Surface and bulk passivation of multicrystalline silicon solar cells by ...

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Basically, materials for manufacturing silicon solar cells can be distinguished
according to the type of crystal into three categories: monocrystalline, polycrystalline
and amorphous. In order to produce a monocrystalline silicon cell, absolutely pure
semiconductor material is necessary. Monocrystalline rods are extracted from melted
silicon and then sawed into thin plates. This production process guarantees a
relatively high level of efficiency. The production of polycrystalline cells is more
cost-efficient. In this process, liquid silicon is poured into blocks that are subsequently
sawed into plates. During solidification of the material, crystal structures of varying
sizes are formed, at whose borders defects emerge. As a result of this crystal defect,
the solar cell is less efficient. If a silicon film is deposited on glass or another
substrate material, this leads to the so-called amorphous or thin layer cell. The layer
thickness amounts to less than 1 μm; so the production costs are lower due to the low
material costs. However, the efficiency of amorphous cells is much lower than that of
the other two cell types. Because of this, they are primarily used in equipment that
require low power (watches, pocket calculators) or as facade elements.
Silicon solar cell technology has greatly advanced in the past three decades.
Crystalline silicon is the dominant material in today's photovoltaic industry, and is
expected to remain so in the coming decades (~ 80% of solar cells produced at
present are crystalline silicon solar cells and the remaining 20% are mostly nonsilicon
solar cells) [28].
1.4 Structure of A Crystalline Si Solar Cell
Crystalline silicon is the primary example of a homojunction solar cell. A single
crystal silicon is altered so that one side is p-type, dominated by positive holes, and
the other side is n-type, dominated by negative electrons. The p/n junction is located