Tunable Luminance Of Multinary Cu-In-Zn-S-based Semiconductor Quantum Dots And Their Applications In Electroluminescent Light-emitting Diodes

Cd-based colloidal semiconductor quantum dots(QDs)are one of the most promising candidates for next generation luminescent materials.However,the intrinsic toxicity and pollution of Cd elements restrict the further development of Cd-based QDs.Therefore,tremendous efforts have been devoted in exploiting Cd-free QDs.Among different types of Cd-free QDs,multinary copper chalcogenide compounds as a competitive candidate have attracted much attention due to their low-toxicity and earth-abundant characteristics.However,as compared to Cd-based QDs,there are a lot of problems to be solved for multinary copper chalcogenide compounds,such as relatively low photoluminescent(PL)and electroluminescent(EL)performance.Consequently,it is necessary to exploit a strategy for improving the luminescent performance and the device performance of the electroluminescent light-emitting diodes,which has becomes a research hot-spot.This thesis focused on the synthesis of CIS-based QDs and relevant light emitting diodes.The main contents and innovations include four parts:1.The quaternary CIZS alloy quantum dots were prepared by a one-step reaction method,and the growth mechanism of CIZS quantum dots was studied.The research results proved that CIZS was formed by the diffusion of Zn²⁺to ternary CuInS₂.By adjusting the ratio of Cu/Zn precursor dosage,the emission range of CIZS quantum dots was effectively adjusted from 510 to 680 nm.On this basis,the further passivation of the surface was achieved by injecting Zn precursor to the reaction solution.After this,the photoluminescence performance is further improved that can reach 50-70%.The polymer film based on CIZS/ZnS quantum dots with three colors:i.e.,red,yellow and green has excellent luminescence performance and stability,which proved its good solid luminescence properties.2.The controlling of the nanostructure of CIZS quantum dots can be realized by adjusting the amount of Zn precursor dosage.It's has been proved that the diffusion of Zn²⁺and the epitaxial growth of ZnS can be used for regulating the nanostructure of CIZS-based quantum dots.By controlling the injection volume and injection speed of the Zn precursor,the diffusion of Zn²⁺and the epitaxial growth of the ZnS shell layer are effectively controlled,the number of internal and surface defect states is reduced,and a core-shell structure with a gradient distribution of elements is realized.The luminescence of the prepared CIZS-based quantum dots exhibits a single exponential decay,and the photoluminescence quantum yield is as high as 90%.A white light photoluminescence diode based on the quantum dots was prepared by a simple process method,and its efficiency exceeded 60 lm/W,reaching the leading level of similar materials.3.An electroluminescent diode(QLED)based on red,yellow,and green CIZS/ZnS quantum dots was constructed by the all-solution process,and the influence of the thickness of the electron transport layer Zn O nanoparticles,the concentration of quantum dots and the aging time on the device performance was studied.By optimizing the carrier injection and transport balance,the quantum dot electroluminescent diodes of three different colors all showed a lower starting voltage (less than 2V).Among them,the yellow electroluminescent diode has the best performance,and its peak external quantum efficiency(EQE)reached 2.42%,the highest brightness is 3061 cd/m².4.The wide emission spectrum of CIZS/ZnS quantum dots is conducive to its application in the field of lighting.On the basis of not changing the device structure,the hole transport material TFB can be used to emit blue light and compare it with the yellow CIZS/ZnS quantum dots are mixed as the light-emitting layer to construct a white photoluminescent diode.The energy transfer between TFB and CIZS/ZnS quantum dots is studied,and the energy between TFB and CIZS/ZnS quantum dots is optimized by changing the annealing temperature of the composite film.Transmission efficiency.After annealing at 95?,the color coordinates of the white light device are(0.33,0.32),the color rendering index is as high as 90,and the maximum brightness of the device reaches?1500 cd/m2,which has good stability.In conclusion,through the research on the synthesis method of CIZS quantum dots,this work successfully prepared high-quality CIZS quantum dots and realized the structural control of the quantum dots,which significantly improved the fluorescence efficiency and stability of CIZS quantum dots.On this basis,the green,yellow and red CIZS QD-LEDs were constructed by using the all-solution method.White QD-LEDs with high rendering index were prepared by take advantage of CIZS's character of wide spectrum.This work answered some key questions about the synthesis and devices'construction of CIZS QDs,which contributed to the development of this field.