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A raindrop solar cell can work either on rainy days to collect mechanical energy of the raindrops or on sunny days to harvest solar energy, which achieves high energy conversion efficiency in various energy environments. However, the low efficiency of raindrop energy harvesting is a dominating barrier to the raindrop solar cells in practical applications. In this work, a MoO

As accurate step counting is a critical indicator for exercise evaluation in daily life, pedometers give a quantitative prediction of steps and analyze the amount of exercise to regulate the exercise plan. However, the merchandized pedometers still suffer from limited battery life and low accuracy. In this work, an integrated self-powered real-time pedometer system has been demonstrated. The highly integrated system contains a porous triboelectric nanogenerator (P-TENG), a data acquisition and processing (DAQP) module, and a mobile phone APP. The P-TENG works as a pressure sensor that generates electrical signals synchronized with users' footsteps, and combining it with the analogue front-end (AFE) circuit yields an ultrafast response time of 8 ms. Moreover, the combination of a mini press-to-spin-type electromagnetic generator (EMG) and a supercapacitor enables a self-powered and self-sustained operation of the entire pedometer system. This work implements the regulation of TENG signals by electronic circuit design and proposes a highly integrated system. The improved reliability and practicality provide more possibilities for wearable self-powered electronic devices.

The components in traditional human–machine interaction (HMI) systems are relatively independent, distributed and low-integrated, and the wearing experience is poor when the system adopts wearable electronics for intelligent control. The continuous and stable operation of every part always poses challenges for energy supply. In this work, a triboelectric technology-based all-in-one self-powered HMI system for wireless remote telemetry and the control of intelligent cars is proposed. The dual-network crosslinking hydrogel was synthesized and wrapped with functional layers to fabricate a stretchable fibrous triboelectric nanogenerator (SF-TENG) and a supercapacitor (SF-SC), respectively. A self-charging power unit containing woven SF-TENGs, SF-SCs, and a power management circuit was exploited to harvest mechanical energy from the human body and provided power for the whole system. A smart glove designed with five SF-TENGs on the dorsum of five fingers acts as a gesture sensor to generate signal permutations. The signals were processed by the microcontroller and then wirelessly transmitted to the intelligent car for remote telemetry and control. This work is of paramount potential for the application of various terminal devices in self-powered HMI systems with high integration for wearable electronics.

MXenes are a large class of two-dimensional (2D) materials widely studied recently since they have good water solubility and are able to tune the work function (WF) of materials without changing their electronic characteristics. Based on this, aqueous solution-processed indium-free zinc tin oxide (ZTO) thin-film transistors (TFTs) have been fabricated under an annealing temperature of 300 °C and successfully optimized. This optimization is achieved by fabricating a channel layer into a homojunction structure (MXene doped ZTO/ZTO) to form a two-dimensional electron gas (2DEG). Through doping the specific concentrations of Ti3C2Tx MXenes into the upper layer ZTO thin films, the TFTs exhibit enhanced field-effect mobilities (μFE) of 10.77 cm2 V−1 s−1 and 13.06 cm2 V−1 s−1 as well as a large on/off current ratio of more than 108. Moreover, compared with the undoped double-layer ZTO TFTs, the homojunction devices show better stability, mainly resulting from the transformation in leading conduction mode. Finally, through applying the homojunction channel on the solution-processed aluminum oxide (AlOx) dielectric layer, the μFE exhibits a further enhanced value of 28.35 cm2 V−1 s−1. This is the first report to apply MXenes to the channel layer of TFTs and to fabricate solution-processed ZTO thin films via an aqueous solvent under 300 °C.

