DefectControlandInterfaceModificationforHighPerformancePerovskiteLight-EmittingDiodes

Abstract

Inrecentyears,metalhalideperovskite(MHP)materialshavegarneredattentionasmaterialsfortheirpotentialusedinvariousoptoelectronicdevicessuchassolarcells,lasers,photodetectors,andlight-emittingdiodes(LEDs).MHPexhibitoutstandingelectricalandopticalproperties,includinghighchargemobility,narrowemissionspectra,tunablecolors,andhighphotoluminescencequantumyields(PLQY).Thesecharacteristicshavespurredextensiveresearchintothefundamentalpropertiesofperovskitematerialsandtheirpotentialapplicationsasnext-generationdisplaymaterials.However,thecrystalstructureofperovskitematerialscontainsweakionicbonds,renderingthemvulnerabletodegradationbyexternalfactorssuchasoxygenandmoisture,whichleadstoreducedstability.Thislimitationcanbeaddressedthrougheffectivecontrolofdefectsontheperovskitesurfaceusingvarioussurfacepassivationstrategies.Consequently,developinghighlyefficientandstableperovskiteLEDsbycontrollingdefectsintheperovskiteemittingmaterialiscrucialforachievinghighluminescenceefficiencyandsuperiorstability.Inthisthesis,variousstrategiesforhigh-efficientandstableperovskitelightemittingdevicesaresuggested,whichelucidatecontrollingdefectsontheperovskitesurfacebyintroducingorganicligandsandmetalionsontotheperovskitenanocrystal'ssurfaceandadjustmentofenergybarrierswithinperovskiteLEDs. InChapter1,anintroductiontoperovskitematerialsisprovided,alongwiththeresearchbackgroundandanoverviewoftheoverallstudyinthisthesis.Inthiscontext,thecurrentdevelopmentstatusandclassificationofperovskitematerials,thepropertiesofperovskitematerialsandbasicbackgroundknowledgeonperovskite-basedLEDsarepresented. InChapter2,asynthezingmethodforpassivatingthesurfaceofblueperovskitenanocrystalsusingcadmiumionsisproposed,andthedifferencesbetweensurfacedopingandbulkdopingofperovskitenanocrystalsarediscussed.Thisapproachdemonstratesthattheintroductionofcadmiumionsontothenanocrystalsurfacecaneffectivelysuppressthehalidedefectformation.Furthermore,byemployinganadditionalorganicligandexchangeprocess,high-qualityblueperovskitenanocrystalswithhighphotoluminescencequantumyieldandstabilityarerealized. InChapter3,strategyforintroducingvariousdivalenttransitionmetalionsontothesurfaceofgreenperovskitenanocrystalsduringtheorganicligandengineeringprocessissuggested.Thisapproacheffectivelycontrolsdefectsgeneratedduringtheligandengineeringprocessandadjuststhesurfacelatticestructureofperovskitenanocrystalstoenhancethedensityofsurfaceorganicligands,therebyeffectivelypassivatingthenanocrystalsurface.ThesurfaceengineeringapproachesforperovskitenanocrystalspresentedinChapters2and3providevaluableinsightsintothemethodsforimprovingtheperformanceandstabilityofperovskite-basedLEDs. InChapter4,amethodforminimizingthebarrierstoelectronandholeinjectioninperovskiteluminescentdevicesisproposed,focusingonthedevelopmentandoptoelectronicapplicationsofbinaryblendedsmallmolecule/polymerholetransportlayer.Itwasconfirmedthattheenergybarrierisreducedwhenusingmixedholetransportlayerscomparedtoconventionalhigh-molecularholetransportlayers.WhenappliedtoPeLEDs,thisapproachexhibitedbalancedchargeinjectionandminimizedleakagecurrent,enablingtheimplementationofhigh-performancebluePeLEDs.Thisdemonstratesthefeasibilityofachievingbalancedelectronandholeinjectionthroughthedevelopmentofchargetransportlayerswithappropriateworkfunctionsandoffersamethodforthestructuraldesignofhigh-efficientPeLEDs. Subsequently,Chapter5suggeststhatthevariousapproachesforhigh-performanceandstableperovskitelight-emittingdevicesdemonstratedinthisthesiscanbeeffectivestrategiesfordevelopinglight-emittingmaterialsanddevicestructuresfornext-generationlight-emittingdiodes.