Process-induced defects in solar cell silicon

Abstract

The microstructure of as-grown and processed, edge-defined film-fed grown, silicon ribbons was studied in order to identify the basic mechanisms responsible for the change of the as-grown defect structure during processing at elevated temperatures. The short heat treatment required to diffuse the p-n junction was sufficient to cause heterogeneous precipitation of impurity atoms, particularly transition metals. In addition, an elastic recovery of the ribbon occurred by dislocation glide, resulting in the formation of a polygonizationlike structure of sub boundaries in the base. Mechanism are suggested by which twin boundaries, acting as dislocation obstacles, can concentrate the relatively low average dislocation densities typical of edge-defined film-fed grown ribbons (104 cm−2 to 108 cm−2) to values which are sufficient to induce the formation of subgrainlike boundary structures.