Amorphous silicon-germanium (a-SiGe) solar cells with graded Ge fraction along the film depth profile are deposited at elevated rate of 4 angstrom/s in a pressure range of 2-4 Torr. A properly graded GeH(4) flow pattern characterized by a low starting ratio of GeH(4):H(2) is the key towards achieving highly stable a-Si/a-SiGe tandem cells of 12.94% initial and 11.22% stable efficiencies. A fully laminated module with 38 x 38 mm(2) aperture area made from the tandem cell exhibits an initial efficiency of 10.81%, which shows that the high rate deposited a-Si/a-SiGe tandem cells are promising for practical module applications. (C) 2010 Elsevier B.V. All rights reserved.