A variety of approaches are explored for crystalline silicon thin film solar cells on foreign substrates, According to their grain size, we classify these films as either microcrystalline, polycrystalline, or monocrystalline. The first two materials are directly deposited onto foreign substrates, whereas monocrystalline films are transferred from a wafer to a foreign substrate. We describe device results, analyze underlying material properties and discuss prospects and limitations of these approaches. In contrast to the limited performance of micro- and polycrystalline Si thin film solar cells imposed by the presence of grain boundaries, we expect transfer approaches to result in thin film solar cell efficiencies in the range of 18-20%. This approach therefore opens an avenue to an efficient and competitive Si-based thin film technology in the near future. (C) 2002 Elsevier Science B.V. All rights reserved.