Skin-like electronics that can adhere seamlessly to human skin or within the body are highly desirable for applications such as health monitoring, medical treatment, medical implants and biological studies, and for technologies that include human-machine interfaces, soft robotics and augmented reality. Rendering such electronics soft and stretchable-like human skin-would make them more comfortable to wear, and, through increased contact area, would greatly enhance the fidelity of signals acquired from the skin. Structural engineering of rigid inorganic and organic devices has enabled circuit-level stretchability, but this requires sophisticated fabrication techniques and usually suffers from reduced densities of devices within an array. We reasoned that the desired parameters, such as higher mechanical deformability and robustness, improved skin compatibility and higher device density, could be provided by using intrinsically stretchable polymer materials instead. However, the production of intrinsically stretchable materials and devices is still largely in its infancy: such materials have been reported, but functional, intrinsically stretchable electronics have yet to be demonstrated owing to the lack of a scalable fabrication technology. Here we describe a fabrication process that enables high yield and uniformity from a variety of intrinsically stretchable electronic polymers. We demonstrate an intrinsically stretchable polymer transistor array with an unprecedented device density of 347 transistors per square centimetre. The transistors have an average charge-carrier mobility comparable to that of amorphous silicon, varying only slightly (within one order of magnitude) when subjected to 100 per cent strain for 1,000 cycles, without current-voltage hysteresis. Our transistor arrays thus constitute intrinsically stretchable skin electronics, and include an active matrix for sensory arrays, as well as analogue and digital circuit elements. Our process offers a general platform for incorporating other intrinsically stretchable polymer materials, enabling the fabrication of next-generation stretchable skin electronic devices.

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Soft and conformable wearable electronics require stretchable semiconductors, but existing ones typically sacrifice charge transport mobility to achieve stretchability. We explore a concept based on the nanoconfinement of polymers to substantially improve the stretchability of polymer semiconductors, without affecting charge transport mobility. The increased polymer chain dynamics under nanoconfinement significantly reduces the modulus of the conjugated polymer and largely delays the onset of crack formation under strain. As a result, our fabricated semiconducting film can be stretched up to 100% strain without affecting mobility, retaining values comparable to that of amorphous silicon. The fully stretchable transistors exhibit high biaxial stretchability with minimal change in on current even when poked with a sharp object. We demonstrate a skinlike finger-wearable driver for a light-emitting diode.

Harvesting energy from our living environment is an effective approach for sustainable, maintenance-free, and green power source for wireless, portable, or implanted electronics. Mechanical energy scavenging based on triboelectric effect has been proven to be simple, cost-effective, and robust. However, its output is still insufficient for sustainably driving electronic devices/systems. Here, we demonstrated a rationally designed arch-shaped triboelectric nanogenerator (TENG) by utilizing the contact electrification between a polymer thin film and a metal thin foil. The working mechanism of the TENG was studied by finite element simulation. The output voltage, current density, and energy volume density reached 230 V, 15.5 μA/cm 2 , and 128 mW/cm 3 , respectively, and an energy conversion efficiency as high as 10−39% has been demonstrated. The TENG was systematically studied and demonstrated as a sustainable power source that can not only drive instantaneous operation of light-emitting diodes (LEDs) but also charge a lithium ion battery as a regulated power module for powering a wireless sensor system and a commercial cell phone, which is the first demonstration of the nanogenerator for driving personal mobile electronics, opening the chapter of impacting general people's life by nanogenerators. KEYWORDS: Energy harvesting, triboelectric nanogenerator, self-powered system, lithium ion battery A rapid expansion of electronic devices 1−4 toward wireless, portability, and multifunction desperately needs the development of independent and maintenance-free power sources. 5−7 The emerging technologies for mechanical energy harvesting 8−10 are effective and promising approaches for building self-powered systems because of a great abundance of mechanical energy existing in our living environment and human body. Since 2006, piezoelectric nanogenerators (PNGs) 11−14 have been developed to efficiently convert tinyscale mechanical energy into electricity. Recently, another creative invention is the cost-effective and robust triboelectric nanogenerators (TENGs) 15−17 based on the universally known contact electrification effect. 18,19 TENG harvests mechanical energy through a periodic contact and separation of two polymer plates. However, in order to realize sustainable driving of electronic devices/systems, the output of TENG must be significantly improved through a rational design.The two different types of nanogenerators presented above have a similar underlying physical process 12,17 for producing electricity: generation of immobile charges (ionic charges for PNG or electrostatic charges on insulators for TENG), and a periodic separation and contact of the oppositely charged surfaces to change the induced potential across the electrodes, which will drive the flow of free electrons through an external load. The electrical output and efficiency are radically determined by the effectiveness of the above two processes.As for the charge generation in TENG, maximizing the generation of electrostatic charges on opposit...

