Exploration of Controllable Poring and Oscillation Phenomenon on FTO Conductive Substrates with Electrochemical Cathodization

The essential requisites of a transparent conductive film encompass optical transparency and electrical conductivity. However, there exists a growing demand for these films to possess structured surfaces, thereby enabling supplementary functionalities. Nonetheless, the fabrication of such structured surfaces has encountered challenges. This study reported a strategy to engineer controlled porous structures ranging from nanometers to hundreds of nanometers on fluorine-doped tin oxide (FTO) substrates through electrochemical cathodization along with reduction of Sn4+ to metal Sn in acidic electrolytes. In electrolytes with HNO3, distinct electrochemical oscillations were observed during the course of FTO cathodization. These oscillations resulted from periodic alterations in the surface structure of the substrate, and the pattern of the oscillations is sensitive to the components of electrolytes. Despite these structural modifications, the structured FTO maintained crucial optical and conductive properties, as evidenced by the minimal deviations observed in the photoelectrochemical performance between the structured and unmodified FTO when utilized in WO3 photoanodes.