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Since their debut in 2012, triboelectric nanogenerators (TENGs) have attained high performance in terms of both energy density and instantaneous conversion, reaching up to 500 W m-2 and 85%, respectively, synchronous with multiple energy sources and hybridized designs. Here, a comprehensive review of the design guidelines of TENGs, their performance, and their designs in the context of Internet of Things (IoT) applications is presented. The development stages of TENGs in large-scale self-powered systems and technological applications enabled by harvesting energy from water waves or wind energy sources are also reviewed. This self-powered capability is essential considering that IoT applications should be capable of operation anywhere and anytime, supported by a network of energy harvesting systems in arbitrary environments. In addition, this review paper investigates the development of self-charging power units (SCPUs), which can be realized by pairing TENGs with energy storage devices, such as batteries and capacitors. Consequently, different designs of power management circuits, supercapacitors, and batteries that can be integrated with TENG devices are also reviewed. Finally, the significant factors that need to be addressed when designing and optimizing TENG-based systems for energy harvesting and self-powered sensing applications are discussed.

Soft and elastic fiber‐based electronic devices exhibiting high electromechanical stability are highly desirable for sustainable and continuous utilization in various applications. However, effectively assembling the cathode and anode in a single body without unwanted interconnections and realizing an intimate contact interface between the electrode and substrate remain challenging. Here, an electrical shortage‐free one‐body fiber system with double‐helix buckle electrodes created by torsion‐ and strain‐mismatch between carbon nanotube (CNT) ribbons and a rubber substrate is reported. The as‐used CNT ribbons serve as the strain‐insensitive electrode, while the rubber mandrel‐core fiber acts as the key matrix in the following three aspects: as an elastic substrate that ensures reversible structural changes during mechanical deformations; as a dielectric layer for capacitive strain sensing; and as an electrothermal expansion element for tensile contraction. Moreover, because of the mismatch‐induced torque‐balance structure, the helically wrapped CNT buckle electrodes can effectively absorb the applied stresses without noticeable delamination and electrical conductance loss. Consequently, the double‐helix buckle fiber system can reliably provide multiple functions, viz. detection of various deformations (e.g., stretching, twisting, and pressing), electrochemical energy storage with excellent strain tolerance, and reversible electrothermal tensile actuation. [ABSTRACT FROM AUTHOR]

Flexible piezoelectric sensors have been spotlighted as an essential human–machine interface (HMI) by obtaining high‐quality data from omnipresent biomechanical inputs. Because human voice is the most intuitive bio‐signal among them, flexible piezoelectric acoustic sensors (f‐PAS) have a potential to shift the paradigm of HMI technologies. Despite the reported outstanding performance such as high sensitivity and speaker recognition accuracy, the theoretical investigation of f‐PAS has been insufficient to realize future customized development, because sensing principles are fundamentally different from commercialized microphones. Here, a theoretical framework of self‐powered f‐PAS by using mechanical and electrical physics is introduced. First of all, the basic theory of f‐PAS is compared with the auditory system of human cochlear. Based on the biomimetic trapezoidal shape, the resonant frequencies are analyzed with various structural and material conditions. In addition, the piezoelectricity of f‐PAS is derived to predict the sensitivity and SNR prior to experiments. To investigate sensor properties under the medium condition that is similar to human ear, the acoustic responses depending on the states of matter are theoretically compared. Finally, the distance limit of f‐PAS is studied with the correlations between piezoelectricity and sound pressure, which would provide novel strategies of functional material design for future applications of f‐PAS. [ABSTRACT FROM AUTHOR]

Flexible film capacitors with high energy storage density (Wrec) and charge–discharge efficiency (η) are a cutting-edge research topic in the current field of energy storage. In this work, flexible all-inorganic (Pb0.91La0.06)ZrO3 ((PbLa)ZrO3) thin films are designed and integrated on mica substrates by a sol–gel method. By adjusting the rapid annealing temperature of (PbLa)ZrO3 thin films, the influence of the microstructure on the electrical properties and energy storage performances has been comprehensively investigated. The results show that the (PbLa)ZrO3 thin films annealed at 550 °C have a nanocrystalline structure, which is beneficial to reducing energy loss and improving insulation performance. A large Wrec of 42.0 J cm−3 and an outstanding η of 90.2% are achieved in (PbLa)ZrO3 films via nanocrystalline engineering. Moreover, the flexible capacitor films exhibit good temperature stability (25–140 °C), frequency stability (1–10 k Hz), bending stability (104 cycles) and electric fatigue stability (107 cycles). This work is expected to promote the application of (PbLa)ZrO3-based film capacitors in energy storage systems. [ABSTRACT FROM AUTHOR]

