Transformation of Polarization Mechanisms by Dimensional Reduction in Lead-Free Silver Bismuth Bromide Double-Perovskite Thin Films

Lead-freehalideperovskitematerialsarediscussedasalternativematerialsto replacelead-containingperovskitesandminimizerisksto humanhealthandthe environment.Dimensionalreductionof theoctahedralmetalhalidenetworkby incorporatinglargerorganiccationsincludingphenethylammonium(PEA)representsan attractiveoppor-tunityto tailortheirpropertiestowardapplications.Here,differencesincharacteristicsunderan appliedconstantvoltageare detected,whicharisefromthe dimensionalreductionof the Cs2AgBiBr6double-perovskiteto(PEA)4AgBiBr8. Thinfilmsconsistingof thesecompoundswerespin-coatedontomicrostructuredinterdigitatedelectrodearrays.Current−voltageandKelvinprobeforcemicroscopymeasurementswereperformedto revealthe overallor locallyresolvedconsequencesof an appliedelectricfield.Bothmaterialsshoweda reversibleion displacementin smallelectricfields.At higherfieldstrengths,however,Cs2AgBiBr6exhibiteda persistentcontactmodificationat the interfaceof the perovskiteandthecontactmetaldueto migratingions,whereas(PEA)4AgBiBr8stillshoweda reversibleseparationof ions.Insulatinginterlayersthatwidelyattenuatethe currentdemonstratethattheseeffectsare inducedby electricfieldsonly,independentof chargeinjection.Theobtainedresultsprovidean explanationof improvementsof perovskitecontactsby interfacialengineering,inparticular,describinghowa two-dimensional(2D)perovskitelayerreducesthe hysteresisandinterfacialresistancein contactto athree-dimensional(3D)double-perovskite