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Introducing engineering
Introducing engineering

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5.15.1 Materials and pollution

There are various chemicals and solvents used in both bulk and thin film processing. No heavy metals are used in silicon cell production, either in bulk processing or in amorphous thin film. Cyanide compounds and toxic gases are used, however, but these are controlled by burn off, good practice and recycling. In this regard the industry is no worse than many other 'high-tech' processors.

Some of the exotic semiconductor compounds proposed as more efficient alternatives to silicon involve the toxic elements cadmium and selenium, but the quantities are not large because of the extreme thinness of the active material. (1 m 2 of a cadmium telluride cell contains a maximum of about 2 cm 3 of cadmium.) Of course, multiplied by many metres squared this does add up to a potential problem. However, within the cells the material is sealed and so is isolated from the environment. Tests have shown that even in the event of fire toxic contamination is very localised because the combustion products have low volatility. In processing, careful procedure and regular checks can minimise risks to workers, and recycling procedures have shown that very little toxic material escapes to the environment. Decommissioning of cells has also been addressed: containment and recycling of the toxic elements is quite feasible. There remains the question as to whether this will be practical on an administrative and economic basis.