Systematic characterization of multi-crystalline silicon String Ribbon wafer

The String Ribbon technology provides multi-crystalline silicon wafers for low cost and high efficiency solar cells (16% efficiency on untextured cells). This paper deals with the systematic characterization of standard String Ribbon wafer material produced by the Sovello AG. The investigations of the grain structure, the dislocation density (EPD), the minority carrier lifetime τ and the interstitial iron content Fei show a clear correlation between lifetime, EPD, and interstitial iron concentration. High lifetime areas consist mainly of Σ3 twinned grains with low EPD and low interstitial iron content in the range of 4×1011 atoms/cm³. The dislocation and interstitial iron distribution is non-uniform over the ribbon width.

► String Ribbon wafer have an inhomogeneous dislocation distribution.
► The EPD is independent from crystal grain orientation.
► String Ribbon wafer have an inhomogeneous distribution of interstitial Fei.
► The carrier lifetime is influenced by high EPD and high Fei content.
► Twins with low EPD and low metal content are favourable for high lifetime.