Semiconductor/electrolyte interfaces attract intense interest to convert solar energy to chemical fuels. Although many analytical models describing the photocurrent−voltage response of these devices exist, they have difficulty to reproduce full numerical simulations under small anodic bias. Herein, we derived an analytic model of a weakly absorbing n-type semiconductor/electrolyte interface with a slow rate of water oxidation reaction, fast recombination rate, and under small anodic bias. Excellent overlap of our model was demonstrated with full numerical simulations. The analytic model enabled us to derive an equation for impedance of the semiconductor/ electrolyte interface in the dark and under illumination. The comparison of analytic and measured impedance allows to extract the reaction rate for redox reaction from the dark impedance and the direct bulk recombination constant of the semiconductor from the impedance under illumination.
The efficiency of most semiconductor photoelectrodes for water splitting is limited by a slow reaction with electrolyte and a fast recombination. Among the recombination pathways, trap-mediated recombination due to doping and material processing is often the dominant process. Impedance spectroscopy under illumination is a popular and powerful method to investigate time constants of recombination and reaction. Traditionally, an equivalent circuit is involved in the analysis of impedance spectroscopy, nevertheless, it provides limited direct information about the microscopic quantities related to diffusion, reaction, and recombination. In the present study, a theoretical model for diffusion-limited photocurrent under small voltage bias and its application for the simplified evaluation of equivalent circuits for impedance analysis are presented. Full numerical simulations of the semiconductor transport equations are used to validate the theoretical model for typical values of carrier lifetime. This combination of theoretical approximations, equivalent circuit models, and full simulations provides an important background for the analysis of recombination and transport properties of photoelectrode materials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.