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Highly efficient multiple exciton generation in colloidal PbSe and PbS quantum dots.

Randy J Ellingson1, Matthew C Beard, Justin C Johnson

  • 1Center for Basic Sciences, National Renewable Energy Laborarory, Golden, Colorado 80401, USA. randy_ellington@nrel.gov

Nano Letters
|May 12, 2005
PubMed
Summary

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Ultra-efficient multiple exciton generation (MEG) in quantum dots (QDs) creates multiple excitons from a single photon. This study demonstrates MEG in PbSe and PbS QDs with quantum yields up to 300%.

Area of Science:

  • Materials Science
  • Nanotechnology
  • Physical Chemistry

Background:

  • Quantum dots (QDs) exhibit unique optical properties due to quantum confinement.
  • Multiple Exciton Generation (MEG) is a process where a single high-energy photon generates more than one electron-hole pair (exciton).
  • Efficient MEG in QDs is crucial for next-generation solar cells and photodetectors.

Purpose of the Study:

  • To investigate and report ultra-efficient multiple exciton generation (MEG) in colloidal lead selenide (PbSe) and lead sulfide (PbS) quantum dots.
  • To characterize the MEG process using transient absorption spectroscopy across various probe energies.
  • To develop a new theoretical model for MEG based on the coherent superposition of excitonic states.

Main Methods:

  • Transient absorption spectroscopy was employed to study MEG.

Related Experiment Videos

  • Measurements were conducted using both intraband and interband probe energies.
  • Experimental and theoretical calculations of size-dependent interband transition energies for PbSe QDs were performed.

    • Main Results:

    • Quantum yields of 300% were achieved for PbSe QDs, indicating the creation of approximately three excitons per absorbed photon.
    • The threshold photon energy for MEG was found to be twice the QD energy gap.
    • The biexciton effect was observed to influence transient absorption data, particularly near the lowest interband transition.

    Conclusions:

    • Colloidal PbSe and PbS QDs exhibit ultra-efficient MEG, paving the way for enhanced optoelectronic devices.
    • The study provides a deeper understanding of the MEG mechanism, including the role of the biexciton effect.
    • A novel model for MEG based on excitonic state superposition offers new theoretical insights.