white light-emitting devices based on carbon dots electroluminescence

1、3502Chem.Commun.2011473502–3504ThisjournaliscTheRoyalSocietyofChemistry2011Citethis:Chem.Commun.2011473502–3504Whitelightemittingdevicesbasedoncarbondots’electroluminescencewFuWangzacYonghuaChenzbcChunyanLiuaDonggeMabRec

2、eived6thDecember2010Accepted19thJanuary2011DOI:10.1039c0cc05391kWedemonstratethefirstwhitelightemittingdeviceiginatingfromsinglecarbondotcomponents.Amaximumexternalquantumefficiencyof0.083%atacurrentdensityof5mAcm?2witha

3、colrenderingindexof82isrealizedindicatingthatcarbondotshavegreatpotentialtobeanalternativephosphffabricatingwhitelightelectroluminescentdevices.Thedevelopmentofwhitelightemittingdevices(WLEDs)hasbeenthesubjectofintenseac

4、ademicresearchfyearsaimingattheirpotentialapplicationsinlowcostbacklightinginliquidcrystaldisplaysfullcoldisplaysasnextgenerationlightingsourcesenvisionedtoreplacetheincescentlightbulbfluescentlamp.1–9Generallythreekinds

5、ofWLEDshavebeenproposedincludinginganicwhitelightemittingdiodes(IWLEDs)10allganicwhitelightemittingdiodes(OWLEDs)11–13colloidalquantumdotsbasedwhitelightemittingdiodes(QWLEDs).5–714–17ComparedtoIWLEDsOWLEDsaremeattractiv

6、eowingtotheirhighresolutionpossibleflexibilityflargescaleproduction.Howeverduetotheirlowenvironmentalstabilityshtdevicelifetimesatthehighluminancecurrentregimesrequiredflightinglackofreliablelowcostfabricationtechniquesf

7、largeareastherearestillchallengesfthemassivefabricationofOWLEDs.1415InthisscenariotheQWLEDswhicharefabricatedbyintegratingcolloidalsemiconductquantumdots(QDs)astheemissivelayerganicmaterialsastheelectronholetransptlayeri

8、ntohybridoptoelectronicstructureshaveturnedouttobeapromisingfieldofscientificendeavour.ThisisbecauseQWLEDscombinethediversityofganicmaterialswiththehighperfmanceelectronicopticalpropertiesofinganicnanocrystals.Toobtainwh

9、itelightfromsuchdevicesabalancedmixtureofredgreenblueemittingnanocrystalshavetobecombinedintoasingledevice.71415HoweverthecolqualityishardtoreplicatefthebroadbvisibleptionofthesolarspectrumduetothenarrowbemissionofQDs.Al

10、thoughpurewhitelightemittingdevicesbasedonultrasmallCdSenanocrystalsalonehavebeenfabricatedrecently16theirexternalquantumefficiencyisonly0.00013%.MeoversemiconductQDscontainingcadmiumotherheavymetalshavehightoxicityevena

11、trelativelylowconcentrationswhichgreatlylimitstheirpracticalapplications.Theemerginglightemittingquantumsizedcarbondots(CDs)appeartobeapromisingalternativetosemiconductQDssincetheywereproposedbySunetal.in2006.18Thesurfac

12、epassivatedCDscombineseveralmeritsoftraditionalsemiconductbasedquantumdotssuchastuneableluminescenceemissionresistancetophotobleachingeaseofbioconjugationwithoutincurringtheburdenofintrinsictoxicityelementalscarcity.19Ap

13、reviousreptalreadydemonstratedthathighqualitywhitelightcanbeachievedfromCDfilmwhenpumpedwitha407nmlaser.20HoweverthefundamentalresearchpotentialapplicationsofCDsarerarelystudiedduetolowquantumyield(QY)complicatedsyntheti

14、cmethods.Recentlyanovelonestepapproachtosynthesizehighlyluminescent(QYexceeding50%)CDsinnoncodinatingsolventhasbeendevelopedbyourgroup.21UsingthismethodwedemonstrateWLEDsiginatingfromtheCDsfthefirsttimenamedCWLEDs.Themax

15、imumexternalquantumefficiencyofthisdeviceisover0.08%atthecurrentdensityof5mAcm?2.TheCommissionInternationald’Eclairage(CIE)codinatesof(0.400.43)withacolrenderingindex(CRI)of82arenotdependantonthedrivingvoltage.Theresults

