Environmental Engineering Reference
In-Depth Information
enhanced absorption of a major part of the solar spectrum, multi-
electronexcitation(orimpactionisation)andmulti-stepabsorption
process (or the impurity PV effect) to enhance the performance of
PV devices. The graded bandgap multi-layer device design has been
experimentally tested using well-researched GaAs-based system.
Despite only two growths having been carried out, the highest
reported
V
oc
0.86
has been achieved. The short circuit current density values for
these initial devices are low in the range 12-24 mAcm
-
2
,dueto
undesirable doping concentrations in the front and back regions of
the device. The highest e
ciency achieved from these two growths
is
∼
19% and this value can be increased by optimising the doping
concentrations at different regions of this device. These results
indicate that the new thought process is in the right direction and
future work using low-cost growth techniques to produce this new
device structure has a bright future.
The PV effect observed in complete darkness highlights the
importance of the new design which is capable of converting the
infrared(IR)radiationpresentinthesurroundingstoelectricpower.
The combination of the PV power created by sunlight together with
thepowerproducedbythesurroundingheatradiationwillenhance
the overall power output of solar panels. This effect should produce
high conversion e
ciencies exhibiting quantum e
ciencies above
100%. The IR radiation available in the surroundings is also coming
from our energy source, the sun.
≈
1175 mV with the highest possible FF
≈
12.3 Conclusions
PV research requires new ways of thinking moving away from
traditional thought process. Thin-film solar cells have a very bright
future, but the material issues and device physics understanding
must be improved in order to achieve high-e
ciency and low-cost
products. A good part of the scientific research must be devoted
to revisiting the existing wisdom from time to time with an open
mindandmakingtherequiredimprovements.Otherwise,theerrors
willpropagatethroughthescientificliteraturefordecadeshindering
