Photoelectrochemical properties of anodic silver sulphide thin films

We have investigated the semi-conducting properties and photoelectrochemical characterization of Ag2S thin films electrodeposited galvanostatically onto silver substrate from alkaline S2− bath. Films grown with a low current density not exceeding 20 μA cm−2 are uniform and well adhered. An optimal thickness of 1.34 μm 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 VSCE and a donor density of 5.63 × 1016 cm−3 were determined. The conduction band, located at 3.28 eV, is made up of mainly Ag-5s wave function. Ag2S is long lived and under illumination, it is stabilized by holes consumption reactions involving Sn2−/S2− 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 (10−2–105 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.