讲稿20-有机发光二极管-第八部分课件

OrganicLEDs–part8

ExcitonDynamicsinDisorderedOrganicThinFilms

QuantumDotLEDsHandoutonQD-LEDs:Coeetal.,Nature420,800(2002).April29,2003–OrganicOptoelectronics-Lecture20b1OrganicLEDs–part8ExcitonExcitonDynamicsinTimeDependantPL2ExcitonDynamicsinTimeDepenDynamicSpectralShiftsofDCM2inAlq3•MeasurementperformedondopedDCM2:Alq3films•Excitationatλ=490nm(onlyDCM2absorbs)~DCM2PLredshifts>20nmover6ns~Wavelength[nm]3DynamicSpectralShiftsofDCMTimeEvolutionof4%DCM2inAlq3PLSpectrum4TimeEvolutionof4%DCM2inAElectronicProcessesinMoleculesdensityofavailableS1orT1states5ElectronicProcessesinMolecuTimeEvolutionofDCM2SolutionPLSpectra6TimeEvolutionofDCM2SolutioSpectralShiftdueto~ExcitonDiffusion~~IntermolecularSolidStateInteractions~7SpectralShiftdueto~ExcitonExcitonicEnergyVariations8ExcitonicEnergyVariations8ExcitonDistributionintheExcitedState(S1orT1)~TimeEvolvedExcitonThermalization~EXCITONDIFFUSIONLEADSTOREDUCTIONINFWHM9ExcitonDistributionintheEx101011111212TimeEvolutionofPeakPLinNeatThinFilms13TimeEvolutionofPeakPLinNParametersforSimulatingExcitonDiffusionobservedradiativelifetime(τ)NormalizedIntegratedSpectralIntensityFörsterradius(RF)►Assignvalueforallowedtransfers:►AssumeGaussianshapeofwidth,wDOS►CenteratpeakofinitialbulkPLspectrum►MolecularPLspectrumimplied…excitonicdensityofstates(gex(E))14ParametersforSimulatingExciFittingSimulationtoExperiment–DopedFilms•Goodfitspossibleforalldatasets•RFdecreaseswithincreasingdoping,fallingfrom52Åto22Å•wDOSalsodecreaseswithincreasingdoping,rangingfrom0.146eVto0.120eV15FittingSimulationtoExperimeFittingSimulation–NeatFilms•Spectralshiftobservedineachmaterialsystem•MoleculardipoleandwDOSarecorrellated:lowerdipolescorrespondtolessdispersion•Evenwithnodipole,somedispersionexists•Experimentaltechniquegeneral,andyieldsfirstmeasurementsofexcitonicenergydispersioninamorphousorganicsolids16FittingSimulation–NeatFilmTemporalSolidStateSolvationuponexcitationbothmagnitudeanddirectionoflumophoredipolemomentcanchangeFOREXAMPLEforDCM:µ1–µ0>20Debye!~from5.6Dto26.3D~followingtheexcitationtheenvironmentsurroundingtheexcitedmoleculewillreorganizetominimizetheoverallenergyofthesystem(maximizeµ•Eloc)17TemporalSolidStateSolvationExcitonDistributionintheExcitedState(S1orT1)~TimeEvolvedMolecularReconfiguration~DIPOLE-DIPOLEINTERACTIONLEADSTOENERGYSHIFTINDENSITYOFEXCITEDSTATESlog(Time)18ExcitonDistributionintheExFusionofTwoMaterialSetsHybriddevicescouldenableLEDs,SolarCells,Photodetectors,Modulators,andLaserswhichutilizethebestpropertiesofeachindividualmaterial.EfficientOrganicSemiconductorsFlexibleEmissiveFabricationofrationalstructureshasbeenthemainobstacletodate.19FusionofTwoMaterialSetsHybInorganicNanocrystals–QuantumDotsQuantumDotSIZESyntheticrouteofMurrayetal,J.Am.Chem.Soc.115,8706(1993).20InorganicNanocrystals–QuantFusionofTwoMaterialSetsQuantumDotsOrganicMolecules21FusionofTwoMaterialSetsQuaIntegrationofNanoscaleMaterialsQuantumDotsandOrganicSemiconductorsZnSovercoatingshell(0to5monolayers)OleicAcidorTOPOcapsSyntheticroutesofMurrayetal,J.Am.Chem.Soc.115,8706(1993)andChen,etal,MRSSymp.Proc.691,G10.2.TrioctylphosphineoxideTris(8-hydroxyquinoline)Aluminum(III)3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazoleN,N'-Bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidineN,N'-Bis(3-methylphenyl)-N,N'-bis-(phenyl)-benzidine22IntegrationofNanoscaleMater1.Asolutionofanorganicmaterial,QDs,andsolvent…2.isspin-coatedontoacleansubstrate.3.Duringthesolventdryingtime,theQDsrisetothesurface…4.andself-assembleintograinsofhexagonallyclosepackedspheres.OrganichoststhatdepositasflatfilmsallowforimagingviaAFM,despitetheAFMtipbeingaslargeastheQDs.Phasesegregationisdrivenbyacombinationofsizeandchemistry.PhaseSegregationandSelf-Assembly231.AsolutionofanorganicOrgAstheconcentrationofQDsinthespin-castingsolutionisincreased,thecoverageofQDsonthemonolayerisalsoincreased.MonolayerCoverage–QDconcentration24AstheconcentrationofMonolayCdSe(ZnS)/TOPOPbSe/oleicacidQD-LEDPerformance25CdSe(ZnS)/TOPOPbSe/oleicacidQFullSizeSeriesofPbSeNanocrystalsfrom3nmto10nminDiameter26FullSizeSeriesofPbSeNanocDesignofDeviceStructuresQDsarepoorchargetransportmaterials...Isolatelayerfunctionsofmaximizedeviceperformance1.Generateexcitonsonorganicsites.2.TransferexcitonstoQDsviaFörsterorDexterenergytransfer.3.QDelectroluminescence.PhaseSegregation.Butefficientemitters…Useorganicsforchargetransport.Needanewfabricationmethod

