SYNTHESIS OF SILVER DOPED ZINC OXIDE NANOPARTICLES USING Citrus reticulata PEEL EXTRACT AND THEIR CHARACTERIZATION FOR POTENTIALAPPLICATION IN SOLAR CELLS

Abstract

Nanoparticles (NPs) are materials ranging in size between 1-100 nm. The NPs are used in solar cells due to their unique properties. Solar cells have become an alternative lead to green energy but their application is limited by factors such as cost, efficiency and availability. In this study, silver-doped zinc oxide (Ag-ZnO) NPs were synthesized using Citrus reticulata peel extract. Effects of silver doping concentration on the structural and optical properties of ZnONPs were studied by varying the concentration of silver dopant at (0.1, 0.25, 0.5, 0.75, 1.0, 1.5, and 2.0 mol %). Effects of growth temperature on the structural and optical properties of ZnONPs was studied by varying the growth temperature of NPs at (25, 30, 40, 50, 60 and 70 ℃). The NPs were prepared via green synthesis method. The prepared and annealed Ag-ZnONPs were characterized using X-ray diffraction (XRD), Ultra-Violet visible (UV-vis), Fourier transmission infra-red (FT-IR) spectroscopy and photoluminescence spectroscopy (PL). The XRD pattern of Citrus reticulata capped ZnONPs displayed hexagonal wurtzite structure. The Debye Scherrer formula was used to calculate the crystal size of nanoparticles. All nanoparticles formed were in the range of 8-14 nm. The 0.1% Ag-ZnO had the highest intensity in XRD pattern at plane peak (101). The crystal size of nanoparticles ranged from 15.29-19.87 nm. At 0.5% Ag-ZnONPs, the XRD peak shifted to the higher 2 theta degrees compared to other doping concentrations. At varying growth temperature, the crystal size range from 15.54-17.87 nm. The FT-IR spectra of Citrus reticulata capped ZnO and Ag-ZnO nanoparticles showed absorption in both functional group and fingerprint regions. The stretching vibration of Zn-O was observed between 470-420 cm-1. When concentration of Ag dopant was varied, the stretching vibration of metal oxide was observed 459-470 cm-1. The PL results of the samples showed UV emission peaks at 350 to 450 nm.Increase in Ag concentration shift emission to a higher wavelength. The bandgap energies of nanoparticles were estimated using Tauc’s plot. The bandgap energy increased from 3.00 to 3.29 when capped. When doped with different mol % of silver, the bandgap energies increase at lower concentrations from 3.30 for pure ZnONPs to 3.69 and 3.61 for 0.25 and 0.5 Ag-ZnONPs mol% respectively. At higher concentrations, the bandgap energy decreased to 3.03, 3.13, 3.10 and 3.17 eV for 2.0, 1.5, 1.0 and 0.75 mol% respectively. The bandgap energy decreased from 3.03 eV at 25 and 40 ℃ to 2.94 eV at 30, 60, and 70 ℃ and 2.85 eV at 50 ℃. The Ag-ZnONPs were successfully synthesized by the green synthesis method, and doping the ZnO with higher mol % of silver at a growth temperature of 50 ℃ presents good crystallization, good optical and luminescence properties that can be tested as aphotoanode component in dye sensitized solar cells