In addition to mobile electrons and holes, the mobile ions in metal halide perovskites redistribute under an applied electric field. It negates many benefits of standard spectroscopic techniques to quantify mobility, such as nanosecond to millisecond transient methods, time-of-flight and space charge limited current measurements. Indeed, an accurate estimation of charge carrier density is hindered by early-time recombination, the branching ratio of excitons to free-carriers and sensitivity to short-range conductivity. It is also important to understand the long-range charge transport within the metal halide perovskite for optimisation of operating devices, where the charges have to travel over on the order of microns, and if these properties change in different carrier density regimes, or through different methods of processing the films. Here this presentation introduces applied methodologies and also highlights an advanced optical and electrical methodologies: Photoinduced transmission and reflection (PITR), Transient photoconductivity (TPC) and Pulsed-voltage space charge limited current (PV-SCLC). With these methods, we accurately estimated the internal free-carrier density during photo-excitation, accounting for both early-time recombination and exciton-to-free-carrier branching ratios to determine long-range charge carrier mobility in metal halide perovskite thin films and single crystals, to be reliable value over many orders of magnitude of charge density. We believe this study is the accurate evaluation of photo-induced long-range mobility of metal halide perovskites, and therefore represents a powerful handle for future optimisation of perovskite solar cells and optoelectronic devices.

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A hybridized electromagnetic-triboelectric nanogenerator is to utilize electromagnetic and triboelectric nanogenerators to simultaneously scavenge mechanical energy from one mechanical motion. As compared with the individual energy harvesting unit, the hybridized nanogenerator has much larger output power, higher conversion efficiency so that it can be used to solve the power source issue of some devices with larger power consumption. The hybridized nanogenerators have the potential applications in self-powered sensors, wearable devices, and networks.
Rapid advancements in various energy harvesters impose the challenge on integrating them into one device structure with synergetic effects for full use of the available energies from our environments. We report a multi-effects coupled nanogenerator based on ferroelectric barium titanate, promoting the ability to simultaneously scavenging thermal, solar, and mechanical energies. By integration of a pyroelectric nanogenerator, a photovoltaic cell and a triboelectric-piezoelectric nanogenerator in one structure with only two electrodes, multi-effects interact with each other to alter the electric output, and a complementary power source with peak current of ~ 1.5 µA, platform voltage of ~ 6 V and peak voltage of ~ 7 V is successfully achieved. Compared with traditional hybridized nanogenerators with stacked architectures, the one-structure-based multi-effects coupled nanogenerator is smaller, simpler and less costly, showing prospective in practical applications and represents a new trend of all-in-one multiple energy scavenging.

Beyond the rigid or flexible frame-based electronics, the development of stretchable electronics for implementing wearable/attachable electronics or electronic/ionic skin, consisting of transistor, luminescence devices, smart sensors, and energy devices received great attention. It is required to be thin, light, stretchable, and transparent to be integrated with clothes/wears or attached on or implanted into curved human body. The triboelectric nanogenerators (TENG) convert mechanical energy into electrical energy is receiving great attention as a sustainable power source for portable/stretchable electronics because of its simple structure, many materials options, low cost/easy fabrication, and superior power output performance. In this presentation, we introduce polymer gel based stretchable, transparent, and high performance TENG that can harvest biomechanical energy and tactile sensing. We have fabricated ionic/nonionic polymer gel based dielectric layers and investigated its dielectric property, electrical conductivity, and triboelectric property. The fabricated polymer gel has improved its transparency and stretchability. Beside it exhibited an extremely improved dielectric constant and very strong triboelectric behavior that can contribute to enhanced TENG performance. In addition, we introduce a new type of tactile sensor based on charge displacement current that can sense position and pressure without electrode grid patterning.

