Joo+Kim
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Lens-free OLEDs with Efficiency comparable to that of Inorganic LEDs
(from left: Professor Seunghyup Yoo and PhD candidate Jinouk Song)
The use of organic light-emitting diodes (OLEDs) has extended to various applications, but their efficiency is still lagging behind inorganic light-emitting diodes. In this research, a KAIST team provided a systematic way to yield OLEDs with an external quantum efficiency (EQE) greater than 50% with an external scattering medium.
Having properties suitable for thin and flexible devices, OLEDs are popular light sources for displays, such as mobile devices and high quality TVs. In recent years, numerous efforts have been made to apply OLEDs in lighting as well as light sources for vehicles.
For such applications, high efficiency is of the upmost importance for the successful deployment of light sources. Thanks to continuous research and the development of OLEDs, their efficiency is steadily on the rise, and a level equivalent to inorganic LEDs has been demonstrated in some reports.
However, these highly efficient OLEDs were often achieved with a macroscopic lens or complex internal nanostructures, which undermines the key advantages of OLEDs as an affordable planar light sources and tends to hinder their stable operation, thus putting a limitation to their commercialization.
Among various methods proven effective for OLED light extraction, a team led by Professor Seunghyup Yoo at the School of Electrical Engineering focused on the external scattering-based approach, as it can maintain planar geometry and compatibility with flexibility. It is also able to be fabricated on a large scale at a low cost and causes no interference with electrical properties of OLEDs.
Conventionally, research on enhancing OLED light extraction using light scattering has been conducted empirically in many cases. This time, the team developed comprehensive and analytical methodology to theoretically predict structures that maximize efficiency.
Considering OLEDs with the external scattering layers as a whole rather than two separate entities, the researchers combined the mathematical description of the scattering phenomena with the optical model for light emission within an OLED to rapidly predict the characteristics of many devices with various structures. Based on this approach, the team theoretically predicted the optimal combination of scattering layers and OLED architectures that can lead to the maximum efficiency.
Following this theoretical prediction, the team experimentally produced the optimal light scattering film and incorporated it to OLEDs with orange emitters having a high degree of horizontal dipole orientation. As a result, the team successfully realized OLEDs exhibiting EQE of 56% and power efficiency of 221 lm/W. This is one of the highest efficiencies ever realized for an OLED unit device without the help of a macroscopic lens or internal light extraction structures.
Professor Yoo said, “There are various technologies developed for improving OLED light extraction efficiency; nevertheless, most of them have not reached a level of practical use. This research mainly provides a systematic way to attain an EQE of 50% or higher in OLEDs while keeping in mind the constraints for commercialization. The approach shown here can readily be applied to lighting devices or sensors of wearable devices.”.
This research, co-led by Professor Jang-Joo Kim from Seoul National University and Professor Yun-Hi Kim from Gyeongsang National University, was published in Nature Communications on August 10, 2018. (J. Song et al. Nature Communications, 9, 3207. DOI: 10.1038/s41467-018-05671-x)
Figure 1.Photographs of OLEDs with SiO₂ -embedded scattering layers according to scatterance
2018.10.26 View 7583 -
KAIST to Host FinTech Conference 2018
KAIST will be hosting a FinTech Conference with Princeton University (USA), Tsinghua University (China), and EDHEC Business School (France) in Seoul from April 12 to 13 titled State of the Art in Robo-Advising Systems: Financial Technologies for Enhanced Social Security.
The Bendhein Center for Finance and Department of Operations Research and Financial Engineering from Princeton University, Fintech Lab from Tsinghua University, and the Risk Institute from EDHEC will participate as co-hosting organizations in this conference organized by the Department of Industrial & Systems Engineering and the KAIST Center for Wealth Management Technologies.
The conference will discuss issues required for providing customized asset management to the public in terms of theory, technology, and industry.
During the conference, KAIST President Sung-Chul Shin and Chairman and CEO of the National Pension Service Sung Joo Kim will deliver welcoming addresses.
Professor John Mulvey from Princeton University, Professor Michael Dempster from Cambridge University, Professors Wei Xu and Changle Lin from Tsinghua University, Professor Lionel Martellini from EDHEC, and Professor Woo Chang Kim from KAIST are some of the invited speakers at the event.
Moreover, renowned experts in related fields will also participate in the conference, including Founder of Vanguard Group John Bogle, Jin Lee from Ant Financial, Youngsuh Cho from Shinhan Financial Group, Jung-Hwan Lee from Samsung Asset Management, and Hye Young Sung from the National Pension Service Research Institute.
Professor Kim said, “Only a small number of wealthy people can receive life-cycle customized asset management services due to the high cost structure; however, new technology derived from the Fourth Industrial Revolution can reduce the service price in an innovative manner, ultimately leading it to be popularized.”
“In an era with the poverty rate of older people reaching almost 50%.Fintech can enable individuals to manage their assets in an active manner, reinforcing social security without additional social costs in the period,” he added.
These four universities have been hosting the FinTech Conference since 2017. China will host the conference this fall, followed by France next year.
Samsung Asset Management, Alibaba Group, and Ant Financial will sponsor the conference. Anyone interested in this event can find more details at http://wmt.kaist.ac.kr/conference.html.
2018.04.02 View 6821 -
A Glance at the 2017 KAIST Literary Awards Ceremony
Since KAIST is a university specializing in science and engineering, people may think that the students rarely engage in literary activities. But KAIST students also excel in writing literature.
The 23rd KAIST Literary Award Ceremony was held on December 14 on the KAIST main campus. The award was established in 1995 to encourage students’ creative activities and to promote literary attainment. It is open to all KAIST students from undergraduate to masters and PhD students. This year, 43 students submitted a total of 68 literary works in the genres of poetry, novel, critique, and scenario.
KAIST professors Dong Ju Kim, Bong Gwan Jun, and Yunjeong Jo from the School of Humanities & Social Sciences participated as judges for the awards and they were joined by writers from the 8th Endless Road Program who served as invited judges for the novels and scenarios.
The Endless Road Program is a KAIST project for supporting artists who are engaged in literary works including scenarios, novels, webtoons, and movies by providing residences and funds. Novelists Jin Young Choi and Hak Chan Kim participated as judges for the novels and a drama scriptwriter, Joo Kim, as a judge of the scenarios.
After thorough evaluation, four submissions were chosen as awardees.
Section
Award
Name
Poetry
Winner
Sung Gil Moon (PhD candidate from the College of Business)
Runner-up
Jong Ik Jeon (Undergraduate student)
Novel
Winner
Joo Hwan Kim
(Undergraduate from the Dept. of Chemical and Biomolecular Engineering)
Runner-up
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Essay & Critique
Winner
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Runner-up
Jung Joon Park
(PhD candidate from the Dept. of Bio and Brain Engineering)
Scenario
Winner
-
Runner-up
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The literary works as well as a review of the awards will be published in the KAIST Times in 2018.
2017.12.15 View 6820