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The piezo-phototronic effect (a coupling effect of piezoelectric, photoexcitation and semiconducting properties, coined in 2010) has been demonstrated to be an ingenious and robust strategy to manipulate optoelectronic processes by tuning the energy band structure and photoinduced carrier behavior. The piezo-phototronic effect exhibits great potential in improving the quantum yield efficiencies of optoelectronic materials and devices and thus could help increase the energy conversion efficiency, thus alleviating the energy shortage crisis. In this review, the fundamental principles and challenges of representative optoelectronic materials and devices are presented, including photocatalysts (converting solar energy into chemical energy), solar cells (generating electricity directly under light illumination), photodetectors (converting light into electrical signals) and light-emitting diodes (LEDs, converting electric current into emitted light signals). Importantly, the mechanisms of how the piezo-phototronic effect controls the optoelectronic processes and the recent progress and applications in the above-mentioned materials and devices are highlighted and summarized. Only photocatalysts, solar cells, photodetectors, and LEDs that display piezo-phototronic behavior are reviewed. Material and structural design, property characterization, theoretical simulation calculations, and mechanism analysis are then examined as strategies to further enhance the quantum yield efficiency of optoelectronic devices via the piezo-phototronic effect. This comprehensive overview will guide future fundamental and applied studies that capitalize on the piezo-phototronic effect for energy conversion and storage.

Contact-electrification is a universal effect for all existing materials, but it still lacks a quantitative materials database to systematically understand its scientific mechanisms. Using an established measurement method, this study quantifies the triboelectric charge densities of nearly 30 inorganic nonmetallic materials. From the matrix of their triboelectric charge densities and band structures, it is found that the triboelectric output is strongly related to the work functions of the materials. Our study verifies that contact-electrification is an electronic quantum transition effect under ambient conditions. The basic driving force for contact-electrification is that electrons seek to fill the lowest available states once two materials are forced to reach atomically close distance so that electron transitions are possible through strongly overlapping electron wave functions. We hope that the quantified series could serve as a textbook standard and a fundamental database for scientific research, practical manufacturing, and engineering., The mechanism of contact electrification remains a topic of debate. Here, the authors present a quantitative database of the triboelectric charge density and band structure of many inorganic materials, verifying that contact electrification between solids is an electron quantum transition effect.

Triboelectrification is a well-known phenomenon that commonly occurs in nature and in our lives at any time and any place. Although each and every material exhibits triboelectrification, its quantification has not been standardized. A triboelectric series has been qualitatively ranked with regards to triboelectric polarization. Here, we introduce a universal standard method to quantify the triboelectric series for a wide range of polymers, establishing quantitative triboelectrification as a fundamental materials property. By measuring the tested materials with a liquid metal in an environment under well-defined conditions, the proposed method standardizes the experimental set up for uniformly quantifying the surface triboelectrification of general materials. The normalized triboelectric charge density is derived to reveal the intrinsic character of polymers for gaining or losing electrons. This quantitative triboelectric series may serve as a textbook standard for implementing the application of triboelectrification for energy harvesting and self-powered sensing., Triboelectric charging is a well-known phenomenon, but triboelectric polarization has only been ranked qualitatively. Here the authors develop a quantified triboelectric series for a wide range of polymers by measuring triboelectric charge density with respect to a liquid metal at well-defined conditions.

Despite recent progress in producing perovskite nanowires (NWs) for optoelectronics, it remains challenging to solution-print an array of NWs with precisely controlled position and orientation. Herein, we report a robust capillary-assisted solution printing (CASP) strategy to rapidly access aligned and highly crystalline perovskite NW arrays. The key to the CASP approach lies in the integration of capillary-directed assembly through periodic nanochannels and solution printing through the programmably moving substrate to rapidly guide the deposition of perovskite NWs. The growth kinetics of perovskite NWs was closely examined by in situ optical microscopy. Intriguingly, the as-printed perovskite NWs array exhibit excellent optical and optoelectronic properties and can be conveniently implemented for the scalable fabrication of photodetectors.

Triboelectric nanogenerators (TENGs) have attracted increasing attention because of their excellent energy conversion efficiency, the diverse choice of materials, and their broad applications in energy harvesting devices and self-powered sensors. New materials have been explored, including green materials, but their performances have not yet reached the level of that for fluoropolymers. Here, a high-performance, fully green TENG (FG-TENG) using cellulose-based tribolayers is reported. It is shown that the FG-TENG has an output power density of above 300 W m-2 , which is a new record for green-material-based TENGs. The high performance of the FG-TENG is due to the high positive charge density of the regenerated cellulose. The FG-TENG is stable after more than 30 000 cycles of operations in humidity of 30%-84%. This work demonstrates that high-performance TENGs can be made using natural green materials for a broad range of applications.

