Flexible hybrid eu3+ doped P(VDF-HFP) nanocomposite film possess hypersensitive electronic transitions and piezoelectric throughput

A self-powered mechanical energy harvester based on CH3NH3PbI3 doped P(VDF-HFP)/PANI composite films

Piezoelectric polymers, particularly poly(vinylidene fluoride) (PVDF) and its copolymers attract attention from researchers due to their stretchability, flexibility, lightweight, and most importantly their biocompatible nature. In this research work, we report on the preparation of polymer composite films as flexible piezoelectric generators (PGs) and their electroactive phase (β- and γ-phase) formation. The piezoelectric properties of copolymer poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) have been enhanced by incorporating polyaniline (PANI) and methylammonium lead iodide (CH3NH3PbI3) into it for a higher yield of the electroactive phases where a traditional electrical poling treatment was avoided. The remarkable enhancement in the piezoelectric phase (i.e., β-phase) of the P(VDF-HFP) copolymer has been reported in this work, and it is found that the overall improvement of the piezoelectric β-phase and the conversion of the degree of crystallinity is governed by the incorporation of the PANI and CH3NH3PbI3 fillers as revealed by the attenuated total reflectance (ATR) and X-ray diffraction (XRD) analysis. The X-ray photoelectron spectroscopy (XPS) analysis further confirmed the interfacial dipole-dipole interaction of PANI with the P(VDF-HFP) copolymer matrix. Piezoelectric generators (PGs) fabricated from the composite films show an open circuit piezoelectric voltage output of 5 volts and an output power of 8.2 nW. The capacitor charging capability by simple repetitive finger touch and release motions (a pressure amplitude of ∼14 kPa) of the flexible PGs promises their applicability as a piezoelectric-based energy harvester where different mechanical vibrations can be utilized.

A Flexible Multifunctional PAN Piezoelectric Fiber with Hydrophobicity, Energy Storage, and Fluorescence

Lightweight, flexible, and hydrophobic multifunctional piezoelectric sensors have increasingly important research value in contemporary society. They can generate electrical signals under the action of pressure and can be applied in various complex scenarios. In this study, we prepared a polyacrylonitrile (PAN) composite fiber doped with imidazolium type ionic liquids (ILs) and europium nitrate hexahydrate (Eu (NO₃)₃·6H₂O) by a facile method. The results show that the PAN composite fibers had excellent mechanical properties (the elongation at break was 114% and the elastic modulus was 2.98 MPa), hydrophobic self-cleaning ability (water contact angle reached 127.99°), and can also emit light under UV light irradiation red fluorescence. In addition, thanks to the induction of the piezoelectric phase of PAN by the dual fillers, the composite fibers exhibited efficient energy storage capacity and excellent sensitivity. The energy density of PAN@Eu-6ILs reached a maximum of 44.02 mJ/cm³ and had an energy storage efficiency of 80%. More importantly, under low pressure detection, the sensitivity of the composite fiber was 0.69 kPa⁻¹. The research results show that this PAN composite fiber has the potential to act as wearable piezoelectric devices, energy storage devices, and other electronic devices.

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.

Eu3+-Doped Electrospun Polyvinylidene Fluoride-Hexafluoropropylene/Graphene Oxide Multilayer Composite Nanofiber for the Fabrication of Flexible Pressure Sensors

The development of flexible materials with higher piezoelectric properties and electrostrictive response is of great significance in many applications such as wearable functional devices, flexible sensors, and actuators. In this study, we report an efficient fabrication strategy to construct a highly sensitive (0.72 kPa^-1), red light-emitting flexible pressure sensor using electrospun Eu³⁺-doped polyvinylidene fluoride-hexafluoropropylene/graphene oxide composite nanofibers using a layer-by-layer technology. The high β-phase concentration (96.3%) was achieved from the Eu³⁺-doped P(VDF-HFP)/GO nanofibers, leading to a high piezoelectricity of the composite nanofibers. We observed that a pressure sensor is enabled to generate an output voltage of 4.5 V. Furthermore, Eu³⁺-doped P(VDF-HFP)/GO composite nanofiber-based pressure sensors can also be used as an actuator as it has a good electrostrictive effect. At the same time, the nanofiber membrane has excellent ferroelectric properties and good fluorescence properties. These results indicate that this material has great application potential in the fields of photoluminescent fabrics, flexible sensors, soft actuators, and energy storage devices.

Emerging Pyroelectric Nanogenerators to Convert Thermal Energy into Electrical Energy

Pyroelectric energy harvesting systems have recently received substantial attention for their potential applications as power generators. In particular, the pyroelectric effect, which converts thermal energy into electrical energy, has been utilized as an infrared (IR) sensor, but upcoming sensor technology that requires a miniscule amount of power is able to utilize pyroelectric nanogenerators (PyNGs) as a power source. Herein, an overview of the progress in the development of PyNGs for an energy harvesting system that uses environmental or artificial energies such as the sun, body heat, and heaters, is provided. It begins with a brief introduction of the pyroelectric effect, and various polymer and ceramic materials based PyNGs are reviewed in detail. Various approaches for developing polymer-based PyNGs and various ceramic materials-based PyNGs are summarized in particular. Finally, challenges and perspectives regarding the PyNGs are described.

