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Triboelectrification is a phenomenon that generates electric potential upon contact. Here, we report a viral particle capable of generating triboelectric potential. M13 bacteriophage is exploited to fabricate precisely defined chemical and physical structures. By genetically engineering the charged structures, we observe that more negatively charged phages can generate higher triboelectric potentials and can diffuse the electric charges faster than less negatively charged phages can. The computational results show that the glutamate-engineered phages lower the LUMO energy level so that they can easily accept electrons from other materials upon contact. A phage-based triboelectric nanogenerator is fabricated and it could produce ∼76 V and ∼5.1 μA, enough to power 30 light-emitting diodes upon a mechanical force application. Our biotechnological approach will be useful to understand the electrical behavior of biomaterials, harvest mechanical energy, and provide a novel modality to detect desired viruses in the future.

As the internet of things (IoT) era approaches, various sensors, and wireless electronic devices such as smartphones, smart watches, and earphones are emerging. As the types and functions of electronics are diversified, the energy consumption of electronics increases, which causes battery charging and maintenance issues. The piezoelectric nanogenerator (PENG) received great attention as an alternative to solving the energy issues of future small electronics. In particular, polyvinylidene fluoride (PVDF) piezoelectric polymer-based PENGs are strong potential candidate with robust mechanical properties and a high piezoelectric coefficient. In this review, we summarize the recent significant advances of the development of PVDF-based PENGs for self-powered energy-harvesting systems. We discuss the piezoelectric properties of the various structures of PVDF-based PENGs such as thin film, microstructure, nanostructure, and nanocomposite.

With the development of technology, electronic devices are becoming more miniaturized and multifunctional. With the development of small electronic devices, they are changing from the conventional accessory type, which is portable, to the patchable type, which can be attached to a person's apparel or body, and the eatable/implantable type, which can be directly implanted into the human body. In this regard, it is necessary to address various technical issues, such as high-capacity/high-efficiency small-sized battery technology, component miniaturization, low power technology, flexible technology, and smart sensing technology. In addition, there is a demand for self-powered wireless systems in particular devices. A piezoelectric/triboelectric nanogenerator (PENG/TENG) can generate electric energy from small amounts of mechanical energy such as from blood flow and heartbeats in the human body as well as human movement, so it is expected that it will enable the development of self-powered wireless systems. Due to their unique properties, such as flexibility, transparency, mechanical stability, and nontoxicity, 2D materials are optimal materials for the development of implantable and patchable self-powered nanodevices in the human body. In this Review, the studies related to patchable and implantable devices for the human body using PENGs/TENGs based on 2D materials are discussed.

Next-generation memory and energy harvesting devices require a higher output performance for charging lectric devices. Generally, it is very limited to control charge transfer through triboelectricity in triboelectric materials. Here, using ferroelectric polarization, it is found that both the amount and direction of charge transfer in triboelectric materials can be controlled. The ferroelectric-dependent triboelectricity in a ferroelectric co-polymer film is explored using atomic force microscopy (AFM). Ferroelectric surfaces are rubbed with the AFM tip after poling with positive and negative bias voltages to achieve a triboelectric effect. The surface potential of the positively (negatively) poled area becomes smaller (larger) after rubbing the film surface with the AFM tip. Furthermore, the power output from the triboelectric nanogenerator is dependent on the ferroelectric polarization state. The results indicate that the amount and direction of the charge transfer in triboelectricity can be controlled by the ferroelectric polarization state.

Transparent and flexible (TF) microheaters are required in wearable devices, labs-on-chip, and micro-reactors. Nevertheless, conventional microheaters are rigid or opaque or both. Moreover, the resistances of conventional metallic microheaters are too low to be effectively powered by wearable energy harvesters. Here, we demonstrate the first TF microheaters by taking advantage of chemical vapor deposition (CVD)-grown graphene heating tracks and of a hexagonal boron nitride (h-BN) sheet for passivation; the h-BN sheet increases the maximum temperature by ~80%. Our TF microheaters show excellent temperature uniformity and can reach temperatures above 200 °C in just 4 s, with power consumption as low as 39 mW. Additionally, since the CVD-graphene sheet resistance is orders of magnitude higher than that of typical metallic heaters, our devices can be effectively powered by wearable energy harvesters. As a proof-of-concept, we demonstrate the first self-powered, wearable microheater which achieves a temperature increase of 8 °C when operated by a sound driven textile-based triboelectric nanogenerator. This is a key milestone towards next generation microheaters with applications in portable/wearable personal electronics, wireless health, and remote and mobile environmental sensors.

The search for harvesting both the mechanical and solar energies from a single hybrid system is of significant value and represents a new trend in energy harvesting technologies. This single hybrid system can utilize both the energy sources easily available from nature and most importantly it is clean and sustainable. It is a novel technique involving completely different physical principles utilized for scavenging different types of energies. This report presents studies of a hybrid power generator made a direct-current piezoelectric nanogenerator based on ZnO nanosheets and a bulk heterojunction organic solar cell based on an inverted structure. The device shows much larger electric power output compared to its two individual power output components, which facilitates more effective multi-type energies harvesting and clarifies a mechanism for realizing multi-functional energy devices.

