Synthesis Of High Quality Blue ZnSe-Based Core-Shell Quantum Dots And Their Applications In Electroluminescence Devices

Colloidal quantum dots（QDs）are the key components of the next generation light-emitting diodes（LED）because of their high stability,adjustable emission spectrum,narrow band width and wide emission spectrum range.After nearly 30 years of fruitful investment,QLED technology based on quantum dots has undergone tremendous development and its brightness and external quantum efficiency（EQE）are comparable to the most advanced organic luminescent devices.Among them,Cd-based QLED,which is famous for its high brightness,high efficiency and long life,still faces two major challenges.First,the performance development of red,green and blue primary color devices is uneven.Compared with red and green QLED,blue devices have lower efficiency and shorter life,which is not conducive to the application of full-color display in the future.Second,the toxicity of heavy metal cadmium restricts its application in electronic products.The environmentally friendly ZnSe has excellent development prospects.The bulk material has a band gap of 2.7e V and exciton binding energy of 21 me V,which is a direct band gap semiconductor material.By controlling the size of the quantum dots ZnSe quantum dots can be a good emitting material for blue light.However,ZnSe quantum dots are unstable in oxygen,so there is no corresponding theoretical study or mechanism explanation.Moreover,due to the relatively large bulk band gap,the PL coverage range of ZnSe quantum dots is usually changed from near ultraviolet light to ultraviolet light,so it is difficult to achieve dark blue luminescence.Based on this,in this paper,on the basis of the preparation of blue-purple ZnSe quantum dots,the causes of the instability of quantum dots in oxygen environment were studied,so as to achieve the purpose of improving the fluorescence quantum yield and stability of ZnSe/ZnS quantum dots,and to study the effect of Te doping amount on the peak change and device performance of ZnTeSe/ZnSe/ZnS.The thesis is mainly divided into the following two parts:（1）Study on defect state suppression and QLED application of ZnSe/ZnS quantum Dots.In this chapter,a strategy of surface defect state regulation by size engineering was proposed.Two ZnSe quantum dots with crystal core sizes（4.2 nm and 10.16 nm）were designed and synthesized mainly by regulating nucleation temperature and changing precursor injection times.It was found that QDs with small size had more defect state luminescence and lower fluorescence efficiency.In the oxygen exposure environment,the surface defect states of QDs were studied by experimental and theoretical simulation,with emphasis on revealing the root of fluorescence instability of ZnSe quantum dots.The study shows that the effect of defective states produced by quantum dots in oxygen will be minimized when the QDs size exceeds the critical diameter（8.5 nm）.The quantum yield,stability and EQE of large-size ZnSe/ZnS QDs are greatly improved.The fluorescence yield of ZnSe/ZnS QDs is up to 80%,and the EQE is up to 12.2%.（2）Synthesis and QLED Study of Pure Blue ZnTeSe/ZnSe/ZnS Core-shell quantum Dots.To solve the problem that ZnSe/ZnS QDs can not achieve pure blue emission,this paper adopts Te doping strategy to achieve peak redshift.Firstly,the Te/Se molar ratio（0.019%）was fixed,and the effects of nucleation temperature,ligand type,reaction time and other factors on the optical properties of ZnTeSe/ZnSe/ZnS QDs were studied to determine the optimal synthesis scheme.A series of ZnTeSe/ZnSe core-shell blue QDs with fluorescence peaks ranging from 440 nm to 475 nm were successfully prepared by further adjusting the Te/Se ratio in ZnTeSe crystal nuclei to achieve continuous regulation of fluorescence peaks,with quantum yields above 80%.Finally,a series of blue light devices are constructed.When Te content is 0.047%,the emissionpeak of the device is 475 nm,and the luminance and EQE reach 38138 cd m^-2 and 8.64%,respectively.