Upgraded Metallurgical Grade (UMG) Silicon: Quality, Applications and Process Economics

Prior to the Chinese success in the multi GW production of cheap polycrystalline silicon using the Siemens process, the purification of upgraded metallurgical grade (UMG) silicon to obtain a silicon material for photovoltaic (PV) applications remained a globally pervasive problem. The results were unsatisfactory in terms of solar cell efficiency, but relevant for several research by-products, such as the development of a cheap and efficient silicon purification process exhibiting directional solidification, and some additional knowledge reagrding MG silicon preparation using pure feedstocks. Recently, Ferrosolar and the Institute of Energia Solar in Madrid (Spain) were able to demonstrate that metallurgical silicon is indeed a material able to produce solar cells exhibiting efficiencies of 20% or more.

Currently, the challenge is to understand whether this route, based on the well- known and well-defined process steps of MG-Si production in a carbothermic furnace, followed MG-Si purification via slagging, volatilization evaporation, and leaching is cost-effective be competitive in comparison to the production of polysilicon via the Siemens process. Additionally, there is significant interest in determining whether this process can be further improved to match the solar cell efficiency exhibited by electronic grade silicon. Furthermore, it would be useful to determine whether UMG silicon cab be used successfully as feedstock for Czochralski-grown monocrystalline silicon ingots. Eventually, it remains to determine whether segments of the UMG silicon route could be utilized for the recycling of solar cell materials and various silicon wastes, and to assess its potential in other applications beside PV.

The aim of this Research Topic is to provide answers to each of these questions using a multidisciplinary approach, which would involve individual contributions from both research and industry. Therefore, the specific themes which the Research Topic will be addresses, will be:

- The state of the art with respect to the economics of the MG silicon process;
- Potential improvements of the process in terms of material purity and PV efficiency;
- A possible output of the UMG process concerning the economic recycling of solar cell materials and other silicon wastes.

Keywords: Process details, PV applications, Recycling solar cell waste, Recycling EG silicon waste, UMG silicon as feedstock in CZ furnaces

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