Micropatterned P(VDF‐TrFE) Film‐Based Piezoelectric Nanogenerators for Highly Sensitive Self‐Powered Pressure Sensors

Here micropatterned poly(vinylidenefluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) films‐based piezoelectric nanogenerators (PNGs) with high power‐generating performance for highly sensitive self‐powered pressure sensors are demonstrated. The microstructured P(VDF‐TrFE)‐based PNGs reveal nearly five times larger power output compared to a flat film‐based PNG. The micropatterning of P(VDF‐TrFE) polymer makes itself ultrasensitive in response to mechanical deformation. The application is demonstrated successfully as self‐powered pressure sensors in which mechanical energy comes from water droplet and wind. The mechanism of the high performance is intensively discussed and illustrated in terms of strain developed in the flat and micropatterned P(VDF‐TrFE) films. The impact derived from the patterning on the output performance is studied in term of effective pressure using COMSOL multiphysics software.     

Highly Porous Polymer Aerogel Film‐Based Triboelectric Nanogenerators

A novel class of high performance polymer porous aerogel film‐based triboelectric nanogenerators (A‐NGs) is demonstrated. The A‐NGs, made of a pair of highly porous polymer films, exhibit much higher triboelectric outputs than the corresponding dense polymer film‐based triboelectric nanogenerators (D‐NGs) under the same mechanical stress. The triboelectric outputs of the A‐NGs increase significantly with increasing porosity, which can be attributed to the increase in contact area and the electrostatic induction in the porous structure, thereby leading to additional charges on the porous surface. Remarkably, the A‐NG fabricated using porous chitosan aerogel film paired with the most porous polyimide (with a porosity of 92%) aerogel film demonstrates a very high voltage of 60.6 V and current of 7.7 µA, corresponding to a power density of 2.33 W m^?2, which is sufficient to power 22 blue light‐emitting‐diodes (LEDs). This is the first report on triboelectric nanogenerators (TENGs) employing porous polymer aerogel films as both positive and negative materials to enhance triboelectric outputs. Furthermore, enhancing the tribopositive polarity of the cellulose aerogel film via silanization using aminosilane can dramatically improve the triboelectric performance. Therefore, this study provides new insights into investigating porous materials with tunable triboelectric polarities for high performance TENGs.     

Sustainable Nanotextured Wave Energy Harvester Based on Ferroelectric Fatigue‐Free and Flexoelectricity‐Enhanced Piezoelectric P(VDF‐TrFE) Nanofibers with BaSrTiO3 Nanoparticles

Here, ultrathin, flexible, and sustainable nanofiber‐based piezoelectric nanogenerators (NF‐PENGs) are fabricated and applied as wave energy harvesters. The NF‐PENGs are composed of poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) nanofibers with embedded barium strontium titanate (BaSrTiO₃) nanoparticles, which are fabricated by using facile, scalable, and cost‐effective fiber‐forming methods, including electrospinning and solution blowing. The inclusion of ferroelectric BaSrTiO₃ nanoparticles inside the electrospun P(VDF‐TrFE) nanofibers enhances the sustainability of the NF‐PENGs and results in unique flexoelectricity‐enhanced piezoelectric nanofibers. Not only do these NF‐PENGs yield a superior performance compared to the previously reported NF‐PENGs, but they also exhibit an outstanding durability in terms of mechanical properties and cyclability. Furthermore, a new theoretical estimate of the energy harvesting efficiency from the water waves is introduced here, which can also be employed in future studies associated with various nanogenerators, including PENGs and triboelectric nanogenerators.     

