Excitons - Centro de Ciencias de Benasque Pedro SPP rE rdr ... A substantial fraction of excitons that

  • View
    213

  • Download
    0

Embed Size (px)

Text of Excitons - Centro de Ciencias de Benasque Pedro SPP rE rdr ... A substantial fraction of excitons...

  • Excitons +Solarcells

    Ultrafastcoherentchargeandenergytransferinplasmonicandlightharvestingsystems:Takingmoviesofelectronic

    motioninnanosystems

    RalfVogelgesang1,SarahM.Falke1, Antonietta DeSio1,CarloA.Rozzi3,ElisaMolinari3,AngelRubio4,

    DanieleBrida2,GiulioCerullo2,JensChristoffers1, ChristophLienau1

    Nanolight 2014,Benasque02.03.2014

    (1) (2) (3) (4)

  • LighttoCurrent ConversioninanArtificial LightHarvesting System

    C. A. Rozzi et al., Nature Comm., 4, 1602 (2013).

  • CaseI:stronglycoupledExciton+SPP

  • J. Bellessa et al., PRL 93, 036404 (2006)J. Dintinger et al., PRB 71, 035424 (2005)

    P. Vasa et al., PRL 101, 116801 (2008)T. Schwartz et al., PRL 106, 196405 (2011)

    Angle-resolved transmission spectra

    Strong exciton-SPP coupling Ultrastrong coupling regime Switching capability Dynamics ??? Nanostructures ???

    Photochromic moleculesonsilverfilms

  • 2,2'-dimethyl-8-phenyl-5,6,5',6'-dibenzothiacarbocyanine chloride

    Narrow absorption spectrum

    Linear optical properties

    Ground state

    One exciton aggregate state

    Dipole moment: 100D per exciton

    1

    0

    Two level system

    Without grating

    Broad band laser pulse

    Angle depedent Reflectivity(R)

    Jaggregated(cyanine)dye

  • Nanostructuredgoldgratings:SPPresonators

    Grating parametersoptimized for long SPP lifetimes

    Angle resolved linear reflectivity

    Nano-slit array on metal surface

    Incident pulseReflected pulse

    Reflectivity of a nano-slit array on gold film

  • Electric field distributions inside the nanostructures

    R X SPPr E r dr

    Rabi splitting energy Vacuum field strength per mode

    VESPP

    0

    Electricfield localization innanoslit arrays

  • LinearopticsofmetalJaggregatehybridstructures

    Exciton (X) and SPP coupled via optical dipole interaction

    Mode overlap and dipole coupling:Polariton formation

    Molecular aggregate coated gold grating

    Incident pulseReflected pulse

    SPP

    X

    k ()

    R 1s

    tBr

    illoui

    nzo

    ne

    1st

    Brillo

    uin

    zone

    Coupled X-SPP mode formation

    SPP

    X-SPP UP

    X-SPP LP

    RX

    P. Vasa et al., ACS Nano 4, 7759 (2010)

  • Rabi splitting energy of ~60 meVA substantial fraction of excitons that do not couple to SPP

    Linearreflectivity:Strong coupling betweenexcitons andsurface plasmonpolaritons

    grating constant: a0 = 430 nm

  • www.youtube.com

    ExcitonSPP dynamicsinthe strong coupling regime

  • ExcitonSPPcoupling:Timedomainrepresentation

    UP

    LP

    Ultrafast excitation

    Exciton

    Plasmon

    Time

    Num

    ber d

    ensi

    ty (n

    )

    Periodic exchange of electromagnetic energy between excitons and surface plasmon polaritons

  • RealtimeobservationofRabioscillationsUP

    LP

    First real-time observation of Rabi oscillations between excitons and plasmons

    Strong reduction in radiative lifetime

    P. Vasa et. al, Nature Photonics 7, 128 (2013)

  • Densitymatrixsimulations

    Exciton creation (population nx) reduces the Rabi splitting!

