In fl uence of Dynamic Disorder and Charge − Lattice Interactions on Optoelectronic Properties of Halide Perovskites - Munson, Asbury -

《In fl uence of Dynamic Disorder and Charge − Lattice Interactions on Optoelectronic Properties of Halide Perovskites - Munson, Asbury -》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

pubs.acs.org/JPCCPerspectiveInfluenceofDynamicDisorderandCharge−LatticeInteractionsonOptoelectronicPropertiesofHalidePerovskitesKyleT.MunsonandJohnB.Asbury*CiteThis:J.Phys.Chem.C2021,125,5427−5435ReadOnlineACCESSMetrics&MoreArticleRecommendationsABSTRACT:Theoriginsofmanyuniquepropertiesofhalideperovskitesemiconductorscanbetracedtocharge−latticeinteractionsthatleadtolargepolaronformationcombinedwiththeirunusualelectronicstructureofdefects.However,theabilitytounderstandandcontroltheinterplayoftheseelectronicstateswithdynamicdisorderarisingfromstructuralfluctuationsofthemetalhalideframeworkisneededtoguidecontinueddevelopmentofnewvariantsofthesematerials.InthisPerspective,weexaminetheinfluencethatdynamicdisorderhasoncharge−latticeinteractionsinhalideperovskitematerialsthatleadtochargelocalizationandlargepolaronformation.Furthermore,wedescribehowtheinterplayofmaterialcomposition,structuraldynamics,andlargepolaronformationinfluencesradiativeandnonradiativeband-edgerecombination.Insightsabouthowtocontrolthisinterplaymayinformdevelopmentofrelatedmetalhalidesemiconductorsincluding2DRuddlesden−Popper,doubleperovskite,andnanocrystallinesystemswithtailoredradiativeandchargetransportpropertieswhileavoidingtoxicelements.25■INTRODUCTIONperovskites.Consistentwiththishypothesis,recenttheoreti-Theextraordinaryperformanceofhalideperovskite-basedcalworkhassuggestedthatthelatticefluctuationsthatleadtophotovoltaicsismainlyduetothelownonradiativepolaronformationmaygeneraterepulsiveinteractionsbetween12oppositelychargedcarriers.11Latticefluctuationsmayalsorecombinationrates,micrometercarrierdiffusionlengths,3,4affectthecoolingratesofabove-bandgap“hot”carriersandmicrosecondcarrierlifetimesexhibitedinthismaterial26,27class.Thesepropertiesenablehalideperovskitephotovoltaicfollowingopticalexcitation.Inparticular,theformationdevicestoexhibithighopen-circuitvoltagesdespitebeingoflargepolaronsmaysuppressthecarrierscatteringeventsthatprocessedfromsolution.5Halideperovskitesalsopossessother28leadtocarriercoolinginhalideperovskites.DownloadedviaBUTLERUNIVonMay16,2021at12:27:09(UTC).favorableoptoelectronicproperties,suchassmallexcitonTheabovereportshighlighttheneedtounderstandthe67bindingenergiesandhighabsorptioncoefficients,makinginterplaybetweendynamicdisorderduetofluctuationsofthethemidealmaterialsforawidevarietyofoptoelectronic12,218,9perovskitelatticeandthecharge−latticeinteractionsthatapplicationsbeyondphotovoltaicssuchaslasersand21−2410leadtopolaronformationFurthermore,theexactnatureLEDs.Seehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.ofthecharge−latticeinteractions,howtheyaremodulatedbyThereisgrowingconsensusintheliteraturethatcharge−latticeinteractionscausechargecarrierstoself-trapintolargetheunderlyingstructureandcomposition,andhowtheseinpolaronicstatesandthatthesestatesfigureprominentlyintheturnaffecttheoptoelectronicpropertiesofmetalhalideremarkableoptoelectronicpropertiesofhalideperovskiteperovskiteshasnotbeenfullyelucidated.Suchknowledge11−20materials.Forexample,contemporaryworkusingfar-IR,willbecriticalforunderstandinghowthereduceddimension-terahertz,orRamanspectroscopytoexaminepolaronalityandmodifiedcrystalstructuresofmetalhalidesemi-frequenciesandestimatesofdielectricpropertiesandcarrierconductorssuchas2DRuddlesden−Popper29−31anddoubleeffectivemassesdemonstratesthatthiscouplingiswellperovskitematerials32−34influencetheirlightemittinganddescribedbyFröhlich-typeinteractionsofchargeswithpolaroptoelectronicproperties.phononmodesinmethylammoniumleadhalideperov-21−24skites.Thesepolaronicstatesareconsideredtobe“large”inhalideperovskitesbecausethepolarizationcloudReceived:December5,2020createdbydistortionsoftheperovskitelatticearoundchargeRevised:February5,2021carriersspanseveralunitcells.20Published:February16,2021Theformationoflargepolaronsisthoughttobetheoriginoftheslowsecondorderrecombinationratesandmoderatechargecarriermobilitiesexhibitedinthree-dimensional©2021AmericanChemicalSocietyhttps://dx.doi.org/10.1021/acs.jpcc.0c108895427J.Phys.Chem.C2021,125,5427−5435

