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Graphene-Based Transparent Electrodes for Highly Efficient Flexible OLEDs
A Korean research team developed an ideal electrode structure composed of graphene and layers of titanium dioxide and conducting polymers, resulting in highly flexible and efficient OLEDs.
The arrival of a thin and lightweight computer that even rolls up like a piece of paper will not be in the far distant future. Flexible organic light-emitting diodes (OLEDs), built upon a plastic substrate, have received greater attention lately for their use in next-generation displays that can be bent or rolled while still operating.
A Korean research team led by Professor Seunghyup Yoo from the School of Electrical Engineering, KAIST and Professor Tae-Woo Lee from the Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH) has developed highly flexible OLEDs with excellent efficiency by using graphene as a transparent electrode (TE) which is placed in between titanium dioxide (TiO2) and conducting polymer layers. The research results were published online on June 2, 2016 in Nature Communications.
OLEDs are stacked in several ultra-thin layers on glass, foil, or plastic substrates, in which multi-layers of organic compounds are sandwiched between two electrodes (cathode and anode). When voltage is applied across the electrodes, electrons from the cathode and holes (positive charges) from the anode draw toward each other and meet in the emissive layer. OLEDs emit light as an electron recombines with a positive hole, releasing energy in the form of a photon. One of the electrodes in OLEDs is usually transparent, and depending on which electrode is transparent, OLEDs can either emit from the top or bottom.
In conventional bottom-emission OLEDs, an anode is transparent in order for the emitted photons to exit the device through its substrate. Indium-tin-oxide (ITO) is commonly used as a transparent anode because of its high transparency, low sheet resistance, and well-established manufacturing process. However, ITO can potentially be expensive, and moreover, is brittle, being susceptible to bending-induced formation of cracks.
Graphene, a two-dimensional thin layer of carbon atoms tightly bonded together in a hexagonal honeycomb lattice, has recently emerged as an alternative to ITO. With outstanding electrical, physical, and chemical properties, its atomic thinness leading to a high degree of flexibility and transparency makes it an ideal candidate for TEs. Nonetheless, the efficiency of graphene-based OLEDs reported to date has been, at best, about the same level of ITO-based OLEDs.
As a solution, the Korean research team, which further includes Professors Sung-Yool Choi (Electrical Engineering) and Taek-Soo Kim (Mechanical Engineering) of KAIST and their students, proposed a new device architecture that can maximize the efficiency of graphene-based OLEDs. They fabricated a transparent anode in a composite structure in which a TiO2 layer with a high refractive index (high-n) and a hole-injection layer (HIL) of conducting polymers with a low refractive index (low-n) sandwich graphene electrodes. This is an optical design that induces a synergistic collaboration between the high-n and low-n layers to increase the effective reflectance of TEs. As a result, the enhancement of the optical cavity resonance is maximized. The optical cavity resonance is related to the improvement of efficiency and color gamut in OLEDs. At the same time, the loss from surface plasmon polariton (SPP), a major cause for weak photon emissions in OLEDs, is also reduced due to the presence of the low-n conducting polymers.
Under this approach, graphene-based OLEDs exhibit 40.8% of ultrahigh external quantum efficiency (EQE) and 160.3 lm/W of power efficiency, which is unprecedented in those using graphene as a TE. Furthermore, these devices remain intact and operate well even after 1,000 bending cycles at a radius of curvature as small as 2.3 mm. This is a remarkable result for OLEDs containing oxide layers such as TiO2 because oxides are typically brittle and prone to bending-induced fractures even at a relatively low strain. The research team discovered that TiO2 has a crack-deflection toughening mechanism that tends to prevent bending-induced cracks from being formed easily.
Professor Yoo said, “What’s unique and advanced about this technology, compared with previous graphene-based OLEDs, is the synergistic collaboration of high- and low-index layers that enables optical management of both resonance effect and SPP loss, leading to significant enhancement in efficiency, all with little compromise in flexibility.” He added, “Our work was the achievement of collaborative research, transcending the boundaries of different fields, through which we have often found meaningful breakthroughs.”
