Environmental Engineering Reference
In-Depth Information
Figure 6.6
The possibility of multi-charge carrier creation by an
avalanche effect and multi-step charge carrier creation using infrared (IR)
photonsthroughanimpurityPVeffectintandemcellsconnectedinparallel
configuration.
the semiconductor layers, anywhere from the front to the back.
This effect could also contribute to the PV activity, as shown
in Fig. 6.6, enhancing the current collection from this type of
device structure. The defects in semiconductors are di
cult to
remove — the only possibility is to minimise their concentrations.
In this case, the natural defects present are used to the device's
advantage rather than the detrimental recombination process. The
photo-generated electrons and holes are separated by the whole
device thickness, and hence recombination has been minimised.
Intentionally introduced inter-bands may only be useful if they are
promotinge-hpairs,byminimisingtherecombinationprocess.This
will bereally challenging to achieve in apractical device.
The advances made in the growth of p
+
,p,i,n,andn
+
-type
CIS and CIGS materials [3, 4] using electrodeposition are very
relevant to the fabrication of multi-layer devices connected in
parallel. In addition, the simultaneous bandgap engineering needed
to achieve values in the range of
∼
2.20 to
∼
1.00 eV has been
established [5]. By varying both bandgap and electrical conduction
type, using previously described electrodeposition techniques [3-
7], it is possible to fabricate device structures of the type shown in
