Efficient Si-on-Ge tandem solar cell

We propose and simulate a thin-film crystalline solar photovoltaic cell comprised of two junctions - one in the Si top layer and the other in the Ge bottom layer. Assuming an anti-reflection coating on the front surface, we have shown that optimal solar cells favor a thin Si layer and a thicker Ge layer. For AM1.5G solar irradiance, we predict efficiency of ~20 % for a cell in which the Si film thickness is 7 mum and the Ge film thickness is 91 mum.