Efficiency improvements of silicon solar cells by absorption enhancement with germanium

This paper presents a theoretical investigation of the germanium effect on the absorption coefficient in polycrystalline silicon alloys to improve solar cell efficiency. The underlying objective is to enhance the efficiency or reduce the cell thickness of the standard photovoltaic system for terrestrial application without sacrificing the benefits of the well known silicon cell technology. The study is based on the comparison of a standard polycrystalline Si cell (taken as reference) and the same cell with 8% atomic of germanium. The Si and SiGe material was processed by an extension of the POLIX method, and samples were characterized by infrared spectroscopy in the near infrared range. We find an optical absorption gain three times greater for Si/sub 0.92/Ge/sub 0.08/ as compared to Si. As we justify, all parameters of each cell are taken to be equal except for the absorption coefficient in the infrared range. We show, as a result of the computer device modeling, that significant gains in cell efficiencies can be obtained. We have also studied the influence of the Si/sub 0.92/Ge/sub 0.08/ cell thickness and half the thickness shows an efficiency still greater than the reference Si cell.