1TheJournalofPhysicalChemistryCpubs.acs.org/JPCCPerspectiveInthisPerspective,wedescriberecentexperimentalstudiestheperovskitestructure;however,chloride(Cl−)anionsalsothatusedtemperature-dependent,mid-infraredtransienthavebeenused.Interestingly,thecompositionofstate-of-the-absorption(mid-IRTA)spectroscopyandtime-resolvedartperovskitedevicescommonlyincludesseveraldifferentA-photoluminescence(TRPL)spectroscopytoexaminethesitecations,B-sitemetalions,andX-sitehalideionssuchas5effectoflargepolaronformationonband-edgerecombinationFA0.79MA0.16Cs0.05Pb0.85Sn0.15I2.5Br0.5.inhalideperovskitesatcarrierdensitiescloselymatchedtoInstarkcontrasttootherinorganicsemiconductorssuchasthoseofoperatingphotovoltaicdevicestominimizehigherSiandGaAs,thehalideperovskitelatticeismechanicallysoftorderrecombinationartifacts.Wethenhighlightrecent12anddynamicallydisordered.Avarietyofexperimentalmeasurementsofthestructuralfluctuationsthatarecorrelatedmethodshavebeenusedtoexaminetheanharmonicnaturewithlargepolaronformationusingmid-IRTAspectroscopyto14,37,38oftheperovskitelattice.Forexample,Ramanspectros-probethevibrationaldynamicsofthehalideperovskitelattice.copyandmoleculardynamicssimulationshaveshownthattheFurthermore,weexaminetheinfluencethatvariousA-sitelow-frequencyvibrationalmodesoftheperovskitelattice’sBX3cationshaveonthedynamicsoflargepolaronformationandframeworkundergolargeamplitudedisplacementsatroomtheirdelocalizationlengths,bindingenergies,andinfluenceontemperature.39Likewise,neutrondiffractionmeasurementschargerecombinationusingaseriesofleadbromideperovskitealsohavebeenusedtoinvestigatethestructuraldynamicsoffilms.Finally,wediscusshowthecharge−latticeinteractionstheperovskitelattice.40Figure1BshowstherefinedstructurethatleadtopolaronformationmaybemodifiedbyionofaMAPbI3perovskitesinglecrystalobtainedfromneutronsubstitutionandsuggestfuturestudiesusingmid-IRTAdiffractionmeasurements.Thestructurehighlightstheatomicspectroscopythatcanbeusedtobuildstructure−functiondisplacementsoftheiodineatomsthatarisefromthecorrelationstopredicthowthecompositionsofnewmetalanharmonicnatureoftheperovskitelatticeatroomtemper-halidesemiconductorsinfluencetheiroptoelectronicandlightature.Thesedisplacementsarerepresentedasellipsoidsinthe29−34emittingproperties.figure.ThestructurealsohighlightsthedisorderednatureoftheMAcations,whichappearasa“sphere”inthecenterofthe■RESULTSANDDISCUSSIONBX3framework.Organiccationsinhybridorganic−inorganicperovskites,Thethree-dimensionalhalideperovskitesutilizedinstate-of-the-artphotovoltaicdevicesshareacommonABXstructuresuchasMAPbI3,interactwiththematerial’sinorganic3frameworkmainlyviaion−ion,ion−dipole,andhydrogenwhereAisamonovalentcation,Bisadivalentmetalion,and4135,36bondinginteractions.However,inthehigh-temperatureXisahalideanion(Figure1A).TheA-siteionsusedtotetragonalandcubicphasesofthematerial,theseinteractionsformhalideperovskitesaretypicallyeithersmallorganic42arenotstrongenoughtoimmobilizetheorganicions.Asamolecules,suchasmethylammonium(MA)andformamidi-result,organiccationscanrotaterapidlywithintheperovskitenium(FA),orinorganicions,suchascesium(Cs).Lead(Pb)andtin(Sn)arecommonlyusedastheB-sitemetalion.Iodidelattice’sBX3framework.Numerousexperimentalreportshave(I−)andbromide(Br−)anionstypicallyoccupytheXsiteofexaminedtherotationaldynamicsoforganiccationsinhalideperovskites.Forexample,polarization-resolvedtwo-dimen-sionalinfrared(2DIR)spectroscopywasusedtoinvestigate43,44therotationalmotionofMAionsinhalideperovskites.Fromthesemeasurements,theauthorsdeterminedthatMAcationsinMAPbI3perovskitefilmsundergotwodistinctwobbling-in-cone(∼0.3ps)androtationalmotions(∼3ps),respectively(Figure1C).Similardynamicsalsowereobtainedfrompolarizationresolved2DIRmeasurementsofFAionsin45FAPbI3thinfilms.Formoreinformationabouttherotationaldynamicsoforganiccations,wedirectthereadertoarecent42perspectivefromBakulinandco-workers.ThedisorderednatureofboththeinorganicBX3frameworkandA-sitecationshasledseveralinvestigatorstoproposethatfluctuationsoftheperovskitelatticeunderpintheremarkableoptoelectronicpropertiesexhibitedinthisclassofmateri-46−48al.Evidenceforcharge−latticeinteractionsarisingfromelectron−phononcouplinginhalideperovskiteshasbeen49obtainedfromtemperature-dependentPL,chargecarrier18,4750Figure1.(A)Representationoftheperovskiteunitcelldepictingthemobility,two-dimensionalelectronicspectroscopy,and23,51inorganicAX3frameworkandthestructureofcommonAsitecationsTHzmeasurements.Suchexperimentsledinvestigatorstousedinstate-of-the-artdevices.Reprintedwithpermissionfromrefproposethatfluctuationsoftheperovskitelatticecausecharge28.Copyright2016AmericanChemicalSociety.(B)Refinedcarrierstoself-trapintolargepolaronicstateswithinthestructureofaMAPbI3singlecrystalobtainedfromneutrondiffractionmaterial.12,20,25Thesestudiesalsorevealedthatthecharge−measurements.Thestructurehighlightsthedisorderednatureofthelatticecouplinginmetalhalideperovskitesisrelativelyweak,perovskite’sMAcationsandthelargedisplacement(ellipsoids)oftheconsistentwithFröhlich-typeinteractionsofchargecarriersmaterial’shalideions.Reprintedwithpermissionfromref40.21−24withpolarLOphonons.TheformationoflargepolaronsCopyright2015RoyalSocietyofChemistry.(C)Cartoon12,20representationoftherotationalmotionofMAcationsinhalideprolongstherecombinationlifetimesofchargecarriersandperovskites.Reprintedwithpermissionfromref42.Copyright2018mayalsoshieldchargecarriersfromdefectswithinthe52AmericanChemicalSociety.material.Itislikelythatthesepropertiesfacilitatetheability5428https://dx.doi.org/10.1021/acs.jpcc.0c10889J.Phys.Chem.C2021,125,5427−5435

2TheJournalofPhysicalChemistryCpubs.acs.org/JPCCPerspectivetodeposithigh-performancehalideperovskitematerialsusingaenergyandaDrude-likefreecarrierabsorptiontailathigher5358varietyofsolution-processeddepositionmethods.transitionenergies.TheoriginofthisbehaviorcanbetracedTheconnectionbetweenthestructuralandelectronictoacombinationofshortandlong-rangecharge−latticepropertiesofhalideperovskiteshasencouragedstudiesthatinteractionsthatdefinethekineticandpotentialenergiesofinvestigatethedynamicsofchargecarriersinthesematerialschargecarriersinteractingwiththeirself-generatedpolarization35,54followingphotoexcitation.However,ithasbeenchalleng-cloudsintheinorganicsublattice.ThespectrumappearinginingtodrawdirectcorrelationsbetweenstructuralfluctuationsFigure2AalsoshowsnarrowvibrationalfeaturesoftheMAandpolarondynamicsusingtraditionalspectroscopictechni-cationswithintheMAPbI3film.Thesevibrationalfeaturesques,suchasTRPLalone.Inpart,thisisduetoTRPLserveasdirectprobesofthestructuraldynamicsofthemeasurementsbeingaffectedonlyindirectlybynonradiativeperovskitelatticeinthepresenceofchargecarriers.recombinationpathwaysamongtheband-edgestatesoftheConsequently,analysisofthesevibrationalfeaturesenabledmaterialandbecausenumerousprocessescancontributetothetheinvestigatorstoobtainmechanisticinformationaboutthe55observedspectraandkinetics.structuraloriginofpolaronformationinhalideperovskiteRecently,advancesinmid-IRTAspectroscopyhaveenabledoptoelectronicmaterials.Themeasurementsoftheexcited-thetechniquetobeusedtodirectlyprobethespectroscopicstatevibrationaldynamicsoftheperovskitelatticearesignaturesoflargepolaronsinhalideperovskitesatlowdiscussedbelow.photogeneratedchargecarrierdensities(3×1016cm−3)Theabilitytomeasurethedynamicsoflargepolaronsatlow212followingopticalexcitationat532nmand500nJ/cm.excitationdensitiesenabledtheirdynamicstobedirectlyTheseexcitationconditionsproducetransientcarrierdensitiescomparedtoTRPLmeasurementsunderidenticalconditionsthatcloselyresemblecarrierdensitiesthatoccurundersteady-12(Figure2B).Figure2Cdisplaysnormalizedrecombination56,57statesolarillumination,allowingthedynamicsoflargekineticsoflargepolarons(fromtheirmid-IRabsorptions)polaronstobemeasuredunderconditionsrelevanttocomparedwiththenormalizedPLdecaysofaMAPbI3filmfunctioningoptoelectronicdevices.Figure2Ashowsthemeasuredunderidenticalconditions(532nm,500nJ/cm2excitationdensity)at190and290K.WenotethatanalysisoftheshapesofthelargepolaronabsorptionspectraappearinginFigure2Aasafunctionoftemperatureallowedinvestigatorstodeterminethatthedelocalizationlengthoflargepolaronsdecreasedfrom∼11nmat190Kto∼9nmat290K,indicatingthatchargecarriersweremorespatiallylocalizedat20highertemperatures.Thus,comparingthelargepolaronandTRPLdecaykineticsallowedtheeffectsofcarrierlocalizationonband-edgerecombinationtobedetermined.Atlowertemperature(190K),wherechargecarriersaremoredelocalized,theTRPLdynamicsexhibitedband-edgeemissioninquantitativeagreementwiththedynamicsofchargecarriersprobedusingmid-IRTAspectroscopy(Figure2C,left).However,atroomtemperature(290K),thelifetimeofchargecarriersprobedinthemid-IRincreased20-foldrelativetothelowertemperaturemeasurementanddeviatedfromtheradiativerecombinationkineticsmeasuredusingTRPLunderthesameconditions(Figure2C,right).Theseresultsarealsoconsistentwithtemperature-dependent20measurementsofbimolecularrecombinationcoefficients,Figure2.(A)Mid-IRTAspectrumoflargepolaronsinahalidewhichshowedthatchargecarrierlocalizationalsodecreasesperovskitefilmmeasuredata30nstimedelayfollowingbandgapexcitation.Theinsetshowsthetransitionsthatappearinthebimolecularrecombinationrateswithinthematerial.spectrum.(B)SchematicshowingTRPLandTRIRmeasurementsTheabovecomparisonrevealsthatthelocalizationofchargeperformedunderidenticallowexcitationdensityconditions.(C)carriersintolargepolaronicstatesatelevatedtemperaturesTRPLdecayversusmid-IRTArecombinationkineticsmeasuredatslowschargecarrierrecombinationwithinthematerial.290K(right)and190K(left)plottedonalogarithmictimeaxis.TheHowever,theformationoflargepolaronsalsoquenchesmid-IRTAandTRPLdecaykineticsmatchwithinexperimentalphotoluminescence(Figure2C,ref12).Thus,whilepolaronprecisionatlowertemperaturebutdeviateathighertemperatureformationmaybeadvantageousforphotovoltaicdevicesduebecauseofcarrierlocalizationcausedbycharge−latticeinteractionstoprolongedchargecarrierlifetimes,itmayhinderthethatareenhancedbydynamicdisorderatelevatedtemperatures.59efficienciesofperovskite-basedLEDs.Forexample,theReprintedwithpermissionfromref12.Copyright2018Elsevier.efficienciesoflightemittingdiodesfabricatedusingtwo-59dimensional(2D)lead-halideperovskitesaretypicallylowlargepolaronspectraobtainedfrommid-IRTAspectroscopyand,insomecases,canonlybemeasuredatcryogenic60,61measurementsofapolycrystallineMAPbI3filmfollowinga30temperatures.Thesepoorefficienciesmaybedueto12nstimedelayafterbandgapexcitation.Suchpolycrystallineenhancedelectron−phononinteractionsandpolaronforma-MAPbI3filmswillbecalledsimplyMAPbI3filmshereandintionwithinthematerial,whichhasbeenreportedpreviouslyby16thefollowing.TheinsetofFigure2AshowsthetransitionsthatSilvaandco-workers.However,certainintrinsicdistortionsappearinthespectrum.Theabsorptionspectraoflargeinlowdimensionalhalideperovskitescanleadtopolaronic29,30polaronsarecharacterizedbyasharpabsorptiononsetataexcitonswithefficientbroadbandemission.Thesetransitionenergythreetimesthelargepolaronself-trappingobservationsunderscoretheneedtounderstandtheinterplay5429https://dx.doi.org/10.1021/acs.jpcc.0c10889J.Phys.Chem.C2021,125,5427−5435