Self‐Compensated Insulating ZnO‐Based Piezoelectric Nanogenerators

Remarkable enhancement of piezoelectric power output from a nanogenerator (NG) based on a zinc oxide (ZnO) thin film is achieved via native defect control. A large number of unintentionally induced point defects that act as n‐type carriers in ZnO have a strong influence on screening the piezoelectric potential into a piezoelectric NG. Here, additional oxygen molecules bombarded into ZnO lead to oxygen‐rich conditions, and the n‐type conductivity of ZnO is decreased dramatically. The acceptor‐type point defects such as zinc vacancies created during the deposition process trap n‐type carriers occurring from donor‐type point defects through a self‐compensation mechanism. This unique insulating‐type ZnO thin film‐based NGs (IZ‐NGs) generates output voltage around 1.5 V that is over ten times higher than that of an n‐type ZnO thin film‐based NG (around 0.1 V). In addition, it is found that the power output performance of the IZ‐NG can be further increased by hybridizing with a p‐type polymer (poly(3‐hexylthiophene‐2,5‐diyl):phenyl‐C₆₁‐butyric acid methyl ester) via surface free carrier neutralization.     

Semitransparent,Flexible, and Self‐Powered Photodetectors Based on Ferroelectricity‐Assisted Perovskite Nanowire Arrays

Transparent and flexible photodetectors hold great promise in next‐generation portable and wearable optoelectronic devices. However, most of the previously reported devices need an external energy power source to drive its operation or require complex fabrication processes. Herein, designed is a semitransparent, flexible, and self‐powered photodetector based on the integrated ferroelectric poly(vinylidene‐fluoride‐trifluoroethylene) (P(VDF‐TrFE)) and perovskite nanowire arrays on the flexible polyethylene naphthalate substrate via a facile imprinting method. Through optimizing the treatment conditions, including polarization voltage, polarization time, and the concentration of P(VDF‐TrFE), the resulting device exhibits remarkable detectivity (7.3 × 10¹² Jones), fast response time (88/154 µs) at zero bias, as well as outstanding mechanical stability. The excellent performance is attributed to the efficient charge separation and transport originating from the highly oriented 1D transport pathway and the polarization‐induced internal electric field within P(VDF‐TrFE)/perovskite hybrid nanowire arrays.     

Ultrahigh‐Performance Flexible and Self‐Powered Photodetectors with Ferroelectric P(VDF‐TrFE)/Perovskite Bulk Heterojunction

Flexible and self‐powered perovskite photodetectors attract widespread research interests due to their potential applications in portable and wearable optoelectronic devices. However, the reported devices mainly adopt an independent layered structure with complex fabrication processes and high carrier recombination. Herein, an integrated ferroelectric poly(vinylidene‐fluoride‐trifluoroethylene) (P(VDF‐TrFE)) and perovskite bulk heterojunction film photodetector on the polyethylene naphthalate substrate is demonstrated. Under the optimum treatment conditions (the polarization voltage and time, and the concentration of P(VDF‐TrFE)), the photodetector exhibits a largely enhanced performance compared to the pristine perovskite device. The resulting device exhibits ultrahigh performance with a large detectivity (1.4 × 10¹³ Jones) and fast response time (92/193 µs) at the wavelength of 650 nm. The improved performance is attributed to the fact that the polarized P(VDF‐TrFE)/perovskite hybrid film provides a stronger built‐in electric field to facilitate the separation and transportation of photogenerated carriers. These findings provide a new route to design self‐powered photodetectors from the aspect of device structure and carrier transport.     

A High‐k Fluorinated P(VDF‐TrFE)‐g‐PMMA Gate Dielectric for High‐Performance Flexible Field‐Effect Transistors

A newly synthesized high‐k polymeric insulator for use as gate dielectric layer for organic field‐effect transistors (OFETs) obtained by grafting poly(methyl methacrylate) (PMMA) in poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) via atom transfer radical polymerization transfer is reported. This material design concept intents to tune the electrical properties of the gate insulating layer (capacitance, leakage current, breakdown voltage, and operational stability) of the high‐k fluorinated polymer dielectric without a large increase in operating voltage by incorporating an amorphous PMMA as an insulator. By controlling the grafted PMMA percentage, an optimized P(VDF‐TrFE)‐g‐PMMA with 7 mol% grafted PMMA showing reasonably high capacitance (23–30 nF cm^?2) with low voltage operation and negligible current hysteresis is achieved. High‐performance low‐voltage‐operated top‐gate/bottom‐contact OFETs with widely used high mobility polymer semiconductors, poly[[2,5‐bis(2‐octyldodecyl)‐2,3,5,6‐tetrahydro‐3,6‐dioxopyrrolo [3,4‐c]pyrrole‐1,4‐diyl]‐alt‐[[2,2′‐(2,5‐thiophene)bis‐thieno(3,2‐b)thiophene]‐5,5′‐diyl]] (DPPT‐TT), and poly([N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)) are demonstrated here. DPPT‐TT OFETs with P(VDF‐TrFE)‐g‐PMMA gate dielectrics exhibit a reasonably high field‐effect mobility of over 1 cm² V^?1 s^?1 with excellent operational stability.     