Professor Lee said, “We expect that our technology will pave the way to develop an OLED light source for highly flexible and wearable displays, or flexible sensors that can be attached to the human body for health monitoring, for instance.”
The research paper is entitled “Synergistic Electrode Architecture for Efficient Graphene-based Flexible Organic Light-emitting Diodes” (DOI. 10.1038/NCOMMS11791). The lead authors are Jae-Ho Lee, a Ph.D. candidate at KAIST; Tae-Hee Han, a Ph.D. researcher at POSTECH; and Min-Ho Park, a Ph.D. candidate at POSTECH.
This study was supported by the Basic Science Research Program of the National Research Foundation of Korea (NRF) through the Center for Advanced Flexible Display (CAFDC) funded by the Ministry of Science, ICT and Future Planning (MSIP); by the Center for Advanced Soft-Electronics funded by the MSIP as a Global Frontier Project; by the Graphene Research Center Program of KAIST; and by grants from the IT R&D Program of the Ministry of Trade, Industry and Energy of Korea (MOTIE).
Figure 1: Application of Graphene-based OLEDs
This picture shows an OLED with the composite structure of TiO2/graphene/conducting polymer electrode in operation. The OLED exhibits 40.8% of ultrahigh external quantum efficiency (EQE) and 160.3 lm/W of power efficiency. The device prepared on a plastic substrate shown in the right remains intact and operates well even after 1,000 bending cycles at a radius of curvature as small as 2.3 mm.
Figure 2: Schematic Device Structure of Graphene-based OLEDs
This picture shows the new architecture to develop highly flexible OLEDs with excellent efficiency by using graphene as a transparent electrode (TE).
2016.06.07 View 14160 -
Special Lecture by Professor Sung-Hou Kim of UC Berkeley
As part of its special lecture series, the Department of Biological Sciences at KAIST has invited Professor Sung-Hou Kim of the Department of Chemistry at the University of California, Berkeley, to lecture on his research in structural biology. He will speak twice on May 23 and 30, respectively, on the topics “Origin of Universe and Earth—A Narrative” and “Origin of Life and Human Species—A Narrative.”
Professor Kim's research addresses the structural basis of molecules to reveal how they communicate with each other to activate or inhibit particular processes in cell growth, cell differentiation, and cancer. Using the single-crystal X-ray diffraction technology, he discovered, for the first time in the world, the three-dimensional (3-D) structure of a transfer RNA (t-RNA) and received much praise for this work from the scientific community. Since then, he has been cited as a candidate for a Nobel Prize in Chemistry for many years.
He also examined the 3-D structures of a RAS protein in normal and cancer cells and identified the mutations of the RAS protein as a cause for cancer. His work has assisted in the development of target drugs for cancer treatment. In recent years, he has adopted a computational biology approach to study the structure and function of biological genomics, with which he has tried to predict disease-sensitive genes.
Professor Kim graduated from Seoul National University in 1962 and received his Ph.D. degree in chemistry from the University of Pittsburgh in the United States in 1966. He worked at the Massachusetts Institute of Technology (MIT) as a senior research scientist, and has taught at UC Berkeley since 1978.
2016.05.23 View 7036 -
KAIST, NTU, and Technion Collaborate for Research in Emerging Fields
KAIST, Nanyang Technological University (NTU) of Singapore, and Technion of Israel signed an agreement on April 11, 2016 in Seoul to create a five-year joint research program for some of the most innovative and entrepreneurial areas: robotics, medical technologies, satellites, materials science and engineering, and entrepreneurship. Under the agreement, the universities will also offer dual degree opportunities, exchange visits, and internships.
In the picture from the left, Bertil Andersson of NTU, Sung-Mo Kang of KAIST, and Peretz Lavie of Technion hold the signed memorandum of understanding.
