Synthesis And Surface Passivation Of MAPbBr₃ Perovskite Quantum Dots And Its Application In Light Emitting Diodes

MAPbBr₃ perovskite quantum dots（PQDs）have potential to become the most promising materials for next-generation display due to their excellent optical properties and simple preparation process.However,application of MAPbBr₃ PQDs is still limited by several problems:（i）How to improve the stability of MAPbBr₃ PQDs without decreasing their photoelectric properties;（ii）How to prepare a compact and flat PQD film;（iii）How to effectively limit exciton recombination process in PQD luminescent layer.These problems prevent not only their wide application for PQD light emitting diodes（LEDs）,but also their large-scale commercialization.Therefore,such issues are needed to be urgently solved.Focusing on the above problems,this paper proposes some strategies to improve PQDs stability and their LEDs performance according to the optimization from synthesis,surface passivation,film formation and LEDs device construction.The main work is as follows:（1）A room-temperature synthesis method was investigated for MAPbBr₃ PQDs with a uniform particle size,homogeneously dispersity,and easy to filming and processing.We systematically studied the ligand-assisted reprecipitation（LARP）method for MAPbBr₃ PQDs.By tuning the ratio of the precursors,a simple but efficient method was optimized.It should be noted that PQDs parpared by this method required no post-processing,which can effectively reduce the shedding of organic ligands during the centrifugation.We also used LaMer model to analyze the synthetic mechanism of PQDs.The as-prepared MAPbBr₃ PQDs showed good film-forming properties according to the improved coverage,continuity and flatness of PQD films.Furthermore,a double-layer hole transport layer was introduced to improve the injection efficiency of holes and effectively limit exciton recombination in the PQD light-emitting layer.Based on above results,the brightness and efficiency of the LED device were improved by up to one order of magnitude.（2）SiO₂-coating was used to improve the stability of MAPbBr₃ PQDs.The MAPbBr₃ PQDs were encapsulated by a-O-Si-O-space network by hydrolysis condensation of tetraethyl orthosilicate（TEOS）.The photoluminescence quantum yield（PLQY）of MAPbBr₃ PQDs@SiO₂was greatly improved.The hydrolysis condensation mechanism of TEOS in MAPbBr₃ PQDs solution was studied.Though thestability and performance of MAPbBr₃ PQDs@SiO₂ were much imporved,the size of MAPbBr₃ PQDs@SiO₂ was too larger to significantly decrease the quality of the film formation.What is more,the byproducts of TEOS after hydrolysis condensation process were difficult to accurately controlled and quantitatively analyzed,which influenced the following processing.Furthermore,the large amount of insulating SiO₂ particles presented in the light-emitting region.As a result,the device can not work properly.（3）Poly（ethylene oxide）（PEO）was employed to passivate MAPbBr₃ PQDs,which significantly enhanced film coverage,device stability and electroluminescent performances.The introduction of PEO formed MAPbBr₃ PQDs:PEO composite structure greatly passivated the surface defects of PQDs and sufficiently decreased the loss of surface organic ligands.The PLQY of MAPbBr₃ PQDs:PEO for both PQD solution and film increased more than 50%.Moreover,the using of PEO efficiently confined electrons within the PQD emission layer and generated extremely stable green electroluminescence in PQD LEDs.The performance of both external quantum efficiency and current efficiency were improved with enhancement factors of more than 18 times.In this thesis,the improvement of synthetic method of MAPbBr₃ PQDs and the post-passivation treatment of PQDs not only improved their PLQY and stability,but also improved the quality of the film.Our work provides a robust fundamental research for the fabrication of stable PQDs,high-quality PQD films and efficient PQD-based LEDs.