Size and composition dependent multiple exciton generation efficiency in PbS, PbSe, and PbSxSe1-x alloyed quantum dots

Aaron G. Midgett, Joseph M. Luther, John T. Stewart, Danielle K. Smith, Lazaro A. Padilha, Victor I. Klimov, Arthur J. Nozik, Matthew C. Beard

Research output: Contribution to journalArticle

107 Citations (Scopus)

Abstract

Using ultrafast transient absorption and time-resolved photoluminescence spectroscopies, we studied multiple exciton generation (MEG) in quantum dots (QDs) consisting of either PbSe, PbS, or a PbSxSe1-x alloy for various QD diameters with corresponding bandgaps (Eg) ranging from 0.6 to 1 eV. For each QD sample, we determine the MEG efficiency, ηMEG, defined in terms of the electron-hole pair creation energy (εeh) such that ηMEG = Eg/ εeh. In previous reports, we found that ηMEG is about two times greater in PbSe QDs compared to bulk PbSe, however, little could be said about the QD-size dependence of MEG. In this study, we find for both PbS and PbSxSe1-x alloyed QDs that ηMEG decreases lineally with increasing QD diameter within the strong confinement regime. When the QD radius is normalized by a material-dependent characteristic radius, defined as the radius at which the electron-hole Coulomb and confinement energies are equivalent, PbSe, PbS, and PbSxSe1-x exhibit similar MEG behaviors. Our results suggest that MEG increases with quantum confinement, and we discuss the interplay between a size-dependent MEG rate versus hot exciton cooling.

Original languageEnglish
Pages (from-to)3078-3085
Number of pages8
JournalNano letters
Volume13
Issue number7
DOIs
Publication statusPublished - Jul 10 2013

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Keywords

  • Multiple exciton generation
  • PbS quantum dots
  • carrier multiplication
  • exciton dynamics
  • quantum size effects
  • solar energy conversion

ASJC Scopus subject areas

  • Bioengineering
  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanical Engineering

Cite this

Midgett, A. G., Luther, J. M., Stewart, J. T., Smith, D. K., Padilha, L. A., Klimov, V. I., Nozik, A. J., & Beard, M. C. (2013). Size and composition dependent multiple exciton generation efficiency in PbS, PbSe, and PbSxSe1-x alloyed quantum dots. Nano letters, 13(7), 3078-3085. https://doi.org/10.1021/nl4009748