410 research outputs found

    TADF Technology for Efficient Blue OLEDs: Status and Challenges from an Industrial Point of View

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    The rise of OLED technology for display applications over the past decade was impressive. Today, OLED displays can be found everywhere, for example, in smartphones, TVs, smartwatches, monitors, cars, or digital cameras. However, as technology advances, the need for better OLED materials which help to improve energy efficiency and resolution of OLED displays is growing. While for the red and green pixels, phosphorescent materials have allowed for a boost in performance, the use of fluorescent materials for the blue pixel still limits the efficiency of OLED displays. Academic research has demonstrated many improvements regarding the efficiency of blue OLEDs using phosphorescent or TADF materials. However, studies on the limitations of device lifetime are rare. In the present chapter, the development of blue OLEDs based on TADF emitters is discussed from an industrial point of view. First, the material design principles for TADF molecules as well as the requirements for efficient blue TADF emitters are discussed. Moreover, a short literature overview on the latest improvements in blue TADF materials in academia and industry is presented. Finally, an outlook on this technology, its industrial possibilities, and alternatives is given

    Study of TADF Emitters in OLEDs

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    Delayed fluorescence through thermally activated delayed fluorescence (TADF) has great potential for the creation of inexpensive and highly efficient white lighting applications, with superior colour rendering. Currently the highest external quantum efficiencies are achieved with small donor-acceptor-donor molecules utilising intramolecular charge transfer (ICT) states, and these molecules require a suitable host matrix to reside in. This thesis studies the effect of host material on the model molecule 2d, a proven efficient TADF emitter through diligent photophysical investigation. A combination of steady state and nanosecond time resolved spectroscopic studies confirm the importance of a high host triplet level to ensure that the ICT state is the lowest energy excited state to avoid high levels of quenching. More interestingly it is shown that the functional group combination of emitter and host is crucial in achieving efficient TADF in OLED devices. In particular combinations where both the host and dopant are carbazole-based should be avoided due to the formation of carbazole dimer. The effect of such dimerisation is to lower the host triplet level significantly, and further to deactivate the ability of the 2d dopant to produce the ICT state required for TADF by locking the 2d dopant in the โ€˜planarโ€™ configuration. It is therefore clear that the chemical composition of the host is of critical importance for the design of future OLED devices. Experiment also suggests that there is a complex interplay between exciplex and ICT emission in 2d systems in the solid state, insofar as CT emission of any description has so far only been observed in conditions where exciplex can and does occur

    A figure of merit for efficiency roll-off in TADF-based organic LEDs

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    Funding: We are grateful to the Engineering and Physical Sciences Research Council of the UK for financial support through grants EP/R035164/1 and EP/P010482/1.Organic light-emitting diodes (OLEDs) are a revolutionary light-emitting display technology that has been successfully commercialized in mobile phones and TVs1,2. The injected charges form both singlet and triplet excitons, and for high efficiency it is important to enable triplets as well as singlets to emit light. Currently materials that harvest triplets by thermally activated delayed fluorescence (TADF) are a very active field of research as an alternative to phosphorescent emitters which usually employ heavy metal atoms3,4. Whilst excellent progress has been made, there is a severe decrease of efficiency as the drive current is increased, i.e. efficiency roll-off, in most TADF OLEDs. At present much of the literature suggests that efficiency roll-off should be reduced by minimising the energy difference between singlet and triplet excited states (EST) in order to maximise the rate of conversion of triplets to singlets via reverse intersystem crossing (kRISC) 5-20. We analyse the efficiency roll-off in a wide range of TADF OLEDs and find that neither of these parameters fully accounts for the reported efficiency roll-off. By considering the dynamic equilibrium between singlets and triplets in TADF materials, we propose a figure of merit (FOM) for materials design to reduce efficiency roll-off and discuss its correlation with reported data of TADF OLEDs. Our new FOM will guide the design and development of TADF materials that can reduce efficiency roll-off. It will help improve the efficiency of TADF OLEDs at realistic display operating conditions and expand the use of TADF materials to applications that require high brightness, such as lighting, augmented reality, and lasing.Peer reviewe

