Flexible Piezoelectric Nanogenerator Research Articles

Enhancement of ZnO-based flexible nano generators via a sol–gel technique for sensing and energy harvesting applications

Zinc oxide (ZnO) is a remarkable inorganic semiconductor with exceptional piezoelectric properties compared to other semiconductors. However, in comparison to lead-based hazardous piezoelectric materials, its properties have undesired limitations. Here we report a 5∼6 fold enhancement in piezoelectric features via chemical doping of copper matched to intrinsic ZnO. A flexible piezoelectric nanogenerator (F-PENG) device was fabricated using an unpretentious solution process of spin coating, with other advantages such as robustness, low-weight, improved adhesion, and low cost. The device was used to demonstrate energy harvesting from a standard weight as low as 4 gm and can work as a self-powered mass sensor in a broad range of 4 to 100 gm. The device exhibited a novel energy harvesting technique from a wind source due to its inherent flexibility. At three different velocities (10∼30 m s−1) and five different angles of attack (0∼180 degrees), the device validated the ability to discern different velocities and directions of flow. The device will be useful for mapping the flow of air apart from harvesting the energy. The simulation was done to verify the underlining mechanism of aerodynamics involved.

Self-Powered Piezoelectric Nanogenerator Based on Wurtzite ZnO Nanoparticles for Energy Harvesting Application

We report the synthesis procedure of hexagonal wurtzite structure of zinc oxide (ZnO) nanoparticles via hydrothermal route to use as a main component of piezoelectric nanogenerator. The ZnO nanoparticles are dispersed into polydimethylsiloxane (PDMS) to fabricate the high performance flexible piezoelectric nanogenerator (FPNG).The output voltage and power generated from the FPNG is around 20 V and 20 μW respectively. It is also capable to charge up the capacitors within very short span of time (for example, about 2V is reached at 96s). It is demonstrated that the output power generated from the FPNG can directly drive several commercial blue light emitting diodes (LEDs)that ensuring the applicability as a self-powered energy harvester.

High-performance piezoelectric-energy-harvester and self-powered mechanosensing using lead-free potassium–sodium niobate flexible piezoelectric composites

A flexible piezoelectric nanogenerator (PENG) was fabricated based on a new inorganic piezoelectric KNN–BNZ–AS–Fe, which exhibited the great potential in energy harvesting and self-powered mechanosensing.

Flexible piezoelectric nanogenerators based on PVDF-TrFE nanofibers

In this paper, electrospun piezoelectric PVDF-TrFE nanofibers were used for the fabrication of two types of flexible nanogenerator (NG) devices based on the direct piezoelectric effect, allowing the conversion of mechanical energy into electrical energy. The first one is composed of quite well aligned thin film nanofibers of about 35 μm and the second one is composed of random nanofibers of about 50 μm. The influence of the applied stress and strain rate on the output for both types of NG was studied. It is shown that the pulse peaks generated by NG increase with the applied mechanical strain frequency, the generated output is also proportional to the applied stress amplitude. The first NG loaded in bending mode can generate a maximum voltage of 270 mV. By connecting two devices in series/parallel, the voltage/current value could be multiplied by two. The second NG which was biased in compression mode using a shaker controlled by a force sensor, can generate a potential of about 7 V under 3.6 N applied force.

Bio-waste onion skin as an innovative nature-driven piezoelectric material with high energy conversion efficiency

Development of non-toxic, ultra-sensitive, and flexible bio-inspired piezoelectric nanogenerator has become a great challenge for next generation biomedical applications. High performance organic/inorganic materials based piezoelectric nanogenerators suffer from several unavoidable problems such as complex synthesis and high toxicity. Biodegradable and biocompatible piezoelectric material is utmost needed in in-vivo condition to harvest energy for biomedical applications. Here, we report a novel bio-piezoelectric nanogenerator (BPNG) using naturally abundant self-aligned cellulose fibrous untreated onion skin (OS) as efficient piezoelectric material having piezoelectric strength of ∼ 2.8 pC/N. The fabricated OSBPNG generated output voltage, current, instantaneous power density and high piezoelectric energy conversion efficiency of ≈ 18V, ≈ 166nA, ≈ 1.7μW/cm2, and ≈ 61.7%, respectively, and turn on 30 green LEDs by a single device under repeated compressive stress of ≈ 34kPa and ≈ 3.0Hz frequency. In addition, maximum output voltage (≈ 106V) was achieved when 6 units are connected in series, which instantaneously turns on 73 combined LEDs (30 green, 25 blue, and 18 red). OSBPNG is highly effective during throat movement such as coughing, drinking and swallowing. Furthermore, because it works at very low pressure originating from heart pulse or beat, it could be used in pacemakers and health care units. Finally, OSBPNG successfully differentiates speech signals, indicating its potential for speech recognition.

