Publications

The development of wearable electronics, implantable devices and internet of things put forward an ever-growing demand on distributed power supply, providing an opportunity for technologies that can harvest energy locally from environment. As a promising energy harvesting technology, triboelectric nanogenerators (TENGs) show merits of easy fabrication, low cost, abundant choice of structures and materials compared with other energy harvesting technologies. The working principle of the TENG is based on the conjugation of triboelectrification of dielectric materials and electrostatic induction and its theoretical fundamental can be derived from the Maxwell’s displacement current. The practical application of TENGs imposes a challenging requirement to improve the power density of the device, which is highly related to the charge density because it has a quadratic dependence on the charge density. The enhancement of the charge density is restricted mainly by two issues for normal TENG devices under certain intensity of contact or rubbing. The first one is the triboelectrification capability of tribomaterial pairs with certain surface topographies, and the other is the discharge caused by air breakdown. In previous studies, great efforts have been conducted to improve the charge density, based on material selection, structure optimization, surface modification or environment control. The corona charging is a relative facile method that is widely adopted, which can inject charges into dielectric films to enhance the charge density from under 100 μC m -2 to about 240 μC m -2 . However, the injected charges are not stable and the dielectric materials are restricted to electrets. High vacuum environment can suppress air breakdown, which can greatly enhance the charge density to 660 μC m -2 for Cu versus polytetrafluoroethylene (PTFE), and 1003 μC m -2 with an extra ferroelectric barium titanate (BT) layer. Still, this method is restricted by high requirements of device packaging. To develop a facile and universal method to enhance the charge density of TENG devices, an integrated self-charge-pumping TENG (SCP-TENG) device with features of floating layer structure and charge pumping is proposed in this work. Derived from normal TENGs, the proposed device adopts a floating layer to store and bind charges for electrostatic induction, while a TENG based charge pump is designed to continuously pump charges into the floating layer at the same time. The SCP-TENG can operate like normal TENGs, while accumulating bound charges with high efficiency to ultrahigh effective surface density of 1020 μC m -2 in ambient conditions, which has potentials to be further elevated in the future. More importantly, this method is rather facile and robust compared to other charge density enhancing approaches, providing an important strategy to achieve ultrahigh-performance for TENG devices, which is crucial for various practical applications ranging from wearable electronics to blue energy.

Growing demand in portable electronics raises a requirement to electronic devices being stretchable, deformable, and durable, for which functional polymers are ideal choices of materials. Here, the first transformable smart energy harvester and self-powered mechanosensation sensor using shape memory polymers is demonstrated. The device is based on the mechanism of a flexible triboelectric nanogenerator using the thermally triggered shape transformation of organic materials for effectively harvesting mechanical energy. This work paves a new direction for functional polymers, especially in the field of mechanosensation for potential applications in areas such as soft robotics, biomedical devices, and wearable electronics.

Abstract Low power electronics endowed with artificial intelligence and biological afferent characters are beneficial to neuromorphic sensory network. Highly distributed synaptic sensory neurons are more readily driven by portable, distributed, and ubiquitous power sources. Here, we report a contact-electrification-activated artificial afferent at femtojoule energy. Upon the contact-electrification effect, the induced triboelectric signals activate the ion-gel-gated MoS 2 postsynaptic transistor, endowing the artificial afferent with the adaptive capacity to carry out spatiotemporal recognition/sensation on external stimuli (e.g., displacements, pressures and touch patterns). The decay time of the synaptic device is in the range of sensory memory stage. The energy dissipation of the artificial afferents is significantly reduced to 11.9 fJ per spike. Furthermore, the artificial afferents are demonstrated to be capable of recognizing the spatiotemporal information of touch patterns. This work is of great significance for the construction of next-generation neuromorphic sensory network, self-powered biomimetic electronics and intelligent interactive equipment.

Abstract The general concept of dielectric polarization density ( P ) is a macroscopic description of the underlying microscopic structure in the presence of an external electric field and polarized materials itself. A time‐dependent polarization P S induced by a non‐electric field also exists in practice due to the mechanically driven relative motion of media owing to the effects of contact electrification or piezoelectricity. In this work, the starting point is to consider the difference between P and P S , and how P S enters into the governing equations, since it describes the dielectric polarization density without an applied electric field, finally modifying the constitutive relations, Faraday's law, and Maxwell's equations. On this background, a 3D mathematical‐physical model for the sliding mode freestanding triboelectric nanogenerators (TENGs) is established that is taken as an example to confirm the relationship of free charge distribution and dynamics of output power. What needs to be emphasized is that the method of segmented uniform charge distribution is effective and the physical basis for modeling construction and analysis. Finally, we summarized the mathematical‐physical models of TENGs in rectangular coordinates, cylindrical coordinates, and spherical coordinates, building a bridge to reveal the underlying principle behind the microscopic polarization and energy conversion.

FePtCu nanoparticles with varying composition were prepared by the simultaneous polyol reduction of platinum acetylacetonate and copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate) and the thermal decomposition of iron pentacarbonyl. As prepared the particles had a fcc structure with an average diameter of 3.5 nm and were superparamagnetic. Heat treatment of the self-assembled films at temperatures above 550 °C transformed the particles from the fcc to the L10 phase, give in-plane coercivities as high as 9000 Oe. X-ray diffraction revealed that the Cu remained in the films and the presence of an extra peak, indicating a second phase was present. Consistent with two or more phases, the magnetic hysteresis curves could be decomposed into a hard component (Hc>5000 Oe) and a soft component (Hc<2000 Oe). Unlike our earlier results for Ag in FePt, adding Cu to FePt did not lower the temperature required for phase transformation from the fcc to the L10 phase.

Highly flexible, robust, and sensitive infrared nanosensors were fabricated based on carbon nanoparticles that were synthesized through a simple and low-cost flame method. The infrared nanosensor devices showed sharp infrared photoresponse with a response time of ∼68 ms and a maximum photocurrent change of ∼52.9%. The devices showed a superhydrophobic property with a contact angle larger than 150° and a sliding angle of ∼4°. The mechanism for the enhanced infrared photoresponse from carbon nanoparticles is discussed.

Visible light communication (VLC) simultaneously provides illumination and communication via light emitting diodes (LEDs). Keeping a low bit error rate is essential to communication quality, and holding a stable brightness level is pivotal for illumination function. For the first time, a piezo‐phototronic effect controlled visible light communication (PVLC) system based on InGaN/GaN multiquantum wells nanopillars is demonstrated, in which the information is coded by mechanical straining. This approach of force coding is also instrumental to avoid LED blinks, which has less impact on illumination and is much safer to eyes than electrical on/off VLC. The two‐channel transmission mode of the system here shows great superiority in error self‐validation and error self‐elimination in comparison to VLC. This two‐channel PVLC system provides a suitable way to carry out noncontact, reliable communication under complex circumstances.