Comments on the Potential of FZ Silicon for Solar Cells

The reasons why FZ silicon, up to now, could not be commercially launched in the terrestrial PV market are the smaller maximum crystal sizes (diameter, lengths) and the need of expensive high-quality feed rods being of limited sizes, too. Today, the biggest FZ crystal diameter on the market is 200 mm. This would fit a quadratic wafer format of 150 x 150 mm2, but growing such crystals is still extremely sophisticated and expensive, too. However, future progress in FZ growth development, as mentioned before, could make FZ solar cells competitive or even superior to CZ cells. 

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. 

The purest single crystals from silicon can be grown after the crucible-free FZ crystal growth technique, presently (2008) with a maximum diameter of 200 mm. The low energy effort for the growth and no need for a crucible are the economic advantages. 

The feedstock silicon for FZ growth has to be of high purity and structural perfection and is rather expensive. The development of low-cost feed rods is crucial for the commercial terrestrial solar application. 

The growth of quadratic FZ crystals could reduce the material waste for solar cell production. High carrier diffusion length and low oxygen concentration enable the highest solar cell efficiencies of about 25% in laboratory scale. 

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