Study On Cross-Linking Stabilization And Defect Passivation Of Quasi-Two Dimensional Perovskite Light-Emitting Diodes

Perovskite materials are promising for light-emitting diode devices due to their high photoluminescence quantum yield,easy spectral-tuning,high color purity,inexpensive material cost,and low-temperature solution processability.The maximum external quantum efficiency（EQE）of perovskite light-emitting diodes（Pe LEDs）has exceeded 20%as a result of the development of perovskite materials,especially quantum well structured quasi-2D perovskite.Due to the weak interaction of ionic crystals,the organic cations can decompose or dissociate within the perovskite,and halogen ions will migrate along defects under the external fields,which leads to the deterioriation of efficiency and stability of Pe LEDs.Herein,two cross-linkable bulky organic cations were selected to apply into quasi-2D perovskite systems and the corresponding Pe LEDs have been prepared.Then the impacts of organic large-size cations and their cross-linking on the micro-nano structure,the passivation ability of defects and optoelectronic properties,as well as stability of Pe LEDs were further investigated.The main results and conclusions are:（1）Pe LED with enhanced efficiency and stability were prepared by introducing the alkenyl amine cation 3-butenylamine hydrochloride（BUACl）into the quasi 2D PEA₂Cs_n-1Pb_nBr_3n+1 upon the crosslinking of BUACl.It was found that the cross-linked BUACl can form an amorphous phase,which filled the grain boundaries to inhibit ion migration,and the layer spacing is further reduced to facilitate charge transport,improving the photoluminescence quantum yield.The cross-linked passivation groups exhibit stronger ability to passivate defects,while forming new chemical bonds and reducing van der Waals interactions.In the optimized device,the luminance reaches20177 cd/m²,the EQE is increased from 3.1%to 5.2%and T₅₀ is increased from 95.7s to 150 s.（2）4-vinylbenzylammonium hydrobromide（VBABr）molecules with larger steric hindrance were photoinitiated to crosslink,then the crosslinked molecules imparted excellent water stability as well as better photostability to quasi 2D perovskite films.The larger hindrance in the cross-linked molecules leads to the reduction of grain size together with ammonium group,thus the luminance and efficiency were enhanced in the optimized device.More alkyl chains are generated after prolonged light irradiation,which results in the reduction of leakage current and the improvement of efficiency.The steric hindrance also suppresses ion migration with enhanced stability.In addition,the spectral stability and phase purity of VBABr in low-dimensional mixed halogen perovskite are enhanced,and the corresponding pure blue light device with EL of 478nm was prepared with a maximum luminance of 152 cd/m² and a current efficiency of0.52 cd/m².