Structural and Optical Properties of ZnO:Al:Ga Co-Doped Nanoparticles: Investigation on the Effects of pH of the Precursor Solution via a Simple Sol-Gel Route

Abstract

Zinc oxide (ZnO) has unique properties that are suitable for solar cell applications. However, there is need to improve its effectiveness by incorporating dopants into ZnO structure. This study investigates how pH affects the material characteristics of ZnO:Al:Ga co-doped nanoparticles Nps) with the goal of maximizing their application in solar cell technology. After the nanoparticles were synthesized using the sol-gel process at different pH values, their optical, morphological, and structural characteristics were analyzed using various techniques. The observed wurtize crystalline structure of ZnO:Al:Ga Nps was validated by X-ray diffraction (XRD) analysis, with the crystallite size estimated to be ranging from 18.83 to 20.94 nm for pH values 7 to 13. The XRD pattern of the as-prepared ZnO:Al:Ga Nps matched well with the Wurtize ZnO crystal structure with variation in peak intensities observed. Scanning electron microscopy (SEM) displayed aggregation of nanoparticles when the precursor pH increased from 7 to 13. The produced ZnO:Al:Ga Nps showed absorption peaks varying from 380 – 376 nm for precursor pH values 7 – 13, with band gap energy range of 3.26 – 3.29 eV as determined from the UV-Vis analysis. Decreased transmittance was observed with the higher pH values of 11–13 due to its larger particles or aggregation tendencies. In addition, chemical bonds and functional groups were examined using Fourier-transform infrared spectroscopy (FTIR). The results confirmed formation of ZnO:Al:Ga Nps as seen in the FTIR peaks corresponding to Zn-O, Al-O, and Ga-O stretching modes between 400 and 590 cm-1 . Additionally, the presence of OH stretching bands above the 3000 cm-1 region indicates surface hydroxylation.