2,303 research outputs found

    Lead-Free Hybrid Perovskite Light-Harvesting Material for QD-LED Application

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    Most recently, organic-inorganic semiconductor light harvester materials, have arisen as a new class of functional element and attracts the research community due to its outstanding optoelectronic properties. Organic-inorganic perovskites are solution process that is easy for the fabrication of devices at low temperature. Additionally, up to date, perovskite quantum dots have emerged as the most efficient light harvester for LEDs and display applications, with high color purity, color tunability, and photoluminescence quantum yield up to 100%. However, the presence of lead in organic-inorganic perovskites and the stability issue of perovskite materials are the significant challenges for the research community. To date, some lead substitute materials have been tried to enhance the film morphology and production of the less toxic light harvester. In this chapter, we focus on the lead substitution on B sight with homovalent cations like Sn2+, Mn2+, Cd2+, and Zn2+ cations. These lead substitutions not only reduce the toxicity of perovskite material while these dopants also enhance the optical and performance of LEDs. We also included the LEDs application of lead substituted perovskite quantum dots (PQDs) that may be useful for the environmental friendly and highly performing perovskite quantum dot LEDs (PQ-LEDs) shortly

    Roadmap on Perovskite Light-Emitting Diodes

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    In recent years, the field of metal-halide perovskite emitters has rapidly emerged as a new community in solid-state lighting. Their exceptional optoelectronic properties have contributed to the rapid rise in external quantum efficiencies (EQEs) in perovskite light-emitting diodes (PeLEDs) from <1% (in 2014) to approaching 30% (in 2023) across a wide range of wavelengths. However, several challenges still hinder their commercialization, including the relatively low EQEs of blue/white devices, limited EQEs in large-area devices, poor device stability, as well as the toxicity of the easily accessible lead components and the solvents used in the synthesis and processing of PeLEDs. This roadmap addresses the current and future challenges in PeLEDs across fundamental and applied research areas, by sharing the community's perspectives. This work will provide the field with practical guidelines to advance PeLED development and facilitate more rapid commercialization.Comment: 103 pages, 29 figures. This is the version of the article before peer review or editing, as submitted by an author to Journal of Physics: Photonics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

    Roadmap on perovskite light-emitting diodes

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    In recent years, the field of metal-halide perovskite emitters has rapidly emerged as a new community in solid-state lighting. Their exceptional optoelectronic properties have contributed to the rapid rise in external quantum efficiencies (EQEs) in perovskite light-emitting diodes (PeLEDs) from <1% (in 2014) to over 30% (in 2023) across a wide range of wavelengths. However, several challenges still hinder their commercialization, including the relatively low EQEs of blue/white devices, limited EQEs in large-area devices, poor device stability, as well as the toxicity of the easily accessible lead components and the solvents used in the synthesis and processing of PeLEDs. This roadmap addresses the current and future challenges in PeLEDs across fundamental and applied research areas, by sharing the communityโ€™s perspectives. This work will provide the field with practical guidelines to advance PeLED development and facilitate more rapid commercialization

    ๊ธˆ์† ์‚ฐํ™”๋ฌผ ๋ฐ ์ด์ฐจ์› ๋‚˜๋…ธ ๋ฌผ์งˆ ๊ธฐ๋ฐ˜์˜ ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ: ์„ฑ๋Šฅ ์ตœ์ ํ™” ๋ฐ ์–‘์ž์  ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ์— ๋Œ€ํ•œ ์‘์šฉ

