Optimization of SnS based heterojunction to improve its photovoltaic performance

Abstract

Recent developments in energy generation highlights the role of thin film solar cells as effective technology to provide clean, renewable and cost-effective energy. Thin film solar cells made from earth-abundant, non-toxic materials with adequate physical properties such as band-gap energy, large absorption coefficient and p-type conductivity are needed in order to replace the current technology based on scarce, expensive and toxic elements. Here we have chosen tin sulphide as it has high theoretical photoelectron conversion efficiency (>20%), less toxicity, good chemical stability and its constituent elements are abundant in earth’s crust. However, SnS-based solar cells' claimed power conversion efficiency (η) remained below 4%. This thesis reports on possibility of modification of the properties and photovoltaic performance of chemically prepared SnS thin film by changing the pH of the bath solution and annealing temperature. A further enhancement of efficiency was obtained using the SiO 2 /ZnO 1D Photonic crystals for light trapping. Simulation work was done as the pre laboratory. Photonic crystals, which are considered the optical analogue of crystals, are capable of controlling the flow of light. In this work, 1D photonic crystals were simulated using MIT electromagnetic equation propagation (MEEP) software, which is free and open software. Meep implements the finite- difference time-domain (FDTD) method. The 1D photonic crystals with different layers were simulated, and the transmission spectra were plotted using MEEP software. The effect of the dielectric contrast on the width and position of the photonic bandgap was investigated using the simulated transmission spectra. Transmission spectra with different numbers of layers were plotted, and it was found that eleven layers are enough for creating a stop band. The ZnO and SiO 2 films with acceptable optical and structural properties were coated using the RF magnetron sputtering technique, and the transmission spectra was investigated. The results were comparable with the simulations. The (ITO/PC/SnS/CdS/Ag) heterojunction was fabricated and the cell parameters with and without PC were compared. It was observed that the performance of the solar cell improved by using 1D PC as back reflectors. This work gives a simple and cost-effective method of fabricating SnS based solar cell and improving its efficiency using 1D Photonic Crystals.