16、indicatethatCDscanactasanewclassofphosphmaterialfachievinghighperfmanceWLEDs.ThesimpledeviceschematicdiagramsenergylevelschemicalstructuresoftheganiccompoundsemployedinthiswkalongwithaschematicdrawingofCDspassivatedwith1

17、hexadecylamineareshowninFig.1.ThedevicemaintainsthearchitectureoftrilayernanocrystalELdevicesdescribedpreviously.15–17Briefly40nmthickpoly(34ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)wasusedasthebufferlaye

18、rontheanodeindertoincreasetheanodewkfunctionfrom4.7eV(ITO)to5.0eVtoreducethesurfaceroughnessoftheanode.22TheamphousCDs21weresynthesizedbythermalcarbonizingcitricacidinhotoctadecenewith1hexadecylamineasthepassivationagent

19、.ToapplytheCDsinLEDstheaspreparedaKeyLabatyofPhotochemicalConversionOptoelectronicMaterialsTechnicalInstituteofPhysicsChemistryChineseAcademyofSciencesBeijing100190P.R.China.Email:.bStateKeyLabatyofPolymerPhysicsChemistr

20、yChangchunInstituteofAppliedChemistryChineseAcademyofSciencesChangchun130022P.R.China.Email:mdg1014@ciac.cGraduateSchooloftheChineseAcademyofSciencesBeijing100806P.R.ChinawElectronicsupplementaryinfmation(ESI)available:D

21、etailsofthesynthesisofCDsdevicesfabricationopticalpropertyofCDsintolueneCVmeasurement.SeeDOI:10.1039c0cc05391k.zBothauthscontributedequallytothiswk.ChemCommDynamicArticleLinkswww.rsc.gchemcommCOMMUNICATION3504Chem.Commun

22、.2011473502–3504ThisjournaliscTheRoyalSocietyofChemistry2011multicolemittingCDsarehardtoisolatebysizeiveprecipitationcolumnchromatography.ByoptimizingthedevicestructureoftheCWLEDswefoundthethicknessoftheCDslayerplayedacr

23、iticalroleinELefficiencymaximumluminanceofthedevice.TheoptimizedthicknessoftheCDslayerwasaround20nm.IncreasingthethicknessofCDsfilmupto35nmreducingitto10nmwouldobviouslydecreasetheELefficiency.Thiswasexplainedinaprevious

24、reptbypoergetransptationbetweenphosphsinathickerfilmthepresenceofvoidsgrainboundariesinterstitialspacesinthethinnerfilmrespectively.22Fig.4ashowsthecurrentdensity–voltage–brightnessoftheCWLEDs.Thecurrentdramaticallyincre

25、asesasthedrivenvoltageisincreased.Theturnonvoltageisabout6VwhichisalittlehigherthantheturnonvoltageoftheQDsblend.7Themaximumbrightnessoutputof35cdm?2crespondingtoacurrentefficiencyof0.022cdA?1isrealizedatacurrentdensityo

26、f160mAcm?2at9V.AsshowninFig.4bthemaximumexternalquantumefficiency(EQE)oftheCWLEDsis0.083%atacurrentdensityof5mAcm?2.ItiscomparablewiththeWLEDsbasedonfullQDswhoseEQEareintherange0.00013–0.36%.714–16Thepresentwkshowsthatma

27、kingpurewhiteLEDswithCDsaloneispossiblegivinganopptunityfsimplehighqualitylightsourceswithexcellentcolstability.Furtherinvestigationisnecessarywillbepursued.TherelativelyhighturnonvoltagethelowEQEarespeculatedtobeaconseq

28、uenceoftheinsulatinglayerof1hexadecylaminewhichispassivatedontheCDs’surface.Thisisinagreementwithpreviousresearch25inwhichthepassivationlayeristypically0.5nmthick.Itfmsaminimaltunnellingbarrierftheelectronsholesthatpasst

29、hrough.Inviewofthishypothesisweexpectthatfurtheroptimizationofthegeinjection(holeselectrons)aswellasthecarrierbalancewithmaterialdevelopmentsbysynthesizingCDswithaconjugatedsurfacewillleadtoanefficiencyclosetothewelldeve

30、lopedOWLEDs.InconclusionWLEDsbasedonCDshavebeensuccessfullydemonstratedfthefirsttime.TheproposeddeviceprovidesapotentialgeneralmethodffabricatingnovelELdevicescombiningtheadvantagesofganicpolymersintermsofefficientcarrie

31、rtransptflexibilitywiththeCDsintermsoflowcostphotochemicalstabilityreducedtoxicity.ThiswillopenupnewavenuestosimplehighqualityCDsbasedlightsourcesthatapproximatenaturalsunlight.TheperfmanceoftheCWLEDsisexpectedtobefurthe

