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Single-mode plasmonic lasing has great potential for use in photonic and sensing applications. In this work, single-mode lasing is realized using a plasmonic-enhanced woven microfiber that shows ultrahigh sensitivity to the ambient environment. This plasmonic-enhanced microfiber is fabricated by spraying Ag nanospheres onto rhodamine 6G-doped polymer microfibers. Single-mode laser emission with an ultranarrow linewidth (0.1 nm) and a low threshold (18.8 kW/mm2) is achieved in the microfiber using the effects of mode selection and plasmonic enhancement provided by the Ag nanospheres. A large wavelength shift in the single-mode lasing is observed when the proposed laser is used as a sensor and exposed to a humid or acidic environment. The wavelength shift is attributed to refractive index variations in the microfiber caused by either moisture absorption or chemical reactions. In humidity sensing, the laser's sensitivity is as high as 826.6 pm/% relative humidity (RH) and the detection limit is 0.051% RH. An innovative strategy for acetic acid gas sensing is proposed that uses the chemical reaction with rhodamine 6G, and its minimum response time is 5 min. Because of the microfiber's excellent fabric compatibility, a wearable sensor is fabricated by weaving the plasmonic-enhanced microfiber into clothes, and this sensor demonstrates extreme bending stability. The results reported here provide a novel approach to the design and fabrication of ultrasensitive wearable sensors for multifunctional sensing applications.

When the power conversion efficiency (PCE) of perovskite solar cells (PSCs) rapidly approaches that of commercial solar cells, the stability becomes the most important obstacle for the commercialization of PSCs. Aside from the widely studied slow PCE degradation, the PSCs also show a unique rapid PCE degradation. Although the degradation due to oxygen and humidity can be avoided by encapsulation, that due to bias voltage, light and heat could not be effective suppressed and will lead to considerable degradation. Usually, the rapid PCE degradation is believed to be from ion migration. However, a systematic investigation is yet to be carried out. This work quantitatively and systematically investigated the relationships between external fields (bias voltage, light or heat), ion migration and device performance. By comparing the performance of reference PSCs after 90 min degradation under these fields, we conclude that (1) the electric field affects the spatial distribution of mobile ions; (2) the light field changes the mobile ion densities and drives the ion migration; (3) the heat field results in perovskite decomposition as well as changing the mobile ion densities. In addition to the analysis of the reference device, we experimentally proved that the improved device stability upon introducing phenethylammonium iodide (PEAI) or poly-methyl methacrylate (PMMA) layers originates from the inhibition of mobile ion density and migration.

Hybrid lead halide perovskites have made great strides in next-generation photovoltaic and optoelectronic devices. Random lasers based on perovskite materials have been intensively investigated, but the miniaturization of perovskite random lasers has not been achieved up to now. Here, we report the fabrication of perovskite random lasers based on perovskite films deposited on the optical fiber facets using a dip-coating method. Under optical pumping conditions, random lasing was observed with minimum threshold energy of 32.3 μJ/cm2 at ~550 nm; also, the lasing threshold decreased with increasing diameter of the optical fiber. The results show that the random lasing emission originates from the scattering between the perovskite crystal grains, and the decreased threshold is attributed to the increased active area of the perovskite film. The directionality of perovskite random lasers indicates that the divergence angle of the laser beam is less than 60°. We also demonstrate that the perovskite random laser on the fiber facet can prevent speckle formation and improve image quality. These results may promote the applications of random lasers in compact sources and integrated optoelectronic devices.

Flexible perovskite solar cells (F-PSCs) are attracting tremendous research interest due to their light weight and flexibility. However, the poor quality of perovskite films caused by deformation of flexible substrates during a general heat treatment process hinders the fabrication of high efficiency flexible cells. Here, a simple gradient heat treatment (GHT) process is developed to effectively improve the crystal quality of perovskite films and the efficiency of F-PSCs. The results show that a smaller temperature fall-off gradient will be beneficial to the further growth of perovskite films, which helps to further enhance the crystalline quality. Compared with the conventional method, the power conversion efficiency (PCE) of F-PSCs fabricated by a GHT process with a relatively small gradient significantly improved by 31%, and the maximum PCE increased to 17.37%. This work provides a new idea for ameliorating the quality of perovskite films and enhancing the performances of F-PSCs.

