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KAIST Team Develops Semi-Transparent Solar Cells with Thermal Mirror Capability
A research team led by KAIST and Sungkyunkwan University professors has created semi-transparent perovskite solar cells that demonstrate high-power conversion efficiency and transmit visible light while blocking infrared light, making them great candidates for solar windows. Modern architects prefer to build exteriors designed with glass mainly from artistic or cost perspectives. Scientists, however, go one step further and see opportunities from its potential ability to harness solar energy. Researchers have thus explored ways to make solar cells transparent or semi-transparent as a substitute material for glass, but this has proven to be a challenging task because solar cells need to absorb sunlight to generate electricity, and when they are transparent, it reduces their energy efficiency. Typical solar cells today are made of crystalline silicon, but it is difficult to make them translucent. Semi-transparent solar cells under development use, for example, organic or dye-sensitized materials, but compared to crystalline silicon-based cells, their power-conversion efficiencies are relatively low. Perovskites are hybrid organic-inorganic halide-based photovoltaic materials, which are cheap to produce and easy to manufacture. They have recently received much attention as the efficiency of perovskite solar cells has rapidly increased to the level of silicon technologies in the past few years. Using perovskites, a Korean research team led by Professor Seunghyup Yoo of the Electrical Engineering School at KAIST and Professor Nam-Gyu Park of the Chemical Engineering School at Sungkyunkwan University developed a semi-transparent solar cell that is highly efficient and, additionally, functions very effectively as a thermal-mirror. The team has developed a top transparent electrode (TTE) that works well with perovskite solar cells. In most cases, a key to success in realizing semi-transparent solar cells is to find a TTE that is compatible with a given photoactive material system, which is also the case for perovskite solar cells. The proposed TTE is based on a multilayer stack consisting of a metal film sandwiched between a high refractive-index (high-index) layer and an interfacial buffer layer. This TTE, placed as a top-most layer, can be prepared without damaging ingredients used in perovskite solar cells. Unlike conventional transparent electrodes focusing only on transmitting visible light, the proposed TTE plays the dual role of passing through visible light while reflecting infrared rays. The semi-transparent solar cells made with the proposed TTEs exhibited average power conversion efficiency as high as 13.3% with 85.5% infrared rejection. The team believes that if the semi-transparent perovskite solar cells are scaled up for practical applications, they can be used in solar windows for buildings and automobiles, which not only generate electrical energy but also enable the smart heat management for indoor environments, thereby utilizing solar energy more efficiently and effectively. This result was published as a cover article in the July 20, 2016 issue of Advanced Energy Materials. The research paper is entitled “Empowering Semi-transparent Solar Cells with Thermal-mirror Functionality.” (DOI: 10.1002/aenm.201502466) The team designed the transparent electrode (TE) stack in three layers: A thin-film of silver (Ag) is placed in between the bottom interfacial layer of molybdenum trioxide (MoO3) and the top high-index dielectric layer of zinc sulfide (ZnS). Such a tri-layer approach has been known as a means to increase the overall visible-light transmittance of metallic thin films via index matching technique, which is essentially the same technique used for anti-reflection coating of glasses except that the present case involves a metallic layer. Traditionally, when a TE is based on a metal film, such as Ag, the film should be extremely thin, e.g., 7-12 nanometers (nm), to obtain transparency and, accordingly, to transmit visible light. However, the team took a different approach in this research. They made the Ag TE two or three times thicker (12-24 nm) than conventional metal films and, as a result, it reflected more infrared light. The high refractive index of the ZnS layer plays an essential role in keeping the visible light transmittance of the proposed TTE high even with the relatively thick Ag film when its thickness is carefully optimized for maximal destructive interference, leading to low reflectance (and thus high transmittance) within its visible light range. The team confirmed the semi-transparent perovskite solar cell’s thermal-mirror function through an experiment in which a halogen lamp illuminated an object for five minutes through three mediums: a window of bare glass, automotive tinting film, and the proposed semi-transparent perovskite solar cell. An infrared (IR) camera took thermal images of the object as well as that of each window’s surface. The object’s temperature, when exposed