Non‐volatile Ferroelectric Poly(vinylidene fluoride‐co‐trifluoroethylene) Memory Based on a Single‐Crystalline Tri‐isopropylsilylethynyl Pentacene Field‐Effect Transistor

A new type of nonvolatile ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) memory based on an organic thin‐film transistor (OTFT) with a single crystal of tri‐isopropylsilylethynyl pentacene (TIPS‐PEN) as the active layer is developed. A bottom‐gate OTFT is fabricated with a thin P(VDF‐TrFE) film gate insulator on which a one‐dimensional ribbon‐type TIPS‐PEN single crystal, grown via a solvent‐exchange method, is positioned between the Au source and drain electrodes. Post‐thermal treatment optimizes the interface between the flat, single‐crystalline ab plane of TIPS‐PEN and the polycrystalline P(VDF‐TrFE) surface with characteristic needle‐like crystalline lamellae. As a consequence, the memory device exhibits a substantially stable source–drain current modulation with an ON/OFF ratio hysteresis greater than 10³, which is superior to a ferroelectric P(VDF‐TrFE) OTFT that has a vacuum‐evaporated pentacene layer. Data retention longer than 5 × 10⁴ s is additionally achieved in ambient conditions by incorporating an interlayer between the gate electrode and P(VDF‐TrFE) thin film. The device is environmentally stable for more than 40 days without additional passivation. The deposition of a seed solution of TIPS‐PEN on the chemically micropatterned surface allows fabrication arrays of TIPS‐PEN single crystals that can be potentially useful for integrated arrays of ferroelectric polymeric TFT memory.     

Unidirectional High‐Power Generation via Stress‐Induced Dipole Alignment from ZnSnO3 Nanocubes/Polymer Hybrid Piezoelectric Nanogenerator

The extremely stable high‐power generation from hybrid piezoelectric nanogenerator (HP‐NG) based on a composite of single‐crystalline piezoelectric perovskite zinc stannate (ZnSnO₃) nanocubes and polydimethylsiloxane without any electrical poling treatment is reported. The HP‐NG generates large power output under only vertical compression, while there is negligible power generation with other configurations of applied strain, such as bending and folding. This unique high unidirectionality of power generation behavior of the HP‐NG provides desirable features for large‐area piezoelectric power generation based on vertical mechanical compression such as moving vehicles, railway transport, and human walking. The HP‐NGs of ZnSnO₃ nanocubes exhibit high mechanical durability, excellent robustness, and high power‐generation performance. A large recordable output voltage of about 20 V and an output current density value of about 1 μA cm^?2 are successfully achived, using a single cell of HP‐NG obtained under rolling of a vehicle tire.     

Processing and Low Voltage Switching of Organic Ferroelectric Phase‐Separated Bistable Diodes

The processing of solution‐based binary blends of the ferroelectric random copolymer poly(vinylidene fluoride‐trifluoroethylene) P(VDF‐TrFE) and the semiconducting polymer poly(9,9‐dioctylfluorenyl‐2,7‐diyl) (PFO) applied by spin‐coating and wire‐bar coating is investigated. By systematic variation of blend composition, solvent, and deposition temperature it is shown that much smoother blend films can be obtained than reported thus far. At a low PFO:P(VDF‐TrFE) ratio the blend film consists of disk‐shaped PFO domains embedded in a P(VDF‐TrFE) matrix, while an inverted structure is obtained in case the P(VDF‐TrFE) is the minority component. The microstructure of the phase separated blend films is self‐affine. From this observation and from the domain size distribution it is concluded that the phase separation occurs via spinodal decomposition, irrespectively of blend ratio. This is explained by the strong incompatibility of the two polymers expressed by the binary phase diagram, as constructed from thermal analysis data. Time resolved numerical simulation of the microstructure evolution during de‐mixing qualitatively shows how an elevated deposition temperature has a smoothening effect as a result of the reduction of the repulsion between the blend components. The small roughness allowed the realization of bistable rectifying diodes that switch at low voltages with a yield of 100%. This indicates that memory characteristics can be tailored from the outset while processing parameters can be adjusted according to the phase behavior of the active components.     