Hybrid organic–inorganic perovskites have attracted tremendous attention for solar cell application due to their outstanding properties. However, further studies are still needed to fully address the carrier recombination issue at grain boundaries which lowers the device performance, and its environmental stability issues. Fluoride additive engineering is found to be a good method to successfully passivate defects in perovskite films. Here, we developed a simple method to improve the device power conversion efficiency as well as its environmental stability, by introducing the polytetrafluoroethylene (PTFE) additive within the perovskite organic precursor in a two-step deposition method. The built-in electric field effect induced by PTFE induces the migration of photo-generated carriers, suppressing the electron–hole recombination, thus improving the short circuit current and then the photovoltaic performance. We obtained a maximum efficiency of 20.48% for PTFE 5%-based PSCs compared to the pristine one which was only 14.27%. Furthermore, it is also demonstrated that the PTFE-based PSC device exhibits strong environmental stability. The device presented only 5% PCE loss over 42 days of storage in an ambient environment.

Perovskite solar cells (PSCs) have gained tremendous research interest because of their tolerance of defects, low cost, and facile processing. In PSC devices, PbI2 has been utilized to passivate defects at perovskite film surfaces and GBs; however, a systematic mechanism of PbI2 in situ passivation for enhancing the solar cells efficiency has not been fully explored. Here, this work, we systematically studies the effect of the precise PbI2 ratio and the PbI2 in situ passivation mechanism based on trap density, carrier lifetime, Fermi level, and so forth. This study finds the appropriate ratio of I/Pb to be around 2.57:1 using energy-dispersive spectroscopy. After the moderate excess PbI2 in situ passivation, the trap density is reduced from 6.12 × 1016 to 3.38 × 1016 cm-3, and the carrier lifetime is extended from 168.35 to 368.77 ps by using fs-TA spectroscopy. This result indicates that the moderate excess PbI2 in situ passivation can reduce the trap density and suppress the nonradiative recombination. The efficiency of solar cell has shown a nearly 11.3% improvement of 19.55% for an I/Pb ratio of 2.57:1 compared with 2.69:1. It also demonstrates that the efficiency of PSCs can be enhanced effectively by PbI2 in situ passivation.

In recent years, due to their high photo-to-electric power conversion efficiency (PCE) (up to 23% (certified)) and low cost, perovskite solar cells (PSCs) have attracted a great deal of attention in photovoltaics field. The high PCE can be attributed to the excellent physical properties of organic–inorganic hybrid perovskite materials, such as a long charge diffusion length and a high absorption coefficient in the visible range. There are different diffusion lengths of holes in electrons in a PSC device, and thus the electron transporting layer (ETL) plays a critical role in the performance of PSCs. An alternative for TiO2, to the most common ETL material is SnO2, which has similar physical properties to TiO2 but with much higher electron mobility, which is beneficial for electron extraction. In addition, there are many facile methods to fabricate SnO2 nanomaterials with low cost and low energy consumption. In this review paper, we focus on recent developments in SnO2 as the ETL of PSCs. The fabrication methods of SnO2 materials are briefly introduced. The influence of multiple SnO2 types in the ETL on the performance of PSCs is then reviewed. Different methods for improving the PCE and long-term stability of PSCs based on SnO2 ETL are also summarized. The review provides a systematic and comprehensive understanding of the influence of different SnO2 ETL types on PSC performance and potentially motivates further development of PSCs with an extension to SnO2-based PSCs.

