Slide Number 1Slide Number 2Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18OLEDs vs. LEDsSlide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Shadow Mask PatterningInkjet PrintingSlide Number 37Slide Number 38Slide Number 39Slide Number 40Slide Number 41Slide Number 42Slide Number 43Slide Number 44Slide Number 45Slide Number 46Slide Number 47Slide Number 48Slide Number 49Slide Number 50Slide Number 51Slide Number 52Slide Number 53Slide Number 54Slide Number 55Slide Number 56Slide Number 57Slide Number 58Slide Number 59Slide Number 60Slide Number 61Slide Number 62Slide Number 63Slide Number 64Organic Electronics:Opportunities and Challengesin Solid-State LightingGeorge MalliarasDepartment of Materials Science and Engineering, Cornell University&Cornell NanoScale Science and Technology Facility Email: [email protected]• Introduction to organic semiconductors & devices• Organic light emitting diodes- Processing and patterning- Charge injection and transport- Mobile ions- Degradation• Organic thin film transistors- Morphology of organic films- Contact effects- Structure of organic films• Organic photovoltaic cells- Influence of morphology - Energy vs. charge transfer• ConclusionsOrganic electronics: The big threeOLEDs OTFTs OPVsKodakSiemensDuPontSonyU. of LinzOrganic electronics: a booming fieldOrganic semiconductor familiesMolecularly Doped Functional Small MoleculesPolymers (MDP) PolymersCommon organic semiconductorsTPDAlq3PentacenePPVCarbon as a semiconductorCH2=CH2En= ⎯⎯⎯ n2n=1,2,3,...ħ2π22mL2LUMOHOMOEG≈ ⎯⎯⎯ħ2π22maN• Hybridization: sp2and pZ• Particle in a box:EGTuning of optical propertiesBlueRedR.E. Gill et. al., Adv. Mater. 6, 132 (1994).CovionTuning of electrical propertiesOpportunities and challenges(+) Ease of processing (+) Tunability of electronic properties(+) Integration with biological systems(+/-) Significant ionic mobility(-) Low-end performance (-) Stability in devicesWill complement Si, not replace itOrganic light emitting diodes (OLEDs)Pioneer(2001 - demo)Pioneer(1997)Motorola(2001)Kodak(2004)Sony(2004)Sony(2007)OLEDs vs. liquid crystalsEfficiency of white OLEDsKido group, Yamagata U.IdemitsuIMESYamagata Univ,MatsushitaNHKGEKodak/SanyoPrincetonYear504030201002 03 04 05 06 07 08Princeton Univ./UDCPrinceton Univ./UDCGEPrinceton UnivOsramNovaledsNEDO Organic Device ProjectYamagata Univ.Luminous Efficiency (lm/W)OLEDs vs. LEDsLEDs OLEDsTransportExtended states give rise to mobilities of 1000 cm2/Vsec or higherHopping among localized states results in low mobilities – typically in the range of 10-6-10-3cm2/Vsec Dopingn- or p-doped, with substitutional dopant densities of 1015-1020cm-3Usually undoped. Doping requires loading in the % range.Excited statesWeak electron-phonon coupling and weakly bound excitonsStrong electron-lattice coupling, exciton binding energies of 0.5 eVPurityWell-controlled and characterized. Impurities mostly unknown.OLED structure and operationITOCah+e-AnodeLUMOCathodeHOMOOLED characteristicsNeed for low work function