Innovation Strategy Selection Facilitates High-Performance Flexible Piezoelectric Sensors

Piezoelectric sensors with high performance and low-to-zero power consumption meet the growing demand in the flexible microelectronic system with small size and low power consumption, which are promising in robotics and prosthetics, wearable devices and electronic skin. In this review, the development process, application scenarios and typical cases are discussed. In addition, several strategies to improve the performance of piezoelectric sensors are summed up: (1) material innovation: from piezoelectric semiconductor materials, inorganic piezoceramic materials, organic piezoelectric polymer, nanocomposite materials, to emerging and promising molecular ferroelectric materials. (2) designing microstructures on the surface of the piezoelectric materials to enlarge the contact area of piezoelectric materials under the applied force. (3) addition of dopants such as chemical elements and graphene in conventional piezoelectric materials. (4) developing piezoelectric transistors based on piezotronic effect. In addition, the principle, advantages, disadvantages and challenges of every strategy are discussed. Apart from that, the prospects and directions of piezoelectric sensors are predicted. In the future, the electronic sensors need to be embedded in the microelectronic systems to play the full part. Therefore, a strategy based on peripheral circuits to improve the performance of piezoelectric sensors is proposed in the final part of this review.

High-Performance Electronic Cloth for Facilitating the Rehabilitation of Human Joints

The concern about easily characterizing the conditions of human joints to facilitate rehabilitation during recovery training has been out of sight, even though it is acknowledged that timely recovering functions of injured joints is a must. To facilitate the situation to be addressed, a stretchable, air-permeable electronic cloth (SApEC) was fabricated by electrostatic spinning and hot-pressing. The SApEC consists of conductive-elastic fabric Ag and composite nanofibrous membrane (CNFM) with components of poly(vinylidene fluoride- co-hexa-fluoropropyiene) and thermoplastic urethane. The electronic cloth not only owns chemical stability and ultralight weight, but scavenges triboelectric signals from joint movements. These characters allow the SApEC to be an easy and convenient indicator to indicate the activity of joints, when users get rehabilitation training in non-hospital places. With the assistance of several electronic components, the SApEC could control alarms, such as a warning lamp. This favorable ability allows the SApEC to make alerts, once users face any accidents again, like sudden fall or heart failure. Given the advantages mentioned above, it is reasonable to believe that the SApEC has a promising prospect in portable and wearable electronics, involving indicating rehabilitation of joints and keeping an eye on users' safety.

Toward High Power Generating Piezoelectric Nanofibers: Influence of Particle Size and Surface Electrostatic Interaction of Ce-Fe2O3 and Ce-Co3O4 on PVDF

Development of flexible piezoelectric nanogenerator (PENG) is a real challenge for the next-generation energy-harvesting applications. In this paper, we report highly flexible PENGs based on poly(vinylidene fluoride) (PVDF)/2 wt % Ce-Fe₂O₃ and PVDF/2 wt % Ce-Co₃O₄ nanocomposite fibers. The incorporation of magnetic Ce-Fe₂O₃ and Ce-Co₃O₄ greatly affects the structural properties of PVDF nanofibers, especially the polymeric β and γ phases. In addition, the new composites enhanced the interfacial compatibility through electrostatic filler-polymer interactions. Both PVDF/Ce-Fe₂O₃ and PVDF/Ce-Co₃O₄ nanofibers-based PENGs, respectively, produce peak-to-peak output voltages of 20 and 15 V, respectively, with the corresponding output currents of 0.010 and 0.005 μA/cm² under the force of 2.5 N. Enhanced output performance of the flexible nanogenerator is correlated with the electroactive polar phases generated within the PVDF, in the presence of the nanomaterials. The designed nanogenerators respond to human wrist movements with the highest output voltage of 0.15 V, for the PVDF/Ce-Fe₂O₃ when subjected to hand movements. The overall piezoelectric power generation is correlated with the nanoparticle size and the existing filler-polymer and ion-dipole interactions.

A hybrid strain and thermal energy harvester based on an infra-red sensitive Er3+ modified poly(vinylidene fluoride) ferroelectret structure

In this paper, a novel infra-red (IR) sensitive Er3+ modified poly(vinylidene fluoride) (PVDF) (Er-PVDF) film is developed for converting both mechanical and thermal energies into useful electrical power. The addition of Er3+ to PVDF is shown to improve piezoelectric properties due to the formation of a self-polarized ferroelectric β-phase and the creation of an electret-like porous structure. In addition, we demonstrate that Er3+ acts to enhance heat transfer into the Er-PVDF film due to its excellent infrared absorbance, which, leads to rapid and large temperature fluctuations and improved pyroelectric energy transformation. We demonstrate the potential of this novel material for mechanical energy harvesting by creating a durable ferroelectret energy harvester/nanogenerator (FTNG). The high thermal stability of the β-phase enables the FTNG to harvest large temperature fluctuations (ΔT ~ 24 K). Moreover, the superior mechanosensitivity, SM ~ 3.4 VPa-1 of the FTNG enables the design of a wearable self-powered health-care monitoring system by human-machine integration. The combination of rare-earth ion, Er3+ with the ferroelectricity of PVDF provides a new and robust approach for delivering smart materials and structures for self-powered wireless technologies, sensors and Internet of Things (IoT) devices.

Enhanced electro-active phase in a luminescent P(VDF–HFP)/Zn2+ flexible composite film for piezoelectric based energy harvesting applications and self-powered UV light detection

An electro-active P(VDF–HFP)/Zn²⁺ composite film scavenges the mechanical energy that enabled self-powered UV light detection.