Triboelectric nanogenerator (TENG) can convert mechanical energy into electrical energy and has been regarded as a promising portable power source. However, the low output power restricts TENG’s applications in energy harvesters and sensors. Herein, we developed an effective way of increasing TENG’s output power by combining ferroelectricity and conduction of the triboelectric materials. For this purpose, a conductive interlayer modulated ferroelectric nanocomposite was used as the negative triboelectric material. Compared with the conventional ferroelectric nanocomposites based TENG, the transferred triboelectric charge density of the conductive interlayer modulated ferroelectric nanocomposite based TENG can reach 105.70 μC m−2 from 17.50 μC m−2, while the output power density increases to 7.21 W m−2 from 0.11 W m−2. The boosted output performance can be attributed to the existence of a conductive intermediate layer in the negative triboelectric material, which induces charge trapping and enhances ferroelectric polarization of the nanocomposites. Apart from being used as wearable energy harvesters, the TENG device also exhibits a promising application in parachuting surveillance for preventing potential injuries. Furthermore, TENG device has numerous possible application scenarios for future airborne troops. This work provides a brand-new strategy for enhancing contact electrification, showing strong potential in design of high output TENGs.

Triboelectric nanogenerators (TENGs) are attracting more and more attention since they can convert various mechanical energies into electric energy. However, in traditional TENGs for harvesting rotation energy, most of the contacts between two triboelectric materials are rigid-to-rigid contact with very large friction force, which limits their practical application. Here, we report an ultra-low-friction triboelectric-electromagnetic hybrid nanogenerator (NG). A freestanding mode TENG and a rotating electromagnetic generator (EMG) are integrated together to realize the complementary individual merits. The very soft and elastic contact between the two triboelectric materials in the TENG results into very small friction force. The influences of the type and the dimensions of the dielectric material on the performance of the TENG are studied systematically from theory to experiments. The results indicate that the open-circuit voltage and the transfer charge of the TENG increase with the rotation speed, which is very different from a traditional rotary TENG and is due to the increase of the contact area. The optimized TENG has a maximal load voltage of 65 V and maximal load power per unit mass of 438.9 mW/kg under a speed rotation of 1000 rpm, while the EMG has a maximal load voltage of 7 V and maximal load power density of 181 mW/kg. This demonstration shows that the hybrid NG can power a humidity/temperature sensor by converting wind energy into electric energy when the wind speed is 5.7 m/s. Meanwhile, it can be used as a self-powered wind speed sensor to detect wind speed as low as 3.5 m/s.

Ocean waves are one of the most power dense energy sources in the environment. Triboelectric nanogenerators (TENGs) have been demonstrated to effectively harvest mechanical energy carried by low frequency, random/irregular actuation, such as from ocean waves. In this work, a novel design of triboelectric nanogenerator based on the Pelamis snake energy harvester is presented. The sea snake based TENG, with its lightweight structure, was able to harvest energy effectively at low amplitude ocean wave by utilizing charged polytetrafluroethylene balls that would roll due to the wave's curvature. With the integration of springs to connect different segments, the segments are able to bend easily, allowing the enclosed balls to move faster, producing higher output power. The design of an air gap structure allows each segments of the sea snake based TENG to minimize electrostatic induction from ions in sea water, and solve the effect of dielectric shielding from the water on the device performance, as the water, if it is close to the TENG's electrodes, has a detrimental effect causing an increase of the TENG's internal capacitance, which would result in a low voltage with the same amount of charge being transformed. Thus, this illustrates the importance of the air gap structure to minimize low voltage due to high internal capacitance. This further shows the sea snake based triboelectric nanogenerator could be used in actual ocean conditions, such as in high salinity water environment. The added tampered spring to replace the air gap was able to allow the balls on the TENG to move more quickly, as it increased the rotational angle, and the TENG has a maximum power density of 3 W/m3 under actuation. Due to the minimization of dielectric shielding of device performance, the sea snake TENG exhibits a high voltage in simulated water wave conditions.

The ubiquitous sensors have accelerated the realization of Internet of Things (IoT) but also raised challenges to the current overcrowding radio frequency (RF) based communications. The optical wireless communication (OWC) that utilizes the wide optic bandwidth can well solve the spectrum crisis and is an appealing complementary solution to the IoT applications. However, the additional direct current (DC) power supply and complicated modulating and power management circuits may limit the large-scale deployment of OWC systems. In this paper, by integrating with triboelectric nanogenerators (TENGs), the light-emitting diode (LED) could be directly transformed into a wireless transmitter that conveys the information associated with mechanical stimuli without additional power supply. With the customized TENG devices and the help of advanced image processing and machine learning techniques, three demonstrations with functions of optical remote control, pressure sensing, and security authentication, were demonstrated. The concept and results in this paper may greatly broaden the application of IoT through the integration of OWC and TENG.

