讲稿20. 有机发光二极管-第八部分ppt课件

OrganicLEDspart8,ExcitonDynamicsinDisorderedOrganicThinFilmsQuantumDotLEDs,HandoutonQD-LEDs:Coeetal.,Nature420,800(2002).,April29,2003OrganicOptoelectronics-Lecture20b,1,ExcitonDynamicsinTimeDependantPL,2,DynamicSpectralShiftsofDCM2inAlq3,MeasurementperformedondopedDCM2:Alq3filmsExcitationat=490nm(onlyDCM2absorbs),DCM2PLredshifts20nmover6ns,Wavelengthnm,3,TimeEvolutionof4%DCM2inAlq3PLSpectrum,4,ElectronicProcessesinMolecules,densityofavailableS1orT1states,5,TimeEvolutionofDCM2SolutionPLSpectra,6,SpectralShiftdueto,ExcitonDiffusionIntermolecularSolidStateInteractions,7,ExcitonicEnergyVariations,8,ExcitonDistributionintheExcitedState(S1orT1),TimeEvolvedExcitonThermalization,EXCITONDIFFUSIONLEADSTOREDUCTIONINFWHM,9,10,11,12,TimeEvolutionofPeakPLinNeatThinFilms,13,ParametersforSimulatingExcitonDiffusion,observedradiativelifetime(),NormalizedIntegratedSpectralIntensity,Frsterradius(RF),Assignvalueforallowedtransfers:,AssumeGaussianshapeofwidth,wDOSCenteratpeakofinitialbulkPLspectrumMolecularPLspectrumimplied,excitonicdensityofstates(gex(E),14,FittingSimulationtoExperimentDopedFilms,GoodfitspossibleforalldatasetsRFdecreaseswithincreasingdoping,fallingfrom52to22wDOSalsodecreaseswithincreasingdoping,rangingfrom0.146eVto0.120eV,15,FittingSimulationNeatFilms,SpectralshiftobservedineachmaterialsystemMoleculardipoleandwDOSarecorrellated:lowerdipolescorrespondtolessdispersionEvenwithnodipole,somedispersionexistsExperimentaltechniquegeneral,andyieldsfirstmeasurementsofexcitonicenergydispersioninamorphousorganicsolids,16,TemporalSolidStateSolvation,uponexcitationbothmagnitudeanddirectionoflumophoredipolemomentcanchangeFOREXAMPLEforDCM:1020Debye!from5.6Dto26.3D,followingtheexcitationtheenvironmentsurroundingtheexcitedmoleculewillreorganizetominimizetheoverallenergyofthesystem(maximizeEloc),17,ExcitonDistributionintheExcitedState(S1orT1),TimeEvolvedMolecularReconfiguration,DIPOLE-DIPOLEINTERACTIONLEADSTOENERGYSHIFTINDENSITYOFEXCITEDSTATES,log(Time),18,FusionofTwoMaterialSets,HybriddevicescouldenableLEDs,SolarCells,Photodetectors,Modulators,andLaserswhichutilizethebestpropertiesofeachindividualmaterial.,Efficient,OrganicSemiconductors,Flexible,Emissive,Fabricationofrationalstructureshasbeenthemainobstacletodate.,19,InorganicNanocrystalsQuantumDots,QuantumDotSIZE,SyntheticrouteofMurrayetal,J.Am.Chem.Soc.115,8706(1993).,20,FusionofTwoMaterialSets,QuantumDots,OrganicMolecules,21,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,22,1.Asolutionofanorganicmaterial,QDs,andsolvent2.isspin-coatedontoacleansubstrate.3.Duringthesolventdryingtime,theQDsrisetothesurface4.andself-assembleintograinsofhexagonallyclosepackedspheres.,OrganichoststhatdepositasflatfilmsallowforimagingviaAFM,despitetheAFMtipbeingaslargeastheQDs.,Phasesegregationisdrivenbyacombinationofsizeandchemistry.,PhaseSegregationandSelf-Assembly,23,AstheconcentrationofQDsinthespin-castingsolutionisincreased,thecoverageofQDsonthemonolayerisalsoincreased.,MonolayerCoverageQDconcentration,24,CdSe(ZnS)/TOPO,PbSe/oleicacid,QD-LEDPerformance,25,FullSizeSeriesofPbSeNanocrystalsfrom3nmto10nminDiameter,26,DesignofDeviceStructures,QDsarepoorchargetransportmaterials.,Isolatelayerfunctionsofmaximizedeviceperformance,1.Generateexcitonsonorganicsites.2.TransferexcitonstoQDsviaFrsterorDexterenergytransfer.3.QDelectroluminescence.,PhaseSegregation.,Butefficientemitters,Useorganicsforchargetransport.,Needanewfabricationmethodinordertobeabletomakesuchdoubleheterostructures:,27,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,28,ELRecombinationRegionDependenceonCurrent,Coeetal.,Org.Elect.(2003),29,SpectralDependenceonCurrentDensity,TOPDOWNVIEWoftheQDMONOLAYER,ExcitonrecombinationwidthfarexceedstheQDmonolayerthicknessathighcurrentdensity.Toachievetruemonochromeemission,newexcitonconfinementtechniquesareneeded.,CROSS-SECTIONALVIEWofQD-LED,30,BenefitsofQuantumDotsinOrganicLEDs,Demonstrated:SpectrallyTunablesinglematerialsetcanaccessmostofvisiblerange.SaturatedColorlinewidthsof35nmFul