Stabilization of Si Photoanodes in Aqueous Electrolytes through Surface Alkylation

A two-step chlorination/alkylation method was used to introduce −CnH₂ₙ₊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 K₄Fe(CN)₆−0.05 M K₃Fe(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 −CH₃ and −C₂H₅ groups displayed significant improvements in stability while displaying excellent electrochemical properties when used as photoelectrodes in the aqueous Fe(CN)₆^(3-/4-) electrolyte.