Journal
NANO LETTERS
Volume 10, Issue 8, Pages 3019-3027Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nl101490z
Keywords
Multiple exciton generation; carrier multiplication; solar energy conversion; semiconductor nanocrystals; quantum dots
Categories
Funding
- Division of Chemical Sciences, Geosciences, and Biosciences in the Office or Basic Energy Sciences of the Department of Energy
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences
- DOE [AC36-086038308]
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Multiple excitor) generation (MEG) in quantum dots (QDs) and impact ionization (II) in bulk semiconductors are processes that describe producing more than one electron hole pair per absorbed photon. We derive expressions for the proper way to compare MEG in QDs with II in bulk semiconductors and argue that there are important differences in the photophysics between bulk semiconductors and QDs. Our analysis demonstrates that the fundamental unit of energy required to produce each electron hole pair in a given QD is the band gap energy. We find that the efficiency of the multiplication process increases by at least 2 in PbSe QDs compared to bulk PbSe, while the competition between cooling and multiplication favors multiplication by a factor of 3 in QDs. We also demonstrate that power conversion efficiencies in QD solar cells exhibiting MEG can greatly exceed conversion efficiencies of their bulk counterparts, especially if the MEG threshold energy can be reduced toward twice the QD band gap energy, which requires a further increase in the MEG efficiency. Finally, we discuss the research challenges associated with achieving the maximum benefit of MEG in solar energy conversion since we show the threshold and efficiency are mathematically related.
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