EU-Korea workshop on Advanced Materials

Resume : Welcome to EU-Korea workshop

Resume : KONNECT/KORANET projects

Resume : A thermoelectric voltage is developed when a temperature difference is applied for a conducting material. In general, the thermoelectric voltage is proportional to the temperature difference with a proportional constant called Seebeck coefficient or thermopower. Recently, we have developed first scanning Seebeck microscopy generating nanoscale to atomic scale images of structural disorders and atomic scale defects in epitaxial graphene [1] and found that the thermoelectric images closely associate with electronic states at the Fermi energy [2]. In this talk, I will review the experiment and theory including how to interpret the thermoelectric images with first-principles surface wave functions of graphene. [1] S. Cho, S. D. Kang, W. Kim, E.-S. Lee, S.-J. Woo, K.-J. Kong, I. Kim, H.-D. Kim, T. Zhang, J. A. Stroscio, Y.-H. Kim and H.-K. Lyeo, arXiv:1305.2845, Nature Mater. 12, 913 (2013). [2] E.-S. Lee, S. Cho, H.-K. Lyeo and Y.-H. Kim, arXiv:1307.3742, Phys. Rev. Lett. 112, 136601 (2014).

Resume : While structure-property relationships have been well established in many areas of materials science, lattice thermal conductivity remains poorly understood. I will discuss recent progress in this regard, drawing from anharmonic lattice dynamic calculations[1] as implemented in the open-source package PHONOPY. We highlight a number of new material systems with remarkably low lattice thermal conductivity, beyond current high-performing thermoelectric materials. The work has been performed in collaboration with researchers at KAIST and Seoul National University. [1] Thermal physics of the lead chalcogenides PbS, PbSe, and PbTe from first principles, Physical Review B 89, 205203 (2014).

Resume : Nature has found cryptobiotic ways to preserve genetic information and protect cellular components against external stresses, such as nutrient deprivation, desiccation, high temperatures, radiation, and caustic chemicals. For example, a bacterial endospore, usually formed in response to nutrient deficiency, is a non-dividing, dormant body, which possesses a thin but tough proteinaceous coat at its outmost layer. Beneath the coat is a buffering cortex layer of peptidoglycan. This hierarchical shell structure allows the endospore to survive for many years (in some cases, up to millions of years) under hostile conditions found naturally that can easily and quickly kill normal cells. Recent studies have sought to chemically control and tailor the metabolic behaviors of non-spore-forming cells, as well as enhancing their viability against adverse environmental conditions, by forming thin (< 100 nm), tough artificial shells. These living “cell-in-shell” structures, called artificial spores, enable control of cell division, protection against physical and chemical stresses, and cell-surface functionalizability, as well as providing the cells with exogenous properties that are not innate to the cells but are introduced chemically, such as magnetism, heat-tolerance, and UV-resistance. In this talk are discussed chemical approaches to individually encapsulate living cells within thin and tough shells, such as inorganic silica and organic poly

Resume : GaN light-emitting diodes (LEDs) have attracted much attention due to their applications in general lighting, TVs, sterilization, and excitation sources for portable optical analysis. Large-area p-doped graphene transparent conductive electrodes were successfully integrated in GaN-based LEDs through chemical doping using AuCl3 solutions, then characterized by SEM, transmittance measurements, micro-Raman spectroscopies, I-Vs, ELs and sheet resistance measurements. Sheet resistance was significantly decreased after chemical doping. I-V characteristics and EL intensities were dramatically improved. Doped graphene transparent conductive electrodes can be a good alternative to ITO-based transparent conductive electrodes in LEDs.

