Synthesis,Optical Properties And Application Of Highly Stable CsPbX₃ Nanocrystals

In recent years,all-inorganic perovskite?CsPbX₃,X=Cl,Br,I?nanocrystals have attracted widespread attention due to their excellent light-emitting performance,high photoelectric conversion efficiency,and low preparation cost.They have broad application prospects in many fields of optoelectronic applications such as light-emitting diodes?LEDs?,lasers,and solar cells.At present,the current methods of preparing CsPbX₃ nanocrystals range from high temperature hot-injection method,room temperature supersaturated recrystallization,ultrasonic to anion/cation exchange.However,the pristine CsPbX₃ nanocrystals synthesized by these methods are ionic crystals and have large surface energy,resulting in high sensitivity to water,air,light and other environments.They can be easily degraded by these fators.Therefore,before commercial applications,it is crucial to explore other ways to improve the stability of CsPbX₃ nanocrystals.This thesis successfully reports a series of ways on preparing perovskite nanocrystals by means of post-synthesis and inorganic material encapsulation.The stability of the perovskite nanocrystals have been greatly improved and the luminescence performance of the material is systematically studied and white light emitting diode?WLED?devices were successfully prepared.The main research contents are as follows:?1?CsPbX₃ nanocrystals were pre-synthesized by high temperature hot-injection method,and then they were post-treated with an aqueous solution of halogen salt to passivate surface defects.The effects of halogen salt types,processing time and solution concentration on sample morphology and optical properties were systematically investigated.The CsPbX₃ nanocrystals obtained have nearly100%fluorescence quantum yields?PLQY?with uniform size.More importantly,the stability is better than pristine.?2?CsPbX₃ nanocrystals was anchored in the kaolinite?KL?matrix were successfully prepared by high temperature hot-injection method.Using KL as a template in two steps.Thus obtained composite shows uniform size CsPbX₃ nanocrystals distributed on the KL.The optical properties of the prepared CsPbX₃-KL composite were characterized.It is found that the composites have higher PLQY?such as Cs Pb Br₃-KL is 73%?and better air stability than pristine CsPbX₃ nanocrystals.At the same time,a WLED was fabricated using the resulting microscale composites,exhibiting Commission Internationale de I'Eclairage?CIE?color coordinates of?0.34,0.31?and the color gamut exceeds 129%of the national television standards committee?NTSC?television color standards.?3?A simple solvent-free grinding method was used to encapsulate the CsPbX₃ nanocrystals using Y-type zeolite which is a kind of inorganic molecular sieve materials.The optimum composite concentration of CsPbX₃-Y zeolite?CsPbX₃-Y?was obtained by optimizing the feeding ratio of Y-zeolite to perovskite.By changing the type and proportion of halogen anions,the obtained the fluorescence emission spectrum can be adjusted to the green range?502-522 nm?.When the obtained composites are stored in the air environment for seven days,it shows that the photoluminescence?PL?intensity drops to about 85%of the original intensity,while the PL intensity of pristine CsPbX₃nanocrystals is only 10%.Also,a WLED was fabricated using the resulting CsPbX₃-Y composites and commercial phosphor K₂Si F₆:Mn⁴⁺,showing CIE color coordinates of?0.298,0.309?.