Preparation Of Inorganic Quantum Dots In Ambient Air And Their Application In Light Emitting Diodes

Quantum dot light emitting diodes(QLEDs)have received a tremendous amount of attention over the past two decades because of their unique properties,such as high color purity,self-light emitting,solution processed and simplified fabrication process.QLEDs are rapidly emerging as promising electroluminescent devices in display and solid-state lighting fields.The performance of QLEDs has recently made impressive progresses,e.g.external quantum efficiency reaching 21%,brightness over 460 000 cd/m2 an d current efficiency more than 100 cd/A.However,fundamental issues from the principle of QLEDs are not still well understood,such as optimization measures for the synthesis of quantum dots and fabrication of devices,especially for the stability issue of devices.In this dissertation,we focused on synthesizing quantum dots and fabricating devices in the ambient condition,to simplified the fabrication process and reduce the material cost.The detailed contents are as follows:1.In this work,we developed a simple and direct method to synthesize thin-shell CdSe/ZnxCd1-xS core/shell quantum dots in ambient condition.A low-temperature(90℃-115 ℃)synthetic scheme was developed for highly luminescent CdSe/ZnxCd1-xS core/shell QDs by employing short-chain tert-dodecanethiol as the ligand and low-boiling xylene as the solvent.Thiol-capped CdSe/ZnxCd1-xS core/shell QDs with two monolayers of the shells were directly synthesized in open air,including CdSe/2ZnS,CdSe/2Zn0.5Cd0.5S,and CdSe/2CdS core/shell QDs.These short-chain ligand capped and thin-shell QDs were used as the emitting layers to fabricate QLEDs and a maximum current efficiency of 12.5 cd/A was obtained.2.We proposed and demonstrated a novel solution approach to synthesize CsPbX3(X=Cl,Br,I)perovskite nanocrystals at room temperature in the ambient condition.By this method,we can employ organic acid with different chain length as the ligand and low-boiling-point toluene as the solvent to synthesize perovskite quantum dots(PQDs).This facile strategy enables us to prepare gram-scale CsPbBr3 PQDs with a photoluminescence quantum yields(PLQY)approaching 80%.Once the highly luminescent CsPbBr3 PQDs are obtained,high quality alloyed CsPbX3(X=Cl,Br,I)PQDs with full color emission can be easily synthesized by substituting Br ions with Cl-or I-ions.The emission peak positions of CsPbX3(X＝Cl,Br,I)PNCs can be finely controlled in a wide range of 440 nm-682 nm by a simple anion post-exchange reaction.3.We found that PbBr2 can be easily dissolved in nonpolar toluene in the presence of tetraoctylammonium bromide,which allows us to homogeneously prepare CsPbBr3 and CH3NH3PbBr3 PQDs and prevents the use of harmful polar organic solvents.Highly luminescent CsPbBr3 PQDs with 80%-90%PLQYs are homogeneously synthesized at room temperature in ambient condition.An electroluminescence device has been successfully fabricated by using high-quality CsPbBr3 PQDs as the emitting layer.4.In this work,we simplified the traditional device architechture of QLEDs.We substituted the hole transport layer of traditional QLEDs with an insulating Mg(OH)2 layer and hole transport layer-free all-inorganic QLEDs were fabricated successfully.We utilized insulating Mg(OH)2 layer to reduce the quenching of QDs and balance the electron and hole charge transportation.All of the device fabrication procedures were carried out in ambient condition except for thermally evaporating and the completed QD-LEDs were measured in the open air without any encapsulation.As a result,a maximum luminance of 2930 cd/m2 and current efficiency of 1.08 cd/A were obtained with a low turn-on voltage of 1.6 V.