Preparation And Properties Of High Stable All-inorganic Perovskite CsPbBr₃ Quantum Dots Film Composites

Cs Pb X₃（X=Cl,Br,I）all-inorganic perovskite quantum dots as a new type of luminescent materials,due to their excellent performance and simple preparation process,have shown great potential in many fields such as light-emitting diodes,white LED lighting,solar cells,etc.However,low formation energy and unstable structure lead perovskite quantum dots to easily decomposed under the action of water,oxygen,light and heat,resulting in a decrease in optical properties.In this paper,the crystal growth process of CsPbBr₃ quantum dots was explored by changing the content of precursor and reaction temperature.EVA resin was used as the matrix materials for the flexible film and the coating materials for quantum dots.Then amorphous SiO₂ was further used for the secondary wrapping of CsPbBr₃ quantum dots to avoid the direct contact with moisture and oxygen molecules,so as to improve the stability of quantum dots.The research content and main conclusions are as follows:（1）CsPbBr₃ quantum dots were synthesized using oleic acid（OA）and oleylamine（OAm）as ligands by supersaturated recrystallization method,and the crystal growth process of quantum dots was studied by TEM and HRTEM characterization.The experimental results show that the crystal growth process of CsPbBr₃ quantum dots is collectively impacted by ostwald ripening and self-assembly mechanism.With the increase of precursor content and reaction temperature,the critical size of quantum dots decreases,and the enhancement of self-assembly effect leads to the increase of quantum dots of large particles and the size distribution gradually widened.Through controlling the content of precursor and reaction temperature,quantum dots van be synthesized with reasonable size and uniform distribution.When the amount of precursor added is 0.2 m L and the reaction temperature is 20℃-30℃,the average size of the synthesized CsPbBr₃ quantum dots is about 10 nm.（2）In order to improve the stability of CsPbBr₃ quantum dots,EVA resin was used as the coating materials for quantum dots and CsPbBr₃ QDs/EVA film composites were prepared.The effects of the amount of precursor added and the reaction temperature on the optical properties of the prepared film materials were investigated respectively.SEM,EDS,XRD,TG,FT-IR,PL and other characterization methods were used to study their microstructure,phase composition,thermal properties and optical properties,respectively.The results show that when the amount of precursor added is0.2 m L and the reaction temperature is 30℃,CsPbBr₃ QDs/EVA film has high fluorescence intensity,luminous peak is at 521 nm and half-height width is 21 nm.After 40 h of immersion in water,the fluorescence intensity can maintain at 67.6%.After 30 h of ultraviolet light exposure,the fluorescence intensity retention is 69%.The fluorescence intensity retention is 63.4%in air for 90 days.The above results display that EVA resin coating can effectively isolate quantum dots from moisture and oxygen,which obviously improves the water resistance,light stability and long-term stability in air of CsPbBr₃ quantum dots.However,moisture and oxygen molecules still can enter the interior of the materials through the pores remaining on the surface of the film,destroying the structure of quantum dots.（3）On the basis of the above experiment,the amorphous SiO₂ formed by the hydrolysis of TEOS was adopted to wrap the quantum dots twice.The effects of content of TEOS and reaction temperature on the optical properties of CsPbBr₃QDs@SiO₂/EVA films were studied.The results show that when the addition amount of TEOS is 0.06 m L and the reaction temperature is 35℃,amorphous SiO₂ forms an effective package for quantum dots.The distribution of CsPbBr₃ quantum dots around10 nm in SiO₂ is uniform,and the prepared CsPbBr₃ QDs@SiO₂/EVA film has better luminous performance.After immersed in water for 40 h,the fluorescence intensity can still maintain at 84%.After 40 h of ultraviolet light,the fluorescence intensity of the materials maintains at 77.7%.After 120 days in air,the fluorescence intensity of the materials can still maintain 77.6%of the original fluorescence intensity.Through the secondary encapsulation of silica,the stability in all aspects of CsPbBr₃ quantum dots has been improved.Silica not only prevents quantum dots from the further erosion of water and oxygen molecules,but also inhibits the phase transition and anion exchange of quantum dots,which plays a very good role in protecting CsPbBr₃ quantum dots.