process of fabricating conventional single- and polycrystalline
silicon PV cells begins very pure semiconductor-grade polysilicon
- a material processed from quartz and used extensively throughout
the electronics industry.
The polysilicon is then heated to
melting temperature, and trace amounts of boron are added to the
melt to create a P-type semiconductor material. Next, an ingot, or
block of silicon is formed, commonly using one of two methods:
by growing a pure crystalline silicon ingot from a seed crystal
drawn from the molten polysilicon or
2) by casting the molten
polysilicon in a block, creating a polycrystalline silicon
Individual wafers are then sliced from the ingots using
wire saws and then subjected to a surface etching process. After
the wafers are cleaned, they are placed in a phosphorus diffusion
furnace, creating a thin N-type semiconductor layer around the
entire outer surface of the cell.
Next, an anti-reflective coating
is applied to the top surface of the cell, and electrical contacts
are imprinted on the top (negative) surface of the cell.
aluminized conductive material is deposited on the back (positive)
surface of each cell, restoring the P-type properties of the back
surface by displacing the diffused phosphorus layer.
Each cell is
then electrically tested, sorted based on current output, and
electrically connected to other cells to form cell circuits for
assembly in PV modules.