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Piezoelectric two-dimensional (2D) transition-metal dichalcogenides such as molybdenum disulfide (MoS2) have recently attracted significant attention owing to their applicability for fabrication of flexible power generators. In this study, novel piezoelectric nanogenerators (PNGs) consisting of 2D piezoelectric MoS2 shells are fabricated where an Al2O3 thin layer deposited on the surface of polystyrene (PS) beads is used to avoid collapse of the spherical MoS2 shells under the high growth temperature. In addition, the MoS2 shell size is controlled by adjusting the PS bead size and the effects of the MoS2 shell size on power generation characteristics are investigated. Our PNG based on the piezoelectric MoS2 shells produces a peak output voltage of approximately 1.2 V at a pressure of 4.2 kPa. The minimum pressure for power generation by tapping is 0.3 kPa. This novel method is very promising for development of the next-generation PNGs based on 2D semiconductor piezoelectric materials.

A bouncing water droplet not only contains mechanical energy, but also electrostatic energy due to the triboelectric charges on its surface that are generated by its contacts with the surrounding environment. Here, we report development of contact electrification-based water droplet-driven triboelectric nanogenerator (Wd-TENG) for harvesting energy from the water-droplet bouncing between two superhydrophobic surfaces. The Wd-TENG consists of polytetrafluoroethylene balls on the bottom and zinc oxide nanosheets on the top; two surfaces of the device obtain electric energy during the contact electrification from the bouncing water, and additionally, maximize the bouncing motions of the droplets. The device produced a short-circuit current and an open-circuit voltage of 1.3 μA and 1.4 V, respectively. Besides, power-generating performances of the Wd-TENG at various angles of inclination were also investigated, and it showed voltage outputs of 5.5 V, 16 V, 9.8 V, and 6.8 V at the inclination angles of 52°, 58°, 64°, and 70°, respectively. These results demonstrate that the Wd-TENG is potentially a strong candidate for scavenging energy from raindrops.

Molybdenum disulfide (MoS2) monolayer is one of the most promising materials for next-generation electronic/optoelectronic devices because of its prominent piezoelectric property that can modulate Schottky barrier height and control transport behaviors without applying any external gate bias. In this work, we systematically investigated temperature dependence of piezotronic effect of chemical vapor deposition grown MoS2 monolayer by measuring transport behaviors under strains from 0% to 0.3% with various sample temperatures ranging from 270 K to 320 K. It was found that piezoelectric effect in MoS2 monolayer significantly depends on sample temperature. Due to less screening effect of piezoelectric potential generated in MoS2 with a mechanical strain at low temperature, the piezotronic effect is significantly enhanced when the sample temperature is decreased from 320 K to 270 K, revealing that the piezoelectric effect becomes stronger at lower temperature.

In this work, we studied the surface potential of a metal–polymer hybrid layer and its effect on the performance of a triboelectric nanogenerator (TENG). Ag nanowires (AgNWs) separately embedded in two different polymers–one with a positive tribopotential and the other with a negative tribopotential–were prepared as model hybrid systems. The surface potentials of the hybrid system were systematically investigated by Kelvin probe force microscopy. The results demonstrated that each component of the hybrid layer affected the other component because of the difference in their work functions. The following two important findings were obtained. First, the surface potential of each polymer shifted drastically toward that of Ag and the surface potential of Ag shifted toward that of each polymer. Second, higher density of AgNWs led to higher Ag-induced charge density in the polymer, which consequently resulted in larger shift in the surface potential of the polymer. TENG performance measurements revealed that the tribopotential difference between the contact surfaces of the AgNW–polymer hybrid layer and the perfluoroalkoxy alkane (or Nylon) used as the top triboelectric layer governed the TENG performance. Our systematic investigation of the surface potential of a hybrid surface consisting of two materials with different surface potentials provides insight into the design of triboelectric layers for high-performance TENGs.

