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TYPES OF SOLAR CELLS TECHNOLOGIES 11

Figure 1.5 (Continued)

a technology to cast wafers from silicon powder. Cast wafers thus far have proven to
be somewhat thicker and less efficient than the conventional sliced silicon wafers;
however, they can be manufactured faster and avoid the 30 percent waste produced
by wafer sawing.

Thin-film solar cell technology The core material of thin-film solar cell tech-
nology is amorphous silicon. This technology instead of using solid polycrystalline
silicon wafers uses silane gas, which is a chemical compound that costs much less
than crystalline silicon. Solar cell manufacturing involves a lithographic-like process
where the silane film is printed on flexible substrates such as stainless steel or
Plexiglas material on a roll-to-roll process.
Silane (SiH ) is also called silicon tetrahydride, silicanel, or monosilane, which is
4
a flammable gas with a repulsive odor. It does not occur in nature. Silane was first dis-
covered in 1857 by F. Wohler and H. Buffy by reacting hydrochloric acid (HCL) with
an Al-Si alloy.
Silane is principally used in the industrial manufacture of semiconductor devices
for the electronic industry. It is used for polycrystalline deposition, interconnection
or masking, growth of epitaxial silicon, chemical vapor deposition of silicon
diodes, and production of amorphous silicon devices such as photosensitive films
and solar cells.
Even though thin-film solar power cells have about 4 percent efficiency in convert-
ing sunlight to electricity compared to the 15 to 20 percent efficiency of polysilicon
products, they have an advantage that they do not need direct sunlight to produce
electricity, and as a result, they are capable of generating electric power over a longer
period of time.