Synthesis,Surface-Passivated Procedure Of CsPbBr₃ Perovskite Nanoplates And Its Application In Pure-blue Light-Emitting Diodes

Metal halide perovskite（MHPs）LEDs have been developing quickly in recent years owing to their promising properties,such as high photoluminescence quantum yield（PLQY）,high color purity,adjustable bandgap,and solution processability.Benefiting from these advantages,great progress has been made for perovskite LEDs to achieve exceeded 20%external quantum efficiency（EQE）for green,red,and near-infrared perovskite LEDs.It is promising to make a breakthrough for promotion the developmentof next-generation lighting and display devices once high-performance blue perovskite LEDs can be successfully achieved,since blue emission is the core element among red,green and blue three primary colors that restrains electroluminescent performances of full-color or white perovskite LEDs.Currently,three problems limited to blue LED fabrication:（i）The blue LED prepared by mixed halides MHPs,which takes place most easily phase segregation;（ii）another smart strategy is on the basis of quantum confinement effect to achieve two-dimensional（2D）MHPs NPLs,whose inherent surface defects seriously damaged its properties,and whose ligands on the surface of NPLs especially constrained its electrical properties and thus sequent optoelectronic properties;（iii）the film exhibited lower coverage by spin coating method,which leads to the short circuit between HTL and ETL,accompany by excessive EL peak.Finally,due to the wide band gap of blue MHPs,mismatched energy levels usually lead to a large charge injection barrier,significantly affecting device efficiency.Centering on the above questions,we made the following inquiries:（1）By introducing 4-aminobenzenesulfonic acid（SA）as a ligand,green CsPbBr₃ NCs that can luminesce in n-butanol stably and pure blue CsPbBr₃ NPLs were synthesized in the room-temperature.Firstly,we selected SA from two kinds of short chain ligands through simple solubility screening.SA is a short-chain sulfonic acid ligand and desirable to improve the problem with poor conductivity due to long chain insulating ligand.Then the synthetic scheme was explored that the NCs with PL peak at 518.4nm which could luminesce in n-butanol stably without further treatment was synthesized by a simple microemulsion method at room temperature,and the SA ligand completely replaced the traditional OA ligand.Further,the possibility that the aniline completely replaced the long chain OAm was explored.However,due to the high polarity of aniline,it is impossible to synthesize stable luminous NCs.Finally,the ligand exchange strategy was adopted to synthesize blue NPLs with stable emission and good dispersion.The PL peak was 460nm,located in the pure blue region（2）The passivation mechanism and the effects of SA on the optical properties and stability of NPLS were investigated by ligand exchange with SA.We characterized and analyzed the optical properties,structure and stability of NPLs passivated with SA,and discussed in detail the passivation mechanism of SA and the effect of SA on the conductivity of NPLs.The optical properties and morphology of NPLs were not significantly changed after SA passivation.It should be noted that using NPLs to fabricate LED needs multi-step washing process.Although the optical properties of NPLS decreased significantly after washing process,but NPLs with SA passivation had higher PLQY,PL lifetime,and improved stability.By XPS and FTIR spectroscopy characterization,it was confirmed that SA can replace part of the surface ligand and Br^-to form a stronger Pb²⁺-SO3^--to passivate NPLs.Through the preparation of Hole-Only devices,it was proved that SA passivation significantly reduced the defect density of NPLs films and increased the hole conductivity,which provided a good basis for the preparation of high-performance blue LED.（3）The high efficiency pure-blue LED based on CsPbBr₃ NPLs can be achieved via SA passivation,MABr treatment,alternate droplet/spin coating method and device structure optimization.We propose analternate droplet/spin coating method to improve the coverage and thickness of NPLs layer,which can effectively suppress the emission of the transport layer,improved LED performance and spectral reproducibility.By SA passivation,the device efficiency can be increased to 1.1%in conventional device structures that only use PVK for the HTL layer.After the introduction of PTAA,the EQE was increased to 2.01%.Finally,the PLQY of the NPLs after multi-step washing can be improved by introducing MABr in demulsification process.The a CsPbBr3 NPLs based pure-blue LED with 3.18%maximum EQE can be achieved via MABr treatment with the CIE of EL emission is（0.138,0.046）,which is very close to the standard of Rec.2020（0.131,0.046）.