Recently, research on energy harvesting has attracted great attention as a solution to energy depletion and environmental problems due to the use of fossil fuels such as coal, natural gas, and oil. To be precise, harvesting technology converts the energy sources around us such as solar, heat, and mechanical energy into electrical energy. It has the advantage of being able to supply and sustain energy on a permanent basis, rather than being non-renewable, and it is also eco-friendly. Among the various energy harvesting techniques, nanogenerators based on piezoelectric and triboelectric phenomena can generate electrical energy based on mechanical energy sources, which are usually ubiquitous, there are no restrictions due to weather, time, or space, and this technology is also user-friendly. Recently, two-dimensional (2D) materials have been chosen for implementing piezo/triboelectric nanogenerators. The 2D materials have transparency, flexibility, and a high surface-to-volume ratio. Owing to the very low thickness of the atomic unit, a stacking structure using 2D materials can be also made to form a very thin device, which is applicable for insertion into the body or wearable electronic devices. In this review, we summarize the characteristics and research results on piezo/triboelectric energy harvesters based on 2D layered structure materials.

Triboelectric nanogenerators (TENGs), which have demonstrated that all moving things in the universe can generate electricity in a sustainable way are currently being developed to be integrated with electronics, and to improve user convenience. The electrically charged surface upon a contact electrification phenomenon caused by contact of the materials determines the output performance of TENGs. This review focuses on the electrification and surface charge density characteristics of various fluoropolymer-based materials as active materials that have been investigated to realize high performance TENGs, and the results of the study of their applications. Furthermore, the characteristics of electrification with differently polymerized P(VDF-TrFE) as TENGs’ active materials and their applications are reviewed. The boosted output performance characteristics when used as a matrix material and integrated with a composite system with a high dielectric constant material are also reviewed. Finally, the paper presents three perspectives on the direction of TENG research for future improvement, namely material, structure, and circuitry.

Recently, electrostatic kinetic energy harvesters regained strong attention through the development of new triboelectric generators for harvesting green and renewable energy. These devices use a triboelectric dielectric layer as electret for polarizing their capacitance and they behave similarly to electret generators. However, triboelectric-based electret nanogenerators (T-ENG) have specificities arising from the contact electrification phenomenon and leading to different performances. For better understanding T-ENG, we investigated their electrical modeling with lumped-elements and multiphysics simulation in light of last researches on electret generators. To take into account T-ENG specificities, we experimentally measured the amplitude of the triboelectric effect on perfluoroalkoxy alkane films. This approach allowed fully simulating T-ENG and the model was found in agreement with experimental results. Understanding and verifying the model is capital, but to go further toward the application of T-ENG, we reused two electret circuits to extract the T-ENG model parameters in view of facilitating their realistic modeling and practical development into application.

Conventional p-CuInSe2 absorbers for solar cells have been homogenously synthesized using multi-step process despite a narrow crystal phase region in the phase diagram and the existence of various secondary phases. In contrast, here we propose artificially-designed heterophasic blended copper indium selenide compounds for water splitting photoanodes using a simple one-step annealing synthetic process where the electrodeposited metal precursors were directly annealed with Se vapor injection and without additional intermediate steps. The resultant product is revealed to possess a novel “phase-blended structure” comprising two phases of p-type CuInSe2 and n-type CuIn3Se5 crystals. The CuInSe2 nanoparticles with a higher Cu fraction are three-dimensionally (3D) embedded in the n-type CuIn3Se5 matrix, which has been verified by various analysis methods such as X-ray diffraction, transmission electron microscopy, and capacitance-voltage curve. The average diameter of the CuInSe2 nanoparticles is 66.8 nm and the interval between the nanoparticles in the CuIn3Se5 matrix is 67.6 nm. Consequently, the phase-blended structure photoabsorber exhibits a remarkably enhanced anodic photocurrent of 12.7 mA/cm2 at 1.23 V versus the reversible hydrogen electrode. The considerably enhanced photocurrent gain of the phase-blended structure photoanode is attributed to the excellent charge separation facilitated by the built-in potential generated from the 3D p-n junction.

