[en] Highlights: • Charge transfer between TENG and the inner capacitor of voltmeters makes the measured voltage lower than its actual value. • A general charge compensation strategy is proposed for calibrating the measured voltage of a TENG. • The FCD method and VCF method are developed to calibrate the open-circuit voltage of TENGs. • The output voltage of a TENG is calibrated through the equivalent impedance including the inner capacitance of voltmeter. The voltage is a key parameter of a triboelectric nanogenerator (TENG). However, when the voltage is measured by the voltmeters with a capacitive measurement circuit, there is a charge transfer between the TENG and the inner capacitor, making the measured voltage lower than its actual value. In this paper, a general charge compensation strategy is proposed for calibrating the measured voltage of a TENG based on the analysis of the capacitive measurement circuit. Two methods, the fixed capacitance derivation (FCD) and the variable capacitance fitting (VCF), are developed to calibrate the open-circuit voltage (V_oc) of TENGs, and the calibration formulas of V_oc are given, respectively. Firstly, a sliding freestanding triboelectric-layer mode TENG is taken as an example and the two methods are used to calibrate actual V_oc. The results are consistent with that measured by the ammeter with non-capacitive measurement circuit, verifying the validity of the charge compensation strategy. For the other three basic working modes TENGs, the measured V_oc are calibrated by the FCD method, which illustrate the universality of the charge compensation strategy. Finally, the relationship between the output voltage of a TENG and the load impedance is calibrated through the equivalent impedance including the inner capacitance of the voltmeter. The proposed charge compensation strategy for calibrating the voltage of a TENG measured by a capacitive circuit is of great theoretical and application significance for the establishment of a comprehensive evaluation system for TENG’s output performance.

[en] Highlights: • A self-powered photodetection system based on Pulsed-TENG is developed. • The output voltage of Pulsed-TENG and the photodetection results are not affected by the frequency of mechanical stimuli. • Based on the output characteristic of Pulsed-TENG, both current and voltage modes are developed. • Based on the voltage mode, a self-powered photodetection system with visual display function is developed. The self-powered sensing systems based on impedance matching effect have been proposed by using a triboelectric nanogenerator (TENG) as power source, which have attracted widespread attention in the field of Internet of Things. However, the output voltage and current of the conventional TENG are affected by not only the load impedance but also the working frequency of TENG, leading to inaccurate sensing results in actual working environments with random mechanical stimuli. For solving this problem, a self-powered sensing system using a Pulsed-TENG with a synchronous trigger switch has been proposed here, in which the output voltage and current of Pulsed-TENG are independent on its working frequency. The measured performances of a self-powered photodetector have verified that same detection results could be obtained for various rotation frequencies of a rotating Pulsed-TENG. Two self-powered detection modes, current mode and voltage mode, have been developed. In the current detection mode, the output current increased linearly with light intensity, and the detectable range of light intensity is 0–1 W/m². In the voltage detection mode, the output voltage is inversely proportional to the light intensity, and the detectable range of light intensity is 9–403 W/m². Finally, a self-powered photodetection system with visual display function has been developed, in which the light intensity can be displayed intuitively by the number of lighted LEDs. Since the output voltage and current of Pulsed-TENG are independent on its working frequency, the self-powered sensing system based on Pulsed-TENG proposed here has provided a promising strategy suitable for the actual working environments with random mechanical stimuli.

[en] Highlights: • Rotational Pulsed-TENGs have rarely been developed because of the difficulty in designing rational STMSs. • Rotating freestanding Pulsed-TENGs (RF-Pulsed-TENGs) are realized through integrating STMSs on electrode layer. • Both alternating current and unidirectional current RF-Pulsed-TENGs are realized. • The on–off states of the STMSs can match well with the rotation frequency of the RF-Pulsed-TENGs. • A self-powered system consisting of gearbox, efficient passive PMC, and an RF-Pulsed-TENG has been demonstrated. With the merits of zero internal equivalent resistance and maximized output energy, the pulsed mode triboelectric nanogenerators (TENGs) can achieve impedance matching with the power management circuits (PMCs), showing wide application prospects in self-powered systems. The key for developing Pulsed-TENGs lies in designing synchronously triggered mechanical switches (STMSs). However, rotational TENGs, as a promising configuration for harvesting mechanical energy, have rarely been designed as pulsed mode because of the difficulty in fabricating rational STMSs. Herein, rotating freestanding triboelectric-layer Pulsed-TENGs (RF-Pulsed-TENGs) are realized through integrating STMSs on triboelectric layers in one step by printed circuit board process. Since the on-off states of the STMSs can match well with the rotation frequency, the output voltage and energy of the RF-Pulsed-TENGs are maximized regardless of the rotation frequency or load resistance. Both alternating current and unidirectional current output RF-Pulsed-TENGs have been realized, and the energy storage efficiency of their corresponding passive PMCs can reach 51.6% and 52.0%, respectively. The system consisting of a gearbox, a passive PMC, and a RF-Pulsed-TENG has been demonstrated to power a range of electronic devices, such as calculators, electronic watches, and temperature/humidity meters, offering significant advantages and promising applications in efficient mechanical energy harvesting and self-powered sensing.

