Environmental Engineering Reference
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Figure 1.3 Theenergybanddiagramofap-i-ndiodeandthemechanisms
of PV activity within the device.
One improvement generally used is the fabrication of p-i-n-
type interfaces. The energy band diagram of a p-i-n device is
shown in Fig. 1.3, and an intrinsic (or insulating) semiconductor is
sandwiched between p- andn-type semiconducting layers.
ThisarrangementalignstheFermilevelsofthetwosemiconduc-
tors through the intrinsic layer to create a strong internal electric
field throughout the i-layer and hence control the width of the
depletion region for a specific application. This is also a reliable
method to form a high potential barrier approaching the bandgap
of the semiconducting material used ( E g φ b ). Animation to
illustrate the formation and use of a p-i-n diode as a solar cell is
presented in Dharme's blog at www.apsl.org.uk. This will be helpful
inunderstandingelectrontransferduringjunctionformation,band-
bendingprocess,andvisualisationofthePVactionsofthep-i-n-type
solar cell device.
1.4.3 Hetero-Junctions
A hetero-junction is another simple modification of the p-n-type
interface. Instead of one semiconducting material on both sides of
a homo-junction, two different semiconductors are used to form
the interface (Fig. 1.4). The main difference is the existence of
two different energy bandgaps on either side. An advantage of
 
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