We report here a simple and effective approach, named scalable sweeping-printing-method, for fabricating flexible highoutput nanogenerator (HONG) that can effectively harvesting mechanical energy for driving a small commercial electronic component. The technique consists of two main steps. In the first step, the vertically aligned ZnO nanowires (NWs) are transferred to a receiving substrate to form horizontally aligned arrays. Then, parallel stripe type of electrodes are deposited to connect all of the NWs together. Using a single layer of HONG structure, an open-circuit voltage of up to 2.03 V and a peak output power density of ∼11 mW/cm 3 have been achieved. The generated electric energy was effectively stored by utilizing capacitors, and it was successfully used to light up a commercial light-emitting diode (LED), which is a landmark progress toward building self-powered devices by harvesting energy from the environment. This research opens up the path for practical applications of nanowire-based piezoelectric nanogeneragtors for self-powered nanosystems.KEYWORDS Nanogenerator, ZnO, nanowire, light-emitting diode, self-powering E nergy harvesting is critical to achieve independent and sustainable operations of nanodevices, aiming at building self-powered nanosystems. 1-3 Taking the forms of irregular air flow/vibration, ultrasonic waves, body movement, and hydraulic pressure, mechanical energy is ubiquitously available in our living environment. It covers a wide range of magnitude and frequency from cell contraction to ocean waves. The mechanical-electric energy conversion has been demonstrated using piezoelectric cantilever working at its resonating mode. [4][5][6][7] However, the applicability and adaptability of the traditional cantilever based energy harvester is greatly impeded by the large unit size, large triggering force and specific high resonance frequency. Recently, a series of rationally designed nanogenerators (NGs) with piezoelectric nanowires (NWs) have shown great potentialtoscavengetinyandirregularmechanicalenergy. [8][9][10][11][12][13][14][15] However, insufficient electric output hinders their practical applications. We report here a simple and effective approach, named scalable sweeping-printing-method, for fabricating flexible high-output nanogenerator (HONG). An open-circuit voltage of up to 2.03 V and a peak output power density of ∼11 mW/cm 3 have been achieved. The generated electric energy was effectively stored by utilizing capacitors, and it was successfully used to light up a commercial lightemitting diode (LED), which is a landmark progress toward building self-powered devices by harvesting energy from the environment. Furthermore, by optimizing the density of the NWs on the substrate and with the use of multilayer integration, a peak output power density of ∼0.44 mW/cm 2 and volume density of 1.1 W/cm 3 are predicted.The mechanism of converting mechanical energy by a single ZnO NW that is laterally bonded to a substrate has been discussed in details in our previous rep...

