Enhancement of performance of triboelectric generators by introduction of micro- and nano-structures on triboelectric films

Wearable or portable electronic devices are ubiquitous because those enrich our life considering comfortability, efficiency and healthcare. However, those devices are nothing but accessories without electric power. Exchanging or recharging batteries are not always reachable for the devices. Energy harvesting systems which harvest energy from human motions are a good alternative or assist for batteries to secure electric power. Among other energy harvesters, a triboelectric generator (TEG) has attracted much interest with respect to its simplicity and lightweight. Many works have been done to enhance performance of TEGs to apply them for practical uses. Among them, introduction of structures on surface is a rational approach because triboelectricity is a contact electrification. In this review, works of enhancement of TEG's output performance are highlighted with respect to structural modification on the surface of triboelectric films. Molding or imprinting straightforwardly introduces micro-, nano-, or hierarchical structures on triboelectric surfaces and the TEG with a film of pyramidal structures exhibited up to 800% increase in the output compared with flat ones. Porous structures with pores on and inside polymeric films also showed up to 800% increase in the output. And TEGs based on nano-fibers with hierarchical structures on them showed up to around 2000% improvement in electrical outputs.