Piezoelectric semiconductor materials have emerged as the most attractive material for nanogenerator (NG)-based prototype applications, such as piezotronics, piezophotonics and energy harvesting, due to the coupling of piezoelectric and semiconducting dual properties. Understanding the mechanisms for high power generation, charge transport behavior, energy band modulations, and role of depletion width in piezoelectric semiconducting p–n junction, through piezoelectric charges developed by external mechanical strains, are essential for various NGs. Here, we demonstrate enhancement of the output power of one-dimensional zinc oxide (ZnO) nanowires (NWs)-based NG using a p-type semiconductor polymer, by controlling their energy band at depletion width in the piezoelectric semiconducting p–n junction interface and native defects presented in as-grown ZnO NWs. The piezoelectric output performance from the P3HT-coated ZnO NWs-based NG was several times higher than that from the pristine ZnO NWs-based NG, under application of the same vertical compressive strain. Holes from the p-type P3HT polymer significantly reduced the piezoelectric potential screening effect caused by free electrons in ZnO. Theoretical investigations using COMSOL multiphysics software were also carried out, in order to understand the improvement in the performance of surface passivated ZnO NWs-based NG, in terms of free carriers concentration and holes diffusion, due to the formation of p–n junction at the interface of ZnO and P3HT, and depletion width change.

Here, we report the synthesis of lead-free single-crystalline two-dimensional (2D) vanadium(V)-doped ZnO nanosheets (NSs) and their application for high-performance flexible direct current (DC) power piezoelectric nanogenerators (NGs). The vertically aligned ZnO nanorods (NRs) converted to NS networks by V doping. Piezoresponse force microscopy studies reveal that vertical V-doped ZnO NS exhibit typical ferroelectricity with clear phase loops, butterfly, and well-defined hysteresis loops with a piezoelectric charge coefficient of up to 4 pm/V, even in 2D nanostructures. From pristine ZnO NR-based NGs, alternating current (AC)-type output current was observed, while from V-doped ZnO NS-based NGs, a DC-type output current density of up to 1.0 μAcm(-2) was surprisingly obtained under the same vertical compressive force. The growth mechanism, ferroelectric behavior, charge inverted phenomena, and high piezoelectric output performance observed from the V-doped ZnO NS are discussed in terms of the formation of an ionic layer of [V(OH)4(-)], permanent electric dipole, and the doping-induced resistive behavior of ZnO NS.

Here we report a new type of stretchable transparent piezoelectric nanogenerator (NG) using an organic piezoelectric material consisting of poly(vinylidene fluoride trifluoroethylene) [P(VDF-TrFE)] sandwiched with mobility-modified chemical vapor deposition-grown graphene electrodes by ferroelectric polarization into P(VDF-TrFE). This new type of NG has a very high sensitivity and mechanical durability with fully flexible, rollable, stretchable, foldable, and twistable properties. We also investigated the mobility-modified graphene electrodes with ferroelectric P(VDF-TrFE) remnant polarization, and a mechanism is proposed for switching the mobility of the carriers by the ferroelectric remnant polarization. Upon exposure to the same input sound pressure, the measured output performance of the stretchable NG with a thin polydimethylsiloxane stretchable rubber template is up to 30 times that of a normal NG with a plastic substrate. Upon exposure to an air flow at the same speed, the measured output voltage from the stretchable NG is about 8 times larger than that of the normal NG.

In this work, a sulfur (S) vacancy passivated monolayer MoS2 piezoelectric nanogenerator (PNG) is demonstrated, and its properties before and after S treatment are compared to investigate the effect of passivating S vacancy. The S vacancies are effectively passivated by using the S treatment process on the pristine MoS2 surface. The S vacancy site has a tendency to covalently bond with S functional groups; therefore, by capturing free electrons, a S atom will form a chemisorbed bond with the S vacancy site of MoS2 . S treatment reduces the charge-carrier density of the monolayer MoS2 surface, thus the screening effect of piezoelectric polarization charges by free carrier is significantly prevented. As a result, the output peak current and voltage of the S-treated monolayer MoS2 nanosheet PNG are increased by more than 3 times (100 pA) and 2 times (22 mV), respectively. Further, the S treatment increases the maximum power by almost 10 times. The results suggest that S treatment can reduce free-charge carrier by sulfur S passivation and efficiently prevent the screening effect. Thus, the piezoelectric output peaks of current, voltage, and maximum power are dramatically increased, as compared with the pristine MoS2 .

Monitoring of human activities can provide clinically relevant information pertaining to disease diagnostics, preventive medicine, care for patients with chronic diseases, rehabilitation, and prosthetics. The recognition of strains on human skin, induced by subtle movements of muscles in the internal organs, such as the esophagus and trachea, and the motion of joints, was demonstrated using a self-powered patchable strain sensor platform, composed on multifunctional nanocomposites of low-density silver nanowires with a conductive elastomer of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate/polyurethane, with high sensitivity, stretchability, and optical transparency. The ultra-low-power consumption of the sensor, integrated with both a supercapacitor and a triboelectric nanogenerator into a single transparent stretchable platform based on the same nanocomposites, results in a self-powered monitoring system for skin strain. The capability of the sensor to recognize a wide range of strain on skin has the potential for use in new areas of invisible stretchable electronics for human monitoring. A new type of transparent, stretchable, and ultrasensitive strain sensor based on a AgNW/PEDOT:PSS/PU nanocomposite was developed. The concept of a self-powered patchable sensor system integrated with a supercapacitor and a triboelectric nanogenerator that can be used universally as an autonomous invisible sensor system was used to detect the wide range of strain on human skin.

