A comparative study on photoelectrochemical activity of ZnO/TiO2 and TiO2/ZnO nanolayer systems under visible irradiation

TiO2/ZnO and ZnO/TiO2 nanolayer thin films were synthesized using sol–gel method. Optical analysis revealed high transmittance of the films in the visible range with almost the same bandgap energy for the both systems. XPS technique shows stoichiometric formation of TiO2 and ZnO on the surface of TiO2/ZnO and ZnO/TiO2 layers, respectively. According to AFM observations and its data analysis, the TiO2/ZnO films exhibited a higher surface roughness and more effective interfaces with electrolyte during redox reactions. Based on photoelectrochemical measurements, TiO2/ZnO nanolayer photoanode possesses a lower charge transfer resistance and higher transient time for charge carriers (e and h+) and hence a higher photocurrent density under visible light irradiation as compared with the ZnO/ TiO2 nanolayer system. 2011 Elsevier Ltd. All rights reserved