Chemically Derivatized n-Type Semiconducting Germanium Photoelectrodes. Persistent Attachment and Photoelectrochemical Activity of Ferrocene Derivatives

Attachment of trichlorosilylferrocene (I) and (1,1 '-ferrocenediyl)dichlorosilane (II) to pretreated n-type Ge surfaces by hydrolytic reaction is described. Characterization of the derivatized surface by cyclic voltammetry in C2H5OH or CH3CN solutions of 0.1 M [n-Bu4N] CIO4 shows persistently attached electroactive groups. Cyclic waves persist for hundreds of scans between oxidized and reduced form of the attached electroactive species. The position of the anodic current peak depends on the illumination intensity, though an anodic peak does obtain in the dark at ~0.5 V vs. SCE for attached I or II. Illumination moves the anodic peak by up to ~200 mV more negative, consistent with expected photoeffects for an n-type semiconductor. Comparison of the derivatized electrode with a naked n-type Ge photoelectrode exposed to electrolyte solutions of ferrocene shows that the interface energetics and kinetics are essentially unchanged by the surface derivatization. Conversion of light to electricity using an n-G-based photoelectrochemical cell is possible, but output parameters are very low for an electrolyte solution containing ferrocene and ferricenium.