Ion concentration in water is a key criterion for evaluating water quality. In this work, we developed a self-powered on-line ion concentration monitor in water transportation based on impedance matching effect of triboelectric nanogenerator (TENG). A rotary disc-shaped TENG (RD-TENG) and an ion concentration sensor were fabricated based on the industrial printed circuit board (PCB) technology. Flowing water in the pipeline acts as the energy source to drive the RD-TENG and generate an open-circuit (Voc) of 210 V. The ion concentration sensor exhibits a nearly pure resistance characteristic under the alternating current (AC) signal with the frequency below 500 Hz, corresponding to the rotation speed of 250 rpm for the RD-TENG. The impedance matching relationship between the RD-TENG and the ion concentration sensor was experimentally studied and applied to elucidate the sensing mechanism. Finally, a self-powered sensing system integrated with an alarm circuit was assembled which exhibits excellent responsibility and high sensitivity. The change of ion concentration with only 1 × 10−5 mol/L can light up an alarm LED.

Constructing electronic systems without an external power source is urgently required toward self-powered photodetection. In this work, we proposed a self-driven photodetection system with a MoS2 nanosheets photodetector as light intensity sensor, a vertical contact-separate mode triboelectric nanogenerator (CS-TENG) as power source, and several LEDs as alarm. The MoS2 based planar photodetector was fabricated by conventional photolithography technique and lift-off process. It is highly sensitive for visible light illumination with high current on-off ratio and excellent reproducibility characteristics under light on-off switching. When conjuncting these functional devices, the induced output voltage of the CS-TENG is tuned by the load resistance of the photodetector, which is responded to the light intensity. The mechanism can be ascribed to the impedance matching effect between specific output characteristics of TENG and working status of photodetector. By adding a Zener diode acts as a voltage regulator, the self-driven renders the voltage and current varying from 1.58 to 20.60 V and 0.06–4.78 μA in a range of light intensity from 0 to 3.19 W/m2, respectively. Finally, it is demonstrated that the output of CS-TENG varies with the variable working states of the MoS2 photodetector and then accurately reflects on the lighted number of LEDs.

Self-healable soft conductors, which can withstand certain degrees of deformation and can recover from damage spontaneously, are essential for wearable applications. In this work, a soft hydrogel based self-healing triboelectric nanogenerator (HS-TENG), which is highly deformable, and both mechanically and electrically self-healable, has been successfully fabricated from a poly(vinyl alcohol)/agarose hydrogel. The incorporation of photothermally active polydopamine particles and multiwalled carbon nanotubes (MWCNTs) allows the HS-TENG to be physically self-healed in ∼1 min upon exposure to near-infrared (NIR) light. At the same time, the chemical self-healing of the HS-TENG can be triggered by water spraying at 25 °C when introducing water-active dynamic borate bonds into the hydrogel. The applicability of the HS-TENG as a soft energy device to harvest human motion energies has been demonstrated. By tapping the HS-TENG with various deformations, the rectified electricity can charge commercial LEDs with sustainable energy. Working in single-electrode mode, the electrical outputs of the HS-TENG in terms of short-circuit transferred charge (Qsc), open circuit voltage (Voc) and short-circuit current (Isc) reach ∼32 nC, ∼95 V and ∼1.5 μA, respectively, and remain stable even with 200% strain since the MWCNTs disperse evenly in the matrix and play the role of conductive fillers in the HS-TENG.

The ecofriendly combustion synthesis (ECS) and self-combustion synthesis (ESCS) have been successfully utilized to deposit high-k aluminum oxide (AlOx) dielectrics at low temperatures and applied for aqueous In2O3 thin-film transistors (TFTs) accordingly. The ECS and ESCS processes facilitate the formation of high-quality dielectrics at lower temperatures compared to conventional methods based on an ethanol precursor, as confirmed by thermal analysis and chemical composition characterization. The aqueous In2O3 TFTs based on ECS and ESCS-AlOx show enhanced electrical characteristics and counterclockwise transfer-curve hysteresis. The memory-like counterclockwise behavior in the transfer curve modulated by the gate bias voltage is comparable to the signal modulation by the neurotransmitters. ECS and ESCS transistors are employed to perform synaptic emulation; various short-term and long-term memory functions are emulated with low operating voltages and high excitatory postsynaptic current levels. High stability and reproducibility are achieved within 240 pulses of long-term synaptic potentiation and depression. The synaptic emulation functions achieved in this work match the demand for artificial neural networks (ANN), and a multilayer perceptron (MLP) is developed using an ECS-AlOx synaptic transistor for image recognition. A superior recognition rate of over 90% is achieved based on ECS-AlOx synaptic transistors, which facilitates the implementation of the metal-oxide synaptic transistor for future neuromorphic computing via an ecofriendly route.