High‐Performance Ferroelectric Memory Based on Phase‐Separated Films of Polymer Blends

High‐performance polymer memory is fabricated using blends of ferroelectric poly(vinylidene‐fluoride‐trifluoroethylene) (P(VDF‐TrFE)) and highly insulating poly(p‐phenylene oxide) (PPO). The blend films spontaneously phase separate into amorphous PPO nanospheres embedded in a semicrystalline P(VDF‐TrFE) matrix. Using low molecular weight PPO with high miscibility in a common solvent, i.e., methyl ethyl ketone, blend films are spin cast with extremely low roughness (R_rms ≈ 4.92 nm) and achieve nanoscale phase seperation (PPO domain size < 200 nm). These blend devices display highly improved ferroelectric and dielectric performance with low dielectric losses (<0.2 up to 1 MHz), enhanced thermal stability (up to ≈353 K), excellent fatigue endurance (80% retention after 10⁶ cycles at 1 KHz) and high dielectric breakdown fields (≈360 MV/m).     

Stretchable Energy‐Harvesting Tactile Interactive Interface with Liquid‐Metal‐Nanoparticle‐Based Electrodes

Energy‐harvesting electronic skin (E‐skin) is highly promising for sustainable and self‐powered interactive systems, wearable human health monitors, and intelligent robotics. Flexible/stretchable electrodes and robust energy‐harvesting components are critical in constructing soft, wearable, and energy‐autonomous E‐skin systems. A stretchable energy‐harvesting tactile interactive interface is demonstrated using liquid metal nanoparticles (LM‐NPs)‐based electrodes. This stretchable energy‐harvesting tactile interface relies on triboelectric nanogenerator composed of a galinstan LM‐NP‐based stretchable electrode and patterned elastic polymer friction and encapsulation layer. It provides stable and high open‐circuit voltage (268 V), short‐circuit current (12.06 µA), and transferred charges (103.59 nC), which are sufficient to drive commercial portable electronics. As a self‐powered tactile sensor, it presents satisfactory and repeatable sensitivity of 2.52 V·kPa^?1 and is capable of working as a touch interactive keyboard. The demonstrated stretchable and robust energy‐harvesting E‐skin using LM‐NP‐based electrodes is of great significance in sustainable human–machine interactive system, intelligent robotic skin, security tactile switches, etc.     

驻极体的研究现状

驻极体是电介质物理、材料科学、传感器工程及生物医学的重要交叉学科。近年来，驻极体在生物驻极体、驻极体的应用及有机驻极体的非线性光学效应等方面取得了瞩目的进展。文章就上述几个问题，从材料制备、实验方法和驻极体的应用等方面进行了综述。     

Biocompatible Poly(lactic acid)‐Based Hybrid Piezoelectric and Electret Nanogenerator for Electronic Skin Applications

Human machine interface (HMI) devices, which can convert human motions to electrical signals to control/charge electronic devices, have attracted tremendous attention from the engineering and science fields. Herein, the high output voltage from a nonpiezoelectric meso‐poly(lactic acid) (meso‐PLA) electret‐based triboelectric nanogenerator (NG) is combined with the relatively high current from a double‐layered poly(l ‐lactic acid) (PLLA)‐based piezoelectric nanogenerator (PENG) for an E‐skin (electronic skin) (HMI) device application. The hybrid NG with a cantilever structure can generate an output voltage of 70 V and a current of 25 µA at the resonance frequency of 19.7 Hz and a tip load of 4.71 g. Moreover, the output power of the hybrid NG reaches 0.31 mW, which is 11% higher than that from the PLLA‐based PENG. Furthermore, it is demonstrated that the PLA‐based hybrid NG can be used to turn a light‐emitting diode light on and off through an energy management circuit during a bending test. Finally, it is demonstrated that the PLA‐based woven E‐skin device can generate the output signals of 35 V (V_oc) and 1 µA (I_sc) during an elbow bending test. The advantages of biocompatible, ease of fabrication, and relatively high output power in the hybrid NG device show great promise for future E‐skin applications.     