Flexible ZnO nanorod-based piezoelectric nanogenerators on carbon papers

We report on the fabrication of ZnO nanorod (NR)-based flexible piezoelectric nanogenerators (PENGs) on carbon paper (CP). Structural investigations indicate that the ZnO NRs grew well along the porous CP surface. Optical investigation shows that the crystal quality of the ZnO NRs on the CP was comparable to that of NRs grown on Si substrate. As the molar concentration increased from 10–70 mM, the output voltage and current increased consistently from 3.6–6.8 V and 0.79–1.45 μA, respectively. The enhancements of the voltage and current were attributed to the enhanced accumulation of the potentials generated by the increased number of ZnO NRs in the PENG devices. Therefore, the porous CP enhanced the PENG performance due to the higher surface area, and provided a super-flexible self-powering platform.

Performance evaluation of nanogenerators based on Ag doped ZnO nanorods

Pure and Ag doped zinc oxide (ZnO) nanorods were synthesized by a simple hydrothermal synthesis method on the surface of indium doped tin oxide (ITO) coated polyethylene terephthalate (PET) substrate to answer a question whether or not Ag is a suitable dopant for flexible piezoelectric nanogenerators based on ZnO nanorods. The size distribution analysis of ZnO nanograins in the seed layer, pure and Ag doped ZnO nanorod arrays by using Lifshitz- Slyozov- Wagner (LSW) model indicates that the Ag impurity reduces the growth activation energy of ZnO nanorods. The room temperature photoluminescence emission intensity of doped ZnO nanorods changes versus concentration. The performance measurements of nanogenerators indicate a reproducible behavior of devices under periodic bending/releasing cycles and a linear relationship of open circuit voltage (VOC) and force. The piezovoltage measurements show a reduction of VOC and sensitivity of pure samples from ∼8.4mV and 26.25mV/N, respectively, to 5.2mV and 20.00mV/N by adding silver impurity into ZnO nanorods.

Enhanced β‐phase in PVDF polymer nanocomposite and its application for nanogenerator

Harvesting energy from the ambient mechanical energy by using flexible piezoelectric nanogenerator is a revolutionary step toward achieving reliable and green energy source. Polyvinylidene fluoride (PVDF), a flexible polymer, can be a potential candidate for the nanogenerator if its piezoelectric property can be enhanced. In the present work, we have shown that the polar crystalline β‐phase of PVDF, which is responsible for the piezoelectric property, can be enhanced from 48.2% to 76.1% just by adding ZnO nanorods into the PVDF matrix without any mechanical or electrical treatment. A systematic investigation of PVDF‐ZnO nanocomposite films by using X‐ray diffractometer, Fourier transform infrared spectroscopy, and polarization‐electric field loop measurements supports the enhancement of β‐phase in the flexible nanocomposite polymer films. The piezoelectric constant (d33) of the PVDF‐ZnO (15 wt%) film is found to be maximum of approximately −1.17 pC/N. Nanogenerators have been fabricated by using these nanocomposite films, and the piezoresponse of PVDF is found to enhance after ZnO loading. A maximum open‐circuit voltage ~1.81 V and short‐circuit current of 0.57 μA are obtained for 15 wt% ZnO‐loaded PVDF nanocomposite film. The maximum instantaneous output power density is obtained as 0.21 μW/cm2 with the load resistance of 7 MΩ, which makes it feasible for the use of energy harvesting that can be integrated to use for driving small‐scale electronic devices. This enhanced piezoresponse of the PVDF‐ZnO nanocomposite film‐based nanogenerators attributed to the enhancement of electroactive β‐phase and enhanced d33 value in PVDF with the addition of ZnO nanorods.

Flexible piezoelectric nanogenerator in wearable self-powered active sensor for respiration and healthcare monitoring

A wearable self-powered active sensor for respiration and healthcare monitoring was fabricated based on a flexible piezoelectric nanogenerator. An electrospinning poly(vinylidene fluoride) thin film on silicone substrate was polarized to fabricate the flexible nanogenerator and its electrical property was measured. When periodically stretched by a linear motor, the flexible piezoelectric nanogenerator generated an output open-circuit voltage and short-circuit current of up to 1.5 V and 400 nA, respectively. Through integration with an elastic bandage, a wearable self-powered sensor was fabricated and used to monitor human respiration, subtle muscle movement, and voice recognition. As respiration proceeded, the electrical output signals of the sensor corresponded to the signals measured by a physiological signal recording system with good reliability and feasibility. This self-powered, wearable active sensor has significant potential for applications in pulmonary function evaluation, respiratory monitoring, and detection of gesture and vocal cord vibration for the personal healthcare monitoring of disabled or paralyzed patients.