cathodeLow work function cathode requiredfor efficient electron injectionITOCaMgAlAgBilayer devicesAnodeHole-transport layerCathodeElectron-transportlayerOther architecturesEmissive LayerDopantsSmall molecules for OLEDsConjugated polymers for OLEDsC8H17C8H17 n n nSOO nS nPPPPFOPPVPEDOTP3HTMultilayer devices from small moleculesB. W. D’Andrade, et al., Adv. Mat., 16, 624 (2004).ITONPD(40 nm)5.5 eV2.4 eVTCTA(10 nm)2.3 eV5.7 eVTPBI(25 nm)2.8 eV6.3 eVLiF/Al4.1 eVITO4.7 eV2.6 eV5.1 eVFIr63.1 eVUGH4(9 nm)7.2 eVPQIr5.0 eV2.7 eVIr(ppy)36.1eVEnergy transfer from B→G→RMultilayer devices from small moleculesB. W. D’Andrade, et al., Adv. Mat., 16, 624 (2004).Stacked OLEDsKido labs, Yamagata U.H. Kanno, et al., Adv. Mater.,18, 339, 2006.(+) High brightness and efficiency(+) Long operational stability due to reduced heat and charge(-) Highly transparent charge generation layer(-) Carrier balancing in each sub-pixel(-) Tuning optical path for white emissionIo ,VoLo3xLoIo ,3xVoConventional OLEDStacked OLED (SOLED)cathodeITOorganic layers-+charge generation layer-+-+-+Stacked OLEDsH. Kanno, et al., Adv. Mater.,18, 339, 2006.ITO4.72.45.51.65.02.45.96.13.03.06.4NPDIr(ppz)3mCPCBPBphenBphen : LiNPDIr(ppz)3mCPBphenBphen : LiCBPAlMoO31.91.94.8 4.82.42.45.51.65.06.13.03.06.4FlzlrIr(ppy)3PQIrunit : eVNNNNIr3FlzIr mCP5.9Stacked OLEDsH. Kanno, et al., Adv. Mater.,18, 339, 2006.10-310-210-1100101102010203040500102030100cd/m2External efficiency (%)Current density (mA/cm2)1-SOLED2-SOLED3-SOLED1000cd/m2 power efficiency (lm/W)Multilayer devices from polymersNNONNOnNIr3NNOSO3NaPFO-ETMPFO-F (1%)mCOnm=99%, n=1%PVK-SO3Lit-Bu-PBD-SO3NaIr(HFP)3NnSO3LiHeeger group, UCSBRed dopantBlue emitting hostGreen dopantRGB schemesPatterned emittersMicrocavitiesColor filtersFluorescent convertersStackedShadow Mask Patterning•Alignment is difficult•Features widen causing shorts•Complex shapes impossible•Evaporation onlyGapSubstrateShadow MaskSourceInkjet PrintingThe Cambridge Research Laboratory of Epson•Serial process•Inks must be specially formulated•Polymer performance laggingXerox PARCEfficiencyη = b ⋅ Φ ⋅ (1/2n2)Fraction of charge that forms excitonsFraction of excitons that decay radiativelyDepends on photophysics:Singlet: Φ = (1/4) ⋅ ΦPLTriplet: Φ = ΦPLFraction of photons that escape waveguiding(22%)External quantum efficiency of an OLEDOutcoupling efficiencyT. Yamasaki, K. Sumioka, and T. Tsutsui, Appl. Phys. Lett. 76, 1243 (2000).V. B u l o v i c , V. B . K h a l f i n, G. Gu, P. E. Burrows, D. Z. Garbuzov, and S. R. Forrest, Phys. Rev. B 58, 3730 (1998).T. Tsutsui, M. Yahiro, H. Yokogawa, K. Kawano, and M. Yokoyama, Adv. Mater. 13, 1149 (2001).V. Bulovic, V. B. Khalfin, G. Gu, P. E. Burrows, D. Z. Garbuzov, and S. R. Forrest, Phys. Rev. B 58, 3730 (1998).Electron-hole recombinationJh/JJe/JAnode CathodexbExternal Quantum Efficiency: η = b⋅Φ/2n2Energetics of semiconductorsFigure of merit: mobility, μ (cm2/V·sec)ConductionbandVal en cebandShallowtrapDeeptrapv=μ·Eεx+-Space charge effectsLow voltages: Ohm’s lawJOHM=