Piezoelectric generators (PEGs) are a promising power source for future self-powered electronics by converting ubiquitous ambient mechanical energy into electricity. However, most of the high-output PEGs are made from lead zirconate titanate, in which the hazardous lead could be a potential risk to both humans and environment, limiting their real applications. III-Nitride (III-N) can be a potential candidate to make stable, safe, and efficient PEGs due to its high chemical stability and piezoelectricity. Also, PEGs are preferred to be flexible rather than rigid, to better harvest the low-magnitude mechanical energy. Herein, a high-output, lead-free, and flexible PEG (F-PEG) is made from GaN thin film by transferring a single-crystalline epitaxial layer from silicon substrate to a flexible substrate. The output voltage, current density, and power density can reach 28 V, 1 μA·cm–2, and 6 μW·cm–2, respectively, by bending the F-PEG. The generated electric power by human finger bending is high enough to light...

The piezotronic effect and piezo-phototronic effect on materials and devices have been widely studied in binary semiconductors. Wide-band ternary semiconductors are a great class of materials with potential application in nano/microdevices, because of their continuously tunable physical properties with composition. Here, we first demonstrate the piezo-photronics effect of ternary wurtzite structured nanowires (NWs), opening an innovative materials system. Single-crystal ternary CdSxSe1–x (x = 0.85, 0.60, and 0.38) NWs were synthesized with site-controlled compositions via a chemical vapor deposition process, and high-performance visible photodetectors (PDs) with fast response speed (

Rapid advancements in stretchable and multifunctional wearable electronics impose a challenge on corresponding power devices that they should have comparable portability and stretchability. Here, we report a highly stretchable and washable all-yarn-based self-charging knitting power textile that enables both biomechanical energy harvesting and simultaneously energy storing by hybridizing triboelectrical nanogenerator (TENG) and supercapacitor (SC) into one fabric. With the weft-knitting technique, the power textile is qualified with high elasticity, flexibility, and stretchability, which can adapt to complex mechanical deformations. The knitting TENG fabric is able to generate electric energy with a maximum instantaneous peak power density of ∼85 mW·m–2 and light up at least 124 light-emitting diodes. The all-solid-state symmetrical yarn SC exhibits lightweight, good capacitance, high flexibility, and excellent mechanical and long-term stability, which is suitable for wearable energy storage devices. The ...

Developing lightweight, flexible and sustainable sensor networks with miniaturized integration and functionality for the Internet of Things (IoT) remains a challenge and an urgent demand for the next-generation electronic devices. Paper-based electronics, which represents one of the main green electronics in the future, have been considered as one of the most exciting technologies to meet the consumption of the frequently upgraded electronics. Here, we presented an ultrathin (about 200 µm) and lightweight paper-based self-powered system that consists of a paper-based triboelectric/piezoelectric hybrid nanogenerator and a paper-based supercapacitor. Under human motions such as flipping the page and moving the book/document, the as-fabricated self-powered system built-in the smart book/document was capable of sustaining power for portable devices, such as continuously driving LEDs and the temperature/humidity sensor. With the signal-processing circuit, the paper-based system was further developed into a wireless human-machine interaction system for documents management and smart reading. The ultrathin and highly flexible characteristics of the self-powered system not only endow the device with power generation feature for portable devices, but also build up the wireless human-machine interactions in developing potential applications for the IoT.

Although silicon (Si) devices are the backbone of modern (opto-)electronics, infrared Si-photosensing suffers from low-efficiency due to its limitation in light-absorption. Here, we demonstrate a large improvement in the performance, equivalent to a 366-fold enhancement in photoresponsivity, of a Si-based near-infrared (NIR) photodetector (PD) by introducing the piezo-phototronic effect via a deposited CdS layer. By externally applying a −0.15‰ compressive strain to the heterojunction, carrier-dynamics modulation at the local junction can be induced by the piezoelectric polarization, and the photoresponsivity and detectivity of the PD exhibit an enhancement of two orders of magnitude, with the peak values up to 19.4 A/W and 1.8 × 1012 cm Hz1/2/W, respectively. The obtained maximum responsivity is considerably larger than those of commercial Si and InGaAs PDs in the NIR waveband. Meanwhile, the rise time and fall time are reduced by 84.6% and 76.1% under the external compressive strain. This work provides ...

