This review offers a critical overview of recent developments in lead-free piezoelectric materials and flexible device architectures for self-powered wearable and Internet of Things systems. It examines the scientific and technological rationale for replacing conventional battery-dependent power sources with ambient mechanical energy harvesters, and it evaluates the relative merits of inorganic ceramics, organic polymers, and composite systems in achieving efficient electromechanical conversion under practical operating conditions. The discussion further considers compositional tuning, phase boundary engineering, microstructural optimization, and device-level integration as key strategies for improving piezoelectric output, mechanical compliance, durability, and manufacturability. By connecting fundamental materials design with application-driven device requirements, the review identifies the principal challenges and emerging directions necessary for the realization of reliable, scalable, and sustainable electronic platforms.

Renewable energy harvesting technologies, which convert ambient resources such as wind into electrical energy, have attracted significant attention as sustainable power sources for self-powered systems. However, the long-term applicability of wind energy harvesters in remote or extreme environments has not yet been fully discussed, particularly in terms of structural robustness and environmental adaptability. In this study, we designed a double-clamped flutter-type triboelectric generator (DFTEG) for efficient wind energy harvesting and evaluated its output performance under various simulated outdoor conditions. The DFTEG features a modular acrylic frame with a magnet-based assembly for easy maintenance and film replacement, utilizing PTFE films and aluminum electrodes to maximize the charge density difference according to the triboelectric series. Structural optimization revealed that a single-film configuration with a length of 110 mm produced the most stable flutter vibration and a large effective contact area, achieving a maximum open-circuit voltage of 42.28 V and a short-circuit current of 2.89 μA. Furthermore, performance evaluations under various environmental variables, including relative humidity, temperature, and sand particles interference, confirmed consistent electrical output across diverse environmental conditions. These results demonstrate the potential of the proposed DFTEG as an environmentadaptive independent power source capable of stable operation under complex environmental factors.

The expansion of smart healthcare and wearable electronics has intensified the need for fabric-based sensors that integrate conformally with the human body for continuous bio signal monitoring. However, the heavy reliance of conventional devices on external batteries remains a major obstacle to commercialization, necessitating the development of flexible piezoelectric energy harvesters that convert biomechanical energy into sustainable power. Here, we present a highly flexible and wearable piezoelectric energy harvester (PEH) fabricated by a screen-printing of BaTiO₃ nanoparticlePDMS composites onto a fabric substrate. An optimized piezo-ceramic filler concentration of 70 wt% yielded a peak output voltage of 0.52 V and a current of 40 nA under the mechanical bending deformations. The fabricated PEH demonstrated exceptional mechanical and electrical stability, showing no performance degradation of over 5,000 repetitive bending cycles. These results indicate that a PEH can function as a stable self-powered source within complex clothing environments, offering a promising pathway for next-generation autonomous wearable sensor systems.

Metamaterials, as artificially engineered structures with unconventional mechanical and acoustic properties, have recently emerged as a transformative platform for enhancing the capabilities of triboelectric nanogenerator (TENG) systems. Since the invention of TENG devices, extensive efforts have been devoted to improving charge density, output stability, and overall performance. Conventional performance optimization strategies mainly rely on device-level improvements such as surface chemistry modification, microstructuring, and nanopatterning. However, limited emphasis has been given to system-level development of smart self-powered intelligent systems. The integration of metamaterials into TENG devices opens a new era by enabling frequency-selective localization, mechanical impedance matching, and controllable deformation pathways. These engineered mechanical structures not only improve energy harvesting efficiency but also introduce new functionalities into the system. This review systematically summarizes recent advances in metamaterial-integrated TENG systems across four major application domains: (i) energy harvesting, (ii) acoustic telecommunication and acoustic-to-electric conversion, (iii) self-powered sensing, and (iv) vibration suppression and monitoring. Overall, the integration of metamaterials into TENG systems will pave the way for next-generation sustainable, intelligent, self-powered devices with diverse functionalities.

