Triboelectric nanogenerators (TENGs), a new green energy, that have various potential applications, such as energy harvesters andself-powered sensors. The output performance of TENGs has been improving rapidly, and their output power significantly increasedsince they were first reported owing to improved triboelectrification materials and interfacial material engineering. Because the operationof a TENG is based on contact electrification in which electric charges are exchanged at the interface between two materials, its outputcan be increased by increasing the contact area and charge density. Material surface modification with microstructures or nanostructureshas increased the output performance of TENGs significantly because not only does the sharp micro/nano morphology increases thecontact area during friction, but it also increases the charge density. Chemical treatment in which ions or functional groups are addedhas also been used to improve the performance of TENGS by modifying the work functions, charge densities, and dielectric constantsof the triboelectric materials. In addition, ultrahigh output power from TENGs without using new materials or treatments has beenobtained in many studies in which special structures were designed to control the current release or to collect the charge current directly.
In this review, we discuss physical and chemical treatments, bulk modifications, and interfacial engineering for enhancing TENG performanceby improving contact electrification and electrostatic induction.