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Photoelectrochemical in situ studies of passive films on cadmium

The formation, growth, reduction and solid state properties of passive films on Cd in a polysulfide solution were studied under dark and modulated light conditions using impedance, cyclic voltammetry, optical methods and SEM analysis. It was found that a thin barrier photoactive film of cadmium sulfide is formed under controlled potential scans. At more positive potentials, a thicker layer containing both sulfide and hydroxide or oxide is initially deposited, enhancing photoactivity and n-type semiconductor behavior. The semiconductor properties of these passive films are discussed on the basis of capacitance and photoelectrochemical measurements. Anodic CdS films are not suitable for photovoltaic purposes because of their limited thickness and small crystal size. The results of this study suggest that thicker films containing hydroxide or oxide species can be equilibriated to a more effective composition for photoanodes by appropriate post-treatment.

Cd; passive films; photoelectrochemical properties

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