Study On The Stability And Anion Exchange Mechanism Of Cesium Lead Halide Perovskites Nanocrystals

In recent years,CsPbX₃?X=Cl,Br,I?perovskite nanocrystals?NCs?have become attractive for their use in many fields such as photovoltaic cells,photodetectors,LEDs,and lasers due to their outstanding optical and electrical properties.However,perovskites are easily destroyed by temperature,UV light,moisture,and oxygen because of their ionic crystal structure.Significant halide ionic migration has been reported in these materials and is considered to play an important role in charging hysteresis,light-induced phase segregation,and photoinstability.Therefore,researching CsPbX₃ perovskite nanocrystals and halide anion migration and improving their stability are very important.The following are the main research of this thesis:?1?We developed an approach to in situ synthesize CsPbX₃ NCs into porous silicacolloidal spheres,which can effectively prevent anion exchange and increase photo stability.We first reported that the anion exchange between CsPbX₃ nanocrystals is mainly driven by physical collision of the nanocrystals,not requiring a bridge such as a solvent.We subsequently used an optimized ratio of green,red,and blue Si O₂/CsPbX₃composites as solid-state luminescent materials to fabricate single-layer white light-emitting diodes?WLEDs?.After the WLED has worked 8 h,there was no conspicuous change of its PL spectrum,demonstrating great photostability.?2?We reported the visualization of halide anion interdiffusion between Cs Pb Br₃nanorods and Cs Pb I₃ nanowires using high resolution transmission electron microscope.We proved that the anion migration between adjacent CsPbX₃ nanocrystals?the interval is around 1.5 nm due to OA/OAm ligands?can occur in solid state.?3?CsPbX₃ NCs are typically synthesized by the hot-injection methods,where oleicacid?OA?and oleylamine?OAm?are generally used as surface-protecting ligands.The deattaching of the ligands generally deteriorates the PLQY of NCs,as well as their dispersibility in solvents.We demonstrated that by incorporating dopamine into the traditional OA/OAm system,monodisperse CsPbX₃NCs with excellent optical properties can be achieved.More importantly,the presence of dopamine can dramatically improve the stability of CsPbX_3.Compared with the samples capped with OA/OAm ligands,the dopamine-capped samples maintained their luminous properties after 1 h of UV irradiation and immersion in polar solvents.