Highly efficient flexible piezoelectric nanogenerator and femtosecond two-photon absorption properties of nonlinear lithium niobate nanowires

We present a high performance flexible piezoelectric nanogenerator (NG) device based on the hydrothermally grown lead-free piezoelectric lithium niobate (LiNbO3) nanowires (NWs) for scavenging mechanical energies. The non-linear optical coefficient and optical limiting properties of LiNbO3 were analyzed using femtosecond laser pulse assisted two photon absorption techniques for the first time. Further, a flexible hybrid type NG using a composite structure of the polydimethylsiloxane polymer and LiNbO3 NWs was fabricated, and their piezoelectric output signals were measured. A large output voltage of ∼4.0 V and a recordable large current density of about 1.5 μA cm−2 were obtained under the cyclic compressive force of 1 kgf. A subsequent UV-Vis analysis of the as-prepared sample provides a remarkable increase in the optical band gap (UV absorption cut-off, ∼251 nm) due to the nanoscale size effect. The high piezoelectric output voltage and current are discussed in terms of large band gap, significant nonlinear optical response, and electric dipole alignments under poling effects. Such high performance and unique optical properties of LiNbO3 show its great potential towards various next generation smart electronic applications and self-powered optoelectronic devices.

High‐Performance Piezoelectric Nanogenerators with Imprinted P(VDF‐TrFE)/BaTiO3 Nanocomposite Micropillars for Self‐Powered Flexible Sensors

Piezoelectric nanogenerators with large output, high sensitivity, and good flexibility have attracted extensive interest in wearable electronics and personal healthcare. In this paper, the authors propose a high-performance flexible piezoelectric nanogenerator based on piezoelectrically enhanced nanocomposite micropillar array of polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE))/barium titanate (BaTiO3 ) for energy harvesting and highly sensitive self-powered sensing. By a reliable and scalable nanoimprinting process, the piezoelectrically enhanced vertically aligned P(VDF-TrFE)/BaTiO3 nanocomposite micropillar arrays are fabricated. The piezoelectric device exhibits enhanced voltage of 13.2 V and a current density of 0.33 µA cm-2 , which an enhancement by a factor of 7.3 relatives to the pristine P(VDF-TrFE) bulk film. The mechanisms of high performance are mainly attributed to the enhanced piezoelectricity of the P(VDF-TrFE)/BaTiO3 nanocomposite materials and the improved mechanical flexibility of the micropillar array. Under mechanical impact, stable electricity is stably generated from the nanogenerator and used to drive various electronic devices to work continuously, implying its significance in the field of consumer electronic devices. Furthermore, it can be applied as self-powered flexible sensor work in a noncontact mode for detecting air pressure and wearable sensors for detecting some human vital signs including different modes of breath and heartbeat pulse, which shows its potential applications in flexible electronics and medical sciences.

(Invited) Flexible Polymer Nanogenerators for Biomechanical Energy Harvesting

Harvesting mechanical energy from biological systems possesses great potential for in-vivo powering implantable electronic devices. Nanogenerator (NG) is a promising technology for harvesting biomechanical energy either in vivo or ex vivo. In this talk, I present a development of flexible piezoelectric nanogenerator (NG) based on mesoporous poly(vinylidene fluoride) (PVDF) films. Monolithic mesoporous PVDF was fabricated by a template-free sol-gel-based approach at room temperature. By filling the pores of PVDF network with poly(dimethylsiloxane) (PDMS) elastomer, the composite’s modulus was effectively tuned over a wide range down to the same level of biological systems. A close match of the modulus between NG and the surrounding biological component is critical to achieve practical integration. Upon deformation, the composite NG exhibited appreciable piezoelectric output that was comparable to or higher than other PVDF-based NGs. An artificial artery system was fabricated using PDMS with the composite NG integrated inside. Effective energy harvesting from simulated blood pressure fluctuation was successfully demonstrated. The simple and effective approach for fabricating mesoporous PVDF with tunable mechanical properties provided a promising route toward the development of self-powered implantable devices. In vivo biomechanical energy harvesting was further demonstrated. The PVDF NG was encapsulated by polydimethylsiloxane (PDMS) and embedded into rodents. No toxicity or incompatibility sign was found in the host after carrying the packaged NG for 6 weeks. Moreover, the electric output of this NG was extremely stable and exhibited no deterioration after 5 days of in vivo operation or 1.512 x 108 times mechanical deformation. This NG device could practically output a constant voltage of 52 mV via a 1 mF capacitor under living circumstance. The outstanding efficiency, magnificent durability and exceptional biocompatibility promise this mesoporous PVDF-based NG in accomplishing self-powered bioelectronics with potentially lifespan operation period.