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    ํ•™์œ„๋…ผ๋ฌธ(๋ฐ•์‚ฌ) -- ์„œ์šธ๋Œ€ํ•™๊ต๋Œ€ํ•™์› : ๊ณต๊ณผ๋Œ€ํ•™ ์ „๊ธฐยท์ •๋ณด๊ณตํ•™๋ถ€, 2021.8. ๊ณฝ์ •ํ›ˆ.๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ๋ฅผ ์ง‘์ ํ•œ ์ „์ž ๋””์Šคํ”Œ๋ ˆ์ด์˜ ๊ฐœ๋ฐœ์€ ๋›ฐ์–ด๋‚œ ์žฅ์ ์œผ๋กœ ์ธํ•ด ํฐ ๊ด€์‹ฌ์„ ๋ฐ›์•„์™”๋‹ค. ์ง€๋‚œ ์ˆ˜์‹ญ ๋…„ ๋™์•ˆ ๋Šฅ๋™ ๋งคํŠธ๋ฆญ์Šค ์•ก์ • ๋””์Šคํ”Œ๋ ˆ์ด ๋ฐ ์œ ๊ธฐ ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ์™€ ๊ฐ™์€ ํ‰ํŒ ๋””์Šคํ”Œ๋ ˆ์ด์— ๋Œ€ํ•œ ์—ฌ๋Ÿฌ ์—ฐ๊ตฌ๊ฐ€ ๋ณด๊ณ ๋˜์—ˆ์Šต๋‹ˆ๋‹ค. ์ด๋Ÿฌํ•œ ์šฐ์ˆ˜ํ•œ ์„ฑ๊ณผ์—๋„ ๋ถˆ๊ตฌํ•˜๊ณ , pํ˜• ์‚ฐํ™”๋ฌผ/๋‚˜๋…ธ ๋ฐ˜๋„์ฒด์˜ ๊ฐœ๋ฐœ๊ณผ ๋ฐฑํ”Œ๋ ˆ์ธ ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ๋กœ ๊ตฌ๋™๋˜๋Š” ์–‘์ž์  ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ์˜ ๊ตฌ๋™์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๋Š” ์ œํ•œ์ ์ž…๋‹ˆ๋‹ค. pํ˜• ๋ฐ˜๋„์ฒด์˜ ์ „๊ธฐ์  ํŠน์„ฑ์€ ์ด๋™๋„๊ฐ€ ๋‚ฎ๊ณ , ์˜คํ”„ ์ „๋ฅ˜๊ฐ€ ๋†’์œผ๋ฉฐ, ์†Œ์ž์˜ ๋ถˆ์•ˆ์ •์„ฑ์ด ์žˆ๊ธฐ ๋•Œ๋ฌธ์ž…๋‹ˆ๋‹ค. ์ด๋Ÿฌํ•œ ์˜๋ฏธ์—์„œ ์šฐ๋ฆฌ๋Š” ์•ž์„œ ์–ธ๊ธ‰ํ•œ ์‘์šฉ์„ ์œ„ํ•œ p-ํ˜• ์‚ฐํ™”๋ฌผ/๋‚˜๋…ธ ๋ฌผ์งˆ ๊ธฐ๋ฐ˜ ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ์™€ ์ฝœ๋กœ์ด๋“œ ์–‘์ž์  ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ๋ฅผ ์—ฐ๊ตฌํ–ˆ์Šต๋‹ˆ๋‹ค. ๋จผ์ €, ์šฐ๋ฆฌ๋Š” ์œ ์—ฐํ•œ ์ „์ž ์žฅ์น˜์— ์ž ์žฌ์ ์œผ๋กœ ๋งค๋ ฅ์ ์ธ ๋‚˜๋…ธ ์™€์ด์–ด ๊ตฌ์กฐ๋กœ ํ˜•์„ฑ๋œ ๋Œ€์ฒด ์ „๊ทน์œผ๋กœ ์ „๊ธฐ์  ํŠน์„ฑ์„ ์œ„ํ•ด ์Šคํ”„๋ ˆ์ด ์ฝ”ํŒ…๋œ ๋‹จ์ผ๋ฒฝ ํƒ„์†Œ๋‚˜๋…ธ ํŠœ๋ธŒ๋ฅผ ์†Œ์Šค ๋ฐ ๋“œ๋ ˆ์ธ ์ „๊ทน์œผ๋กœ ์‚ฌ์šฉํ•˜๋Š” p ํ˜• ์ฃผ์„ ์‚ฐํ™”๋ฌผ (SnO) ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ๋ฅผ ๊ตฌํ˜„ํ–ˆ์Šต๋‹ˆ๋‹ค. ํด๋ฆฌ๋จธ ์—์น˜ ์Šคํ† ํผ ์ธต์— SU-8์ด ์žˆ๋Š” SnO ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ์˜ ์†Œ์ž ๊ตฌ์กฐ๋Š” SnO ์ฑ„๋„ ์ธต์˜ ์—ดํ™” ์—†์ด ์›ํ•˜๋Š” ์˜์—ญ์—์„œ ๋‹จ์ผ๋ฒฝ ํƒ„์†Œ๋‚˜๋…ธํŠœ๋ธŒ์˜ ์„ ํƒ์  ์—์นญ์„ ๊ฐ€๋Šฅํ•˜๊ฒŒ ํ•ฉ๋‹ˆ๋‹ค. ๋˜ํ•œ ๋‹จ์ผ๋ฒฝ ํƒ„์†Œ๋‚˜๋…ธํŠœ๋ธŒ ์ „๊ทน์œผ๋กœ ์‚ฌ์šฉํ•˜๋Š” SnO ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ๋Š” ์ ์ ˆํ•œ ์ฑ„๋„ํญ๊ณผ ์ •๊ทœํ™”๋œ ์ „๊ธฐ์  ์ปจํƒ ํŠน์„ฑ (~ 1 kฮฉ cm), ์ „๊ณ„ ํšจ๊ณผ ์ด๋™์„ฑ (~ 0.69 cm2/Vs), ๋ฌธํ„ฑ์ „์••์ดํ•˜ ์Šค์œ™ (~ 0.4 V/dec) ๋ฐ ์ „๋ฅ˜ ์˜จ-์˜คํ”„ ํŠน์„ฑ (Ion/Ioff ~ 3.5ร—103)์„ ์„ฑ๊ณต์ ์œผ๋กœ ๊ตฌํ˜„ํ•˜์˜€์Šต๋‹ˆ๋‹ค. ๋˜ํ•œ ์˜จ๋„์— ๋”ฐ๋ฅธ ์ „๊ธฐ์  ์ปจํƒ ๋ฐ ์ฑ„๋„ ํŠน์„ฑ์€ Ni ์ „๊ทน์— ํ•„์ ํ•˜๋Š” ์ ์ ˆํ•œ ์ ‘์ด‰ ์ €ํ•ญ๊ณผ ํ•จ๊ป˜ ๋ฌด์‹œํ•  ์ˆ˜ ์žˆ๋Š” ์ˆ˜์ค€์˜ ๊ฐ€์ „์ž๋  ํ…Œ์ผ ์Šคํ…Œ์ดํŠธ์˜ 3 x 10-3 eV ํ™œ์„ฑํ™” ์—๋„ˆ์ง€๋กœ SnO ์ฑ„๋„ ์ „์†ก์„ ์„ค๋ช…ํ•ฉ๋‹ˆ๋‹ค. ๋‘˜์งธ, ์šฐ๋ฆฌ๋Š” ๋จผ์ € ์ƒ๋ณดํ˜• ํŠธ๋žœ์ง€์Šคํ„ฐ๋ฅผ ๊ตฌํ˜„ํ•˜์—ฌ p (๋˜๋Š” n ํ˜•) MoTe2 ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ์— ์˜ํ•ด ์ œ์–ด๋˜๋Š” ์–‘์ž์  ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ ๊ตฌ๋™์„ ์‹œ์—ฐํ•ฉ๋‹ˆ๋‹ค. ์ด ์—ฐ๊ตฌ์—์„œ๋Š” MoTe2 ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ์˜ ์œ ํ˜• ๋ณ€ํ™˜์„ ์œ„ํ•ด Poly-L-lysine (PLL)์— ์˜ํ•œ ๋ถ„์ž ๋„ํ•‘์„ ๋„์ž…ํ•˜๊ณ , ์–‘์ž์  ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ ์„ฑ๋Šฅ ํ–ฅ์ƒ์„ ์œ„ํ•ด ํ‘œ๋ฉด ๋ฆฌ๊ฐ„๋“œ ๋ณ€ํ˜•์„ ํ™œ์šฉํ•ฉ๋‹ˆ๋‹ค. ์ด์™€ ๊ด€๋ จํ•˜์—ฌ PLL ์ฒ˜๋ฆฌ๋Š” ์ „๊ธฐ์  ํŠน์„ฑ์˜ ์ €ํ•˜์—†์ด MoTe2 ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ์˜ ๋›ฐ์–ด๋‚œ ์œ ํ˜• ๋ณ€ํ™˜์„ ๋‹ฌ์„ฑํ•˜์—ฌ, ์•ˆ์ •์ ์ธ p (๋˜๋Š” n ํ˜•) ์œ ํ˜• ์žฅ์น˜๋ฅผ ํ™•๋ณดํ•˜์—ฌ ๋ณด์™„ ํšŒ๋กœ์˜ ๊ฐ€์šฉ์„ฑ์„ ๋ณด์žฅํ•ฉ๋‹ˆ๋‹ค. ๋˜ํ•œ, ์˜ฅํ‹ธ ์•„๋ฏผ์œผ๋กœ ๋ฆฌ๊ฐ„๋“œ ์น˜ํ™˜๋œ ์–‘์ž์ ์€ ์–‘์ž์  ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ์—์„œ ๊ท ํ˜• ์žกํžŒ ์ „์ž/์ •๊ณต ์ฃผ์ž…์„ ์ƒ์„ฑํ•˜์—ฌ, ์ „๋ฅ˜ ํšจ์œจ (ฮทA = 13.9 cd/A)์ด ๊ฐœ์„ ๋˜๊ณ  ์ˆ˜๋ช…์ด ๋” ๊ธธ์–ด์ง‘๋‹ˆ๋‹ค (L0 = 3000 cd/m2์—์„œ T50 = 66 h). ๊ฒฐ๊ณผ์ ์œผ๋กœ MoTe2 ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ๋Š” ์ ์ ˆํ•œ ์Šค์œ„์นญ ํŠน์„ฑ์„ ๊ฐ€์ง„ ๋””์Šคํ”Œ๋ ˆ์ด ๋ฐฑํ”Œ๋ ˆ์ธ ํŠธ๋žœ์ง€์Šคํ„ฐ, ๊ด‘ ์ „๋ฅ˜ ์ƒ์„ฑ์— ๋Œ€ํ•œ ๋‚ด์„ฑ ๋ฐ ์ž‘๋™ ์•ˆ์ •์„ฑ์„ ํฌํ•จํ•˜์—ฌ ์–‘์ž์  ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ๋ฅผ ๊ตฌ๋™ํ•˜๋Š” ๋Šฅ๋ ฅ์„ ๋ณด์—ฌ์ค๋‹ˆ๋‹ค. ์ด ๋…ผ๋ฌธ์—์„œ ์šฐ๋ฆฌ๋Š” ์œ ๋งํ•œ ์‘์šฉ์„ ์œ„ํ•œ ์‚ฐํ™”๋ฌผ/๋‚˜๋…ธ ๋ฌผ์งˆ ๊ธฐ๋ฐ˜ ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ์™€ ๋ฆฌ๊ฐ„๋“œ ์น˜ํ™˜ ๊ธฐ์ˆ ์ด ์ ์šฉ๋œ ํ›„๋ฉด ๋ฐœ๊ด‘ ์ ์ƒ‰ ์–‘์ž์  ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ์— ๋Œ€ํ•ด ๋…ผ์˜ํ•ฉ๋‹ˆ๋‹ค. ๋ฐฑํ”Œ๋ ˆ์ธ ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šค๋กœ pํ˜• SnO์™€ MoTe2๋ฅผ ์‚ฌ์šฉํ•˜๊ณ , ์ƒˆ๋กœ์šด ๋””์Šคํ”Œ๋ ˆ์ด ์žฅ์น˜๋กœ CdSe ์–‘์ž์  ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ๋ฅผ ์‚ฌ์šฉํ•œ ์šฐ๋ฆฌ์˜ ์—ฐ๊ตฌ ์„ฑ๊ณผ๋Š” ์œตํ•ฉ ์—ฐ๊ตฌ๋ฅผ ์œ„ํ•œ ๊ตฌ์ƒ ๋ถ„์•ผ์—์„œ ์ž ์žฌ์ ์œผ๋กœ ์‚ฌ์šฉ๋  ์ˆ˜ ์žˆ์Šต๋‹ˆ๋‹ค.The development of electronic displays integrated with Thin Film Transistors (TFTs) has been great interests due to their superb merits. For the past decades, several studies have been reported for the flat-panel displays (FPDs) such as active-matrix liquid crystal display (LCD) and organic light-emitting diode (OLED). Despite of these excellent achievements, progress of p-type oxide/nano semiconductors and operation of quantum dot light-emitting diode (QLED) driven by backplane TFTs are limited. This is because the electrical characteristics of p-type semiconductor have low mobility, high off current, and device instability. In this sense, we investigated p-type oxide/nano material-based TFTs and colloidal quantum dot light-emitting diodes (QLEDs) for the afore-mentioned application. First, we implemented p-type tin oxide (SnO) TFTs with spray-coated single-wall carbon nanotube (SWNTs) as source and drain electrodes for their electrical characteristics as alternative electrodes formed of nanowire structures, which are potentially attractive for flexible electronics. The device architecture of SnO TFTs with a polymer etch stop layer (SU-8) enables the selective etching of SWNTs in a desired region without the detrimental effects of SnO channel layers. In addition, SnO TFTs with SWNT electrodes as substitutes successfully demonstrate decent width normalized electrical contact properties (~1 kฮฉ cm), field effect mobility (~0.69 cm2/Vs), sub-threshold slope (~0.4 V/dec), and current on-off ratio (Ion/Ioff ~ 3.5ร—103). Furthermore, temperature-dependent electrical contact and channel properties elucidate SnO channel transports with an activation energy of 3ร—10-3 eV, interpreted as a negligible level of valence-band tail states, together with decent contact resistance comparable to that of Ni electrodes. Second, we firstly demonstrated the QLEDs operation modulated by p (or n-type) MoTe2 TFTs with the realization of complementary type transistor. In this study, molecular doping by Poly-L-lysine (PLL) as an electron dopant is adopted for a type conversion of MoTe2 TFTs, and surface ligand modification is utilized for the improvement of QLED performance. In this regard, the PLL treatment achieves the outstanding type conversion of MoTe2 TFTs without any degradation of electrical properties, leading to securing reliable p (or n-type) devices, thus, availability of complementary circuits. Furthermore, ligand modified QDs capped with octylamine result in balanced electron/hole injection in QLEDs, yielding improved current efficiency (ฮทA =13.9 cd/A) and longer lifetimes (T50 = 66 h at L0 = 3000 cd/m2). As a result, MoTe2 TFTs demonstrate their capabilities to drive the QLEDs for the envisioned application including display backplane transistor with decent switching properties, immunity for generation of photocurrent, and operation stability. In this thesis, we discuss the oxide/nano material based TFTs and ligand modified bottom emitting red QLEDs for many promising applications. Our research achievements using p-type SnO and MoTe2 as backplane TFTs, and CdSe QLED as novel display device can be used in potentially envision fields for the convergence research.Chapter 1 1 1.1 An Overview of Thin Film Transistors 1 1.2 An Overview of Quantum Dot Light-Emitting Diodes 8 1.3 Outline of Thesis 13 Chapter 2 15 2.1 Materials 15 2.1.1 Synthesis of ZnO Nanoparticles 15 2.1.2 Synthesis of Red Light-Emitting CdSe/Cd1-xZnxS Quantumd Dots 15 2.2 Device Characterization of Thin Film Transistors 17 2.2.1 Characterization for Thin Film Transistor 17 2.2.2 Characterization of Light Response 18 2.3 Device Characterization of Quantum Dot Light-Emitting Diodes 18 2.3.1 Current-voltage-luminance Measurement of QLEDs 18 2.3.2 Efficiency Calculation Methods 21 2.3.3 Other Characterization Methods 22 Chapter 3 24 3.1 Devic Fabrication of SnO TFTs with Spray-Coated Single Walled Carbon Nanotubes as S/D Electrodes 26 3.2 Electrical Performance of SnO TFTs 30 3.3 Contact Resistance of Spray-coated SWNTs as S/D Electrodes 33 3.4 Summary 40 Chapter 4 41 4.1 Description of QLED display driven by MoTe2 TFTs 45 4.2 Ligand Modification of Red CdSe/Cd1-xZnxS Quantum Dots 49 4.3 Type Conversion of MoTe2 TFTs via Electron-Donated Charge Enhancer 54 4.4 Light-Insensitive Behaviors on Photocurrent Generation in MoTe2 TFTs 61 4.5 Operation of QLEDs Driven by Channel-type Controlled MoTe2 TFTs 66 4.6 Summary 70 Chapter 5 71 Bibilography 73 ํ•œ๊ธ€ ์ดˆ๋ก 81๋ฐ•