    Experiment

    0 1R R Xt n t Parametric variation of the Rabi frequency

    P. Vasa et al., ACS Nano 4, 7559 (2010)

    Simulation

  • UP/LPRabioscillations

    UP

    LP

  • SPPExcitonicMatter(Colorcenters,Quantumdots)

    Input(Source)

    Output(Drain)

    Control pulse(Gate)

    |g>

    |e>

    2LevelSystem

    OutlookCase I:OpticalTransistor

  • Case II:Organic Solars CellsasLightHarvesting Systems

    Polymer Fullerene

    Anode

    Cathode

    LUMOAcceptor

    HOMOAcceptor

    LUMODonor

    HOMODonorEnergy

    ++

    --

    -

    h

    1

    23

    3

    ~50fs

    1. Absorption ofaphoton leads tothe formation ofanexcitoninthe polymer2. ExcitonDiffusion toapolymer:acceptor interface (if necessary)3. ExcitonDissociation leading tospatially separated charges4. ChargeTransport tothe electrodes

  • Cc

    OC NH

    -carotene:hole stabilization(hole acceptor)

    porphyrin:light absorption

    fullerene:electron acceptor

    C. A. Rozzi, S. M. Falke et al., Nature Comm 4, 1602 (2013).

    Asupramoleculartriad:anartificial modelsystem mimicking solarenergy conversion

  • Courtesy:NicolaSpallanzani,FrancaManghi andElisaMolinari(UModena)

    Triad:photoinducedcharge transferdynamics

  • Triad

    Porphyrin-Fullerene Diad

    Porphyrin

    s. also G. Kodis et al, J. Phys. Org. Chem. 17, 724 (2004).

    Triad:absorption spectra

  • Ultrafast pumpprobe spectroscopy ofsupramoleculartriad

    Excitation centered at540nm(2.296eV)

    Wavelength

    (nm)

  • PumpProbeTrace ( T/T)ofTriad(Excitation onthe porphyrin)

    CT!

    The carotenemoiety oscillates

  • Analysisofthe carotene oscillations

    CT!Methyl rocking

    mode(1003 cm-1)

    C-C stretch(1155 cm-1) C=C stretch

    (1523 cm-1)

  • Analysisofthe carotene oscillations

    Now that we understand the carotene oscillations we can safely remove them from the data

  • PumpProbeTrace ( T/T)ofTriad(Excitation onthe porphyrin)

    CT!

  • PumpProbeTrace ( T/T)ofTriad(Excitation onthe porphyrin)

    CT!

    Coherent oscillations ofthe resonance wavelengthofthe charge transfer band

  • Coherent charge oscillations

    CT!

    DFTCalculations Comparison ExperimentDFT

    Time delay (fs)

    C. A. Rozzi, S. M. Falke et al., Nature Comm 4, 1602 (2013).

  • Coherent dynamics DFTSimulations

    C. A. Rozzi, S. M. Falke et al., Nature Comm 4, 1602 (2013).

  • Coherent dynamics DFTSimulations

    Linkergroups locked

  • Qualitativepicture for the electron transfer

    The coupling between electronic andnuclear degrees offreedom is important

  • Coherent dynamics DFTSimulations

    Motionofthe ionic lattice

  • Twodifferentcasestudiesforquantumcoherentchargetransferdynamics

    SupramolecularCPC60triad(covalentlybound)

    OrganicsolarcellP3HT/PCBM(noncovalentlybound)

    Thequantumcoherentcouplingbetweenelectronsandnucleiisofcentralimportanceforthechargetransferinartificiallightharvestingandorganicsolarcellsystems

    C.A.Rozzietal.,Nat.Comm.4,1602(2013)S.M.Falkeetal.,submitted (2014)

    SummaryCaseII:LightHarvesting

  • UltrafastUltrafastNanoopticsNanooptics

    Thank you!Thank you!