A novel growth method for high speed deposition of large-grain polycrystalline silicon layers on foreign substrates is described. The deposited silicon layers with a thickness of 10-40 mu m on high temperature glass substrate exhibit good uniformity and large grain sizes up to 20 mu m. A typical deposition rate is 3 mu m/min for a source/substrate temperature of 1100/950 degrees C. The growth method is based on iodine vapor transport of silicon at atmospheric pressure with a vertical thermal gradient. A gravity trapping effect allows use of an open-tube system without much loss of the volatile gas species or reduced iodine partial pressure, as is the case in a normal open system involving a carrier gas. The material appears to be an excellent candidate for thin-layer crystalline silicon solar cells.