Achievement of p–n homojuncted GaN enables the birth of III-nitride light emitters. Owing to the wurtzite-structure of GaN, piezoelectric polarization charges present at the interface can effectively control/tune the optoelectric behaviors of local charge-carriers (i.e., the piezo-phototronic effect). Here, we demonstrate the significantly enhanced light-output efficiency and suppressed efficiency droop in GaN microwire (MW)-based p–n junction ultraviolet light-emitting diode (UV LED) by the piezo-phototronic effect. By applying a −0.12% static compressive strain perpendicular to the p–n junction interface, the relative external quantum efficiency of the LED is enhanced by over 600%. Furthermore, efficiency droop is markedly reduced from 46.6% to 7.5% and corresponding droop onset current density shifts from 10 to 26.7 A cm–2. Enhanced electrons confinement and improved holes injection efficiency by the piezo-phototronic effect are revealed and theoretically confirmed as the physical mechanisms. This stud...

Atomic vapor cell which is one of the core devices of quantum sensing has a very important impact on the accuracy of detection, especially in the Rydberg-atom based electromagnetic field sensing. Metamaterials provide a feasible scheme for improving the performance of the vapor cell because of their excellent ability to control electromagnetic waves. In this paper, a new type of vapor cell with low perturbation for measuring electric field is proposed to eliminate the field distortion in presence of the vapor cell. The vapor cell is composed of three sets of parallel metamaterials with characteristics of perfect-electric-conductor (PEC), perfect- magnetic-conductor (PMC) and low permittivity (LPM), respectively. At the same time, the effects of vapor cell size and wall thickness on the electric field inside the vapor cell are compared. Finally, a preparation scheme of LPM with a limited size on a glass substrate is proposed.

It is known that contact-electrification (or triboelectrification) usually occurs between two different materials, which could be explained by several models for different materials systems ( Adv. Mater. 2018, 30, 1706790; Adv. Mater. 2018, 30, 1803968). But contact between two pieces of the chemically same material could also result in electrostatic charges, although the charge density is rather low, which is hard to understand from a physics point of view. In this paper, by preparing a contact-separation mode triboelectric nanogenerator using two pieces of an identical material, the direction of charge transfer during contact-electrification is studied regarding its dependence on curvatures of the sample surfaces. For materials such as polytetrafluoroethylene, fluorinated ethylene propylene, Kapton, polyester, and nylon, the positive curvature surfaces are net negatively charged, while the negative curvature surfaces tend to be net positively charged. Further verification of the above-mentioned trends was obtained under vacuum (∼1 Pa) and higher temperature (≤358 K) conditions. Based on the received data acquired for gentle contacting cases, we propose a curvature-dependent charge transfer model by introducing curvature-induced energy shifts of the surface states. However, this model is subject to be revised if the mutual contact mode turns into a sliding mode or more complicated hard-pressed contact mode, in which a rigorous contact between the two pieces of the same material could result in nanoscale damage/fracture and possible species transfer. Our study provides a primitive step toward understanding the basics of contact-electrification.

Silicon photonics is now widely accepted as a key technology in a variety of systems. But owing to material limitations, now it is challenging to greatly improve the performance after decades of development. Here, we show a high-performance broadband photodetector with significantly enhanced sensitivity and responsivity operating over a wide wavelength range of light from near-ultraviolet to near-infrared at low power consumption. The specially designed textured top ceiling electrode works effectively as an antireflection layer to greatly improve the absorption of near-infrared light, thereby overcoming the absorption limitation of near-infrared light. Instead of the conventional p-n junction and p-intrinsic-n junction, we introduce a ∼15 nm thick alumina insulator layer between a p-type Si substrate and n-type ZnO nanowire (NW) arrays, which significantly enhances the charge carrier separation and collection efficiency. The photosensing responsivity and sensitivity are found to be nearly 1 order of magnitude higher than that of a reference device of p-Si/n-ZnO NW arrays, significantly higher than the commercial silicon photodiodes as well. The light-induced charge carriers flow across the appropriate thickness of insulator layer via the quantum mechanical Fowler-Nordheim tunneling mechanism. By virtue of the piezo-phototronic effect, the charge density at the interfaces can be tuned to alter the energy bands and the potential barrier distance for tunneling. Additionally, along with the use of incident light of different wavelengths, the influence of the insulator layer on the transport of electrons and holes separately is further investigated. The demonstrated concepts and study would lead to sensitivity improvement, quality enhancement of data transfer, decrease of power consumption, and cost reduction of silicon photonics.