Transparent, Flexible Piezoelectric Nanogenerator Based on GaN Membrane Using Electrochemical Lift-Off.

A transparent and flexible piezoelectric nanogenerator (TF PNG) is demonstrated based on a GaN membrane fabricated by electrochemical lift-off. Under shear stress on the TF PNG by finger force (∼182 mN), the GaN membrane effectively undergoes normal stress and generates piezoelectric polarization along the c-axis, resulting in the generation of piezoelectric output from the TF PNG. Although the GaN layer is 315 times thinner than the flexible polyethylene terephthalate (PET) substrate, the low Young's modulus of PET allows the GaN membranes to absorb ∼41% of the applied strain energy, which leads to their large lattice deformation under extremely low applied stress. Maximum output voltage and current values of 4.2 V and 150 nA are obtained, and the time decay of the output voltage is discussed.

PVDF based flexible piezoelectric nanogenerators using conjugated polymer:PCBM blend systems

Piezoelectric energy harvesting technology has received much attention as a powerful source of energy for a self-powered system. In this study, three main conjugated polymers that have delocalized π-electrons and excellent charge transport properties were studied: poly(3-hexylthiophene) (P1), poly[(4,8-di-(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)-alt-(5,5′-yl-4,4′-bis(dodecyl)-2,2′-bithiophene)] (P2) and poly[(4,8-di-(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)-alt-(5,5′-yl-4,4′-bis(2-ethylhexyl)-2,2′-bithiophene)] (P3). Each of three polymers was blended with phenyl-C61-butyric acid methyl ester (PCBM61), and the blend systems were used to make PVDF based piezoelectric nanogenerators (PNG-0–3). Polymers showed bimodal structures that have a majority edge-on orientation, forming a minority face-on orientation. At a 2Hz frequency and 0.2mm displacement, the output voltages (peak-to-peak) of PNG-(0–3) were 35.0V, 41.2V, 42.2V and 43.1V, respectively, and the output currents (peak-to-peak) were 558.5nA, 569.5nA, 572nA and 589nA, respectively. The energy conversion efficiencies of PNGs (0–3) were 6.47%, 11.62%, 13.36%, and 14.33%, respectively; therefore, the efficiency was improved by up to about 2.2 times.

Radial growth of zinc oxide nanowire for piezoelectric nanogenerator application

Nano- and micro-self-biased sensors employed environmental harvested energy, which are provided by different methods, such as piezoelectric. Piezoelectric materials are capable of producing electrical energy from environmental mechanical force. In this paper, a radial layer of well-arrayed hexagonal zinc oxide nanowires is grown on carbon fiber substrate using a two-step Chemical deposition method of metal salt growth. The resulted morphology is examined using Field Emission Scanning Electron Microscopy (FESEM) micrographs and X-ray Diffraction (XRD) pattern which indicates the quality and the crystallization order of the samples. In addition, composition of the material is studied using a Fourier Transform Infrared (FTIR) spectroscopy method. The results show that zinc oxide nanowires are well managed in vertical direction on the cylindrical carbon fibers. The hexagonal nanowires are grown with a length from 206 to 286 nm (Nanometer) and the diameter from 75 to 103 nm. The results of FTIR spectroscopy and XRD also illustrate the wurtzite structure of zinc oxide. The synthesized nanowires are then applied in a flexible capacitive piezoelectric nanogenerator consisting of a thin Ag layer as the upper contact and a carbon substrate as the back contact which are separated by a PMMA dielectric film. The output current and voltage are measured by applying a random pulse mechanical force on the upper contact. A maximum voltage and current of 14 mV (millivolt) and 20 nA (nanoampere) are generated at the output of nanogenerator, respectively.

