Synthesis And Passivation Of FA_0.8Cs_0.2PbBr₃ Nanocrystals And Their Application In Light-emitting Diodes

Perovskite light-emitting diodes?LEDs?based on perovskite nanocrystals?NCs?have a broad application prospect due to intrinsic advantages of perovskite NCs,e.g.,high photoluminescence quantum yield?PLQY?,wide color gamut,high color purity and strong quantum confinement effect.Among them,mixed cation perovskite NCs have the advantages of both all inorganic and organic-inorganic hybrid quantum dots?QDs?,which have excellent optical properties,good stability,and simple preparation process without high temperature and inert gas protection.However,there are still many problems in the preparation and application of mixed cation perovskite NCs.The problems of carrier injection efficiency,radiation recombination efficiency,carrier injection balance and stability should be considered in devices based on NCs.The surface defects of perovskite NCs and the defects generated at the interface between the perovskite emission layer and the carrier transport layer easily induce non-radiative recombination,which affects the optical properties of NCs and the electroluminescence?EL?performance of LEDs.Moreover,the stability of NCs also limits the development of perovskite NCs in the field of LEDs.To address these issues,we tried to improve the optical performance of NCs and then their device efficiency from the perspective of the high-quality NCs synthesis,surface ligands passivation of NCs,device fabrication and interfacial defects passivation in this thesis.The main work is as follows:?1?The mixed cations FA_0.8Cs_0.2PbBr₃ NCs with high PLQY,good dispersion and high crystallinity were synthesized.On the basis of the ligand-assisted reprecipitation?LARP?strategy,the synthesis method was optimized to solve the limited solubility of cesium bromide?CsBr?in N,N-dimethylformamide?DMF?.FA_0.8Cs_0.2PbBr₃ NCs were successfully prepared by doping cesium ions in the synthesis process of FAPbBr₃ NCs.By optimizing the synthesis conditions,the amount of the precursor solution injected into poor solvent toluene was changed,and the optical properties and crystallinity of NCs were observed.Finally,NCs with excellent PL properties and crystallinity were obtained.On this basis,perovskite LEDs were fabricated,and the effects of synthesis conditions and the kinds of NCs on the EL performance of the device were compared.The best device performance with maximum luminance and current efficiency of 2775 cd/m² and 6.1cd/A was finally obtained.?2?The interfacial layer was introduced to suppress the exciton quenching and passivate interfacial defects so as to improve device EL performance.By modifying the transport layer of poly?3,4-ethylenedioxythiophene?:poly?styrenesulfonicacid??PEDOT:PSS?with tetrabutylammonium bromide?TBAB?interfacial layer,the direct contact between NCs and transport layer was avoided,so the exciton quenching and non-radiative recombination was supressed and the density of defect states was reduced.The luminance and efficiency of LEDs based on FA_0.8Cs_0.2PbBr₃perovskite NCs were greatly improved with maximum luminance and current efficiency of 13001 cd/m² and 9.64 cd/A,respectively.?3?FA_0.8Cs_0.2PbBr₃ NCs was passivated with 3-amino-6-methoxy2-bromopyridine?ABMeo Py?ligand to improve the performance and stability of both NCs and device efficiency.Traditional octylamine and oleic acid ligands were partially replaced by ABMeo Py,which made the PLQY of NCs reach 95.99%and the NCs solution can be stably stored for more than half a year.The passivation on FA_0.8Cs_0.2PbBr₃ NCs inhibits non-radiative recombination and reduces the density of NCs surface defect states.The maximum luminance and current efficiency of LEDs based on ABMeo Py-passivated NCs as the light-emitting layer have been improved to 9459 cd/m² and 15.49cd/A.In addition,EL spectrum has maintained high stability even under high voltage driving.In summary,FA_0.8Cs_0.2PbBr₃ NCs with high quality and high stability were prepared by optimizing their synthesis methods and conditions.Then the performance and efficiency of the device were improved by interfacial defect passivation.The non-radiation recombination was inhibited and defect density was reduced by the ligand passivation of NCs defects with the mechanism analyzed in detail.In addition,the stability of NCs and the reproductivity of devices have also been significantly improved.This work provides a good reference for the subsequent synthesis of high quality,high stability mixed-cation NCs and the preparation of high-performance perovskite LEDs.