Analysis and optimization of technological parameters for high performance of the mechanically stacked Si/Ge solar cell

In this paper, we design and optimize a mechanically stacked dual-junction Si/Ge solar cell, focusing on the thicknesses and doping concentrations that yield the best photovoltaic output parameters. Specifically, this study provides a theoretical analysis of the technological parameters necessary to achieve a high-efficiency tandem solar cell using silicon and germanium, materials that benefit from well-established and controllable manufacturing technologies. The aim of our work is to simulate the electrical behavior of each cell separately: the upper Si cell (Top-cell) and the lower Ge cell (Bottom-cell), using SCAPS-1D simulation software. This is achieved through numerical simulations of the current-voltage (J-V) characteristic and the spectral response curve. We estimated an efficiency ranging from 21.63 to 30.62% under AM1.5G solar irradiance, with solar intensity varying from 1 to 1000 suns, for a cell with a thickness of 97.05 μm. Our investigation centres on identifying key photovoltaic output parameters such as open-circuit voltage (VOC), short-circuit current (JSC), fill factor (FF), and conversion efficiency (η), leading to the development of a better mechanically stacked Si/Ge solar cell. We optimize these photovoltaic quantities by varying the technological parameters of the emitter and the base of each cell, particularly in terms of thickness and doping. The results show that under standard conditions (AM1.5G, 0.1 W/cm², and 300 K), the calculated electrical parameters are as follows: VOC = 0.959 V, JSC = 25.699 mA/cm², FF = 86.76%, and η = 21.63%. Furthermore, with this mechanically stacked cell, the useful spectrum range is extended compared to a single-junction solar cell. This theoretical work proposes a new configuration that could potentially bring such a tandem cell to market in the near future.