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

doi:10.1021/nl4009748

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

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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 PbS_xSe_1-x alloy for various QD diameters with corresponding bandgaps (E_g) ranging from 0.6 to 1 eV. For each QD sample, we determine the MEG efficiency, η_MEG, defined in terms of the electron-hole pair creation energy (ε_eh) such that η_MEG = E_g/ ε_eh. In previous reports, we found that η_MEG 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 PbS_xSe_1-x alloyed QDs that η_MEG 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 PbS_xSe_1-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 language	American English
Pages (from-to)	3078-3085
Number of pages	8
Journal	Nano Letters
Volume	13
Issue number	7
DOIs	https://doi.org/10.1021/nl4009748 https://doi.org/10.1021/nl4009748
State	Published - 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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title = "Size and Composition Dependent Multiple Exciton Generation Efficiency in PbS, PbSe, and PbSxSe1-x Alloyed Quantum Dots",

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.",

keywords = "carrier multiplication, exciton dynamics, Multiple exciton generation, PbS quantum dots, quantum size effects, solar energy conversion",

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

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AU - Midgett, Aaron G.

AU - Luther, Joseph M.

AU - Stewart, John T.

AU - Smith, Danielle K.

AU - Padilha, Lazaro A.

AU - Klimov, Victor I.

AU - Nozik, Arthur J.

AU - Beard, Matthew C.

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N2 - 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.

AB - 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.

KW - carrier multiplication

KW - exciton dynamics

KW - Multiple exciton generation

KW - PbS quantum dots

KW - quantum size effects

KW - solar energy conversion

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JO - Nano Letters

JF - Nano Letters

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ER -

Size and Composition Dependent Multiple Exciton Generation Efficiency in PbS, PbSe, and PbSxSe1-x Alloyed Quantum Dots

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