Several valuable scientific investigations have been conducted these last few years in materials design and device engineering for perovskite solar cells (PSCs) to make them competitive compared to traditional silicon-based photovoltaic technologies. Consequently, high power conversion efficiency beyond 25% is nowadays reported. However, their long-term stability remains a significant challenge to overcome. Herein, the influence of fluorinated compounds on each layer of PSCs devices and their impact on the resulted device performances and stability is spotlighted. The fluorinated compounds exhibit attractive properties due to their very high electronegativity attributed to the fluorine atom, and their strong hydrophobicity. Thus, the introduction of these compounds is found to be a successful strategy to positively suppress the surface trap states, enhancing charge collection and reducing interfacial charge recombination. Besides, a better film quality and better energy level alignment is obtained, resulting in the improvement of device photovoltaic parameters such as the open-circuit voltage (Voc ), short-circuit current (Jsc ), and fill factor (FF), and then, the device's overall power conversion efficiency (PCE). Their long-term stability is also found to further be improved.

In industrial manufacturing, alloying can contribute to the passivation of active metals and markedly improve their corrosion resistance. This inspires us to solve the current critical problem of Ag nanowires (Ag NWs) that have poor stability against chemical and electrochemical corrosion. These problems have seriously limited the applications of Ag NWs in optoelectronic devices where they are used for transparent conductive electrodes. Here, a kind of transparent conductive electrode based on Ag@Pt alloy-walled hollow nanowires (Ag@Pt AHNWs) is successfully fabricated by introducing 12 mol % Pt into long Ag NWs to form Ag@Pt alloy. The as-synthesized electrodes exhibit better optical transmittance (82% at the wavelength of 550 nm) under high electrical conductivity (28.73 Ω/sq–1), high thermal stability up to 400 °C for 11 h, and remarkable mechanical flexibility (remaining stable after 5000 cycles bending), as well as high resistance against chemical and electrochemical corrosion. The Ag@Pt AHNWs electr...

Ultrasonic waves are existing in water and in our living environment, but harvesting the sonic wave energy especially in water is rather challenging, simply because of the high pressure generated by water. In this work, a triboelectric nanogenerator (TENG) has been designed using spherical pellets as the media for performing the contact-separation operation during ultrasonic wave excitation for energy harvesting. The fabricated TENG can attain an instantaneous output current from several milliamps to about one hundred milliamps and achieve an output power of 0.362 W/cm 2 at an ultrasonic wave frequency of 80 kHz. The average power conversion efficiency of the TENG has reached 13.1%. The equivalent output galvanostatic current is 1.43 mA, which is the highest value reported so far. The developed TENG pellets has been demonstrated to continuously power up to 12 lamps with 0.75 W each, and can continuously drive a temperature-humidity meter, an electronic watch, and directly drive a health monitor. This study presents the outstanding potential of TENG for underwater applications.

As a green and eco-friendly technology, triboelectric nanogenerator (TENG) can harvest energy from human motion to generate electricity, so TENGs have been widely applied in wearable electronic devices to replace traditional batteries. However, the surface of these TENGs is easily contaminated and breeds bacteria, which is a threat to human health. Here, we report an antibacterial composite film-based triboelectric nanogenerator (ACF-TENG) that uses Ag-exchanged zeolite (Ag-zeolite) and polypropylene (PP) composite film as the triboelectric layer. Adding a small amount of Ag-zeolite with excellent antibacterial properties can increase the dielectric permittivity and improve the surface charge density of composite films, which enhances the output performance of the ACF-TENG. The open-circuit voltage (VOC), short-circuit current (ISC), and transferred charge (QTr) of the ACF-TENG are about 193.3, 225.4, and 233.3% of those of a pure PP film-based TENG, respectively. Because of the silver in the Ag-zeolite, ...

