Research And Application On Improving The Air Stability Of PbS Quantum Dots

Quantum dots（QDs）is a kind of solution-processable semiconductor material,which has attracted much attention in the research and application development of solar cell,light-emitting diode（LED）,photodetector,laser and so on.Infrared light-emitting diodes（IR-LED）are widely used in communication,military and medical fields.Lead sulfide（PbS）QDs are considered as one of the most promising next-generation photoelectric materials due to their advantages of low cost,solution processing,large area processing and good air stability.In recent years,the research of IR-LED based on PbS has made great progress,but for IR-LED with large working wave,especially in the telecommunication band,the air stability of PbS QDs limits its further development in this field.For small size PbS QDs,the surface of the dots is eight oleic acid coordination（111）crystal planes.As the size of（100）crystal increases,it is not easy to combine with oleic acid ligand and is very easy to be oxidized.To solve this problem,in this paper,the air stability and luminescence performance of PbS QDs were improved by means of epitaxial CdS shell and surface modification,and quantum dot light-emitting diodes（QLED）were prepared for photoelectric performance characterization.The details are as follows:（1）PbS/CdS core-shell QDs with epitaxial CdS shells were prepared by continuous ion layer adsorption reaction（SILAR）.Core-shell structure is the most used method to improve the stability of QDs.PbS/CdS core-shell QDs are prepared by SILAR.Compared with the cation exchange method,this method can achieve accurate control of the shell thickness by controlling the stoichiometry of Cd and S precursors injected at high temperature.In this paper,the effects of reaction temperature,time and CdS shell thickness on the luminescence properties of PbS/CdS QDs were studied in detail during the preparation of PbS/CdS by SILAR.When the reaction temperature was 120℃,the fluorescence peak of the CdS shell was significantly redshifted,the diffraction peak moved to the direction of large angle and the quantum dot size increased after the PbS nuclear coating,indicating that the PbS/CdS QDs with epitaxial CdS shell were successfully prepared by SILAR mechanism.（2）In this paper,by studying the effects of the coordination of thiol on PbS qds and PbS/CdS QDs,it is found that thiol forms coordination with the（100）crystal plane of PbS QDs,and the coupling occurs between adjacent PbS QDs along the（100）crystal plane,which greatly reduces the contact between air and（100）crystal plane,and enhances the air stability of PbS QDs.Meanwhile,thiol modified the surface defects of PbS QDs and PbS/CdS QDs to improve fluorescence properties.Compared with PbS/CdS without thiol coordination,the introduction of thiol improved the fluorescence intensity by more than 70%and the device performance by 3 times.For the thiol coordinated PbS/CdS quantum dots,the maximum radiance is 18.3W·sr^-1·m²,and the external quantum efficiency can still be maintained at about 0.5%under the higher working current（～1000 m A/cm²）.