Modelling of CdTe/Si Tandem Solar Cell With a Magnesium Doped Zinc Oxide Window Layer and Introducing a Surface Defects Layer Between Emitter/Absorber

Abstract

In this research, we have tried to enhance the performance of the existing single-junction CdTe based thin-film solar cell by creating tandem or multi-junction structures. Solar Cell Capacitance Simulator (SCAPS-1D) has been used to model the top cell (CdTe) and the bottom cell (Si) thin-film structures. These two structures were separately modelled and simulated by newly introduced SCAPS script. SCAPS scripting was used to reprogram the software to combine the two structures. The top cell window layer, CdS was replaced by Magnesium doped Zinc Oxide (MZO) to increase the performance of the top cell. In both top and bottom cell structures p+ CdTe layer and p+ Si layer (acting as a back surface field) were added between the back contact and absorber to reduce the back contact recombination. A surface defect layer (SDL) was added concerning the discontinuities between the emitter and the absorber. The optimization procedure was conducted by varying the thickness and carrier concentration of the absorber layers. We have observed overall solar cell performances improvement of the tandem solar cell structure, n-SnO2/n-MZO/p-CdTe/p+-CdTe/n+-Si/n-Si/p-Si/p+-Si, with efficiency of 25.54% , Voc = 1.70 V, Jsc = 17.58 mA/cm2 and FF = 0.85. This tandem structure confirms the best performances compared to the recorded 14.7% efficiency of the single junction CdTe baseline model.

Keywords: multi-junction, SCAPS-1D, tandem, photovoltaics, magnesium doped zinc oxide, surface defect layer, thin-films