Flexible Energy Harvester Research Articles

Fabrication and evaluation flexible lead-free piezoelectric energy harvesters on stainless steel foils

Fabrication and evaluation flexible lead-free piezoelectric energy harvesters on stainless steel foils

Laser induced flexible micro-supercapacitor for pressure sensing

Portable, wearable electronic devices have spurred the rapid development of flexible and stretchable energy harvesting/storage devices with high energy density, superior mechanical stability, and long cycle life. Micro-supercapacitor (MSC) has attracted wide interest due to their advantages of high power density, rapid charge and discharge, and long cycle life. Fabrication of flexible supercapacitors based on laser induced graphene (LIG) has shown strong advantages and potential for flexible sensor power supply. The purpose of this paper is to propose and develop a laser induced flexible micro-supercapacitor (FMSC) for pressure sensors. FMSC is manufactured from a planar forked finger electrode made of graphene induced by CO2 laser radiation commercial Polyimide (PI) film and PVA polymer gel electrolyte. The FMSCs prepared by this method exhibit good electrochemical properties and excellent mechanical properties. The microscopic morphology of LIG was investigated using SEM, and the optimal laser-induced power was determined to be 12.5%. In this paper, a novel fork-finger electrode pattern was applied to improve the performance of FMSCs by optimizing the structure of planar interdigital electrodes, and the FMSCs prepared at 12.5% power showed excellent supercapacitance performance at a voltage window of 0.8 V with a specific capacitance of 2.21 mF/cm2. The FMSCs were made by assembling commercial PI films, PVA, and H3PO4 simple materials, which makes it possible to prepare FMSCs at low cost and high efficiency based on laser direct writing technology. FMSCs provide energy to the flexible sensors and continuously collect energy to charge FMSCs through an integrated flexible energy harvester, which makes FMSCs promising for flexible self-powered wireless sensing platforms.

Polyaniline/SWCNT composite films prepared via the solvent-induced strategy for flexible energy harvesting

Flexible thermoelectric nanocomposite films are prepared via a facile solvent-induced strategy, exhibiting high power factor at room temperature. The thermoelectric module prepared from the films exhibits excellent output performance.

Plasma-jet printing of colloidal thermoelectric Bi2Te3 nanoflakes for flexible energy harvesting.

Thermoelectric generators (TEGs) convert temperature differences into electrical power and are attractive among energy harvesting devices due to their autonomous and silent operation. While thermoelectric materials have undergone substantial improvements in material properties, a reliable and cost-effective fabrication method suitable for microgravity and space applications remains a challenge, particularly as commercial space flight and extended crewed space missions increase in frequency. This paper demonstrates the use of plasma-jet printing (PJP), a gravity-independent, electromagnetic field-assisted printing technology, to deposit colloidal thermoelectric nanoflakes with engineered nanopores onto flexible substrates at room temperature. We observe substantial improvements in material adhesion and flexibility with less than 2% and 11% variation in performance after 10 000 bending cycles over 25 mm and 8 mm radii of curvature, respectively, as compared to previously reported TE films. Our printed films demonstrate electrical conductivity of 2.5 × 103 S m-1 and a power factor of 70 μW m-1 K-2 at room temperature. To our knowledge, these are the first reported values of plasma-jet printed thermoelectric nanomaterial films. This advancement in plasma jet printing significantly promotes the development of nanoengineered 2D and layered materials not only for energy harvesting but also for the development of large-scale flexible electronics and sensors for both space and commercial applications.

Multifunctional flexible Ag2Te-nylon nanocomposite freestanding film for harvesting thermal and mechanical energy

Constructing a multifunctional material for harvesting different types of energy requires a novel strategy that can offer a higher output while simultaneously reducing the device's size and increasing its usability. Here we have developed a flexible Ag2Te-nylon nanocomposite film-based hybrid device using a vacuum filtration technique that can harvest simultaneously thermal and mechanical energy using the thermoelectric and triboelectric effect. The flexible hybrid device can generate a power of ∼ 35 nW corresponding to a power density of 58 µW/cm2 through simple finger touch by thermoelectric effect, whereas an output power of ∼7 nW corresponding to a power density of 23 nW/cm2 can be generated via rubbing with fingertips due to the triboelectric effect. In the Ag2Te-PVDF nanocomposite film, an output power of 0.3 µW (corresponding to a power density of 1 µW/cm2) has been achieved while rubbing with fingertips. The fabricated device in this study is the only one of its kind where a single material can harvest thermal and mechanical energy. The flexible film's hybrid energy harvesting feature, along with the advantages of low cost and simple synthesis, makes it a promising choice for harvesting energy from human activities.

