Silicon is the dominant material for production of solar cells. In this Feature Article by Di Sabatino and Stokkan (pp. 641–648), the authors review some of the latest work carried out at Norwegian University of Science and Technology (NTNU) to understand the role of defects and impurities on materials properties. Specifically they report on some of the work done on defects, crystallization and characterization. It has been demonstrated that defects and impurities, often arising during the silicon ingot production and, due to the presence of impurity sources throughout the silicon solar cell value chain, have a detrimental effect on device performances. Crystallization is the first step in the solar cell value chain. During crystallization, crystal defects, such as grain boundaries and dislocations, develop and impurities, such as dopants and metals, distribute. By controlling the process we can also control the defect formation and impurity segregation. The micrograph shows typical dislocation clusters in a multicrystalline silicon wafer.