    White Organic Light-Emitting Diodes with Thermally Activated Delayed Fluorescence Emitters

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    Recently, thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) have attracted both academic and industrial interest due to their extraordinary characteristics, such as high efficiency, low driving voltage, bright luminance, lower power consumption, and potentially long lifetime. In this chapter, various approaches to realize white OLEDs (WOLEDs) with TADF emitters have been introduced. The recent development of WOLEDs based on all TADF emitters, WOLEDs based on TADF and conventional fluorescence emitters, and WOLEDs based on TADF and phosphorescence emitters is highlighted. Particularly, the device structures, design strategies, working mechanisms, and electroluminescent processes of the representative high-performance WOLEDs with TADF emitters are reviewed. Moreover, challenges and opportunities for further enhancement of the performance of WOLEDs with TADF emitters are presented

    New Generation of High Efficient OLED Using Thermally Activated Delayed Fluorescent Materials

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    The search for efficient materials for organic light emitting diodes is one of the most imperative research area. The focus is to obtain a bright large area emitter, limited by the low internal quantum efficiency of conventional organic emitters. Recently, a new generation of the organic materials (TADF) with a theoretical internal quantum efficiency up to 100%, opened new frameworks. However, significant challenges persist to achieve full understanding of the TADF mechanism and to improve the OLEDs stability. Starting from the photo-physical analysis, we show the relationship with the molecular electrical carrier dynamics and internal quantum efficiencies. The OLED structure, fabrication, and characterization are also discussed. Several examples for the full color emitters are given. Special emphasis on experimental results is made, showing the major milestones already achieved in this field

    1,3,4-oxadiazole-based deep-blue thermally activated delayed fluorescence emitters for organic light emitting diodes

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    We are grateful to the EPSRC for financial support (grants EP/P010482/1, EP/J01771X, EP/J00916 and EP/R035164/1). We gratefully acknowledge funding through the EPSRC NSF- CBET lead agency agreement (EP/R010595/1, 1706207) and a Leverhulme Trust Research Grant (RPG-2017-231). We thank the EPSRC UK National Mass Spectrometry Facility at Swansea University for analytical services. Z.L. and W. L. thank the China Scholarship Council (grant numbers 201703780004 and 201708060003)A series of four 1,3,4-oxadiazole-based thermally activated delayed fluorescence (TADF) derivatives are reported as emitters for organic light emitting diodes (OLEDs). As a function of the nature of the substituent on the weak 1,3,4-oxadiazole acceptor their emission color could be tuned from green-blue to blue. The highly twisted conformation between carbazoles and oxadiazoles results in effective separation of the HOMO and the LUMO resulting in a small singlet-triplet splitting. The corresponding singlet-triplet energy gaps (โˆ†EST) range from 0.22 to 0.28 eV resulting in an efficient reverse intersystem crossing (RISC) process and moderate to high photoluminescence quantum yields (ฮฆPL), ranging from 35 to 70% in a DPEPO matrix. Organic light-emitting diodes (OLEDs) based on i-2CzdOXD4CF3Ph achieve maximum external quantum efficiency (EQEmax) of up to 12.3% with a sky-blue emission at CIE of (0.18, 0.28) while the device based on i-2CzdOXDMe shows blue emission at CIE of (0.17, 0.17) with a maximum EQE of 11.8%.PostprintPeer reviewe

    ์‚ผ์ค‘ํ•ญ ์—ฌ๊ธฐ์ž ์ˆ˜ํ™• ์ „๋žต์„ ํ™œ์šฉํ•œ ๊ณ ํšจ์œจ ์ง„์ฒญ์ƒ‰ ์œ ๊ธฐ๋ฐœ๊ด‘์†Œ์ž