Negatively polarized ferroelectric polymer β-P(VDF-TrFE) shows higher positive triboelectric properties than skin, which could lead to new medical applications. Kelvin force microscope measurements and triboelectric nanogenerator characterizations are performed to demonstrate this new property. In addition, how many negative charges are exchanged by contact electrification between the negatively polarized β-P(VDF-TrFE) and the skin is estimated.

Here we report a fully flexible, foldable nanopatterned wearable triboelectric nanogenerator (WTNG) with high power-generating performance and mechanical robustness. Both a silver (Ag)-coated textile and polydimethylsiloxane (PDMS) nanopatterns based on ZnO nanorod arrays on a Ag-coated textile template were used as active triboelectric materials. A high output voltage and current of about 120 V and 65 μA, respectively, were observed from a nanopatterned PDMS-based WTNG, while an output voltage and current of 30 V and 20 μA were obtained by the non-nanopatterned flat PDMS-based WTNG under the same compressive force of 10 kgf. Furthermore, very high voltage and current outputs with an average value of 170 V and 120 μA, respectively, were obtained from a four-layer-stacked WTNG under the same compressive force. Notably it was found there are no significant differences in the output voltages measured from the multilayer-stacked WTNG over 12 000 cycles, confirming the excellent mechanical durability of WTNGs. Finally, we successfully demonstrated the self-powered operation of light-emitting diodes, a liquid crystal display, and a keyless vehicle entry system only with the output power of our WTNG without any help of external power sources.

Poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)), as a ferroelectric polymer, offers great promise for energy harvesting for flexible and wearable applications. Here, this paper shows that the choice of solvent used to dissolve the polymer significantly influences its properties in terms of energy harvesting. Indeed, the P(VDF-TrFE) prepared using a high dipole moment solvent has higher piezoelectric and pyroelectric coefficients and triboelectric property. Such improvements are the result of higher crystallinity and better dipole alignment of the polymer prepared using a higher dipole moment solvent. Finite element method simulations confirm that the higher dipole moment results in higher piezoelectric, pyroelectric, and triboelectric potential distributions. Furthermore, P(VDF-TrFE)-based piezoelectric, pyroelectric, and triboelectric nanogenerators (NGs) experimentally validate that the higher dipole moment solvent significantly enhances the power output performance of the NGs; the improvement is about 24% and 82% in output voltage and current, respectively, for piezoelectric NG; about 40% and 35% in output voltage and current, respectively, for pyroelectric NG; and about 65% and 75% in output voltage and current for triboelectric NG. In brief, the approach of using a high dipole moment solvent is very promising for high output P(VDF-TrFE)-based wearable NGs.

Hydrophobic sponge structure-based triboelectric nanogenerators using an inverse opal structured film for sustainable energy harvesting over a wide range of humid atmosphere have been successfully demonstrated. The output voltage and current density reach a record value of 130 V and 0.10 mA cm(-2) , respectively, giving over 10-fold power enhancement, compared with the flat film-based triboelectric nanogenerator.

Mechanical energy is a potential energy source for self-powered electronic devices. Due to their unique semiconducting and piezoelectric properties, wurtzite-structured nanomaterials have been considered as potential candidates for piezoelectric nanogenerators that convert mechanical energy into electricity. In the present work, we report on the growth of Ga-doped ZnO (GZO) nanorods and investigate the performance of nanogenerators fabricated from undoped ZnO (UZO) nanorods, low Ga-doped ZnO (LGZO) nanorods, and high Ga-doped ZnO (HGZO) nanorods. A nanogenerator integrated with LGZO nanorods exhibited a current density of 1.2 microA/cm2, an enhancement over the 0.4 microA/cm2 and 0.7 microA/cm2 current densities of nanogenerators integrated with UZO and HGZO nanorods, respectively.

It is essential to stabilize and enhance the power output performance of piezoelectric nanogenerators (NGs) in order to use them as a sustainable power source for wireless sensors, microelectronics, and optoelectronic devices. Here, we report a facile route to stabilize and maximize the output performance of a zinc oxide (ZnO) nanorod (NR)-based NG in the presence of ultraviolet (UV) light by reducing the piezoelectric potential screening effect caused by the free electrons in the ZnO NRs via surface passivation. We experimentally and theoretically investigated the piezoelectric potential drop in the ZnO NR-based NG due to the piezoelectric potential screening effect. A simple thermal annealing treatment was applied to the pristine ZnO NRs in air atmosphere to stabilize the output performance of the NG even in the presence of UV light. The piezoelectric output voltage from the surface-passivated NG was approximately 25 times higher than that from the NG with no passivation under UV light illumination.