Nanogenerators and piezoelectric are the two recently developed technologies for effective harvesting of ambient mechanical energy for self-powered systems. Ever since the wide-range applications of laptop computers and cell phones, the search for power sources for driving portable electronics has become increasingly important. The current technology mainly relies on rechargeable batteries. However, considering trillions of different devices widely used in health monitoring, infrastructure and environmental monitoring, internet of things and defense technologies, the traditional batteries may not meet or may not be the choice for power sources. The nanogenerator was invented to meet these technological challenges. There are currently three effects commonly used for converting tiny physical motion into electricity: piezoelectric, triboelectric and pyroelectric effect. Piezoelectricity, a phenomenon known for centuries, is an effect of the production of electrical potential in a substance as the pressure on it changes. Piezo-photonics has attracted much attention because it may find broad applications in mechano-optical conversion, structural health diagnosis, nondestructive analysis, novel light sources and displays. The piezo-phototronic effect is a result of three-way coupling among piezoelectricity, photonic excitation and semiconductor transport, which allows tuning and controlling of electro-optical processes by strain-induced piezopotential. This tutorial will include two sessions, while the morning session is about fundamental studies, and the afternoon session is about the applications.

Nanogenerators and Piezotronics ― History and fundamental principles
Zhong Lin Wang, Georgia Institute of Technology

Wang will first introduce the fundamental science, engineering approach and technological applications of nanogenerator as a sustainable, self-sufficient power source for micro-/nanosystems by harvesting energy from our body and living environment. Wang will then introduce the fundamentals of piezotronics and piezo-phototronics and to give an updated progress about their applications in energy science, electronics and sensors.

Piezotronics and Piezo-Phototronics—From Fundamental Science to Applications
Caofeng Pan, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences

Piezotronics concerns the devices fabricated using the piezopotential as a “gate” voltage to tube/control charge carrier transport at a contact or junction. The piezo-phototronic effect is to use the piezopotential to control the carrier generation, separation, transport, and/or recombination for improving the performance of optoelectronic devices, such as photon  detector, solar cell, and LED. In this tutorial, Pan will first give an in-depth introduction of the mechanisms and applications of nanowire-based piezotronics and piezo-phototronics.

Theory of Piezotronics
Yan Zhang, University of Electronic Science and Technology of China

Zhang will introduce fundamental piezotronic theory established, piezotronic p-n junction and metal-semiconductor contact models. The class of materials includes wurtzite and two-dimentional piezoelectric semiconductors, such as ZnO, GaN, InN, CdS and monolayer MoS2.

Standardized Evaluation of Nanogenerators
Yunlong Zi, The Chinese University of Hong Kong

Zi will systematically introduce the evaluation standards and standardized evaluation methods for nanogenerators. Starting from cycles of maximized energy output, the figures-of-merit will be proposed. And then, considering the breakdown effect, the maximized energy output should be modified by reducing the breakdown areas. Finally, the experimental characterization methods will be introduced and the output energy density will be introduced and compared between different nanogenerators.

Modeling and Conditioning Triboelectric Nanogenerators
Philippe Basset, ESIEE Paris

For TENG, a power management circuit is needed to generate a low DC voltage for the load, while implementing a high voltage interface at the transducer’s side, so to maximize the converted power. Basset will present an overview of the main architectures for power management systems proposed to date for triboelectric nanogenerators, and the various circuits will be compared based on electrical simulations.

Human-Compatible Designs of Nanogenerators for Harvesting Energy from Human Bodies
Sihong Wang, University of Chicago

Wang will first introduce the overall needs and technological challenges for harvesting mechanical energy from human bodies, towards realizing sustainable power sources for human-integrated electronics. Then, Wang will introduce the major approaches in material and device designs for achieving both high power output and multi-aspect biocompatibility, based on the requirements from different body locations.

Triboelectric Nanogenerator as A New Platform for Energy Harvesting & Wireless Energy Transfer Technologies
Sang-Woo Kim, Sungkyunkwan University

As main topics, Kim will introduce recent global achievements regarding highly robust and efficient TENGs with multifunctional materials, which provides new insights to an innovative energy solution for various wearable electronics, IoT sensors, bio/healthcare applications. In addition, he will share with audiences about a new wireless energy transfer technology based on ultrasound-driven TENG in a body.

Flexotronics in Centrosymmetric Semiconductors
Yong Qin, Lanzhou University

Qin will first elaborate on the fundamental science of flexotronic effect in centrosymmetric semiconductors, which serve as the basis for understanding and utilizing the interfacial polarization engineering in the new area of flexotronics. Then, he will provide an overview of the development of flexotronics, and discuss the relationship between the piezotronics and the flexotronics. Finally, he will give a perspective about their further development and potential applications in emerging fields of enhanced solar technology, active electronics/optoelectronics, hybrid-spintronics etc.