Recent advances on ink-based printing techniques for triboelectric nanogenerators: Printable inks, printing technologies and applications

With the rapid development of the Internet of Things (IoTs), triboelectric nanogenerator (TENG) has provided boundless potential in converting distributed low-frequency mechanical energy into electricity and constructing real-time self-powered sensing system. Although the revolutionary and pioneering advancements of TENGs have attracted enormous attentions in the development of various features such as flexibility, environmental friendly and highly integration, further improvement of advanced manufacturing methods is still essential for usage towards practical application and eventually commercialization. Compared with traditional preparation methods including complicated photoetching and nanomanufacturing, ink-based printing techniques can be employed to manufacture TENGs owing to low cost, superior fabrication accuracy, highly versatile and satisfactory production efficiency. In this review, up-to-date TENGs fabricated via ink-based printing methods are highlighted, focusing on different printing methods, including inkjet printing, extrusion based printing, spray coating, electrospinning based printing approach and screen printing. The classification of inks and the current applications of ink-based printed TENGs are also summarized and discussed. Furthermore, the existing challenges and prospects are finally stated to put forward further progressing research.