ZnO micro- and nano-structures for the design of piezoelectric composites: recent advances in energy harvesting applications

One of the current world’s challenging issues concerns the design, development, and exploitation of efficient devices for energy harvesting that, in the last few years, has gathered a growing interest not only from academia but also from an industrial point of view. Although the general concept of (macro)energy harvesting has been successfully exploited for centuries in the design of passive solar power systems, as well as wind and water mills, only during the last 10 to 15 years there has been particular attention toward the development of effective (micro)energy harvesting systems, exploiting the energy from the ambient provided by light, radiofrequency radiation, or motion/vibration/thermal sources. These (micro)energy harvesting systems require efficient and reliable materials to convert the input environmental energy into an exploitable electrical output. In this context, among the most currently employed ceramics, zinc oxide (ZnO), both micro- and nano-structured, is gaining more and more importance in the design of energy harvesting devices because of its interesting features that comprise low cost, high piezoelectric characteristics, and ease of production, among others. The present work aims to summarize the current state-of-the-art on the use of ZnO micro- and nano-structures for the design and manufacturing of advanced piezoelectric devices and to provide the reader with some recent progress that may pave the way toward further advances in the forthcoming years.