The potential of replacing crosslinked polyethylene (XLPE) with an eco-friendly alternative, polypropylene (PP), as insulating material is investigated for overhead power distribution lines. Although XLPE exhibits excellent electrical and mechanical properties, the byproducts generated during crosslinking pose environmental challenges. PP is a viable alternative because of recyclability and absence of byproducts during crosslinking. This study evaluated alternating current (AC) breakdown strength, contact angle, and tracking resistance of two commercially available XLPE samples and three types of PP (PP1, PP2, PP3) with varying additive content. AC breakdown strength, analyzed using the Weibull distribution, facilitated relative comparison of insulation performance. PP2 exhibited scale parameters comparable to or exceeding those of XLPE. Contact angles exceeding 90° displayed hydrophobicity across all samples. To address pass/fail evaluation limitations, arcing images from tracking tests were analyzed using the box-counting method for fractal dimension analysis. Fractal dimensions increased with arcing extent, and complexity increased with test duration. Tracking resistance performance order was PP3, PP1, CC, PP2, OC which was attributed to enhanced heat dissipation properties of filler additives. The proposed quantitative method for comparing tracking resistance through fractal dimension analysis, explored the feasibility of using PP insulating materials in overhead power distribution lines.

The increasing global demand for renewable energy has accelerated the deployment of offshore wind farms, thereby highlighting the need for advanced development and performance assessment techniques for dynamic submarine cables used in floating offshore wind systems. These cables are continuously subjected to combined thermal, electrical, and mechanical stresses, with mechanical loading playing a particularly dominant role. As a result, dynamic submarine cables exhibit degradation behaviors that differ significantly from those of conventional fixed submarine cables. This paper presents the design and implementation of a comprehensive evaluation system capable of applying combined thermal, electrical, and mechanical stresses to dynamic submarine cables. The system was validated using a 66 kV wet type submarine cable through commissioning tests and insulation performance measurements. Electrical stress of 72 kV, thermal stress exceeding 95°C, and mechanical stress corresponding to a bending radius of 20 times the cable diameter over 20 cycles were applied to verify system reliability. The subsequent insulation assessments quantitatively confirmed performance variations induced by the combined stresses. The results demonstrate that the proposed platform is the first system capable of simultaneously applying thermal, electrical, and mechanical stresses to dynamic submarine cables, and its operational performance has been successfully validated. This platform enables realistic reliability evaluation of dynamic cables used in floating offshore wind farms and is expected to improve the overall operational reliability of offshore wind power systems.

The rapid proliferation of artificial intelligence (AI) servers and high-performance computing systems has significantly elevated the technical and reliability requirements for multilayer ceramic capacitors (MLCCs). In such systems, MLCCs are critical passive components that must deliver high capacitance, fast transient response, and robust insulation performance under high temperature, voltage, and current density. This review examines the material, structural, and process innovations that underpin MLCC performance in AI applications. Key topics include the development of ultrathin dielectric layers (<0.5 μm), rare-earth doped BaTiO₃-based dielectrics with enhanced DC bias stability, and core-shell microstructures designed for temperature and field resilience. The paper also explores insulation degradation mechanisms―such as vacancydriven conduction and demixing―and advanced reliability assessment methodologies, including HALT, TSDC, and the tipping point framework. Comparisons with automotive-grade MLCCs highlight the unique requirements of AI systems, such as ultraminiaturization, high volumetric efficiency, and ppm-level field failure rates. Finally, the review discusses emerging trends in MLCC technology, including particle engineering, interface stabilization, and advanced lamination techniques, and provides insight into the future direction of capacitor development tailored to AI data center environments.