Perovskite Piezoelectric-Based Flexible Energy Harvesters for Self-Powered Implantable and Wearable IoT Devices

In the ongoing fourth industrial revolution, the internet of things (IoT) will play a crucial role in collecting and analyzing information related to human healthcare, public safety, environmental monitoring and home/industrial automation. Even though conventional batteries are widely used to operate IoT devices as a power source, these batteries have a drawback of limited capacity, which impedes broad commercialization of the IoT. In this regard, piezoelectric energy harvesting technology has attracted a great deal of attention because piezoelectric materials can convert electricity from mechanical and vibrational movements in the ambient environment. In particular, piezoelectric-based flexible energy harvesters can precisely harvest tiny mechanical movements of muscles and internal organs from the human body to produce electricity. These inherent properties of flexible piezoelectric harvesters make it possible to eliminate conventional batteries for lifetime extension of implantable and wearable IoTs. This paper describes the progress of piezoelectric perovskite material-based flexible energy harvesters for self-powered IoT devices for biomedical/wearable electronics over the last decade.

Lead-Free MDABCO-NH4I3 Perovskite Crystals Embedded in Electrospun Nanofibers.

In this work, we introduce lead-free organic ferroelectric perovskite N-methyl-N'-diazabicyclo[2.2.2]octonium)-ammonium triiodide (MDABCO-NH4I3) nanocrystals embedded in three different polymer fibers fabricated by the electrospinning technique, as mechanical energy harvesters. Molecular ferroelectrics offer the advantage of structural diversity and tunability, easy fabrication, and mechanical flexibility. Organic-inorganic hybrid materials are new low-symmetry emerging materials that may be used as energy harvesters because of their piezoelectric or ferroelectric properties. Among these, ferroelectric metal-free perovskites are a class of recently discovered multifunctional materials. The doped nanofibers, which are very flexible and have a high Young modulus, behave as active piezoelectric energy harvesting sources that produce a piezoelectric voltage coefficient up to geff = 3.6 VmN-1 and show a blue intense luminescence band at 325 nm. In this work, the pyroelectric coefficient is reported for the MDABCO-NH4I3 perovskite inserted in electrospun fibers. At the ferroelectric-paraelectric phase transition, the embedded nanocrystals display a pyroelectric coefficient as high as 194 × 10-6 Cm-2k-1, within the same order of magnitude as that reported for the state-of-the-art bulk ferroelectric triglycine sulfate (TGS). The perovskite nanocrystals embedded into the polymer fibers remain stable in their piezoelectric output response, and no degradation is caused by oxidation, making the piezoelectric perovskite nanofibers suitable to be used as flexible energy harvesters.

Breakage-resistant hydrogel electrode enables ultrahigh mechanical reliability for triboelectric nanogenerators

Hydrogel based triboelectric nanogenerators (H-TENGs) are deemed as one of most promising flexible energy harvesting and self-powered systems due to its multifunctionality, but the poor mechanical properties of hydrogel electrode bring a major risk of shortening the service life of H-TENGs in case of huge physical impact. Herein, a durable conductive hydrogel electrode with breakage-resistant capacity is developed utilizing the Hofmeister effect on starch polymers through solvent-exchange strategy. Owing to bundled starch chains within hydrogel, the breakage-resistant hydrogel electrode possesses excellent mechanical reliability, including outstanding modulus, fracture energy, anti-puncture capacity and long-term stability. Furthermore, the reliable hydrogel electrode endows triboelectric nanogenerator with good electrical output performances and superb damage immunity, prolonging its service life under accidental physical impact. More significantly, this fabricated triboelectric nanogenerator shows great potential in high-impact application. This investigation offers a versatile and effective way to design next generation hydrogel-based triboelectric nanogenerator with superior damage immunity and long-service life.

