Stabilization of Si Photoanodes in Aqueous Electrolytes through Surface Alkylation

A two-step chlorination/alkylation method was used to introduce −C n H 2 n +1 ( n = 1−6) functionality onto single-crystal, (111)-oriented, n-type Si surfaces. H-terminated Si photoanodes were unstable under illumination in contact with an aqueous 0.35 M K 4 Fe(CN) 6 −0.05 M K 3 Fe(CN) 6 electrolyte. Such electrodes displayed low open-circuit voltages and exhibited a pronounced time-dependent deterioration in their current density vs potential characteristics due to anodic oxidation. In contrast, Si surfaces functionalized with −CH 3 and −C 2 H 5 groups displayed significant improvements in stability while displaying excellent electrochemical properties when used as photoelectrodes in the aqueous Fe(CN) 6 3-/4- electrolyte.