The lack of theoretical understanding of triboelectrification has hindered the development of energy harvesting technologies like triboelectric nanogenerators. Focusing on polytetrafluoroethylene, a material with a strong triboelectric output, a model predictive of its triboelectric behavior, driving the development of improved nanogenerators are formulated. With a combined computational‐experimental approach it is shown that defluorination enhances polytetrafluoroethylene nanoscale triboelectric charging. Then a model, explaining the macroscale triboelectric output as determined by the competition of two mechanisms is developed. Defluorination enhances charging while also reducing the interface gap, favoring the backflow of electrons, and possibly reducing charging. However, numerical analysis shows that backflow is negligible, aligning with the prediction of increased triboelectric output. By building triboelectric nanogenerators with defluorinated polytetrafluoroethylene samples, achieved by X‐ray irradiation, a one‐order‐of‐magnitude output increase is demonstrated. The predictive models, supported by experiments, lead to an improved strategy for designing effective energy harvesting devices and new applicative breakthroughs. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the structural, microstructural, dielectric, and energy storage properties of Nd and Mn co-doped Ba0.7Sr0.3TiO3 [(Ba0.7Sr0.3)1−xNdxTi1−yMnyO3 (BSNTM) ceramics (x = 0, 0.005, and y = 0, 0.0025, 0.005, and 0.01)] via a defect dipole engineering method. The complex defect dipoles (M n T i " − V O ∙ ∙ ) ∙ and (M n T i " − V O ∙ ∙) between acceptor ions and oxygen vacancies capture electrons, enhancing the breakdown electric field and energy storage performances. XRD, Raman, spectroscopy, XPS, and microscopic investigations of BSNTM ceramics revealed the formation of a tetragonal phase, oxygen vacancies, and a reduction in grain size with Mn dopant. The BSNTM ceramics with x = 0.005 and y = 0 exhibit a relative dielectric constant of 2058 and a loss tangent of 0.026 at 1 kHz. These values gradually decreased to 1876 and 0.019 for x = 0.005 and y = 0.01 due to the Mn2+ ions at the Ti4+- site, which facilitates the formation of oxygen vacancies, and prevents a decrease in Ti4+. In addition, the defect dipoles act as a driving force for depolarization to tailor the domain formation energy and domain wall energy, which provides a high difference between the maximum polarization of Pmax and remnant polarization of Pr (ΔP = 10.39 µC/cm2). Moreover, the complex defect dipoles with optimum oxygen vacancies in BSNTM ceramics can provide not only a high ΔP but also reduce grain size, which together improve the breakdown strength from 60.4 to 110.6 kV/cm, giving rise to a high energy storage density of 0.41 J/cm3 and high efficiency of 84.6% for x = 0.005 and y = 0.01. These findings demonstrate that defect dipole engineering is an effective method to enhance the energy storage performance of dielectrics for capacitor applications. [ABSTRACT FROM AUTHOR]

Extensively studied transfer methods for producing high-performance flexible micro-light-emitting diodes (µLEDs) have limitations like high process cost and size constraints. Herein, we report a novel inorganic-based laser lift-off (ILLO) process, in which a new BaTiO3 (BTO) sacrificial layer is used to fabricate flexible thin-film µLEDs. The process, associated laser conditions, and carrier substrate types were optimized using theoretical simulations and experiments. The BTO sacrificial layer was successfully applied to the ILLO process via laser–material interactions, as verified by material analyses. Vertically structured flexible µLEDs were realized using BTO-based delamination, demonstrating the method's applicability to next-generation electronics. [ABSTRACT FROM AUTHOR]

In this study, Pb(Mg1/3Nb2/3)O3–Pb(Zr,Ti)O3 (PMN-PZT) single crystals were doped with hardener Mn at variable concentrations to fabricate a high-output magneto-mechano-electric (MME) generator. The dielectric constant and dielectric loss (tan δ) of the PMN-PZT crystal were gradually decreased by doping with 0 to 0.8 mol% hardener Mn acceptor. Owing to the low energy loss and enhanced energy conversion properties of the Mn-doped hard-type PMN-PZT, the MME generator achieved an improved magnetoelectric coefficient of 783.09 V per cm·Oe, and the corresponding mechanical quality factor was 315 at 0.8 mol% Mn under resonance frequency operation conditions. The Mn-modified MME device can generate a root mean square output power of 3.3 mW when an alternating current magnetic field of 8 Oe is applied, which is ∼1.8 times higher than that of the MME generator fabricated without Mn-doping. Finally, the electric power of the hard-type PMN-PZT MME generator was directly utilized to produce a self-powered light dimming system composed of an MME harvester, an energy conversion circuit, a CdS ambient light sensor, and a light-emitting diode. [ABSTRACT FROM AUTHOR]

In response to the increasing demand for wearable devices, the development of flexible energy harvesters as self-powering systems to replace batteries is accelerating. Flexible magnetoelectric (ME) composites, which can convert practical electrical energy from a magnetic field source, have attracted considerable attention for application in wearable magnetic devices. In this study, a 2-2 type structure based on a flexible magnetostrictive film with cobalt ferrite (CoFe2O4, CFO) nanofibers was adopted to obtain appropriate flexibility and magnetoelectric properties. The flexible ME composite was completely fabricated by coating piezoelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) onto a magnetostrictive film composed of CFO nanofibers and a polyimide matrix. Moreover, we conducted a multiphysics simulation and theoretically proved that a higher strain could be transferred to the piezoelectric layer at higher CFO concentrations, thus resulting in the generation of high magnetoelectric signals from the ME composite. The flexible, robust, and mechanically-stable ME composite reached an output voltage of 0.52 V and a current signal of 25 nA under an external AC magnetic field at 1 Hz. This study led to the development of a fully-flexible design of a bilayer ME composite prepared using a simple fabrication process providing a future avenue for wearable magnetoelectric energy harvesting. [ABSTRACT FROM AUTHOR]