Abstract
This paper describes the ultrafast decay of the band-edge exciton in PbS quantum dots (QDs) through simultaneous recombination of the excitonic hole and electron with the surface localized ion pair formed upon adsorption of tetracyanoquinodimethane (TCNQ). Each PbS QD (R = 1.8 nm) spontaneously reduces up to 17 TCNQ molecules upon adsorption of the TCNQ molecule to a sulfur on the QD surface. The photoluminescence of the PbS QDs is quenched in the presence of the reduced TCNQ species through ultrafast (≤15-ps) non-radiative decay of the exciton; the rate constant for the decay process increases approximately linearly with the number of adsorbed, reduced TCNQ molecules. Near-infrared and mid-infrared transient absorption show that this decay occurs through simultaneous transfer of the excitonic electron and hole, and is assigned to a four-carrier, concerted charge recombination mechanism based on the observations that (i) the PL of the QDs recovers when spontaneously reduced TCNQ1- desorbs from the QD surface upon addition of salt, and (ii) the PL of the QDs is preserved when another spontaneous oxidant, ferrocinium, which cannot participate in charge transfer in its reduced state, is substituted for TCNQ.
Original language | English (US) |
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Pages (from-to) | 46-53 |
Number of pages | 8 |
Journal | Chemical Physics |
Volume | 471 |
DOIs | |
State | Published - Jun 1 2016 |
Funding
This research was supported as part of the Argonne-Northwestern Solar Energy Research (ANSER) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science , Basic Energy Sciences (BES), via Grant DE-SC0001059, and by the National Science Foundation through a Graduate Research Fellowship to K.E. (DGE-1324585). Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors(s) and do not necessarily reflect the views of the National Science Foundation. FTIR was performed in the Keck-II facility of NUANCE Center at Northwestern University. The NUANCE Center is supported by the International Institute for Nanotechnology , MRSEC (NSF DMR-1121262), the Keck Foundation, the State of Illinois, and Northwestern University. The authors thank Michael Mattei for his help in performing bulk electrolysis experiments, and Dr. Christopher Thompson for helpful discussions.
Keywords
- PbS quantum dot
- Simultaneous electron and hole transfer
- TCNQ
ASJC Scopus subject areas
- General Physics and Astronomy
- Physical and Theoretical Chemistry