Synthesis Of Red Quantum Dots With Gradient Alloy Core/Shell Structure And Performance Research Of QLED

Quantum Dots(QDs),as a kind of inorganic semiconductor material,have attracted extensive attention from researchers due to their advantages such as narrow emission spectrum,continuous adjustable spectrum,high photoluminescent quantum yield,good stability,and solubility.As one of the three primary colors,the research of red QDs and light emitting diode(QLED)play an important role in promoting their application in the fields of lighting and display.At present,red QLED devices are mostly constructed based on Cd Se/Cd S and Cd Se/Zn S core-shell QDs,and the external quantum efficiency(EQE)has reached 20%.Although the photoluminescent quantum yield(PL QY)of Cd Se/Cd S and Cd Se/Zn S quantum dots is close to 100%,there is a relatively large energy level barrier between the QDs shell material and the hole transport layer(HTL)in the device,which impedes hole injection and leads to an imbalance between electron and hole injection.In addition,during the operation of the device,the EQE of the device rolls off with the increase of current density at a higher voltage.Therefore,starting from the quantum dot energy level structure,this paper optimizes the energy band array of core/shell QDs based on the characteristics of different materials with different energy band positions,improves the injection balance of the carrier of the device and alleviates the external quantum efficiency roll-off of the device.The main work of this paper is as follows:(1)The synthesis of high quality Cd Zn Se/Zn Se red quantum dots and their application in QLED devicesFirst of all,high quality Cd Zn Se gradient alloy quantum dots cores are synthesized by adjusting the ratio of Cd/Zn.Then,Cd Zn Se gradient alloy quantum dots cores were coated with the Zn Se shell.And red Cd Zn Se/Zn Se core/shell quantum dots with fluorescence peak at 638 nm and photoluminescent quantum yield of 70% were successfully prepared.Finally,QLED devices based on Cd Zn Se/Zn Se quantum dots have the maximum EQE of 14.71% and the maximum luminance of 106,493 cd/m2.(2)Cd Zn Se/Zn Se/Zn S and Cd Zn Se/Zn Se/Zn Se S/Zn S red quantum dots synthesis and QLED devices applicationOn the basis of Cd Zn Se/Zn Se quantum dots,Zn Se S and Zn S shells further grow.Meanwhile,Cd Zn Se/Zn Se/Zn S and Cd Zn Se/Zn Se/Zn Se S/Zn S quantum dots with full-width at half-maximum which less than 30 nm,a photoluminescent quantum yield which is more than 90%,and a photoluminescent peak of about 626 nm are realized through accurating regulation of shell growth temperature,time and thickness.Among them,the highest EQE of QLED devices based on Cd Zn Se/Zn Se/Zn S quantum dots is 20.92% and the highest luminance is 159,590 cd/m2.The Cd Zn Se/Zn Se/Zn Se S/Zn S quantum dots with Zn Se S alloy layer can significantly improve the performance of QLED devices: on one hand,the highest EQE and the highest luminance can reach 22.87% and 241,167 cd/m2,respectively,which is 9.3% and 51.1% higher than QDs without Zn Se S;on the other hand,EQE is always above 20% in the luminance range of 10,000 cd/m2-210,000 cd/m2,which effectively inhibits the device efficiency roll-off.