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Title: Multiple Exciton Generation in Colloidal Silicon Nanocrystals

Abstract

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 {identical_to} Eg = 1.20 eV) to be 2.4 {+-} 0.1E{sub g} and find an exciton-production quantum yield of 2.6 {+-} 0.2 excitons per absorbed photon at 3.4E{sub g}. 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 withinmore » the Earth's crust, and poses no significant environmental problems regarding toxicity.« less

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
982283
DOE Contract Number:  
AC36-08GO28308
Resource Type:
Journal Article
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 7; Journal Issue: 8, 2007
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 77 NANOSCIENCE AND NANOTECHNOLOGY; ABSORPTION; ABSORPTION SPECTROSCOPY; ABUNDANCE; CONFINEMENT; CONVERSION; ENERGY; EXCITONS; INDUSTRY; INTERACTIONS; MERCAPTOETHYLGUANIDINE; PHOTONS; PHOTOVOLTAIC CELLS; SILICON; SOLAR CELLS; TOXICITY; TRANSIENTS; YIELDS; Basic Sciences

Citation Formats

Beard, M C, Knutsen, K P, Yu, P, Luther, J M, Song, Q, Metzger, W K, Ellingson, R J, and Nozik, A M. Multiple Exciton Generation in Colloidal Silicon Nanocrystals. United States: N. p., 2007. Web. doi:10.1021/nl071486l.
Beard, M C, Knutsen, K P, Yu, P, Luther, J M, Song, Q, Metzger, W K, Ellingson, R J, & Nozik, A M. Multiple Exciton Generation in Colloidal Silicon Nanocrystals. United States. https://doi.org/10.1021/nl071486l
Beard, M C, Knutsen, K P, Yu, P, Luther, J M, Song, Q, Metzger, W K, Ellingson, R J, and Nozik, A M. Mon . "Multiple Exciton Generation in Colloidal Silicon Nanocrystals". United States. https://doi.org/10.1021/nl071486l.
@article{osti_982283,
title = {Multiple Exciton Generation in Colloidal Silicon Nanocrystals},
author = {Beard, M C and Knutsen, K P and Yu, P and Luther, J M and Song, Q and Metzger, W K and Ellingson, R J and Nozik, A M},
abstractNote = {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 {identical_to} Eg = 1.20 eV) to be 2.4 {+-} 0.1E{sub g} and find an exciton-production quantum yield of 2.6 {+-} 0.2 excitons per absorbed photon at 3.4E{sub g}. 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.},
doi = {10.1021/nl071486l},
url = {https://www.osti.gov/biblio/982283}, journal = {Nano Letters},
number = 8, 2007,
volume = 7,
place = {United States},
year = {2007},
month = {1}
}