Triboelectric and Piezoelectric Effects in a Combined Tribo‐Piezoelectric Nanogenerator Based on an Interfacial ZnO Nanostructure

In this contribution, combined triboelectric and piezoelectric generators (TPEG) with a sandwich structure of aluminum‐polydimethylsiloxane/polyvinylidene fluoride composite‐carbon (Al‐PPCF‐Carbon) are fabricated for the purpose of mechanical energy harvesting. Improved by the surface modification of PPCF with zinc oxide (ZnO) nanorods through a hydrothermal method, the TPEG generates an open‐circuit voltage (V_oc) of ≈40 V, a short‐circuit current (I_sc) of 0.28 μA with maximum power density of ≈70 mWm^?2_, and maximum conversion efficiency of 34.56%. Subsequently, in order to understand the transduction mechanism of the triboelectric and piezoelectric effects, analyses focusing on the potential composition ratio in the final output and the impact of ZnO interfacial nanostructure are carried out. The observed potential ratio between triboelectric and piezoelectric effects is 12.75:1 and the highest potential improvement by ZnO nanorods of 21.8 V is achieved by the TPEG fabricated with spacer. Finally, the relationships between the voltage, power density, conversion efficiency, and the external load resistances are also discussed. Overall, the fabricated TPEG is proved to be a simple and effective nanogenerator in mechanical energy conversion with enhanced output potential and conversion efficiency.     

Control of Current Hysteresis of Networked Single‐Walled Carbon Nanotube Transistors by a Ferroelectric Polymer Gate Insulator

Films made of 2D networks of single‐walled carbon nanotubes (SWNTs) are one of the most promising active‐channel materials for field‐effect transistors (FETs) and have a variety of flexible electronic applications, ranging from biological and chemical sensors to high‐speed switching devices. Challenges, however, still remain due to the current hysteresis of SWNT‐containing FETs, which has hindered further development. A new and robust method to control the current hysteresis of a SWNT‐network FET is presented, which involves the non‐volatile polarization of a ferroelectric poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) gate insulator. A top‐gate FET with a solution‐processed SWNT‐network exhibits significant suppression of the hysteresis when the gate‐voltage sweep is greater than the coercive field of the ferroelectric polymer layer (≈50 MV m^?1). These near‐hysteresis‐free characteristics are believed to be due to the characteristic hysteresis of the P(VDF‐TrFE), resulting from its non‐volatile polarization, which makes effective compensation for the current hysteresis of the SWNT‐network FETs. The onset voltage for hysteresis‐minimized operation is able to be tuned simply by controlling the thickness of the ferroelectric film, which opens the possibility of operating hysteresis‐free devices with gate voltages down to a few volts.     

All‐Polymer Bistable Resistive Memory Device Based on Nanoscale Phase‐Separated PCBM‐Ferroelectric Blends

All polymer nonvolatile bistable memory devices are fabricated from blends of ferroelectric poly(vinylidenefluoride–trifluoroethylene (P(VDF‐TrFE)) and n‐type semiconducting [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM). The nanoscale phase separated films consist of PCBM domains that extend from bottom to top electrode, surrounded by a ferroelectric P(VDF‐TrFE) matrix. Highly conducting poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) polymer electrodes are used to engineer band offsets at the interfaces. The devices display resistive switching behavior due to modulation of this injection barrier. With careful optimization of the solvent and processing conditions, it is possible to spin cast very smooth blend films (R_rms ≈ 7.94 nm) and with good reproducibility. The devices exhibit high I_on/I_off ratios (≈3 × 10³), low read voltages (≈5 V), excellent dielectric response at high frequencies (?_r ≈ 8.3 at 1 MHz), and excellent retention characteristics up to 10 000 s.     