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Organic-inorganic metal halide perovskite solar cells (PSCs) have been improved rapidly, and their photoelectric conversion efficiency (PCE) was increased from 3.8% in 2009 to over 25% in 2020. Since PSCs can be produced easily and inexpensively by simple processes such as printing and coating, the world-wide activities of research and development have been conducted for the commercialization of this technology. However, since the organic substances used in PSCs are unstable with respect to the ambient air, moisture, and heat, there has been a great deal of interest in improving durability, recently. In addition, the components of PSCs, such as hole transport materials (e.g., spiro-OMeTAD) and metal counter electrodes (e.g., Au or Ag), are expensive, and utilization of such materials can be a hindrance for the low-cost PSCs. Using only low-cost materials (without Au, Ag and spiro-OMeTAD), in 2013, the group of Hongwei Han (HUST, Wuhan, China) first reported hole-conductor-free fully-printable multi-porous-layered-electrode perovskite solar cells (MPLE-PSCs). The MPLE-PSCs show extremely high stability against light and heat. In this presentation, the latest progress about MPLE-PSCs will be shown in our group (for example, stability at 120°C for 4500 h, and at 85°C-85%RH for 2000 h).

Recently, metal halide perovskite solar cells (PSCs) has reached a certificated efficiency of 25.5% within a decade and will definitely keep increasing rapidly to 26%. Among various approaches, the interfacial engineering is the crucial one to maximize the performance of PSCs, which not only can control the interfacial charge extraction properties but also can improve the quality of absorber layer with enlarged grain size and reduced defects. Herein, we will introduce several effective passivating materials and techniques to boost the performance of PSCs. First of all, PTAA, which is commonly used as hole transport layers (HTM), is used as a thin interfacial layer to modify the interfacial properties of PSCs. Secondly, post-treatment with FAI/IPA can effectively rebalance the composition of facial perovskite layer for reduced defects density and better quality. Thirdly, passivating agents containing various functional groups are employed to improve the quality of perovskite absorbers, and the mechanism of those interfacial engineering will be introduced.

The all-inorganic lead halide perovskite without volatile component would be a promising alternative candidate for high efficiency photovoltaics. However, the all inorganic black phase CsPbI3 face the challenges of low room temperature phase stability and relative low efficiency. To enhance the performance and stability of all-inorganic CsPbI3 perovskite, the 2D/3D configuration was introduced to stabilize the black phase CsPbI3. The 2D based on EDAPbI4 help stabilize black phase CsPbI3 to achieve up to >11% efficiency. Furthermore, a facile organic cation surface termination approach was developed to significantly enhance the stability and performance of α-CsPbI3 solar cell with >15% efficiency. The bifunctional stabilization of CsPbI3 with gradient Br doping and organic cation termination finally improve the efficiency of CsPbI3 perovskite solar cells to a record value of 17% with enhanced stabilities. Recently, a concept new beta phase CsPbI3 with better phase stability push the efficiency up to 19%. In all, the CsPbI3 perovskite would be an ideal candidate for stable and efficient perovskite photovoltaics

The tandem solar cells, which based on dual junctions combining wide-bandgap top cells (e.g., ~1.7–1.9 eV) and narrow-bandgap bottom cells (e.g., ~0.9–1.3 eV) are considered as an effective strategy to overcome the Schokley-Queisser (S-Q) limit (~31-33%) of single-junction solar cells. Organic-inorganic metal halide perovskite (PVSK) materials is one of the most promising candidates for the top- and bottom-cell in tandem devices (e.g., PVSK/PVSK, PVSK/Cu(In,Ga)Se2 (CIGS), and PVSK/Si) owing to their flexible bandgap-tunability, low-cost processing, and various
formation routes like spin-coating, blade-coating, vacuum deposition. One of the critical challenges in developing tandem devices using perovskite is to prepare highly efficient wide- or narrow-bandgap perovskite solar cells (PSCs) for top- and bottom-cells, respectively. Among the various efforts such as composition engineering, morphology control, contact layer improvement, and defect passivation for improving the performance of PSCs, the formation of a 2-dimensional (2D) passivation layer using large organic cations (e.g., butylammonium or phenethylammonium) have been considered one of the most promising approaches. However, some challenges have led to lower performance in 3D/2D mixed PVSK due to the limitation of charge transport caused by the long and bulky organic cation from the 2D passivation layer. This presentation introduces the various strategies like cation/anion engineering in 2D parts and dipole engineering to demonstrate a highly efficient 3D/2D PSCs with various bandgap (1.23 eV and 1.68 eV). Based on our strategies, we finally demonstrated highly efficient and stable PVSK based tandem solar cells with various kinds of bottom cells combination like Perovskite, CIGS, and Si.

