Environmental Engineering Reference
In-Depth Information
impurity PV activity could also pump electrons into the conduction
bandusingdifferentcombinationsofmostoftheIRradiation.These
e-h pairs are also effectively separated, accelerated, and collected in
the external circuit, enhancing the short circuit current density of
the device. The improvement in the performance of tandem solar
cellswillmanifestitselfmainlyinhighshortcircuitcurrentdensities
sincebothopencircuitvoltageandfillfactorvaluesareapproaching
their maximum values in such devices.
The removal of tunnel junctions from tandem solar cells and the
adoption of a parallel configuration will lead to high performance
next-generationsolarcellsinthefuture.Theinitialtestingofparallel
configurations using GaAs/AlGaAs systems has been carried out,
andtheexperimentalresultsarepresentedinthenexttwochapters.
6.5 Summary
Different ways of connecting solar cell structures to effectively
harvest photons in tandem solar cells have been considered by
revisiting relevant device designs. It is found that the present use
of a series connection or tunnel junction approach is detrimental
to charge carrier separation and collection through the tandem
cells. Each tunnel junction introduced to the solar cell structure
deceleratesthechargecarriersandallowsthemtorecombineatthe
vicinity of the tunnel junction. The adoption of parallel connections
has several advantages over series connections, and there is high
potential for achieving enhanced e
ciencies in next-generation
solar cells. In these devices, charge carriers are continuously
accelerated across the whole device and collected in the external
circuit. Multi-charge-carrier production by impact ionisation and
impurity PV mechanisms are also built into this system to enhance
its performance through the possibility of increasing the short
circuit current density.
References
1. M. A. Green (11-18 May 2003) Proceedings of the 3rd World Conference
on Photovoltaic Energy Conversion, Osaka, Japan, pp. 50-54.
