Surface-alkylated and metal nano-dotted n-Si electrodes for efficient and low-cost solar energy conversion

A surface alkylated and metal nano-dotted n-Si electrode yields an efficient and stable photovoltaic characteristic in an aqueous redox electrolyte. It generates a high photovoltage due to a unique effect of metal nano-contact and is stabilized by surface alkylation. In the present work, we have prepared a composite electrode, composed of the surface methylated and Pt nano-dotted n-Si single crystal electrode and a tungsten trioxide (WO ₃) particulate thin film, to decompose water into oxygen and H ⁺ ions under solar irradiation. The onset potential of the oxygen evolution photocurrent for the composite electrode shifts to the negative by about 0.2 V compared with that for the WO₃ electrode alone, indicating that the two-step, Z-scheme mechanism operates in the composite electrode, leading to generation of a high photovoltage that comes from a series sum of the photovoltage in the Si and that in the WO₃. It is discussed that a composite "polycrystalline Si / visible-light responsive metal-oxide thin-film" electrode is a promising approach to high-efficiency and low-cost solar water splitting.