inordertobeabletomakesuchdoubleheterostructures:27DesignofDeviceStructuresQDsAgeneralmethod?Phasesegregationoccursfordifferent1)organichosts:TPD, NPD,andpoly-TPD.2)solvents:chloroform, chlorobenzene,and mixtureswithtoluene.3)QDcorematerials: PbSe,CdSe,and CdSe(ZnS).4)QDcappingmolecules: oleicacidandTOPO.5)QDcoresize:4-8nm.6)substrates:Silicon, Glass,ITO.7)Spinparameters: speed,acceleration andtime.•Thisprocessisrobust,butfurtherexplorationisneededtobroadlygeneralizethesefindings.•Fortheexploredmaterials,consistentdescriptionispossible.•Wehaveshownthattheprocessisnotdependentonanyonematerialcomponent.PhasesegregationQD-LEDstructures28Ageneralmethod?PhasesegregaELRecombination

RegionDependence

onCurrent

Coeetal.,Org.Elect.(2003)29ELRecombination

RegionDependSpectralDependenceonCurrentDensityTOPDOWNVIEWoftheQDMONOLAYERExcitonrecombinationwidthfarexceedstheQDmonolayerthicknessathighcurrentdensity.Toachievetruemonochromeemission,newexcitonconfinementtechniquesareneeded.CROSS-SECTIONALVIEWofQD-LED30SpectralDependenceonCurrentBenefitsofQuantumDotsinOrganicLEDsDemonstrated:•SpectrallyTunable–singlematerialsetcanaccessmostofvisiblerange.•SaturatedColor–linewidthsof<35nmFullWidthatHalfofMaximum.•Caneasilytailor“external”chemistrywithoutaffectingemittingcore.•Cangeneratelargeareainfraredsources.Potential:•HighluminousefficiencyLEDspossibleeveninredandblue.•Inorganic–potentiallymorestable,longerlifetimes.Theidealdyemolecule!31BenefitsofQuantumDotsinOrOrganicLEDs–part8

