State of the silicon casting art

The principal attributes of the two main technologies for casting polycrystalline silicon for solar cells are reviewed. Silicon casting at Solarex is discussed in detail, with emphasis on work to improve the electronic quality of the material by modifications to the thermal environment of the casting station. The effects of three specific modifications on gross crystal structure and cell performance are reported. The results are interpreted in light of the temperature and power parameters of the casting run. Silicon cast under these conditions shows improved columnar structure in its grain growth and less side-wall nucleation. Devices made from this material yield 10-11% better efficiency.