Recently, triboelectric nanogenerator (TENG) has been invented as a new energy technology and widely utilized in renewable and sustainable energy harvesting. Here we report a regular dodecahedron device integrated with 12 sets of multilayer wavy-structured robust triboelectric nanogenerators (WS-TENGs) for harvesting water wave energy. Each WS-TENG is composed of a wavy-structured Cu–Kapton–Cu film and two fluorinated ethylene propylene (FEP) thin films sputtered with metal electrodes as a sandwich structure. A hard ball is enclosed inside a polyhedron made by WS-TENGs as the walls; a collision of the ball with the WS-TENG in responding to the kinetic motion of water wave converts mechanical energy into electricity. A high output voltage and current of about 250 V and 150 μA, respectively, are measured by a single unit of WS-TENGs in water. Considering the units can be connected into a net structure, the average output power is expected to be 0.64 MW from 1 km2 surface area in a depth of 5 m. By the virtues of cost effective, low-carbon and environmentally friendly, the development of WS-TENGs can be a significant step towards the large-scale water wave energy harvesting and have great prospects for the blue energy.

Tribotronics is a new field developed by coupling triboelectricity and semiconductor, which can drive triboelectric-charge-controlled optoelectronic devices by further introducing optoelectronics. In this paper, a tribotronic phototransistor (TPT) is proposed by coupling a field-effect phototransistor and a triboelectric nanogenerator (TENG), in which the contact-induced inner gate voltage by the mobile frictional layer is used for modulating the photodetection characteristics of the TPT. Based on the TPT, alternatively, a coupled energy-harvester (CEH) is fabricated for simultaneously scavenging solar and wind energies, in which the output voltage on the external resistance from the wind driven TENG is used as the gate voltage of the TPT for enhancing the solar energy conversion. As the wind speed increases, the photovoltaic characteristics of the CEH including the short-circuit current, open-circuit voltage, and maximal output power have been greatly enhanced. This work has greatly expanded the functionality of tribotronics in photodetection and energy harvesting, and provided a potential solution for highly efficient harvesting and utilizing multitype energy.

A GaN/Si nanoheterostructure array was synthesized using the functional substrate of silicon nanoporous pillar array (Si-NPA) by CVD method. An n-GaN nanocolumnar/p-Si nanocrystalline nanoheterojuction array solar cell was fabricated and the GaN nanocolumnar grew along the [0001] direction. The device has an average integrated reflection of ∼4.79% at the range of 300-1200 nm. The solar cell showed aVoc of 0.82 V, aJsc of 23.21 mA, aFF of 38.3% and a maximum power conversion efficiency of 7.29%. The results provide a new conception of mass-nanoheterojuctions for photovoltaic filed.

In recent years, triboelectric nanogenerators have attracted much attention because of their unique potential in self-powered nanosensors and nanosystems. In this paper, we report a cylindrical spiral triboelectric nanogenerator (S-TENG), which not only can produce high electric output to power display devices, but also can be used as a self-powered displacement sensor integrated on a measurement ruler. At a sliding speed of 2.5 m/s, S-TENG can generate a short-circuit current (I SC) of 30 µA and an open-circuit voltage (V OC) of 40 V. As the power source, we fabricate a transparent and flexible hand-driven S-TENG. Furthermore, we demonstrate a self-powered S-TENG-based measuring tapeline that can accurately measure and display the pulled-out distance without the need for an extra battery. The results obtained indicate that TENG-based devices have good potential for application in self-powered measurement systems.

Using high-quality and polarity-controlled GaN nanowires (NWs), we studied the piezotronic effect in crystal orientation defined wurtzite structures. By applying a normal compressive force on c-plane GaN NWs with an atomic force microscopy tip, the Schottky barrier between the Pt tip and GaN can be effectively tuned by the piezotronic effect. In contrast, the normal compressive force cannot change the electron transport characteristics in m-plane GaN NWs whose piezoelectric polarization axis is turned in the transverse direction. This observation provided solid evidence for clarifying the difference between the piezotronic effect and the piezoresistive effect. We further demonstrated a high sensitivity of the m-plane GaN piezotronic transistor to collect the transverse force. The integration of c-plane GaN and m-plane GaN indicates an overall response to an external force in any direction.