2016.04.14 View 11805 -
Efficient Methane C-H Bond Activated by KAIST and UPenn Teams
Professor Mu-Hyun Baik of the Chemistry Department at KAIST and his team collaborated with an international team to discover a novel chemical reaction, carbon-hydrogen borylation using methane, and their research results were published in the March 25th issue of Science.
For details, please refer to the following press release from the Institute for Basic Sciences (IBS) in Korea and the University of Pennsylvania in the United States.
Efficient Methane C-H Bond Activation Achieved for the First Time
The Institute for Basic Science, March 24, 2016
Penn Chemists Lay Groundwork for Countless New, Cleaner Uses of Methane
University of Pennsylvania, March 24, 2016
2016.03.25 View 9801 -
Public Lectures on the Korean Language and Alphabet
The School of Humanities and Social Sciences at KAIST will offer public lectures on the Korean language and alphabet, Hangul, from March 22, 2016 to April 26, 2016.
The lectures, which are entitled “The Riddle of Hangul,” will take place on campus in Daejeon.
A total of six lectures will be held on such topics as the origin of Korean, the grammar of ancient Korean in the Chosun Dynasty (1392-1897), and subsequent developments in contemporary Korean.
Professor Jung-Hoon Kim, who is responsible for organizing the public lecture program, said, “The audience will have an interesting opportunity to understand the history of Korean and its mechanism, while reviewing the unique spelling system of Hangul. I hope many people will show up for these wonderful classes.”
For further information and registration, please visit: http://hss.kaist.ac.kr. All lectures, available only in Korean, are free and open to the public.
2016.03.15 View 9108 -
K-Glass 3 Offers Users a Keyboard to Type Text
KAIST researchers upgraded their smart glasses with a low-power multicore processor to employ stereo vision and deep-learning algorithms, making the user interface and experience more intuitive and convenient.
K-Glass, smart glasses reinforced with augmented reality (AR) that were first developed by KAIST in 2014, with the second version released in 2015, is back with an even stronger model. The latest version, which KAIST researchers are calling K-Glass 3, allows users to text a message or type in key words for Internet surfing by offering a virtual keyboard for text and even one for a piano.
Currently, most wearable head-mounted displays (HMDs) suffer from a lack of rich user interfaces, short battery lives, and heavy weight. Some HMDs, such as Google Glass, use a touch panel and voice commands as an interface, but they are considered merely an extension of smartphones and are not optimized for wearable smart glasses. Recently, gaze recognition was proposed for HMDs including K-Glass 2, but gaze cannot be realized as a natural user interface (UI) and experience (UX) due to its limited interactivity and lengthy gaze-calibration time, which can be up to several minutes.
As a solution, Professor Hoi-Jun Yoo and his team from the Electrical Engineering Department recently developed K-Glass 3 with a low-power natural UI and UX processor. This processor is composed of a pre-processing core to implement stereo vision, seven deep-learning cores to accelerate real-time scene recognition within 33 milliseconds, and one rendering engine for the display.
The stereo-vision camera, located on the front of K-Glass 3, works in a manner similar to three dimension (3D) sensing in human vision. The camera’s two lenses, displayed horizontally from one another just like depth perception produced by left and right eyes, take pictures of the same objects or scenes and combine these two different images to extract spatial depth information, which is necessary to reconstruct 3D environments. The camera’s vision algorithm has an energy efficiency of 20 milliwatts on average, allowing it to operate in the Glass more than 24 hours without interruption.
The research team adopted deep-learning-multi core technology dedicated for mobile devices. This technology has greatly improved the Glass’s recognition accuracy with images and speech, while shortening the time needed to process and analyze data. In addition, the Glass’s multi-core processor is advanced enough to become idle when it detects no motion from users. Instead, it executes complex deep-learning algorithms with a minimal power to achieve high performance.
