In Situ Preparation And Luminescence Properties Of Biphase Perovskite Nanocrystals In Polymer

All-inorganic metal halide perovskite nanocrystals have many advantages,such as high photoluminescence quantum yield,tunable emission wavelength,and narrow half-peak width.They have numerous applications in light-emitting diodes,displays,solar cells,and photodetectors.However,due to their low formation energy,high ion mobility,and surface defects,perovskite nanocrystals are susceptible to decomposition under external factors such as moisture,temperature,and chemical environment,leading to poor stability.This greatly limits their application in optoelectronic devices.Therefore,how to improve the stability and optoelectronic properties of perovskite nanocrystals has become an important research topic in the field of optoelectronic materials.Researchers have proposed various strategies to protect perovskite nanocrystals from decomposition in practical applications.For example,introducing inorganic or polymer protective layers to form a core-shell structure and increasing surface ligands to slow down the decomposition rate of nanocrystals.However,current methods still cannot achieve perfect encapsulation of perovskite nanocrystals.Therefore,exploring effective encapsulation strategies and materials to enhance the stability of perovskite nanocrystals is necessary.To accomplish this,this article conducted research in the following two aspects:1.A synthesis method was proposed based on humidity-induced phase transformation,and a dual-phase structured Cs Pb Br₃/Cs Pb₂Br₅perovskite nanocrystal was synthesized in situ in polyurethane（PU）,forming a Cs Pb Br₃/Cs Pb₂Br₅@PU composite film.The reaction mechanism,luminescence performance,and stability of the composite material were studied.XRD,SEM,EDS,and UV-Vis absorption spectra were used to confirm the in situ growth of Cs Pb Br₃/Cs Pb₂Br₅perovskite nanocrystals in the PU matrix.Thanks to the flexibility and chemical stability of the PU material and the superior optoelectronic properties of perovskite nanocrystals,the luminescent composite film exhibited excellent flexibility and fluorescence stability under light,heat,and water conditions.In addition,by combining Cs Pb₂Br₅/Cs Pb Br₃@PU film,red fluorescence powder K₂Si F₆:Mn⁴⁺（KSF）,and blue light LED chip,a wide color gamut WLED device was successfully developed,which is expected to be applied in flexible display backlighting.The unique synthesis method also provides new ideas for the field of polymer encapsulated perovskite nanocrystals.2.A room temperature synthesis method was developed by ligand regulation to in situ produce a Cs Pb Br₃/Cs₄Pb Br₆dual-phase structured perovskite nanocrystal in polymers,and the luminescence performance and mechanism of the composite material was explored.The2-methylimidazole ligand regulation and re-precipitation method was successfully used at room temperature to prepare Cs Pb Br₃/Cs₄Pb Br₆@PDMS and Cs Pb Br₃/Cs₄Pb Br₆@EVA composite films with excellent luminescence performance.The dual-phase perovskite structure in polymers was confirmed by XRD,TEM,and UV-Vis absorption spectra.The presence of the 2-methylimidazole ligand not only controls the size and dispersion of Cs Pb Br₃in the composite material but also helps to obtain controllable mono-dispersed hexagonal Cs₄Pb Br₆.This simple and effective strategy can be easily performed at room temperature,and the in-situ encapsulation reduces the contact time between Cs Pb Br₃nanocrystals and external environment,displaying a PLQY exceeding 80%.By double protection of Cs₄Pb Br₆NCs and polymers,the stability of Cs Pb Br₃NCs in water and air is significantly improved.Finally,Cs Pb Br₃/Cs₄Pb Br₆@EVA composite film was successfully applied in white light LED devices,with CIE chromaticity coordinates of（0.331,0.332）,emitting standard white light.