Tribotronics is a new field about the devices fabricated using the electrostatic potential created by contact electrification as a “gate” voltage to tune/control charge carrier transport in semiconductors. In this paper, an organic tribotronic transistor is proposed by coupling an organic thin film transistor (OTFT) and a triboelectric nanogenerator (TENG) in vertical contact-separation mode. Instead of using the traditional gate voltage for controlling, the charge carrier transportation in the OTFT can be modulated by the contact-induced electrostatic potential of the TENG. By further coupling with an organic light-emitting diode, a contact-electrification-gated light-emitting diode (CG-LED) is fabricated, in which the operating current and light-emission intensity can be tuned/controlled by an external force–induced contact electrification. Two different modes of the CG-LED have been demonstrated and the brightness can be decreased and increased by the applied physical contact, respectively. Different from the conventional organic light-emitting transistor controlled by an electrical signal, the CG-LED has realized the direct interaction between the external environment/stimuli and the electroluminescence device. By introducing optoelectronics into tribotronics, the CG-LED has open up a new field of tribophototronics with many potential applications in interactive display, mechanical imaging, micro-opto-electro-mechanical systems, and flexible/touch optoelectronics.

A tribotronic logic device is fabricated to convert external mechanical stimuli into logic level signals, and tribotronic logic circuits such as NOT, AND, OR, NAND, NOR, XOR, and XNOR gates are demonstrated for performing mechanical-electrical coupled tribotronic logic operations, which realize the direct interaction between the external environment and the current silicon integrated circuits.

UV is a high-energy electromagnetic radiation that has been widely used in industrial production and the scientific research domain. In this work, a deep UV light emission was obtained using triboelectrification induced plasma discharge without any extra power supply. By a mechanical friction between polymer and quartz glass, the triboelectric charges cause a changing electric field, which may bring plasma discharge of low pressure gas (Ar-Hg) and give out 253.7 nm irradiation. The UV light caused by continuous friction can excite a trichromatic phosphor and afford a bright white light emission. A UV sterilization experiment shows that ∼98% of Escherichia coli can be killed in 30 min by UV irradiation, which reveals that a self-powered sterilization apparatus with good sterilization effect was fabricated. This work provides a novel design to fabricate a self-powered UV light emitting device using low-frequency mechanical friction and realizes the coupling of triboelectrification and plasma luminescence, which may further expand the application of UV light in special circumstances.

Based on a triboelectric nanogenerator (TENG), the first active micro-actuator for optical modulation driven by mechanical energy without external power or mechanical joint is presented. This demonstrates the enormous potential of TENGs for independent and sustainable self-powered micro/nano electromechanical systems, and opens up new -applications of TENGs in triboelectric-voltage-controlled devices.

Effectively harvesting ambient energy is a key approach for realizing self-powered systems for portable electronics, wireless sensing, implanted devices, security and so on. It is generally desired that adding a power harvester should not add much weight, volume or additional components to the electronics. In this work, a cover-sheet-based (CS) triboelectric nanogenerator (TENG) is developed based on the protection structure of an electronics, such as a smart phone, for generating power for mobile electronics through conversion of mechanical energy. It consists of a slider and two stators. Each stator comprises of two complementary micro-grating electrodes. At a sliding velocity 1 m s −1 , the CS-TENG produces an output current of 88.8 μA, and a voltage of 2372 V. As a thin cover for mobile electronics, under the hand motions, the CS-TENG can light up household light bulbs or directly driving a mobile temperature meter without the use of a battery. In addition, springs are added to make the CS-TENG suitable for scavenging vibration energy from body motion. This study immediately opens the applications of TENG for conventional sensor systems.

