As we know that
solar cell is a semiconductor material that converts light to electricity, this
semi conductor material may be silicon or gallium or cadmium telluride but the
crystalline silicon solar cell is the most commonly used to generate
electricity representing 95 % of the market share.
How
solar cells work?
Regarding
crystalline silicon cell, the silicon atom has 4 bonding electrons at the outer
shell and all silicon atoms is connecting to each other by sharing electrons to
complete the outer shell for each cell to 8 electrons and hence the result is
silicon lattice.
To generate the
solar cell we introduce impurities (doping atoms) into this silicon lattice to
form to type of crystalline silicon:
Type
one called : N- type silicon : impurities are
phosphorus atoms with (5) electrons in the outer shell so we have one electron
more for each connection between one silicon cell and one phosphorus cell so at
N – type crystalline silicon we have abundant of negative electrons.
Type
two called : P- type silicon: impurities are boron
atoms with (3) electrons in the outer shell so we have one electron less (hole)
for each connection between one silicon cell and one boron cell so at P – type crystalline
silicon we have abundant of positive holes .
If we bring
p-type silicon layer together with n-type silicon layer a p-n junction is
formed, at this junction the abundant electrons and abundant holes will start
to diffuse in opposite directions to each other but fortunately some positive
charge atoms remain at n-type layer (at transition region) and some negative
charge atoms remain at p-type layer (at transition region), this create a
region known as space charge region with an electric field that opposed to the
movement of the transition and that result in stopping the diffusion of holes
and electrons.
If the solar
cell two contacts are externally connected to each other by an outer electrical
wire the electrons will flow in wire generating electrical current in the condition that it will be enough energy to
motivate electrons.
Now if the solar
cell (p-n semiconductor) is exposed to the light (input energy) photons and
electrons diffusion will occur and the space region will formed and hence a
voltage will present on the solar cell contacts and if the electrical circuit
is closed , the current will flow…this process as whole is called photovoltaic
which mean converting sun light to electricity.