Flexible Energy Harvesting Device Based on Porous Piezoelectric Sponge

Flexible Energy Harvesting Device Based on Porous Piezoelectric Sponge

Advanced Functional Composite Materials toward E‐Skin for Health Monitoring and Artificial Intelligence

AbstractElectronic skin (E‐skin), especially the wearable sensors efficiently detect various stimuli attracted huge research interest owing to their potential applications in health monitoring and artificial intelligence. On the other hand, functional polymer composites possessing excellent properties such as light weight, good flexibility, and superior electrical performances, are promising candidates as building blocks for flexible electronics. Accordingly, tremendous efforts are devoted to the development of polymer composites with functional properties for E‐skin applications. Here, recent advances on the controlled fabrication of various fillers based functional polymer composites and their diverse applications in E‐skin are reviewed. In addition, contemporary studies on fabrication strategies, working mechanisms, and device performance for E‐skin based on the functional polymer composites are reviewed, including flexible pressure sensors, strain sensors, temperature sensors, energy harvesters, and transistors. Furthermore, the applications of functional composite based flexible electronics in healthcare and artificial intelligence are discussed. Finally, the existing challenges and opportunities for the functional composite materials based E‐skin are summarized.

All‐Ceramic Flexible Piezoelectric Energy Harvester

AbstractWith the rapid development of self‐powered electronics such as wearables, implantable devices, and sensor networks, there is an increasing demand for power sources that have a high power density and a long lifespan to keep the entire system operational. Flexible piezoelectric materials with the capability of mechanical‐to‐electrical energy conversion have attracted significant interest because of their immense potential for harvesting human biomechanical energy. Herein, 3 mol.% yttrium stabilized zirconia ribbon ceramic is selected as a unique substrate to manufacture a large‐scale and all‐ceramic flexible Pb(Zr0.52Ti0.48)O3 piezoelectric energy harvester via the cost‐effective one‐step process. The flexible piezoelectric energy harvester delivers excellent performance with an open‐circuit voltage of ~105 V and short‐circuit current of ~0.58 µA under mechanical strain equivalent to human movement. Moreover, the output voltage of a flexible piezoelectric energy harvester varies linearly with strain, allowing it a promising candidate as a self‐powered strain sensor. Of particular importance is that a large‐scale piezoelectric energy harvester (4 × 4 cm2) can simultaneously light up eight commercial light emitting diodes without any external power source and circuit. This research provides an innovative approach to the fabrication of high‐performance and large‐scale flexible piezoelectric energy harvesters as well as self‐powered micromechanical devices.

A 22-m Operation Range Semi-Passive UHF RFID Sensor Tag With Flexible Thermoelectric Energy Harvester

This article presents a wireless temperature sensor tag able to work in both fully passive mode and in semi-passive mode when assisted by a flexible thermoelectric generator (TEG). The sensor tag consists of an EPC C1G2/ISO 18000-6C ultrahigh-frequency (UHF) radio frequency identification (RFID) integrated circuit (IC) connected to a low-power microcontroller unit (MCU) that samples and collects the temperature from a digital temperature sensor. With a temperature gradient as low as 2.5 °C, the test results show that the TEG provides an output power of 400 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$ </tex-math></inline-formula> W with an output voltage of 40mV. Bymeans of an up-converter in order to boost the TEG output voltage, this harvester supplies the power required to the sensor tag for a 2-conv/s data rate in semi-passive mode. Moreover, when the tag operates in semi-passive mode, a communication range of 22.2 m is measured for a 2-W effective radiated power (ERP) reader. To the best of our knowledge, the proposed TEG-assisted sensor tag shows the longest communication range and the only one that provides stable external power at low-temperature gradients. The measured performance and the chosen architecture allow using the wireless sensor in multiple industrial or biomedical applications.

Expedient secondary functions of flexible piezoelectrics for biomedical energy harvesting.

Flexible piezoelectrics realise the conversion between mechanical movements and electrical power by conformally attaching onto curvilinear surfaces, which are promising for energy harvesting of biomedical devices due to their sustainable body movements and/or deformations. Developing secondary functions of flexible piezoelectric energy harvesters is becoming increasingly significant in recent years via aiming at issues that cannot be addressed or mitigated by merely increasing piezoelectric efficiencies. These issues include loose interfacial contact and pucker generation by stretching, power shortage or instability induced by inadequate mechanical energy, and premature function degeneration or failure caused by fatigue fracture after cyclic deformations. Herein, the expedient secondary functions of flexible piezoelectrics to mitigate above issues are reviewed, including stretchability, hybrid energy harvesting, and self-healing. Efforts have been devoted to understanding the state-of-the-art strategies and their mechanisms of achieving secondary functions based on piezoelectric fundamentals. The link between structural characteristic and function performance is unravelled by providing insights into carefully selected progresses. The remaining challenges of developing secondary functions are proposed in the end with corresponding outlooks. The current work hopes to help and inspire future research in this promising field focusing on developing the secondary functions of flexible piezoelectric energy harvesters.

