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Ultra-pure silicon for solar cells

After silicon has been produced from quartz and carbon, it needs to be refined to achieve high enough purity for it to be usable for solar cell production. This has traditionally been done by adapting a process developed for the microelectronic industry, where silicon is purified via a gas phase. This process is energy intensive, and the result has a somewhat higher purity level than needed.

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Alternative metallurgical refining methods requires a lot less energy and will therefore leave a significant lower climate footprint. Norwegian industry holds a leading position when it comes to refining of solar cell silicon, including recycling of kerf. 

In SINTEF we are working closely with the industry and academia, but we have also extensive in-house laboratories for process development. 

Examples of work on silicon refining: 

  • Directional solidification as a refining step 
  • Grain boundary engineering to redistribute the impurities in the silicon grain boundary for further hydrometallurgical purifications. The grain boundary engineering is now carried out by doping calcium and manganese into silicon feedstock.  
  • Vacuum degassing at elevated temperatures and gas refining to remove impurity elements such as boron, phosphorus, and calcium. 
  • Slag refining process for decarbonization of the diamond-wire saw silicon kerf 
  • Hydrometallurgy, including use of hydrofluoric acid. 
  • Electrochemical refining.