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    ํ•™์œ„๋…ผ๋ฌธ (๋ฐ•์‚ฌ) -- ์„œ์šธ๋Œ€ํ•™๊ต ๋Œ€ํ•™์› : ๊ณต๊ณผ๋Œ€ํ•™ ์žฌ๋ฃŒ๊ณตํ•™๋ถ€, 2020. 8. ๊น€์žฅ์ฃผ.OLEDs have been commercialized in mobile display as well as flexible or large-area displays because they have various advantages such as high color gamut and light weight. In addition, OLEDs have been applied to lighting products because they can be fabricated as a surface or flexible light source, and have high color temperature and color rendering index. For several decades, the development of various emitters such as phosphorescence and TADF materials has enabled the production of highly efficient OLEDs and contributed to the commercialization of OLEDs. However, in order for OLED to become more widely available in the future, more development and research must be conducted to increase the efficiency and color purity of blue OLED. In this research, triplet harvesting methods were explored and the efficient deep-blue OLEDs were developed. In chapter 2, the high T1 exciplex host suitable for deep-blue phosphorescent OLEDs (phOLEDs) is introduced. The exciplex hosts for deep-blue OLEDs had not been reported at that time because of the difficulties in identifying suitable molecules. A deep-blue-emitting exciplex system with an exciplex energy of 3.0 eV is developed based on the molecular property analysis. And the exciplex system is applied to the deep-blue phosphorescent OLEDs. The blue PhOLEDs exhibited maximum external quantum efficiency of 24% with CIE color coordinates of (0.15, 0.21) and longer lifetime than the single host devices. In chapter3, thermally activated delayed fluorescent (TADF) emitters with narrow blue emission spectrum are introduced. Both emitters exhibit narrow emission spectra with the full width half maximum (FWHM) less than 65 nm due to the rigid donor and acceptor unit. Furthermore, long molecular structure along the transition dipole moment direction results in a high horizontal emitting dipole orientation ratio over 80%. By combining the effects, the OLED utilizing DBA-SAB as the emitter exhibits maximum EQE of 25.7% and CIE coordinates of (0.144, 0.212). Moreover, even a higher efficiency deep blue TADF OLED with a maximum EQE of 28.2% and 1931 Commission Internationale de l'รฉclairage (CIE) coordinates of (0.142, 0.090) is realized. In chapter 4, triplet-triplet annihilation process is studied and blue OLEDs with thin efficiency-enhancement layer (EEL) is developed. Insertion of a very thin EEL (3 nm) between the deep blue emitting layer (EML) and the electron transport layer enhanced the EQE of the blue device by 44% compared to the device without the EEL, resulting in an EQE of 7.9% and a current efficiency of 9.0 cd Aโˆ’1 at 1000 cd mโˆ’2; the CIE coordinates of the emitting color were (0.13, 0.14). The transient electroluminescence showed that the efficiency enhancement originates from the tripletโˆ’triplet annihilation (TTA) process in the EEL, followed by energy transfer to the emitting dye in the EML.์œ ๊ธฐ๋ฐœ๊ด‘๋‹ค์ด์˜ค๋“œ(์ดํ•˜ OLED)๋Š” ๋””์Šคํ”Œ๋ ˆ์ด์— ์‚ฌ์šฉ๋˜๋Š” ๊ฒฝ์šฐ ์ž์ฒด ๋ฐœ๊ด‘ ํŠน์„ฑ์œผ๋กœ ์ธํ•ด ๋น›์„ ๋ฐํ˜€์ฃผ๋Š” ๊ด‘์›(๋ฐฑ๋ผ์ดํŠธ)๊ฐ€ ๋ถˆํ•„์š”ํ•˜๋‹ค. ๋”ฐ๋ผ์„œ ๊ธฐ์กด ์•ก์ • ๋””์Šคํ”Œ๋ ˆ์ด์— ๋น„ํ•ด ์–‡๊ณ  ๊ฐ€๋ฒผ์šด ๋””์Šคํ”Œ๋ ˆ์ด ์ œ์ž‘์ด ๊ฐ€๋Šฅํ•˜๋ฉฐ ๋ช…์•”๋น„๊ฐ€ ์šฐ์ˆ˜ํ•˜๋‹ค. ๋˜ํ•œ ๊ธฐํŒ ์„ ํƒ์— ์ œํ•œ์ด ์ ์–ด ์œ ์—ฐ, ํˆฌ๋ช… ๊ธฐํŒ์— ์ ์šฉ๋  ์ˆ˜ ์žˆ๋‹ค๋Š” ์žฅ์ ์ด ์žˆ๋‹ค. ์ด๋Ÿฌํ•œ ์žฅ์ ๋“ค์„ ๊ฐ€์ง„ ์œ ๊ธฐ๋ฐœ๊ด‘๋‹ค์ด์˜ค๋“œ๋Š” ์†Œํ˜• ๋ชจ๋ฐ”์ผ ๊ธฐ๊ธฐ์˜ ๋””์Šคํ”Œ๋ ˆ์ด์— ์ ์šฉ๋˜๊ธฐ ์‹œ์ž‘ํ•œ ์ด๋ž˜ ๋””์Šคํ”Œ๋ ˆ์ด ๋ฐ ์กฐ๋ช… ๋ถ„์•ผ์—์„œ ํ™œ์šฉ๋˜๋ฉฐ ์ ์šฉ ๋ฒ”์œ„๋ฅผ ๋„“ํ˜€๊ฐ€๊ณ  ์žˆ๋‹ค. ๊ณ ํšจ์œจ๊ณผ ๊ธด ์ˆ˜๋ช…์„ ๋ณด์ด๋Š” ์ ์ƒ‰, ๋…น์ƒ‰ OLED๊ฐ€ ๊ฐœ๋ฐœ๋˜์—ˆ์œผ๋‚˜ ์•„์ง๊นŒ์ง€ ์ฒญ์ƒ‰ OLED์˜ ์„ฑ๋Šฅ์€ ๊ทธ์— ๋ฏธ์น˜์ง€ ๋ชปํ•œ๋‹ค. ๋”ฐ๋ผ์„œ ๊ณ ํ’ˆ์งˆ ๋””์Šคํ”Œ๋ ˆ์ด๋ฅผ ์œ„ํ•ด์„œ๋Š” ์ฒญ์ƒ‰ ์†Œ์ž์˜ ๊ฐœ์„ ์ด ํ•„์š”ํ•˜๋‹ค๊ณ  ํ•  ์ˆ˜ ์žˆ๋‹ค. ์ผ๋ฐ˜ ํ˜•๊ด‘ ๋ฐœ๊ด‘์ฒด๋Š” ์ „๊ธฐ์ ์œผ๋กœ ์ƒ์„ฑ๋˜๋Š” ์—ฌ๊ธฐ์ž ์ค‘ 25%์— ๋ถˆ๊ณผํ•œ ์ผ์ค‘ํ•œ ๋งŒ์„ ๋ฐœ๊ด‘ ์—ฌ๊ธฐ์ž๋กœ ์‚ฌ์šฉํ•˜๊ธฐ ๋•Œ๋ฌธ์— ๋‚ฎ์€ ํšจ์œจ์„ ๋ณด์ธ๋‹ค. ํšจ์œจ์„ ๋†’์ด๊ธฐ ์œ„ํ•ด์„œ๋Š”75%๋ฅผ ์ฐจ์ง€ํ•˜๋Š” ์‚ผ์ค‘ํ•ญ์„ ํšจ์œจ์ ์œผ๋กœ ํ™œ์šฉํ•˜๋Š” ๊ฒƒ์ด ์ค‘์š”ํ•˜๋‹ค. ์ง„์ฒญ์ƒ‰ ๋ฐœ๊ด‘์„ ์œ„ํ•ด์„œ๋Š” ์ข์€ ๋ฐœ๊ด‘ ์ŠคํŽ™ํŠธ๋Ÿผ๊ณผ ๋†’์€ ๋ฐœ๊ด‘ ์—๋„ˆ์ง€๋ฅผ ๊ฐ–๋Š” ๋ฐœ๊ด‘์ฒด๋ฅผ ์‚ฌ์šฉํ•ด์•ผ ํ•œ๋‹ค. ๋ณธ ๋…ผ๋ฌธ์—์„œ๋Š” ํšจ์œจ์ ์ธ ์ง„์ฒญ์ƒ‰ ๋ฐœ๊ด‘์ฒด์™€ ์‚ผ์ค‘ํ•ญ ์ˆ˜ํ™• ์ „๋žต์„ ํ™œ์šฉํ•œ ์ง„์ฒญ์ƒ‰, ๊ณ ํšจ์œจ OLED ๊ฐœ๋ฐœ์— ๋Œ€ํ•œ ์ฃผ์ œ๋ฅผ ๋‹ค๋ฃจ๊ณ  ์žˆ๋‹ค. ์ œ 2 ์žฅ์—์„œ๋Š” ์ฒญ์ƒ‰ ๋ฐœ๊ด‘์— ์ ํ•ฉํ•œ ์—‘์‹œํ”Œ๋ ‰์Šค (exciplex) ํ˜ธ์ŠคํŠธ ๊ฐœ๋ฐœ์— ๋Œ€ํ•œ ๋‚ด์šฉ์„ ๋‹ค๋ฃฌ๋‹ค. ์ƒˆ๋กญ๊ฒŒ ๊ฐœ๋ฐœ๋œ ์—‘์‹œํ”Œ๋ ‰์Šค ํ˜ธ์ŠคํŠธ๋ฅผ์™€ ์ผ์ค‘ํ•ญ๊ณผ ์‚ผ์ค‘ํ•ญ ๋ชจ๋‘ ๋ฐœ๊ด‘์— ์ฐธ์—ฌ ๊ฐ€๋Šฅํ•œ ์ธ๊ด‘ ๋ฐœ๊ด‘์ฒด๋ฅผ ์ด์šฉํ•ด ๊ณ ํšจ์œจ ์ฒญ์ƒ‰ ์ธ๊ด‘ ์†Œ์ž๋ฅผ ์ œ์ž‘ํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค. ์—‘์‹œํ”Œ๋ ‰์Šค ํ˜ธ์ŠคํŠธ๋ฅผ ์‚ฌ์šฉํ•˜๋Š” OLED๋Š” ๋ฐœ๊ด‘์ธต์œผ๋กœ์˜ ์ „ํ•˜ ์ฃผ์ž…์ด ์šฉ์ดํ•˜๋ฉฐ, ๋ฐœ๊ด‘์ธต์˜ ์ „ํ•˜ ๋ฐ€๋„๊ฐ€ ์ƒ๋Œ€์ ์œผ๋กœ ๋‚ฎ์•„ ์†Œ์ž์˜ ์„ฑ๋Šฅ์ด ๋‹จ์ผ ํ˜ธ์ŠคํŠธ์— ๋น„ํ•ด ์šฐ์ˆ˜ํ•˜๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ์ฒญ์ƒ‰ OLED์˜ ๊ฒฝ์šฐ ์ฒญ์ƒ‰ ๋ฐœ๊ด‘์ฒด์˜ ๋„“์€ ๋ฐด๋“œ๊ฐญ๊ณผ ๋†’์€ ์‚ผ์ค‘ํ•ญ ์—๋„ˆ์ง€ (T1)๋กœ ์ธํ•ด ์—‘์‹œํ”Œ๋ ‰์Šค ํ˜ธ์ŠคํŠธ๋ฅผ ์ฒญ์ƒ‰ ์†Œ์ž์— ์ ์šฉํ•˜๊ธฐ๊ฐ€ ์‰ฝ์ง€ ์•Š๋‹ค๊ณ  ์—ฌ๊ฒจ์ ธ ์™”๋‹ค. ์ด๋Ÿฌํ•œ ํ•œ๊ณ„๋ฅผ ํ•ด๊ฒฐํ•˜๊ณ ์ž ์นด๋ฐ”์กธ ๊ธฐ๋ฐ˜์˜ ์ •๊ณต์ „๋‹ฌ๋ฌผ์งˆ๊ณผ ํฌ์Šคํ•€ ์˜ฅ์‚ฌ์ด๋“œ ๊ธฐ๋ฐ˜์˜ ์ „์ž์ „๋‹ฌ ๋ฌผ์งˆ์„ ์‚ฌ์šฉํ•ด ๋†’์€ ๋ฐœ๊ด‘ ์—๋„ˆ์ง€๋ฅผ ๊ฐ–๋Š” ์—‘์‹œํ”Œ๋ ‰์Šค ์‹œ์Šคํ…œ์„ ๊ฐœ๋ฐœํ•˜์˜€์œผ๋ฉฐ ์ด๋ฅผ ์ ์šฉํ•œ ์†Œ์ž๋ฅผ ์ œ์ž‘ํ•˜์˜€๋‹ค. ์†Œ์ž๋Š” ๋†’์€ EQE์™€ ์šฐ์ˆ˜ํ•œ ์ƒ‰ ์ขŒํ‘œ๋ฅผ ๋‚˜ํƒ€๋‚ด์—ˆ์œผ๋ฉฐ ์—‘์‹œํ”Œ๋ ‰์Šค ํ˜ธ์ŠคํŠธ๊ฐ€ ์ฒญ์ƒ‰์— ์ ์šฉ๋  ์ˆ˜ ์žˆ๋‹ค๋Š” ๊ฒƒ์„ ์ฆ๋ช…ํ•˜์˜€๋‹ค. 3์žฅ์—์„œ๋Š” ์—ด ํ™œ์„ฑ ์ง€์—ฐ ํ˜•๊ด‘ ํŠน์„ฑ์„ ๋ณด์ด๋Š” ๋ฐœ๊ด‘์ฒด์˜ ํŠน์„ฑ์„ ๋ถ„์„ํ•˜์˜€๋‹ค. ์—ด ํ™œ์„ฑ ์ง€์—ฐ ํ˜•๊ด‘ ๋ฌผ์งˆ์€ ์ „์ž ์ฃผ๊ฒŒ ๋ฐ ๋ฐ›๊ฒŒ๊ฐ€ ์„œ๋กœ ์—ฐ๊ฒฐ๋˜์–ด ์žˆ์œผ๋ฉฐ ๋‘˜ ๊ฐ„์˜ ์ „์ž ๊ตํ™˜์œผ๋กœ ๋ฐœ๊ด‘์ด ๋ฐœ์ƒํ•œ๋‹ค. ์ผ๋ฐ˜์ ์œผ๋กœ ๋„“์€ ๋ฐ˜์น˜ํญ์œผ๋กœ ์ธํ•ด ์ฒญ์ƒ‰ ๋ฐœ๊ด‘์ด ์‰ฝ์ง€ ์•Š์„ ๊ฒƒ์œผ๋กœ ์—ฌ๊ฒจ์กŒ์œผ๋‚˜ ์ฒญ์ƒ‰ ๋ฐœ๊ด‘์— ์ ํ•ฉํ•œ ์—๋„ˆ์ง€ ๋ ˆ๋ฒจ์„ ๊ฐ€์ง€๋ฉฐ ๋‹จ๋‹จํ•œ ๊ตฌ์กฐ๋ฅผ ๊ฐ–๋Š” ์ „์ž ์ฃผ๊ฒŒ์™€ ๋ฐ›๊ฒŒ๋ฅผ ์ด์šฉํ•ด ๋†’์€ ๋ฐœ๊ด‘ ์—๋„ˆ์ง€์™€ ์ข์€ ๋ฐ˜์น˜ํญ์„ ๊ฐ–๋Š” ์ฒญ์ƒ‰ ํ˜•๊ด‘ ๋ฐœ๊ด‘์ฒด๋“ค์„ ๊ฐœ๋ฐœํ•˜์˜€๋‹ค. DFT ๊ณ„์‚ฐ์„ ์ด์šฉํ•ด ๋ถ„์ž์˜ ํŠน์„ฑ์„ ์˜ˆ์ธกํ•˜๊ณ  ์‹คํ—˜์„ ํ†ตํ•ด ํŠน์„ฑ์ด ์ž˜ ์˜ˆ์ธก๋˜์—ˆ์Œ์„ ํ™•์ธํ•˜์˜€๋‹ค. ๊ธด ๋ถ„์ž๊ตฌ์กฐ๋กœ 80% ์ด์ƒ์˜ ๋†’์€ ์ˆ˜ํ‰ ๋ฐฐํ–ฅ ์Œ๊ทน์ž ๋ฐฐํ–ฅ ๋น„์œจ์„ ๋‚˜ํƒ€๋‚ด์—ˆ์œผ๋ฉฐ ๋ฐœ๊ด‘์ฒด๋“ค์„ ์ด์šฉํ•ด ์†Œ์ž๋ฅผ ์ œ์ž‘ํ•œ ๊ฒฐ๊ณผ 28.2% EQE, CIE ์ƒ‰์ขŒํ‘œ (0.142, 0.090)์„ ๋ณด์ด๋Š” ์†Œ์ž๋ฅผ ๊ตฌํ˜„ํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค. ์ œ 4์žฅ์—์„œ๋Š” ์‚ผ์ค‘ํ•ญ-์‚ผ์ค‘ํ•ญ ์†Œ๋ฉธ (์ดํ•˜ TTA) ๊ณผ์ •์„ ํ†ตํ•ด ์‚ผ์ค‘ํ•ญ ์ˆ˜ํ™•์„ ํ•˜๋Š” ์†Œ์ž์˜ ํŠน์„ฑ์„ ๋ถ„์„ํ•˜์˜€๋‹ค. TTA ๋ฌผ์งˆ์˜ ๋†’์€ ์•ˆ์ •์„ฑ์œผ๋กœ ์ธํ•ด ์•„์ง๊นŒ์ง€ ์ƒ์šฉํ™”๋œ ๋””์Šคํ”Œ๋ ˆ์ด์˜ ์ฒญ์ƒ‰ ์†Œ์ž์—๋Š” TTA ๋ฌผ์งˆ์ด ์‚ฌ์šฉ๋˜๊ณ  ์žˆ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ TTA๋ฅผ ์ด์šฉํ•œ ์†Œ์ž์˜ ๊ฒฝ์šฐ ๊ธฐ์กด ํ˜•๊ด‘์— ๋น„ํ•ด ๋ฐœ๊ด‘์— ์ฐธ์—ฌํ•˜๋Š” ์—ฌ๊ธฐ์ž ๋น„์œจ์ด ์ฆ๊ฐ€ํ•˜๊ธด ํ•˜์ง€๋งŒ ์•ž์„œ 2, 3์žฅ์—์„œ ๋‹ค๋ฃจ์—ˆ๋˜ 100% ์—ฌ๊ธฐ์ž ํ™œ์šฉ์ด ๊ฐ€๋Šฅํ•œ ์ธ๊ด‘ ๋ฐ TADF์— ๋น„ํ•ด 30% ์ˆ˜์ค€์˜ ๋‚ฎ์€ ๋ฐœ๊ด‘ ์—ฌ๊ธฐ์ž ๋น„์œจ์„ ๋ณด์ธ๋‹ค. 4์žฅ์—์„œ๋Š” TTA๊ณผ์ •์˜ ๋ฉ”์ปค๋‹ˆ์ฆ˜ ๋ถ„์„์„ ํ†ตํ•ด TTA ํšจ์œจ์˜ ํ•œ๊ณ„๋ฅผ ๋ถ„์„ํ•˜๊ณ ์ž ํ•˜์˜€์œผ๋ฉฐ ๋ถ„์„์„ ๋ฐ”ํƒ•์œผ๋กœ TTA ํšจ์œจ์„ ๋†’์ผ ์ˆ˜ ์žˆ๋Š” ์†Œ์ž ๊ตฌ์กฐ๋ฅผ ์ œ์•ˆํ•˜์˜€๋‹ค.Chapter 1. Introduction 1 1.1 Brief introduction to Organic Light-Emitting Diodes 1 1.2 Parameters that governs the efficiency of OLEDs 4 1.3 Strategies for harvesting triplet excitons 8 1.4 Challenges for realizing high-efficiency deep blue OLEDs 14 1.5 Outline of the thesis 15 Chapter 2. An Exciplex Host for Deep-Blue Phosphorescent Organic Light-Emitting Diodes 17 2.1 Introduction 17 2.2 Experimental 19 2.3 Result and discussion 21 2.4 Conclusion 35 Chapter 3. Highly efficient deep blue OLEDs using TADF emitter with narrow emission spectrum and high horizontal emitting dipole orientation 36 3.1 Introduction 36 3.2 Experimental 39 3.3 Result and discussion 41 3.4 Conclusion 58 Chapter 4. Enhanced Tripletโˆ’Triplet annihilation of Blue Fluorescent Organic Light-Emitting diodes by Generating Excitons in Trapped Charge-Free Regions 59 4.1 Introduction 59 4.2 Experimental 62 4.3 Result and discussion 64 4.4 Conclusion 95 Chapter 5. Summary and Conclusion 96 Bibliography 99 ์ดˆ ๋ก 114 CURRICULUM VITAE 118 List of Publications 120 List of Presentations 121Docto

