Chapter-12 - Perovskite-solar-cel - 2019 - Nanomaterials-for-Solar-Cell-Applicat - 图文

CHAPTER12

Perovskitesolarcells

JunmingLi,QiongWangandAntonioAbate

HelmholtzCenterforMaterialsandEnergy,Berlin,Germany

Contents

12.1Introduction

12.2Halideperovskitematerials

12.2.1Structuralproperties

12.2.2Optoelectronicproperties12.3Perovskitesolarcells

12.3.1Ahistoricaloverview12.3.2Devicearchitectures

12.3.3Depositionmethodsofperovskitefilms12.4Characterization

12.4.1Currentàvoltagecharacterization12.4.2Estimationofdevicestability12.5Remainingchallenges

12.5.1Toxicityofperovskitesolarcells

12.5.2Long-termstabilityofperovskitesolarcells12.6SummaryandoutlookReference

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12.1Introduction

Halideperovskiteswerefirstusedasvisible-lightsensitizersindye-sensitizeliquidjunctionsolarcellswithapowerconversionefficiency(PCE)of3%à4%in2009[1].Halideperovskitesexhibitoutstandingoptoelectronicpropertiesthatmakethistypeofsemiconductorahugesuccessinphotovoltaicapplications[2].Along-termdurableperovskitesolarcell(PSC)withaPCEof9.7%wasreportedin2012.Afterthat,tre-mendousresearchhasbeenconducted,focusingontheoptoelectronicapplicationofhalideperovskitesaswellastheinvestigationoftheabnor-malelectronicpropertiesofthematerials[3].Today,acertifiedPCEof23.3%hasbeenreported,whichiscomparabletosinglecrystallinesilicon

NanomaterialsforSolarCellApplications

DOI:https://doi.org/10.1016/B978-0-12-813337-8.00012-6?2019ElsevierInc.Allrightsreserved.

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(24.4%)andpolycrystallinesiliconsolarcells(19.9%)[4,5].ThenotableachievementsinPSCsareattributedtothetunablebandgapofperovskites,spanningfrom1.2to2.4eV[6],longchargecarrierdiffusionlength[7],developmentofnewperovskitematerials,andadvancesinperovskitefilmdeposition.Thestabilityofhalideperovskiteshasbeenthemainobstacleforthecommercialization.UnderstandingthedegradationmechanismofPSCsandthedevicearchitecturemaygivetheanswerforthelong-termstabilityinPSCs.Aspresentedinthefollowsection,wewillgiveabriefintroductionaboutthebasicphysicalpropertiesoftheseperovskitematerialsandthesolarcellsbasedonthem.

12.2Halideperovskitematerials12.2.1Structuralproperties

HalideperovskitesadoptthegeneralchemicalformulaofAMX3,whereAistheorganicorinorganiccation,Misthemetal,andXisthehalogen.Thestabilityofthecrystalstructureishighlydependentonthesizeoforganiccationandtheinteractionbetweentheorganiccationandthecorner-sharingMX642octahedral.TheGoldschmidttolerancefactortisareliableempiricalindextopredictwhetherornotastableperovskitestructurecanbeformedorpresented,definedinthefollowingequation:[8]

rA1rX

t5p???2erA1rMT

(12.1)

whererA,andrM,andrXaretheradiioftheorganic/inorganiccation,metalion,andhalideions.Inhalideperovskites,thecellparametersincreaseasthehalidechangesfromchlorine(Cl2,rCl251.81?),bromine(Br2,rBr251.96?)toiodine(I2,rI252.2?).Themostcommonlyusedinorganicororganicmonovalentcationsincludemethylammonium(MA1,rMA151.8?)[9],formamidinium(FA1,rFA151.9à2.2?),rubidium(Rb1,rRb152.9?),andcesium(Cs1,rCs153?)[10à12].ThesuitabledivalentmetalionsbasedonEq.(12.1)includetin(Sn21,rSn2151.1?)andlead(Pb21,rPb2151.19?).Whentequalsto1,itinducesacubicsymmetryandiscomposedofabackboneofacornersharingMX6-octahedralwithcuboctahedravoidsoccupiedbytheA-cation,asshowninFig.12.1.

Mostoftheknownhalideperovskiteshavetvaluesintherangeof0.75à1.00atroomtemperature,withanorthorhombic,rhombohedral,

Perovskitesolarcells419

Figure12.1CubicperovskitestructureofAMX3,whereAcationoccupiesthelatticecorners,Mcationoccupiestheinterstitialsite,andXanionsoccupythelatticefaces.AdaptedfromliteratureG.E.Eperon,etal.,Formamidiniumleadtrihalide:abroadlytun-ableperovskiteforefficientplanarheterojunctionsolarcells,EnergyEnviron.Sci.7(3)(2014)982à988.r2008Wiley-VCH.

