Effect of sulfosalicylic acid (C7H6O6S) on the electrodeposition of pure ZnS nanocrystal thin films from acidic solutions

Sulfosalicylic acid (C7H6O6S) as a special additive was applied to favor the deposition of pure zinc sulfide (ZnS) nanocrystal thin films on ITO substrates from acidic solutions by potentiostatic technique with subsequent annealing. XRD, EDX, Raman, SEM and UV–vis–NIR analyses demonstrate that a proper concentration of C7H6O6S additive (0.2 mM) in the electrolyte containing 20 mM Zn2+, 20 mM S2O32−, 0.375 mM SO32− and 200 mM LiCl can greatly contribute to the controllable growth of pure cubic ZnS film along (2 0 0) orientation at potential of −1.1 V vs. SCE. The film possesses a uniform surface with an average crystallite size ca. 40.9 nm, and a band gap ca. 3.68 eV. Electrochemical studies indicate that C7H6O6S could adsorb on ITO surface and act as a hydrogen bond donor for free Cl−. The adsorption of C7H6O6S blocks some active sites used for the deposition of S, while the role of hydrogen bond donor promotes the deposition of Zn element by decreasing the concentration of [ZnCl4]2− and increasing the concentration and mobility of Zn2+ in electrochemical double layer. Consequently, the addition of C7H6O6S narrows the deposition potential gap of S and Zn elements in the range of −1.0 to −1.2 V, thus resulting in their co-deposition to form pure ZnS.