Enhanced photoelectrochemical activity of electro-synthesized CdS–Bi 2S 3 composite films grown with self-designed cross-linked structure

Abstract

In the present investigation thin semiconductor films of CdS, Bi 2S 3 and their intermixed composite films have been electro-synthesized onto conducting glass substrate from nonaqueous bath containing various levels of the precursor salts of Cd 2+ and Bi 3+. Spectrophotometric measurements determine the band gap energies of the composite films at ∼2.53 eV and ∼1.37 eV corresponding to the binary systems CdS and Bi 2S 3, respectively. The film matrices exhibit a unique structure of cross-linked nanoporous Bi 2S 3 mesh containing spherical shaped CdS crystals distributed uniformly on the top of the surface as detected from the morphological studies through scanning electron microscopy and transmission electron microscopy. X-ray diffraction studies show crystalline structure of the films of which the chemical compositions were determined through energy dispersive analysis of X-ray. The film matrices enriched with Cd exhibit high dielectric property as obtained from the capacitance measurement and substantial thermal stability derived from thermogravimetry and differential thermal analysis. These films are found to be highly fluorescent in nature when subjected to spectrofluorimetric analysis. The Raman spectral data exhibit characteristic peaks that are associated with Cd–S and Bi–S bonds as well as the defects created by metal oxides. The spectrum also demonstrates that the changes in the relative position of the overtone bands are associated with compositional variation of the film surface. The study of electrochemical polarization of different films, derives the inherent stability of the matrices towards dissolution. This was followed by anodic stripping voltammetry to estimate the dissolved cations during polarization. Photoelectrochemical measurements demonstrate n-type semiconductivity of the films with high order of donor density and reasonable photoactivity under illuminated condition. It may be summarized that the blended intermix of CdS–Bi 2S 3 film acquires tailor made properties desirable for photoelectrochemical application and displays solar conversion efficiency of the order of ∼1%.