The usage of crystalline silicon in solar cells to convert sunlight directly into electricity is one of the fastest growing industries worldwide. A major challenge of all solar cell research is that electricity from solar cells currently is too expensive for being competitive. An essential issue is therefore the solar cell efficiency. Defects like impurities and dislocations that originate from the crystallization process strongly influence on the performance. A dislocation is a crystallographic defect, o r irregularity, within a crystal structure. While the effects of many impurities can be mitigated through processes used during the solar cell fabrication, the dislocations cause particular problems in multi-crystalline silicon solar cells, since the ener gy required for removing such defects is excessively high. Typically the dislocations exhibit an inhomogenous distribution in the material where zones with the highest dislocation density are often associated with a locally reduced efficiency. It is not c lear what causes these strong variations. Impurities in the form of dissolved atoms or particles are believed to play an important role. A reduced level of impurities can be achieved by controlling the convection in the melt. Advanced numerical modelling of these phenomena is addressed in the present project. Numerical work is accompanied by material characterization using a chemical process to map the dislocation structure and density in real silicon blocks made from directional casting. A challenge will be to combine experimental data, fundamental theory and process simulations providing temperature and strain histories to build a model that can capture the key phenomena leading to the observed dislocation pattern. For IFE this project will strengthen t he competence in the field of silicon materials science in particular and in the field of computational materials science in general. Norwegian companies focusing on photovoltaics will benefit from this.
SIP-NHD-Strategiske instituttprogram finansiert av NHD