To ensure the long-term reliability of flexible photovoltaic (FPV) modules, it is crucial to develop an effective moisture barrier layer that prevents the infiltration of moisture and oxygen. We developed such a layer composed of parylene (700 nm) and AlOx (70 nm), optimizing its material properties, moisture-blocking performance, and processing conditions. The barrier layer applied to the Ethylene Tetrafluoroethylene (ETFE) substrate demonstrated a water vapor transmission rate (WVTR) of 6.33 × 10^-2 g/m²/day and an average visible light transmittance (AVT) of 85.3% over the 380-780 nm wavelength range. For the FPV module with this barrier, Damp/Heat (DH) reliability testing was conducted at 85℃ and 85% relative humidity for up to 1,000 hours. During testing, the power conversion efficiency (PCE) decreased slightly from 25.4% (0 hr) to 24.7% (1,000 hr), reflecting a minimal reduction of only 0.7%. The primary cause of degradation was identified as a -4% relative change in shortcircuit current density (JSC) before and after DH testing. Consequently, the ETFE/parylene/AlOx multilayer moisture barrier proved highly effective in ensuring the long-term reliability of solar modules.

The rapid evolution of wearable technology has driven a surge in demand for sustainable, self-powered electronic devices. Flexible thermoelectric materials, capable of converting body heat into electricity, have emerged as a promising solution for powering next-generation wearables. This review comprehensively examines recent progress in organic (polymer-based) and hybrid thermoelectric materials, focusing on their design, fabrication, and integration into flexible architectures suitable for conformal contact with human skin. Key developments include advanced doping strategies, post-treatment techniques, and composite engineering, particularly in conductive polymers such as PEDOT: PSS and P3HT, which have significantly enhanced power factors and mechanical flexibility. Additionally, the integration of high-performance inorganic materials into stretchable systems has further elevated device efficiency and durability. The review highlights breakthroughs, ongoing challenges, and future opportunities in realizing practical, scalable, and high-efficiency wearable thermoelectric generators for sustainable energy harvesting applications.

Abstract In this study, to develop composition ceramics for energy harvesting devices, Pb(Ni_1/3Nb_2/3)O₃-Pb(Zr Ti)O₃ system ceramics substituted with Pb(Mg_1/2W_1/2)O₃ were manufactured by conventional mixed oxide method using Li₂CO₃ and Na₂CO₃ (LNCO) as sintering aids. Their microstructure and piezoelectric properties were also investigated. At the specimen sintered at 930℃, high values of piezoelectric properties appeared: the dielectric constant (εr) of 2,522 planar electromechanical coupling factor kp of 0.602, and k₃₁ of 0.385, d31 = 229 [pC/N], g₃₁ = 10.13 [mV.m/N], Qm of 70, respectively. These values were suitable for the application of devices such as energy harvesting devices and ultrasonic devices.

With the extensive industrial growth driven by the Fourth Industrial Revolution and the excessive use of fossil fuels, greenhouse gas emissions have accelerated global warming. Energy harvesting technologies have garnered significant attention as a potential solution to this issue. Among them, triboelectric nanogenerators (TENGs) have emerged as promising candidates for energy collection and conversion. However, TENGs typically face limitations in providing an efficient energy supply due to their high output voltage and low output current. To overcome these challenges, numerous studies have explored various methods to enhance the output performance by increasing the surface area of the triboelectric materials. Herein, we report a high-output TENG fabricated through a simple scratch process. By utilizing sandpaper, typically used for abrasion or polishing, the surface roughness of the triboelectric material PFA was increased through surface scratching. The surface-engineered TENG, prepared through this simple and rapid process, demonstrated enhanced output characteristics with a voltage of 276 V and a current of 72 μA, showing a 21% increase in voltage and a 41% increase in current compared to the non-engineered counterpart, providing sufficient energy to power an LED. These results indicate that the scratch-based surface modification process using sandpaper offers an effective solution for improving triboelectric output performance, establishing TENGs as a key contributor to sustainable energy supply.

Energy harvesting technology offers an innovative solution for providing self-sustaining power to wearable and implantable electronic devices. However, traditional energy harvesters face limitations in operating within electrolytic environments or at low motion speeds. To overcome these challenges, a mechano-electrochemical energy harvester using carbon nanotubes has been developed. This technology relies on electrochemical ion movement to induce changes in electrochemical double-layer capacitance, enabling operation within electrolytes and optimizing performance at low deformation speeds. This environmentally friendly and sustainable energy solution is expected to play a crucial role in the advancement of future smart systems and wearable technologies.

