A simplified diagram showing construction of a crystalline silicone (c-Si)
photovoltaic cell helps to better understand the PV technology. Crystalline
silicon is the most widely used material for PV cell fabrication. An n-type
dopant is diffused into a p-type silicon wafer to create the p-n junction.
Depending on the process, it might start out with an n-type waver, followed by a
p-type layer.
Next, front and back metal contacts are formed on either side of the wafer so
that the cell can be electrically connected to an external circuit. Electrical
conductors or wires are connected to each contact and when the conductors are
connected to the load, the circuit is complete.
The n-type and p-type layers are placed side by side on the silicon wafer.
Some excess electrons from the n-type layer move into the p-type layer so holes
remain in their place. This can be described as holes moving from the p-layer
into the n-layer. These electrons and holes create an electric field in the
junction area of the semiconductor.
During PV cell operation, this field forces the electrons (that are freed by
the photons in the p-type layer) to move to the top of the n-type layer while
the holes move to the p-type layer. The electrons flow through the contact,
wiring, and load in the outside circuit and then return to the p-type layer
where they recombine with the holes. Of course, the notation for the
conventional direction of current flow is opposite to the direction of electron
flow.
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