Study On Surface Modification Of All-inorganic Perovskite Quantum Dots And Properties Of LED Devices

In recent years,perovskite quantum dots have been widely studied in the field of light-emitting diodes,solar cells and other optoelectronic devices due to their advantages of high fluorescence quantum yield,pure luminescence color,adjustable emission peak position,low cost and simple preparation methods.Compared with organic-inorganic hybrid perovskite quantum dots,all-inorganic perovskite quantum dots have better chemical and optical stability,and have greater potential in perovskite quantum dot light-emitting diodes,and are expected to become the leader of the next generation of display technology.However,there are a large number of halogen vacancies and uncoordinated Pb²⁺ion defects on the surface of perovskite quantum dots synthesized by high temperature thermal injection method,which form non-radiative recombination centers in the quantum dots and affect the improvement of luminescent properties.In addition,it is inevitable to introduce surfactants as surface ligands during the synthesis process,and the insulation of surface ligands is relatively large,which will affect carrier transport.In view of the above problems,this thesis studies the properties of Cs Pb Cl_xBr_3-x quantum dots from the perspective of surface modification of quantum dots,and introduces the synthesis method,surface modification principle and process,optical properties and LED device preparation of quantum dots.The main research contents are as follows:（1）Cs Pb Br₃ quantum dots were synthesized by thermal injection synthesis.The(1and uncoordinated Pb²⁺ions defects on the surface of the quantum dots were successfully passivated by ODADBr using solvent surface treatment technology.These defects decreased from 35.2 me V to 31.4 me V after passivation.Through EDS element analysis,it is proved that the surplus Br^-ions in ODADBr provide a bromine-rich environment,thus improving the stability of quantum dot materials.Through TEM,TRPL,and PL,it was found that the size distribution of Cs Pb Br₃ quantum dots passivated with 0.2 mg ODADBr was more uniform,and their luminescence performance was the best.Research shows that ODADBr successfully reduces the defect density on the surface of quantum dots,forming a more complete perovskite octahedral structure,making Cs Pb Br₃ quantum dots have more excellent luminescent properties.（2）The original quantum dots and the Cs Pb Br₃ quantum dots passivated by 0.2mg ODADBr were applied to the light-emitting layer of light-emitting diodes respectively.Through AFM,UPS,and single carrier device testing,it was found that quantum dot films with low defect density have better interface contact and more balanced carrier injection and transmission.The peak brightness of Cs Pb Br₃ quantum dot LEDs with low defect density has been increased by five times,reaching 53872cd/m²,and the external quantum efficiency has been improved by nearly four times,and their working life has also been greatly improved.Furthermore,the defect density in the passivated quantum dots was reduced by an order of magnitude through the single active layer devices.（3）Referring to the purification experience of Cs Pb Br₃ quantum dots,we optimized the purification process of quantum dots,successfully prepared Cs Pb Cl Br₂quantum dots,and used n-hexane to induce the secondary growth of grains between adjacent Cs Pb Cl Br₂ quantum dots.Through TEM,it was found that most of the quantum dots grew up due to mutual integration,resulting in the red shift of the absorption peak and photoluminescence peak of the quantum dots.AFM data show that the secondary growth of quantum dot film has lower surface roughness and better surface uniformity.By continuously irradiating Cs Pb Cl Br₂ quantum dot films with 405nm excitation light,the decay trend of their photoluminescence intensity with time was tested.The experiment proved that the PL intensity of quantum dot films with secondary growth characteristics with a volume ratio of 5:1 gradually increased when continuously irradiated with excitation light for about 15 minutes,and the total PL intensity decreased the slowest after continuous irradiation for a certain period of time,Moreover,the peak brightness of LEDs fabricated from quantum dots has increased by2.4 times as much as the original quantum dot LED,reaching 403 cd/m².These excellent optical properties have led to further development in the research and application of perovskite quantum dots.