Resume : Zinc oxide (ZnO) and Tin dioxide (SnO2) films are becoming a popular alternative to common transparent conductive oxides (TCO) such as Indium Tin oxide (ITO) often used in silicon (e.g. polymorphous & Heterojunction cells) and II-VI (e.g. CIGS, CdTe) based solar cells. This is due to their good optical properties and relatively low cost. They have a large band gap which assures a high transparency in the visible range and, when deposited in thin film form, the thickness can be easily tuned to produce an anti-reflection coating. In this talk, I will present the effect of rare earth doping in these promising TCO on the photon conversion properties and their potential use as interfacial layers for photovoltaic solar cells. Doping wide band gap semiconductors, such as ZnO and SnO2, with trivalent rare earth (RE) ions is well known to enhance their optical activity. In fact, RE are well known for their optical transitions involving the 4f shell. We were interested to study the electronic transfer between these oxides and the rare earth (RE) for photon shifting or down conversion and possible applications for silicon-based solar cells. In particular, we focused on RE emitting in the region between 500 and 1000 nm, where the spectral response of the solar cell is high. Trivalent rare earth ions, such as Yb+3 and Nd3+ exhibit luminescence just above the band gap of silicon. If an efficient transfer between ZnO and RE ions is possible, an increase in the conversion efficiency is expected. Magnetron reactive sputtering has, therefore, been used to obtain high-quality oriented ZnREO and SnREO2 films. Photoluminescence measurements indicated that an efficient electronic transfer from ZnO [1] and SnO2 [2] to RE+3 ions is achieved. In particular, excitation dependent PL allows deeper insight into the RE electronic levels. 1. M. Balestrieri, G. Ferblantier, S. Colis, G. Schmerber, C. Ulhaq-Bouillet, D. Muller, A. Slaoui, and A. Dinia; Structural and optical properties of Y-doped ZnO films deposited by magnetron reactive sputtering for photon conversion. Solar Energy Materials & Solar Cells 117, 363 (2013). 2. K. Bouras, J.-L. Rehspringer, G. Schmerber, H. Rinnert, S. Colis, C. Leuvrey, G. Ferblantier, D. Ihiawakrim, M. Balestrieri, A. Dinia and A. Slaoui. Optical and structural properties of Nd doped SnO2 powder fabricated by the sol-gel method. Journal of Materials Chemistry C, accepted (2014).

Resume : Now, in Korea, global warming issues made new strategy and policy on clean energy development. Government declared 30% reducing target of CO2 emission on the basis of 2005 by the end of 2030. In addition, government also wants to increase the renewable energy sources to 11% of total consuming of electricity by 2035. Fuel Cell is included one of the most practical NRE (New and Renewable Energy) sources for reducing CO2 emission in Korea, because it has high efficiency with low emission levels. In addition, Korea, the worlds 10th energy consuming and importing has been strongly longing for the realization of Hydrogen and Fuel Cell energy system in order to solve the problems in both energy security and environment. From these reasons, the R&D activities on Fuel Cell technology in Korea started from the late of 1980’s. Government programs, which has a goal for commercialization, had been executed since that time and started dissemination of Fuel cell System as one of NRE source. Now, with the government supporting policy for dissemination of NRE and strong interest in private companies Fuel Cell Industry in Korea rapidly increased. Looking at the Fuel Cell industry in Korea at this moment, a number of company related Fuel Cell business are now over ten companies and the incomes of those companies showed over $ 1.170 billion in 2012. Stationary power generation capacity from Fuel cell system in Korea showed over 160 MW even in 2014. In the field of Fuel cell vehicle, Hyundai-Kia motor company declared that it’s mass production line that have capability to manufacture more than 1,000 cars per year was established on 2013. Plus, for infrastructure, fourteen hydrogen stations for refueling of FC vehicles were constructed and eight sites are now operating. Fuel Cell technology was nearly closed to early stage of commercialization in Korea, so the R/D in hydrogen and fuel cell technology, started to focus on the development of core materials and components rather than system integration. The strategy of R/D is to elucidate basic mechanism for commercial adoption of fuel cell, to promote innovative technology for reducing price, and to enhance the performance and durability. When it comes to the current status of Fuel Cell R/D, the industrial R&D was designed for market transformation (on-going and planned) and Core technologies intended for technical breakthroughs was also designed as well. Development of hydrocarbon based membrane and MEA, low-cost and high-performance PEMFC system have been executed now. Core components for compact PEMFC system with variable pressure operation and 5 kW-class PEMFC system for stationary applications also have been executed. In addition, 20kW class biogas-fueled PEMFC and PEMFC-battery and DMFC-battery power packs have also developed. Development of SOFC materials and components with improved reliability, 1 kW SOFC micro-CHP for residential application and 10 kW class SOFC systems with improved durability were also developing now. In MCFC, the project on core materials and components for extending the stack life of MCFCs has been executes as well.

