Silicon (Si), one of the most abundant materials in the Earth’s crust, is the semiconductor
used in crystalline form (c-Si) for 90% of the PV applications today (Chapter 5).
Surprisingly, other semiconductors are better suited to absorb the solar energy spectrum.
This puzzle will be explained further in Section 1.10. These other materials are in
development or initial commercialization today. Some are called thin-film semiconductors,
of which amorphous silicon (a-Si) (Chapter 12), copper indium gallium diselenide
(Cu(InGa)Se2 or CIGS) (Chapter 13), and cadmium telluride (CdTe) (Chapter 14) receive
most of the attention. Solar cells may operate under concentrated sunlight (Chapter 11)
using lenses or mirrors as concentrators allowing a small solar cell area to be illuminated
with the light from larger area. This saves the expensive semiconductor but adds complexity
to the system, since it requires tracking mechanisms to keep the light focused
on the solar cells when the sun moves in the sky. Silicon and III-V semiconductors
(Chapter 9), made from compounds such as gallium arsenide (GaAs) and gallium indium
phosphide (GaInP) are the materials used in concentrator technology that is still in its
demonstration stage.