Optimization of the absorber layer thicknesses and the surface defect densities of CdTe/Si tandem device

Abstract

In this research, the performance variation of a newly modeled tandem device was investigated. A thin-film photovoltaic tandem device was created with a CdS/CdTe top cell configuration and a thick Si bottom cell configuration. The goal of this numerical simulation study was to enhance the performance of the tandem photovoltaic device. Therefore several modifications and optimizations were done to the device structure. An Mg-doped ZnO-based (MZO) layer was used as a High Resistance Transparent (HRT) layer with a very thin CdS layer. The thickness of the CdS was reduced to minimize its parasitic absorption property. The top and the bottom cell models were developed by using a special script introduced in SCAPS-1D solar cell capacitance simulator software. An artificial surface defect layer (SDL) was introduced between the window and the absorber of the top cell. The optimization procedure was carried out by altering the thicknesses of the top and the bottom absorbers and also varying the defect concentrations of the CdS/SDL interface and SDL/CdTe interface. The current matching condition of the tandem device and the device performance under the AM1.5G spectrum were also investigated. As the outcomes, we have identified the minimum possible defect density concentrations required for the window to absorber interfaces of the top cell to achieve the optimum performance. The experimental research work is suggested to further confirm the modeling results of the tandem device structure.

KEYWORDS: Thin-film, Tandem, Surface Defect Layer, Defect Density, Bandgap, SCAPS-1D