Figure12.2Correlationsbetweentolerancefactorandhalideperovskitescrystalstructures.AdaptedfromliteratureZ.Li,etal.,Stabilizingperovskitestructuresbytuningtolerancefactor:formationofformamidiniumandcesiumleadiodidesolid-statealloys,Chem.Mater.28(1)(2015)284à292.r2015AmericanChemicalSociety.

ortetragonalstructure[14à17].Iftislargerthan1,thismeansthatanon-perovskitephasewillbeformed.ThecorrelationbetweentheperovskitecrystalstructureandthetolerancefactorisschematicallyillustratedinFig.12.2.

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Figure12.3Calculatedoctahedralfactorandtolerancefactorsforvariouscombina-tionsofhalideperovskites.AdaptedfromliteratureQ.Chen,etal.,Underthespotlight:theorganicàinorganichybridhalideperovskiteforoptoelectronicapplications,NanoToday10(3)(2015)355à396[18].r2015Elsevier.

ComplementingtheGoldschmidttolerancefactor,theoctahedralfac-torμwasdevelopedtoassessthefitofMcationintotheX6octahedron,whichisdefinedas:[13]

rMμ5(12.2)

rXwhererMandrXaretheionicradiiofMcationandXanion,respectively.Aplotofμagainsttofcommonhalideperovskitescanbeconstructed.Fig.12.3showarangeoftoleranceandoctahedralfactorsthatallowinaperovskitestructurewithdifferentA,M,andXions.

12.2.2Optoelectronicproperties

Althoughthehalideperovskiteswerestudiedadecadeago[19à21],onlyrecentlytheyaregivenenoughattentionafterthesuccessfulapplicationinsolarcells.Inadditiontophotovoltaicapplications,halideperovskitesareconsideredasthemostcompellingcandidateforseveraloptoelectronicapplications,suchaslasing[22,23],lightemittingdevices[24à28],andphotodetector[29,30].

Theoperationofasolarcellstartswiththelightabsorptionofthephotovoltaicmaterial.Comparedwithconventionalphotovoltaicmateri-als,theadvantagesofperovskitematerialincludethehighabsorptioncoef-ficient,andthefaciletunnabilityintheiropticalbandgap.Byadjusting

Perovskitesolarcells421

CsPb(CI/Br)3

CsPbCI3

CsPbBr3

CsPb(I/Br)3

CsPbI3

MA

MAPbI3

MA(Sn/Pb)I3

MASnl3

MASn0.8Pb0.2I3

Norm. PL400

450500550600650

700750800Wavelength (nm)

850900950100010501100

Figure12.4RepresentativephotoluminescencespectraofdifferentcompositionsfromthemostblueCsPbCl3tothemostredshiftedCH3NH3(Sn0.8/Pb0.2)I3perovskite.AdaptedfromliteratureM.Salibaetal.,Perovskitesolarcellsfromtheatomictothefilmlevel,Angew.Chem.(2017)2554à2569[36].r2017Wiley-VCH.

theradiusofcationsandionsinAMX3,theopticalbandgapofperovs-kitescanbetunedfrom1.36eV(CH3NH3SnI3)to3.06eV(CsPbCl3)[31à34].Dopingtin-perovskitewithasmallamountofleadleadstoafurtherdecreaseintheopticalbandgap.Themostlowestopticalbandgapisof1.15eVachievedbythelead-tinmixcompositionCH3NH3Sn0.8Pb0.2I3[35](Fig.12.4).

Theabsorptioncoefficient(α)defineshowefficientthematerialabsorbsthelight.Ingeneral,asemiconductorthathasadirectbandgapshowsahigherabsorptioncoefficientthananindirectsemiconductor.Forindirectbandgapmaterial,thelightabortionrequiresaphononassistedtransition.Adirectbandgapdoesn’tneedtheadditionalphononassistedtransition,whichusuallyresultsinastrongerabsorptioncoefficient[37].Halideperovskitesusedinphotovoltaicaredirectbandgapmaterialsthatexhibitastrongabsorption.Themeasurementoftheabsorptioncoeffi-cientofCH3NH3PbI3isgiveninFig.12.5[38].Theabsorptioncoeffi-cientofCH3NH3PbI3wasestimatedtobe1.53104cm21at550nm,indicatingthatthepenetrationdepthfor550nmlightisapproximately0.66μm,anditincreasesto2μmfora700nmlightwiththeabsorptioncoefficientof0.53104cm21.ThismeansmostofthevisiblelightcanbeabsorbedbyCH3NH3PbI3filmwithinalayerthinnerthan2μm.Nonlinearabsorption,forexample,two-photonabsorptionwasalsoobservedinperovskitematerials[39,40],themultimodalabsorptionmakesitpossibletodetectawiderrangeoflightandusedasphotodetector.

Whenitisunderillumination,thephotogeneratedchargecarriersinasolarcellcanbefreeelectronàholepairsorexcitonsdependingonthenatureofthephotovoltaicmaterialandthecontacts.Inparticular,theexcitonbindingenergyisanimportantfactorfordeterminingthedevice