    A review of fused-ring carbazole derivatives as emitter and/or host materials in organic light emitting diode (OLED) applications

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    This review focuses on fused-ring carbazole derivatives, their molecular design, electronic and photophysical properties, and in particular their applications as the emitter and/or the host material in the emitting layer of organic light emitting diodes (OLEDs), with emphasis on recent developments. This review is timely because of the rapidly expanding research into fused-ring carbazoles, predominantly indolocarbazole, indenocarbazole, benzofurocarbazole, benzothienocarbazole and diindolocarbazole derivatives. To our knowledge this class of materials has not been reviewed previously. The appeal of fused-ring carbazoles is their extended ฯ€-electron systems with good thermal stability, tunable frontier orbital energies that enable a wide gamut (red, green, blue and white) emission colour, high photoluminescence quantum yields, and versatility for chemical functionalisation at different sites, leading to outstanding OLED efficiencies. This review is divided into sections according to the moleculesโ€™ role in OLEDs: namely, as conventional luminescent emitters โ€“ especially in the deep-blue region; as state-of-the-art hosts for phosphorescent iridium-based emitters; as thermally activated delayed fluorescence (TADF) emitters with high external quantum efficiency; and as multiresonance (MR) emitters with unprecedented high colour purity. We conclude by highlighting the challenges and the great opportunities for fused-ring carbazole derivatives in OLEDs and other optoelectronic applications

    Tetradentate Cyclometalated Platinum(II) Complexes for Efficient and Stable Organic Light-Emitting Diodes

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    As one of the most important phosphorescent emitters, tetradentate cyclometalated platinum(II) complexes have attracted much attention in recent years, because of the high luminescent efficiency, emission spectra, and color tuned easily, especially for the development of high-efficient deep-blue and โ€œpureโ€ blue emitters and single-doped white organic light-emitting diodes (OLEDs). Also, some platinum(II)-based OLEDs exhibited superior operational stability, indicating their potentials in full-color display and solid-state lighting applications. In this chapter, we will introduce the recent advances of the tetradentate cyclometalated platinum(II) complexes, including pyrazole, N-heterocyclic carbene, imidazole and pyridine-based complexes, molecular design, photophysical properties, and some of their device performances
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