A novel tri-layer flexible piezoelectric nanogenerator based on surface- modified graphene and PVDF-BaTiO3 nanocomposites

The fabrication and characterization of a novel tri-layer piezoelectric nanogenerator (PNG) based on poly(vinylidene fluoride) (PVDF), barium titanate (BTO), and surface-modified n- type graphene (n-Gr) have been investigated. The n-Gr, with its majority of negative charge carriers, plays a vital role in enhancing the energy-harvesting performance by aligning the dipoles in one direction. The tri-layer structure obtains by stacking two layers of PVDF-BTO nanocomposite films, one on each side of the n-Gr layer. The fabricated tri-layer PNG shows a maximum output voltage of 10V (pk-pk) along with a current of 2.5μA (pk-pk) at an applied force of 2N. Furthermore, the PNG Exhibits 5.8μW instantaneous power at 1MΩ load resistance. Moreover, the fabricated device demonstrated good stability even after 1000 pressing–releasing cycles. This novel tri-layer PNG structure can opens a promising avenue for future piezoelectric generating technologies.

Patterned growth of ZnO nanowires on flexible substrates for enhanced performance of flexible piezoelectric nanogenerators

Flexible piezoelectric nanogenerators (NGs) based on patterned growth of ZnO nanowires (PNWs) by the hydrothermal method are proposed for high-efficiency energy harvesting applications. The use of the PNWs in ZnO-based FPNGs results in a significant improvement in terms of the magnitude of the output currents of up to 6 times when compared with pristine ZnO NW-based FPNGs without patterned growth mode. The maximum output current was measured to be about 150 nA, which was enough to drive some micro/nanoelectronic devices. The improved output performance is mainly attributed to the patterned growth mode in FPNGs, which may significantly reduce the piezoelectric potential screening effect caused by free electrons in ZnO. This strategy may provide a highly promising platform as energy harvesting devices for viable industrial applications in portable/wearable nanodevices.

Flexible piezoelectric nanogenerators based on a transferred ZnO nanorod/Si micro-pillar array

Flexible piezoelectric nanogenerators (PNGs) based on a composite of ZnO nanorods (NRs) and an array of Si micro-pillars (MPs) are demonstrated by a transfer process. The flexible composite structure was fabricated by hydrothermal growth of ZnO NRs on an electrochemically etched Si MP array with various lengths followed by mechanically delaminating the Si MP arrays from the Si substrate after embedding them in a polydimethylsiloxane matrix. Because the Si MP arrays act as a supporter to connect the ZnO NRs electrically and mechanically, verified by capacitance measurement, the output voltage from the flexible PNGs increased systematically with the increased density ZnO NRs depending on the length of the Si MPs. The flexible PNGs showed 3.2 times higher output voltage with a small change in current with increasing Si MP length from 5 to 20 μm. The enhancement of the output voltage is due to the increased number of series-connected ZnO NRs and the beneficial effect of a ZnO NR/Si MP heterojunction on reducing free charge screening effects. The flexible PNGs can be attached on fingers as a wearable electrical power source or motion sensor.

Fabrication of wearable semiconducting piezoelectric nanogenerator made with electrospun-derived zinc sulfide nanorods and poly(vinyl alcohol) nanofibers

We report the fabrication of flexible, low cost, and wearable piezoelectric nanogenerators (NG) composed of a poly(vinyl alcohol) (PVA) nanofiber web and oriented zinc sulfide (ZnS) nanorods (NRs) by a facile and scalable electrospinning technique. The piezoelectric performance of the NG is found to be increased by simply stacking the nanofiber web mats, where the ZnS NRs are incorporated in the PVA fiber matrix. Furthermore, we also designed a large area wearable nanogenerator (WNG) to harvest mechanical energy from acoustic random vibrations and convert it into electrical energy, and an improved acoustic sensitivity of 2 V Pa−1 is observed. This indicates that the WNG is ultrasensitive to random mechanical vibration, and possesses potential utility as a sustainable power source and sensitive pressure sensor particularly suited for portable electronics and wearable technology.

Fabrication of lead-free Ba(Zr0.2Ti0.8)O3–(Ba0.7Ca0.3)TiO3 nanoparticles and the application in flexible piezoelectric nanogenerator

Recently, flexible nanogenerators have attracted much attention due to the continuous demand of portable electronic devices. Thus, in our present work, a flexible piezoelectric nanogenerator (pNG) was fabricated by mixing 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 nanoparticles (BCTZ NPs) and a PDMS polymer matrix. The flexible device exhibited excellent performance with maximum open-circuit voltage of 0.6V and short-circuit current of 7.5nA. BCTZ NPs were prepared by a reaction between a metallic salt and a metallic oxide in a solution of composite-hydroxide eutectic. XRD pattern showed BCTZ NPs to have pure perovskite structure. In this paper, the structure, morphology of the BCTZ NPs, and electric property of the BCTZ-based pNG were systematically studied. With the advantages of small-size, environmentally friendly, high flexibility, and high-sensitivity to external vibration, BCTZ will open up a range of new applications.