One method to increase the output of solar modules is the application of the Half-cut technique, which requires a scribing process involving direct irradiation of infrared lasers on the solar cells. During this process, the laser melts the surface of the solar cells at high temperatures, enabling mechanical division, but this can lead to output loss due to thermal degradation caused by the laser. To minimize such losses, a low-temperature and low-loss division method has been devised. In this study, we compared the electrical characteristics and leakage currents affecting output degradation between the newly devised low temperature and low-loss cell division method and the conventional laser division method. Additionally, we conducted a 3-point flexural test to evaluate the mechanical properties of both methods.

Climate conditions, especially transport and storage, are a very important factor in the process of sampling and testing insulation oil in the field. The samples of insulating oil exposed to the atmosphere affect the dielectric strength, total acid number and moisture test value by oxygen and high humidity environment and may also affect the results according to the criteria specified in each test. Therefore, reliable test values for insulating oil testing require consideration of the atmospheric environment of the test site, including oxygen and humidity. In this paper, each test was conducted on insulating oil exposed to various time and humidity environments, and the effect of the atmospheric environment on the test results was analyzed by comparing and analyzing with the first insulating oil.

The polymer crystallization process, promoting the formation of ferroelectric β-phase, is essential for developing polyvinylidene fluoride (PVDF)-based high-performance piezoelectric energy harvesters. However, traditional high-temperature annealing is unsuitable for the manufacture of flexible piezoelectric devices due to the thermal damage to plastic components that occurs during the long processing times. In this study, we investigated the feasibility of introducing a flash lamp annealing that can rapidly induce the β-phase in the PVDF layer while avoiding device damage through selective heating. The flash lightirradiated PVDF films achieved a maximum β-phase content of 76.52% under an applied voltage of 300 V and an on-time of 1.5 ms, a higher fraction than that obtained through thermal annealing. The PVDF-based piezoelectric energy harvester with the optimized irradiation condition generates a stable output voltage of 0.23 V and a current of 102 nA under repeated bendings. These results demonstrate that flash lamp annealing can be an effective process for realizing the mass production of PVDF-based flexible electronics.

In this paper, the electrical properties of liquid insulating oil were analyzed by changing the ambient temperature change at 10℃ in-tervals from 0℃ to 30℃ through an insulation breakdown experiment in order to analyze the insulation performance of liquid in-sulating oil that varies according to temperature changes. As a result, it was confirmed through experiments that the lower the am-bient temperature, the higher the insulation breakdown voltage, depending on both the electrode shape and the electrode interval, and it was determined that the lower the ambient temperature, the higher the insulation performance of the liquid insulating oil.

The energy demand in the world is expected to exceed 740 million TJ by 2040 and our dependence on fossil fuels needs to be switched to sustainable and renewable energy sources like solar energy. Building Integrated Photovoltaic (BIPV) is one of the best approaches to extracting solar energy. There are more than 200 BIPV products in the market currently but when it comes to integrating these products into the technical aspects such as buildings’ structural integrity, thermal, daylight retainment and aesthetic prospects to be considered. The share of BIPV integration potential of different building types in the world of residential, agricultural, industrial, commercial and other buildings account for 66%, 4.8%, 8.1%, 19.9%, and 1.2% accordingly. Many solar technologies developed to achieve architectural requirements, but the main problem is the trade-off between efficiency and aesthetic appeal, which is less than 10% in coloured and transparent solar modules. This paper discusses the different applications of solar photovoltaics (PV) in building architecture, technical requirements, and different module technologies. The article provides a comprehensive guide for researchers and designers working on the development of BIPV integrations.