32、rimprovedassoonasthedetailsoftheunderlyingphysicalmechanismoftheCDsarethoughlywkedoutthesyntheticparameterscanbeadjustedaccdingly.Notesreferences1G.L.TuC.Y.MeiQ.G.ZhouY.X.ChengY.H.GengL.X.WangD.G.MaX.B.JingF.S.WangAdv.Fu

33、nct.Mater.200616101.2B.W.D.radeS.R.FrestAdv.Mater.2004161585.3S.CoeSullivanJ.S.SteckelW.K.WooM.G.BawendiV.BulovicAdv.Funct.Mater.2005151117.4J.ZhaoJ.A.BardeckerA.M.MunroM.S.LiuY.H.NiuI.K.DingJ.LuoB.ChenA.K.Y.JenD.S.Ginge

34、rNanoLett.20066463.5M.J.BowersJ.R.McBrideS.J.RosenthalJ.Am.Chem.Soc.200512715378.6H.S.ChenS.J.J.WangC.J.LoJ.Y.ChiAppl.Phys.Lett.200586131905.7P.O.AnikeevaJ.E.HalpertM.G.BawendiV.BulovicNanoLett.200772196.8BuildingEnergyD

35、ataBook2006.USDepartmentofEnergySilverSpringMDUSA2006:buildingsdatabook.eren.doe.gov.9J.Y.TsaoLightEmittingDiodes(LEDs)fGeneralIlluminationOptoelectronicsIndustryDevelopmentAssociationWashingtonDC2002.10M.R.KramesJ.BhatD

36、.CollinsL.CookM.G.GrafdR.FletcherN.F.GardnerW.GotzC.H.LoweryM.LudowiseP.S.MartinG.MuellerR.MuellerMachS.RudazD.A.SteigerwaldS.A.StockmanJ.J.WiererPhys.StatusSolidiA2002194380.11J.KidoK.HongawaK.OkuyamaK.NagaiAppl.Phys.Le

37、tt.1995672281.12Y.SunN.C.GiebinkH.KannoB.MaM.E.ThompsonS.R.FrestNature2006440908.13G.SchwartzS.ReinekeT.C.RosenowK.WalzerK.LeoAdv.Funct.Mater.2009191319.14Y.LiA.RizzoR.CingolaniG.GigliAdv.Mater.2006182545.15A.RizzoM.Mazz

38、eoM.BiasiucciR.CingolaniG.GigliSmall200842143.16M.A.SchreuderK.XiaoI.N.IvanovS.M.WeissS.J.RosenthalNanoLett.201010573.17S.CoeW.WooM.BawendiV.BulovicNature2002420800.18Y.P.SunB.ZhouY.LinW.WangK.A.S.FernoP.PathakM.J.Mezian

39、iB.A.HarruffX.WangH.F.WangP.J.G.LuoH.YangM.E.KoseB.L.ChenL.M.VecaS.Y.XieJ.Am.Chem.Soc.20061287756.19S.N.BakerG.A.BakerAngew.Chem.Int.Ed.2010496726.20F.WangM.KreiterB.HeS.P.PangC.Y.LiuChem.Commun.2010463309.21F.WangS.P.Pa

40、ngL.WangQ.LiM.KreiterC.Y.LiuChem.Mater.2010224528.22Q.J.SunY.A.WangL.S.LiD.Y.WangT.ZhuJ.XuC.YangY.F.LiNat.Photonics20071717.23X.WangLi.CaoS.T.YangF.LuM.J.MezianiL.TianK.W.SunM.A.BloodgoodY.P.SunAngew.Chem.Int.Ed.20104953

41、10.24G.ChengM.MazzeoA.RizzoY.Q.LiY.DuanG.GigliAppl.Phys.Lett.200994243506.25P.O.AnikeevaJ.E.HalpertM.G.BawendiV.BulovicNanoLett.200992532.26H.LiuT.YeC.MaoAngew.Chem.Int.Ed.2007466473.27L.TianD.GhoshW.ChenS.PradhanX.Chang

42、S.ChenChem.Mater.2009212803.28A.B.BourlinosA.StassinopoulosD.AnglosR.ZbilM.KarakassidesE.P.GiannelisSmall20084455.29J.H.KwakW.K.BaeM.ZnH.WooH.YoonJ.LimS.W.KangS.WeberH.J.ButtR.ZentelS.LeeK.C.LeeAdv.Mater.2009215022.Fig.4