Resistive random access memory (RRAM) devices are receiving increasing extensive attention due to their enhanced properties such as fast operation speed, simple device structure, low power consumption, good scalability potential and so on, and are currently considered to be one of the next-generation alternatives to traditional memory. In this review, an overview of RRAM devices is demonstrated in terms of thin film materials investigation on electrode and function layer, switching mechanisms and artificial intelligence applications. Compared with the well-developed application of inorganic thin film materials (oxides, solid electrolyte and two-dimensional (2D) materials) in RRAM devices, organic thin film materials (biological and polymer materials) application is considered to be the candidate with significant potential. The performance of RRAM devices is closely related to the investigation of switching mechanisms in this review, including thermal-chemical mechanism (TCM), valance change mechanism (VCM) and electrochemical metallization (ECM). Finally, the bionic synaptic application of RRAM devices is under intensive consideration, its main characteristics such as potentiation/depression response, short-/long-term plasticity (STP/LTP), transition from short-term memory to long-term memory (STM to LTM) and spike-time-dependent plasticity (STDP) reveal the great potential of RRAM devices in the field of neuromorphic application.

The portable UV photodetector is used to timely remind humans of overexposure to UV radiation. However, the traditional UV photodetector cannot meet the practical demands, and the power supply problem hinders its further development. In this work, we demonstrated a flexible, transparent, and self-powered UV photodetector by coupling of triboelectric and photoelectric effects. The device integrates a flexible ZnO nanoparticle (NP) UV photodetector, a transparent- and flexible-film-based TENG (TFF-TENG), commercial chip resistors, and LEDs on the PET thin film. The TFF-TENG could harvest mechanical energy from finger tapping and sliding motion and power the ZnO NP UV photodetector to realize self-powered detection. The voltage of the constant resistors connected with the UV photodetector in series changes from 0.5 to 19 V under the UV light with power intensities increasing from 0.46 to 21.8 mW/cm2, and the voltage variation is reflected by the number of LEDs directly. The excellent flexibility and transparency of the device could extend its application scenarios; for example, such a portable device could be applied to real-time monitoring of the UV radiation to remind humans of intense UV light.

Triboelectric nanogenerators (TENGs), as a new emerging and cost-effective approach, shows a promising prospective for harvesting blue energy. However, several challenges still exist limiting output performance, such as the package and low frequency of water wave. Here, we proposed an atmospheric pressure difference driven energy harvesting methodology for harvesting low-frequency ocean wave energy, especially for near-shore ocean waves. Through the methodology, it enables to transform intermittent and low frequency water wave movement into stored-energy and then release the energy in form of airflow and trigger continuous and high frequency movement, which greatly improves working efficiency of TENGs. With the smart design of a soft membrane, this methodology can well achieve waterproof effect by outer framework and be well matched different frequency ocean waves. To demonstrate the feasibility, two specific TENG structures have been demonstrated as examples: a flutter-driven TENG (FD-TENG) driven by lower speed airflow and a disc-shaped TENG (DS-TENG) triggered by stronger airflow. This methodology demonstrates perspectives toward blue energy dream and further expands the practical application of TENGs for large-scale blue energy from water wave in oceans.

