Improving Photovoltaics with High Luminescence Efficiency Quantum Dot Layers
Improving Photovoltaics with High Luminescence Efficiency Quantum Dot Layers
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Date
2015
Authors
Chen, James
Gagner, DJ
Griffiths, Kevin
Hitz, Emily
Horiguchi, Akira
Joyce, Ryan
Kim, Byung Yub
Lee, Michael
Lee, Seongwoo
Raul, Alex
Advisor
Munday, Jeremy
Citation
DRUM DOI
Abstract
A solar cell relies on its ability to turn photons into current. Because short wavelength photons
are typically absorbed near the top surface of a cell, the generated charge carriers recombine
before being collected. But when a layer of quantum dots (nanoscale semiconductor particles) is
placed on top of the cell, it absorbs short wavelength photons and emits them into the cell at
longer wavelengths, which enables more efficient carrier collection. However, the resulting
power conversion efficiency of the system depends critically on the quantum dot luminescence
efficiency – the nature of this relationship was previously unknown. Our calculations suggest
that a quantum dot layer must have high luminescence efficiency (at least 80%) to improve the
current output of existing photovoltaic (PV) cells; otherwise, it may worsen the cell’s efficiency.
Our quantum dot layer (using quantum dots with over 85% quantum yield) slightly reduced the
efficiency of our PV cells. We observed a decrease in short circuit current of a commercial-grade
cell from 0.1977 A to 0.1826 A, a 7.6% drop, suggesting that improved optical coupling from the
quantum dot emission into the solar cell is needed. With better optical coupling, we predict
current enhancements between ~6% and ~8% for a solar cell that already has an antireflection
coating. Such improvements could have important commercial impacts if the coating could be
deployed in a scalable fashion.