Optimization and characterization of advanced solar cells based on thin-film a-Si:H/SiGe hetero-structure

Introducing Ge atoms to the Si lattice in Si-based solar cells is an effective approach in improving their characteristics. Especially, current density of the cell can be enhanced without deteriorating its open circuit voltage, due to the modulation of material band-gap and the formation of a hetero-structure. The electrical parameters of an a-Si:H/a-SiGe hetero-structure double junction solar cell, such as the open-circuit voltage (VOC), short circuit current density (ISC), fill factor (FF), and the efficiency are investigated in this work, based on the optimization of the Ge content in the film. The concentration of Ge was changed between 0% and 30%. Optimization shows that for an appropriate Ge concentration, the efficiency of a-Si:H/a-SiGe solar cell is improved by about 6.5% compared with the traditional a-Si:H solar cell. The band-gap of SiGe plays a critical role in the solar cell design. This paper presents a novel design and optimization procedure of parameters for a dual junction amorphous silicon thin film solar cell, where a simulated maximum efficiency of 23.5% is obtained. The parameters used in the optimization of the cell's power are the doping concentration and the thickness of layers.