Negative Shifts in the Flatband Potential by Adsorption of Iodide Ions on Surface-Alkylated and Pt Nanodotted n-Si(111) Electrodes for Improvement of Solar Cell Characteristics

The flatband potential and solar cell characteristics for surface-alkylated and Pt nanodotted n-Si(111) electrodes have been studied in redox electrolytes using various alkyls as the surface-terminating group. It is found that the for the surface-methylated and Pt nanodotted n-Si(111) electrodes shifts toward the negative with increasing concentration in the electrolyte, in parallel to the equilibrium redox potential , and thus the open-circuit photovoltage remains nearly constant among various redox electrolytes with different . The constant is observed only for the redox couples with varied concentrations and not for other redox couples, indicating that it is not caused by the Fermi level pinning via a surface state. The shift with the concentration is explained in terms of the adsorption in the form of a complex at surface Si–I bonds, which are formed at nonmodified (naked) Si sites. The n-Si electrodes modified with long-chain alkyls show similar negative shifts in the by iodine adsorption. The measurements in the dark and under illumination have also shown that the Pt nanodots act as an efficient catalyst (gate) for interfacial electron transfer.