Professor Yoo said, “We have succeeded in fabricating a low-power multi-core processer that consumes only 126 milliwatts of power with a high efficiency rate. It is essential to develop a smaller, lighter, and low-power processor if we want to incorporate the widespread use of smart glasses and wearable devices into everyday life. K-Glass 3’s more intuitive UI and convenient UX permit users to enjoy enhanced AR experiences such as a keyboard or a better, more responsive mouse.”
Along with the research team, UX Factory, a Korean UI and UX developer, participated in the K-Glass 3 project.
These research results entitled “A 126.1mW Real-Time Natural UI/UX Processor with Embedded Deep-Learning Core for Low-Power Smart Glasses” (lead author: Seong-Wook Park, a doctoral student in the Electrical Engineering Department, KAIST) were presented at the 2016 IEEE (Institute of Electrical and Electronics Engineers) International Solid-State Circuits Conference (ISSCC) that took place January 31-February 4, 2016 in San Francisco, California.
YouTube Link: https://youtu.be/If_anx5NerQ
Figure 1: K-Glass 3
K-Glass 3 is equipped with a stereo camera, dual microphones, a WiFi module, and eight batteries to offer higher recognition accuracy and enhanced augmented reality experiences than previous models.
Figure 2: Architecture of the Low-Power Multi-Core Processor
K-Glass 3’s processor is designed to include several cores for pre-processing, deep-learning, and graphic rendering.
Figure 3: Virtual Text and Piano Keyboard
K-Glass 3 can detect hands and recognize their movements to provide users with such augmented reality applications as a virtual text or piano keyboard.
2016.02.26 View 13258 -
KAIST Commencement 2016
KAIST hosted its 2016 commencement ceremony on February 19, 2016 at the Sports Complex on campus.
KAIST celebrated the event with five thousand participants including graduating students, faculty, guests, Vice Minister Nam-Ki Hong of Science, ICT and Future Planning of Korea, Chairman Jang-Moo Lee of KAIST's Board of Trustees, and President Jeong-Sik Ko of the KAIST Alumni Association.
President Patrick Aebischer of the Swiss Federal Institute of Technology in Lausanne (EPFL), Switzerland, and the former Speaker of the National Assembly of Korea Chang-Hee Kang received honorary doctorates in science and technology for their contributions to the advancement of science and engineering in education and research.
KAIST granted 570 doctoral degrees, 1,329 master’s degrees, and 867 bachelor degrees on this day.
Yoon-Bum Lee of the Chemistry Department graduated with honors; Woo-Young Jin of the Mathematical Sciences Department received the Chairman’s Award of the KAIST Board and Eun-Hee Yoo of the Biological Sciences Department for the KAIST Presidential Award. Min-Hyun Cho and Yoon-Seok Chang were recipients of the President’s Award of the KAIST Alumni Association and the President’s Award of the University Supporting Association, respectively.
President Steve Kang addressed the ceremony and congratulated the graduates, saying,
“Now, your task is to make significant contributions to your communities: be leaders in your fields and remain active members of society. Given your academic knowledge and vision for the future, I encourage you to dream big.”
2016.02.23 View 42428 -
KAIST Graduate Han Receives a 2016 PECASE Award
President Barack Obama of the United States (US) announced 105 recipients of the 2016 Presidential Early Career Awards for Scientists and Engineers (PECASE) on February 18. Among the awardees was a graduate from the Department of Electrical Engineering at KAIST.
Dr. Jin-Woo Han has worked as a research scientist at the National Aeronautics and Space Administration (NASA) Ames Research Center since graduating from KAIST in 2010. This year, he is the only awardee who received a doctoral degree from a Korean university to become a recipient of the highest honor bestowed by the US government on science and engineering professionals in the early stages of their independent research careers.
The awards ceremony will take place in early spring at the White House in Washington, D.C.
Dr. Han has been involved in the development of radiation tolerant semiconductor devices as well as radiation and gas sensors under Dr. Meyya Meyyappan, Chief Scientist of the Center for Nanotechnology at NASA Ames Research Center.
KAIST and the NASA Ames Research Center made a research collaboration agreement in 2008, under which KAIST has sent 12 post-doctoral fellows to the center to date.
