Concentration effect of aluminum nitrate on the Crystalline−Amorphous transition between Al-doped ZnO nanorods and nanostructures prepared by electrochemical deposition

Abstract

Abstract In this study, an electrochemical deposition was conducted to prepare Al:ZnO. Products in three distinct phases were obtained depending on the [Al3+] added in the bath of 2.0\u202fmM zinc nitrate. For convenient description, [Al3+] (total range 0–1000\u202fμM) was termed as dilute (i.e., [Al3+]\u202f \u202f250\u202fμM). Field-emission scanning electron microscopy revealed that a compact phase of nanorods was deposited in the dilute [Al3+], a mixed phase consisting of nanorods and nanosheets was deposited in the medium [Al3+], and a loose phase of cloudy floc was produced in the concentrated [Al3+]. By analyzing the reaction products with grazing incidence X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, we distinguished the crystal film of aluminum-doped zinc oxide nanorods from the amorphous hydroxides. Mott-Schottky measurements revealed that the specimen of nanorods doped with 2.84\u202fat.% Al displays the highest carrier concentration (3.83\u202f×\u202f1018\u202fcm−3) and demonstrates the highest electric conductivity among the specimens in a compact phase of nanorods. Photovoltaic tests showed that these films have fill factor and solar cell power conversion efficiency of 70.6 and 2.15%, respectively. By means of cathodic polarization and analysis of basic chemistry in aqueous solution, we propose a comprehensive mechanism to illustrate the type of products depending on [Al3+].