Modeling Transfer of Electrons between Energy States of an Electrolyte and CdS Thin Films using Gerischer Model

Abstract

A number of models have been developed to describe electron transfer between electrolytes and group II–VI binary semiconductors. In this report, a study was conducted to describe and model electron transfer between an inorganic semiconductor, (i.e. CdS) and a ferric oxidizing/reducing agent [i.e. K₃Fe(CN)₆/K₄Fe(CN)₆]. We describe the interfacial electron transfer using the semi-classical theory approaches as described by Marcus and later developed by Gerischer and therefore called Gerischer model as it is applied to heterogeneous electron transfer in a semiconductor - electrolyte interface. CdS thin films were grown by electro-deposition method on the indium tin oxide (ITO) substrates and were used as electrodes. The data collected was used to determine the kinetic constant rates and re-orientation energies as measured in the solutions with different concentration of redox system, Fe⁺³/ Fe⁺². Experiments showed that when concentration of oxidized species increased and causing an increase in  activity, the kinetic constant rates decreases inversely. Equally light induced current at 0.0V/Ag was higher when the ratio of the oxidant-reductant (i.e. 2/0.02 and 0.2/0.02) was high. EIS studies revealed that for the two ratios of. 2/0.02 and 0.2/0.02, the difference of current density was comparable to the transfer of the charge carriers for the oxidant-reductant electrolyte at 2/0.02 with respect to 0.2/0.02.