UMG Silicon and BOSCO Solar Cells

One significant cost driver in silicon (Si) photovoltaics (PV) is the energy-extensive purification of Si. By avoiding the gaseous phase during purification, upgraded metallurgical-grade (UMG) Si promises significant cost reduction compared with the standard Siemens route. This thesis investigates the suitability of p-type multicrystalline Si substrates originating from different UMG Si feedstock for PV applications. Furthermore, the both sides collecting and contacted (BOSCO) solar cell is investigated in detail.

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One significant cost driver in silicon (Si) photovoltaics (PV) is the energy-extensive purification of Si. By avoiding the gaseous phase during purification, upgraded metallurgical-grade (UMG) Si promises significant cost reduction compared with the standard Siemens route. This thesis investigates the suitability of p-type multicrystalline (mc) Si substrates originating from different UMG Si feedstock for PV applications.
Previously existing issues of characterising UMG Si are resolved, and a record efficiency for large-area mc aluminium back-surface field UMG Si solar cells has been achieved. Furthermore, the both sides collecting and contacted (BOSCO) solar cell has been investigated, which, i.a., exhibits double-sided emitter regions that increase charge carrier collection efficiency and a metallisation grid on the rear side that enables bifacial applications, i.e., also illumination impinging on the cell's rear side contributes to power generation. The BOSCO cell's suitability to prevent current loss in lower-quality Si substrates is shown, with this advantage being even more pronounced for bifacial applications. Hence, the BOSCO cell concept enables the extension of bifacial applications, which have so far been limited to highest-quality substrates, to a much wider material class.