Table Of ContentDevice Architecture and Materials for Organic
Light-Emitting Devices
Sarah Schols
Device Architecture
and Materials
for Organic Light-
Emitting Devices
Targeting High Current Densities
and Control of the Triplet Concentration
SarahSchols
LargeAreaElectronics(LAE)
Imec
Kapeldreef75
3000Leuven,VlaamsBrabant
Belgium
[email protected]
ISBN978-94-007-1607-0 e-ISBN978-94-007-1608-7
DOI10.1007/978-94-007-1608-7
SpringerDordrechtHeidelbergLondonNewYork
LibraryofCongressControlNumber:2011928673
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Preface
This book is a reprint of the manuscript entitled “Device architecture and mate-
rials for organic light-emitting devices”, that was submitted to the jury deciding
on the achievement of my PhD at the Katholieke Universiteit Leuven in Belgium.
It is the result of five years fascinating research at imec in Leuven, Belgium, be-
tween2004and2009.DifferentpeoplecontributedtomyworkandIwanttoshow
gratitude to all of them. First, I would like to thank my two promoters, Prof. Paul
Heremans(KUL/imec)andProf.RobertMertens(KUL/imec)whogavemetheop-
portunitytostartaPhDinaninspiringenvironmentasimec.Iamalsoverygrateful
totheotherPhDjurymemberswhotookthetimetocarefullyreadmymanuscript:
Prof.MarkvanderAuweraer(KUL),Prof.JanEngelen(KUL),Prof.HenningSir-
ringhaus(UniversityofCambridge),Prof.UliLemmer(UniversitätKarlsruhe)and
Prof. Adhemar Bultheel (KUL). My special thanks go to Andrey Kadashchuk for
introducingmeintotheexcitingworldofspectroscopyandforthemanyscientific
discussions, but of course also all other colleagues of the Polymer and Molecular
ElectronicsgroupatimecwithwhomIworkedtogetherduringmyPhDaregrate-
fully acknowledged. Besides, I would like to thank Thilo Stöferle (IBM Research
Zurich),TobiasPlötzing(RWTHAachen)andThorstenWahlbrink(AMOGmbH)
forthenicecollaboration.TheFWOisacknowledgedforthefinancialsupport.Fi-
nally, I warmly thank my family for their continuous support and interest in my
work.
SarahSchols
v
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 OrganicSemiconductors . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 SemiconductingPropertiesofOrganicMaterials . . . . . . 2
1.1.2 ChargeTransportinOrganicMaterials . . . . . . . . . . . 4
1.1.3 OpticalTransitionsinOrganicMaterials . . . . . . . . . . 6
1.2 StateoftheArtOrganicLight-EmittingDevices . . . . . . . . . . 9
1.2.1 OrganicLight-EmittingDiodes . . . . . . . . . . . . . . . 9
1.2.2 OrganicLight-EmittingTransistors . . . . . . . . . . . . . 11
1.3 OrganicSemiconductorLasers . . . . . . . . . . . . . . . . . . . 13
1.3.1 GeneralAspectsofLaserAction . . . . . . . . . . . . . . 13
1.3.2 MotivationforPlasticLasers . . . . . . . . . . . . . . . . 15
1.3.3 LasinginOrganicSemiconductors . . . . . . . . . . . . . 17
1.3.4 ProspectsforElectricallyPumpedOrganicLasers . . . . . 27
1.4 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2 MaterialsandExperimentalTechniques . . . . . . . . . . . . . . . . 33
2.1 SampleFabrication . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.1.1 MaterialsUsedinthisWork . . . . . . . . . . . . . . . . . 33
2.1.2 DepositionTechniques. . . . . . . . . . . . . . . . . . . . 34
2.1.3 FabricationofPhotonicFeedbackStructures . . . . . . . . 37
2.2 DeviceCharacterization . . . . . . . . . . . . . . . . . . . . . . . 41
2.2.1 TransistorMeasurementandParameterExtraction . . . . . 41
2.2.2 CharacterizationofOLEDs . . . . . . . . . . . . . . . . . 42
2.2.3 Time-ResolvedPhotoluminescenceMeasurements . . . . . 43
2.2.4 Time-ResolvedPump-ProbeExperiments. . . . . . . . . . 45
2.2.5 AmplifiedSpontaneousEmissionandLossMeasurements . 46
2.2.6 DeterminationofThermallyStimulatedLuminescence . . . 47