through the glass window, rose to 36.8 Celsius degrees whereas both the tinting film and the cell allowed the object to remain below 27 Celsius degrees. The tinting film absorbs light to block solar energy, so the film’s surface became hot as it was continuously exposed to the lamp light, but the proposed semi-transparent solar cell stayed cool since it rejects solar heat energy by reflection, rather than by absorption. The total solar energy rejection (TSER) of the proposed cell was as high as 89.6%. Professor Yoo of KAIST said, “The major contributions of this work are to find transparent electrode technology suitable for translucent perovskite cells and to provide a design approach to fully harness the potential it can further deliver as a heat mirror in addition to its main role as an electrode. The present work can be further fine-tuned to include colored solar cells and to incorporate flexible or rollable form factors, as they will allow for greater design freedom and thus offer more opportunities for them to be integrated into real-world objects and structures such as cars, buildings, and houses.” The lead authors are Hoyeon Kim and Jaewon Ha, both Ph.D. candidates in the School of Electrical Engineering at KAIST, and Hui-Seon Kim, a student in the School of Chemical Engineering at Sungkyunkwan University. This research was supported mainly by the Climate Change Research Hub Program of KAIST. Picture 1: Semi-transparent Perovskite Solar Cell This picture shows a prototype of a semi-transparent perovskite solar cell with thermal-mirror functionality. Picture 2: A Heat Rejection Performance Comparison Experiment This picture presents thermal images taken by an infrared camera for comparing the heat rejection performance of bare glass, automotive tinting film, and a semi-transparent perovskite solar cell after being illuminated by a halogen lamp for five minutes.
GSIS Graduates Its First Doctor
The Graduate School of Information Security at KAIST (GSIS) granted its first doctoral degree to Il-Goo Lee at the university’s 2016 commencement on February 19, 2016. Lee received the degree for his dissertation entitled “Interference-Aware Secure Communications for Wireless LANs.” He explained the background of his research: “As we use wireless technology more and more in areas of the Internet of Things (IoT), unmanned vehicles, and drones, information security will become an issue of major concern. I would like to contribute to the advancement of communications technology to help minimize wireless interference between devices while ensuring their optimal performance.” Based on his research, he developed a communications technique to increase wireless devices’ energy efficiency and the level of their security, and created a prototype to showcase that technique. He plans to continue his research in the development of the next generation WiFi chip sets to protect the information security of IoT and wireless devices. Since its establishment in March 2011, KAIST’s GSIS has conferred 50 master’s and one doctoral degrees.
Professors Jeon and Choi Receive the Young Scientist Award
Professors Seokwoo Jeon of the Department of Materials Science and Engineering and Jang Wook Choi of the Graduate School of Energy, Environment, Water and Sustainability (EEWS) at KAIST received the Young Scientist Award. The award ceremony took place at the Korea Press Center in Seoul. Presented by the Ministry of Science, ICT and Future Planning of Korea and the National Academy of Engineering of Korea, the Young Scientist Award is given to outstanding scientists under the age of 40 who have demonstrated excellence in their research in the field of natural science. Each year the award is given to three scientists in different areas. Professor Jeon was recognized for his achievement in creating a new property of materials. He studied synthesis and development of low-dimensional nanomaterials and developed a large area nanostructure. Professor Choi’s research area was to discover optimal materials for rechargeable batteries. By applying his research, he developed rechargeable batteries with high efficiency, making the wearable system more feasible.
Partnership with École Centrale Paris
Courtesy of École Centrale Paris News: http://www.ecp.fr/lang/en/home/news?actuID=48892 Strengthening of the partnership betwenn CentraleSupélec and KAIST University, South Korea The two institutions signed a new agreement. Hervé Biausser (left in the picture), Director of CentraleSupélec, has met Sung-Mo Steve Kang (right in the picture), the President of the Korea Advanced Institute of Science and Technology (KAIST). They signed an agreement aiming to strengthen the partnership between the two institutions concerning research and higher education. CentraleSupélec and KAIST have cooperated since 2010 on research projects in the context of the Erasmus Mundus BEAM and EASED programs, which are coordinated by CentraleSupélec. The next step is now the application of graduate academic mobility in the common fields of excellency of the institutions: energy, electronic, physics and mathematics.
