Surface Modification Of CsPbBr₃ Nanoplatelets And Photoelectric Properties Of Blue Led Devices

CsPbX₃（X=Cl,Br,I）perovskite nanocrystals hold great potential for applications in flat-panel display and solid-state lighting,owing to their facile color tunability,high color purity,and wide color gamut etc.Pure-blue perovskite LEDs（PeLEDs）with the emission wavelength of～465 nm,as one of the three primary colors indispensable for full-color display and white lighting,suffer from poor color stability,low EQE,and short operational lifetime.2D Cs Pb Br₃nanoplatelets are considered as ideal pure blue-emitting emitters,due to their narrow emission bandwidth,large exciton binding energies and thickness-tunable emission.However,the solid-state photoluminescence quantum yields（PL QY）and electrical conductivity of NPLs are still difficult to improve,which seriously hinders the improvement of their devices performance.In view of those problems,the research demonstrated in this dissertation focuses on the key challenges of the blue-emitting NPL LEDs,aiming to improve the device performance by material design and device structure optimization.The achieved results of the dissertation are as follows.We proposed in situ NH₄⁺-rich coating strategy,that is,ammonium bromide（NH₄Br）was introduced into Cs Pb Br₃precursor to control crystal growth kinetics and passivate surface defects,which enables us to realize short ligand（butylamine and myristic acid）-capped Cs Pb Br₃NPLs with high carrier injection efficiency and controlled emission characteristics.Further,with short conjugation ligands—phenethylammonium bromide（PEABr）postsynthetic treatment,we can dramatically enhance their electrical performance and luminous efficiency（film PL QY over 80%）.With these benefits,a remarkable electroluminescence efficiency of 2%（λ=463 nm）has been achieved,a record for blue perovskite NPLs-based LEDs at that time.Based on the short-chain ligand-capped NPLs prepared in the previous part,we proposed a post-treatment passivation strategy based on Gd Br₃-DMF solvent shell,which further improves their optical and electrical performance.In this method,the free diffusion of highly active Gd³⁺ions is restricted by the solvated shell constructed by DMF solvent molecules and Gd³⁺ions,leading to a negligible change on the surface ligand density and emission color.Meanwhile,this stable Gd³⁺-DMF solvation structure provides more available Br^-ions and gives them adequate freedom of movement,which contributes to rapid defects passivation and dramatic increase in luminous efficiency（PL QYs from 35 to 98.2%）.We use these Gd Br₃-NPLs as the emission layer and achieve a significant electroluminescence efficiency of 2.4%（λ=464 nm）.Finally,we proposed a novel interfacial engineering method with sodium dodecyl sulfate-oxygen plasma（SDS-OP）to further improve the device performance.Experimental results reveal that a short OP treatment on the top of the SDS-coated Ni O_xfilm significantly deepens the Ni O_xwork function（from 4.23 to 4.85 e V）because of the synergistic effect of SDS layer dipoles and the increase in the concentration of Ni³⁺species.Moreover,the SDS-OP layer inhibit the mass nonradiative recombination at the Ni O_x-NPLs interface.As a result,using Ni O_x/SDS-OP film as a HTL,the device achieves high efficiency and stable pure blue emission（λ=465 nm）,and its brightness and operational lifetime are 1.5-and 2.6-fold higher than PEDOT:PSS-based devices,respectively.The main significance of this dissertation is as follows.（i）An in situ NH₄⁺-rich coating strategy is proposed to achieve short ligand-capped Cs Pb Br₃NPLs with high carrier injection efficiency and controlled emission characteristics.（ii）The effect of metal ion solvation structure on the luminescence properties of Cs Pb Br₃NPLs and the related mechanism were revealed,and the photoelectric properties of Cs Pb Br₃NPLs were further improved by the post-treatment of Gd Br₃-DMF solvent shell.（iii）A SDS-OP interface passivation strategy was proposed,which inhibited exciton quenching at the Ni O_x-Cs Pb Br₃NPLs interface and improved hole injection efficiency.The research results of this dissertation have an important role in promoting the development of efficient and stable blue-emitting NPL PeLEDs.