The Internet of Things (IoT) device is a key component for Industry 4.0, which is the network in homes, factories, buildings, and infrastructures to monitor and control the systems. To demonstrate the IoT network, batteries are widely utilized as power sources, and the batteries inevitably require repeated replacement due to their limited capacity. Magneto-mechanoelectric (MME) generators are one of the candidate to develop self-powered IoT systems since MME generators can harvest electricity from stray alternating current (AC) magnetic fields arising from electric power cables. Herein, we report a magnetomechano- triboelectric generator enabled by a ferromagnetic-ferroelectric composite. In the triboelectric nylon matrix, a ferromagnetic carbonyl iron powder (CIP) was introduced to induce magnetic force near the AC magnetic field for MME harvesting. Additionally, a ferroelectric ceramic powder was also added to the MME composite material to enhance the chargetrapping capability during triboelectric harvesting. The final ferromagnetic-ferroelectric composite-based MME triboelectric harvester can generate an open-circuit voltage and a short-circuit current of 110 V and 8 μA, respectively, which were enough to turn on a light emitting diode (LED) and charge a capacitor. These results verify the feasibility of the MME triboelectric generator for not only harvesting electricity from an AC magnetic field but also for various self-powered IoT applications.

Energy harvesting technology, which converts wasted energy sources in everyday life into usable electric energy, is gaining attention as a solution to the challenges of charging and managing batteries for the driving of IoT sensors, which are one of the key technologies in the era of the fourth industrial revolution. Hybrid energy harvesting technology involves integrating two or more energy harvesting technologies to generate electric energy from multiple energy conversion mechanisms. In this study, a hybrid energy harvesting device called TMPPEG (thermo-magneto-piezoelectric-pyroelectric energy generator), which utilizes low-grade waste heat, was developed by incorporating PVDF polymer piezoelectric components and optimizing the system. The variations in piezoelectric output and thermoelectric output were examined based on the spacing of the clamps, and it was found that the device exhibited the highest energy output when the clamp spacing was 2 mm. The voltage and energy output characteristics of the TMPPEG were evaluated, demonstrating its potential as an efficient hybrid energy harvesting component that effectively harnesses low-grade waste heat.

Stretchable piezoelectric energy harvester (S-PEHs) based on composite materials are considered one of the potential candidates for realizing wearable self-powered devices for smart clothing and electronic skin. However, low energy conversion performance and expensive stretchable electrodes are major bottlenecks hindering the development and application of S-PEHs. Here, we fabricated the S-PEH by adopting the piezoelectric composites with enhanced stress transfer properties and kirigamipatterned textile electrodes. The optimum contents of piezoelectric BaTiO₃ nanoparticles inside the carbon nanotube/ecoflex composite were selected as 30 wt% considering the trade-off between stretchability and energy harvesting performance of the device. The final S-PEH shows an output voltage and mechanical stability of ~5 V and ~3,000 cycles under repeated 150% of tensile strain, respectively. This work presents a cost-effective and scalable way to fabricate stretchable piezoelectric devices for self-powered wearable electronic systems.

In this paper, in order to analyze high electrical insulation and cooling performance using mineral oil, the liquid insulating oil was changed in electrode shape and distance between electrodes to compare and analyze electrical characteristics according to equal electric field, quasi-equivalent electric field, and unequal electric field. As a result, the breakdown voltages were 36,875 V and 36,875 V in the form of sphere-sphere and plate-plate electrodes with equal electric fields. The breakdown voltage was 31,475 V in the sphere-plate electrode type, which is a quasi-equilibrium field, and the breakdown voltage was 28,592 V, 27,050 V, and 22,750 V in the needle-needle, sphere-needle, and needle-plate electrode types, which are unequal fields. Through this, it is possible to know the difference in breakdown voltage according to the type of electric field. The more equal the field, the higher the breakdown voltage, and the more unequal field, the lower the breakdown voltage. The difference in insulation breakdown voltage could be seen depending on the type of electric field, the insulation breakdown voltage was higher for the more equal electric field, and the insulation breakdown voltage was lower for the more unequal electric field. Also, it was confirmed that the closer the distance between the electrodes, the higher the insulation breakdown voltage, the higher the insulation breakdown current, and the insulation breakdown voltage and the insulation breakdown current were proportional.