KAIST Invites Entrepreneurs and Experts to Participate in a Social Technology Innovation Symposium
The Research Institute for Social Technology and Innovation (RISTI) at KAIST hosted the Social Technology Innovation Symposium on November 4, 2015 in KI building, to which 100 social business entrepreneurs and experts in the field were invited. Social businesses refer to activities of companies, which strive to resolve social problems such as environmental issues, income inequality, and aging societies while seeking profit at the same time. This is different from companies taking social responsibility and non-profit organization serving the community in that they attempt to solve social problems through a sustainable business model. Held under the theme of “technology capabilities of companies and social business strategies,” this symposium was the first to gather representatives from social venture companies, medium-sized enterprises, and major companies at one place to share their experiences in a social business and to discuss future tasks. The symposium was divided into sessions with three different topics ranging from social business strategies using information technology, a social business and its business model, and social business strategies of major companies. The symposium started with keynote speeches delivered by Professor HongKyu Lee, RISTI, and Professor Hong-Tak Lim, RISTI, who discussed the role of technology in a social business. It was followed by plenary sessions led by CEOs who are running social businesses such as the Sharing and Technologies Incorporated Project, Simwon Technology, Ecojun Company, Underdogs, and the Farming Fund as well as by representatives from a social responsibility section of CJ management team and the social responsibility council of SK. In the future, these talks will serve as a medium to share their experiences in social businesses and to discuss the role of technology in the business. Some talks touched upon topics such as development of platforms for social innovation, social businesses employing disabled workers, and crowd funding for farming. The Director of RISTI, Professor HongKyu Lee said, “The symposium will be the first to have people from leading companies in social businesses in Korea in one place.” He added, “This will be a great opportunity for anyone to know what will be the future of social businesses, which were created to solve the social problems caused by capitalism.” The symposium was sponsored by the Ministry of Trade, Industry, and Energy of Korea.
Professors Sukbok Chang and Jang-Wook Choi Receive the 2015 Knowledge Award from the Korean Government
The Ministry of Science, ICT and Future Planning (MISP) of the Republic of Korea announced the 2015 Knowledge Awards on October 20, 2015. Two KAIST professors received the award. Established in 2009, the awards are presented to Korean scientists whose publications have contributed to the international science community. Specifically, the MISP used the two biggest science databases, Science Citation Index Expanded (SCIE) and Scopus, to identify ten highly cited papers ranked in the top 1% by total citations in the past ten years. Professor Sukbok Chang of Chemistry (left in the picture below) is a global authority in the field of catalytic hydrocarbon functionalization. His paper entitled “Palladium-catalyzed C-H Functionalization of Pyridine N-Oxides: Highly Selective Alkenylation and Direct Arylation with Unactivated Arenes,” which was published in the Journal of the American Chemical Society in 2008, was once selected by Thomson Reuters as one of the “Most Influential Research Papers of the Month.” In 2011, the American Chemical Society included his paper in the list of the top 20 research papers that were most frequently cited in the last three years. Professor Jang-Wook Choi of the Graduate School of EEWS (Energy, Environment, Water, and Sustainability) has been known for his leading research in rechargeable battery, supercapacitor, and materials chemistry. In particular, his work on secondary fuel cells attracted significant attention from academia and industry in Korea. Professor Choi developed a super-thin flexible lithium-ion battery this year, thinner than a credit card, which lasts longer than the existing batteries and with greater performance. He also developed new electrode materials for next-generation sodium-ion and magnesium secondary fuel cells. Professor Sukbok Chang (left) and Professor Jang-Wook Choi (right)
KAIST's Research Team Receives the Best Paper Award from the IEEE Transaction on Power Electronics
A research team led by Professor Chun T. Rim of the Department of Nuclear and Quantum Engineering at the Korea Advanced Institute of Science and Technology (KAIST) has received the First Prize Papers Award from the IEEE (Institute of Electrical and Electronics Engineers) Transactions on Power Electronics (TPEL), a peer-reviewed journal that covers fundamental technologies used in the control and conversion of electric power. A total of three research papers received this award in 2015. Each year, TPEL’s editors select three best papers among those published in the journal during the preceding calendar year. In 2014, the TPEL published 579 papers. Professor Rim’s paper was picked out as one of the three papers published last year for the First Prize Papers Award. Entitled “Generalized Active EMF (electromagnetic field) Cancel Methods for Wireless Electric Vehicles (http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6684288&tag=1),” the paper proposed, for the first time in the world, three generalized design methods for cancelling the total EMF generated from wireless electric vehicles. This technology, researchers said, can be applied to any wireless power transfer systems. The award ceremony will be held at the upcoming conference of the 2015 IEEE Energy Conversion Congress and Expo in September in Montreal, Canada.
