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 journalArticlepeer-review

142 Scopus Citations

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 languageAmerican English
Pages (from-to)3078-3085
Number of pages8
JournalNano Letters
Volume13
Issue number7
DOIs
StatePublished - 10 Jul 2013

NREL Publication Number

  • NREL/JA-5900-58777

Keywords

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

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