Multiple Exciton Generation in Colloidal Silicon Nanocrystals

doi:https://doi.org/10.1021/nl071486l

Title: Multiple Exciton Generation in Colloidal Silicon Nanocrystals

Full Record
Other Related Research

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 »« less

Authors:: Beard, M C; Knutsen, K P; Yu, P; Luther, J M; Song, Q; Metzger, W K; Ellingson, R J; Nozik, A M

Publication Date:: 2007-01-01

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.

Copy to clipboard


                    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

Copy to clipboard


                    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.

Copy to clipboard


                    
@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}

}

Copy to clipboard

Journal Article:

https://doi.org/10.1021/nl071486l

Other availability

Find in Google Scholar

Search WorldCat to find libraries that may hold this journal

Save / Share:

Export Metadata

Save to My Library

Similar records in OSTI.GOV collections:

Atomistic Time-Domain Simulations of Light-Harvesting and Charge-Transfer Dynamics in Novel Nanoscale Materials for Solar Hydrogen Production.

Other Prezhdo, Oleg V

Funded by the DOE grant (i) we continued to study and analyze the atomistic detail of the electron transfer (ET) across the chromophore-TiO2 interface in Gratzel cell systems for solar hydrogen production. (ii) We extensively investigated the nature of photoexcited states and excited state dynamics in semiconductor quantum dots (QD) designed for photovoltaic applications. (iii) We continued a newly initiated research direction focusing on excited state properties and electron-phonon interactions in nanoscale carbon materials. Over the past year, the results of the DOE funded research were summarized in 3 review articles. 12 original manuscripts were written. The research results weremore »« less
Full Text Available
Variations in the Quantum Efficiency of Multiple Exciton Generation for a Series of Chemically Treated PbSe Nanocrystal Films

Journal Article Beard, M C ; Midgett, A G ; Law, M ; ... - Nano Letters

We study multiple exciton generation (MEG) in two series of chemically treated PbSe nanocrystal (NC) films. We find that the average number of excitons produced per absorbed photon varies between 1.0 and 2.4 ({+-} 0.2) at a photon energy of {approx}4E{sub g} for films consisting of 3.7 nm NCs and between 1.1 and 1.6 ({+-} 0.1) at hv {approx}5E{sub g} for films consisting of 7.4 nm NCs. The variations in MEG depend upon the chemical treatment used to electronically couple the NCs in each film. The single and multiexciton lifetimes also change with the chemical treatment: biexciton lifetimes increase withmore »« less
https://doi.org/10.1021/nl803600v
Multiple Exciton Generation in PbSe Quantum Dots and Quantum Dot Solar Cells

Conference Beard, M. C. ; Semonin, O. E. ; Nozik, A. J. ; ...

Multiple exciton generation in quantum dots (QDs) has been intensively studied as a way to enhance solar energy conversion by channeling the excess photon energy (energy greater than the bandgap) to produce multiple electron-hole pairs. Among other useful properties, quantum confinement can both increase Coulomb interactions that drive the MEG process and decrease the electron-phonon coupling that cools hot-excitons in bulk semiconductors. We have demonstrated that MEG in PbSe QDs is about two times as efficient at producing multiple electron-hole pairs than bulk PbSe. I will discuss our recent results investigating MEG in PbSe, PbS and PbSxSe1-x, which exhibits anmore »« less
Approaches to Future Generation Photovoltaics and Solar Fuels: Multiple Exciton Generation in Quantum Dots, Quantum Dot Arrays, Molecular Singlet Fission, and Quantum Dot Solar Cells

Conference Nozik, Arthur J. ; Beard, Matt C. ; Johnson, Justin C. ; ...

One potential, long-term approach to more efficient future generation solar cells is to utilize the unique properties of quantum dots (QDs) and unique molecular chromophores to control the relaxation pathways of excited states to produce enhanced conversion efficiency through efficient multiple electron-hole pair generation from single photons . We have observed efficient multiple exciton generation (MEG) in PbSe, PbS, PbTe, and Si QDs and efficient singlet fission (SF) in molecules that satisfy specific requirements for their excited state energy level structure to achieve carrier multiplication. We have studied MEG in close-packed QD arrays where the QDs are electronically coupled inmore »« less
Quantum Dot Solar Cells: High Efficiency through Multiple Exciton Generation

Conference Hanna, M C ; Ellingson, R J ; Beard, M ; ...

Impact ionization is a process in which absorbed photons in semiconductors that are at least twice the bandgap can produce multiple electron-hole pairs. For single-bandgap photovoltaic devices, this effect produces greatly enhanced theoretical thermodynamic conversion efficiencies that range from 45-85%, depending upon solar concentration, the cell temperature, and the number of electron-hole pairs produced per photon. For quantum dots (QDs), electron-hole pairs exist as excitons. We have observed astoundingly efficient multiple exciton generation (MEG) in QDs of PbSe (bulk Eg = 0.28 eV), ranging in diameter from 3.9 to 5.7nm (Eg = 0.73, 0.82, and 0.91 eV, respectively). The effectivemore »« less
Full Text Available

Similar Records