A patchable triboelectric nanogenerator (TENG) is highly promising for self-powered human-motion detection, but it may undergo repeated stretching/releasing cycles during daily activities of a human, which may lead to mechanical fracture of each component and degradation in electrical output performance of the TENG device. Here, we report a fully stretchable and durable triboelectric nanogenerator (TENG) with gold (Au) nanosheets (NSs) embedded into both PDMS matrix and micropyramid-patterned PDMS. It was found that a new design of the Au NS electrodes dramatically improves the mechanical flexibility and stretchability, enabling to achieve the outstanding output stability of the Au NS electrode-based TENG (Au NS-TENG) during 10,000 cycles of repeated pushing and stretching tests. Our fully stretchable and durable Au NS-TENGs were successfully applied to the hand joints that can be used in the self-powered human-motion detection processes for wearable applications.

Triboelectric nanogenerators (TENG) can effectively generate electrical energy from the otherwise wasted mechanical energy in our environment. However, since vibration energy scavengers are usually driven at their resonant frequency, vibrating TENGs (VTENG) can provide maximized output power only within a few Hz of input frequencies. Here, we report tandem TENGs which are able to optimally scavenge abundant vibration energy under a wide band of input frequencies (tens of Hz and beyond). We first investigate the dynamic response of a single VTENG by parametric analyses (external forces, mass, stiffness, and gap distance) according to input frequencies. Based on coupled behavior, we complete a design protocol for a single VTENG, providing optimal power generation at a given frequency. Finally, we demonstrate a tandem system of resonant VTENGs, where maximum output power can be produced over a broad range of input frequencies between 15 and 40 Hz. It is expected that our design protocol enables optimal energy conversion for an individual TENG and that tandem design will be practically useful for consistently scavenging a wide band of vibration energy from environmental sources such as vehicles, wind, and waves.

Doping to graphene is essential for developing graphene-based electronic devices and circuits, while traditional doping methods to graphene are still challenging due to unstable doping characteristics and unavoidable damage to the graphene structure. Here, we demonstrate piezoionic-powered strain and touch sensors using mechanically doped graphene with solid polymer electrolyte (SPE). Due to the piezoionic effect in SPE, the Dirac point voltage of an SPE-coated graphene field-effect transistor (S-GFET) is shifted left/right upon compressive/tensile strain. This mechanical strain tuned piezoionic doping to graphene that enables to obtain different Dirac point voltage of S-GFET for a piezoionic-powered strain sensor. When the S-GFET acted as a strain sensor, the S-GFET exhibited stable output signals against to continuous strain and was able to distinguish between tension and compression without any additional components. The strain sensor mounted on a hand very effectively responded to the hand joint movement. Additionally, it was found that the device is also suitable for touch sensing due to the coupling of triboelectrification and the electronic transport in the S-GFET.

We report a facile and cost-effective route for fabricating highly efficient triboelectric energy harvesters via formation of artificially well-tailored interlocked interface with a nanostructured Ni electrode and polydimethylsiloxane (PDMS). The interlocked interface formed between the nano-pillar Ni electrode and nano-pillar PDMS composite thin film effectively enhanced the triboelectricity of a triboelectric nanogenerator (TENG) by increasing the surface contact area and contact time, related to the frictional forces. The output power of four different kinds of TENGs was evaluated to confirm the effect of the surface morphology, especially the interlocked interface. A dramatic enhancement of the output voltage (~100 V) was observed with a current of up to ~23 μA. The effectiveness of the interlocked TENG (i-TENG) was also demonstrated by the greater efficiency for charging a capacitor compared with the flat-to-flat contact TENG (flat TENG).

