There are many factors which influence the performances of a Si tandem solar cell,such as materials,interfaces,and structures.According to the photogenerated current continuity rule and photovoltaic material option rule,the current matching of a Si tandem solar cell was investigated.It had been demonstrated in this paper that the current matching was one of the important factors which affected the fill factor and conversion efficiency of a Si tandem solar cells.It has been also found that the current matching can be achieved by adjusting the thickness of each component cell.As a result of research,the best efficiency of 8.28%,7.52%,and 6.74% for a Si/a Si,a Si/a SiGe and a Si/a Si/a SiGe tandem solar cells with area of 400cm 2 have been obtained respectively.