Resume : Optofluidics employ fluids and relevant actuations for controlling light propagation phenomena; optofluidic devices can find applications in biosensing, actuating and switching operations. There have been integrated fiber and free space optical components, in which, pneumatic, electrostatic or magnetofluidic control of liquids results to refractive, absorptive, and light scattering effects. Nonetheless, the control of the fluidic properties of photonic circuits by solely utilizing light still constitutes a challenge. We demonstrate an all-light controlled optofluidic device developed on a microstructured optical fiber (MOF) Fabry-Perot (FP) interferometer, where zinc oxide (ZnO) nanolayer operates as a light triggered wettability surface element. ZnO is known for its tuneable wettability properties based on the creation of oxygen surface defects upon ultraviolet (UV) light irradiation and thermal annealing treatment. Here, we use an excimer laser emitting at 248 nm and a CW green laser emitting at 532 nm (at modest irradiation doses of few J/cm2 for both wavelengths) for controlling the liquid flow inside the MOF-FP cavity, through the ZnO wettability actuation. Results on the spectral tuning of the MOF-FP cavity, while employing the ZnO surface wettability, are presented, and analyzed with respect to their temporal behavior. Also, a discussion on the origin of the light controlled wettability of the ZnO is also appended; while being supported by photoluminescence data.

Resume : Solid oxide fuel cells (SOFCs) offer several advantages over low-temperature fuel cells, e.g., high thermodynamic efficiency, fast electrode kinetics, and internal reforming capability. An interconnect is a key SOFC component that provides electrical connection between adjacent cells and separates fuel and oxidant gases. The interconnects can be divided broadly into two categories – ceramic and metallic interconnects. A thin and gastight ceramic layer is deposited onto a porous support, and metallic interconnects are coated with conductive ceramics to improve their surface stability. Here, we report on SOFC interconnect coatings based on conductive perovskite and spinel oxides. A dual-layer ceramic interconnect is first discussed that consists of an n-type and p-type conducting layers. Then, protective ceramic coatings on metallic interconnects are presented, which are capable of mitigating oxide scale growth and inhibiting Cr evaporation. The synthesis of oxide materials and their electrical/thermal expansion properties are discussed in detail, followed by a description of coating processes. We demonstrate that the dense interconnect or protective layers are fabricated by a simple and cost-effective coating–sintering process and they exhibit low resistance and high stability under SOFC operating conditions.

Resume : Natural gas reformer

Resume : Micro pressure sensors have drawn much attention for recent decades due to the unique benefits of small size, low cost and high performance. In this study, a micro field effect transistor (FET) pressure sensor was fabricated using the commercial complementary metal oxide semiconductor (CMOS) process and micro electromechanical systems (MEMS) technology. The pressure sensor produces a change in current when applying a pressure to the sensing element and the electrical circuit was utilized to convert the current variation of the pressure sensor into the voltage output. The fabricated FET pressure sensor showed nearly perfect linear response for the pressure variation in the range of 0-1,200 kPa pressures. Experimental results showed that the pressure sensor had a sensitivity of 0.0096 μA/kPa in the pressure range of 0-1200 kPa. The developed FET pressure sensor with the micro-machined Si diaphragm structure showed good pressure sensing performances, and the proposed sensor design is found to be suitable for a pressure sensor device due to the highly sensitive pressure sensing responses and fast response/recovery properties to pressure changes.

