon (NC) encapsulated CoFe alloy nanoparticles (NPs) supported on MoO2@MoS2 heterojunction nanosheets (CC/MoS2@MoO2@CoFe) is obtained. It exhibits remarkable activity and durability for both bifunctional oxygen evolution and reduction reactions (OER/ORR), attributed to the ternary heterojunction formed by NC-coated CoFe alloy NPs uniformly dispersed among the MoO2@MoS2 nanosheets, along with oxygen vacancies at heterogeneous interfaces between MoS2, MoO2, and Co0.72Fe0.28 alloy. As a binder-less self-supporting electrode, the assembled aqueous ZAB demonstrates a maximum power density of 113.6 mW cm–2, surpassing that of Pt/C + RuO2 (75.2 mW cm–2), along with excellent cycling stability. Furthermore, the CC/MoS2@MoO2@CoFe-based flexible ZABs achieve a maximum power density of 54.1 mW cm–2, exhibit good cycling stability for up to 120 cycles, and show outstanding flexibility. This study paves the way for the practical integration of flexible ZABs into wearable electronic devices, heralding a new era of portable power solutions.

Electrospinning as a Method for Fabrication of Nanofibrous Photocatalysts Based on Gallium Oxide

Photocatalysts are currently widely used in various research and industrial fields, from water and air purification to solar energy, from self‐cleaning surfaces to wearable biosensors and electronic devices. Among semiconductors, the growing interest is attracted to gallium oxide, especially β‐Ga2O3, due to the unique physical, chemical (especially acid‐resistance), physical–chemical, photochemical properties, and redox potential. These photocatalysts can be used not only as suspended mixture, but also in the form of films, nanoparticles, and nanofibers. The last one is more challenging due to the high level of surface‐to‐volume ratio, porousness, air and water permeability, and excellent morphological and physical–mechanical properties. Moreover, electrospinning techniques, in comparison with fabrication of nanoparticles, allow to obtain photocatalytic devices without usage of additional carrying base, which simplify the industrial process. However, to date there are limited publications related to the Ga2O3 electrospun nanofibers. The aim of this review is to summarize current results of gallium oxide electrospun nanofibers preparation. Special attention is given to the technological parameters of the electrospinning, the polymer solution receipts, and the properties of such nanomaterials and its potential application. Despite the limited number of publications related to Ga2O3 fibers fabrications, that data collected in this review article demonstrate great potential for practical applications.

One-Step Fabrication of 2.5D CuMoOx Interdigital Microelectrodes Using Numerically Controlled Electric Discharge Machining for Coplanar Micro-Supercapacitors

With the increasing market demands for wearable and portable electronic devices, binary metal oxides (BMOs) with a remarkable capacity and good structure stability have been considered as a promising candidate for fabricating coplanar micro-supercapacitors (CMSCs), serving as the power source. However, the current fabrication methods for BMO microelectrodes are complex, which greatly hinder their further development and application in BMO CMSCs. Herein, the one-step fabrication of 2.5D CuMoOx-based CMSCs (CuMoCMSCs) has been realized by numerically controlled electric discharge machining (NCEDM) for the first time. In addition, the controllable capacity of CuMoCMSCs has been achieved by adjusting the NCEDM-machining voltage. The CuMoCMSCs machined by a machining voltage of 60 V (CuMoCMSCs60) showed the best performance. The fabricated CuMoCMSCs60 with binary metal oxides could operate at an ultra-high scanning rate of 10 V s−1, and gained a capacity of 40.3 mF cm−2 (1.1 mA cm−2), which is more than 4 times higher than that of MoOx-based CMSCs (MoCMSCs60) with a single metal oxide. This is because CuMoOx BMOs materials overcome the poor electroconductivity problem of the MoOx single metal oxide. This one-step and numerically controlled fabrication technique developed in this research opens a new vision for preparing BMO materials, BMO microelectrodes, and BMO microdevices in an environmental, automatic, and intelligent way.

High-Performance Organic Field-Effect Transistors and Inverters with Good Flexibility and Low Operating Voltage.

