The scientific objectives of the proposed experiments are to decrypt fundamental mechanisms of the solidification of crystalline silicon (Si) for photovoltaic (PV) applications. The original experiments consist of synchrotron X-ray imaging (radiography and diffraction imaging/topography) applied to the in situ monitoring of Si solidification. The main issues of the defect formation, ranging from dislocations to grains, and of their complex interaction and dependence will be studied at high temperatures during heating, melting (1414°C) and solidification. These experiments will generate original and key fundamental results. Moreover, this knowledge can contribute to answer to the challenge of defect control to obtain higher PV efficiency for all most advanced fabrication processes of crystalline Si PV cells.