Metal halide perovskites (MHPs) for photovoltaic applications have the general stoichiometry formula of ABX3, with A as the monovalent organic or inorganic cation, B as the divalent lead or tin cation, and X as the halide anion. The A cation itself does not directly contribute to the band edge states. However, the A cation was found to significantly influence the physical, chemical, and optoelectronic properties of MHPs. Resultingly, engineering of the A cation has enabled important breakthroughs to enhance the performance and stability of perovskite solar cells (PSCs). In this presentation, I will report novel ‘A’ site cation engineering strategies for enhancing power conversion efficiencies (PCEs) and stability of the PSCs. Incorporation of over- or under-sized ‘A’ was found to induce strain in the bulk lattice of the MHPs, allowing for modulation of ion migration energetics in the bulk lattice. We demonstrate the induced strain can enhance the activation energy barrier for ion migration to significantly improve operational stability of the PSCs. In addition, I will also report utilization of bulky organic cationsto passivate surface defects of the MHP thin films. The rational strategies for maximizing the surface passivation effects with minimized side effects will be presented.

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In addition to mobile electrons and holes, the mobile ions in metal halide perovskites redistribute under an applied electric field. It negates many benefits of standard spectroscopic techniques to quantify mobility, such as nanosecond to millisecond transient methods, time-of-flight and space charge limited current measurements. Indeed, an accurate estimation of charge carrier density is hindered by early-time recombination, the branching ratio of excitons to free-carriers and sensitivity to short-range conductivity. It is also important to understand the long-range charge transport within the metal halide perovskite for optimisation of operating devices, where the charges have to travel over on the order of microns, and if these properties change in different carrier density regimes, or through different methods of processing the films. Here this presentation introduces applied methodologies and also highlights an advanced optical and electrical methodologies: Photoinduced transmission and reflection (PITR), Transient photoconductivity (TPC) and Pulsed-voltage space charge limited current (PV-SCLC). With these methods, we accurately estimated the internal free-carrier density during photo-excitation, accounting for both early-time recombination and exciton-to-free-carrier branching ratios to determine long-range charge carrier mobility in metal halide perovskite thin films and single crystals, to be reliable value over many orders of magnitude of charge density. We believe this study is the accurate evaluation of photo-induced long-range mobility of metal halide perovskites, and therefore represents a powerful handle for future optimisation of perovskite solar cells and optoelectronic devices.

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All-solid-state lithium batteries (ASSLBs) have the potential to increase energy density, improve safety, and allow for lower manufacturing costs compared to conventional, liquid-based Li-ion batteries. In this talk, I will first present cobalt-free solid-state Li batteries using 50 um-thick sulfide-based solid electrolyte (SE). We demonstrate a high-energy ASSLB using an organic cathode material. The use of organic materials in ASSLBs brings many new possibilities to the technology due to their unique feature set of material availability, mechanical properties, electrode reaction characteristics. Furthermore, the thickness of SE layer dictates the cell-level energy density and it is desirable to make the SE layer as thin as possible while maintaining uniformity and defect-free. We show a strong correlation between the solid loading of dispersions and the quality of tape-casted thin SE films. We developed an imaging technique to characterize large areas of films and to quantify their quality by using histograms of the tonal contrast within the images. Stable cycling of Li metal could be realized when inserting a unique designed interlayer in between solid electrolyte and Li metal. In the second half of this talk, I will present an air-free vessel design for operando diagnosis of ASSLBs. The vessel is equipped with a micro-cell mount where electrochemical tests are performed in situ. Heating and pressure applying/sensing modules are also integrated in the platform. The air-free design allows transfer of an air-sensitive ASSLBs between different analytical instruments. We demonstrate successful operando characterizations of microstructures under electron microscopy and optical microscope. A consolidated in situ structural-chemical-mechanical diagnostic platform is under development that will provide unprecedented insights into the failure mechanisms of ASSLBs.

