The
efficiency of a solar cell can be substantially increased by
opening new energy gaps within the semiconductor band gap. This creates
additional optical absorption pathways which can be fully exploited
under concentrated sunlight. Here we report a new approach to opening
a sizable energy gap in a single junction GaAs solar cell using an
array of InAs quantum dots that leads directly to high device open
circuit voltage. High resolution imaging of individual quantum dots
provides experimentally obtained dimensions to a quantum mechanical
model which can be used to design an optimized quantum dot array.
This is then implemented by precisely engineering the shape and size
of the quantum dots resulting in a total area (active area) efficiency
of 18.3% (19.7%) at 5 suns concentration. The work demonstrates that
only the inclusion of an appropriately designed quantum dot array
in a solar cell has the potential to result in ultrahigh efficiency
under concentration.
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