Study On The Synthesis Of High-efficiency CdSe Quantum Dots And The Performance Of LED Devices

Semiconductor quantum dots exhibit different photoluminescence and electroluminescent properties due to their quantum size effect and tunneling effect.They are applied to many fields,such as light-emitting diodes,biomarker imaging,lasers and Dan Guangzi sources.The quantum dots tend to cause oxidation in the environment and the carriers are trapped on the surface,resulting in a decrease in the quantum efficiency of photoluminescence.In order to avoid this,another semiconductor material is deposited around the core to form a protective shell to reduce surface defects and thus improve the fluorescence performance.In order to prepare Cd Se quantum dots with different properties by using eighteen enoles with high melting point and low toxicity,the QDs of different properties were obtained by coating the shell and preparing alloy.The QLED was prepared by using the prepared quantum dots as the luminescent layer,and the optimum process conditions for the preparation of QLED were explored.The main contents are as follows:(1)Using CdO and Se as precursors,high quality red light CdSe quantum dots were prepared by hot injection method.The corresponding emission peaks for samples of 20 s,40s,1min,2min,3min and 5min are 602 nm,628nm,633 nm,645nm,657 nm and 651 nm.The growth time of CdSe quantum dots is from 20 s to 3min,and the particle size increases from 3.79 nm to about 5.66 nm.The average life span of the synthesized quantum dots is 27.7ns,which is longer than that of the traditional fluorescent material.However,there are obvious defects on the surface of CdSe quantum dots,which need to be coated on the surface to improve the fluorescence properties.(2)The CdSe/ZnS quantum dots were synthesized by using CdSe as the raw material,adding S powder and zinc acetate as coating materials.The sample launch peak of different sampling time is red from 642 nm to 647 nm,and the half height and width is 33 nm.The results of analysis for XRD diffraction peak at between CdSe and ZnS,HRTEM showed that the particles are approximately spherical and well dispersed,the particle size is about 6.98 nm,compared with the same growth time CdSe particle size increased,the same growth time before and after coating coated quantum dots redshift 10 nm,also shows that ZnS is in good CdSe the surface of the epitaxial growth.There is no characteristic absorption peak of ZnS single nanocrystalline in the absorption spectrum,which also shows that ZnS is a good epitaxial growth on the surface of CdSe.The CdSe/ZnS emission spectrum of the change of Cd/Zn ratio appears red shift.(3)Using CdO,zinc acetate,Se and S as precursors,eighteen olefins and oleic acid as solvent,Se and S precursors were implanted at high temperature,and the CdZnSeS quantum dots of alloy properties were obtained.HRTEM shows that the particles are spherical and well dispersed.The growth time of the alloy quantum dots is from 1min to 10 min,and the particle size increases from 5.23 nm to 7.09 nm.The emission peak wavelength ranges from 649 nm to 660 nm.It is clear from the XRD diagram of different Cd/Zn ratios that the thickness of the alloy shell becomes thinner when the proportion of Cd/Zn decreases,and the main component is CdSe.The emission peaks of the quantum dots of the alloy structure are red shift with the combination of the sample emission spectra and the UV visible absorption spectra.(4)The CdZnSeS nanoparticle synthesized by thermal injection method is used as the luminescent layer material,and the ITO/PEDOT/TFB/CdZnSeS quantum dot /ZnO/Al structure quantum dot electroluminescent device is fabricated.By adjusting the concentration and speed of each layer,and analyzing a series of parameters,such as device brightness,current density,external quantum efficiency(EQE)and current efficiency,we find the optimum concentration and speed of each layer.