Acknowledgment: This work is supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Vehicle Technologies Program under Contract DE-EE0008234 and DE-EE0008864 (Program manager: Tien Duong).

Electrifying transportation systems to reduce our dependence on fossil fuels is a critical priority to address climate change, and more powerful and affordable batteries are key to accelerate the adoption of zero-emission electric vehicles (EV). Recently, we developed a stable, fast-charging battery that comprises i) a lithium metal anode, ii) a heavy-metal free cathode involving iodide conversion reactions, and iii) a stable liquid electrolyte with high flash point. The unique combination of these materials has demonstrated remarkable performance including outstanding power density, fast charging time, and prolonged cycle life, surpassing conventional lithium-ion batteries. In this talk, the fundamental electrochemistry and interfacial phenomenon responsible for this new battery system’s excellent performance will be discussed along with our strategies to accelerate the process of further improvement and optimization of this battery system.

Graphitic C3N4 is prepared to work as a bifunctional photocatalyst for Li-O2 battery to accelerate formation and decomposition of Li2O2 under UV light irradiation. At 0.04 mA cm-2, the discharge voltage of Li-O2 battery is significantly increased to 3.22 V, surpassing the thermodynamic limit of 2.96 V, and the charge voltage is reduced to 3.38 V. After the plasmonic Au nanoparticles (NPs) are loaded onto nitrogen-deficient C3N4 to form Au/NV-C3N4 heterojunction, its absorption and carrier lifespan are significantly enhanced to visible light and prolonged. The achievable discharge voltage of Au/NV-C3N4 reaches 3.16 V, surpassing the equilibrium voltage by 200 mV; the charge voltage was decreased to 3.26 V at 0.05 mA cm-2, corresponding to an ultrahigh round-trip efficiency of 97.0%. The superior battery performances are rewarded by the plasmon-induced hot electron transfer from Au to NV-C3N4 and good matching of carrier lifespan with oxygen redox kinetics on Au/NV-C3N4. At the same time, metal-organic polymer nanosheets of Co-TABQ as a cathode catalyst promote formation and oxidation of Li2O2 under visible light. It was revealed that Co atoms of Co-TABQ are oxygen reduction sites. During discharge, O2 is adsorbed on the Co atoms and reduced to LiO2 by accepting electrons in its π2p* orbitals from the dz2 and dxz orbitals of Co atoms of the illuminated Co-TA BQ, and it then transforms to the final product of Li2O2. Upon charging, the holes in the VB of the illuminated Co-TABQ oxidize Li2O2 to Li+and O2 without intermediates with an applied voltage.

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The ongoing surge in demand for flexible/wearable electronics, self-powered systems, soft robotics, and Internet of Things (IoT) has inspired the relentless pursuit of form factor-free, high-performance power sources that can be monolithically and seamlessly integrated with various electronic devices. From the viewpoint of cell design and architecture, conventional assembly and materials have pushed the power sources to lack of variety in form factors, thus imposing formidable challenges on their integration into versatile-shaped electronic devices. This talk describes a new class of nanoprinted artistic power sources, with particular attention to their design diversity and performance compatibility with newly emerging complex-structured electronic devices. The printed power sources are fabricated directly on arbitrary objects of complex geometries through a variety of simple, low-cost and scalable nanoprinting processes. Their salient features include various form factors, shape conformability, and monolithic integration with devices of interest. A key-enabling technology for the nanoprinted power sources is the design of battery inks (in particular, electrode and electrolyte inks), with a focus on their rheology and electrochemistry. Our research interests are directed to discussing effects of the battery inks on printing processability, nanostructure (focusing on bicontinuous ion/electron transport channels), artistic versatility, and electrochemical performance of the resulting nanoprinted power sources. We envision that the nanoprinted power sources open a new avenue towards form factor-free/monolithic integrated power sources with object-tailored design versatility and dimensional conformability.

