Home  About us  Contact
 

Exciton Diffusion (exciton + diffusion)

Distribution by Scientific Domains
Polymers and Materials Science66%
Physics and Astronomy22%

Terms modified by Exciton Diffusion

  • exciton diffusion length
    		•

    Selected Abstracts

    Study of Energy Transfer and Triplet Exciton Diffusion in Hole-Transporting Host Materials

    ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
    Chao Wu
    Abstract A device structure is used in which the hole-transporting layer (HTL) of an OLED is doped with either fluorescent or phosphorescent emitters, that is, anode/HTL-host/hole blocker/electron-transporting layer/cathode. The HTL hosts have higher HOMO energy allowing holes to be transported without being trapped by dopant molecules, avoiding direct recombination on the dopant. The unconventional mismatch of HOMO energies between host and dopant allow for the study of energy transfer in these host/guest systems and triplet exciton diffusion in the HTL-host layers of OLED devices, without the complication of charge trapping at dopants. The host materials examined here are tetraaryl- p- phenylenediamines. Data shows that Förster energy transfer between these hosts and emissive dopant in devices is inefficient. Triplet exciton diffusion in these host materials is closely related to molecular structure and the degree of intermolecular interaction. Host materials that contain naphthyl groups demonstrate longer triplet exciton diffusion lengths than those with phenyl substituents, consistent with DFT calculations and photophysical measurements. [source]

    Exciton,Exciton Annihilation in Mixed-Phase Polyfluorene Films

    ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010
    Paul E. Shaw
    Abstract Singlet,singlet annihilation is studied in polyfluorene (PFO) films containing different fractions of , -phase chains using time-resolved fluorescence. On a timescale of >15,ps after excitation, the results are fitted well by a time-independent annihilation rate, which indicates that annihilation is controlled by 3D exciton diffusion. A time-dependent annihilation rate is observed during the first 15,ps in the glassy phase and in the , -phase rich films, which can be explained by the slowdown of exciton diffusion after excitons reach low-energy sites. The annihilation rate in the mixed-phase films increases with increasing fraction of , -phase present, indicating enhanced exciton diffusion. The observed trend agrees well with a model of fully dispersed, -phase chromophores in the surrounding glassy phase with the exciton diffusion described using the line-dipole approximation for an exciton wavefunction extending over 2.5,nm. The results indicate that glassy and, -phase chromophores are intimately mixed rather than clustered or phase-separated. [source]

    Study of Energy Transfer and Triplet Exciton Diffusion in Hole-Transporting Host Materials

    ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
    Chao Wu
    Abstract A device structure is used in which the hole-transporting layer (HTL) of an OLED is doped with either fluorescent or phosphorescent emitters, that is, anode/HTL-host/hole blocker/electron-transporting layer/cathode. The HTL hosts have higher HOMO energy allowing holes to be transported without being trapped by dopant molecules, avoiding direct recombination on the dopant. The unconventional mismatch of HOMO energies between host and dopant allow for the study of energy transfer in these host/guest systems and triplet exciton diffusion in the HTL-host layers of OLED devices, without the complication of charge trapping at dopants. The host materials examined here are tetraaryl- p- phenylenediamines. Data shows that Förster energy transfer between these hosts and emissive dopant in devices is inefficient. Triplet exciton diffusion in these host materials is closely related to molecular structure and the degree of intermolecular interaction. Host materials that contain naphthyl groups demonstrate longer triplet exciton diffusion lengths than those with phenyl substituents, consistent with DFT calculations and photophysical measurements. [source]

    Exciton Diffusion Measurements in Poly(3-hexylthiophene),

    ADVANCED MATERIALS, Issue 18 2008
    Paul E. Shaw
    The problem of making reliable measurements of exciton diffusion lengths in organic semiconductors is addressed. The exciton diffusion length is an extremely important quantity in the operation of organic solar cells. We focus on the polymer P3HT because of its widespread use in solar cells and are able to fit the exciton diffusion in a range of films with a single diffusion constant, showing that our approach is particularly robust. [source]