    Luminescence in sulfides : a rich history and a bright future

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    Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications. Upon doping with Ce3+ and Eu2+, the luminescence can be varied over the entire visible region by appropriately choosing the composition of the sulfide host. Main application areas are flat panel displays based on thin film electroluminescence, field emission displays and ZnS-based powder electroluminescence for backlights. For these applications, special attention is given to BaAl2S4:Eu, ZnS:Mn and ZnS:Cu. Recently, sulfide materials have regained interest due to their ability (in contrast to oxide materials) to provide a broad band, Eu2+-based red emission for use as a color conversion material in white-light emitting diodes (LEDs). The potential application of rare-earth doped binary alkaline-earth sulfides, like CaS and SrS, thiogallates, thioaluminates and thiosilicates as conversion phosphors is discussed. Finally, this review concludes with the size-dependent luminescence in intrinsic colloidal quantum dots like PbS and CdS, and with the luminescence in doped nanoparticles

    ์œ ๊ธฐ๋ฐœ๊ด‘์†Œ์ž์— ๋Œ€ํ•œ ๋‹ค์–‘ํ•œ ๊ด‘์ถ”์ถœ ๊ตฌ์กฐ์™€ ๋ฐฐํ–ฅ ๋ถ„๊ทน ๋ถ„์ž์˜ ํšจ๊ณผ