The urgent demand for portable electronics has promoted the development of high-efficiency, sustainable, and even stretchable self-charging power sources. In this work, we propose a flexible self-charging power unit based on folded carbon (FC) paper for harvesting mechanical energy from human motion and power portable electronics. The present unit mainly consists of a triboelectric nanogenerator (FC-TENG) and a supercapacitor (FC-SC), both based on folded carbon paper, as energy harvester and storage device, respectively. This favorable geometric design provides the high Young’s modulus carbon paper with excellent stretchability and enables the power unit to work even under severe deformations, such as bending, twisting, and rolling. In addition, the tensile strain can be maximized by tuning the folding angle of the triangle-folded carbon paper. Moreover, the waterproof property of the packaged device make it washable, protect it from human sweat, and enable it to work in harsh environments. Finally, the as-prepared self-charging power unit was tested by placing it on the human body to harvest mechanical energy from hand tapping, foot treading, and arm touching, successfully powering an electronic watch. This work demonstrates the impressive potential of stretchable self-charging power units, which will further promote the development of high Young’s modulus materials for wearable/portable electronics.

With the development of fuel cell vehicles, the hydrogen leakage detector is urgent to satisfy the safety requirements of the vehicles with low power consumption. In this work, a self-powered hydrogen leakage detector based on impedance adjustable windmill-like triboelectric nanogenerator (WL-TENG) has been demonstrated. It could harvest wind energy during the driving of hydrogen fuel vehicle to power the whole sensing system. The inherent impedance and matching region of WL-TENG can be tuned effectively by adjusting the center angle of the windmill plate. The resistance of the Pd/ZnO nanorods based hydrogen sensor changes from 300 kΩ to 60 kΩ under pure air atmosphere to 1000 ppm H2. Then, a matching WL-TENG with 3° center angle was series connected to H2 sensor to construct the self-powered H2 sensing system. Finally, by introducing 150 kΩ divider constant resistor, the voltage across it increases from ~15 V to ~60 V with the H2 concentration increasing from 0 to 1000 ppm. The output voltage of WL-TENG varies with the variable working states of the gas sensor and then directly reflects on the on/off status of the LEDs parallel connected to the divider resistor. This work contributes to the development of impedance matching theory of TENG and further expand its application on self-powered sensing system.

The rapid development of wearable electronics has led to an enormous demand for power sources that are wearable, small-scale, flexible and compatible. In this work, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the liquid electrode and silicone rubber as the triboelectric/encapsulation layer were introduced to design a stretchable PEDOT:PSS liquid electrode-based triboelectric nanogenerator (PL-TENG). The elastic silicone rubber and PEDOT:PSS liquid electrode with a special macromolecular structure endowed PL-TENG with extraordinary flexibility and conductivity simultaneously. Working under the single-electrode mode with different motion frequencies from 0.5 to 2.5 Hz, PL-TENG generated open-circuit voltage of 265 V, short-circuit current of 24.9 μA and short-circuit charge quantity of 85 nC. The output performances still maintained the original values after washing in saline, storing for one month and stretching 10 000 times. At the same time, PL-TENG could also produce stable electrical outputs even when deformed into a variety of shapes including stretching in different directions, bending and twisting. All of these features demonstrated the excellent resistance of PL-TENG to sweat, time and deformation. When attached to a human body, PL-TENG could provide a sufficiently stable power output to drive wearable electronics sustainably.

Triboelectric nanogenerator (TENG) has shown great advances in converting low-frequency discrete mechanical energy into electricity and multifunctional real-time self-powered sensing systems. It has confirmed that the air breakdown effect is the main factor limiting the maximum effective power output of the TENG. Charges generated on the surface of TENGs diffuse into the atmosphere and internal triboelectric layer, resulting in charge loss and decrease of surface charge density. Breaking through the limitation of air breakdown and prolonging charge decay time are the two priorities for boosting TENG output. By embedding superior intermediate layer into TENG induced output enhancement provides an effective strategy to improve the output performance. Here, the working mechanisms of different materials belonging to the classifications of metals, inorganic non-metal materials, and organic polymers as the intermediate layer are reviewed elaborately. Moreover, the influences of structure parameters, such as thickness of dielectric layer, dielectric layer number, and ground connection design are discussed accordingly. Future challenges and optimizations for improvement of the intermediate layer are finally presented in the review.