Multiple Exciton Generation in Colloidal Silicon Nanocrystals
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- 作者：Matthew C. Beard ; Kelly P. Knutsen ; Pingrong Yu ; Joseph M. Luther ; Qing Song ; Wyatt K. Metzger ; Randy J. Ellingson ; Arthur J. Nozik
- 刊名：Nano Letters
- 出版年：2007
- 出版时间：August 2007
- 年：2007
- 卷：7
- 期：8
- 页码：2506 - 2512
- 全文大小：283K
- 年卷期：v.7,no.8(August 2007)
- ISSN：1530-6992
文摘
Multiple exciton generation (MEG) is a process whereby multiple electron-hole pairs, or excitons, are produced upon absorption of a singlephoton in semiconductor nanocrystals (NCs) and represents a promising route to increased solar conversion efficiencies in single-junctionphotovoltaic cells. We report for the first time MEG yields in colloidal Si NCs using ultrafast transient absorption spectroscopy. We find thethreshold photon energy for MEG in 9.5 nm diameter Si NCs (effective band gap 
images/entities/equiv.gif"> Eg = 1.20 eV) to be 2.4 ± 0.1Eg and find an exciton-production quantum yield of 2.6 ± 0.2 excitons per absorbed photon at 3.4Eg. While MEG has been previously reported in direct-gap semiconductorNCs of PbSe, PbS, PbTe, CdSe, and InAs, this represents the first report of MEG within indirect-gap semiconductor NCs. Furthermore, MEGis found in relatively large Si NCs (diameter equal to about twice the Bohr radius) such that the confinement energy is not large enough toproduce a large blue-shift of the band gap (only 80 meV), but the Coulomb interaction is sufficiently enhanced to produce efficient MEG. Ourfindings are of particular importance because Si dominates the photovoltaic solar cell industry, presents no problems regarding abundanceand accessibility within the Earth's crust, and poses no significant environmental problems regarding toxicity.