A new technique for the directional solidification growth of multi-crystalline silicon (mc-Si) ingot was developed by GCL-POLY Energy Holdings Ltd. This technique is called as S2 and has been used recently for industrial production. The average conversion efficiency of the solar cells fabricated by S2 mc-Si wafers is increased by 0.62% compared with the traditional mc-Si solar cells using conventional solar cell processing. In order to understand the origin of the high cell performance, ensure the process reproducibility and further improve the technique, this paper analyzes the grain structures of the S2 mc-Si wafers by light microscopy and scanning electron microscopy supported with electron back scatter diffraction. Our analysis indicates that the increased performance of the S2 mc-Si solar cells is contributed to low dislocation density, uniform and highly oriented grains with high percentage of electrically inactive grain boundary (Sigma 3 grain boundary). (C) 2013 Elsevier B.V. All rights reserved.