Graphene-on-SiC - ISOM

TECHNOLOGY SOLAR CELLS
Strategies for enhancing
photovoltaic performance
There are many options for improving the performance of III-V solar
cells, including inserting quantum wells and dots to extend spectral
coverage and adding nanoparticles and diffraction gratings to boost
light trapping. Insights into all these approaches are outlined by Sudha
Mokkapati, Samuel Turner, Haofeng Lu, Lan Fu, Hark Hoe Tan and
Chennupati Jagadish from The Australian National University.
EfficiEncy is thE kEy metric for solar cells. increasing
this ups the energy produced by the cell, and in turn cuts
generation costs and trims the footprint of the cell required to
deliver a given output.
One option for enhancing the performance of a conventional
solar cell is to modify its design by inserting structures that
stretch the spectral absorption to longer wavelengths. Adding
quantum wells and dots can realize this, with greater spectral
absorption increasing short-circuit current densities that could
ultimately boost the overall efficiency of the solar cell. Gains in
current resulting from the incorporation of wells or dots also
open up new opportunities for bandgap engineering, allowing
better current matching between different sub-cells of
a tandem solar cell. for example, in a Ge-inGaAsinGaP
tandem solar cell, inserting inGaAs
quantum wells or quantum dots into the
inGaAs middle sub-cell transfers
current from the currentoverproducing
bottom subcell
to the current-limiting
middle sub-cell.
to improving solar cell performance. for example, keith
Barnham’s group at imperial college, London, have increased
the spectral response of an AlGaAs reference cell by turning to
GaAs-AlGaAs quantum well solar cells, while our team
at the Australian national University have enjoyed
similar success by replacing a GaAs reference
cell with a inGaAs-GaAs quantum dot solar
cell (see figure 1 for details of the
bandstructure of these novel cells).
A handful of
research
groups have
pursued these
approaches
30 www.compoundsemiconductor.net April/May 2013