A vacuum directional solidification with high temperature gradient was performed to prepare low cost solar-grade multicrystalline silicon (mc-Si) directly from metallurgical-grade mc-Si. The microstructure characteristic, grain size, boundary, solid-liquid growth interface, and dislocation structure under different growth conditions were studied. The results showed that directionally solidified multicrystalline silicon rods with high density and orientation could be obtained when the solidification rate was below 60μm/s. The grain size gradually decreased with increasing the solidification rate. The control of obtaining planar solid-liquid interface at high temperature gradient was effective to produce well-aligned columnar grains along the solidification direction. The growth step and twin boundaries were preferred to form in the microstructure due to the faceted growth characteristic of mc-Si. The dislocation distribution was inhomogeneous within crystals and the dislocation density increased with the increase of solidification rate. Furthermore, the crystal growth behavior and dislocation formation mechanism of mc-Si were discussed.

Preparation, Microstructure and Dislocation of Solar-Grade Multicrystalline Silicon by Directional Solidification from Metallurgical-Grade Silicon. H.Su, J.Zhang, L.Liu, H.Fu: Transactions of Nonferrous Metals Society of China, 2012, 22[10], 2548-53