Organic-Electroluminescent-Diodes-1987

OrganicelectroluminescentdiodesC.W.TangandS.A.VanSlykeCitation:AppliedPhysicsLetters51,913(1987);doi:10.1063/1.98799Viewonline::=pdfcovPublishedbytheAIPPublishingArticlesyoumaybeinterestedinElectroluminescencepropertyoforganiclightemittingdiode(OLED)AIPConf.Proc.1569,364(2013);10.1063/1.4849295PulsedelectroluminescencefromorganicbilayerlightemittingdiodesAppl.Phys.Lett.69,1291(1996);10.1063/1.117395StronglydirectedsinglemodeemissionfromorganicelectroluminescentdiodewithamicrocavityAppl.Phys.Lett.68,2633(1996);10.1063/1.116205Sharplydirectedemissioninorganicelectroluminescentdiodeswithanoptical‐microcavitystructureAppl.Phys.Lett.65,1868(1994);10.1063/1.113043DirectedbeamemissionfromfilmedgeinorganicelectroluminescentdiodeAppl.Phys.Lett.62,666(1993);10.1063/1.108859Thisarticleiscopyrightedasindicatedinthearticle.ReuseofAIPcontentissubjecttothetermsat::220.181.108.117On:Mon,18May201504:21:32Organicelectroluminescentdiodesc.W.TangandS.A.VanSlykeResearchLaboratories.CorporateResearchGroup.EastmanKodakCompany.Rochester.NewYork14650(Received12May1987;acceptedforpublication20July1987)Anovelelectroluminescentdeviceisconstructedusingorganicmaterialsastheemittingelements.Thediodehasadouble-layerstructureoforganicthinfilms,preparedbyvapordeposition.Efficientinjectionofholesandelectronsisprovidedfromanindium-tin-oxideanodeandanalloyedMg:Agcathode.Electron-holerecombinationandgreenelectroluminescentemissionareconfinedneartheorganicinterfaceregion.Highexternalquantumefficiency(1%photon/electron),luminousefficiency(1.5lm/W),andbrightness(1000cd/m2)areachievableatadrivingvoltagebelowIOV.Organicmaterialshavepreviouslybeenconsideredforthefabricationofpracticalelectroluminescent(EL)de­vices.ITheprimaryreasonisthatalargenumberoforganicmaterialsareknowntohaveextremelyhighfluorescencequantumefficienciesinthevisiblespectrum,2.3includingtheblueregion.someapproaching100%.Inthisregard,theyareideallysuitedformulticolordisplayapplications.However,thedevelopmentoforganicELdeviceshasnotbeensuccessfulsofar,onereasonbeingthathighvoltageisgenerallyrequiredtoinjectchargesintoorganiccrystals(e.g.,anthracene).InearlyattemptsbyHelfrichandSchneider,4Dresner,IandWilliamsandSchadt,5thedrivevoltagewasontheorderof100Voraboveinordertoachieveasignificantlightoutput.Therefore,theELdevicepower-conversionefficiencyisquitelow,typicallylessthan0.1%W/W,despitethereportedhighexternalquantumef­ficiencyof~5%photon/electron.Inanattempttoreducethedrivevoltage,Vincettetal.nusedthinorganicfilmsofsimilarmaterialsintheirELdevices.TheyreportedELop­erationbelow30V.However,thequantumefficiencyoftheirELdiodeswasonlyabout0.05%,presumablyowingtotheinefficiencyofelectroninjectionandtheinferiorqualityoftheevaporatedanthracenefilms.Otherorganicthin-filmELwork7.Xreportedsimilarperformance.Anotherfactorforthelackofdevelopmentisperhapsthequestionoflong­termstabilityoforganicELdiodes.Thereareveryfewre­porteddataontheorganicELstabilityintheliterature.oInthisletter,wereportanovelthin-filmorganicdevicewithsuperiorELcharacteristics.Itisefficientandcanbedriventohighbrightnessbyalowdcvoltage.IncontrasttomostorganicELcells,whichuseasinglelayeroforganicmaterialsandwichedbetweentwoinjectingelectrodes,ourELdiodeconsistsofadoublelayeroforganicthinfilms,withonelayercapableofonlymonopolartransport.Theorganicmaterialswerechosensuchthatthemorphological,trans­port,recombination,andluminescentpropertieswerecom­patiblewiththeconstructionandoperationofthethin-filmELdiodes.Inaddition,weusedalow-work-functionalloypreparedbyvaporcodepositionasthecathodeforefficientelectroninjection.FigureIshowsthestructureofthepresentELcell.Thesubstrateisanindium-tin-oxide(ITO)coatedglasswithasheetresitanceofabout10-20%(Nesatron™fromPPGIndustries).Itwascleanedbyultrasonicationinamixtureofisopropylalcoholandwater(I:1)anddegreasedintoluenevapor.Thefirstorganiclayer(about750A)ontopofthesubstrateisanaromaticdiamine9ofmolecularstructureshowninFig.1.Thesecondorganiclayeristheluminescentfilm,about600A.Itbelongstoaclassoffluorescentmetalchelatecomplexes.10ThespecificexampleshowninFig.Iis8-hydroxyquinolinealuminum(Alq3)'Thetopelectrodeisanalloyormixtureofmagnesiumandsilverwithanatomicratioof10:I.Theorganiclayers,aswellastheMg:Agelec­trode,werealldepositedbyvacuumdeposition(_10-5Torr).Thesubstratewasnominallyatroomtemperatureandthedepositionratesfortheorganiclayerswereabout2-5A/s.TheMg:Agelectrodewasdepositedbysimultaneousevaporationfromtwoseparatesourcesatatotalrateofabout10A/s.TheorganicdiodeshowninFig.Icanbeoperatedinacontinuousdcorpulsedmode.Itbehaveslikearectifier,theforwardbiascorrespondingtoapositivevoltageontheITOelectrode.Lightemission,seenonlyinforwardbias,wasmeasurablefromaslowasabout2.5V.Figure2showsthecontinuousdccurrentvsvoltage(1-V)andtheradianceexi­tancevsvoltage(B-V)curves.TheshapeoftheJ-Vcurvesformostdiodesisrelativelyindependentofthethicknessoft