Multiple Exciton Generation in Colloidal Silicon Nanocrystals

Matthew C. Beard, Kelly P. Knutsen, Pingrong Yu, Joseph M. Luther, Qing Song, Wyatt K. Metzger, Randy J. Ellingson, Arthur J. Nozik

Research output: Contribution to journalArticlepeer-review

768 Scopus Citations


Multiple exciton generation (MEG) is a process whereby multiple electron-hole pairs, or excitons, are produced upon absorption of a single photon in semiconductor nanocrystals (NCs) and represents a promising route to increased solar conversion efficiencies in single-junction photovoltaic cells. We report for the first time MEG yields in colloidal Si NCs using ultrafast transient absorption spectroscopy. We find the threshold photon energy for MEG in 9.5 nm diameter Si NCs (effective band gap = Eg = 1.20 eV) to be 2.4 ± 0.1Eg and find an excitonproduction quantum yield of 2.6 ± 0.2 excitons per absorbed photon at 3.4Eg. While MEG has been previously reported in direct-gap semiconductor NCs of PbSe, PbS, PbTe, CdSe, and InAs, this represents the first report of MEG within indirect-gap semiconductor NCs. Furthermore, MEG is found in relatively large Si NCs (diameter equal to about twice the Bohr radius) such that the confinement energy is not large enough to produce a large blue-shift of the band gap (only 80 meV), but the Coulomb interaction is sufficiently enhanced to produce efficient MEG. Our findings are of particular importance because Si dominates the photovoltaic solar cell industry, presents no problems regarding abundance and accessibility within the Earth's crust, and poses no significant environmental problems regarding toxicity.

Original languageAmerican English
Pages (from-to)2506-2512
Number of pages7
JournalNano Letters
Issue number8
StatePublished - 2007

NREL Publication Number

  • NREL/JA-270-41889


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