Organic field-effect transistors (OFETs) with good flexibility and low operating voltage, are of great meaning for the low power stretchable and wearable electronic devices. The operating voltage and flexibility are easily affected by the dielectric layers in the OFETs. Bilayer dielectrics comprising both high- and low-permittivity (k) insulating polymers, have been reported. The flexible bilayer dielectrics can combine the advantages of both insulating polymers, which are high charge carriers from low-k polymers and low operating voltage from high-k polymers. However, the effect of film thicknesses in the bilayer dielectrics on the OFET performance is seldom investigated. Here, bilayer dielectrics comprising high-k polyvinyl alcohol (PVA) and low-k polymethylmethacrylate (PMMA) were fabricated. And PVA/PMMA bilayers with three different PVA film thicknesses are carefully investigated. The 300 nm PVA/100 nm PMMA bilayer dielectric makes the pentacene OFETs show the highest hole mobility of 1.24 cm2V-1s-1 and the corresponding inverters give a high voltage gain of 40 and a noise margin of 2.3 V (77% of 1/2 VDD) at low operating voltage of 6 V. Both the pentacene transistors and the inverters still work properly under bending radium of 5.85 mm, proving the good prospects of the PVA/PMMA bilayer dielectric in practical applications.

Enhanced casein organohydrogel coating with the liquid metal catalyst for electric leather in human-machine interaction

Leather’s durability and multi-level structure make it an excellent substrate for electronics. Integrating leather with modern electronic technology to create electronic leather is becoming increasingly popular. However, significant challenges remain, such as adhering conductive media to leather, their penetration and dispersion, and the complexity of preparation. This study presents a new strategy for fabricating electronic leather by combining leather with a casein-based organic hydrogel using coating chemistry techniques. This hydrogel is simple to prepare and exhibits excellent biocompatibility and self-adhesive properties, offering a promising approach to overcome these challenges. Here, we designed casein-stabilized core-shell liquid metal-based catalysts and utilized acrylamide (AM), 2-acrylamido-2-methylpropane sulfonic acid (AMPs), CNTs, and glycerol (Gly) to achieve in situ organohydrogel formation on leather under mild conditions (60 s, 25 °C). The resulting organohydrogel-coated material exhibits outstanding stretchability (tensile stress: 70.3 kPa, tensile strain: 1491.8 %), rapid response (423 ms), and high sensitivity (GF: 7.67) as a strain sensor. This substrate can be employed in designing flexible wearable electronic gloves, facilitating seamless information interaction between humans and devices. This innovation demonstrates significant potential in enhancing the functionality of leather as a wearable electronic device. Combining leather’s natural properties with cutting-edge organohydrogel technology is promising to revolutionize the wearable electronics industry, potentially creating highly versatile and multifunctional electronic skins.

Enhanced performance of flexible BiFeO3 ferroelectric memory with Mica substrate via SrTiO3 buffer layer

BiFeO3 (BFO) application in flexible wearable devices is garnering interest because of its unique ferroelectric and magnetic properties. However, the integration of high-quality BFO films onto flexible substrates presents significant technical challenges. Here, we successfully fabricated high-quality BFO films on mica substrates by using pulsed laser deposition, and report the fatigue characteristics of BFO films on flexible substrates for the first time. The results demonstrated that, after 108 bipolar switching cycles, the polarization only degraded by 0.28%, indicating superior fatigue characteristics compared to previously reported BFO films. Additionally, the device ferroelectric properties remained largely unchanged, with a bending radius of 3.5 mm. The fabricated flexible Pt/BFO/La0.65Sr0.35MnO3(LSMO)/SrTiO3(STO)/mica non-volatile memory devices exhibited mechanical flexibility and fatigue resistance. These findings not only highlight the potential of flexible BFO films for wearable electronic devices and flexible memory devices, they also provide valuable insight for the future development of high-performance flexible ferroelectric materials.

Flexible Magnetoelectric Fiber for Self-Powered Human-Machine Interactive.

