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dc.description.abstractMixed halide perovskites (MHPs) suffer from significant spectral instability which hinders their commercialization and utilization for the light-emitting applications. Despite the considerable efforts, the fundamental reason for their red-shifted electroluminescence remains unclear. In this study, we explore the mechanism of the electroluminescence peak shifts in light-emitting diodes based on MHPs. We investigate four different types of quasi-2D MHPs containing the mixture of bromide and iodide, and show that these halides are spatially uniformly distributed in the ambient environment due to the entropic effect. However, upon the electric field, halides start to migrate toward the anode in a systematic way. Quantum mechanical density functional theory calculations indicate that different halides move at different hopping rates, and that dominant iodide hopping results in the overall halide redistribution. Experimental results also confirm that the spectral shift is correlated with the halide migration. The halide phase redistribution results in the formation of iodide- and bromide-rich domains, and hence induces changes in charge injection pathway. We propose that devices emit dominant red electroluminescence, as holes are transferred selectively to the iodide-rich domains. Overall, our mechanistic study provides insights into the origin of the spectral instability of electroluminescence devices based on MHPs.;본 연구에서는 할라이드 혼합물을 포함하는 유사-이차원 페로브스카이트의 스펙트럼 불안정성을 관측하고, 그에 대한 메커니즘을 규명하였다. 양자 화학 계산 및 전계 발광 스펙트럼 심층 분석 등의 다양한 방법들을 활용하여 발광 다이오드의 작동 과정에서 발생하는 색 변화 현상을 분석하였다. 그 결과, 전기장에 의한 할라이드 이온 이동이 스펙트럼 불안정성을 야기하며, 특히 서로 다른 두 할라이드의 이동 속도 차이에 의해 활성층 내 음이온 재분포가 발생함을 증명하였다. 또한, 열역학적 전하 주입 모델을 제시하여 적색 편이 현상을 설명하였다. 본 연구에서 활용된 분석 방법과 제시된 모델은 페로브스카이트 발광 다이오드 내에서의 이온 거동 및 그로 인한 작동 불안정성에 대한 메커니즘 연구에 폭넓게 활용될 수 있을 것으로 기대된다.-
dc.description.tableofcontentsB. Introduction 1 B-1. Lattice structure of halide perovskites 1 B-2. Electrical and photophysical properties of three-dimensional halide perovskites 3 B-3. Electrical and photophysical properties of quasi-two-dimensional halide perovskites 6 B-4. Perovskite light-emitting diodes 13 B-5. Purpose of this research 30 C. Experimental Section 32 D. Results and Discussion 35 D-1. A proposed mechanism 35 D-2. Materials and characterizations 37 D-3. Electroluminescence performance and spectral instability 42 D-4. Ion migration kinetics: Activation energy 53 D-5. Ion migration kinetics: Applied voltage 67 D-6. Ion migration kinetics: Defect density 72 D-7. Entropy-driven reverse migration 76 D-8. Selective hole injection 78 E. Conclusion 84 References 85 Abstract(in Korean) 114-
dc.format.extent5228782 bytes-
dc.publisher이화여자대학교 대학원-
dc.titleA Theoretical and Experimental Study on the Spectral Instability of Quasi-Two Dimensional Perovskite Light-Emitting Diodes Containing Halide Mixtures-
dc.typeMaster's Thesis-
dc.creator.othernameYoonseo Nah-
dc.format.pageviii, 115 p.-
dc.identifier.major대학원 화학신소재공학과- 8-
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