Developing a successful strategy to maximize the surface charge density is crucial to speed-up the commercialization success of triboelectric nanogenerator. Here, for the first time, the fabrication of positive triboelectric material to donate electrons efficiently to dielectrics is reported, by increasing the stretchability for the uniform contact and by introducing a functional group for the surface potential control. A highly stretchable and conductive film with Ag nanowires and PDMS was fabricated as a base material, in which the portion of nanowires exposed above the embedding surface should be accurately controlled. In specific, positively charged 4-(dimethylamino)pyridine (DMAP) coated Au nanoparticles, prepared by phase transfer method, are coated. The DMAP lowers the effective work function of the nanoparticles by a permanent dipole induced at the DMAP-Au interface and enhances the electron transfer to the dielectrics, confirmed by the Kelvin probe force microscope measurement. The designed nanogenerator gives an output performance up to 80 V and 86 μA, and 2.5 mW in output power, 2.5 times enhancement compared with the conventional TENG. With the integration with AC to DC converting circuit and buck-boost circuit, the nanogenerator produces a constant voltage of 2.6 V. The wireless sensing system, which operates the remote controller, were also demonstrated, turning on a siren.

Due to the interesting semiconducting and optical properties of transition metal dichalcogenides, they have received particular attention for novel electronics and optoelectronics. In addition it is expected that piezoelectric properties of two-dimensional (2D) layered materials are very useful to realize next generation mechanically powered transparent flexible charge-generating devices. Here we report directional dependent piezoelectric effects in chemical vapor deposition grown monolayer MoS2 for flexible piezoelectric nanogenerators (NGs). It was found that the output power obtained from the NG with the armchair direction of MoS2 is about two times higher than that from the NG with the zigzag direction of MoS2 under the same strain of 0.48% and the strain velocity of 70 mm/s. This study provides a new way to effectively harvest mechanical energy using novel flexible piezoelectric NGs based on 2D semiconducting piezoelectric MoS2 for powering low power-consuming electronics and realizing self-powered sensors.

Here we demonstrate a zero-writing-power tribotronic touch memory based on polydimethylsiloxane (PDMS)-passivated two-dimensional (2D) MoS2. Triboelectric charges generated by touching the PDMS friction layer are stored on the dielectric PDMS and act as a gate bias which controls the electronic transport in the underlying 2D MoS2 channel. The shift of the threshold voltage can be as high as ~3.5 V and is retained for almost 1 h. During the writing phase, the memory does not consume any power and does not require any battery or connection to electronics. Besides, during the reading phase, a conventional p++ silicon bottom gate allows to bias the touch memory in the highest sensitivity point, so that the output current can be changed by more than two orders of magnitude by a simple touch. Our results open the way for ultimately power-efficient post-impact detection of very slight touches with applications in safety, security, and robotics.

Inevitable frictional heat, generated by friction, degrades output performance of polymer-based triboelectric nanogenerators (TENGs). To address this issue, we propose to take advantage of using shape memory effect of polyurethane (PU) as a triboelectric layer to not only operate TENG sustainably, but also realize self-boosting power generation performance of TENG by frictional heat. We found that frictional heat sufficiently leads to the glass transition of PU and this transformed PU at elevated temperature contributes to change key parameters, serving to improve performance of TENG, including dielectric constant, work function, and charge trap density. In this work we verified PU harness heat generated by friction and demonstrated 300% increase of the power-generating performance of PU-based TENG with experiencing the glass transition. In addition, we experimentally observed no further temperature elevation around 60 °C in TENG with a continuous rotating friction mode, which offers PU potential to be a promising triboelectric material for high performance TENGs.

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.