KAIST Researchers Develops Hyper-Stretchable Elastic-Composite Energy Harvester
A research team led by Professor Keon Jae Lee (http://fand.kaist.ac.kr) of the Department of Materials Science and Engineering at KAIST has developed a hyper-stretchable elastic-composite energy harvesting device called a nanogenerator. Flexible electronics have come into the market and are enabling new technologies like flexible displays in mobile phone, wearable electronics, and the Internet of Things (IoTs). However, is the degree of flexibility enough for most applications? For many flexible devices, elasticity is a very important issue. For example, wearable/biomedical devices and electronic skins (e-skins) should stretch to conform to arbitrarily curved surfaces and moving body parts such as joints, diaphragms, and tendons. They must be able to withstand the repeated and prolonged mechanical stresses of stretching. In particular, the development of elastic energy devices is regarded as critical to establish power supplies in stretchable applications. Although several researchers have explored diverse stretchable electronics, due to the absence of the appropriate device structures and correspondingly electrodes, researchers have not developed ultra-stretchable and fully-reversible energy conversion devices properly. Recently, researchers from KAIST and Seoul National University (SNU) have collaborated and demonstrated a facile methodology to obtain a high-performance and hyper-stretchable elastic-composite generator (SEG) using very long silver nanowire-based stretchable electrodes. Their stretchable piezoelectric generator can harvest mechanical energy to produce high power output (~4 V) with large elasticity (~250%) and excellent durability (over 104 cycles). These noteworthy results were achieved by the non-destructive stress- relaxation ability of the unique electrodes as well as the good piezoelectricity of the device components. The new SEG can be applied to a wide-variety of wearable energy-harvesters to transduce biomechanical-stretching energy from the body (or machines) to electrical energy. Professor Lee said, “This exciting approach introduces an ultra-stretchable piezoelectric generator. It can open avenues for power supplies in universal wearable and biomedical applications as well as self-powered ultra-stretchable electronics.” This result was published online in the March issue of Advanced Materials, which is entitled “A Hyper-Stretchable Elastic-Composite Energy Harvester.” YouTube Link: “A hyper-stretchable energy harvester” https://www.youtube.com/watch?v=EBByFvPVRiU&feature=youtu.be Figure: Top row: Schematics of hyper-stretchable elastic-composite generator enabled by very long silver nanowire-based stretchable electrodes. Bottom row: The SEG energy harvester stretched by human hands over 200% strain.
