Electron-transfer mechanisms for confirmation of contact-electrification in ZnO/polyimide-based triboelectric nanogenerators

Zinc oxide (ZnO) acting as a versatile material for electronic and optoelectronic devices shows promising applications in triboelectric nanogenerator (TENG)-based self-powered electronics. However, the output performances of ZnO-based TENG are relatively low and the origin of contact-electrification in the ZnO-based TENG is unclear. Here, we fabricate a TENG by using ZnO film and polyimide (PI) acting as positive and negative friction layers, respectively. The work function of the ZnO film is modified by doping with elemental Al, and the conductivity of the ZnO film is additionally enhanced by the presence of graphene-oxide sheets. The output performance is greatly improved and it is sensitive to the work function of ZnO film. These results reveal that electron transfer is the dominant process in contact-electrification for ZnO-based TENGs. This work provides significant insight into understanding the contact-electrification properties of ZnO, thus allowing optimization of ZnO-based self-powered devices.