[en] As a new concept of the device, a hybrid energy harvester integrated with a water droplet triboelectric nanogenerator (WD-TENG) and a solar cell has been reported to convert raindrop energy and solar energy into electricity. However, organic triboelectric layers are usually utilized in previous studies that might be decomposed under long-term UV irradiation, resulting in degradation of the hybrid energy harvester. In this work, a fully inorganic hybrid energy harvester is demonstrated. Superhydrophobic SiO₂ film is introduced to the system as both the triboelectric layer of the WD-TENG and the anti-reflective layer of the solar cell, which could increase the power conversion efficiency (PCE) of the solar cell from 15.17% to 15.71%. Meanwhile, WD-TENG with the SiO₂ triboelectric layer could collect energies from rain droplets. This superhydrophobic SiO₂ film could effectively reduce the dependence of the tilt angle for the WD-TENG and bring up self-cleaning performance for the hybrid energy harvester. Moreover, this fully inorganic architecture could enhance the stability of the hybrid energy harvester, making it a promising strategy in practical applications. (paper)

[en] Highlights: • The detection limit of 7 mPa is the state of art for reported triboelectric self-powered tactile sensors. • The performance of the device maintains well under severe damage condition. • With the ultra-low detection limit, human wrist pulse monitoring has been demonstrated via using our device. Self-powered tactile and pressure sensor is one of the key components for new smart electronic devices which can sense various external physical stimuli without external power supplies. With the potential application in detection of health conditions and sport performances, self-powered tactile sensors have attracted broad attentions. Still, fabrication of self-powered tactile sensors with stretchability, flexibility and low detection limit remains challenge. In this work, a self-powered triboelectric tactile sensor with multi-level structured polydimethylsiloxane (PDMS) triboelectric layer and PDMS/Eutectic Gallium-Indium (EGaIn) alloy composite electrode is demonstrated with simple fabrication process and low-cost. The detection limits of 0.23 Pa (experimental) and 7 mPa (calculated) are the state of art for reported self-powered triboelectric tactile sensor. With this excellent characteristic, monitoring of human wrist pulses is demonstrated by this self-powered triboelectric tactile sensor. Moreover, due to the working mechanism of the triboelectric nanogenerator, this self-powered triboelectric tactile sensor exhibits uncompromising resilience to stretching and even significant damage.

[en] Highlights: • A bi-functional nano-winkled PDMS film is introduced to the solar cell surface as an anti-reflective coating. • The anti-reflective nano-winkled PDMS film also serves as a triboelectric layer to form a WD-TENG. • The energy conversion efficiency of the solar cell is enhanced from 12.55% to 13.57%. • The V_oc and I_sc of the WD-TENG with nano-winkled structures have huge enhancement by 385.5% and 299.1%. • The hybrid energy harvester could collect energies from sunlight and raindrops which enlarges its workable environments. -- Abstract: The hybrid energy harvester composed of a solar cell and a water-drop triboelectric nanogenerator (WD-TENG) has been reported to harvest energy from sunlight or raindrops depends on the changing natural environment. However, the reported integrated WD-TENGs always reduce the light absorption of solar cells, resulting in a decline of solar cell efficiency. Here, a bi-functional nano-wrinkled polydimethylsiloxane (nw-PDMS) film is introduced to fabricate the hybrid energy harvester, serving as both the anti-reflective layer of the solar cell and the triboelectric layer of the WD-TENG, and simultaneously enhancing the energy harvesting efficiency from sunlight and raindrop. With significantly enhanced transmittance due to the anti-reflective coating, the power conversion efficiency of the solar cell has improved from 12.55% to 13.57%. In addition, due to the high aspect ratio, surface fluorination and strong hydrophobicity of the nw-PDMS film, both open circuit voltage (V_OC-T) and short-circuit current (I_SC-T) of the WD-TENG have huge enhancement by 385.5% and 299.1%, respectively. In this work, the introducing of bi-functional nw-PDMS film provides a simple and convenient strategy for designing hybrid energy harvester with enhanced output performances, which is a general route for Si-based solar cell and other kinds of solar cells.

[en] Highlights: • The surface-ionic-gate modulation technique was developed based on triboelectric nanogenerators. • The novel transistor and photodetector of monolayer MoS₂ have been developed by using surface-ionic-gate modulation. • In surface-ionic-gate-based photodetector, the photocurrent recovery time of the monolayer MoS₂ device is only 74 ms. • Reversible modulation could be achieved by combining the surface-ionic-gate with ultraviolet light. • The applications of triboelectric nanogenerator in developing high-performance electronic and optoelectronic nanodevices. -- Abstract: Modulating the carrier transport behavior by gate voltage is an important strategy for developing electronic and optoelectronic devices. However, the previous gate modulation technologies are generally applied in solid/semiconductor or liquid/semiconductor interface. Here, based on the phenomenon of gas discharge powered by a triboelectric nanogenerator (TENG), the technology of surface ionic gate (SIG) in the gas/semiconductor interface has been proposed, and novel transistor and photodetector of monolayer MoS₂ have been developed using SIG modulation. In SIG-based transistor, the gas ions generated in gas discharge are adsorbed on monolayer MoS₂, which act as the gate to modulate the carrier concentration and electrical transport. The modulation results can be controlled step-by-step by the operation cycles of TENG, and a maximum on-off ratio of 10⁴ in current has been obtained. In SIG-based photodetector, the photocurrent recovery time of the monolayer MoS₂ device is about 74 ms, which is reduced approximately 90 times compared to that without SIG modulation. In addition, the photocurrent of SIG-based photodetector increases linearly with time during a period of 120 s, which can be used to develop a novel photodetector for luminous flux. The working mechanism of the SIG-based transistor and SIG-based photodetector have been discussed. The SIG technology proposed here can modulate the electrical transport properties and surface local energy band structure of two-dimensional (2D) materials, which provides promising strategy for developing novel 2D electronic and optoelectronic devices.