3 OrganicLight-EmittingDiodeswithField-EffectElectronTransport 49
3.1 DeviceFabrication . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.2 DeviceOperation . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.3 DevicePerformance . . . . . . . . . . . . . . . . . . . . . . . . . 56
vii
viii Contents
3.3.1 OpticalandElectricalCharacterization . . . . . . . . . . . 56
3.3.2 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.4 ImprovementoftheExternalQuantumEfficiency . . . . . . . . . 60
3.5 SummaryandConclusions . . . . . . . . . . . . . . . . . . . . . 62
4 DevicesBasedonDiperfluorohexyl-quaterthiopheneDerivatives . . 65
4.1 CharacterizationoftheElectron-TransportingMaterialsDFH-4T
andDFHCO-4T . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.2 DevicesBasedonDFH-4T . . . . . . . . . . . . . . . . . . . . . 69
4.2.1 TransistorsBasedonDFH-4T . . . . . . . . . . . . . . . . 69
4.2.2 DFH-4TinOLEDswithField-EffectElectronTransport . . 70
4.3 DevicesBasedonDFHCO-4T. . . . . . . . . . . . . . . . . . . . 72
4.3.1 HighPerformanceDFHCO-4TTransistors . . . . . . . . . 72
4.3.2 DFHCO-4TinOLEDswithField-EffectElectronTransport 76
4.4 Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.5 SummaryandConclusions . . . . . . . . . . . . . . . . . . . . . 78
5 ControloftheTripletConcentrationinOrganicLight-Emitting
Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.1 PulsedExcitationofOLEDswithField-EffectElectronTransport . 82
5.1.1 Pulse-WidthDependenceofOrganicLight-Emitting
Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5.1.2 EffectsInfluencingthePulsedExcitationBehaviorof
OLEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.2 TripletExcitationScavenginginFilmsofConjugatedPolymers . . 86
5.2.1 TripletScavenginginLiquid-StateOrganicDyeLasers . . 86
5.2.2 TripletScavenginginSolid-StateOrganicThinFilms . . . 88
5.3 SummaryandConclusions . . . . . . . . . . . . . . . . . . . . . 94
6 Triplet-EmitterDopedOrganicMaterials . . . . . . . . . . . . . . . 97
6.1 TripletDynamicsandChargeCarrierTrappinginTriplet-Emitter
DopedConjugatedPolymers . . . . . . . . . . . . . . . . . . . . 97
6.1.1 SpectroscopicCharacterization . . . . . . . . . . . . . . . 99
6.1.2 ThermallyStimulatedLuminescenceinCNPPPDoped
withBtp Ir(acac) . . . . . . . . . . . . . . . . . . . . . . 110
2
6.2 OpticalPumpingofTriplet-Emitters . . . . . . . . . . . . . . . . 111
6.2.1 AttemptstoObserveASEUsingBtp Ir(acac) . . . . . . . 112
2
6.2.2 AttemptstoObserveASEUsingF5PhandGDP16b . . . . 113
6.3 SummaryandConclusions . . . . . . . . . . . . . . . . . . . . . 114
7 ValueofOLEDswithField-EffectElectronTransportforLasing
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
7.1 PotentialofOLEDswithField-EffectElectronTransportasLaser
DeviceConfiguration . . . . . . . . . . . . . . . . . . . . . . . . 117
7.1.1 HighCurrentDensities . . . . . . . . . . . . . . . . . . . 118
7.1.2 ReducedAbsorptionLosses . . . . . . . . . . . . . . . . . 119
Contents ix
7.2 OpticallyPumpedLasingExperiments . . . . . . . . . . . . . . . 123
7.2.1 StimulatedEmissioninAlq :DCM . . . . . . . . . . . . 124
3 2
7.2.2 StimulatedEmissioninStacksComprisingAlq :DCM . . 126
3 2
7.2.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 131
7.3 DevicewithIntegratedField-EffectandPhotonicFeatures . . . . . 131
7.4 SummaryandConclusions . . . . . . . . . . . . . . . . . . . . . 133
8 GeneralConclusionsandFutureOutlook . . . . . . . . . . . . . . . 135
8.1 OverviewoftheMainResults . . . . . . . . . . . . . . . . . . . . 135
8.2 SuggestionsforFurtherResearch . . . . . . . . . . . . . . . . . . 137
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
