research industry
rhombus4
Approaching the frontier of
solar cell conversion efficiency
Increasing the conversion
efficiency of triple-junction
solar cells will help to cut
high-concentration PV systems
the cost of this form of
T
he conversion efficiency of a
solar cell is an important sunlight is collected from an area
quantity in photovoltaics (PV). This is 500 – 2000 times larger than that of
power generation. One
because the efficiency eventually solar cell (see Fig. 1), which only
approach to higher
defines the amount of electricity covers a very small fraction of the
generated per area, determines the module area. This slashes the
efficiencies is to push the
size of the land needed for PV amount of solar cell material needed
bandgaps of the sub-cells
installations, and ultimately sets the and cuts cell costs significantly,
cost of solar electricity. Doubling the assuming that the optics and the
towards the theorectical
efficiency of a solar energy system mandatory tracking units can be
ideal, which is approach
reduces the cost per kWh price by produced at low enough cost.
more than a factor of two.
that we have adopted at
In fact, solar cells costs typically
Fraunhofer ISE, says
But, of course this is not the full account for less than 10 percent of
story. Today’s highest efficiency solar the total cost of high-concentration
Frank Dimroth,
cells are made of III-V compound PV systems. In this case the benefit
Wolfgang Guter, and
semiconductors and the of a high efficiency can
manufacturing cost of these devices overcompensate the drawback of
Andreas Bett.
is approximately 50 times higher than significantly higher material costs.
for a state-of-the-art silicon solar cell. Due to their unparalleled
Even at 41% efficiency these solar performance multi-junction solar cells
cells will never become competitive made of III-V compound
with today’s flat-plate silicon based semiconductors are the product of
PV modules. The energy produced choice for this application.
by a III-V flat-plate module would
simply be too expensive. Fraunhofer ISE has a long tradition in
the development of these high-
However, scientists have found a way efficiency solar cells and
to get around this bottleneck and still concentrator systems
[1]
and this
benefit from the extremely high January it achieved a new record
efficiencies by turning to in solar electric conversion efficiency
concentrating optics. In of 41% at 454 suns (1 sun
October 2009 www.compoundsemiconductor.net 21
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