A review of flexible lead-free piezoelectric energy harvester

Piezoelectric nanogenerator has emerged as a promising power generation device that converts mechanical energy into electrical energy. Flexible and stretchable piezoelectric energy harvesters can detect low frequencies like heartbeat, footsteps, ambient noise, and airflow, which is promising for further application. Thus, the development of a lead-free piezoelectric nanogenerator is required owing to its less toxic nature. One-dimensional ZnO (nanowire and nanorods) and perovskite-based materials (BaTiO 3 and BiFeO 3 ) have been widely investigated for piezoelectric nanogenerators because of their excellent piezoelectric properties and environmental friendliness. Hitherto, various electrodes, substrates, nanostructures, and polymers have been utilized to improve the efficiency of piezoelectric devices. In this review, we discuss the state-of-the-art achievements, stretchable piezoelectric nanowire, nanocomposite nanogenerators, and future possibilities of lead-free flexible energy harvesting devices.

Optimal array alignment to deliver high performance in flexible conducting polymer‐based thermoelectric devices

• High charge mobility and optimal oxidation level leads to high power factor;. • Identification of the optimal distance between two adjacent TE arrays for devices;. • A flexible thermoelectric device shows a power density of 1.21 µW∙cm −2 . Flexible thermoelectric devices (F-TEDs) show great potentials to be applied in curved surface for power generation by harvesting low-grade energy from human body and other heat sources. However, their power generation efficiency is constrained by both unsatisfactory constituent materials performance and immature device design. Here, we used an optimal alignment of vertically-aligned poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) arrays to assemble a 2.7 × 3.2 cm 2 F-TEDs, exhibiting a maximum power output of 10.5 µW. Such a high performance can be ascribed to the outstanding power factor of 198 µW m −1 K −2 by the synergetic effect of both high charge mobility and optimal oxidation level and the optimized array alignment that maximizes the temperature difference utilization ratio across the TE legs. Particularly, optimized leg distance of 6 mm and leg length of 12 mm are determined to realize a high temperature difference utilization ratio of over 95% and a record-high output power density of 1.21 µW cm −2 under a temperature difference of 30 K. Further, reliable bending (1000 cycles) and stability (240 h) tests indicate the outstanding mechanical robustness and environmental stability of the developed F-TEDs. This study indicates our reasonable device design concept and facile material treatment techniques secure high-performance F-TEDs, serving as a reference for other flexible energy harvesting devices with wide practical applications.

Flexible fabric-based GaAs thin-film solar cell for wearable energy harvesting applications

GaAs photovoltaic (PV) cells have been extensively studied for flexible energy harvesting devices due to their merits such as thin-film feasibility, flexibility, and high-efficiency. However, GaAs-based thin-film PV cells have a limitation for the applications in wearable platform since they are not compatible with fabric carrier. To handle this problem, we report thin-film transfer technique that involves a sacrificial layer with a double-layer structure, an Au–Au bonding technique, a Cr/Au bilayer to induce metal stress, and an etchant for fast epitaxial lift-off (ELO). In addition, a polyimide layer attached underneath the fabric substrate not only protects the fragile epi layer but also accelerates the lateral etching via spontaneous bending. The application of these techniques enables the successful transfer of GaAs thin-film PV epi structures onto fabric platform without degrading crystal quality. Fabric-based GaAs PV cells are fabricated via the standard PV cell fabrication process. The platform expansion of GaAs thin-film techniques has great potential for large-scale commercialization. • III-V epi-layers onto fabric substrate can be realized without degrading crystal quality. • The GaAs solar cells are directly integrated with fabric platform. • High efficiencies over 17.49% can be achieved on fabric platform. • Fabric-based GaAs solar cells present the stable output power with high flexibility.

Enhancing the Piezoelectric Sensing of CFO@PDA/P(VDF-TrFE) Composite Films through Magnetic Field Orientation.