The PECASE awards, established in 1996 by President Bill Clinton, are coordinated by the Office of Science and Technology Policy within the Executive Office of the US President. Awardees are selected for their pursuit of innovative research at the frontiers of science and technology and their commitment to community services as demonstrated through scientific leadership, public education, or community outreach.
2016.02.23 View 9947 -
Meditox Donates 600 Million KRW Scholarship
On February 17, a Korean biopharmaceutical company Meditox, headed by Chief Executive Officer (CEO) Hyun-Ho Jeong, signed a memorandum of understanding (MOU) with KAIST to establish the “Meditox Fellowship” and donated a total of 600 million Korean won (KRW) to the university to assist in promoting more scientists in the field of biology.
Meditox CEO Hyun-Ho Jeong, KAIST President Steve Kang, Dean of Life Science and Bioengineering College Jung-Hoe Kim, and Dean of the Department of Biological Sciences Byung-Ha Oh participated in the agreement ceremony.
According to the MOU, Meditox will donate 60,000,000 KRW over a ten year period, from which KAIST can draw on to grant scholarships for master’s and doctoral students.
The “Meditox Fellowship” will support promising and enthusiastic students whose finances limit their studies. The first scholarship students for 2016 were: Kwang-Uk Min, In-suk Yeo, Sung-ryung- Lee, Si-on Lee, and Jung-hyun Kim.
Meditox CEO Jeong, who graduated from KAIST’s Department of Biological Sciences, said, "I felt it was important to start the Meditox Fellowship at my alma mater to contribute to the cultivation of outstanding scientists in the field of biological sciences."
He also said that he would plan to launch projects that aim to support not only those who receive the scholarship but also the development of Korea’s biological sciences in general.
President Steve Kang (right) and Chief Executive Officer Hyun-Ho Jeong (left) of Meditox hold the signed memorandum of understanding together.
2016.02.18 View 10395 -
Ph.D. Candidate Seo Wins the Human Tech Paper Award
Hyun-Suk Seo, a doctoral student of KAIST’s Department of Electrical Engineering, received the grand prize of the “22nd Human Tech Paper Award” on February 3, 2016 from Samsung Electronics Co., Ltd.
Seo was the first to receive this prize ever since the Human Tech Paper Award was established 22 years ago. Until last year, the highest prize awarded for KAIST was a gold one.
The “Human Tech Paper Award” was established in 1994 by Samsung Electronics to discover and support outstanding scientists in the field of electrical engineering.
Entitled “Self-Gated Cardiac Cine MRI Using Phase Information,” Seo’s paper presented a technology that would reduce discomforts and inconveniences experienced by patients who take a magnetic resonance imaging (MRI).
This technology uses the speed changes of aorta and the abdominal movements of body to obtain the phase changes of magnetic resonance signals so that MRIs may be taken despite the organs’ movements.
Seo commented on his research, “I wanted to develop a technique that can make MRI a more comfortable experience. I will continue my research on this subject and hope to serve the needs of the society.”
In addition, the “Special Award,” which is given to schools, was awarded to KAIST. KAIST’s Department of Electrical Engineering has also been named the department that has received the second most awards (15 awards) this year.
Oh-Hyun Kwon, Vice President of Samsung Electronics, Steve Kang, President of KAIST, and Nak-In Seo, President of Seoul National University, participated in the event.
Picture: Hyun-Suk Seo (left), the recipient of the grand prize of the 2016 Human Tech Paper Award, and Oh-Hyun Kwon (right), Vice President of Samsung Electronics
2016.02.06 View 9361 -
Asia Pacific Biotech News' Special Coverage of Korean Biotechnology
The Asia Pacific Biotech News covered five major biotechnology research projects sponsored by the Korean government in the areas of biofuels, biomedicine, bio-nano healthcare, and biorefinery.
