Effect of silver doping on optical and electrochemical properties of ZnO photoanode

In this work, the effect of silver doping on structural, morphological, optical and photoelectrochemical properties have been deeply investigated. A set of photoanodes composed of silver-doped zinc oxide thin films (SZO) deposed onto fluorine doped tin oxide substrates (:F) are synthesized using sol-gel technique. Scanning electron microscopy (SEM) analysis reveals that the Ag incorporation leads to an increase of ZnO grain size with uniform spherical size distribution. Surface morphology of silver-doped ZnO thin films (SZO) sounded by Atomic Force Microscopy (AFM) images have shown that surface roughness tends to increase with increasing silver concentration. All the films are highly transparent in the visible region. In addition, band gap energies were found to decrease after Ag doping. A decrease of the photoluminescence intensity is observed for 3% Ag doped photoanode which is attributed to the strong charge separation of the photo-carriers. The overall photoelectrochemical (PEC) performance of the photoanodes was investigated and largely discussed. Moreover, the silver-doped zinc oxide photoanodes are more photoactive than pure ZnO one and the photoanode made with 3% Ag doping yields the highest photocurrent. This behavior is in concordance with photoluminescence measurements. Charge transfer processes at the Ag doped ZnO/electrolyte interface were identified by electrochemical impedance spectroscopy. The donor density and the flat-band potential of ZnO: Ag films were analyzed from the Mott-Schottky plots. It was found that the ZnO photoanode doped with 3% Ag gives the best photoelectrochemical performances.