Synthesis Of High Quality Lead Sulfide Quantum Dots And Study On Their Electroluminescent Devices

Quantum dot-based light-emitting diodes（QLED）,as a kind of novel electroluminescent devices,has attracted much attention at present.It has the advantages of high brightness,low power consumption,and solution-preparation.Infrared QLED has a promising potential in night vision,monitoring,optical communication,and biological image.Lead sulfide（Pb S）quantum dot is one of the ideal infrared luminescent materials,which has the advantages of high quantum yield,broad spectral coverage including visible and infrared spectra,excellent photochemical stability,and solution-processed production.Pb S-based QLED have developed rapidly through the improvement of synthesis chemistry,surface ligand passivation,and device structure engineering.The external quantum efficiency of 4.12%and the radiation brightness of 6.04 W Sr^-1m^-2 were obtained by using Pb S quantum dots with a fluorescence peak at 1.51μm.Most of the researches focused on the optimization of device structure and the multinary bandgap CQD composites for Pb S quantum dot films to modulate the carrier transport.However,the surface traps and stability of Pb S quantum dots,as well as the performances of Pb S-based devices,were significantly affected by the growth processes and surface engineering of Pb S quantum dots.The chemical synthesis of Pb S quantum dots suitable for QLED was still in the primary stage.Therefore,based on the control of growth kinetics and surface passivation of quantum dots,this essay aimed to synthesize high-quality Pb S quantum dots with high monodispersity and controllable surface crystal facets.To explore the factors affecting the surface-related traps and stability,and realize the fabrication of high-efficiency and stability Pb S-based QLED,the specific research contents were as follows:（1）Pb S quantum dots with high monodispersity and controlled crystal facets were synthesized by the continuous precursor injection method,which can effectively separate the nucleation and growth processes.Compared with Pb S quantum dots prepared by the traditional swift injection method,the monodispersity of quantum dots was improved.The excitonic peaks of the absorption spectra were continuously adjustable between 1200 and 1700 nm for the quantum dots grown by the continuous precursor injection method,and their full width at half maximum were always kept at about 100 nm.The growth of（1 1 1）crystal plane driven by kinetics increased the number of oleic acid ligands and decreased the number of defects related to-OH ligands on quantum dot surface.When the Pb S quantum dots with a fluorescence peak at about 1550 nm were used as the luminescent layer,the QLED with structure of ITO/PEDOT:PSS/TFB/Pb S QDs/Zn O/Al showed maximum radiation of 16.7 W Sr^-1m^-2,and maximum EQE of above 0.36%.（2）The effects of halide modification（Cl,Br,I）and Cd S shell on the stability of Pb S quantum dots and QLED were analyzed.The investigations on the passivation effects of different halide ligands demonstrated that the photoluminescence intensity of Pb S quantum dots modified with Pb I₂ ligands increased by more than two times.The modified QDs also showed excellent stability,since the position of the absorption peak and photoluminescence intensity did not change significantly under UV irradiation for one week.Lead halide ligands passivated the defects on the surface of quantum dots and shortened the distance between quantum dots,which reduced the damage of non-polar（1 0 0）crystal plane caused by water and oxygen in air.After the growth of Cd S shell,the fluorescence intensity of quantum dots increased by two times,and Pb S/Cd S still maintained good stability under UV irradiation for one week.QLED based on Pb S/Cd S quantum dots achieved a maximum EQE of 0.5%and a maximum radiation of 19.0 W Sr^-1m^-2,which were greatly improved compared to the QLED based on Pb S quantum dots.