Preparation and Analysis of Cd Doped ZnO Nanostructures for Third Generation Solar Cell

Abstract

The third-generation solar cells are one of the leading candidates for photovoltaic applications, due to its low cost and commercial characteristics which are based on III-IV group materials, especially dye sensitized solar cells (DSSCs). In this dissertation, Sol-gel synthesis is used to prepare the Zinc oxide (ZnO) nanoparticles (NPs), Cadmium (Cd) doped ZnO NPs (with different concentrations), and their thin films for cell fabrication. X-Ray diffraction (XRD) was used to investigate the structural properties (crystalline structure and grain morphology) of nanostructured materials. The results showed that the XRD pattern demonstrates that the ZnO nanostructures are crystalline and have a hexagonal structure, as all diffraction peaks match the crystalline structure of pure ZnO. The decreased crystallinity of the Cd-doped ZnO samples, shows that the doping causes increase in 2𝜃 which represents a steady decrease in the lattice, thereby increasing the crystallite size. Optical properties (absorption, transmission, band gap) of doped and undoped materials were analyzed using UV/Vis spectrophotometer. UV/Vis findings indicate that for nanoparticles with 4% Cd doped ZnO maximum absorption is found. The calculated undoped ZnO band gap is 3.25 eV, whereas the band gap for doped materials shows improved outcome (2% Cd doped ZnO has a band gap of 3.12 eV and 4% Cd doped ZnO has a band gap of 3.04% eV). UV/Vis data depicts that the optical band gap decreases as we increase Cd doping. Scanning Electron Microscope (SEM) is used to study the surface morphology of prepared samples. In the analysis of undoped ZnO, the spherical nanoparticles of 100 nm diameter approximately found whereas 2% Cd doped nanostructures are in cubic and hexagonal forms having 120 nm and bigger size clusters. The 4% Cd doped ZnO indicates that as the doping increases, the diameter of the particles grows, and fused together to produce colonies. The solar simulations (J-V measurements) were performed, the photovoltaic parameters such as open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF) and efficiency (𝜂) were calculated. Simultaneous improvements in photovoltaic performance were achieved by Cd doping. In comparison to others, the ZnO doped with 4% Cd exhibits the higher efficiency (𝜂) of 1.14%