Triboelectric devices are attracting attention from researchers as self-powered electronic systems that can instantly convert mechanical input into electrical energy output. To improve triboelectric energy harvesting performance, increasing the number of contacts as well as the contact area has been carried out by numerous researchers. In this study, we design a shaker-type energy harvester which is called as maracas triboelectric generator (M-TEG), inspired by the structure of maracas, one of the musical percussion instruments. A tripod frame is inserted to the inside of a cylindrical case, which is a device with the electrodes of aluminum and copper. Then, the triboelectric energy harvesting characteristics between polypropylene (PP) balls and the electrodes are measured. The M-TEG with the frame generates the energy harvesting signals up to ~100 V and ~2.5 μA due to larger contact area and numbers, which enhances the voltage and current output by 250% and 610% compared to that without the frame, respectively. This study presents the feasibility of self-powered sensors and toys using improved triboelectric energy performance with a low-cost and simple manufacturing process in the interesting structure.

Heaters using the resistance heating principle are used in various industrial fields that require heat and are also essentially used in bidet among small home appliances. A planar heater and a coil-inserted heater mounted on a conventional commercially used bidet have disadvantages and limitations of complicated manufacturing process and local heating. In this study, silver-palladium (Ag-Pd) powder material was used for a screen-printing process that is more advantageous in achieving simplification than the existing process, and a rod-type heater for bidet was manufactured. The on-off cycle test under actual conditions was conducted to confirm the durability and the capability of the fabricated heater, and the fabricated heater operated more than 2,600 on-off cycles, which means it could be applied for a commercial product. In addition, through the on-off cycles under harsh conditions, the cause of failure was identified after the test that the durability limit temperature of the heater was 850℃. Through Ag-Pd rod heater in this study, it is expected to contribute to the efficient development of electrode materials for heaters and the improvement of the durability of heaters in the future.

Energy harvesting technologies that can convert wasted various energy into usable electrical energy have been widely investigated to overcome the limitation of batteries for the powering of IoT sensors and small electronic devices. Hybrid energy harvesting is known as a technology that enhances the output power of single energy harvesting device by housing two or more various energy harvesting mechanisms. In this study, we introduce a hybrid MME (Magneto-Mechano-Electric) generator coupled with the triboelectric effect. Through FEA modeling, four triboelectric materials, including PI (Polyimide), PFA(Teflon), Cu, and Al, were selected and compared with the expected triboelectric potentials. The effect of surface morphology was investigated as well. Among various combination of triboelectric materials and surface morphologies, PFA-Al combination with the surface morphology having nano-scale square projections showed highest output potential under triboelectrification. It is also experimentally confirmed that output voltage and power of the hybrid MME generator with triboelectric material combinations.

Recently, piezoelectric devices, such as ultrasonic surgery, ultrasonic atomizer, and ultrasonic speaker, are analyzed and designed by finite element simulation methods. However, the discrepancy between the design and the experiment results of the device typically occurs due to the inaccuracy of the piezoelectric material properties. To improve the simulation accuracy, the material properties of the PZT ceramics were better refined using parameter estimation method. The material parameters are elastic stiffness c^E_ij and piezoelectric constant e_ij of PZT ceramics. The impedance curve characteristics for the LTE mode of PZT ceramics were calculated. The mismatch between the simulation and the experimental data were compared and minimized by a least square method. Finally, the simulated impedance data were compared with the experimental data for the various vibration modes of PZT ceramics and the optimized material properties of PZT ceramics were verified. To further verify the accuracy, this method was also applied to piezoelectric PMN-PT single crystals.