Transparent flexible and stretchable nanogenerators (NGs) that harvest various types of mechanical energy exhibit a great potential for powering low-power portable devices and self-powered electronic systems. Integration of transparency, flexibility and stretchability to NGs has gained a lot of interest for realizing the energy harvesting systems in practical life. Flexible piezoelectric nanostructures, which can generate electrical signal when mechanically deformed, are the most promising candidates for piezoelectric NGs, which offer sufficient power to drive portable electronics and cardiac pacemakers. Moreover, triboelectric NGs enlighten a new technique to harvest mechanical energies with high conversion efficiency. This review highlights the recent research progress of transparent and flexible ZnO nanorods/nanowires, two-dimensional ZnO nanosheets, stretchable micro-patterned P(VDF-TrFE) polymer, ZnSnO3 nanocubes-based piezoelectric NGs along with graphene and hydrophobic sponge structure-based triboelectric NGs, and their potential applications in powering portable electronics are summarized and presented. Finally, the power generation under different modes of pressure/friction such as vertical compressive, bending, contact-separation and stretching are collected and the involved future challenges are discussed in terms of device configuration and efficiency.

Silk fibroin-based biodegradable composite-type nanogenerators are demonstrated with controllable lifetime for powering to the implantable devices. The 2D thin film- and 1D wire-type composites consist of the well-dispersed lead-free ferroelectric (BaTiO3, ZnSnO3, Bi0.5(Na0.82K0.18)0.5TiO3, and K0.5Na0.5Nb0.995Mn0.005O3) nanoparticles. Ag nanowires are used to enhance the dispersion of the nanoparticles and polyvinylpyrrolidone prevents Ag nanowires from connecting with each other. A maximum output voltages and current densities of 2.2 V and 0.12 µA/cm2 in the thin film, and 1.8 V and 0.1 µA/cm2 in the wire are obtained under the motion of a foot step for when 30 wt% KNN:Mn nanoparticles are well-dispersed in the solution because of the largest piezoelectric coupling figure of merit. The properties of water-soluble composite films are also controlled with the glycerol content up to two days.

Here we demonstrate the deposition of a high-k dielectric material on graphene using hexagonal boron nitride (h-BN) nanosheets as a buffer layer. The presence of an h-BN layer on top of the graphene facilitated the growth of high-quality Al 2 O 3 by atomic layer deposition (ALD). Simulation results also support the experimental observations and provide an explanation for the suitability of h-BN as a buffer layer in terms of mixed ionic-covalent B–N bonding. Additionally, h-BN works as a protective shield to prevent graphene oxidation during ALD of Al 2 O 3 for the fabrication of graphene-based devices. Finally, triboelectric nanogenerators (TNGs) based on both Al 2 O 3 /h-BN/graphene and Al 2 O 3 /graphene structures are demonstrated for further confirming the importance of h-BN for synthesizing high-quality Al 2 O 3 on graphene. It was found that the Al 2 O 3 /h-BN/graphene-based TNG reveals meaningful electric power generation under a mechanical friction, while no significant electric power output from the Al 2 O 3 /graphene-based TNG is obtained, indicating high charge storage capacity of the dielectric Al 2 O 3 layer on h-BN.

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.

Highly-stretchable piezoelectric hemispheres composed composite thin film nanogenerators are fabricated as a self-powered, exceptionally sensitive sensor for providing sensitive motion information from a human body. The composite films are based on the highly-ordered piezoelectric hemispheres embedded in a soft matrix, polydimethylsiloxane (PDMS) and generate large power output up to 6 V and 0.2 μA/cm2 under normal bending force. The electrical outputs increase by stacking such hemispheres layer-by-layer. The strain sensitivity of the films differs according to the bending direction, and the high sensitivity is achieved by convex bending for hemisphere composite due to the strong electric dipole alignment. The films are attached on the surface of a wrist and its output voltage/current density provides the information on the wrist motion.

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.

