讲稿20.有机发光二极管-第八部分

1,OrganicLEDspart8,ExcitonDynamicsinDisorderedOrganicThinFilmsQuantumDotLEDs,HandoutonQD-LEDs:Coeetal.,Nature420,800(2002).,April29,2003OrganicOptoelectronics-Lecture20b,2,ExcitonDynamicsinTimeDependantPL,3,DynamicSpectralShiftsofDCM2inAlq3,MeasurementperformedondopedDCM2:Alq3filmsExcitationat=490nm(onlyDCM2absorbs),DCM2PLredshifts20nmover6ns,Wavelengthnm,4,TimeEvolutionof4%DCM2inAlq3PLSpectrum,5,ElectronicProcessesinMolecules,densityofavailableS1orT1states,6,TimeEvolutionofDCM2SolutionPLSpectra,7,SpectralShiftdueto,ExcitonDiffusionIntermolecularSolidStateInteractions,8,ExcitonicEnergyVariations,9,ExcitonDistributionintheExcitedState(S1orT1),TimeEvolvedExcitonThermalization,EXCITONDIFFUSIONLEADSTOREDUCTIONINFWHM,10,11,12,13,TimeEvolutionofPeakPLinNeatThinFilms,14,ParametersforSimulatingExcitonDiffusion,observedradiativelifetime(),NormalizedIntegratedSpectralIntensity,Frsterradius(RF),Assignvalueforallowedtransfers:,AssumeGaussianshapeofwidth,wDOSCenteratpeakofinitialbulkPLspectrumMolecularPLspectrumimplied,excitonicdensityofstates(gex(E),15,FittingSimulationtoExperimentDopedFilms,GoodfitspossibleforalldatasetsRFdecreaseswithincreasingdoping,fallingfrom52to22wDOSalsodecreaseswithincreasingdoping,rangingfrom0.146eVto0.120eV,16,FittingSimulationNeatFilms,SpectralshiftobservedineachmaterialsystemMoleculardipoleandwDOSarecorrellated:lowerdipolescorrespondtolessdispersionEvenwithnodipole,somedispersionexistsExperimentaltechniquegeneral,andyieldsfirstmeasurementsofexcitonicenergydispersioninamorphousorganicsolids,17,TemporalSolidStateSolvation,uponexcitationbothmagnitudeanddirectionoflumophoredipolemomentcanchangeFOREXAMPLEforDCM:1020Debye!from5.6Dto26.3D,followingtheexcitationtheenvironmentsurroundingtheexcitedmoleculewillreorganizetominimizetheoverallenergyofthesystem(maximizeEloc),18,ExcitonDistributionintheExcitedState(S1orT1),TimeEvolvedMolecularReconfiguration,DIPOLE-DIPOLEINTERACTIONLEADSTOENERGYSHIFTINDENSITYOFEXCITEDSTATES,log(Time),19,FusionofTwoMaterialSets,HybriddevicescouldenableLEDs,SolarCells,Photodetectors,Modulators,andLaserswhichutilizethebestpropertiesofeachindividualmaterial.,Efficient,OrganicSemiconductors,Flexible,Emissive,Fabricationofrationalstructureshasbeenthemainobstacletodate.,20,InorganicNanocrystalsQuantumDots,QuantumDotSIZE,SyntheticrouteofMurrayetal,J.Am.Chem.Soc.115,8706(1993).,21,FusionofTwoMaterialSets,QuantumDots,OrganicMolecules,22,IntegrationofNanoscaleMaterialsQuantumDotsandOrganicSemiconductors,ZnSovercoatingshell(0to5monolayers),OleicAcidorTOPOcaps,SyntheticroutesofMurrayetal,J.Am.Chem.Soc.115,8706(1993)andChen,etal,MRSSymp.Proc.691,G10.2.,Trioctylphosphineoxide,Tris(8-hydroxyquinoline)Aluminum(III),3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole,N,N-Bis(naphthalen-1-yl)-N,N-bis(phenyl)benzidine,N,N-Bis(3-methylphenyl)-N,N-bis-(phenyl)-benzidine,23,1.Asolutionofanorganicmaterial,QDs,andsolvent2.isspin-coatedontoacleansubstrate.3.Duringthesolventdryingtime,theQDsrisetothesurface4.andself-assembleintograinsofhexagonallyclosepackedspheres.,OrganichoststhatdepositasflatfilmsallowforimagingviaAFM,despitetheAFMtipbeingaslargeastheQDs.,Phasesegregationisdrivenbyacombinationofsizeandchemistry.,PhaseSegregationandSelf-Assembly,24,AstheconcentrationofQDsinthespin-castingsolutionisincreased,thecoverageofQDsonthemonolayerisalsoincreased.,MonolayerCoverageQDconcentration,25,CdSe(ZnS)/TOPO,PbSe/oleicacid,QD-LEDPerformance,26,FullSizeSeriesofPbSeNanocrystalsfrom3nmto10nminDiameter,27,DesignofDeviceStructures,QDsarepoorchargetransportmaterials.,Isolatelayerfunctionsofmaximizedeviceperformance,1.Generateexcitonsonorganicsites.2.TransferexcitonstoQDsviaFrsterorDexterenergytransfer.3.QDelectroluminescence.,PhaseSegregation.,Butefficientemitters,Useorganicsforchargetransport.,Needanewfabricationmethodinordertobeabletomakesuchdoubleheterostructures:,28,Ageneralmethod?,Phasesegregationoccursfordifferent1)organichosts:TPD,NPD,andpoly-TPD.2)solvents:chloroform,chlorobenzene,andmixtureswithtoluene.3)QDcorematerials:PbSe,CdSe,andCdSe(ZnS).4)QDcappingmolecules:oleicacidandTOPO.5)QDcoresize:4-8nm.6)substrates:Silicon,Glass,ITO.7)Spinparameters:speed,accelerationandtime.,Thisprocessisrobust,butfurtherexplorationisneededtobroadlygeneralizethesefindings.Fortheexploredmaterials,consistentdescriptionispossible.Wehaveshownthattheprocessisnotdependentonanyonematerialcomponent.,PhasesegregationQD-LEDstructures,29,ELRecombinationRegionDependenceonCurrent,Coeetal.,Org.Elect.(2003),30,SpectralDependenceonCurrentDensity,TOPDOWNVIEWoftheQDMONOLAYER,ExcitonrecombinationwidthfarexceedstheQDmonolayerthicknessathighcurrentdensity.Toachievetruemonochromeemission,newexcitonconfinementtechniquesareneeded.,CROSS-SECTIONALVIEWofQD-LED,31,BenefitsofQuantumDotsinOrganicLEDs,Demonstrated:SpectrallyTunablesinglematerialsetcanaccessmostofvisiblerange.SaturatedColorlinewidthsof35nm