Effect of methanol concentration on flatband potential shift of n-type Si in CH 3CN/CH 3OH mixture containing a redox couple

Abstract

A photoelectrochemical study is performed on a thermally oxidized n-Si electrode in acetonitrile in the presence of a redox couple dimethylferrocene (DMFc). An oxide layer of 3 nm thickness has been formed at 400°C. The results show that upon ageing the oxidized electrode in the electrolyte, its flatband potential is constant and only a decay of the current with time is observed: the oxide layer becomes progressively thicker. It is found that an SiO 2 layer of about 10 nm leads to a quasi-complete “blocked” electronic exchange between the surface and the solution. Under illumination, a decrease of 0.15 V of the open-circuit voltage ( V oc) is observed. On the other hand, the experimental study of a non-oxidized silicon electrode in a mixture of 90% CH 3CN/ 10% CH 3OH leads to a negative displacement of the flatband potential (−0.3 V) and an increase of the photopotential (0.12 V). A prolonged stability of the electrode with time under illumination is observed. This effect is attributed to the methoxylation of the silicon surface.