Environmental Engineering Reference
In-Depth Information
the overall PV effect. Therefore, when fully optimised, this device
has a huge potential to increase
J
sc
and, hence, the conversion
e
ciency.
8.7 Conclusions
The work presented in this chapter leads to several important
conclusions.
The responsivity measurement as a function of wavelength
is simple and experimentally confirms the existence of impurity
PV effect in the graded bandgap multi-layer devices. These
observations are re-confirmed by the production of high
V
oc
values together with other PV parameters in complete darkness.
The theoretical expectation of the existence of the impurity PV
effect is, therefore, experimentally confirmed for these new device
structures.
The graded bandgap multi-layer solar cell structure has two
power inputs, as shown in Fig. 8.5 — normal solar radiation and
the surrounding heat energy. Heat energy creates charge carriers,
and this process will enhance the overall PV effect of the device
when illuminated. Therefore, when the doping concentrations
are optimised to achieve fully depleted device, higher
J
sc
values
and, hence, higher e
ciencies are expected from this device
design.
The current QE measurement systems miss out some important
information, most probably due to the methods used for data
collection, analysis, and/or presentations of the results. This may
need re-examining and taking appropriate actions to improve this
important PV characterisation technique.
8.8 Summary
A graded bandgap multi-layer solar cell device structure has been
designed to effectively absorb UV, visible, and IR radiation and to
incorporate impact ionisation and impurity PV effects within one