3TheJournalofPhysicalChemistryCpubs.acs.org/JPCCPerspectiveofsuchpolaroniceffectsonexcitedelectronicstatestopredictUnliketheFTIRspectra,boththecenterfrequencyandlineandcontroltheelectronicpropertiesofhalideperovskites.widthoftheN−HbendmodechangewithtemperatureintheBecausetheformationoflargepolaronsinhalideperovskitesexcitedelectronicstate.TheN−Hbendvibrationsoftheslowschargerecombinationandquenchesphotoluminescence,excitedelectronicstatewerefitwithLorentzianfunctionstomodifyingthecharge−latticeinteractionsthatleadtopolaronquantifythechangesintheirlinewidths.ThebestfitfunctionsformationmayallowinvestigatorstotunetheoptoelectronicareoverlaidonthevibrationalspectrashowninFigure3A.Thepropertiesofhalideperovskitesforspecificapplications,suchincreaseinthelinewidthofthevibrationalmodeat310Kaslight-emittingdiodesandlasers.Tothisend,severalindicatesfastervibrationaldephasingoftheN−Hbendinvestigatorshaveexaminedtheexcited-statephonondynam-vibrationalmodeintheexcitedelectronicstateatelevated14icsinlead-halideperovskitesthatleadtopolaronformation.temperatures.ThesefastervibrationaldephasingdynamicsForexample,time-domainRaman(TDR)measurementsofaoriginatefromstructuraldistortionsoftheperovskitelatticeMAPbBr3filmcollectedafterexcitationofthematerial’sthatchangethehydrogenbondingandion−dipoleinteractionsbandgapusingultrashortlaserpulsessuggestedthatthebetweenMAcationsandthematerial’sPbI−inorganic3presenceofphotogeneratedchargecarriersshiftsthe20framework.equilibriumpositionsandvibrationalenergiesoftheperovskiteThefastervibrationaldephasingdynamicsobservedin24lattice.Likewise,timedomainopticalKerreffect(OKE)Figure3Aatelevatedtemperatureswerecorrelatedwiththespectroscopyhaspreviouslybeenusedtoprobetherelaxationself-trappingofchargecarriersintolargepolaronicstates.oftheperovskitelattice’sPb−XmodesfollowingopticalFigure3Bshowstemperature-dependentpolaronabsorption13excitation.spectracollectedunderthesameexperimentalconditionsasAsstatedabove,mid-IRTAspectroscopyisalsocapableof12thevibrationaldynamics.Thetemperature-dependentstudymeasuringtheexcitedstatevibrationaldynamicsthatarerevealsthattheintensityofthemid-IRpolaronabsorptioncorrelatedwithpolaronformationinhalideperovskites.Figurefeatureincreasedasthetemperaturewasraised,indicatingthat3Adisplaysbaselinecorrectedmid-IRTAspectraofaMAPbI3largepolaronformationisenhancedatelevatedtemperatureswhentheperovskitelatticeundergoeslargeramplitudefluctuations.ThisincreaseoflargepolaronformationwasassociatedwithacorrespondingdecreaseoftheradiativequantumyieldatelevatedtemperaturesfromTRPLmeasure-12ments.TheTRPLandmid-IRTAmeasurementswereconductedwiththesameexcitationintensitiesatalltemper-atures,allowingquantitativecomparisonofthechangesofradiativeefficiencieswiththevariationofthedensitiesoflargepolarons.Takentogether,theseresultsindicatethattemper-aturedependentanharmonicfluctuationsoftheperovskitelatticeenhancethecharge−latticeinteractionsthatunderpinpolaronformationandrecombinationmechanismsintheexcitedstateofthisclassofmaterial.Becausepolaronformationdependsonthestructuraldynamicsofthehalideperovskitelattice,severalreportshaveFigure3.(A)Baselinecorrectedmid-IRTAspectraofaMAPbI3filminvestigatedtheinfluencethatthematerial’sA-sitecationsandinitsexcitedelectronicstatecollectedat190and310KfollowinginorganicBX3frameworkhaveonpolaronformationandbandgapexcitationat532nm.ThespectrahighlighttheN−Hbendrecombinationmechanisms.Bothcomputationalandexper-regionofthefilm.ThesmoothcurvesthroughthedatarepresenttheimentalreportshavesuggestedthatthemotionofdipolarLorentzianfunctionsusedtoquantifythefullwidthathalf-maximumorganiccationsaffectspolaronformation,transport,andofthevibrationalfeatures.CorrespondingFTIRspectraareshown25,63−68recombinationinhalideperovskites.Forexample,thebelowthemid-IRTAspectraforcomparison.ReprintedwithorientationalmotionofFAcationsinFAPbI3filmswaspermissionfromref20.Copyright2019AmericanChemicalSociety.suggestedtoinfluencetheelectronicpropertiesofhalide(B)PolaronabsorptionspectraofaMAPbI3filmmeasuredatdifferenttemperaturesfollowingbandgapexcitation.Thedensityofperovskitesonthebasisoftemperature-dependentphoto-63absorbedphotonswasidenticalforalltemperatures,indicatingthatluminescencemeasurements.However