Resume : Geographical limitations and uncertainties about the availability of lithium resources have led researchers to develop alternative battery chemistries such as Na-ion battery. The Na-ion battery has great potential due to the abundance and low price of sodium precursor for large scale energy storage devices. Thus, recently considerable research interest in Na-ion batteries has been rapidly increasing. Spinel NiCo2O4 has been widely investigated as a promising alternative anode material for Li-ion batteries due to its several inherent advantages, including low cost, abundant resources and good environmental benignity. In particular, NiCo2O4 can offer at least twice the capacity of the most common intercalation anode materials and possesses much better electronic conductivity compared to the binary transition metal oxides. The high electronic conductivity is beneficial for fast electron transfer in an electrode, however, the practical applications to the anode material are largely hindered due to its poor cycling performance. Nanostructural engineering can provide facile ion kinetics by a shorter diffusion length, high surface area and better accommodation of the strains, which results in improving the electrochemical energy storage properties. In this work, NiCo2O4 nanoneeldes were fabricated by a hydrothermal route. The physicochemical properties of the NiCo2O4 were characterized and the sodium storage performances were investigated.

Resume : Typical Cu(InGa)Se2 (CIGS) cell has a structure of SLG/Mo/CIGS/CdS/i-ZnO/ZnO:Al, and its current collection is primarily limited by several optical and collection losses of individual layers, i.e., shading from front grid, reflection from ZnO, absorption in ZnO and CdS layers, and incomplete generation and collection in CIGS absorber. In this contribution, Nd-doped ZnO (ZnO:Nd) and SnOx (SnOx:Nd) layer was explored to replace i-ZnO in the conventional CIGS cell structure for the potential use as a down-shifting or down-converting layer, and thus to increase light absorption and carrier collection. The Nd-doped ZnO and SnOx films with various Nd contents were deposited by magnetron sputtering system starting from a Zn target covered with small pieces of Nd, and then characterized by several techniques including XRD, Raman, SEM, TEM, RBS, UV-VIS, PL etc. For examples, the PL measurements revealed that the main emission peaks of Nd were detected in the near infrared region. The substrate temperatures during sputtering varied from 25 deg.C to 400 deg.C to determine optimum temperature for effective emission of Nd and improvement of cell performance. For cell fabrication, CIGS light absorber was prepared by typical three stage co-evaporation and CdS buffer layer was added by standard chemical bath deposition. Device performance of CIGS cell was characterized by QE and I-V measurements.

Resume : Zinc sulfide (ZnS) is an important semiconductor material with a wide energy band gap for various optoelectronic devices. In special, ZnS became an important material for a buffer layer in thin film solar cells because it does not have any environmental issue unlike CdS. It was reported that some amount of ZnO and Zn(OH)2 as the impurities, which are denoted in ZnS(O,OH), are required to be present in the ZnS thin films for fabricating the efficient photovoltaic devices. In this study, ZnS(O,OH) thin films were synthesized by a solution-based deposition method designed by a combination of a continuous flow reactor (CFR) process and a spray method, and then CIGS solar cells were fabricated with the prepared ZnS(O,OH) thin films in order to investigate the influences of the experimental parameters such as flow rate, annealing temperature, time, and film thickness on the performance of ZnS(O,OH) thin films. The CIGS absorber layer was deposited by a RF sputtering for this study. The films were characterized by XRD, SEM, EDX, UV-vis Spectroscopy, and XRD. The performances of the prepared CIGS solar cells were measured with Solar Simulator at AM 1.5. Based on the XRD and EDX, it was found that the molar ratio of zinc to sulfur, the annealing temperature of the as-deposited films, and reaction time exerted an effect on the characteristics of ZnS(O.OH) thin films. About 8% of efficiency was obtained up to now and more in depth investigations are in progress.

