Numerical simulation and experimental investigation of a-Si/a-SiGe tandem junction solar cells

This paper reports numerical modeling and experimental investigation of a-Si/a-SiGe tandem junction solar cells, based on a field-aided collection model. The performances of the composed a-Si/a-SiGe tandem cells could be predicted from the numerical modeling and experimental photovoltaic parameters of the component cells. An optimized choice for the tandem cells has been proposed by the aid of numerical simulation and verified by experimental results for the cases of a fixed a-Si top cell or a fixed a-SiGe bottom cell, respectively. It is found that 1) the highest efficiency (~13%) of the tandem cells can be achieved with a certain mismatch in J
_sc
between the top and bottom cells; 2) a small amount of Ge can be incorporated into a-Si based top cells to obtain an optimized current match with the bottom cell; 3) the J
_sc
of the simulated tandem solar cells is always a little greater, rather than exactly equal to the limiting J
_sc
of the component cells.