Nanocomposites consisting of a flexible piezoelectric polymer and a reinforcing phase have shown great potential for constructing high-performance piezoelectric nanogenerators (PENGs). However, the weak interface and poor dispersion of piezoelectric reinforcing phase significantly impair the electromechanical properties (e.g., effective stress/strain, piezoelectric coefficients) of the nanocomposites, thus severely restricting the performance enhancement of the PENGs. In this study, we hydrothermally synthesized the piezoelectric reinforcing phase of BaTiO3 nanowires, and grafted a layer of high-modulus polymethyl methacrylate (PMMA) onto the nanowire surface via surface-initiated polymerization. The PMMA coating layer forms a strong interface between BaTiO3 nanowires and the polymer matrix [i.e., poly(vinylidenefluoride-co-trifluoroethylene)], which efficiently improves dispersion of the BaTiO3 nanowires and stress transfer at the interface, therefore resulting in an enhanced output performance in the fibrous nanocomposite PENGs. The output voltage and current of the PMMA encapsulated BaTiO3 (PMMA@BaTiO3) nanowires-based PENG can reach to 12.6 V and 1.30 μA, with a maximum output power of 4.25 μW, which is 2.2 times and 7.6 times higher than the PENG with unmodified BaTiO3 nanowires and the PENG without BaTiO3 nanowires, respectively. Furthermore, the flexible PENG exhibits great stability that could continuously generate stable electrical pulses for 6000 cycles without any decline. This study provides a feasible approach of interface tailoring for achieving high-performance piezoelectric nanocomposite and shows the promising potential of the fibrous nanocomposites in biomechanical energy harvesters and smart wearable sensors.

Self-powered ZnO/perovskite heterostructured ultraviolet (UV) photodetectors (PDs) based on the pyro-phototronic effect have been recently reported as a promising solution for energy-efficient, ultrafast-response, and high-performance UV PDs. In this study, the temperature dependence of the pyro-phototronic effect on the photo-sensing performance of self-powered ZnO/perovskite heterostructured PDs was investigated. The current responses of these PDs to UV light were enhanced by 174.1% at 77 K and 28.7% at 300 K owing to the improved pyro-phototronic effect at low temperatures. The fundamentals of the pyro-phototronic effect were thoroughly studied by analyzing the chargetransfer process and the time constant of the current response of the PDs upon UV illumination. This work presents in-depth understandings about the pyrophototronic effect on the ZnO/perovskite heterostructure and provides guidance for the design and development of corresponding optoelectronics for ultrafast photo sensing, optothermal detection, and biocompatible optoelectronic probes.

The open circuit voltage of a conventional H2-O2 fuel cell is limited to ~1.23 V under atmospheric pressure, which limits the efficiency of the system. Here, we reported a dual-electrolyte microfluidic fuel cell system (DEFC), which could stably deliver an open circuit voltage up to 1.76 V at room temperature under atmospheric pressure, and a peak power density of 145 mW/cm2, improved by 3 times compared with that in single electrolyte mode. When operated in the reverse mode, the microfluidic cell can be used for water electrolysis, demonstrating a water split voltage of ~0.74 V and a round trip voltage efficiency of 83.5% at a current density of 100 mA/cm2. The neutralization energy of the two electrolytes, which could be wasted as heat, can be directly utilized to produce electricity or split water with high efficiency. Given the DEFC's features of high open-circuit voltage, low water splitting voltage, and room-temperature operation condition, the reported DEFCs technology presents a superior route for high-efficiency energy conversion and storage system that could revolutionize the fields of large-scale energy storage and portable power systems.

Regenerative fuel cells are a potential candidate for future energy storage, but their applications are limited by the high cost and poor round-trip efficiency. Here we present a switchable pH-differential unitized regenerative fuel cell capable of addressing both the obstacles. Relying on a membraneless laminar flow-based design, pH environments in the cell are optimized independently for different electrode reactions and are switchable together with the cell process to ensure always favorable thermodynamics for each electrode reaction. Benefiting from the thermodynamic advantages of the switchable pH-differential arrangement, the cell allows water electrolysis at a voltage of 0.57 V, and a fuel cell open circuit voltage of 1.89 V, rendering round-trip efficiencies up to 74%. Under room conditions, operating the cell in fuel cell mode yields a power density of 1.3 W cm −2 , which is the highest performance to date for laminar flow-based cells and is comparable to state-of-the-art polymer electrolyte membrane fuel cells.

