The Investigation of Optimal Si-SiGe Hetero-Structure Thin-Film Solar Cell With Theoretical Calculation and Quantitative Analysis

The characteristics of a SiGe hetero-structure solar cell such as short-circuit current density (J_sc), open-circuit voltage (V_oc), fill factor (FF), and efficiency with optimal Ge concentration are investigated in this paper. The average Ge concentration was systematically changed in the range from 0% to 30%. The appropriate addition of Ge in a crystal Si solar cell is an effective way to increase the short-circuit current density, without affecting on the open-circuit voltage, due to the modulation of the material bandgap and hetero-structure. Therefore, the solar cell efficiency can be further improved. With the optimization of Ge concentration and clean process condition, the overall efficiency of a Si_0.9Ge_0.1 solar cell is found to be improved about ~4% than that in the control Si solar cell. The bandgap of the SiGe material, the key parameter for the solar cell design, can be extracted by an electron-hole plasma (EHP) model at different temperatures. Finally, it has also been observed that the SiGe-based solar cell has less operated temperature sensitivity than the Si solar cell for the real application. The theoretical calculation and simulation in this paper can help us to understand and engineer the high-efficiency SiGe solar cell qualitatively.