Photoelectrochemical properties of anodic silver sulphide thin films

We have investigated the semi-conducting properties and photoelectrochemical characterization of Ag(2)S thin films electrodeposited galvanostatically onto silver substrate from alkaline S(2-) bath. Films grown with a low current density not exceeding 20 mu A cm(-2) are uniform and well adhered. An optimal thickness of 1.34 mu m has been determined. At high current density, oxygen evolution occurs simultaneously and provokes crashing of films. From photoelectrochemical measurements, the band gap was found to be 1.85 eV and the transition is indirectly allowed. The Mott-Schottky plot exhibits a linear behavior, characteristic of n-type conductivity, from which a flat band potential of -1.20 V(SCE) and a donor density of 5.63 x 10(16)cm(-3) were determined. The conduction band, located at 3.28 eV, is made up of mainly Ag-5s wave function. Ag(2)S is long lived and under illumination, it is stabilized by holes consumption reactions involving S(n)(2-)/S(2-) redox couple. A conversion efficiency of 1.1% and a fill factor of 0.27 have been obtained. The electrochemical impedance spectroscopy, measured over a wide frequency range (10(-2)-10(5) Hz), reveals contribution of the bulk effect. The experimental data are modeled by shifting the centre of the semi circle down the real axis and interpreted in terms of constant phase element due mainly to the porosity and inhomogeneity of the film. (c) 2011 Published by Elsevier B.V.