The Asia Pacific Biotech News (APBN), a monthly magazine based in Singapore, which offers comprehensive reports on the fields of pharmaceuticals, healthcare, and biotechnology, recently published a special feature on Korea’s biotechnology research and development (R&D) programs.
The magazine feature selected five research programs sponsored by the Korean government, which are either part of the Global Frontier or the Climate Change Technology Development Projects.
The programs are:
Systems Metabolic Engineering Research: Distinguished Professor Sang Yup Lee
of the Chemical and Biomolecular Engineering Department at the Korea Advanced
Institute of Science and Technology (KAIST) has been leading a research group to
develop biorefining technology using renewable non-food biomass to produce
chemicals, fuels, and materials that were largely drawn from fossil resources
through petrochemical refinery processes. Applying a systems metabolic
engineering approach, the group succeeded in modifying the metabolic pathways of
microorganisms. As a result, they produced, for the first time in the world,
engineered plastic raw materials and gasoline. The team also developed a technique
to produce butanol and succinic acid with a higher titer and yield using metabolically
engineered microorganisms.
Next-generation Biomass Research: Under the leadership of Professor Yong-
Keun Chang of the Chemical and Biomolecular Engineering Department at KAIST,
the research project, which belongs to the Global Frontier Project, develops biofuels
and bioproducts utilizing microalgae typically found in water and other marine
systems.
Convergence Research for Biomedicine: Professor Sung-Hoon Kim of Seoul
National University leads this project that develops targeted new drugs based on
convergence research strategies.
Bionano Healthcare Chip Research: Director Bong-Hyun Chung of the Korea
Research Institute of Bioscience and Biotechnology has integrated information and
communications technology, nanotechnology, and biotechnology to develop a
diagnostic kit that can screen toxic germs, virus, and toxic materials in a prompt
and accurate manner.
Biosynergy Research: Led by Professor Do-Hun Lee of the Bio and Brain
Engineering Department at KAIST, this research project develops new treatments
with a multi-target, multi-component approach in the context of systems biology
through an analysis of synergistic reactions between multi-compounds in traditional
East Asian medicine and human metabolites. In East Asian medicine, treatment and
caring of the human body are considered analogous to the politics of governing a
nation. Based on such system, the research focuses on designing a foundation for
the integration of traditional medicine with modern drug discovery and development.
Director Ilsub Baek at the Platform Technology Division of the Ministry of Science, ICT and Future Planning, Republic of Korea, who is responsible for the Global Frontier Program and the Technology to Solve Climate Change, said, “It is great to see that Asia Pacific Biotech News published an extensive coverage of Korea’s several key research programs on biotechnology as its first issue of this year. I am sure that these programs will lead to great outcomes to solve many worldwide pending issues including climate change and healthcare in the aging society.”
Professor Sang Yup Lee, who served as an editor of the feature, said, “At the request of the magazine, we have already published lead articles on our biotechnology research three times in the past in 2002, 2006, and 2011. I am pleased to see continued coverage of Korean biotechnology by the magazine because it recognizes the excellence of our research. Biotechnology has emerged as one of the strong fields that addresses important global issues such as climate change and sustainability.”
2016.02.04 View 13156 -
KAIST Opens a Campus Laundromat
The young and older generations are cooperating to create work places for the local elderly.
The KAIST Graduate Association and the Korean Labor Force Development Institute for the Aged (KORDI) held an opening ceremony for a campus laundromat on January 26, 2016 at the multi-purpose hall of the International Center.
The newly-opened laundromat has two large washing machines, two front-loading washers, and two large dryers that can handle up to 400 kg of laundry.
The KAIST Graduate Association asked KORDI to operate the laundromat to offer job opportunities to seniors in the local community, while providing KAIST students with more conveniences in campus life. As a result, ten seniors are working at the laundromat, providing a variety of cleaning services.
Chan Park, President of the KAIST Graduate Association, said, “I have been contemplating ways in which universities can cooperate with the local community. I hope this particular business model will make a modest improvement in the creation of jobs for the elderly.”
2016.01.26 View 4166