skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Electron–hole exchange blockade and memory-less recombination in photoexcited films of colloidal quantum dots

Authors:
; ;
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Center for Advanced Solar Photophysics (CASP)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1388328
DOE Contract Number:
AC52-06NA25396
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nature Physics; Journal Volume: 13; Journal Issue: 6; Related Information: CASP partners with Los Alamos National Laboratory (lead); University of California, Irvine; University of Colorado; Colorado School of Mines; George Mason University; Los Alamos National Laboratory; University of Minnesota; National Renewable Energy Laboratory
Country of Publication:
United States
Language:
English
Subject:
solar (photovoltaic), solar (fuels), solid state lighting, bio-inspired, electrodes - solar, defects, charge transport, materials and chemistry by design, optics, synthesis (novel materials), synthesis (scalable processing)

Citation Formats

Fidler, Andrew F., Gao, Jianbo, and Klimov, Victor I.. Electron–hole exchange blockade and memory-less recombination in photoexcited films of colloidal quantum dots. United States: N. p., 2017. Web. doi:10.1038/nphys4073.
Fidler, Andrew F., Gao, Jianbo, & Klimov, Victor I.. Electron–hole exchange blockade and memory-less recombination in photoexcited films of colloidal quantum dots. United States. doi:10.1038/nphys4073.
Fidler, Andrew F., Gao, Jianbo, and Klimov, Victor I.. Mon . "Electron–hole exchange blockade and memory-less recombination in photoexcited films of colloidal quantum dots". United States. doi:10.1038/nphys4073.
@article{osti_1388328,
title = {Electron–hole exchange blockade and memory-less recombination in photoexcited films of colloidal quantum dots},
author = {Fidler, Andrew F. and Gao, Jianbo and Klimov, Victor I.},
abstractNote = {},
doi = {10.1038/nphys4073},
journal = {Nature Physics},
number = 6,
volume = 13,
place = {United States},
year = {Mon Mar 20 00:00:00 EDT 2017},
month = {Mon Mar 20 00:00:00 EDT 2017}
}
  • An electron paramagnetic resonance (EPR) study of photoexcited colloidal InP quantum dots (QD) shows the formation of electron and hole adducts. An EPR signal at g = 0.58 is assigned to a nonradiative hole trap that does not form immediately upon illumination, but forms only after the illuminated sample ages and becomes stabilized at room temperature; it then becomes permanent at the InP QD surface. This signal completely disappears upon electron injection into the QD from a reducing agent (sodium biphenyl). Light immediately quenches the signal at g = 0.58, and it re-forms reversibly when the light is turned off.more » A signal at g = 2.055 is assigned to electron surface traps, and it appears in nonetched QD samples; it completely disappears after etching with HF. A signal at g = 2.001 has a very narrow line width and is assigned to delocalized mobile holes that are located in the QD core. A defect model for InP QDs is proposed based on the EPR results reported here plus results from optically detected magnetic resonance experiments reported separately.« less
  • Excitons in quantum dots manifest a lower-energy spin-forbidden 'dark' state below a spin-allowed 'bright' state; this splitting originates from electron-hole (e-h) exchange interactions, which are strongly enhanced by quantum confinement. The e-h exchange interaction may have both a short-range and a long-range component. Calculating numerically the e-h exchange energies from atomistic pseudopotential wave functions, we show here that in direct-gap quantum dots (such as InAs) the e-h exchange interaction is dominated by the long-range component, whereas in indirect-gap quantum dots (such as Si) only the short-range component survives. As a result, the exciton dark/bright splitting scales as 1/R{sup 2} inmore » InAs dots and 1/R{sup 3} in Si dots, where R is the quantum-dot radius.« less
  • Excitonic spectra are calculated for free-standing, surface passivated, InAs quantum dots using atomic pseudopotentials for the single-particle states and screened Coulomb interactions for the two-body terms. We present an analysis of the single particle states involved in each excitation in terms of their angular momenta and Bloch-wave parentage. We find that (i) in agreement with other pseudopotential studies of CdSe and InP quantum dots, but in contrast to k{center_dot}p calculations, the dot wave functions exhibit strong odd-even angular momentum envelope function mixing (e.g., s with p) and large valence-conduction coupling. (ii) While the pseudopotential approach produced very good agreement withmore » experiment for free-standing, colloidal CdSe and InP dots, and for self-assembled (GaAs-embedded) InAs dots, here the predicted spectrum does not agree well with the measured (ensemble average over dot sizes) spectra. (1) Our calculated excitonic gap is larger than the photoluminescence measured one, and (2) while the spacing between the lowest excitons is reproduced, the spacings between higher excitons is not fit well. Discrepancy (1) could result from surface state emission. As for (2), agreement is improved when account is taken of the finite-size distribution in the experimental data. (iii) We find that the single-particle gap scales as R{sup -1.01} (not R{sup -2}), that the screened (unscreened) electron-hole Coulomb interaction scales as R{sup -1.79} (R{sup -0.7}), and that the excitonic gap scales as R{sup -0.9}. These scaling laws are different from those expected from simple models. (c) 2000 The American Physical Society.« less