Surface Modification And Stabilization Of Perovskite Nanocrystals Based On Atomic Layer Deposition

Perovskite nanocrystals(NCs)are now emerging as a new generation of functional semiconductors for illuminations and display applications in view of their ultrahigh photoluminescence quantum yield,extremely narrow PL bandwidth and color tunability.However,their poor stability in light,heat and water environments still hinders practical applications in practical applications due to their ionic character.Atomic layer deposition(ALD)is based on the self-limiting half reactions and has been widely employed to prepare uniform and dense films at high aspect ratio surface on the atomic level.Recently,alumina ALD method has been applied in the stabilization of perovskite NCs.However,a PL quenching was observed in a typical alumina ALD process,which hinders the performance and applicability.In this thesis,a two-step hybrid passivation strategy and silica plasma-enhanced ALD method were developed to modify the surface of perovskite NCs,which enhance the stability and potential of perovskite NCs in practical applications.The main research of this thesis consists of the following sections:1.The interaction mechanism between TMA precursor and organic ligands during alumina ALD process was studied through in-situ FTIR and steady-state PL spectra.It was found that the reorganization of OA ligands from Pb to Al after TMA dosing created more deleterious undercoordinated Pb atoms on the NCs'surface that increases surface trap sites,leading to PL quenching.Based on this mechanism,a two-step hybrid passivation strategy was developed to simultaneously enhance the photoluminescence quantum yield and the stability of perovskite Cs Pb Br₃ NCs with surface halogen replenishment and ALD.The PLQY loss during ALD process was minimized via control of ligands density on the NCs surface.2.The PL quenching was avoided using bis(diethylamino)silane(BDEAS)as the Si precursor,which can not react with the organic ligands on the NCs surface.Subsequently,O₂plasma with high reactivity was used to oxidize the amine ligands of BDEAS precursor while didn't etch the NCs.As a result,a dense and uniform silica coatings with excellent chemical stability was fabricated to encapsulate the perovskite NCs and the obtained Cs Pb Br₃ NCs/Si O₂film exhibits exceptional stability in water,light and heat as compared to the pristine NCs film,which improves their potential in LED illumination and backlight displays.