Page 44 - Applied Photovoltaics

Chapter

2

SEMICONDUCTORS

AND P-N JUNCTIONS

2.1 SEMICONDUCTORS
In 1839 Becquerel observed that certain materials, when exposed to light, produced
an electric current (Becquerel, 1839). This is now known as the photovoltaic effect,
and is the basis of the operation of photovoltaic or solar cells.
Solar cells are manufactured from semiconductor materials; that is, materials that act
as insulators at low temperatures, but as conductors when energy or heat is available.
At present, most solar cells are silicon-based, since this is the most mature
technology. However, other materials are under active investigation and may
supersede silicon in the long term.
The electrical properties of semiconductors can be explained using two models, the
bond and the band models. These models are described briefly below. (More detailed
descriptions are given in Green, 1992 and Neville, 1978.)