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    ํ•™์œ„๋…ผ๋ฌธ (๋ฐ•์‚ฌ) -- ์„œ์šธ๋Œ€ํ•™๊ต ๋Œ€ํ•™์› : ๊ณต๊ณผ๋Œ€ํ•™ ์žฌ๋ฃŒ๊ณตํ•™๋ถ€, 2020. 8. ๊น€์žฅ์ฃผ.Since the first electroluminescence (EL) of organic compound was observed in the anthracene single crystal in 1965, organic light-emitting diodes (OLEDs) have undergone numerous developments, and have recently become the mainstream of small-sized displays. In addition, as OLEDs will have a modest substrate dependency, it has the potential to receive even more attention as the next generation display like flexible or transparent displays. The remaining challenges for OLEDs are high efficiency, and operational stability. In general, because organic materials have a wide emission spectrum, OLED can be a good lighting with a high color rendering index (CRI). It can also be used as a display with high color purity by optimizing the cavity length. However, more than half of the photons generated in OLEDs are dissipated due to total internal reflection by high-refractive-index organic layers and the substrate. Therefore, light extraction technology is required to increase the efficiency and reduce the power consumption of OLEDs. In addition, as mentioned before, it is necessary to consider the lifetime of the device. There have been many studies on the short operation lifetime of OLEDs, and several mechanisms have been proposed, but there is no concrete description of the origin of degradation. Nonetheless, it is obvious that the stability of the layers constituting the OLED should be considered for high operational stability. This thesis concerns two research topics: (1) simple and efficient light extraction method for OLED lighting and display, and (2) improving operation lifetime of OLED using spontaneous orientation polarization molecule. In chapter 1, a brief introduction of OLEDs will be provided. In chapter 2, a facile and effective method for fabricating random organic microstructures for efficient light extraction from blue OLEDs is presented. Simple drop casting of a TCTA and B4PyMPM mixed solution followed by UV curing results in films with irregular-shaped microstructures (DACMs), ideal for light extraction without diffraction patterns. An external quantum efficiency (EQE) of 44.3% is realized by attaching DACMs formed on a polymer film to a blue phosphorescent OLED. The efficiency is improved by 35% compared to a planar device without the light extraction layer, greater than the 22% improvement obtained by using microlens arrays. The method is useful for OLED lighting and potentially in displays because of the simple fabrication method that is applicable to a large area on rigid or flexible substrates, the low material cost, the insolubility of the microstructure in alkyl halide solvents such as chloroform, and the controllability of the structure through the solution process. In chapter 3, we show the damageless light extraction structure for top-emittng organic light-emitting diodes (TEOLEDs). TEOLEDs are used in small displays, due to the high aperture ratios, unblurred imaging, and high color purity. However, the strong cavity structures responsible for these advantages result in a high optical loss within metal electrodes. Furthermore, as there is no substrate in the light path, it is rather complicated to form a structure on the emission surface without damage. Here, we present a facile and effective method for light extraction of TEOLEDs. When 1,5-diaminoanthraquinone (DAAQ) is deposited on the Ag electrode, crystallization occurs immediately and nanowire arrays are formed in the out-of-plane direction. The shape and distribution of nanowire arrays can be controlled by deposition thickness and evaporation rate. In addition, morphological changes affect the transmittance of DAAQ-deposited Ag thin films. DAAQ nanowire arrays were applied to a red