（精选幻灯片）讲稿20. 有机发光二极管-第八部分.ppt

1 OrganicLEDs part8 ExcitonDynamicsinDisorderedOrganicThinFilmsQuantumDotLEDs HandoutonQD LEDs Coeetal Nature420 800 2002 April29 2003 OrganicOptoelectronics Lecture20b 2 ExcitonDynamicsinTimeDependantPL 3 DynamicSpectralShiftsofDCM2inAlq3 MeasurementperformedondopedDCM2 Alq3films Excitationat 490nm onlyDCM2absorbs DCM2PLredshifts 20nmover6ns Wavelength nm 4 TimeEvolutionof4 DCM2inAlq3PLSpectrum 5 ElectronicProcessesinMolecules densityofavailableS1orT1states 6 TimeEvolutionofDCM2SolutionPLSpectra 7 SpectralShiftdueto ExcitonDiffusion IntermolecularSolidStateInteractions 8 ExcitonicEnergyVariations 9 ExcitonDistributionintheExcitedState S1orT1 TimeEvolvedExcitonThermalization EXCITONDIFFUSIONLEADSTOREDUCTIONINFWHM 10 11 12 13 TimeEvolutionofPeakPLinNeatThinFilms 14 ParametersforSimulatingExcitonDiffusion observedradiativelifetime NormalizedIntegratedSpectralIntensity F rsterradius RF Assignvalueforallowedtransfers AssumeGaussianshapeofwidth wDOS CenteratpeakofinitialbulkPLspectrum MolecularPLspectrumimplied excitonicdensityofstates gex E 15 FittingSimulationtoExperiment DopedFilms Goodfitspossibleforalldatasets RFdecreaseswithincreasingdoping fallingfrom52 to22 wDOSalsodecreaseswithincreasingdoping rangingfrom0 146eVto0 120eV 16 FittingSimulation NeatFilms Spectralshiftobservedineachmaterialsystem MoleculardipoleandwDOSarecorrellated lowerdipolescorrespondtolessdispersion Evenwithnodipole somedispersionexists Experimentaltechniquegeneral andyieldsfirstmeasurementsofexcitonicenergydispersioninamorphousorganicsolids 17 TemporalSolidStateSolvation uponexcitationbothmagnitudeanddirectionoflumophoredipolemomentcanchangeFOREXAMPLEforDCM 1 0 20Debye from5 6Dto26 3D followingtheexcitationtheenvironmentsurroundingtheexcitedmoleculewillreorganizetominimizetheoverallenergyofthesystem maximize Eloc 18 ExcitonDistributionintheExcitedState S1orT1 TimeEvolvedMolecularReconfiguration DIPOLE DIPOLEINTERACTIONLEADSTOENERGYSHIFTINDENSITYOFEXCITEDSTATES log Time 19 FusionofTwoMaterialSets HybriddevicescouldenableLEDs SolarCells Photodetectors Modulators andLaserswhichutilizethebestpropertiesofeachindividualmaterial Efficient OrganicSemiconductors Flexible Emissive Fabricationofrationalstructureshasbeenthemainobstacletodate 20 InorganicNanocrystals QuantumDots 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 andsolvent 2 isspin coatedontoacleansubstrate 3 Duringthesolventdryingtime theQDsrisetothesurface 4 andself assembleintograinsofhexagonallyclosepackedspheres OrganichoststhatdepositasflatfilmsallowforimagingviaAFM despitetheAFMtipbeingaslargeastheQDs Phasesegregationisdrivenbyacombinationofsizeandchemistry PhaseSegregationandSelf Assembly 24 AstheconcentrationofQDsinthespin castingsolutionisincreased thecoverageofQDsonthemonolayerisalsoincreased MonolayerCoverage QDconcentration 25 CdSe ZnS TOPO PbSe oleicacid QD LEDPerformance 26 FullSizeSeriesofPbSeNanocrystalsfrom3nmto10nminDiameter 27 DesignofDeviceStructures QDsarepoorchargetransportmaterials Isolatelayerfunctionsofmaximizedeviceperformance 1 Generateexcitonsonorganicsites 2 TransferexcitonstoQDsviaF rsterorDexterenergytransfer 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 Phasesegregation QD LEDstructures 29 ELRecombinationRegionDependenceonCurrent Coeetal Org Elect 2003 30 SpectralDependenceonCurrentDensity TOPDOWNVIEWoftheQDMONOLAYER ExcitonrecombinationwidthfarexceedstheQDmonolayerthicknessathighcurrentdensity Toachievetruemonochromeemission newexcitonconfinementtechniquesareneeded CROSS SECTIONALVIEWofQD LED 31 BenefitsofQuantumDotsinOrganicLEDs Demonstrated SpectrallyTunable singlematerialsetcanaccessmostofvisiblerange SaturatedColor linewidthsof 35