,temperature-depend-theincreaseinamplitudeofthelargepolaronspectraatelevatedentRamanspectroscopymeasurementsrevealedthatthepolartemperaturesisduetoenhancedpolaronformation.Reprintedwithfluctuationsthatunderpinpolaronformationinhalidepermissionfromref12.Copyright2018Elsevier.perovskitesdonotdependonthedipolemomentofthe39material’sA-sitecation.filmcollectedintheMAcation’ssymmetricN−HbendregionToaddresswhetherthedipolarmotionofA-sitecations20influenceschargecarrierdynamicsinhalideperovskites,measuredat310and190K.Thevibrationalfeaturesdepictedinthemid-IRTAspectraarisefromperturbationsofinvestigatorsusedmid-IRTAspectroscopytoexaminepolaronthesymmetricN−Hbendmodecausedbythepresenceofformationandchargerecombinationinhalideperovskiteswith36photogeneratedchargecarriersintheexcitedelectronicstateofdifferenttypesofA-sitecations.Figure4Ashowsthelargethehalideperovskitefilm.Thecorrespondingground-statepolaronabsorptionspectraofMAPbBr3,FAPbBr3,andFTIRspectraofthefilmateachtemperatureappearintheCsPbBr3perovskitefilmsmeasuredunderidenticalexcitationlowerpanelsofFigure3A.SimilarperturbationsofN−Handconditions.Thesimilaritybetweenthemid-IRTAspectra,C−HstretchvibrationalmodesinaMAPbI3filmwerewhoseshapedependsonthedelocalizationlengthandbinding5520,36observedusingrecenttime-resolvedandsteady-statemid-IRenergiesoflargepolarons,indicatedthatthedipolar62measurements.disorder(oralignment)oforganiccationswithinthe5430https://dx.doi.org/10.1021/acs.jpcc.0c10889J.Phys.Chem.C2021,125,5427−5435

4TheJournalofPhysicalChemistryCpubs.acs.org/JPCCPerspectiveAdditionalanalysisofthedecaykineticsusingamethodpreviouslydevelopedtoexaminepolaronrecombinationdynamicsinMAPbI3filmsrevealedthatthebimolecularrecombinationcoefficientsfortheperovskitefilmsexaminedinFigure4wereindistinguishablewithinexperimentalprecision.Thisfindingisconsistentwithpriortime-resolvedterahertzspectroscopymeasurementsofCsPbI3filmsthatshowedsimilarchargetransportandrecombinationkineticscompared69totheirhybridorganic−inorganicMAPbI3analogs.Takentogether,theseresultsindicatethatthedipolarfieldcreatedbyorganiccationsdoesnotaffectrecombinationratesinhalideperovskites.Instead,thecharge−latticeinteractionsleadingtopolaronformation,slowerrecombinationrates,andquenchedphotoluminescencearisefromdistortionsofthematerial’sinorganicsublattice.Theabilitytoprobethemid-infraredopticalabsorptionspectraoflargepolaronsinhalideperovskitesalsoallowedFigure4.(A)(top)Schematicdiagramofthemid-IRTAopticalinvestigatorstodetermineifdipolarorganiccationsinfluencegeometry.(bottom)Mid-IRTAspectraofMAPbBr3,FAPbBr3,andCsPbBr3perovskitefilms.(B)PolarondecaykineticsofMAPbBr3,carrierlocalizationonultrafasttimescales.AsmentionedFAPbBr3,andCsPbBr3perovskitefilmsfollowingbandgapexcitationpreviously,someinvestigatorshavesuggestedthatpolaronat532nm.Thecomparisonsdemonstratethatthedipolarmotionofformationinhalideperovskiteaffectscarriercoolingratesorganiccationsdoesnotaffectpolaronspectraorrecombinationrateswithinthematerial.27,28Thus,understandinghowtocontrolwithinthematerial.(C)Polaronformationkineticsmeasuredinthepolaronformationratesinhalideperovskitesmayleadtotheseriesofleadbromideperovskitefilmsfollowingopticalexcitationatdevelopmentofdesignrulesforhowtoutilizehotcarriersin532nm.Thepolaronformationratesareidenticaldespitetheperovskite-basedoptoelectronics.differentdipolemomentsoftheAsitecations,indicatingthatorganiccationrotationsdonotcontributesignificantlytopolaronformationFigure4Cdisplaystheultrafastmid-IRTAkineticsoftheinhalideperovskites.Reprintedwithpermissionfromref36.largepolaronabsorptionsignalpresentedinFigure4A36Copyright2020AmericanChemicalSociety.followingpulsedexcitationat532nm.Theformationrateoflargepolaronsineachfilmwasestimatedbymonitoringtheperovskitelatticedoesnotinfluencetheextentofcarriergrowthofthelargepolaronabsorptionsignal.Forallofthelocalizationorlargepolaronbindingenergies.ultrafastmid-IRTAkineticsdisplayedinFigure4C,theriseTheinfluenceofdipolarorganiccationsontheoptoelec-timeofthetransientabsorptionsignalwaslimitedbythetronicpropertiesofhalideperovskiteswasfurtherinvestigatedinstrumentresponseoftheultrafastmeasurement(grayline,byexaminingthedecaykineticsofthelargepolaronabsorptionFigure4C),indicatingthatpolaronsformrapidlyinhalidespectrashowninFigure4A.Figure4Brepresentspolaronperovskitesinlessthan150fsfollowingopticalexcitation.decaykineticsofMAPbBr3,FAPbBr3,andCsPbBr3filmsImportantly,theresultspresentedinFigure4Cindicatethatobtainedbyintegratingthefrequencyrangebetween1000andpolaronformationratesdonotdependontheidentityofthe1800cm−1following532nmpulsedexcitation.TheA-sitecation.Furthermore,therisetimesofthepolaroncomparisonshowslittlevariationinthelifetimeoflargeabsorptionsignalsaresignificantlyfasterthanthediffusivepolaronsphotogeneratedwithineachoftheperovskitefilms.motionoforganiccations(∼3ps)obtainedbypolarization-Figure5.(A)(top)PlotshowingthepositionsofnitrogenatomsofFAovertimeinpureandmixed-phaseperovskitefilms.(bottom)VectorautocorrelationfunctionofFAcationsinmixedandpurephaseperovskitefilmsobtainedfrommoleculardynamicssimulationsshowingtheprobabilityofaFAcationremaininginitsinitialorientationasafunctionoftime.Reprintedwithpermissionfromref46.Copyright2017AmericanChemicalSociety.(B)TransientanisotropydynamicsofFAionsobtainedbymeasuringtheCNstretchmode.Reprintedwithpermissionfromref42.Copyright2018AmericanChemicalSociety.5431https://dx.doi.org/10.1021/acs.jpcc.0c10889J.Phys.Chem.C2021,125,5427−5435

5TheJournalofPhysicalChemistryCpubs.acs.org/JPCCPerspective42resolved2DIRmeasurements,indicatingthatthedipolar■CONCLUSIONSANDOUTLOOKmotionoforganiccationsdoesnotunderpinpolaronInthisPerspective,recentmid-IRTAspectroscopystudiesformationinthisclassofmaterial.Rather,distortionsofthewerehighlightedthatexaminedthecharge−latticeinteractionsinorganicsublatticeunderpinpolaronformationonultrafastanddynamicdisorderthatleadtolargepolaronformation.Thetimescalesinhalideperovskites.Thisresultisconsistentwithinfluencethattheseinteractionshaveonband-edgerecombi-low-frequencyRamanspectroscopymeasurements,whichnationandoptoelectronicpropertiesofhalideperovskiteswererevealedthatpolarfluctuationsunderpinningpolaronfor-alsodiscussed.TheformationoflargepolaronswasshowntomationdonotdependonthedipolemomentoftheA-siteslowbimolecularrecombinationwithinthematerials.How-39cationinthisclassofmaterial.Likewise,theoreticalever,theenergeticbarriersintroducedbypolaronformationcalculationshavealsoshownthatFröhlichinteractionsalsoquenchphotoluminescencequantumyields.ThisresultbetweenchargecarriersandphononsoccurpredominatelysuggeststhattheelectronicpropertiesofhalideperovskitescanwiththestretchingandbendingLOphononmodesofthebetunedforspecificapplications(e.g.,photovoltaicsversus70material’sPbI3inorganicsublattice.Theabovefindingslightemittingdiodes)bymodifyingthestructureandrevealthatmixturesofA-sitecationsthatcanaffectthecompositionofthematerials.Furthermore,theresults25,63−68optoelectronicpropertiesofhalideperovskitesmaydopresentedinthisPerspectivedemonstratethatthedipolarsobytheirinfluenceonthestructureanddynamicsofthemotionoforganiccationsdoesnotaffectpolaronformationorinorganiclatticeratherthanfromthedipolarpropertiesofthebimolecularrecombinationinhalideperovskites,indicatingcationsthemselves.Theseobservationsfurtherhighlightthethatinvestigatorsshouldfocusonunderstandinghowneedtounderstandtheinterplayofsuchpolaroniceffectsonmodificationstothestructureanddynamicsoftheperovskiteexcitedelectronicstatestopredictandcontroltheelectroniclattice’sinorganicframeworkaffectthecharge−latticeinter-propertiesofhalideperovskites.actionsthatunderpinpolaronformation.ThesefindingsalsosuggestthateffortstotunethepropertiesWhileclarityisemergingabouttheinfluencethatcharge−ofhalideperovskitesforphotovoltaicandlightemittinglatticeinteractionshaveontheelectronicpropertiesofapplicationsshouldsimilarlyfocusonthestructureandtraditionalhalideperovskitessuchasMAPbI3andrelateddynamicsoftheinorganicsublatticeandhoworganicA-sitematerials,theabilitytopredictandcontroltheseinteractionscationsmayinfluencethissublattice.Recenttheoreticalstudiesinmorecomplexmetalhalidesemiconductorssuchas2DhavesuggestedthatitmaybepossibletotunethestructuralRuddlesden−Popperlayeredmaterials,doubleperovskites,anddynamicsoftheperovskitelatticethatleadtopolaronnanocrystallinesystemsremainstobedeveloped.Futureworkformationbyincorporatingionswithdifferentsizesintotheleveragingthestructuralspecificityofmid-IRTAspectroscopymaterial.46,71Figure5Ahighlightsoneofthesestudies,whichcombinedwiththeabilitytomeasuretheenergeticsandsuggestedthatthemixingofdifferentlysizedA-sitecationsdynamicsoflargepolaronsisexpectedtohelpguideongoing(e.g.,FAandCs)withintheperovskitelatticemayslowtheeffortstounderstandthenatureofcharge−latticeinteractionsdynamicsoftheperovskitelatticebyeffectively“locking”theinthesematerials.Forexample,investigatorsmayusemid-IRmaterial’sinorganicframework.46SuchreducedlatticeTAspectroscopytodirectlyprobethevibrationalmodesoffluctuationsmayleadtosmallercharge−latticecouplingandorganiccationsthatseparatethelayersin2DRuddlesden−29−31wouldbeexpectedtoslowtherotationaldynamicsoftheFAPoppermaterialstoinvestigatethestructuraldistortionscations,consistentwiththemoleculardynamics(MD)andlatticedynamicsinvolvedinchargetransportversussimulationsthatexaminedthedynamicsofFAcationsinradiativerecombination.Similarapproachesmaybeusedtoinvestigatethelatticedynamicsindoubleperovskiteswithmixed-cationperovskites(Figure5A).Theresultsofthethesemixed+1and+3cationsbeinginvestigatedaslead-freeMDsimulationswerelaterconfirmedexperimentallyina32−34alternativestoguideexplorationofthelargeparameterperspectivewrittenbyGallopandco-workerswhoused2DIRspaceofthesematerialstoachievedesiredmaterialproperties.anisotropytoexaminethedynamicsofFAcationsinmixed42Finally,theresultspresentedinthisPerspectivesuggestthatandpurecationperovskitefilms(Figure5B).chargecarriercoolingdynamicsinhalideperovskitescanbeRecallingthatthecompositionofcurrentstate-of-the-art36investigatedusingmid-IRTAspectroscopy.Boththeoreticalperovskite-baseddevicesincludesseveraldifferentA-siteandexperimentalstudieshavesuggestedthattheunusuallycations,B-sitemetalions,andX-sitehalideions,theresultsslowthermalizationkineticsobservedinhalideperovskitesmaypresentedinFigure5suggestthatdevicedevelopersmaybebeduetothepolaronicnatureofchargecarriersinthisclassoftuningthepolaronicpropertiesofhalideperovskitesviaionmaterial.Thus,carriercoolingratesinhalideperovskitefilmssubstitutiontostriketheoptimalbalancebetweenchargemaybecharacterizedonultrafasttimescalesbydirectlytransportandrecombinationforphotovoltaicapplications.Forprobingtheopticalsignaturesoflargepolaronsinthemid-IRexample,mixedcationsystemswithvariousMA,FA,andCsasafunctionofexcitationwavelengthandtemperature.ionratioscanexhibitenhancedphotoluminescencequantum1242,52,72,73Becausepolaronformationistemperature-dependent,theseyieldsandslowerdefect-mediatedrecombination.measurementsareexpectedtoprovideinformationabouthowAdditionally,ionsubstitutionmayalsointroducestaticpolaronformationaffectscarrierthermalizationinthisclassofdisorderthatmayleadtodisorderedcharge−latticecouplingmaterial.andpolaronformation,ashasrecentlybeenreportedby74Nishidaandco-workers.Suchstaticdisordermayalsoslow■chargecarrierrecombinationbyspatiallyseparatingchargeAUTHORINFORMATION75CorrespondingAuthorcarriersinseparateregionsofafilm.ContinuedworkthatcorrelatespolaronrecombinationratesandtransportinmixedJohnB.Asbury−MaterialsResearchInstituteandionperovskiteswithdeviceresultsisexpectedtobeanactiveDepartmentofChemistry,ThePennsylvaniaStateUniversity,areaofresearchintheperovskitecommunity.UniversityPark,Pennsylvania16802,UnitedStates;5432https://dx.doi.org/10.1021/acs.jpcc.0c10889J.Phys.Chem.C2021,125,5427−5435

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