The investigation of optimal Si-SiGe hetero-structure thin-film solar cell with theoretical calculation and quantitative analysis

The device performance such as short circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), and efficiency of solar cells on the multi-crystalline SiGe on the Si with different Ge concentration are compared and investigated in this work. The average Ge concentration was systematically changed in the range from 0% to 30%. The appropriate addition of Ge in crystal Si is the effective way to increase the short circuit current density without affecting the open-circuit voltage, due to the modulation of the material energy band-gap. The band-gap of the SiGe can be extracted by Electron-Hole Plasma (EHP) model at different temperatures. With the optimization of Ge concentration and clean process condition, the overall efficiency of a Si_0.9Ge_0.1 based solar cell is found to be improved about ~4% than the control mc-Si solar cell. Moreover, the SiGe based solar cell has also been observed that it has less operated temperature sensitivity than Si solar cell for the real application. The theoretical calculation and simulation work help us to understand and engineer the high-efficiency SiGe solar cell qualitatively.