Since the ZnO varistor is a semiconductor device, the internal thermal distribution during the varistor operation is recognized as an important factor in the performance and deterioration of the varistor. For an optimal varistor structure design, the thermal runaway phenomenon during the varistor operation was interpreted using the Comsol 5.2 analysis program by a finite element analysis. The maximum temperature of the center measured in the cross section of the ZnO varistor was confirmed to increase as the temperature moved from the lower electrode to the center towards the upper electrode up to 572.6 K. The electrodes are thinned so that the influence of the Schottky barrier is not great. The heat gradient balance is determined to be improved when the electrode of the hybrid form is introduced. The thickness, density, pore distribution, impurity uniformity, and particle size of the ZnO varistor are required, and it is determined that the pyrolysis gradient will be improved regardless of the electrode thickness. When these results are applied to design the ZnO varistor, the optimal structure of the ZnO varistor can be obtained.

Global warming is accelerating due to the use of fossil fuels that have been used continuously for centuries. Now, humankind recognizes its seriousness, and is conducting research on searching for eco-friendly and sustainable energy. In the field of solar energy, which is a kind of eco-friendly and sustainable, many studies are being conducted to enhance the output performance of the module. In this study, the output improvement for the shingled module structure was studied. In order to improve the output performance of the module, the thickness of the encapsulant was increased, and the lamination process conditions have been improved accordingly. After that, the crosslinking rate was analyzed, and the suitability of the lamination process conditions was judged using this. In addition, a peeling test was conducted to analyze the correlation between the adhesion of the encapsulant and the output performance of the module. Finally, the optimization for the encapsulant material and the lamination process conditions for high-power shingled modules was established, and accordingly, the market share of high-power shingled modules in the solar module market can be expected to rise.

Recent advancement of Internet of Things (IoT) and energy harvesting technology enable realization of flexible thermoelectric energy harvester (f-TEH), with technological prowess for use in biomedical monitoring system integrated applications. To expand a flexible thermoelectric energy harvesting platform, the f-TEH must be required for optimized flexible thermoelectric materials and device structure. In response to these demands related to thermoelectric energy harvesting, many research groups have investigated various f-TEHs applied as a power source for wearable electronics. As a key member of the f-TEH, film-based f-TEHs possess significant applicability in research to realize self-powered wearable electronics, owing to their excellent flexibility, low thermal conductivity, and convenient fabrication process. Thus, based on the rapid growth of thermoelectric film technology, this review aims to overview comprehensively the f-TEH made of various inorganic/organic thermoelectric materials including developed fabrication methods, high thermoelectric performance, and wide-range applications.

Liquid-based Triboelectric nanogenerator (L-TENG) is one of the alternatives to solid-based Triboelectric nanogenerator (S-TENG) because of the absence of surface damage which can decrease the durability of the generator. However, the L-TENG also has an obvious drawback of significantly lower output than that of S-TENG. This article produces water-sloshing-based electricity generating device (W-ED) with a new design of L-TENG that improves electrical output in portable form. The dual-electrode system, consisting of closed-loop circuit and inner electrode which enables water to contact directly in the bottle, can generate the open-circuit voltage and the short-circuit current of up to 348 V and 5.1 mA, respectively. By investigating the motion of water for each frequency, we propose that W-ED is suitable device for a variety of human motions. We expect that W-ED can be applied in small electrical devices or sensors in daily-use items.

Piezoelectric energy harvesting technologies, which can be used to convert the electricity from the mechanical energy, have been developed in order to assist or power the wearable electronics. To realize non-toxic and biocompatible electronics, the lead-free (Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃ (BCTZ) nanoparticles (NPs) are being studied with a great attention as flexible energy harvesting device. Herein, piezoelectric hybrid nanocomposites were fabricated using BCTZ NPs-embedded poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] matrix to improve the performance of flexible energy harvester. Output performance of the fabricated energy device was investigated by the well-optimized measurement system during the periodically bending and releasing motions. The generated open-circuit voltage and the short-circuit current of the piezoelectric hybrid nanocomposite-based energy harvester reached up to ~15 V and ~1.1 μA, respectively; moreover, the instantaneous power of 3.5 μW is determined from load voltage and current at the external load of 20 MΩ. This research is expected to cultivate a new approach to high-performance wearable self-powering electronics.