Structural and optical characterizations of n-type doped ZnO by sol-gel method for photovoltaic

This paper presents the effect of Bi doping concentration and annealing temperature on structural and optical properties of zinc oxide thin films. The samples in this study were prepared by sol-gel technique. These thin films were characterized by X-ray diffractometer technique. XRD analysis revealed that the Bi-doped thin films after annealing indicated good preferential orientation along c-axis perpendicular to the substrate, in particular very low concentration of Bi dopant. As a result, it indicated that Bi atoms acting as donor impurities can be in phase of ZnO. The surface morphology was characterized by using SEM (Scanning Electron Microscope). The visible region was measured by UV-VIS spectrophotometer. Finally, the optical band gap of undoped and Bi-doped ZnO thin films were obtained by the Tauc plot. Varying the Bi doped in the range of 0.2-0.6 at.% under annealing temperature at 600 °C caused a no significant change in optical band gap. In contrast, the annealing procedure produced significant changes from 3.27 eV to 3.32 eV in the optical band gap in order to higher blue responsibility for photovoltaic.