Resume : Tin dioxide is one of the most attractive materials studied in the last decade due to its several applications in optoelectronic devices, LCD screens, gas sensors, and solar cells. This n-type semiconductor combines several advantages such as a large band gap (around 3.6 eV for bulk material at 300 K), a high exciton bending energy of 130 meV, a good conductivity and a high carrier concentration, thanks to the high concentration of native oxygen defects. In addition to the TCO properties, doping SnO2 films with rare earth (RE) elements (such as Yb, Pr, Tb, Nd) can enhance their photoluminescence properties thanks to the optical transitions involving the 4f shell of the dopant. However, the transparency and conductivity properties of such RE doped SnO2 films should not be affected by doping. In this paper, we report on the properties of Neodymium doped SnO2 thin films versus the deposition temperature using a reactive magnetron sputtering. The Nd concentration was kept at 0.62 at. % while the substrate temperature was varied from 25 to 400 °C. The crystalline structure was investigated by XRD measurement and TEM microscopy. The chemical composition of the doped films was carefully studied using XPS spectroscopy. No secondary phases like Nd oxides are detected, which indicates that Nd is successfully inserted into the SnO2 host matrix. The UV-Vis-NIR spectroscopy revealed the decrease of the band gap by increasing the deposition temperature until 300°C and then it increases at 400°C. The investigation of the photoluminescence properties under a 325 nm laser excitation show intense emission peaks at 885, 1065 and 1336 nm. Such strong PL signal indicates that Nd3+ ions are optically active in the SnO2 matrix. The electrical properties of the Nd:SnO2 are found to be sensitive to the substrate temperature. Resistivities as low as 0.03 .cm and mobilities as high as 43 cm2/V.s were measured. The Nd:SnO2 films were further inserted into CIGS/CdS based solar cells to serve as TCO as well as photon down shifter layer. The photovoltaic properties showed an increase in cell efficiency by a factor 5 for samples covered with Nd:SnO2 films deposited at 300°C. Such result shows the great potential of these RE doped SnO2 layers to solar conversion.

Resume : Several structural and optical properties of ceria (band gap, refractive index and lattice parameter) make this material very promising for applications in optoelectronics and photovoltaics. In particular, CeO2 can be efficiently functionalized by doping with trivalent rare earth ions to give rise to photon management properties. In this work, we show that Sm and Nd ions can be successfully inserted in CeO2 thin films by using pulsed laser deposition starting from RE-doped pellets. We show that the films are characterized by interesting photon management properties even at a relatively low deposition temperature (400 °C), which is compatible with photovoltaics. By combining the information obtained from different structural (XRD, XAS, …) and optical (absorbance, PL, PLE, …) characterization techniques, we demonstrate the presence of the trivalent ions in CeO2 and provide insight in the electronic level structure and in the transfer mechanisms. In particular, we give evidence that the energy transfer mechanisms can be fully explained only by considering the presence of Ce3+ ions in CeO2. The strong absorption cross section of f-d transitions on Ce3+ ions and high mobility of oxygen vacancies in ceria, that allows the formation of Ce3+ close to RE3+ ions, strongly increase the potential of these layers as downshifters and downconverters.

Resume : Polyaniline-emeraldine base [PANI (EB)] is one of the most studied conducting polymers due to its applications in electronics, optical device, sensors, etc. In order to enhance PANI (EB) functional properties, we have modified the PANI (EB) powder using plasma of low pressure RF (13.56 MHz) capacitively coupled discharge. The modification was based on the process of pulsed plasma polymerization of cyclopropylamine described previously to yield functional coatings containing up to 9 at.% of amine groups. The modified powder was analyzed by attenuated total reflection (ATR) infrared spectroscopy and X-ray photoelectron spectroscopy for chemical structure and electron microscopy for its morphology. Additionally, we have tested activity of plasma modified PANI (EB) against the cancer cells and studied interaction of proteins of the plasma-modified PANI (EB) in comparison with unmodified material.

Resume : We summarize recent research studies done in Korea Institute of Energy Research. Thin film silicon PV research in Korea Institute of Energy Research covers conventional PECVD deposition of hydrogenated amorphous silicon (a-Si:H) and thin film solar cells, silicon heterojunction solar cells, and synthesis of silicon and germanium nanoparticles. Light induced degradation and material quality are known to be major bottlenecks in industrial success of a-Si:H solar cells. Many deposition methods have been reported to produce a-Si:H films of superior material quality. In this work, we have tested different plasma process conditions from standard low-pressure a-Si:H to the film deposited near powder formation conditions, a.k.a. polymorphous silicon. Various PECVD deposited silicon thin films are compared considering their material properties and behavior when incorporated into single-junction solar cells. A wide process window varying hydrogen dilution, deposition pressure, temperature, and RF power have been explored. Wafer surface passivation using intrinsic a-Si:H is a way to realize high efficiency solar cells. Intrinsic a-Si:H works as an ideal material for passivation of crystalline silicon surface due to the low interfacial defect density. We demonstrate recent improvement of silicon heterojunction solar cells in Korea Institute of Energy Research. Synthesis of silicon nanocrystals during CVD process was initially a side effect of powder formation, but it has become over the years an exciting field of research and has opened the way to new opportunities in the field of materials deposition. We introduce various methods to synthesis silicon nanoparticles including CCP and ICP type PECVD, as well as CO2 laser pyrolysis and their application to energy devices.

