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      Observation of biexcitons in nanocrystal solids in the presence of photocharging

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      Author(s)
      Cihan, A. F.
      Martinez, P. L. H.
      Kelestemur Y.
      Mutlugun, E.
      Demir, Hilmi Volkan
      Date
      2013
      Source Title
      ACS Nano
      Print ISSN
      1936-0851
      Publisher
      American Chemical Society
      Volume
      7
      Issue
      6
      Pages
      4799 - 4809
      Language
      English
      Type
      Article
      Item Usage Stats
      227
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      260
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      Abstract
      T In nanocrystal quantum dots (NQDs), generating multiexcitons offers an enabling tool for enhancing NQD-based devices. However, the photocharging effect makes understanding multiexciton kinetics in NQD solids fundamentally challenging, which is critically important for solid-state devices. To date, this lack of understanding and the spectral temporal aspects of the multiexciton recombination still remain unresolved in solid NQD ensembles, which is mainly due to the confusion with recombination of carriers in charged NQDs. In this work, we reveal the spectral temporal behavior of biexcitons (BXs) in the presence of photocharging using near-unity quantum yield CdSe/CdS NQDs exhibiting substantial suppression of Auger recombination. Here, recombinations of biexcitons and single excitons (Xs) are successfully resolved in the presence of trions in the ensemble measurements of time-correlated single-photon counting at variable excitation intensities and varying emission wavelengths. The spectral behaviors of BXs and Xs are obtained for three NQD samples with different core sizes, revealing the strength tunability of the X X interaction energy in these NQDs. The extraction of spectrally resolved X, BX, and trion kinetics, which are otherwise spectrally unresolved, is enabled by our approach introducing integrated time-resolved fluorescence. The results are further experimentally verified by cross-checking excitation intensity and exposure time dependencies as well as the temporal evolutions of the photoluminescence spectra, all of which prove to be consistent. The BX and X energies are also confirmed by theoretical calculations. These findings fill an important gap in understanding the spectral dynamics of multiexcitons in such NQD solids under the influence of photocharging effects, paving the way to engineering of multiexciton kinetics in nanocrystal optoelectronics, including NQD-based lasing, photovoltaics, and photodetection.
      Keywords
      Semiconductor Quantum Dots
      Multiexciton Generation
      Multiexciton Recombination
      Biexciton
      Trion
      Time-resolved Fluorescence
      Permalink
      http://hdl.handle.net/11693/11254
      Published Version (Please cite this version)
      http://dx.doi.org/10.1021/nn305259g
      Collections
      • Department of Electrical and Electronics Engineering 4011
      • Department of Physics 2550
      • Institute of Materials Science and Nanotechnology (UNAM) 2258
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