Photovoltaic effect and tribovoltaic effect at liquid-semiconductor interface

Contact electrification involving semiconductors has attracted attention for that it generates direct current. But its mechanism is still under debate, especially for the liquid-semiconductor cases. Here, the tribo-current is generated by sliding a DI water droplet on a semiconductor wafer, such as Si and TiO2, under the light irradiation. It is revealed that the photoexcited electron-hole pairs at the interface will contribute to the tribo-current, and the enhanced tribo-current increases with the increased light intensity or the decreased light wavelength. The results suggest that the tribo-current at the DI water-semiconductor interfaces is induced by the tribovoltaic effect, in which electron-hole pairs are excited during contact owing to the energy released by the newly formed bonds, which can be named as “bindington”. The electron-hole pairs are further driven by the built-in electric field to move from one side to the other side at the interfaces, generating a direct current. The findings imply that the electron transfer exist at the liquid-solid interface in the CE, and support the “two-step” model for the formation of the electric-double layer, which was first proposed by Wang.