Synthesis Of Methylamine Lead Bromide Perovskite Quantum Dots And Their Application In Light-emitting Diode

Recent years,organic/inorganic hybrid perovskite quantum dots?QDs?have drawn extensive attention due to their premium properties.Compared with the traditional organic light-emitting materials,organic/inorganic hybrid perovskite QDs as direct bandgap semiconductor materials present the characters of high fluorescence quantum yield,high color purity,tunable spectrum in visible light region,simple fabrication process and so on,which have the potential applications in the fields of light-emitting diodes,solar cells,photodetectors and lasers,etc.The purpose of this thesis is to synthesize the CH₃NH₃PbBr₃ perovskite quantum dots with high fluorescence quantum yield,and then to fabricate the high performance quantum dots light-emitting diode?QLED?.The research mainly focuses on the photoelectric properties of perovskite QDs and their application in QLED.Two kinds of hole transport layers based on polymer doped with small molecules and co-doped polymers are used to optimize the device structure and improve its hole transport abililty.The carriers'recombination could be balanced in the emitting layer.As a result,the green QLEDs exhibit the enhanced performance with low turn-on voltage.The main research contents of this work are listed as follows:1.Colloidal CH₃NH₃PbBr₃ perovskite quantum dots with a size of about 5 nm were synthesized by improved ligand-assisted reprecipitation technique,and then were dispersed in n-hexane and toluene solvents,respectively.The morphology and structure of perovskite QDs were characterized by TEM and XRD.The XPS and UPS measurements were performed to analyze the elements and energy levels of perovskite QDs.The effects of different dispersing solvents on film-forming properties of QDs films were investigated by SEM and AFM.The effects of different dispersing solvents on the optical properties of QDs were investigated by steady and transient PL spectra.The results show that the n-hexane solvent has compatibility with the surface ligand of QDs,which can enhance the fluorescence quantum yield and improve the film formation.2.The green QLEDs have been fabricated based on perovskite QDs as the emitting layer,and the device's structure is ITO/PEDOT:PSS/HTL/QDs/TPBi/LiF/Al.Different small molecules doped in polymer PVK were used as hole transport layers to investigate the electroluminescent?EL?performances of the devices.The effect of hole transport layers on perovskite QDs films were analyzed through SEM,AFM and transient PL spectroscopy.The varity of the energy levels of the hole transport layers was characterized by Kelvin probe.The transport resistance of the device was measured by AC impedance spectroscopy.The results show that PVK doped with TAPC as a hole transport layer can significantly improve the hole transport capability of the device and reduce the energy barrier between hole injection layer and emitting layer.So,the carriers'injection could be balanced in emitting layer accordingly.The turn-on voltage of QLED is reduced,and the EL performance of QLED is improved.The optimized QLED show a highest luminance of 6466 cd/m² at 9 V,a maximum current efficiency of 7.06 cd/A,and a low turn-on voltage 3.6 V.3.The co-doped polymers?PVK:PTAA?hole transport layer was prepared by solution method.By adjusting the doping ratio and optimizing its film-forming property,the EL performances of QLEDs were effectively improved.The surface morphology and optical properties of the hole transport layer were characterized by AFM,SEM,steady and transient PL spectra.The energy level and charge transport characteristics of the hole transport layer were analyzed by Kelvin probe,C-AFM and AC impedance spectroscopy.The results show that PVK doping with PTAA can enhance the surface work function of hole transport layer,which can improve the hole transport ability and effectively block the electrons'diffusion to hole transport layer.Thereby,the carriers'recombination in emitting layer can be also balanced.The optimized perovskite QLED exhibits a turn-on voltage of 3.2 V,a maximum luminance of 7352 cd/m²,and a maximun current efficiency of 11.10 cd/A.