Organic neuromorphic electronics are inspired by a biological nervous system. Bio-inspired computing mimics learning and memory in a brain (i.e., the central nervous system), and bio-inspired soft robotics and nervous prosthetics mimics the neural signal transmission of afferent/efferent nerves (i.e., the peripheral nervous system). Synaptic decay time of nerves differ among biological organs, so the decay time of artificial synapses should be tuned for their specific uses in neuro-inspired electronics. However, controlling a synaptic decay constant in a fixed synaptic device geometry for broad applications was not been achieved in previous research of neuromorphic electronic devices despite the importance to achieve broad applications from neuromorphic computing to neuro-prosthetics. Here, we tailored the synaptic decay constant of organic synaptic transistors with fixed materials and devices structure rather than changing the form of presynaptic spikes, which enabled broad applications from neuromorphic computing to neuro-prosthetics. To achieve this, the relation between crystallinity of the polymer semiconductor film and the synaptic decay constant was revealed. The crystallinity of the polymer controlled electrochemical-doping kinetics and resultant synaptic behaviors of artificial synaptic transistors. In this way, we demonstrated not only long-term retention for learning and memory that is useful for neuromorphic computing in ion-gel gated organic synaptic transistor (IGOST) but also the short-term retention for fast synaptic transmission that is useful for emulating peripheral nerves such as sensory and motor nerve. To prove the feasibility of our approach in a two different ways, we first simulated pattern recognition on the MNIST dataset of handwritten digits using an IGOST with long-term retention due to increased crystallinity and then, developed artificial auditory sensory nerves that combines an IGOST with short term retention due to disordered chain morphology in a polymer semiconductor, with a triboelectric acoustic sensor. We expect that our approach will provide a universal strategy to realize wide neuromorphic electronic applications.

A biomimetic-villus structure that has been fabricated using a three-dimensional (3D) printer, which is a high-resolution additive-manufacturing process, is here introduced for the realizing of a large increase of the surface area beyond the structural limitations, and the intestinal-villus structure that can be produced only by a 3D printer is imitated. The surface area of the 3D-printed biomimetic-villus structure was increased by approximately 300% compared with the planar structure, and to achieve the full contact of this increased surface area, polytetrafluoroethylene (PTFE) powder was used as the triboelectric material, resulting in fivefold and fourfold increases of the electric power output performance in the vertical-direction mode and the rotational-direction mode, respectively. In addition, a dust-filtration system was designed using the large electrostatic charge that formed between an acrylonitrile butadien styrene (ABS) surface and PTFE powders, and dust particles of various sizes were efficiently adsorbed. Further, because of the use of the polymer-based ABS and the PTFE powers, the dust filter is stable and easily reusable, and it was experimentally confirmed after a washing that the filtration efficiency of 41% is nondecreasing. As a result, a successful validation of the use of the 3D-printed biomimetic-villus structure with the maximized surface area as an ecofriendly dust-adsorption system as well as a triboelectric nanogenerator was achieved.

Multifunctional ZnO semiconductor is a potential candidate for electronics and optoelectronics applications and can be commercialized owing to its excellent electrical and optical properties, inexpensiveness, relative abundance, chemical stability towards air, and much simpler and wide range of crystal-growth technologies. The semiconducting and piezoelectric properties of environmental friendly ZnO are extremely important for energy harvesting devices. This article reviews the importance of energy harvesting using ZnO nanostructures, mainly focusing on ZnO nanostructure-based photovoltaics, piezoelectric nanogenerators, and the hybrid approach to energy harvesting. Several research and design efforts leading to commercial products in the field of energy harvesting are discussed. This paper discusses the future goals that must be achieved to commercialize these approaches for everyday use.

A flexible hybrid cell (HC) to simultaneously harvest thermal and mechanical energies is demonstrated. The output voltage and current of the HC can be well integrated under simultaneous working condition without sacrificing each output. We also demonstrate the possibility of scavenging both thermal and mechanical energies from skin temperature and body motion. This strategy can provide a highly promising platform as hybrid cells that simultaneously harvest multi-types of energy so that the energy resources can be effectively and complementarily utilized for power sensor network and micro/nano-systems. © 2013 Elsevier Ltd. All rights reserved.