The effect of pre-treatments of F-doped SnO2 substrates for cathodic nucleation of ZnO crystals in aqueous ZnCl2 solution with dissolved O2

Abstract

Effect of surface treatment on F-doped tin oxide (FTO) coated conductive glass substrate was studied for electrodeposition of ZnO employing reduction of dissolved oxygen in ZnCl2 aqueous solution, through electrochemical analysis and observation of the products. Prolonged electrolysis for O 2 reduction reaction (ORR) resulted in a gradual activation of the FTO to reach diffusion limited current, while the diffusion limit could not be reached by the substrates simply soaked in a 45 wt% nitric acid and that partially reduced to metallic Sn. Fitting of the profile of the chronoamperogram to the Scharifker-Hills model revealed instantaneous nucleation mechanism for electrodeposition of ZnO. The higher the electrode activity was, the higher the density of ZnO nucleus was reached to end up with a dense, flat and transparent ZnO thin film with its c-axis well oriented perpendicular to the substrate. Alternatively, transparent and dense film could also be obtained by applying a high overpotential for a short time to deposit particles of metallic Zn that served as nucleus for the growth of ZnO.