    Effect of nanoscale confinement on fluorescence of MEH-PPV/MCM-41 composite

    PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2010
    German M. Telbiz
    Abstract Fluorescence spectra and kinetics of poly(2-methoxy-5-(2,-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV)/MCM41 silica composite have been analyzed at different temperatures and compared with fluorescence properties of MEH-PPV solutions and spin coated films. As follows from this comparison, the composite possesses significantly wider fluorescence spectra, longer fluorescence relaxation and weaker temperature dependence of its intensity. These peculiarities are explained in terms of the reduced exciton diffusion and an increased torsional disorder of polymer chains embedded in pores. [source]

    Exciton dynamics in quantum nano-structures of II,VI diluted magnetic semiconductors fabricated by electron-beam lithography

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004
    A. Uetake
    Abstract Exciton dynamics in quantum dots (QDs) of II,VI diluted magnetic semiconductors (DMSs) has been studied by using an electron-beam lithography technique. The peak energy of excitonic photoluminescence in the QDs shows blue shifts up to 3.5 meV toward the dot diameter of 20 nm, indicating a lateral confinement effect for the exciton. The time-dependent energy shift of the exciton due to the localization is small as 2.9 meV, which originates from the suppression of the exciton diffusion due to the finite dot structure. The coupled QDs composed of a DMS magnetic well (MW) and a non-magnetic well (NW) were sucessfully fabricated, where the exciton energy in the NW was designed to be lower than that in the MW. The spin-polarized excitons migrate from the MW to the NW in magnetic fields and the exciton spin injection is demonstrated in the coupled QDs. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Interface-tailored and nanoengineered polymeric materials for (opto)electronic devices

    POLYMER INTERNATIONAL, Issue 6 2009
    Hong Ma
    Abstract For plastic (opto)electronic devices such as light-emitting diodes (LEDs), photovoltaic (PV) cells and field-effect transistors (FETs), the processes of charge (hole/electron) injection, charge transport, charge recombination (exciton formation), charge separation (exciton diffusion and dissociation) and charge collection are critical to enhance their performance. Most of these processes are relevant to nanoscale and interfacial phenomena. In this review, we highlight the state-of-the-art developments of interface-tailored and nanoengineered polymeric materials to optimize the performance of (opto)electronic devices. These include (1) interfacial engineering of anode and cathode for polymer LEDs; (2) nanoengineered (C60 and inorganic semiconductor nanoparticles) ,-conjugated polymeric materials for PV cells; and (3) polymer and monolayer dielectrics/interfaces for FETs and light-emitting and nano-FETs. Copyright © 2009 Society of Chemical Industry [source]

    Exciton Migration in Conjugated Dendrimers: A Joint Experimental and Theoretical Study

    CHEMPHYSCHEM, Issue 18 2009
    Muhammet E. Köse Prof.
    Abstract We report a joint experimental and theoretical investigation of exciton diffusion in phenyl-cored thiophene dendrimers. Experimental exciton diffusion lengths of the dendrimers vary between 8 and 17 nm, increasing with the size of the dendrimer. A theoretical methodology is developed to estimate exciton diffusion lengths for conjugated small molecules in a simulated amorphous film. The theoretical approach exploits Fermi's Golden Rule to estimate the energy transfer rates for a large ensemble of bimolecular complexes in random relative orientations. Utilization of Poisson's equation in the evaluation of the Coulomb integral leads to very efficient calculation of excitonic couplings between the donor and the acceptor chromophores. Electronic coupling calculations with delocalized transition densities revealed efficient coupling pathways in the bulk of the material, but do not result in strong couplings between the chromophores which are calculated for more localized transition densities. The molecular structures of dendrimers seem to be playing a significant role in the magnitude of electronic coupling between chromophores. Simulated diffusion lengths correlate well with the experimental data. The chemical structure of the chromophore, the shape of the transition densities and the exciton lifetime are found to be the most important factors in determining the size of the exciton diffusion length in amorphous films of conjugated materials. [source]