Resume : Thin films of CuInSe2 (CIS) were grown on Mo-coated glass substrates by spray coating technique using nanocrystalline ink composed of binary Cu-Se and In-Se nanoparticles with iso-butyl alcohol as the solvent. The grown films were subsequently annealed in vacuum (inert) and selenium atmosphere, and the properties of these films examined by various characterization techniques. The vacuum heat-treated films showed CuSe binary phase with CuInSe2, whereas the heat-treated films under excess selenium environment showed a single phase CuInSe2. Micro-Raman analysis showed Cu-Se binary phase in addition with CuInSe2 phase in vacuum annealed as well as selenized films. However, the intensity of CuSe peak was smaller for selenized films. Morphological studies revealed that both vacuum annealed and selenized films had sizable grains. The band gap energies of as-prepared CIS films were estimated from low temperature photoluminescence, and the variation in chemical composition was characterized by EDS. The obtained properties of CIS films are promising to be used for photovoltaic applications.

Resume : Future perspectives of earth-abundant Cu2ZnSnS4 solar cells

Resume : The purpose of this talk is to provide an overview of the most recent theoretical studies undertaken by us in the field of solar energy materials research. On selected examples, the application of our computational tool of choice, density functional theory, will be illustrated to show how ab initio calculations can be of use in the effort to reach a better understanding of energy materials and to occasionally also guide the search for new promising approaches. I will talk about TiO2 based Solar Cells, CIGS & ZnO based solar cells.

Resume : Application of perovskite layers to silicon solar cells

Resume : Modern topics in materials science and energy technology and the need for greater efficiency in energy consumption pave the way for joint research and development collaborations between Europe and South Korea. The semiconductor silicon carbide has become a key-enabling material for power electronic applications. Highly developed labs at Universities and in industrial environments in both countries are ideal seeding points for joint technology development. In the presentation, the model of a joint research and development project in the frame of materials growth of silicon carbide using a common experimental platform, i.e. identical growth setups in both labs in Europe and South Korea, will bedescribed. Benefits and challenges for both partners will be addressed.

Resume : In recent years, there has been a global trend of increasing the penetration of renewable energy into the power system. However, due to the intermittent behavior of renewable energy sources the performance of power system is sometimes critically constrained by stability characteristics especially to bulk power system. Therefore, it has been proposed that the large-scale Energy Storage System (ESS), which power output can be quickly and accurately controlled, will be applied to bulk power system for securing the stability of the power system even with a very high penetration of renewable energy resources. As the power system stability is of high concern during transient period when a disturbance occurs, a very responsive and efficient control algorithm is required to optimize the performance of ESS. An operation strategy is developed to implement the large-scale 4MW/8MWh BESS using Lithium-ion battery (LiB), and to improve the effectiveness of the Lithium-ion battery. The 4MW/8MWh BESS is simultaneously connected with 22.9kV substation bus and distribution line for offshore wind turbines on the sea. Grid connection method of BESS can be configured in three different ways: 1) 4MW/8MWh BESS can be connected in the substation bus; 2) 4MW/8MWh BESS can be connected in the distribution line for wind power; 3) each 2MW/4MWh BESS can be connected in the substation and the distribution line for wind power. Also, a demonstration study scheme on BESS is proposed to confirm the effectiveness of peak shaving, frequency regulation and smoothing of wind power using BESS in Jeju grid.

Resume : Closing remarks of the EU-SK workshop

Resume : Closing remarks of the EU-SK workshop