Bulk crystalline silicon solar cells have been the workhorse of the photovoltaic industry over the past decades. Recent major investments in new manufacturing facilities for monocrystalline and multicrystalline wafer-based cells, as well as for closely related silicon ribbon and sheet approaches, ensure this role will continue well into the future. Such investments suggest that the silicon wafer-based approach has successfully withstood the challenge mounted by thin-film chalcogenide-based cells, in the form of polycrystalline films of CdTe and CuInSe2, as well as that mounted by thin-film cells based on amorphous silicon and its alloys with germanium. The encumbent now faces a fresh challenge by a new wave of thin-film technologies developed in the 1990s, more closely related to the bulk approach and with some advantages over the earlier contenders. One new approach is based on a stack of two silicon thin-film cells, one cell using amorphous silicon and the other mixed-phase microcrystalline silicon. The second uses silicon thin-films in polycrystalline form deposited onto glass, even more directly capturing the strengths of the wafer-based approach. (C) 2003 Elsevier Ltd. All rights reserved.