Synthesis and Characterization of Semiconductor Quantum Dots for Optoelectronic Applications

Abstract

Quantum Dot Sensitized Solar Cells (QDSC) have attracted considerable interest due to their improved photo conversion efficiency. Cadmium sulfide (CdS) and Cadmium sulfide/ Zinc sulfide (CdS/ZnS) quantum dots have been synthesized utilizing an aqueous medium involving cadmium sulphate, zinc acetate, thiourea and ammonium hydroxide. Eco-friendly green method was used to synthesize the Quantum dots (QD) with Moringa oleifera as the source of sulphur. Doping quantum dots with semiconductors of wider band gap will improve the luminescence efficiency and photostability. The CdS quantum dots were covered with ZnS to establish a core/shell system. The formation of ZnS shell protects core surface from oxidation and prevents CdS leaching into the surrounding medium. The structural and surface morphological properties of nanoparticles were studied using Transmission Electron Microscope (TEM), Field Emission Scanning Electron Microscope (FE-SEM), Ultraviolet-Visible light (UV-VIS) Spectrometer, Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). For solar cell applications with quantum dot-sensitization, the CdS and CdS/ZnS quantum dots are assembled onto nanoporous TiO2 films. The Titanium Dioxide (TiO2) layer sensitized with QDs and standard electrolytes are undertaken to explore the best counter electrode materials which further resulted in higher efficiencies in the present study. The photovoltaic studies and the Voltage-Current (V-I) characteristics of the cell were compared with bare TiO2. Photocurrent was measured under the conditions of illumination and non-illumination by using the sun simulator and V-I characteristics of the quantum dot sensitized solar cells and the results obtained were plotted graphically. Approximately 0.25 cm2 (0.5 cm × 0.5 cm) of active area in the resulting cell was exposed to light. The green synthesized quantum dots show higher efficiencies than cells coated with chemically synthesized quantum dots.