Aiming at harvesting ambient mechanical energy for self-powered systems, triboelectric nanogenerators (TENGs) have been recently developed as a highly efficient, cost-effective and robust approach to generate electricity from mechanical movements and vibrations on the basis of the coupling between triboelectrification and electrostatic induction. However, all of the previously demonstrated TENGs are based on vertical separation of triboelectriccharged planes, which requires sophisticated device structures to ensure enough resilience for the charge separation, otherwise there is no output current. In this paper, we demonstrated a newly designed TENG based on an in-plane charge separation process using the relative sliding between two contacting surfaces. Using Polyamide 6,6 (Nylon) and polytetrafluoroethylene (PTFE) films with surface etched nanowires, the two polymers at the opposite ends of the triboelectric series, the newly invented TENG produces an open-circuit voltage up to ∼1300 V and a short-circuit current density of 4.1 mA/m 2 with a peak power density of 5.3 W/m 2 , which can be used as a direct power source for instantaneously driving hundreds of serially connected light-emitting diodes (LEDs). The working principle and the relationships between electrical outputs and the sliding motion are fully elaborated and systematically studied, providing a new mode of TENGs with diverse applications. Compared to the existing vertical-touching based TENGs, this planar-sliding TENG has a high efficiency, easy fabrication, and suitability for many types of mechanical triggering. Furthermore, with the relationship between the electrical output and the sliding motion being calibrated, the sliding-based TENG could potentially be used as a self-powered displacement/speed/acceleration sensor. KEYWORDS: Mechanical energy harvesting, triboelectric nanogenerators, in-plane charge separation, self-powered systems T he fundamental science and practical applicable technologies for harvesting ambient environmental energy 1−6 are not only essential in realizing the self-powered electronic devices and systems 7,8 but also tremendously helpful in meeting the rapid-growing worldwide energy consumptions. Mechanical energy is one of the most universally existing, diversely presenting but usually wasted energies in the natural environment, which has attracted a lot of effort in developing the energy harvesting techniques based on different effects and mechanisms, such as electrostatics, 9,10 piezoelectricity, 11−13 and electromagnetics. 14,15 The triboelectric effect 16,17 is a wellknown phenomenon that can generate electrostatic charges from mechanical contact. However, it has always been deemed as an undesirable effect for electronic systems. The recent invention of triboelectric nanogenerators (TENGs) has made use of this effect to generate electricity through scavenging mechanical energy, which is proven to be extremely efficient, reliable and cost-effective. 18−21 This type of nanogenerator is based on the coupling...

The development of internet of things and the related sensor technology have been a key driving force for the rapid development of industry and information technology. The requirement of wireless, sustainable and independent operation is becoming increasingly important for sensor networks that currently could include thousands even to millions of sensor nodes with different functionalities. For these purposes, developing technologies of self-powered sensors that can utilize the ambient environmental energy to drive the operation themselves is highly desirable and mandatory. The realization of self-powered sensors generally has two approaches: the first approach is to develop environmental energy harvesting devices for driving the traditional sensors; the other is to develop a new category of sensors-self-powered active sensors-that can actively generate electrical signal itself as a response to a stimulation/triggering from the ambient environment. The recent invention and intensive development of triboelectric nanogenerators (TENGs) as a new technology for mechanical energy harvesting can be utilized as self-powered active mechanical sensors, because the parameters (magnitude, frequency, number of periods, etc.) of the generated electrical signal are directly determined by input mechanical behaviors. In this review paper, we first briefly introduce the fundamentals of TENGs, including the four basic working modes. Then, the most updated progress of developing TENGs as self-powered active sensors is reviewed. TENGs with different working modes and rationally designed structures have been developed as self-powered active sensors for a variety of mechanical motions, including pressure change, physical touching, vibrations, acoustic waves, linear displacement, rotation, tracking of moving objects, and acceleration detection. Through combining the opencircuit voltage and the short-circuit current, the detection of both static and dynamic processes has been enabled. The integration of individual sensor elements into arrays or matrixes helps to

For versatile mechanical energy harvesting from arbitrary moving objects such as humans, a new mode of triboelectric nanogenerator is developed based on the sliding of a freestanding triboelectric-layer between two stationary electrodes on the same plane. With two electrodes alternatively approached by the tribo-charges on the sliding layer, electricity is effectively generated due to electrostatic induction. A unique feature of this nanogenerator is that it can operate in non-contact sliding mode, which greatly increases the lifetime and the efficiency of such devices.