We report self-powered velocity and trajectory tracking sensor (VTTS) array for detecting object motion, velocity, acceleration and trajectory based on single-electrode triboelectric nanogenerator. The VTTS was fabricated by a cost-effective and simple-designed grid, which obtained the electric signals by the charge transition between the electrodes and the ground according to the electrostatic induction of objects. A self-powered VTTS arrays (9×9 pixels) with low-node mode was prepared and realized the real-time tracking of position, velocity, acceleration and trajectory for a moving object by visual observation. Using the simply electrode weave technique, a high-resolution VTTS with 41×41 pixels on an active size of 1×1 cm2 was obtained and it only needs the 41+41=82 output ports. The device can detect a tiny displacement and trajectory for the high resolution of 250 μm. This work may provide a innovate design for preparing VTTS with ultrahigh pixels and low-cost.

Harvesting mechanical energy from our surroundings to acquire a steady and high power output has attracted intensive interest due to the fast development of portable electronics. In this work, the disk-structured triboelectric nanogenerator (TENG) was prepared based on the mature printed circuit board (PCB) technology and the composite structure for effectively improving the utilization in space. A narrow grating of 1° was designed to produce high output. Operated at a rotation rate of 1,000 rpm, the TENG produces a high output power density of 267 mW/cm2 (total power output of 25.7 W) at a matched load of 0.93 MΩ. After introducing a transformer, the output power can be managed so that it can be directly used to charge a battery for a smart phone. With the PCB production technology, fabrication of high performance TENG at low cost and large-scale becomes feasible.

Utilizing the coupled metal oxide semiconductor field-effect transistor and triboelectric nanogenerator, we demonstrate an external force triggered/controlled contact electrification field-effect transistor (CE-FET), in which an electrostatic potential across the gate and source is created by a vertical contact electrification between the gate material and a “foreign” object, and the carrier transport between drain and source can be tuned/controlled by the contact-induced electrostatic potential instead of the traditional gate voltage. With the two contacted frictional layers vertically separated by 80 μm, the drain current is decreased from 13.4 to 1.9 μA in depletion mode and increased from 2.4 to 12.1 μA in enhancement mode at a drain voltage of 5 V. Compared with the piezotronic devices that are controlled by the strain-induced piezoelectric polarization charged at an interface/junction, the CE-FET has greatly expanded the sensing range and choices of materials in conjunction with semiconductors. The CE-FET is likely to have important applications in sensors, human–silicon technology interfacing, MEMS, nanorobotics, and active flexible electronics. Based on the basic principle of the CE-FET, a field of tribotronics is proposed for devices fabricated using the electrostatic potential created by triboelectrification as a “gate” voltage to tune/control charge carrier transport in conventional semiconductor devices. By the three-way coupling among triboelectricity, semiconductor, and photoexcitation, plenty of potentially important research fields are expected to be explored in the near future.

To date, quite a few wearable electronics have entered the market, which are changing the life pattern of consumers. However, the limited lifetime and energy storage capacity have made rechargeable batteries the bottleneck in wearable technology, especially with the increase of number of wearable devices and their large distribution. To solve this problem, we demonstrate a woven-structured triboelectric nanogenerator (W-TENG) using commodity nylon fabric, polyester fabric, and conductive silver fiber fabric. With the advantage of being flexible, washable, breathable, wearable, and able to be triggered by a freestanding triboelectric layer, this W-TENG can move freely without any constraint and is suitable for wearable electronics. To demonstrate the potential applications of the W-TENG, the W-TENG is integrated into shoes, coats, and trousers to harvest different kinds of mechanical energy from human motion. This work presents a new approach in applying triboelectric nanogenerator to wearable devices.

The triboelectric nanogenerator (TENG), based on the well-known triboelectric effect and electrostatic induction effect, has been proven to be a simple, cost effective approach for self-powered systems to convert ambient mechanical energy into electricity. We report a flexible and transparent paper-based triboelectric nanogenerator (PTENG) consisting of an indium tin oxide (ITO) film and a polyethylene terephthalate (PET) film as the triboelectric surfaces, which not only acts as an energy supply but also as a self-powered active sensor. It can harvest kinetic energy when the sheets of paper come into contact, bend or slide relative to one another by a combination of vertical contact-separation mode and lateral sliding mode. In addition, we also integrate grating-structured PTENGs into a book as a self-powered anti-theft sensor. The mechanical agitation during handling the book pages can be effectively converted into an electrical output to either drive a commercial electronic device or trigger a warning buzzer. Furthermore, different grating-structures on each page produce different numbers of output peaks by sliding relative to one another, which can accurately act as a page mark and record the number of pages turned. This work is a significant step forward in self-powered paper-based devices.

Energy harvesting from moving objects and machines in our daily life, such as automobile and train, is quite important for powering portable electronics, sensor systems and high fuel efficiency. Here, we present a disc-based design that simulates the braking system in an automobile for harvesting energy when the braking pads are both in contact and in non-contact modes. The mechanisms for the design are based on a conjunction use of triboelectrification and electrostatic-induction processes. The static non-mobile charges for driving the free electrons are created by triboelectrification when the two discs of opposite tribo-polarities are in direct contact during the braking action. The process for generating electricity in non-contact mode is due to the electrostatic induction of the existing tribo-charges on the insulating pad. Our approach demonstrates an effective means for harvesting energy from a rotating disc structure during both braking and non-braking processes, with potential application in motor cycles, automobiles, and even moving trains.

The triboelectric nanogenerator (TENG) is a promising energy harvesting technology that can convert mechanical energy into electricity and can be used as self-powered active sensors. However, previous studies are mostly carried out at room temperature without considering the temperature effect on the electrical performance of TENGs, which is critical for the application of electronics powered by TENGs in different regions in the world. In the present work, a TENG that worked in the single-electrode and contact-separation mode is utilized to reveal the influence of environment temperature on the electrical performance of TENG. The electrical performance of the TENG shows a decreasing tendency, as the temperature rises from −20 to 150 °C, which is controlled by the temperature-induced changes in the ability of storing and gaining electrons for polytetrafluoroethylene (PTFE). The storing electron ability change of PTFE is attributed to two aspects: one is the reduction of relative permittivity of PTFE sheet as the temperature increases, and the other is the variations of effective defects such as the escape of trapped charges in shallow traps and surface oxidation under the effect of temperature perturbation. This work can provide useful information for the application of TENG in both electric power generation and self-powered sensors in the harsh environment.

Hourglass, or sandglass, is known for centuries to record the passage of time. Here, an hourglass triboelectric nanogenerator (HG-TENG) is reported as a power source by harnessing the kinetic energy of falling particles. By employing the geometry of an hourglass and replacing the sand with a mixture of polytetrafluoroethylene (PTFE) pellets and Al balls, the HG-TENG delivers a train of electrical pulses of the same sign without a rectifier bridge. When the volume ratio of the PTFE pellets to the Al balls is 1:1, the HG-TENG is able to light up 160 commercial light emitting diodes intermittently for 18 s. Furthermore, it is demonstrated that the HG-TENG can also serve as a self-powered UV counterfeit detector.

A power-transformed-and-managed triboelectric nanogenerator (PTM-TENG) is invented that is intended to give regulated power output for driving electronics. The design is based on a synchronized mechanical agitation that not only drives the TENG but also switches the connections for the capacitors for lowering the output voltage and increasing the output charges. An energy preservation efficiency of >95% was demonstrated. The PTM-TENG not only detected the external mechanical triggering action but also generated enough power for sending out an infrared signal.

Triboelectric nanogenerators (TENGs) have emerged as a highly effective and easily scalable technology for harvesting mechanical energy. Recently, standards and figure-of-merits have been defined to quantify the performance of TENGs. In this work, the figure-of-merits of rolling-friction-based TENGs are investigated through a theoretical model based on the rolling freestanding mode, including the conductor-to-dielectric and dielectric-to-dielectric cases. By combining finite-element simulations and semi-analytical derivations, the basic properties and resistive load output characteristics of rolling TENGs are calculated for various structural parameters, such as the electrode gap or rod diameter. The average output power is optimized by maximizing the structural figure-of-merit, which depends on the structural parameters. The results gained in this work could provide useful guidance for optimizing the performance of rolling-friction-based TENGs toward practical self-powered systems.

