Ultrafast Interfacial Carrier Transfer And Dynamics In Monolayer WS₂/CsPbBr₃ Quantum Dots Heterostructure

Monolayer transitional metal dichalcogenides(TMDCs)are found to possess exceptional electric properties like monolayer graphene does,which can be applied into optoelectric detectors,micro lasers and even micro logical devices.Howerer,optical absorption of monolayer TMDCs is limited and one effective solution is heterostructure construction of monolayer TMDCs and quantum dots.Recently,lead halide perovskite quantum dots are attractive.Heterostructure of monolayer TMDCs and perovskite quantum dots,mataining both excellent properties,increases light light utilization of monolayer TMDCs a lot.This work focuses on monolayer tungsten disulfide(WS2),one kind of TMDCs,and applying inorganic caesium-lead halide perovskite(CsPbBr3)as absorption layer.Heterostructure of monolayer WS2 and CsPbBr3 quantum dots are made and subsequently studied.Carrier dynamics of monolayer WS2 and the heterostructure are measured,respectively.Energy transfer mechanisms from CsPbBr3 exciton to A-and B-exciton of WS2 in the heterostructure are analyzed.Especially,formation and physics of interlayer exciton are found,in the very first time,in this kind of system.Detailed results are listed as follows:1.Transient absorption spectrum are used to measure A-and B-exciton dynamics of WS2 under different fluences in both monolayer WS2 and the heterostructure in 100 ps region.A-and B-exciton dynamics are divided into one fast part on picosecond scale,corresponding to excitonic Auger recombination,and one slow part on tens of ps scale,corresponding to singal-excitonic nonradiative recombination.Compared with pristine monolayer WS2,fast parts of A-and B-exciton dynamics are decelerated,but slow parts of A-and B-exciton dynamics are accelerated.Under 40μJ/cm~2 fluence,A-exciton signal increases by the maximum of 69%in the heterostructure.2.Energy transfer mechanisms from CsPbBr3 exciton to A-and B-exciton of WS2 in the heterostructure are analyzed in details.Energy transfer from CsPbBr3 exciton to A-exciton of WS2 can be expalined as follow steps.Fristly,CsPbBr3 excitons resolve into electrons and holes,which transfer in the same direction to WS2.Then the newly incoming electrons and holes recombine as A-excitons in WS2.And energy transfer from CsPbBr3 exciton to B-exciton of WS2 is accomplished through“dipole-dipole coupling”.3.Interlayer excitons are found,in the very first time,in the monolayer WS2/CsPbBr3quantum dots heterostructure.As particularly analyzing transient absorption spectrum around A-exciton resonance in pristine WS2 and the heterostructure,interval of zero-points of transient absorption spectrum obviously shortens in the heterostructure.With collisions of A-and B-excitons being ruled out,interlayer excitons,forming by Coulomb force between electrons in WS2 and holes in CsPbBr3 quantum dots,are considered to be the reason.Bulit-in electric field of interlayer excitons stretches across the heterostructure interface and alters absorption spectrum around A-exciton resonance.By establishing decay equation between interlayer exciton and A-exciton,lifetime of interlayer excitons is inferred to be 36.6 ps.