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 V_SCE 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 S_n²⁻/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.