A GaN/Si nanoheterostructure array was prepared by growing GaN nanostructures on silicon nanoporous pillar array (Si-NPA). Based on as-grown and annealed GaN/Si-NPA, two light-emitting diodes (LEDs) were fabricated. It was found that after the annealing treatment, both the turn-on voltage and the leakage current density of the nanoheterostructure varied greatly, together with the electroluminescence (EL) changed from a yellow band to a near infrared band. The EL variation was attributed to the radiative transition being transformed from a defect-related recombination in GaN to an interfacial recombination of GaN/Si-NPA. Ours might have provided an effective approach for fabricating GaN/Si-based LEDs with different emission wavelengths.

Wind-driven triboelectric nanogenerators (TENGs) play an important role in harvesting energy from ambient environments. Compared to single-side-fixed triboelectric nanogenerator (STENG) arrays for harvesting single-pathway wind energy, double-side-fixed triboelectric nanogenerator (DTENG) arrays are developed to harvest bidirectional wind energy. Electrical performances of the STENG and DTENG can be improved due to sticky, abrasive, and electrical properties of the Ti buffer layers among Al, polytetrafluoroethylene (PTFE), and polyimide (Kapton), configuring in triboelectric PTFE/Ti/Al and Al/Ti/Kapton/Ti/Al thin films. Short-circuit current (I SC), open-circuit voltage (V OC), and frequencies of the STENG and DTENG increase with increasing wind velocity ranging from 9.2 to 18.4 m s21, revealing that the moderate I SC, V OC, frequencies, and output powers of the STENG and DTENG reach 67 μA, 57 μA, 334 V, 296 V, 173 Hz, 162 Hz, 5.5 mW and 3.4 mW with a matched load of 4 MΩ at airflow rate of 15.9 m s21, respectively. Compared with counterparts of the single-pathway-harvested STENG arrays, the I SC, durability, and stability of the bidirectional-harvested DTENG can be dramatically improved by a 4 3 1 array connected in parallel because of the improved device configuration, stickiness, and abrasion by adhering Ti buffer layers. The durable DTENG arrays present a step toward practical applications in harvesting bidirectional wind energy for self-powered systems and wireless sensors.

An innovative design is reported of a direct-current triboelectric nanogenerator (DC-TENG) based on a rotating disk design for harvesting rotational mechanical energy. The DC-TENG consists of two disks and two pairs of flexible electric brushes that are made of carbon fiber and contact two electrodes, respectively. During the rotation, two disks have distinct triboelectric polarities for a cyclic in-plane charge separation between them and an alternating current is generated between the two electrodes. Because of the sliding contact and automatically switch between the electric brushes and the two electrodes, the current is reversed in the second half of the cycle and a direct current is generated. The role that the rotating speed and the segmentation number have is thoroughly investigated and shows that there is direct current enhancement not only at higher speed but also with more segments. The DC-TENG has been demonstrated as a constant current source for directly and continuously driving electronic devices and/or charging an energy storage unit without a rectifier bridge. This work presents a novel DC-TENG technology and opens up more potential applications for harvesting rotational mechanical energy and powering electronics.

Nanostructured materials have attracted much attention for enhancing the performance of solar cells due to their unique advantage of high light absorption. In this regard, here we propose a CdS/Si nanoheterojunction array, called CdS/Si-NPA, for harvesting the energy of sunlight. CdS/Si-NPA was obtained by depositing a continuous film of CdS onto silicon nanoporous pillar array (Si-NPA) via a chemical bath deposition (CBD) method and the average reflectance of CdS/Si-NPA was less than 7% in the wavelength range of 200–1000 nm. Under 1 sun air mass (AM) 1.5 G illumination, CdS/Si-NPA exhibits an obvious photovoltaic effect. These results indicate that CdS/Si-NPA has a strong broadband optical antireflection and might be a promising candidate for the assembly of high efficiency solar cells.