High spatial resolution imaging of the charge injection yield at hematite using scanning electrochemical cell microscopy

Abstract

In-depth studies of charge injection and separation processes are important in characterizing the photoelectrochemical (PEC) properties of semiconductor materials, but high spatial resolution observations of the charge injection yield of such materials have not yet been reported. Here, scanning electrochemical cell microscopy (SECCM) is used for spatially resolved electrochemical imaging of the charge injection yield for a model material (hematite). Hydrogen peroxide is introduced as a hole scavenger to reduce the recombination of electrons and holes in the material, thereby achieving a division between charge injection and separation processes during PEC oxidation. Then, by calculating the ratio between the photocurrents before and after the addition of hydrogen peroxide, the distribution of the charge injection yield in the hematite film can be obtained at the nanoscale. The co-imaging of the morphology and the charge injection yield of hematite using SECCM makes it possible to observe the inverse dependence of the charge injection yield on the film thickness, which indicates that the main influence on the photocurrent is the charge injection process. The successful development of this nanoscale imaging method could provide more information to help elucidate the mechanism of the PEC process and, eventually, to aid in the design of more effective PEC materials.