Characterization of Silicon-Film™ sheet material

The Silicon-Film™ process produces a polycrystalline silicon sheet used in the production of solar cells. The process uses low-cost materials and high-throughput equipment for high volume production. This paper reports on the progress in characterizing this relatively new material. Small grain sizes and the presence of impurities are the logical explanation for performance losses in small grain polycrystalline silicon. With advances in the understanding of critical high temperature processes, such has gettering, views on impurity requirements have changed. As polycrystalline silicon sheet material can tolerate higher impurity levels then historically found in CZ grown materials, understanding the allowed impurity concentrations will lead to lower-cost silicon, which in turn will lead to lower-cost solar cells. Similarly, conventional grain size limits are shown to be inaccurate, allowing higher performance than thought possible from smaller grains. To delve into these and other specific material issues, an industry - academic - government team has been established. This paper reports on some of the results found by that team and highlights some of the conclusions that have been drawn as regards impurities and gettering.