In-situ Preparation And Properties Of Salt-coated Cesium Lead Bromide Colour Conversion Films

All-inorganic Cs Pb X₃（X=Cl,Br,I）perovskite quantum dots are the best choice for the full-color conversion layer of Micro light-emitting diode（Mini/Micro-LED）due to their high fluorescence quantum efficiency,tunable fluorescence emission spectrum in visible light range and high color purity.However,due to the agglomeration of nanoparticles,the fluorescence quantum efficiency of Mini/Micro-LED is greatly reduced when it is made into a film.At the same time,problems such as poor environmental stability caused by its own structure also exist,which seriously hinders the commercial application process of Mini/Micro-LED.In this paper,the fluorescence properties and stability of perovskite films were improved by inorganic coating on the basis of in-situ synthesis method.Low cost salt-coated perovskite colour conversion film was prepared by ink-jet printing technology with inorganic salt as modifier,which greatly improved the stability and optical properties,and finally realized the pattern-based display.The specific work content is as follows:（1）The precursor solution containing a sodium chloride inorganic salt was configured using aqueous solution as a main solvent.In this process,dimethyl sulfoxide（DMSO）solution was introduced to optimize the crystal structure and optical properties of perovskite films coated with sodium chloride（Na Cl）.It is found that the synergistic effect of sodium chloride and DMSO can regulate the grain morphology,improve the phase purity and enhance the fluorescence emission of salt-coated perovskite films.When the volume ratio of DMSO to precursor solution reached 1:2,the film showed the best green emission performance due to the effective elimination of non-radiative transition pathway,and its fluorescence quantum efficiency reached 48.2%.In addition,due to the effective coating of sodium chloride and the optimized crystal structure,the prepared films have enhanced thermal stability.（2）DMSO and water were used as binary mixed solvents to prepare perovskite precursor liquid ink containing potassium bromide inorganic salt.In situ preparation of potassium bromide（KBr）salt coated perovskite films with excellent performance was achieved by adjusting the ink composition and accurately controlling the ink jet printing process parameters.The results show that the coating of potassium bromide can not only passivate the surface defects,improve the fluorescence properties of the film,but also improve its stability.When the molar ratio of lead bromide（Pb Br₂）to Cesium bromide（Cs Br）is 1:2.5,the obtained film has a green fluorescence emission quantum efficiency of 65%,and also has significantly improved UV light stability and thermal stability.（3）In order to further improve the fluorescence properties of KBr salt coated perovskite film and realize the application of Mini-LED devices,on the basis of the above work,the film substrate properties and quenching temperature were regulated.The experimental results show that the film printed on PET flexible substrate has a high resolution lattice of 16.7μm and uniform bright green luminescence,and the optimal fluorescence emission quantum efficiency can reach 94%.At the same time,using inkjet printing technology,the patterned colour conversion film with the name of China Jiliang University and Xiamen University has been successfully prepared,which emits bright green light under ultraviolet light.A simple mini-LED was prepared by further packaging.Under the action of 2.95 V voltage and 0.02 A current,bright green light emission could be observed.This study improved the optical properties of photoluminescence of perovskite colour conversion film,which broadens a new idea for further application in flexible devices,pattern-based display and other fields,and has a broad application prospect.