phosphorescent inverted TEOLED, enhancing the external quantum efficiency (EQE) by 8.6% in a narrow full-width-at-half-maximum (FWHM) device, and by 10.6% in a wide FWHM device. The emission spectra of the out-coupled devices are similar to those of the reference devices, as the DAAQ layer is located outside the OLED stacks sandwiched between two highly reflective metal electrodes. The method is useful for OLED displays because it is simple, vacuum-processable, and does not compromise device lifetime or the emission spectrum. In chapter 4, we suggest the importance of patternability of internal light extraction layer. Integration of internal light extraction layers in OLED displays requires electrical connection between driving circuits in the backplane and an OLED electrode, therefore needs fabrication of a via hole. Generally, internal light extraction layers consist of two materials with different refractive indices; thus, good patternability may be difficult with the matched etch selectivities of these two materials. Both the patternability of the internal light extraction layer and high out-coupling efficiency are important so, it needs a proper etchant which arent lowering the extraction efficiency by demolishing its structure. Here, the patternability of light extraction layers is discussed and demonstrated experimentally. The random scattering layer (RSL) composed of SiOx nano scatterers and a TiO2 planarization layer was used in this study and it was patterned by photolithography and wet etching processes. For matching the etching selectivity of those two different materials, a mixture of buffered oxide etchant (BOE) and phosphoric acid (H3PO4), in a volume ratio of 0.5 of H3PO4 to BOE, shows the best results for forming electrical channels through the out-coupling layer. The OLEDs fabricated on this patterned substrate showed similar current density-voltage (J-V) characteristics to OLEDs on a glass substrate with low leakage levels. The device showed over 50% enhancement of external quantum efficiency (EQE; from 21.7% to 32.7%), similar to the device without via holes. Chapter 5 contains a method for improving the stability of electron transporting layer. After the alignment of permanent dipole moment (PDM) was found in Alq3, it was revealed that spontaneous orientation polarization (SOP) was observed in several electron transporting materials. Although studies on the electrical effects of the polarization have been reported, there are few reports on the effects of polarization on the lifetime of device. Here, we observed the SOP characteristics and the change in the lifetime of device when BAlq was doped in PO-T2T with different volume ratios. As the polarization increased, the operation lifetime also increased and the applied voltage change decreased. In addition, the lifetime enhancement was only observed when there was a polarized layer at the interface with the emtting layer (EML). This shows that hole blocking layer (HBL) can enhance the lifetime when it has a negative surface charge at the interface with EML, and also indicates that the SOP characteristics of the molecule should be considered for improving the lifetime.1965 ๋…„, ์•ˆํŠธ๋ผ์„ผ ๋‹จ๊ฒฐ์ •์—์„œ ์œ ๊ธฐ๋ฌผ์˜ ์ฒซ ์ „๊ธฐ ๋ฐœ๊ด‘์ด ๋ฐœ๊ฒฌ๋œ ์ดํ›„, ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž๋Š” ๋งŽ์€ ๋ฐœ์ „์„ ๊ฑฐ๋“ญํ•ด ์ตœ๊ทผ ์†Œํ˜• ๋””์Šคํ”Œ๋ ˆ์ด์˜ ์ฃผ๋ฅ˜๋ฅผ ์ด๋ค˜๋‹ค. ๋˜ํ•œ ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž๋Š” ์ ์€ ๊ธฐํŒ ์˜์กด์„ฑ์„ ๊ฐ–๊ธฐ ๋•Œ๋ฌธ์— ํ”Œ๋ ‰์‹œ๋ธ” ๋””์Šคํ”Œ๋ ˆ์ด๋‚˜ ํˆฌ๋ช… ๋””์Šคํ”Œ๋ ˆ์ด์™€ ๊ฐ™์€ ์ฐจ์„ธ๋Œ€ ๋””์Šคํ”Œ๋ ˆ์ด๋กœ ํ™œ์šฉ๋  ์ˆ˜ ์žˆ๋Š” ์ž ์žฌ๋ ฅ์„ ๊ฐ–๊ณ  ์žˆ๋‹ค. ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž์—์„œ ๋‚จ์€ ๊ณผ์ œ๋Š” ๋†’์€ ํšจ์œจ๊ณผ ๊ตฌ๋™ ์•ˆ์ •์„ฑ์ด๋‹ค. ์ผ๋ฐ˜์ ์œผ๋กœ ์œ ๊ธฐ๋ฌผ์€ ๋„“์€ ๋ฐœ๊ด‘์ŠคํŽ™ํŠธ๋Ÿผ์„ ๋ณด์ด๊ธฐ ๋•Œ๋ฌธ์—, ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž๋Š” ์—ฐ์ƒ‰์„ฑ์ด ๋†’์€ ์กฐ๋ช…์œผ๋กœ ์‚ฌ์šฉ๋  ์ˆ˜ ์žˆ๋‹ค. ๋˜ํ•œ, ๊ด‘ํ•™ ๊ณต์ง„ ๊ตฌ์กฐ ์ตœ์ ํ™”๋ฅผ ํ†ตํ•ด ๋†’์€ ์ƒ‰์ˆœ๋„์˜ ๋””์Šคํ”Œ๋ ˆ์ด๋กœ๋„ ํ™œ์šฉ๋  ์ˆ˜ ์žˆ๋‹ค. ํ•˜์ง€๋งŒ ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž๊ฐ€ ๋ฐฉ์ถœํ•œ ๊ด‘์ž์˜ ์ ˆ๋ฐ˜ ์ด์ƒ์€ ๋†’์€ ๊ตด์ ˆ๋ฅ ์˜ ์œ ๊ธฐ๋ฌผ ๋ฐ ๊ธฐํŒ์œผ๋กœ ์ธํ•œ ๋‚ด๋ถ€ ์ „๋ฐ˜์‚ฌ๋กœ ์†Œ๋ฉธ๋œ๋‹ค. ๋”ฐ๋ผ์„œ, ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž์˜ ํšจ์œจ์„ ์˜ฌ๋ฆฌ๊ณ  ์ „๋ ฅ ์†Œ๋ชจ๋ฅผ ๊ฐ์†Œ์‹œํ‚ค๊ธฐ ์œ„ํ•ด ๊ด‘์ถ”์ถœ ๊ธฐ์ˆ ์€ ํ•„์š”ํ•˜๋‹ค. ์ด์— ๋”๋ถˆ์–ด, ์œ„์—์„œ ์–ธ๊ธ‰ํ•œ ๋ฐ”์™€ ๊ฐ™์ด ์†Œ์ž์˜ ๊ตฌ๋™์‹œ๊ฐ„์— ๋Œ€ํ•œ ๊ณ ๋ ค๋„ ํ•„์š”ํ•˜๋‹ค. ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž์˜ ์งง์€ ๊ตฌ๋™ ์ˆ˜๋ช…์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๋Š” ๋งŽ์ด ์žˆ๊ณ , ๋ช‡๋ช‡ ๋ฉ”์ปค๋‹ˆ์ฆ˜์ด ๋ฐœํ‘œ๋˜์—ˆ์ง€๋งŒ, ์•„์ง ์†Œ์ž ์—ดํ™”์˜ ์ „๋ฐ˜์„ ์„ค๋ช…ํ•  ์ˆ˜ ์žˆ๋Š” ์ด๋ก ์€ ์ „๋ฌดํ•˜๋‹ค. ๊ทธ๋Ÿผ์—๋„ ๋ถˆ๊ตฌํ•˜๊ณ , ๋†’์€ ๊ตฌ๋™ ์•ˆ์ •์„ฑ์„ ์œ„ํ•ด์„  ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž๋ฅผ ๊ตฌ์„ฑํ•˜๋Š” ์ธต์˜ ์•ˆ์ •์„ฑ์„ ๊ณ ๋ คํ•ด์•ผ ํ•˜๋Š” ๊ฒƒ์€ ์ž๋ช…ํ•˜๋‹ค. ๋ณธ ๋…ผ๋ฌธ์€ 2 ๊ฐ€์ง€ ์—ฐ๊ตฌ์ฃผ์ œ: (1) ๋‹จ์ˆœํ•˜๋ฉด์„œ๋„ ํšจ์œจ์ ์ธ ์กฐ๋ช…์šฉ ๊ทธ๋ฆฌ๊ณ  ๋””์Šคํ”Œ๋ ˆ์ด์šฉ ๊ด‘์ถ”์ถœ ๊ตฌ์กฐ, ๊ทธ๋ฆฌ๊ณ  (2) ์ž๋ฐœ์  ๋ฐฐํ–ฅ ๋ถ„๊ทน ๋ถ„์ž๋ฅผ ํ™œ์šฉํ•œ ์†Œ์ž์˜ ์ˆ˜๋ช… ํ–ฅ์ƒ์— ๋Œ€ํ•œ ๋‚ด์šฉ์„ ๋‹ค๋ฃจ๊ณ  ์žˆ๋‹ค. ์ œ1 ์žฅ์€ ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž์— ๋Œ€ํ•œ ๊ฐ„๋žตํ•œ ์„œ๋ก ์„ ๋‹ด๊ณ  ์žˆ๋‹ค. ์ œ2 ์žฅ์€ ํŒŒ๋ž€์ƒ‰ ํ•˜๋ถ€ ๋ฐœ๊ด‘ํ˜• ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž์˜ ์™ธ๋ถ€ ๊ด‘์ถ”์ถœ ํšจ์œจ ํ–ฅ์ƒ์„ ์œ„ํ•œ ์†์‰ฌ์šฐ๋ฉด์„œ๋„ ํšจ์œจ์ ์ธ ๋žœ๋ค ์œ ๊ธฐ ๋งˆ์ดํฌ๋กœ ๊ตฌ์กฐ (DACM)์— ๋Œ€ํ•œ ๋‚ด์šฉ์„ ๋‹ด๊ณ  ์žˆ๋‹ค. TCTA์™€ B4PyMPM ํ˜ผํ•ฉ ์šฉ์•ก์„ ํ•„๋ฆ„์— ๋“œ๋กญ ์บ์ŠคํŒ… ํ›„ UV ๊ฒฝํ™” ์‹œํ‚ค๋ฉด ๋ฌด์ž‘์œ„ ๋ชจ์–‘์˜ ๋งˆ์ดํฌ๋กœ ๊ตฌ์กฐ๋ฌผ์ด ํ˜•์„ฑ๋˜์—ˆ๊ณ , ํšŒ์ ˆ ๋ฌด๋Šฌ๊ฐ€ ์—†์–ด ๊ด‘์ถ”์ถœ๋กœ ์ ํ•ฉํ–ˆ๋‹ค. DACM ํ•„๋ฆ„์„ ๋ถ€์ฐฉํ•œ ์†Œ์ž๋Š” 44.3%์˜ ์™ธ๋ถ€ ๊ด‘์ž ํšจ์œจ์„ ๊ฐ€์กŒ๊ณ , ๊ด‘์ถ”์ถœ ๊ตฌ์กฐ๊ฐ€ ์—†๋Š” ์†Œ์ž ํ‰ํŒ ์†Œ์ž ๋Œ€๋น„ 35%์˜ ํ–ฅ์ƒ์„ ๋ณด์˜€๋‹ค. ๋˜ํ•œ, ๋งˆ์ดํฌ๋กœ ๋ Œ์ฆˆ ์–ด๋ ˆ์ด ํ•„๋ฆ„์— ํ–ฅ์ƒ๋Ÿ‰์ธ 22% ๋ณด๋‹ค ๋†’์€ ์ˆ˜์น˜๋ฅผ ๊ธฐ๋กํ–ˆ๋‹ค. ์ด ๊ตฌ์กฐ๋Š” ๊ธฐํŒ์— ์ƒ๊ด€์—†์ด ๋Œ€๋ฉด์  ๊ณต์ •์ด ๊ฐ€๋Šฅํ•˜๊ณ , ์ €๋ ดํ•œ ์ œ์ž‘ ๊ณต์ •, ํด๋กœ๋กœํฌ๋ฆ„๊ณผ ๊ฐ™์€ ์•Œํ‚ฌ ํ• ๋ผ์ด๋“œ ์šฉ๋งค์— ๊ฐ•ํ–ˆ์œผ๋ฉฐ, ๊ตฌ์กฐ ์ปจํŠธ๋กค๋„ ๊ฐ€๋Šฅํ•˜๊ธฐ ๋•Œ๋ฌธ์— ์กฐ๋ช…์šฉ์œผ๋กœ ๋งค์šฐ ํšจ์œจ์ ์ด๊ณ , ๋””์Šคํ”Œ๋ ˆ์ด์šฉ์œผ๋กœ ํ™œ์šฉ๋  ์ž ์žฌ๋ ฅ์ด ์žˆ๋‹ค. ์ œ3 ์žฅ์€ ์ง„๊ณต ์—ด์ฆ์ฐฉ์„ ํ†ตํ•ด ์†์ƒ ์—†์ด ํ˜•์„ฑํ•œ ์ƒ๋ถ€ ๋ฐœ๊ด‘ํ˜• ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž์šฉ ๊ด‘์ถ”์ถœ ๊ตฌ์กฐ์— ๋Œ€ํ•œ ๋‚ด์šฉ์„ ๋‹ด๊ณ  ์žˆ๋‹ค. ์ƒ๋ถ€ ๋ฐœ๊ด‘ํ˜• ์†Œ์ž๋Š” ๋†’์€ ํ”ฝ์…€ ์ข…ํšก๋น„, ํ๋ ค์ง ์—†๋Š” ์ด๋ฏธ์ง•, ๋†’์€ ์ƒ‰ ์ˆœ๋„๋กœ ์ธํ•ด ์†Œํ˜• ๋””์Šคํ”Œ๋ ˆ์ด์— ํ™œ์šฉ๋˜๊ณ  ์žˆ๋‹ค. ํ•˜์ง€๋งŒ, ์ด๋Ÿฌํ•œ ์ด์ ์„ ์–ป๋Š” ๊ฐ•๊ณต์ง„ ๊ตฌ์กฐ๋Š” ๊ธˆ์† ์ „๊ทน์— ์˜ํ•œ ๋†’์€ ๊ด‘ํ•™ ์†์‹ค์„ ์•ผ๊ธฐํ•œ๋‹ค. ๊ฒŒ๋‹ค๊ฐ€ ์ƒ๋ถ€ ๋ฐœ๊ด‘ํ˜• ์†Œ์ž์—๋Š” ๋น›์˜ ๊ฒฝ๋กœ์— ๊ธฐํŒ์ด ์—†๋Š” ๊นŒ๋‹ญ์— ์†์ƒ ์—†๋Š” ๊ณต์ •์ด ์–ด๋ ต๋‹ค. ์šฐ๋ฆฌ๋Š” 1,5-diaminoanthraquinone (DAAQ) ์œ ๊ธฐ๋ฌผ์˜ ์ง„๊ณต ์—ด์ฆ์ฐฉ์„ ํ†ตํ•ด ์ƒ๋ถ€ ๋ฐœ๊ด‘ํ˜• ์†Œ์ž์˜ ์€ (Ag) ๋ฐ•๋ง‰ ์œ„์— ์†์ƒ ์—†์ด ๊ด‘์ถ”์ถœ ๊ตฌ์กฐ๋ฅผ ํ˜•์„ฑํ–ˆ๋‹ค. DAAQ๋Š” ์€ ๋ฐ•๋ง‰ ์œ„์—์„œ ์ฆ์ฐฉ ์ฆ‰์‹œ ๊ฒฐ์ •ํ™”๋˜์—ˆ์œผ๋ฉฐ, ๊ธฐํŒ์— ์ˆ˜์ง ๋ฐฉํ–ฅ์œผ๋กœ ๋‚˜๋…ธ์™€์ด์–ด๋ฅผ ํ˜•์„ฑํ–ˆ๋‹ค. ๋‚˜๋…ธ์™€์ด์–ด ์–ด๋ž˜์ด์˜ ๋†’์ด, ๋‘˜๋ ˆ, ๊ทธ๋ฆฌ๊ณ  ์ฃผ๊ธฐ๋Š” ์ฆ์ฐฉ ์†๋„ ๋ฐ ๋‘๊ป˜๋กœ ์กฐ์ ˆ ๊ฐ€๋Šฅํ–ˆ๋‹ค. ์ด๋ฅผ ์ƒ๋ถ€ ๋ฐœ๊ด‘ํ˜• ์†Œ์ž์— ์ ‘๋ชฉ์‹œ์ผฐ๊ณ , ์ข์€ ๋ฐ˜์น˜ํญ์˜ ์†Œ์ž์—์„œ๋Š” 8.6%, ๋„“์€ ๋ฐ˜์น˜ํญ์˜ ์†Œ์ž์—์„œ๋Š” 10.6%์˜ ํ–ฅ์ƒ๋Ÿ‰์„ ์–ป์—ˆ๋‹ค. ์ด ๋ฐฉ๋ฒ•์€ ์‰ฌ์šฐ๋ฉฐ, ์†Œ์ž์— ์†์ƒ์„ ์ฃผ์ง€ ์•Š์•„ ์—ดํ™” ์‹œํ‚ค์ง€ ์•Š์œผ๋ฉฐ, ํŒจํ„ฐ๋‹ ๊ณต์ •์ด ํ•„์š” ์—†๊ณ , ์ง„๊ณต๊ณต์ •์ด ๊ฐ€๋Šฅํ•œ ๊นŒ๋‹ญ์— ๋งค์šฐ ์œ ์šฉํ•˜๋‹ค. ์ œ4 ์žฅ์€ ๋‚ด๋ถ€ ๊ด‘์ถ”์ถœ ๊ตฌ์กฐ์˜ ํŒจํ„ฐ๋‹ ํŠน์„ฑ์˜ ์ค‘์š”์„ฑ์— ๋Œ€ํ•ด ์„œ์ˆ ํ•œ๋‹ค. ๋‚ด๋ถ€ ๊ด‘์ถ”์ถœ ๊ตฌ์กฐ๋ฅผ ๋””์Šคํ”Œ๋ ˆ์ด์— ํ™œ์šฉํ•˜๊ธฐ ์œ„ํ•ด์„  ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ (TFT) ์™€ ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž ์ „๊ทน ์‚ฌ์ด์— ์‹ ํ˜ธ๋ฅผ ์ฃผ๊ณ ๋ฐ›์„ ์ˆ˜ ์žˆ๋Š” ํ†ต๋กœ, ์ฆ‰ ๋น„์•„ํ™€ (viahole) ์ด ํ•„์š”ํ•˜๋‹ค. ๋‚ด๋ถ€ ๊ด‘์ถ”์ถœ ๊ตฌ์กฐ๋Š” ์œ„์น˜๊ฐ€ ๋ฐ•๋ง‰ ํŠธ๋žœ์ง€์Šคํ„ฐ์™€ ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž ์‚ฌ์ด์— ์œ„์น˜ํ•œ ๊นŒ๋‹ญ์—, ๊ตฌ์กฐ ์„ค๊ณ„ ์‹œ viahole ํŒจํ„ฐ๋‹์„ ๊ณ ๋ คํ•ด์•ผ ํ•˜์ง€๋งŒ, ์ง€๊ธˆ๊นŒ์ง€ ์ด๋Ÿฐ ๊ณ ๋ ค๋Š” ์ ์—ˆ๋‹ค. ๋˜ํ•œ, ์ผ๋ฐ˜์ ์ธ ๋‚ด๋ถ€ ๊ด‘์ถ”์ถœ๊ตฌ์กฐ๋Š” ๊ณ  ๊ตด์ ˆ ๋ฌผ์งˆ ๋‚ด์—, ๋‚ฎ์€ ๊ตด์ ˆ๋ฅ ์˜ ๊ด‘ ๊ฒฐ์ •์ด ์œ„์น˜ํ•˜๋Š”๋ฐ, ์ด์ข…์˜ ๋ฌผ์งˆ์€ ์‹๊ฐ ์šฉ์•ก์— ๋Œ€ํ•ด ์„œ๋กœ ๋‹ค๋ฅธ ์—์นญ ์„ ํƒ๋น„ (etching selectivity)๋ฅผ ๊ฐ–๊ธฐ ๋•Œ๋ฌธ์—, ๋‚ด๋ถ€ ๊ด‘์ถ”์ถœ๊ตฌ์กฐ์˜ ์†์ƒ ์—†์ด ํŒจํ„ฐ๋‹์ด ๊ฐ€๋Šฅํ•œ ์‹๊ฐ ์šฉ์•ก์„ ์ฐพ๋Š” ๊ฒƒ ๋˜ํ•œ ํ•„์š”ํ•˜๋‹ค. ์šฐ๋ฆฌ๋Š” SiOx ์Šค์บํ„ฐ์™€ TiO2 ํ‰ํƒ„์ธต์„ ๊ฐ–๋Š” ๋‚ด๋ถ€ ๊ด‘์ถ”์ถœ ๊ตฌ์กฐ์˜ ๋น„์•„ํ™€ ํŒจํ„ฐ๋‹์„ ์„ฑ๊ณต์ ์œผ๋กœ ๊ตฌํ˜„ํ•œ ์†Œ์ž๋ฅผ ๋ณด๊ณ ํ•œ๋‹ค. SiOx์™€ TiO2์— ๋Œ€ํ•ด ์œ ์‚ฌํ•œ ์—์นญ ์„ ํƒ๋น„๋ฅผ ๊ฐ–๋Š” buffered oxide etchant (BOE) ์™€ ์ธ์‚ฐ (H3PO4) ์˜ ํ˜ผํ•ฉ ์‹๊ฐ ์šฉ์•ก์„ ํ™œ์šฉํ•ด ์–ธ๋”์ปท (undercut) ๋ฌธ์ œ๊ฐ€ ํ•ด๊ฒฐ๋œ ๋น„์•„ํ™€ ํŒจํ„ฐ๋‹ ๊ณต์ •์„ ํ™•๋ฆฝํ–ˆ์œผ๋ฉฐ, ์ œ์ž‘๋œ ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž์˜ ๋‚ฎ์€ ๋ˆ„์„ค ์ „๋ฅ˜ ๋ฐ ์†์ƒ ์—†๋Š” ๊ด‘์ถ”์ถœ ํšจ์œจ์„ ํ†ตํ•ด ๋น„์•„ํ™€ ํŒจํ„ฐ๋‹์ด ์„ฑ๊ณต์ ์œผ๋กœ ๋˜์—ˆ์Œ์„ ์‹คํ—˜์ ์œผ๋กœ ๋ณด์˜€๋‹ค. ์ œ5์žฅ์€ ์ „์ž ์ „๋‹ฌ์ธต (Electron transporting layer, ETL) ์˜ ์•ˆ์ •์„ฑ์„ ํ–ฅ์ƒ์‹œํ‚ค๊ธฐ ์œ„ํ•œ ๋ฐฉ๋ฒ•์„ ๋‹ด๊ณ  ์žˆ๋‹ค. ์˜๊ตฌ ์Œ๊ทน์ž ๋ชจ๋ฉ˜ํŠธ (permanent dipole moment)์˜ ์ •๋ ฌ์ด ๋น„์ •์งˆ์˜ Alq3 ์œ ๊ธฐ๋ฌผ์—์„œ๋„ ๋ฐœํ˜„๋จ์„ ๋ฐœ๊ฒฌํ•œ ์ดํ›„, ์—ฌ๋Ÿฌ ์ „์ž์ „๋‹ฌ๋ฌผ์งˆ์—์„œ ์ด๋Ÿฌํ•œ ํŠน์„ฑ (๋ฐฐํ–ฅ ๋ถ„๊ทน, orientation polarization)์ด ๋‚˜ํƒ€๋‚จ์ด ๋ฐํ˜€์กŒ๋‹ค. ์ง€๊ธˆ๊นŒ์ง„ ๋ฐฐํ–ฅ ๋ถ„๊ทน์ด ์†Œ์ž์˜ ์ „๊ธฐ์  ํŠน์„ฑ์— ์–ด๋–ป๊ฒŒ ์˜ํ–ฅ์„ ๋ผ์น˜๋Š”์ง€์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๊ฐ€ ์ฃผ๋ฅ˜๋ฅผ ์ด๋ค˜๋‹ค. ํ•˜์ง€๋งŒ ์šฐ๋ฆฌ๋Š” ๋ฐฐํ–ฅ ๋ถ„๊ทน์ด ์œ ๊ธฐ ๋ฐœ๊ด‘์†Œ์ž์˜ ์ˆ˜๋ช…์— ์–ด๋–ค ์˜ํ–ฅ์„ ์ฃผ๋Š”์ง€ ๋ฐํ˜”๋‹ค. ์†Œ์ž์˜ ์—๋„ˆ์ง€ ์ „๋‹ฌ ๊ณผ์ •์— ์ฐธ์—ฌํ•˜์ง€ ์•Š๋Š” BAlq ๋ถ„์ž๋ฅผ ํ™œ์šฉํ•ด ์ „์ž ์ „๋‹ฌ์ธต๊ณผ ๋ฐœ๊ด‘์ธต (EML) ์‚ฌ์ด์— ์Œ์˜ ํ‘œ๋ฉด ์ „ํ•˜ ๋ฐ€๋„๋ฅผ ๋†’ํ˜”์„ ๋•Œ, ์†Œ์ž์˜ ๊ตฌ๋™ ์ˆ˜๋ช…์ด ์ฆ๊ฐ€ํ•จ์„ ๋ณด์˜€๋‹ค. ๋˜ํ•œ ๋ฌผ์งˆ์˜ ์—ดํ™” ์ •๋„๋ฅผ ํŒŒ์•…ํ•  ์ˆ˜ ์žˆ๋Š” ์ „์•• ๋ณ€ํ™”๊ฐ€ ๋‚ฎ์•„์ง์„ ํ†ตํ•ด BAlq์— ์˜ํ•œ ํ‘œ๋ฉด์ „ํ•˜ ๋ณ€ํ™”๊ฐ€ ์ „์ž์ „๋‹ฌ์ธต์˜ ์•ˆ์ •์„ฑ์„ ์˜ฌ๋ฆผ์„ ์•Œ ์ˆ˜ ์žˆ์—ˆ๋‹ค. ๋˜ํ•œ ๋ถ„๊ทน๋œ ์ธต์ด ๋ฐœ๊ด‘์ธต๊ณผ์˜ ๊ณ„๋ฉด์— ์œ„์น˜ํ•  ๊ฒฝ์šฐ์—์„œ๋งŒ ์ˆ˜๋ช…์ด ์ฆ๊ฐ€ํ•˜๋Š” ๊ฒฐ๊ณผ๋ฅผ ํ†ตํ•ด ์ •๊ณต ์ฐจ๋‹จ์ธต (hole blocking layer, HBL) ์ด ์Œ์˜ ํ‘œ๋ฉด ์ „ํ•˜๋ฅผ ๋ฐœ๊ด‘์ธต๊ณผ์˜ ๊ณ„๋ฉด์— ๊ฐ€์งˆ ๊ฒฝ์šฐ, ํ–ฅ์ƒ๋œ ์ˆ˜๋ช…์„ ์–ป์„ ์ˆ˜ ์žˆ๋‹ค๋Š” ๊ฒฐ๋ก ์„ ์–ป์—ˆ์œผ๋ฉฐ, ์ด๋ฅผ ํ†ตํ•ด ๋ถ„์ž์˜ ๋ฐฐํ–ฅ ๋ถ„๊ทน ํŠน์„ฑ๋„ ์†Œ์ž์˜ ์ˆ˜๋ช…ํ–ฅ์ƒ์„ ์œ„ํ•ด ๊ณ ๋ คํ•ด์•ผ ํ•จ์„ ๋ณด์˜€๋‹ค.Chapter 1. Introduction 2 1.1 Brief history of Organic Light-Emitting Diodes (OLEDs) 2 1.2 Efficiency of OLEDs 10 1.3 Light extraction methods for OLEDs 16 1.4 Finite difference time domain (FDTD) method 24 1.5 Operational stability of OLEDs 26 1.6 Outline of the thesis 28 Chapter 2. Random Organic Nano-textured Microstructures by Photo-Induced Crosslinking for Light Extraction of Blue OLEDs 31 2.1 Introduction 31 2.2 Experimental section 34 2.3 Results and Discussion 36 2.4 Conclusion 57 Chapter 3. Random Nanowire Arrays Spontaneously Formed via Vacuum Deposition for Enhancing Light Extraction from Inverted Top-Emitting Organic Light-Emitting Diodes 59 3.1 Introduction 59 3.2 Experimental section 62 3.3 Results and Discussion 65 3.4 Conclusion 77 Chapter 4. Via Hole Patterning of Light Extraction Layer for Electrical Connection 78 4.1 Introduction 78 4.2 Experimental section 80 4.3 Results and Discussion 83 4.4 Conclusion 92 Chapter 5. Improving Operation Lifetime of OLEDs using Spontaneous Orientation Polarization 93 5.1 Introduction 93 5.2 Experimental section 97 5.3 Results and Discussion 99 5.4 Conclusion 124 Chapter 6. Summary and Conclusion 125 Bibliography 128 ์ดˆ ๋ก 142 CURRICULUM VITAE 147 List of Publications 149 List of Presentations 151Docto

