Iron contamination and reusability of seed crystal for quasi-single crystalline silicon ingots for solar cells

The seed crystal is easily contaminated by iron impurity during the directional solidification (DS) process for manufacturing quasi-single crystalline (QSC) silicon ingot, and thus influences its reusability. We investigate the transport and distribution characteristics of iron impurity in DS processes based on different seed preservation time, and reveal the iron contamination level in seed crystal. Additionally, the heights of the bottom iron contaminated region are compared for silicon ingots grown from normal and recycled seed crystals to find out the reusability of the recycled seed crystal. The results show that the total iron concentration in the seed crystal after full solidification is between 10¹⁴ and 10¹⁵ atoms/cm³. The recycled seed crystal can be reused for DS processes with long preservation, whereas it is not recommended for reusing for processes with short preservation.