Environmental Engineering Reference
In-Depth Information
Figure 9.12
The deformation of the energy band diagram during reverse
biasing, followed by the release of the electrical stress. A second diode is
formed at the AlGaAs/GaAs interface due to a Fermi-level shift to a lower
energy level.
3mm
2
solar cells seem to
be very stable, showing the most desirable qualities needed for a
practical solarcell.These3
×
3mm
2
solarcellshavea120nmthick
MgF
2
anti-reflection coating when compared to 0.5 mm diameter
devices. Low concentrations of unwanted defects at interfaces
during processing may have improved the device parameters.
It should be noted that the filling and emptying of defect
levels are also influenced by changes in temperature and light
intensity in addition to the electrical stresses externally applied
to the device. Therefore, the results may vary according to the
dominant effect at a particular situation. The deterioration of
V
oc
during daytime or the light soaking (equivalent to the forward-
biasing effect) and recovery effect during night-time (equivalent to
a zero-bias situation) observed for solar cells can be explained in
terms of defects in the semiconductors or at the interfaces. The
removal (or passivation) of unwanted defects in solar cells will
allow the production of high-e
ciency solar cells and reduce these
undesirable instabilityeffects.
×
The results shown by Fig. 9.9 for 3
