| Energy harvesting has been attracted intensive attention nowadays due to the worldwide energy crisis. Since advanced technologies have managed to reduce the power consumption and efficiency of electronics, it is feasible to exploit the harvested mechanical energy from ambient environment to power electronics or serve as self-powered sensors. Specifically, flexible mechanical energy harvesters have been given intensive attention owing to the fast development of stretchable and wearable electronics. There are several ways to harvest mechanical energy, such as magnetic generators, thermoelectric generators, piezoelectric nanogenerators, and the newly invented triboelectric nanogenerators (TENG). TENGs have attracted great attention due to its advantages of high energy conversion efficiency, easy fabrication process, low cost, low weight, etc. Additionally, apart from being utilized to fabricate piezoelectric nanogenerators due to its semiconductoring and piezoelectric properties, zinc oxcide (ZnO) nanomaterials are also desirable to be applied to construct ultraviolet (UV) detectors owing to its optoelectric porpoerties such as direct wide band, large surface-to-volume ratio, high exciton binding energy, etc.In this dissertation, the research efforts have led to address the issue of energy supply for stretchable and wearable electronics; in this regard, several types of flexible and stretchable TENGs have been developed to harvest mechanical energy and serve as self-powered sensors, and a stretchable power system is developed to directly power wearable electronics. In addition, a serial of ultraviolet detectors based on ZnO nanomaterials are developed and investigated.A stretchable-rubber-based (SR-based) TENG is developed that can not only harvest energy but also serve as self-powered multifunctional sensors. It consists of a layer of elastic rubber and a layer of alu-minum film that acts as the electrode. By stretching and releasing the rubber, the changes of triboelectric charge distribution/density on the rubber surface relative to the aluminum surface induce alterations to the electrical potential of the aluminum electrode, leading to an alternating charge flow between the alu-minum electrode and the ground. The unique working principle of the SR-based TENG is verified by the coupling of numerical calculations and experimental measurements. A comprehensive study is carried out to investigate the factors that may influence the output performance of the SR-based TENG. By integrating the devices into a sensor system, it is capable of detecting movements in different directions. Moreover, the SR-based TENG can be attached to a human body to detect diaphragm breathing and joint motion. This work largely expands the applications of TENG not only as effective power sources but also as active sensors; and opens up a new prospect in future electronics.A scalable approach that substantially expands the stretchability, refines the deformable ability, and extends the scalability of energy harvesters and self-powered sensors has been developed. With conductive liquid contained in a polymer cover, a shape-adaptive triboelectric nanogenerator (saTENG) unit can effectively harvest energy in various working modes. The saTENG can maintain its performance under a strain of as large as 300%. The saTENG is so flexible that it can be conformed to any three-dimensional and curvilinear surfaces. Applications of the saTENG have been demonstrated as a wearable power source and a self-powered sensor to monitor the biomechanical motion. A bracelet-like saTENG worn on the wrist can light up more than 80 LEDs. Owing to the highly scalable manufacturing process, the saTENG can be easily applied for large-area energy harvesting. In addition, the saTENG can be extended to extract energy from mechanical motion using flowing water as the electrode. This approach provides a new prospective for deformable and stretchable power sources as well as self-powered sensors, and has potential applications in various areas such as robotics, biomechanics, physiology, kinesiology, entertainments, etc.A soft, stretchable, and fully-enclosed self-charging power system is developed by seamlessly combining a stretchable triboelectric nanogenerator with a stretchable supercapacitor, which can subject to and harvest energy from almost all kinds of large-degree deformation due to its fully soft structure. The power system is washable and waterproof owing to its fully-enclosed structure and hydrophobic property of its exterior surface. The power system can be worn on the human body to effectively scavenge energy from various kinds of human motion, and it is demonstrated that the wearable power source can be able to drive an electronic watch. This work paves the way for stretchable power sources, and provides new design options for stretchable and wearable electronics.A self-powered, single-electrode-based triboelectric sensor (TES) is reported to accurately detect the movement of a moving object/body in two dimensions. Based on the coupling of triboelectric effect and electrostatic induction, the move-ment of an object on the top surface of a polytetrafluoroethylene (PTFE) layer induces changes in the electrical potential of the patterned aluminum electrodes underneath. From the measurements of the output performance (open-circuit voltage and short-circuit current), the motion information about the object, such as trajectory, velocity, and acceleration is derived in conformity with the preset values. Moreover, the TES can detect motions of more than one objects moving at the same time. In addition, applications of the TES are demonstrated by using LED illuminations as real-time indicators to visualize the movement of a sliding object and the walking steps of a person.There types of UV photodetectors based on ZnO nanomaterials are constructed and investigated. The self-powered UV detector is based on a single ZnO tetrapod/PEDOT:PSS heterostructure, and its self-powered properties were driven by the photovoltaic effect. At zero bias, the detector showed a short-circuit current of-1.1 nA, an open-circuit voltage of～0.2 V, an on/off ratio of～1100, a rise time of～3.5 s and a decay time of～4.5 s when illuminated by the 325 nm UV (0.16 mW). Furthermore, when the UV irradiated the ZnO tetrapod only, the short-circuit current and open-circuit voltage decrease with the increasing distance between the illuminated spot and the heterojunction. In consideration of the multiterminal feature of ZnO tetrapods, our work provides a possible new approach to develop independent and multifunctional nanodevices. The Ohmic UV detector is based on well-aligned ZnO nanorod (NR) arrays grown on the indium-tin-oxide glass, fabricated by a novel and simple method. When the ZnO NRs device is under 365-nm UV illumination (2.01 mW/cm2), it showed a photocurrent of～308.04 μA, an on/off ratio of～5.13x102 and a fast decay time constant of 1.69 s at 1 V applied bias. The ZnO NRS device shows better performance than the conventional ZnO film device, which is due to the larger surface-to-volume ratio and better crystal quality of ZnO NRs. The Schottky UV detector is based on well-aligned ZnO nanorod arrays grown on the Si substrate. The current-voltage (I-V) curve shows double Schottky diode characteristics in the dark and transforms to Ohmic under UV illumination. The photogenerated current under 365 nm UV illumination is almost 25 times higher than that under 254 nm UV illumination, which is due to the easier recombination of electron-hole pairs under 254-nm UV irradiation. |
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