Crucibles for next generation high quality silicon solar cells (CruGenSi)

The CruGenSi project started on August, 1st 2017 and ended on October, 30th 2021. The main goal of the project has been to develop knowledge and expertise in crucibles used to make crystalline silicon ingots for solar cells. The crucibles can be made by different processes and raw materials that will also affect their final quality (total impurity concentration) and structure (grain size and porosity). During these 4 years, we have trained 2 PhDs (Rania Hendawi and Jochen Busam). Rania is a female candidate from Jordan and she will have her PhD dissertation in December 2021. Jochen is from Germany and he will have his dissertation in the summer of 2022. In addition, 4 master students have worked on the project. Through close collaboration between NTNU, SINTEF, IFE and the industrial partner, we have achieved a number of exciting results. Some of the most important results are: -we have increased understanding of the coating and wettability of silicon nitride crucibles. -we have tested a combination of coatings for graphite crucibles and found that two-layer coating has a positive effect on the wetting properties, while there is an optimal concentration of oxygen. -we have managed to quantify the chemical composition of the impurities through the crucible, coating and ingot in the same position before and after crystallization process. These data have been important for model validation. The model shows the distribution of the impurities in different types of crucibles and can help further industry to understand how impurities move through the crucible, coating and ingot. These data are also important for models that predict how impurities affect solar cell efficiency. -crucibles with diffusion barriers show less pollution in the Si ingot and thinner "red zone". Although the pandemic has affected the last period of the project, all partners are satisfied with the results of this KPN project.

The main results are: -educated 2 PhD candidates. -increased understanding of the coating and wettability of silicon nitride crucibles. -increased understanding of quartz crucibles with and without diffusion barriers for silicon solar cells applications. -tested a combination of coatings for graphite crucibles and found that two-layer coating has a positive effect on the wetting properties, while there is an optimal concentration of oxygen. -quantification of the chemical composition of the impurities through the crucible, coating and ingot in the same position before and after crystallization process. These experimental data have been used for model validation. -crucibles with diffusion barriers show less pollution in the Si ingot and thinner "red zone". The outcomes of this project have the potential to further develop the PV industry with focus on silicon ingots production.

Today the main source of impurities that reduce the efficiency of silicon-based solar cells is the crucible used to contain the silicon melt. It is the purpose of this project to understand and reduce the impact of the crucible upon the quality of the final Si-based solar cells. The crucible and coating are the main sources of O, C and N in the Si ingot. Although most of the negative effects of these impurities are known, their formation and transport mechanisms are not fully understood and involve complex interactions. Increased understanding of these mechanisms and interactions is therefore needed. In this proposed project we want to develop knowledge and competence on light impurity elements in crystalline Si by focusing on the crucible materials and on the crucible/coating/silicon system. Crucibles can be made by different processes and raw materials which also will affect their final quality (total impurity concentration) and structure (grain size and porosity). In this project, we want to understand the role of crucible quality and structure upon the crystallization process itself, as well as upon the contamination level, defect density and grain size of Si ingots and wafers. The project involves 2 industries and 3 research partners. 2 PhD candidates will be educated. The consortium partners have expertise on all required aspects. This project can significantly influence the development of low cost and high efficiency solar cells for sustainable energy production, and improve the competitiveness of the industry partners.