Aqueous zinc-based flow batteries are an attractive option for energy storages system due to their inflammability and high energy density. However, Zn dendrite formation, which causes internal short circuit and capacity drop, limits long-term operation of Zn-based batteries. Uncontrolled Zn nucleation/growth or Zn-ion transport leads to inhomogeneous Zn reaction and triggers dendritic Zn growth. In this aspect, advanced engineering of the Zn/substrate and Zn/electrolyte interface, which can control these processes, is strongly demanded. In this talk, we present that an atomistic-designed carbon current collector and a structured interlayer on Zn electrode can control these interfacial processes for inducing dendrite-free Zn deposition. By experimental and computational analysis, the working mechanism of the advanced interfaces is elucidated. The performances and durability of the Zn batteries exploiting the advanced interfaces demonstrate the efficacy of the advanced interfacial engineering on achieving reversible Zn electrode.

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Photoelectrochemical water splitting presents an attractive strategy to produce hydrogen gas as an alternative clean fuel in an environmentally benign and sustainable manner. The key component of a photoelectrochemical cell is a semiconductor electrode (photoelectrode) that absorbs solar light to generate, separate, and transport charge carriers to the semiconductor/electrolyte interface to participate in desired chemical reactions. The electron-hole separation and interfacial charge transfer of the photoelectrode are considerably affected by the interfacial energetics between the photoelectrode and the electrolyte and/or between the photoelectrode and the buffer, protection, or catalyst layers; hence, the interfacial properties of a photoelectrode are as important as the bulk properties of the photoelectrode.
To date, strategies for altering the atomic arrangement at the photoelectrode surface that do not involve extrinsic doping have mainly involved changing the semiconductor surface facets. However, for ternary oxide photoelectrodes with a formula of AxByOz, there exist numerous ways to terminate the surface even for the same facet. For example, the surface can be terminated with A-O or B-O, and the surface A:B ratio may be different from the bulk A:B ratio. In fact, if not grown as single crystals, AxByOz photoelectrodes can have an A-rich or B-rich surface depending on the synthesis method, which can affect their photoelectrochemical properties. However, despite being important and ubiquitous, the effects of surface termination/composition on a ternary oxide photoelectrode have not been systematically studied, and the atomic origin of their effects on interfacial energetics and photoelectrochemical properties have not been elucidated.
In this presentation, we will discuss the effects of surface termination/composition on the interfacial energetics and photoelectrochemical properties of photoanodes using BiVO4 as an example. We will compare epitaxially grown BiVO4 photoelectrodes with V-rich and Bi-rich (010) exposed facets and demonstrate that the surface Bi:V ratio has a considerable effect on the surface energetics and photocurrent generation of BiVO4 even for the same (010) facet.

Photocatalytic water splitting is a challenging reaction because it is an ultimate solution to resources, energy, and environment issues. Photocatalytic CO2 fixation has also attracted attention. These can be regarded as artificial photosynthesis, because light energy is converted to chemical energy. In the present paper, I introduce various metal oxide and sulfide photocatalysts for the water splitting and CO2 reduction.
AgTaO3 and Na0.5Bi0.5TiO3 of valence-band-controlled metal oxide photocatalysts gave 40% at 340 nm and 5.1% at 350 nm of apparent quantum yields, respectively. SrTiO3:Rh and several metal sulfides of a H2-evolving photocatalyst and BiVO4 of an O2-evolving photocatalyst constructed various type of Z-schematic photocatalyst systems with Fe3+/Fe2+, [Co(bpy)3]3+/2+, and a conductive reduced graphene oxide (RGO) as an electron mediator, and even without an electron mediator. Ag cocatalyst-loaded ALa4Ti4O15 (A = Ca, Sr, and Ba) and tantalates photocatalysts such as NaTaO3:Ba with 3.79–4.1 eV of band gaps show activities for CO2 reduction to form CO and HCOOH in an aqueous medium. We also constructed a Z-scheme system using CuGaS2 of a CO2-reducing photocatalyst with BiVO4 of an O2-evolving photocatalyst and RGO of an electron mediator for CO2 reduction using water as an electron donor.