ExcitonDynamicsinDisorderedOrganicThinFilms

QuantumDotLEDsHandoutonQD-LEDs:Coeetal.,Nature420,800(2002).April29,2003–OrganicOptoelectronics-Lecture20b32OrganicLEDs–part8ExcitonExcitonDynamicsinTimeDependantPL33ExcitonDynamicsinTimeDepenDynamicSpectralShiftsofDCM2inAlq3•MeasurementperformedondopedDCM2:Alq3films•Excitationatλ=490nm(onlyDCM2absorbs)~DCM2PLredshifts>20nmover6ns~Wavelength[nm]34DynamicSpectralShiftsofDCMTimeEvolutionof4%DCM2inAlq3PLSpectrum35TimeEvolutionof4%DCM2inAElectronicProcessesinMoleculesdensityofavailableS1orT1states36ElectronicProcessesinMolecuTimeEvolutionofDCM2SolutionPLSpectra37TimeEvolutionofDCM2SolutioSpectralShiftdueto~ExcitonDiffusion~~IntermolecularSolidStateInteractions~38SpectralShiftdueto~ExcitonExcitonicEnergyVariations39ExcitonicEnergyVariations8ExcitonDistributionintheExcitedState(S1orT1)~TimeEvolvedExcitonThermalization~EXCITONDIFFUSIONLEADSTOREDUCTIONINFWHM40ExcitonDistributionintheEx411042114312TimeEvolutionofPeakPLinNeatThinFilms44TimeEvolutionofPeakPLinNParametersforSimulatingExcitonDiffusionobservedradiativelifetime(τ)NormalizedIntegratedSpectralIntensityFörsterradius(RF)►Assignvalueforallowedtransfers:►AssumeGaussianshapeofwidth,wDOS►CenteratpeakofinitialbulkPLspectrum►MolecularPLspectrumimplied…excitonicdensityofstates(gex(E))45ParametersforSimulatingExciFittingSimulationtoExperiment–DopedFilms•Goodfitspossibleforalldatasets•RFdecreaseswithincreasingdoping,fallingfrom52Åto22Å•wDOSalsodecreaseswithincreasingdoping,rangingfrom0.146eVto0.120eV46FittingSimulationtoExperimeFittingSimulation–NeatFilms•Spectralshiftobservedineachmaterialsystem•MoleculardipoleandwDOSarecorrellated:lowerdipolescorrespondtolessdispersion•Evenwithnodipole,somedispersionexists•Experimentaltechniquegeneral,andyieldsfirstmeasurementsofexcitonicenergydispersioninamorphousorganicsolids47FittingSimulation–NeatFilmTemporalSolidStateSolvationuponexcitationbothmagnitudeanddirectionoflumophoredipolemomentcanchangeFOREXAMPLEforDCM:µ1–µ0>20Debye!~from5.6Dto26.3D~followingtheexcitationtheenvironmentsurroundingtheexcitedmoleculewillreorganizetominimizetheoverallenergyofthesystem(maximizeµ•Eloc)48TemporalSolidStateSolvationExcitonDistributionintheExcitedState(S1orT1)~TimeEvolvedMolecularReconfiguration~DIPOLE-DIPOLEINTERACTIONLEADSTOENERGYSHIFTINDENSITYOFEXCITEDSTATESlog(Time)49ExcitonDistributionintheExFusionofTwoMaterialSetsHybriddevicescouldenableLEDs,SolarCells,Photodetectors,Modulators,andLaserswhichutilizethebestpropertiesofeachindividualmaterial.EfficientOrganicSemiconductorsFlexibleEmissiveFabricationofrationalstructureshasbeenthemainobstacletodate.50FusionofTwoMaterialSetsHybInorganicNanocrystals–QuantumDotsQuantumDotSIZESyntheticrouteofMurrayetal,J.Am.Chem.Soc.115,8706(1993).51InorganicNanocrystals–QuantFusionofTwoMaterialSetsQuantumDotsOrganicMolecules52FusionofTwoMaterialSetsQuaIntegrationofNanoscaleMaterialsQuantumDotsandOrganicSemiconductorsZnSovercoatingshell(0to5monolayers)OleicAcidorTOPOcapsSyntheticroutesofMurrayetal,J.Am.Chem.Soc.115,8706(1993)andChen,etal,MRSSymp.Proc.691,G10.2.TrioctylphosphineoxideTris(8-hydroxyquinoline)Aluminum(III)3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazoleN,N'-Bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidineN,N'-Bis(3-methylphenyl)-N,N'-bis-(phenyl)-benzidine53IntegrationofNanoscaleMater1.Asolutionofanorganicmaterial,QDs,andsolvent…2.isspin-coatedontoacleansubstrate.3.Duringthesolventdryingtime,theQDsrisetothesurface…4.andself-assembleintograinsofhexagonallyclosepackedspheres.OrganichoststhatdepositasflatfilmsallowforimagingviaAFM,despitetheAFMtipbeingaslargeastheQDs.Phasesegregationisdrivenbyacombinationofsizeandchemistry.PhaseSegregationandSelf-Assembly541.AsolutionofanorganicOrgAstheconcentrationofQDsinthespin-castingsolutionisincreased,thecoverageofQDsonthemonolayerisalsoincreased.MonolayerCoverage–QDconcentration55AstheconcentrationofMonolayCdSe(ZnS)/TOPOPbSe/oleicacidQD-LEDPerformance56CdSe(ZnS)/TOPOPbSe/oleicacidQFullSizeSeriesofPbSeNanocrystalsfrom3nmto10nminDiameter57FullSizeSeriesofPbSeNanocDesignofDeviceStructuresQDsarepoorchargetransportmaterials...Isolatelayerfunctionsofmaximizedeviceperformance1.Generateexcitonsonorganicsites.2.TransferexcitonstoQDsviaFörsterorDexterenergytransfer.3.QDelectroluminescence.PhaseSegregation.Butefficientemitters…Useorganicsforchargetransport.Needanewfabricationmethod

inordertobeabletomakesuchdoubleheterostructures:58DesignofDeviceStructuresQDsAgeneralmethod?Phasesegregationoccursfordifferent1)organichosts:TPD, NPD,andpoly-TPD.2)solvents:chloroform, chlorobenzene,and mixtureswithtoluene.3)QDcorematerials: PbSe,CdSe,and CdSe(ZnS).4)QDcappingmolecule