    Perovskite Materials, Devices and Integration

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    Perovskites have attracted great attention in the fields of energy storage, pollutant degradation as well as optoelectronic devices due to their excellent properties. This kind of material can be divided into two categories; inorganic perovskite represented by perovskite oxide and organic-inorganic hybrid perovskite, which have described the recent advancement separately in terms of catalysis and photoelectron applications. This book systematically illustrates the crystal structures, physic-chemical properties, fabrication process, and perovskite-related devices. In a word, perovskite has broad application prospects. However, the current challenges cannot be ignored, such as toxicity and stability

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    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

    Improved Charge Injection and Transport of Light-Emitting Diodes Based on Two-Dimensional Materials

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    Light-emitting diodes (LEDs) are considered to be the most promising energy-saving technology for future lighting and display. Two-dimensional (2D) materials, a class of materials comprised of monolayer or few layers of atoms (or unit cells), have attracted much attention in recent years, due to their unique physical and chemical properties. Here, we summarize the recent advances on the applications of 2D materials for improving the performance of LEDs, including organic light emitting diodes (OLEDs), quantum dot light emitting diodes (QLEDs) and perovskite light emitting diodes (PeLEDs), using organic films, quantum dots and perovskite films as emission layers (EMLs), respectively. Two dimensional materials, including graphene and its derivatives and transition metal dichalcogenides (TMDs), can be employed as interlayers and dopant in composite functional layers for high-efficiency LEDs, suggesting the extensive application in LEDs. The functions of 2D materials used in LEDs include the improved work function, effective electron blocking, suppressed exciton quenching and reduced surface roughness. The potential application of 2D materials in PeLEDs is also presented and analyzed
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