Department of Chemical EngineeringHere, the synthetic methods of luminous quantum dots (QDs) and their application for the quantum dot light emitting device (QLED) were introduced. This dissertation composed for the two parts, the metal nitride QDs synthesis, characterization and their application for QLEDs with the perovskite QDs (PeQDs) synthesis, surface treatment, and their application for the PeQLEDs.
Normally, the Cd and Pb chalcogenide semiconductors utilized as the QDs materials. However, the Cd and Pb were regulated from many countries. For the replacement of the Cd and Pb based QDs, the heavy metal free materials demanded for the next generation QDs. From this necessity, the metal nitride chosen as the next-generation eco-friendly QDs materials. Also, the metal nitride QDs utilized for the III-V QDs research as a model system. The combination of the metal and nitrogen precursors focused for the finding the novel synthetic routs of the metal nitride QDs. The metal nitride had prominent stability with optoelectronic properties. However, the synthetic methods of the metal nitride not yet optimized from the low reactivity of the nitrogen sources. Normally, the NH3 gas utilized for the metal nitride material synthesis, but this gas phase precursor had hardness for the exact quantization of the ligand quantity. Also, the complex synthetic pathway with low optoelectronic quality of the conventional colloidal metal nitride QDs hindered general usage of the metal nitride nanomaterials for optoelectronic applications, especially QLEDs. The conventional QDs, which composed for the metal chalcogenide or pnictide, had liquid or solid phase anion precursors. For correct of these problems for the synthesis of the metal nitride, the solid state and/or liquid state nitrogen sources utilized for replacing the gas phase NH3 source. For the band gap control of the metal nitride QDs, the quantum confinement effect, host-guest energy transfer, and the metal alloy ratio control were utilized. From these approaches, the red to blue emitting metal nitride colloidal QDs realized via simple wet-chemical methods. Also, the metal nitride QLED was firstly realized from above luminous colloidal metal nitride QDs.
Secondly, the CsPbX3 PeQDs synthesized and their surface treatment methods developed for the optimization of the photoemission properties. The PeQDs had weak binding strength between the surface binding ligand and the PeQDs. From weak binding strength, the surface binding ligand easily detached from the surface of the PeQDs. Striping of the surface binding ligands induced surface defect sites, and these surface defects caused the non-radiative recombination. For the correct of this issue, the ligand assisted post treatment (LAPT) and the ligand assisted solubility adjustment (LASA) methods developed for the preventing of ligand diffusing out tendency. Firstly, long chain ligand added for colloidal PeQDs solution for reducing diffusion rate of the surface binding ligand. This long chain ligand adding pathway called LAPT. For removing excess ligands with reducing the internal resistance of the PeQDs film, aromatic short chain ligands utilized for surface treatment of the PeQDs under solution and/or film state. The short chain ligand passivation served slower diffusion rate and shorter particle to particle distance than pristine ligand condition. From these above properties, the aromatic short chain ligand treatment realized for optimization of the PeQLEDs performance via reducing surface defect with internal resistance of the photoactive layer. This short chain ligand based surface treatment pathway called LASA. From these approach, the optoelectronic properties of the PeQDs and PeQLEDs improved via simple surface treatment for the PeQDs.
For the deep study of the colloidal QDs synthesis and application, the metal nitride QDs and the PeQDs utilized as model system. From this interdisciplinary research of the synthesis and the device application of the QDs, this dissertation could find and the correct of the various issues of the QDs as described in this dissertation.ope