Flexible large strain sensors are an ideal choice for monitoring human motion, but the current use of flexible strain gauges is hindered by the need for external power sources and long-term operation requirements. Fiber-based sensors, due to their high flexibility, excellent breathability, and the ease with which they can be embedded into everyday clothing, have the potential to become a novel type of wearable electronic device. This paper proposes a flexible self-powered strain sensing material based on the electromagnetic induction effect, composed of a uniform mixture of Ecoflex and Nd2Fe14B, which has good skin-friendliness and high stretchability of over 100%. The voltage output of the magnetoelectric composite fiber remains stable over 5000 stretch-release cycles, reaching up to 969 μV. Based on this novel sensing material, a remote smart car control scheme for a human-machine interaction system was designed, enabling real-time gesture interaction.

Microstructured Self-Healing Flexible Tactile Sensors Inspired by Bamboo Leaves.

Wearable electronic devices with multifunctions such as flexible, integrated, and self-powered play a crucial role in the fields of health monitoring, motion monitoring, and human-computer interaction. However, their core basic components, flexible pressure sensors, face challenges including poor long-term stability and insufficient real-time sensing accuracy. In order to solve the challenges of long-term, stable, and accurate sensing of the sensor, this paper prepares polydimethylsiloxane (SHPDMS) with intrinsic self-healing property and designs a high-sensitivity self-healing capacitive flexible pressure sensor with dual microstructures (grating microstructured electrodes and microporous dielectric layer) as the substrate based on SHPDMS. Specifically speaking, the self-healing of the sensor under mild conditions was realized by introducing reversible imine bonds with low bonding energy into the polydimethylsiloxane (PDMS) flexible substrate, which solved the problem of the material's long-term service durability. A grating-like microstructure was introduced into the flexible electrode by using a spotted bamboo taro leaf as a template, and a dual microstructure sensor was constructed by combining it with a microporous dielectric layer doped with single-walled carbon nanotubes. This way reduces the elastic modulus of the dielectric layer, improves the dielectric constant of the sensor under loading, and thus significantly improves the sensor's sensitivity and extends the measurement accuracy in a low-stress range. The prepared self-healing flexible sensor achieves a sensitivity of 3.6 kPa-1, a minimum detection limit of 5 Pa, a response recovery time of less than 80 ms, and stability over 5000 cycles, which exceeds most previously reported silicone rubber-based capacitive flexible sensors.

Sodium polyacrylate hydrogel electrolyte: Flexible rechargeable supercapacitor using thermally reduced graphene oxide nanosheets

The alternative source of the gel polymer electrolyte (GPE) is introduced by developing the sodium polyacrylate (S-PANa) solid hydrogel electrolyte, which is the front runner in the recent flexible and wearable electronic devices due to their excellent mechanical property, high ionic conductivity, and electrochemical stability. In this work, we synthesized the S-PANa solid hydrogel electrolyte and utilized it for the flexible symmetric supercapacitor using thermally reduced graphene oxide nanosheets (TRGO) coated on carbon cloth as an electrode. The prepared S-PANa hydrogel is of a highly porous nature and has better surface roughness, as examined by the Field Emission Scanning Electron Microscopy (FE-SEM) and 3D nano profiler analysis. The electrochemical characterization of the assembled flexible solid-state hydrogel supercapacitor (FSHSC) reveals the electric double-layer capacitive behavior with an excellent device capacitance of 45.77 mF/cm2. The significant role of diffusion charge re-distribution, overcharging issues, ohmic drop, and leakage current of the FSHSC is studied, followed by self-discharge and leakage current analysis. Moreover, the FSHSC device delivers the maximum energy density of 5.15 μWh/cm2 with a remarkable retention capacitance of 99 % over 10,000 continuous cycles. Further, in practical utilization, the solar-charged FSHSC device can effectively power the electronic LED for a long duration and enhance its efficiency for the development of a sustainable backup power system. Overall, these experimental results demonstrated the significant use of the S-PANa hydrogel-based flexible device, which can be an alternative source in future energy storage systems instead of using gel electrolyte-based flexible devices.