Publications

We present a simple, cost-effective, robust, and scalable approach for fabricating a nanogenerator that gives an output power strong enough to continuously drive a commercial liquid crystal display. Utilizing the conical shape of the as-grown ZnO nanowires, a nanogenerator is fabricated by simply dispersing them onto a flat polymer film to form a rational "composite" structure. It is suggested that the geometry induced unipolar assembly of the conical nanowires in such a composite structure results in a macroscopic piezoelectric potential across its thickness by introducing a mechanical deformation, which may be responsible for driving the flow of the inductive charges between the top and bottom electrodes. A compressive strain of 0.11% at a straining rate of 3.67% s(-1) produces an output voltage up to 2 V (equivalent open circuit voltage of 3.3 V). This is a practical and versatile technology with the potential for powering small size personal electronics.

The piezotronic effect links the mechanical stimuli with various semiconductor devices, promising for low-power-consuming electronic devices, sensitive sensors, and interactive control systems. The persistent requirement for external strains in piezotronic modulation may hinder its application in some circumstances (such as devices on rigid substrate or complicated synergistic piezoelectric modulation on multidevice). Here, we propose an efficient method to realize piezoelectric modulation of optical and electrical properties of MoS2 FET in both static and dynamic manner, expanding the application of piezotronics. Through capacitive coupling between piezo-electret and MoS2 FET, the remanent piezo-potential can efficiently tune the Fermi level of MoS2, programming the initial electrical property for subsequent fabrication of sophisticated devices. The external strain can induce enhanced piezo-potentials to further affect the energy band bending of MoS2 channel, giving rise to high-performance strain sensors (large gauge factor ∼4800, fast response time ∼0.15 s, and good durability >1000 s). The proposed static and dynamic piezopotential tuned MoS2 FET is easy to extend to devices based on other materials, which is highly desired in tunable sensory systems, active flexible electronics, and human–machine interface.

Sustainable monitoring of traffic using clean energy supply has always been a significant problem for engineers. In this study, we proposed a self-powered smart transportation infrastructure skin (SSTIS) as an innovative and bionic system for the traffic classification of a smart city. This system incorporated the self-powered flexible sensors with net-zero power consumption based on the Triboelectric Nanogenerator (TENG) and an intelligent analysis system based on artificial intelligence (AI). The feasibility of the SSTIS was tested using the full-scale accelerated pavement tests (APT) and the long-short term memory (LSTM) deep learning model with a vehicle axle load classification accuracy up to 89.06%. This robust SSTIS was later tested on highway and collected around 869,600 pieces of signals data. The generative adversarial networks (GAN) WGAN-GP (Wasserstein GAN - Gradient Penalty) was used for data augmentation, due to the imbalanced data of different vehicle types in actual traffic. The overall accuracy for on-road vehicle type classification improved to 84.06% using the convolutional neural network ResNet. Finally, we developed a mobile traffic signal information monitoring system based on cloud platform and Android framework, which enabled engineers to obtain the vehicle axle-load information mobilely. This study is the emerging design and engineering application of the self-powered flexible sensors for smart traffic monitoring, which provides a significant advance for intelligent transportation and smart cities in future.

Using the density functional theory, we conducted a study on the electrification upon contact between hydrophobic liquid molecules and water molecules, revealing localized characteristics of contact-electrification. These "localized features" refer to the specific microscale characteristics where electron transfer predominantly occurs at the contact regions, influenced by factors such as atomic distances and molecular orientations. Although the electrostatic potential and the highest occupied molecular orbital-lowest unoccupied molecular orbital gap offer substantial predictive insights for electron transfer across polymer interfaces, they fall short in capturing the complexities associated with the interaction between hydrophobic liquids and water molecules. The electronegativity of elements at the interface and the localization of molecular orbitals play a decisive role in electron transfer. Simultaneously, for liquid molecules with irregular structures, there is no correlation between the "contact area" and the amount of electron transfer. The "contact area" refers to the surface region where two different liquid molecules come into close proximity. It is defined by the surface area of atoms with interatomic distances smaller than the van der Waals radius. This study challenges traditional assumptions about contact-electrification, particularly in liquid-liquid interfaces, providing new insights into the localized nature of this phenomenon.

Electrochemical cells (ECs) are devices that convert chemical energy into electricity through spontaneous oxidation–reduction reactions that occur separately at two electrodes through the transport of protons in the electrolyte solution and the flow of electrons in the external circuit. A triboelectric nanogenerator (TENG) is an effective device that converts mechanical energy into electricity using organic/polymer materials by a contact induced electrification process followed by charge separation. In this paper, we demonstrate the first integration of an EC and a TENG for simultaneously harvesting chemical and mechanical energy, and its application for powering a sensor and even personal electronics. An EC was fabricated using a Cu/NaCl solution/Al structure, on which a thin polydimethylsiloxane (PDMS) film with a micropyramid surface structure was used as the protection layer of the EC for anti-corrosion, anti-contamination and anti-mechanical damage. A TENG was fabricated based on a contact-and-separation process between the PDMS protection layer and the Al electrode layer of the EC. The output performance of the TENG can be increased by embedding BaTiO3 nanoparticles into the PDMS film layer to enhance the dielectric property. Moreover, we also demonstrated that the produced hybrid energies can be stored in a Li-ion battery for lighting up 30 green LEDs.

In article number 1902725, Xiaojing Mu, Zhong Lin Wang, Ya Yang and co-workers report a new mechanism to enhance the output performance of triboelectric nanogenerators. The hot electron-hole pairs decaying from the surface plasmon resonance effectively enhance the output of TENGs while reducing their output impedances. A 4.5-fold enhancement in output power and a 75% reduction in output impedance are acquired.

Triboelectric nanogenerators (TENGs) have attracted much interest in recent years, due to its effectiveness and low cost for converting high-entropy mechanical energy into electric power. The traditional TENGs generate an alternating current, which requires a rectifier to provide a direct-current (DC) power supply. Herein, a dynamic p-n junction based direct-current triboelectric nanogenerator (DTENG) is demonstrated. When a p-Si wafer is sliding on a n-GaN wafer, carriers are generated at the interface and a DC current is produced along the direction of the built-in electric field, which is called the tribovoltatic effect. Simultaneously, an UV light is illuminated on the p-n junction to enhance the output. The results indicate that the current increases 13 times and the voltage increases 4 times under UV light (365 nm, 28 mW/cm2) irradiation. This work demonstrates the coupling between the tribovoltaic effect and the photovoltaic effect in DTENG semiconductors, promoting further development for energy harvesting in mechanical energy and photon energy.

The development of advanced electrical equipment necessitates polymer dielectrics with a higher electric strength. Unfortunately, this bottleneck problem has yet to be solved because current material modification methods do not allow direct control of deep traps. Here, we propose a method for directly passivating deep traps. Measurements of nanoscale microregion charge characteristics and trap parameters reveal a significant reduction in the number of deep traps. The resulting polymer dielectric has an impressively high electrical strength, less surface charge accumulation, and a significantly increased flashover voltage and breakdown strength. In addition, the energy storage density is increased without sacrificing the charge–discharge efficiency. This reveals a new approach to increasing the energy storage density by reducing the trap energy levels at the electrode–dielectric interface. We further calculated and analyzed the microscopic physical mechanism of deep trap passivation based on density functional theory and characterized the contributions of orbital composition and orbital hybridization.