Magnetic nanofiller is helpful for improving the piezoelectric properties of P(VDF-TrFE)-based composites, which shows promising potential as a flexible sensor or energy harvester. In this work, we use the interaction between the magnetic nanofiller and magnetic field to modify the structure of CoFe2O4 (CFO)@polydopamine (PDA)/P(VDF-TrFE) composite, in which CFO@PDA works as the nanofiller into the P(VDF-TrFE) matrix. It was found that the magnetic field orientation during polymer curing can significantly increase the content of the β-phase and d33 of the composite. Regarding a typical composite film with 7 wt % CFO@PDA, the composite exhibits versatile sensing originated from the ball impact, hot-water droplet, bending, and pressing. In a noncontact magnetic field-driven experiment, the magnetic field oriented film produced the highest output voltages of 17.4 mV at 4 Hz and 12 mV at a drive amplitude of 19 Vpp, in contrast to the values of 7.1 mV and 7 mV for the film without magnetic field orientation, respectively. The LED without any charging capacitor can be instantaneously lighted through vertically pressing the oriented films. Thus, this work proposes a strategy of magnetic field orientation to improve the piezoelectric performance of the CFO@PDA/P(VDF-TrFE) multifunctional composite film.

Highly tailorable, ultra-foldable, and resorbable thermoelectric paper for origami-enabled energy generation

Recently, owing to the increased focus on environmental initiatives such as the green campaign and green economy, thermoelectric (TE) energy harvesting technology using polymer-based TE materials has attracted significant attention. Among the various polymers used in TE materials, cellulose plays a crucial role in substituting petroleum-based polymers as it is an abundant natural organic biomass resource. Herein, we first developed the origami and kirigami-enabled resorbable TE paper, with a self-assembled inorganic particle network layer below the cellulose polymer bio-matrix layer, through a simple drop-casting process. The prepared p- and n-type TE papers exhibited relatively high-power factor values of 3.11 and 1.16 μW·m−1·K−2, respectively, at 298 K. Furthermore, the fabricated flexible TE energy harvester (f-TEH) achieved an output performance of 38.55 mV, 12.14 μA, and 95.17 nW for a temperature difference of 24 K without the degradation of electrical and mechanical stability. Finally, we demonstrated the high applicability of TE papers in TEHs of complicated shapes by cutting or folding the materials and analyzing their TE performance. We believe that the results of this study not only present a breakthrough in designing tailorable and foldable TEHs for energy harvesting applications but also have significant implications in the field of green technology.

Synthesis of a nitrogen doped reduced graphene oxide based ceramic polymer composite nanofiber film for wearable device applications

In this study, piezoelectric composite nanofiber films were fabricated by introducing nitrogen-doped-reduced-graphene-oxide as a conductive material to a P(VDF-TrFE) polymer and a BiScO3–PbTiO3 ceramic composite employing an electrospinning process. Nitrogen was doped/substituted into rGO to remove or compensate defects formed during the reduction process. Electro-spinning process was employed to extract piezoelectric composite nanofiber films under self-poling condition. Interdigital electrodes was employed to make planner type energy harvesters to collect electro-mechanical energy applied to the flexible energy harvester. From the piezoelectric composite with interdigital electrode, the effective dielectric permittivity extracted from the conformal mapping method. By introducing BS–PT ceramics and N-rGO conductors to the P(VDF-TrFE) piezoelectric composite nanofiber films, the effective dielectric permittivity was improved from 8.2 to 15.5. This improved effective dielectric constant probably come from the increased electric flux density due to the increased conductivity. Fabricated interdigital electrode using this thin composite nanofiber film was designed and tested for wearable device applications. An external mechanical force of 350 N was applied to the composite nanofiber-based energy harvester with interdigital electrodes at a rate of 0.6 Hz, the peak voltage and current were 13 V and 1.25 μA, respectively. By optimizing the device fabrication, the open-circuit voltage, stored voltage, and generated output power obtained were 12.4 V, 3.78 V, and 6.3 μW, respectively.

An ultrasound-driven implantable wireless energy harvesting system using a triboelectric transducer

<h2>Summary</h2> Wireless power transfer can significantly extend the application range and service life of implantable medical devices, such as pacemakers, neurostimulators, and vascular applicators. However, existing transmission schemes are faced with shortcomings such as weak power, discontinuity, or impact on human health. Here, we design a subcutaneously implantable flexible ultrasound energy harvesting system that integrates a triboelectric nanogenerator (TENG) transducer and a power management circuit into a single flexible printed circuit board. We maximize the TENG transducer performance by choosing an attached-electrode TENG with optimized structural parameters, which offers 66% higher output power and lower impedance than the existing work. Such a flexible system shows broad applications in various environments. It can successfully provide a stable direct current voltage of 1.8 V with >1 mW continuous DC output power and >10 mW instantaneous power, which is sufficient to continuously drive various sensor systems, operate micromotors, and apply nerve stimulation.