Professor Rim Presents at IAEA Workshop in Vienna
Professor Chun-Taek Rim of the Department of Nuclear and Quantum Engineering at KAIST recently attended the International Atomic Energy Agency (IAEA)’s workshop on the Application of Wireless Technologies in Nuclear Power Plant Instrumentation and Control System. It took place on March 30-April 2, 2015, in Vienna, Austria. Representing Korea, Professor Rim gave a talk entitled “Highly Reliable Wireless Power and Communications under Severe Accident of Nuclear Power Plants (NPPs).” About 20 industry experts from 12 countries such as AREVA (France), Westinghouse (US), Oak Ridge National Laboratory (US), Hitachi (Japan), and ENEA (Italy) joined the meeting. The IAEA hosted the workshop to explore the application of wireless technology for the operation and management of NPPs. It formed a committee consisting of eminent professionals worldwide in NPP instrumentation and control systems, communications, and nuclear power to examine this issue in-depth and to conduct various research projects for the next three years. In particular, the committee will concentrate its research on improving the reliability and safety of using wireless technology, not only in the normal operation of nuclear plants but also in extreme conditions such as the Fukushima Daiichi nuclear accident. The complementation, economic feasibility, and standardization of NPPs when applying wireless technology will be also discussed. Professor Rim currently leads the Nuclear Power Electronics and Robotics Lab at KAIST (http://tesla.kaist.ac.kr/index_eng.php?lag=eng). Picture 1: Professors Rim presents his topic at the IAEA Workshop in Vienna. Picture 2: The IAEA Workshop Participants
Dr. Dong-Hee Chung Honored with OYRA by Korean Physicists in America
Dr. Dong-Hee Chung, a KAIST alumnus (class of 2002) who is currently a professor of the Physics Department at the Pennsylvania State University (Penn State), received the 2015 Outstanding Young Researcher Award (OYRA) by the Association of Korean Physicists in America (AKPA). The award ceremony was held on March 3, 2015 at AKPA’s annual conference. According to AKPA, Dr. Chung was recognized for his research achievements in the fields of the early universe, dark energy, and galaxy formation. Dr. Chung finished both his undergraduate and graduate degrees at KAIST and received his doctorate in 2004 from the University of Texas at Austin. He was appointed a professor at Penn State in 2014.
Press Release on Piezoelectric Nanogenerators of ZnO with Aluminium Nitride Stacked Layers by the American Institute of Physics
The American Institute of Physics (AIP) released a news article entitled “Zinc Oxide Materials Tapped for Tiny Energy Harvesting Devices” on January 13, 2015. The article described the research led by Professor Giwan Yoon of the Electrical Engineering Department at KAIST. It was published in the January 12, 2015 issue of Applied Physics Letters. AIP publishes the journal. For the news release, please visit the link below: The American Institute of Physics, January 13, 2015 “Zinc Oxide Materials Tapped for Tiny Energy Harvesting Devices” New research helps pave the way toward highly energy-efficient zinc oxide-based micro energy harvesting devices with applications in portable communications, healthcare and environmental monitoring, and more http://www.aip.org/publishing/journal-highlights/zinc-oxide-materials-tapped-tiny-energy-harvesting-devices
Elsevier Selects a KAIST Graduate's Paper as the Top Cited Papers in 2011-2012
Dr. Myung-Won Seo, a graduate from the Department of Chemical and Bimolecular Engineering at KAIST, published a paper in January 2011 in Chemical Engineering Journal, which was entitled “Solid Circulation and Loop-seal Characteristics of a Dual Circulating Fluidized Bed: Experiments and CFD Simulation.” His paper was selected by Elsevier as the Top Cited Papers of 2011-2012. The Chemical Engineering Journal is a renowned peer-reviewed journal issued by Elsevier. Dr. Seo published another paper, “CFD Simulation with Experiments in a Dual Circulating Fluidized Bed Gasifier,” in January 2012 in Computers & Chemical Engineering, which was also selected as the Most Downloaded Papers in 2012-2013. Dr. Seo graduated with a doctoral degree from KAIST in 2011. He is currently working at the Clean Fuel Laboratory, the Korea Institute of Energy Research, Daejeon, as a researcher. His research areas are coal gasification, upgrading, and liquefaction, as well as energy and chemical production from low-grade fuels such as biomass and wastes.
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