SYNTHESIS AND CHARACTERIZATION OF ZINC-DOPED CADMIUM SELENIDE NANOPARTICLES FOR POSSIBLE APPLICATION IN SOLAR CELLS

Abstract

The increasing global demand for renewable energy has highlighted the need for advanced materials that can improve the efficiency and affordability of solar cells. This research focused on developing CdSe and Zn-CdSe nanoparticles through sol gel synthesis, aiming to optimize key parameters such as doping concentration, growth temperatures, and annealing temperatures to achieve desirable structural and optical characteristics. The synthesized CdSeNPs and Zn-CdSeNPs were characterized using X-ray diffraction (XRD), Ultra-Violet visible (UV-vis), photoluminescence spectroscopy (PL) and Fourier transmission infra-red (FT-IR) spectroscopy. The XRD pattern of CdSeNPs displayed zinc blende cubic and the patterns of CdSe nanoparticles revealed additional peaks at certain growth temperatures. The cubic structure was maintained when Zn doping concentrations were varied as well as variation in the annealing temperature indicating that all dopants had occupied the interstitial sites. Growth temperature of 45oC, Zn doping concentration of 3 mol% and annealing temperature of 275oC displayed highest XRD peak intensities. This is an indication of improved crystallinity at these growth parameters. The crystallite size of nanoparticles determined using Debye-Scherrer formula were observed to generally increase with increase in growth temperature. The largest average crystallite size was obtained at a growth temperature of 75℃. When Zn doping concentration and annealing temperature was varied, it was found that the crystallite size decreased as the parameters were increased. The calculated crystallite sizes of Zn-CdSeNPs ranged from 17.72 to 28.11nm. There was an observation of variation in the lattice strain of the synthesized nanoparticles. Optical analysis displayed changes in the absorbance as growth temperature, Zn doping concentration and annealing temperature were varied. The estimated bandgap energies of nanoparticles estimated using Tauc’s plot were1.83, 1.65, 1.71, 1.66, 1.67, 1.71 and 1.8 eV for samples prepared at a growth temperature of 25, 45, 60, 75, 90, 105 and 120℃ respectively. Doping CdSe with Zn decreased the bandgap energy from 2.23 to 1.92 eV. The band gap energies obtained for samples annealed at 150, 175, 200, 225, 250, and 275℃ are 2.10, 1.96, 2.24, 1.18, 2.53 and 1.23 eV respectively. All the as-prepared samples absorbed light at different wavelengths. This is confirmed by the PL results where varying emission wavelengths were observed. Maximum emission peak intensity was obtained when the samples were prepared at growth temperature of 90℃. Changes in PL emission intensity were noted with varying dopant concentrations and annealing temperatures, indicating their influence on the optical behavior of the nanoparticles. The functional groups determined using from FT-IR spectra showed the expected groups in all the samples with Cd-Se and Zn-Se bond observed at the finger print region. As the concentration of zinc dopant increased, the intensity and sharpness of the peaks increased bands appearing around 500–700 cm⁻¹. In this study, CdSe and Zn-CdSe nanoparticles were successfully synthesized using the sol-gel method. Through systematically experimentation, the optimum growth temperature, doping concentration, and annealing temperature were determined, resulting in enhanced structural and optical properties of the nanoparticles for solar cell applications.