This payer reviews recent progress in large-area a-Si/a-SiGe tandem solar cells at Sanyo. Considerable efforts have been devoted to improving both the stabilized efficiency and the production throughput. High-speed patterning using plasma chemical vaporization machining (CVM) has been successfully applied to the a-Si patterning of a 1200 cm(2) a-Si integrated-type submodule. The optimization of the hydrogen dilution has led to a high stabilized efficiency of 9.7% for a 1200 cm(2) a-Si/a-SiGe tandem submodule whose photovoltaic layers are deposited at 3 Angstrom /s. A scale-up of the submodule size from 1200 to 5400 cm(2) is now being done in a pilot plant, which has been operating since April 1999. (C) 2001 Elsevier Science B.V. All rights reserved.