Electrochemical formation of a novel porous silicon/polypyrrole hybrid structure with enhanced electrical and optical characteristics

The electrochemical formation of a hybrid structure composed of a redox-active polypyrrole (PPy) and porous silicon (PSi) layer is demonstrated. PSi layers with pore sizes (∼200 nm) are prepared by the electrochemical anodization of n-type Si wafer in HF-based solution, whereas the PPy as a p-type conducting polymer was prepared by electro-oxidative polymerization of parent monomers in acetonitrile solution using PSi as a working electrode. Uniform and vertically-oriented PPy nanorod arrays were successfully fabricated inside the porous matrix. After pore filling, the electrical conductivity and photoluminescence of as-fabricated hybrid structure were remarkably enhanced. The PSi/PPy heterojunction was fully characterized by a variety of techniques including field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. Thermal properties were also evaluated using thermo-gravimetric analysis (TGA) measurements. Formation mechanism and surface properties of such hybrid structure along with its electrical and optical characteristics are addressed and thoroughly discussed.