Despite recent rapid advances in metal halide perovskites for use in optoelectronics, the fundamental understanding of the electrical-poling-induced ion migration, accounting for many unusual attributes and thus performance in perovskite-based devices, remain comparatively elusive. Herein, the electrical-poling-promoted polarization potential is reported for rendering hybrid organic-inorganic perovskite photodetectors with high photocurrent and fast response time, displaying a tenfold enhancement in the photocurrent and a twofold decrease in the response time after an external electric field poling. First, a robust meniscus-assisted solution-printing strategy is employed to facilitate the oriented perovskite crystals over a large area. Subsequently, the electrical poling invokes the ion migration within perovskite crystals, thus inducing a polarization potential, as substantiated by the surface potential change assessed by Kelvin probe force microscopy. Such electrical-poling-induced polarization potential is responsible for the markedly enhanced photocurrent and largely shortened response time. This work presents new insights into the electrical-poling-triggered ion migration and, in turn, polarization potential as well as into the implication of the latter for optoelectronic devices with greater performance. As such, the utilization of ion-migration-produced polarization potential may represent an important endeavor toward a wide range of high-performance perovskite-based photodetectors, solar cells, transistors, scintillators, etc.

It is well known that the photovoltaic effect produces a direct current (DC) under solar illumination owing to the directional separation of light-excited charge carriers at the p-n junction, with holes flowing to the p-side and electrons flowing to the n-side. Here, it is found that apart from the DC generated by the conventional p-n photovoltaic effect, there is another new type of photovoltaic effect that generates alternating current (AC) in the nonequilibrium states when the illumination light periodically shines at the junction/interface of materials. The peak current of AC at high switching frequency can be much higher than that from DC. The AC cannot be explained by the established mechanisms for conventional photovoltaics; instead, it is suggested to be a result of the relative shift and realignment between the quasi-Fermi levels of the semiconductors adjacent to the junction/interface under the nonequilibrium conditions, which results in electron flow in the external circuit back and forth to balance the potential difference between two electrodes. By virtue of this effect, the device can work as a high-performance broadband photodetector with extremely high sensitivity under zero bias; it can also work as a remote power source providing extra power output in addition to the conventional photovoltaic effect.

Triboelectric nanogenerators (TENG) is a promising route for harvesting ambient mechanical energy to obtain clean and renewable electricity. However, the durability of materials still limits its practical applications for continuous operation. Here, a radial-arrayed TENG was integrated with a transmission mechanism, which successfully maximized the sustainable operation with less triboelectric material wear and damage. Through the rational design of the transmission mechanism, triboelectric layers were first charged by the contact electrification due to the wave impact from the sides, and charges were transferred by the electrostatic induction continuously because of the tumbler's design. In this case, frictional resistance between the triboelectric layers were successfully eliminated, which largely enhances its robustness and durability. After running for 500 k cycles, there is only 1.8% degradation. The TENG could convert one single impact into multiple cycles of rotations, which improves the energy harvesting efficiency for sustainably driving and charging commercial electronics, immediately demonstrating the feasibility of the TENG as a practical power source with extended lifetime and durability. Given exceptional durability and unprecedented applicability resulting from novel designs, this work provides an attractive strategy for the study of triboelectric nanogenerator's durability and facilitates the development of the self-powered systems.

Flexible and stretchable physical sensors capable of both energy harvesting and self-powered sensing are vital to the rapid advancements in wearable electronics. Even so, there exist few studies that can integrate energy harvesting and self-powered sensing into a single electronic skin. Here, a stretchable and washable skin-inspired triboelectric nanogenerator (SI-TENG) is developed for both biomechanical energy harvesting and versatile pressure sensing. A planar and designable conductive yarn network constructed from a three-ply-twisted silver-coated nylon yarn is embedded into flexible elastomer, endowing the SI-TENG with desired stretchability, good sensitivity, high detection precision, fast responsivity, and excellent mechanical stability. With a maximum average power density of 230 mW m-2 , the SI-TENG is able to light up 170 light-emitting diodes, charge various capacitors, and drive miniature electronic products. As a self-powered multifunctional sensor, the SI-TENG is adopted to monitor human physiological signals, such as arterial pulse and voice vibrations. Furthermore, an intelligent prosthetic hand, a self-powered pedometer/speedometer, a flexible digital keyboard, and a proof-of-concept pressure-sensor array with 8 × 8 sensing pixels are successively demonstrated to further confirm its versatile application prospects. Based on these merits, the developed SI-TENG has promising applications in wearable powering technology, physiological monitoring, intelligent prostheses, and human-machine interfaces.

The metal-insulator transition of vanadium dioxide (VO2 ) is exceptionally sensitive to charge density and electron orbital occupancy. Thus three-terminal field-effect transistors with VO2 channels are widely adopted to control the phase transition by external gating voltage. However, current leakage, electrical breakdown, or interfacial electrochemical reactions may be inevitable if conventional solid dielectrics or ionic-liquid layers are used, which possibly induce Joule heating or doping in the VO2 layer and make the voltage-controlled phase transition more complex. Here, a triboelectric nanogenerator (TENG) and a VO2 film are combined for a novel TENG-VO2 device, which can overcome the abovementioned challenges and achieve electron-doping-induced phase modulation. By taking advantage of the TENG structure, electrons can be induced in the VO2 channel and thus adjust the electronic states of the VO2 , simultaneously. The modulation degree of the VO2 resistance depends on the temperature, and the major variation occurs when the temperature is in the phase-transition region. The accumulation of electrons in the VO2 channel also is simulated by finite element analysis, and the electron doping mechanism is verified by theoretical calculations. The results provide a promising approach to develop a novel type of tribotronic transistor and new electronic doping technology.

