Design,Synthesis And Application Of Quantum Dots Capping Ligands

The quantum dots(QDs),as a kind of new quasi-zero-dimensional nanomaterials,have been favored by a large number of scientists because of their unique and excellent optical properties,since the 1980 s when they first appeared.LED,the fourth generation of illuminant,has energy saving,environmental protection,safety,waterproof and many other advantages.As the perfect combination of QDs and LED,QLED(Quantum Dots Light Emitting Diodes)come out.This maybe the greatest invention along nineteenth Century in the field of light emitting display,or will lead mankind into the Post-LED Era.QLED has many advantages such as good monochromaticity,high color saturation,photochemical stability,high fluorescence quantum yield,long fluorescence lifetime and so on.The excellent characteristics of QDs that other luminous materials can not match,destine it will become the core devices of next-generation lighting and display.Scientists usually improve the performance of the device from the following aspects: preparing QDs specifically for QLED;designing and synthesizing more appropriate surface ligands to modify QDs;building a more reasonable and perfect device structure of QLED.As the core material of QLED,QDs,because of its material itself and the restrictions of the synthesis method,still exist some key issues to be resolved: quantum dots surface defect result in fluorescence quenching;the polymer organic ligand in the surface of QDs will affect the QLED’s current efficiency.Therefore,how to modify the surface of the QDs more appropriate,achieving the performance of QLED device improvement,is a significant and scientific research which so many scientists have concerned and struggled for many years.In this paper,under the guidance of the relevant theory,aiming at the excellent device performance,we designed and synthesized a series of multivalent ligands for QDs,and expected that they could play a practical application value in the performance parameters improvement of QLED device.In the second chapter,in order to improve the current efficiency and lifetime of QLED devices,we designed and synthesized a series of multivalent ligands(four groups,13,in total)for QLED.Respectively,there are 4 tridentate single-chain thiol ligands,4 bidentate single-chain thiol ligands and 4 bidentate double-chain thiol ligands which all with different organic chain length,and 1 bidentate double-chain amine ligand.The purpose of this design is to investigate the effects of the four factors on the QLED device performance: the chain length,number of chains,the number of ligands’ dentate,and the coordination between ligand and QDs surface.Through the regulation and screening of the experimental conditions,we get a more mature synthesis program for thiol and amine ligands,with lower time-consuming and higher yield.In the third chapter,we appliedthe first group of multivalent ligands(tridentate single-chain thiol ligands)to the QLED field.Through the ligand exchange experiment,our ligands replaced the original ones modified to the QDs surface successfully,and then use the modified quantum dots to fabricate green QLED devices.The device which based on TMMN showed excellent device performance: longer lifetime(T50 lifetimes are > 480,000 h,is the longest-lifetime ever reported for green QD-LED);lower turn-on voltage of 2.2 V;higher EQE of 16.5%;well-preserved photoluminescence properties with quantum yields of ~ 90% after ligand exchange;and high color stability.The results of this experiment confirm the rationality of the surface ligand we synthesized,which provides a reference and direction for the further application of other surface ligands in QLED devices.