Silicon feedstock

Figure 11.3 Process flow from silicon feedstock to wafers for the case of multicrystalline silicon.

The availability of abundant, low-price silicon feedstock, in the 10-20 kg range for the long term, is a very important point for the possibility of silicon technology progressing as expected in terms of cost reduction. 

The energy intensity of the processes contributes to the energy payback time of modules. Current silicon feedstock production is energy intensive, around ISOkWhkg . Together with the low silicon utilization, this leads to a module energy payback time between 1.5 and 4 years, which, although much shorter than the module lifetime, needs to decrease. 

With FZ solar cells, the amount of silicon per Watt peak (Wp) would probably be the smallest of the crystalline silicon solar cells. Low-cost silicon feedstock development suitable for FZ is crucial for the future of FZ silicon based photovoltaic. 

There are several impurities in mc-Si, including carbon, oxygen, nitrogen, and iron. Carbon is one of the major impurities in silicon feedstock. When the carbon content exceeds its solubility limit in silicon, it will precipitate to form SiC particles in a directional solidification process. It has been experimentally... 

Fig. 4.7. Substitutional carbon and SiC particle distributions along the center axis of the ingots solidified in a fast-cooling process with different carbon concentrations in silicon feedstock. Unit of Co is 1017 atoms cm-3, (a) substitutional carbon (b) SiC particles...

Ceccaroli, B. Lohne, O. Solar grade silicon feedstock. In Handbook of Photovoltaic Science and Engineering Luque, A., Hegedus, S., Eds. Wiley Chichester, 2003 153-204. 

The PV industry has been very good at reducing costs however, it is going to run up against a barrier in the cost of the silicon feedstock used to make solar cells. Low-cost, low-energy technologies must be developed that can take the raw material (quartz) and refine it into solar-grade silicon. 

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