A long debate on the charge identity and the associated mechanisms occurring in contact-electrification (CE) (or triboelectrification) has persisted for many decades, while a conclusive model has not yet been reached for explaining this phenomenon known for more than 2600 years! Here, a new method is reported to quantitatively investigate real-time charge transfer in CE via triboelectric nanogenerator as a function of temperature, which reveals that electron transfer is the dominant process for CE between two inorganic solids. A study on the surface charge density evolution with time at various high temperatures is consistent with the electron thermionic emission theory for triboelectric pairs composed of Ti-SiO2 and Ti-Al2 O3 . Moreover, it is found that a potential barrier exists at the surface that prevents the charges generated by CE from flowing back to the solid where they are escaping from the surface after the contacting. This pinpoints the main reason why the charges generated in CE are readily retained by the material as electrostatic charges for hours at room temperature. Furthermore, an electron-cloud-potential-well model is proposed based on the electron-emission-dominatedcharge-transfer mechanism, which can be generally applied to explain all types of CE in conventional materials.

An integrated self-charging power unit, combining a hybrid silicon nanowire/polymer heterojunction solar cell with a polypyrrole-based supercapacitor, has been demonstrated to simultaneously harvest solar energy and store it. By efficiency enhancement of the hybrid nanowire solar cells and a dual-functional titanium film serving as conjunct electrode of the solar cell and supercapacitor, the integrated system is able to yield a total photoelectric conversion to storage efficiency of 10.5%, which is the record value in all the integrated solar energy conversion and storage system. This system may not only serve as a buffer that diminishes the solar power fluctuations from light intensity, but also pave its way toward cost-effective high efficiency self-charging power unit. Finally, an integrated device based on ultrathin Si substrate is demonstrated to expand its feasibility and potential application in flexible energy conversion and storage devices.

Photoelectronic properties can be effectively modulated by external mechanical stimulation, which have been widely researched on materials with non-centrosymmetric wurtzite structure. Topological insulator (TI) materials with symmetric crystal structure have been theoretically predicted that its photoelectronic properties would also be greatly modulated through strain modulation effect. Here, for the first time, we experimentally demonstrate the strain modulation effect of TI Bi 2Se3 nanowires (NWs), opening an innovative way to enhance the optoelectronic performance of TI materials. Single-crystal TI Bi2Se3 NWs were synthesized via a micro-environmental control chemical vapor deposition method. Based on these NWs, a high-performance photodetector (PD) with high responsivity, and broadband detection range from ultraviolet to near-infrared were fabricated. By introducing an external 0.54% compressive strain, the photocurrent and responsivity were enhanced by 97% and 503%, respectively, upon excitation by 442 nm light with an intensity of 17.6 mW/cm 2 . A theoretical model of the schematic energy band diagram was proposed to illustrate the enhancement mechanism. The results of theoretical calculation indicate that the conduction band of the TI can be modulated by strain, which can then influence the metal-semiconductor (M-S) junction potential for charges transport. This study reports a high-quality TI Bi 2Se3 NWs based strain-modulated PDs, broadening the family of strain modulation materials system, and offering a promising material for high-performance broadband detectors.

Mechanical energy in ambient, such as water wave, wind, vibration, and human activities, is a green energy that is widely distributed and universally achievable. However, this type of energy has ultra-low frequencies and variable amplitudes, so it is rather challenging to collect them at high efficiency. Here we report a pendulum inspired triboelectric nanogenerator (P-TENG), which could not only boost the output frequency multiple times using a pendulum structure, but also hugely improve the harvesting efficiency through a transformation of impact kinetic energy into potential energy. The P-TENG also has ultrahigh sensitivity and active response to mechanical triggering from a random direction and superior durability for long time operation. A single trigger from the environment, the P-TENG shows a continuous electrical output for 120 s at a frequency of 2 Hz, and its output energy of which is 14.2 times larger than the energy of conventional free-standing TENG. Owing to the air gap between the triboelectric layer and electrodes and the mechanism of electrostatic induction, the P-TENG can work with little frictional resistance and surface wearing, largely enhancing its robustness and durability. The network of P-TENGs was successfully demonstrated to scavenge water wave or wind energy as sustainable power sources. Given the features of exceptional output performance, unprecedented robustness and universal applicability resulting from distinctive mechanism and structure, the P-TENG is a promising method to efficiently harvest energy from the ambient environment with possibility contributing to the blue energy.

