Effect of crystal defects on mechanical properties relevant to cutting of multicrystalline solar silicon

The effect of crystalline defects such as dislocations and grain boundary on the cutting behavior of multicrystalline solar silicon is investigated. Diamond scribing experiments reveal significant intra-granular variations in the critical depth of cut for ductile-to-brittle transition in the material. This is explained by characterizing the local dislocation density variations in (100) and (311) grains of a cast multicrystalline silicon wafer and measuring the corresponding elastic modulus, nanoindentation hardness, and fracture toughness. Measured elastic moduli are shown to be higher than theoretical values for defect-free single crystal silicon of the same crystallographic plane. For a given grain orientation, a higher dislocation density is shown to be correlated with higher fracture toughness and a larger critical depth of cut.