Resistive Switching Memory Integrated with Nanogenerator for Self‐Powered Bioimplantable Devices

Resistive random access memory (ReRAM) devices powered by piezoelectric nanogenerators (NGs) have been investigated for their application to future implantable biomedical devices. Biocompatible (Na_0.5K_0.5)NbO₃ (NKN) films that are grown at 300 °C on TiN/SiO₂/Si and flexible TiN/Polyimide (TiN‐PI) substrates are used for ReRAM and NGs, respectively. These NKN films have an amorphous phase containing NKN nanocrystals with a size of 5.0 nm. NKN ReRAM devices exhibit typical bipolar switching behavior that can be explained by the formation and rupture of oxygen‐vacancy filaments. They have good ReRAM properties such as a large ratio of R_HRS to R_LRS as well as high reliability. The NKN film grown on flexible TiN‐PI substrate exhibits a high piezoelectric strain constant of 50 pm V^?1. The NKN NG has a large open‐circuit output voltage of 2.0 V and a short‐circuit output current of 40 nA, which are sufficient to drive NKN ReRAM devices. Stable switching properties with a large ON/OFF ratio of 10² are obtained from NKN ReRAM driven by NKN NG.     

Impact of crystallization on ferro-, piezo- and pyro-electric characteristics in thin film P(VDF–TrFE)

In this paper, the impact of the crystallization and polymer chain length of the P(VDF–TrFe) on its dielectric, ferroelectric, piezoelectric and pyroelectric properties are studied. X-rays diffraction (XRD) analysis have revealed that a higher β crystalline phase is obtained with a lower polymer chain length corresponding to a higher grain size for a P(VDF–TrFe) composition of 72.2/27.8 mol.%. The polymer chain morphology was characterized by scanning electron microscopy (SEM) where the fibrils orientation and width were extracted. By coupling both XRD analysis and chain morphology analysis, we have established that an increase of the grain size of the polymer chain enhances the ferroelectric and piezoelectric effects of the P(VDF–TrFe) layer. On the other hand, we observed a slight degradation of its pyroelectric properties. In addition, the piezoelectric coefficient (d₃₃) of the P(VDF–TrFe) was enhanced by decreasing the molecular weight (M_w) of the copolymer, exhibiting a maximum value around −50 pC/N for the composition 72.2/27.8 with a molecular weight of 470 kg/mol. On the opposite, the pyroelectric properties were enhanced for the lowest polymer crystalline grain size studied and obtained with the composition 71/29 mol.% with a molecular weight of 505 kg/mol. A pyroelectric coefficient of 37.8 μC/m² K was measured.     

Layer‐by‐Layer Controlled Perovskite Nanocomposite Thin Films for Piezoelectric Nanogenerators

Perovskite nanoparticle‐based nanocomposite thin films strictly tailored using unconventional layer‐by‐layer (LbL) assembly in organic media for piezoelectric nanogenerators (NGs) are demonstrated. By employing sub‐20‐nm BaTiO₃ nanoparticles stabilized by oleic acid ligands (i.e., OA‐BTO_NPs) and carboxylic acid (COOH)‐functionalized polymers, such as poly(acrylic acid) (PAA), the resulting OA‐BTO_NP/PAA nanocomposite multilayers are prepared by exploiting the high affinity between the COOH groups of PAA and the BTO_NPs. The ferroelectric and piezoelectric performance of the (PAA/OA‐BTO_NP)_n thin films can be precisely controlled by altering the bilayer number, inserted polymer type, and OA‐BTO_NP size. It is found that the LbL assembly in nonpolar solvent media can effectively increase the quantity of adsorbed OA‐BTO_NPs, resulting in the dramatic enhancement of electric power output from the piezoelectric NGs. Furthermore, very low leakage currents are detected from the (PAA/OA‐BTO_NP)_n thin films for obtaining highly reliable power‐generating performance of piezoelectric NGs.