Self-powered photodetectors (PDs) have long been realized by utilizing photovoltaic effect and their performances can be effectively enhanced by introducing the piezo-phototronic effect. Recently, a novel pyro-phototronic effect is invented as an alternative approach for performance enhancement of self-powered PDs. Here, a self-powered organic/inorganic PD is demonstrated and the influences of externally applied strain on the pyro-phototronic and the photovoltaic effects are thoroughly investigated. Under 325 nm 2.30 mW cm-2 UV illumination and at a -0.45% compressive strain, the PD's photocurrent is dramatically enhanced from ≈14.5 to ≈103 nA by combining the pyro-phototronic and piezo-phototronic effects together, showing a significant improvement of over 600%. Theoretical simulations have been carried out via the finite element method to propose the underlying working mechanism. Moreover, the pyro-phototronic effect can be introduced by applying a -0.45% compressive strain to greatly enhance the PD's response to 442 nm illumination, including photocurrent, rise time, and fall time. This work provides in-depth understandings about the pyro-phototronic and the piezo-phototronic effects on the performances of self-powered PD to light sources with different wavelengths and indicates huge potential of these two effects in optoelectronic devices.

The authors acknowledge support from King Abdullah University of Science and Technology (KAUST), the Hightower Chair foundation, and the “thousands talents” program for pioneer researcher and his innovation team, China. Y.L.C. thanks China Scholarship Council for supplying oversea scholarship (201706340019).

As previously demonstrated, contact-electrification (CE) is strongly dependent on temperature, however the highest temperature in which a triboelectric nanogenerator (TENG) can still function is unknown. Here, by designing and preparing a rotating free-standing mode Ti/SiO2 TENG, the relationship between CE and temperature is revealed. It is found that the dominant deterring factor of CE at high temperatures is the electron thermionic emission. Although it is normally difficult for CE to occur at temperatures higher than 583 K, the working temperature of the rotating TENG can be raised to 673 K when thermionic emission is prevented by direct physical contact of the two materials via preannealing. The surface states model is proposed for explaining the experimental phenomenon. Moreover, the developed electron cloud-potential well model accounts for the CE mechanism with temperature effects for all types of materials. The model indicates that besides thermionic emission of electrons, the atomic thermal vibration also influences CE. This study is fundamentally important for understanding triboelectrification, which will impact the design and improve the TENG for practical applications in a high temperature environment.

An integrated self-powered dynamic displacement monitoring system by utilizing a novel triboelectric accelerometer for structural health monitoring is proposed and implemented in this study, which can show the dynamic displacement and transmit the alarming signal by accurately sensing the vibration acceleration. The fabricated triboelectric accelerometer based on the noncontact freestanding triboelectric nanogenerator consists of an outer transparent sleeve tube and an inner cylindrical inertial mass that is suspended by a highly stretchable silicone fiber. One pair of copper film electrodes is deposited by physical vapor deposition on nylon film and adhered on the inner wall of the outer tube, while a fluorinated ethylene propylene film with nanowire structures is adhered on the surface of the inner cylindrical inertial mass. The experimental results show that proposed triboelectric accelerometer can accurately sense the vibration acceleration with a high sensitivity of 0.391 V s2 m−1. In particular, the developed accelerometer has superior performance within the low-frequency range. One of the most striking features is that the commercial accelerometer using piezoelectric material is strongly dominated by high-order harmonics, which can cause confusion in computer data analysis. In contrast, the triboelectric accelerometer is only dominated by the base resonance mode.

Silicon underpins nearly all microelectronics today and will continue to do so for some decades to come. However, for silicon photonics, the indirect band gap of silicon and lack of adjustability severely limit its use in applications such as broadband photodiodes. Here, a high-performance p-Si/n-ZnO broadband photodiode working in a wide wavelength range from visible to near-infrared light with high sensitivity, fast response, and good stability is reported. The absorption of near-infrared wavelength light is significantly enhanced due to the nanostructured/textured top surface. The general performance of the broadband photodiodes can be further improved by the piezo-phototronic effect. The enhancement of responsivity can reach a maximum of 78% to 442 nm illumination, the linearity and saturation limit to 1060 nm light are also significantly increased by applying external strains. The photodiode is illuminated with different wavelength lights to selectively choose the photogenerated charge carriers (either electrons or holes) passing through the depletion region, to investigate the piezo-phototronic effect on electron or hole transport separately for the first time. This is essential for studying the basic principles in order to develop a full understanding about piezotronics and it also enables the development of the better performance of optoelectronics.