Conjugated polymers have recently emerged as promising candidates for photocatalytic H2 production owing to their structural designability and functional diversity. However, limited by the fast recombination of photoexcited electrons and holes, their H2 production rates usually fall far behind expectations. To this end, we for the first time design molecular heterostructures of covalent triazine frameworks to facilitate the charge carrier separation and promote the photocatalytic H2 production. Benzothiadiazole and thiophene moieties are selectively incorporated into the covalent triazine frameworks as the electron-withdrawing and electron-donating units respectively via a rationally designed sequential polymerization strategy. Resultant hybrids exhibit much improved charge carrier separation efficiency as evidenced by a range of photophysical and electrochemical characterizations. Most impressively, a significant H2 evolution rate of 6.6 mmol g-1h-1 is measured for the optimal sample under visible light irradiation (λ>420 nm), which is far superior to most other conjugated polymer photocatalysts reported in literature.

Semiconductor materials hold the key for efficient photocatalytic and photoelectrochemical water splitting. In this talk, we will give a brief overview of our recent progress in designing semiconductor nanomaterials for photoelectrochemical energy conversion including solar hydrogen generation. In more details, we have been focusing on a couple of aspects; 1) band-gap engineering, facet and oxygen vacancy control of low-cost metal oxide based semiconductors including TiO2, Fe2O3, BiVO4 and Cu2O for new photoelectrode design, and 2) the combination of high performance photoelectrodes with hybrid perovskite solar cells towards unassisted water splitting process with solar-to-hydrogen conversion efficiency of >6.5%. The resultant material systems exhibited efficient photocatalytic performance and improved power conversion efficiency in solar cells, which underpin sustainable development of solar-energy conversion application.

Solar-chemical production inspired from nature has attracted substantial attention due to a need for developing sustainable future energy as well as chemical resources. In order to achieve a highly efficient solar energy to chemical conversion device using CO2 and water as feedstock the development of several important components such as photoelectrode, catalytic electrodes, membrane, etc. is required. Among them, this lecture focuses on a Cu(InxGa1-x)(SySe1-y)2 (CIGS) thin film photovoltaic technology, which is a very attractive candidate for photoelectrode application of solar-chemical production system because they are durable enough and cost effective with high efficiency. To make the CIGS photovoltaics more cost effective solution processed CIGS thin film preparation has been suggested and developed. In spite of several successful demonstrations most solution based methods resulted in lower photovoltaic performance than vacuum based counterpart to date. In this presentation several strategies for realizing highly efficient and useful solution processed CIGS thin film photovoltaics will be introduced. They include multi-stage paste coating method, doping method, and nanostructuring method that have been being developed in our laboratory.

It is of great importance to reduce the amount of noble metals in the chemical industry. In this sense, single atom or atomically dispersed catalysts have attracted much attention due to high metal utilization and unique catalytic property. In this presentation, we will show a combination of density functional theory (DFT) and experimental approaches to explore the stability and electrocatalyic activity of a wide range of metal single atoms on a TiC support. We also tuned and enhanced the activity of Fe-N-C, atomically dispersed electrocatalyst, by givign the effect of electron withdrawing/donating functionalities.

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Development of DNA-based molecular machines and robots has attracted much attention due to their promising applications in medical, agricultural, and environmental technologies. DNA nanodevices and nanomachines have been constructed based on DNA sequence design, which enables us to program functions and to control the devices and machines according to the program. It is expected to construct cell-like multifunctional and intelligent molecular robots by extending the DNA nanotechnology. In this presentation, we will introduce our recent progress on DNA droplet technology. Cell-sized functional microdroplets have been constructed with DNA nanostructures, and their dynamical functions and behaviors have been controlled in a programmable manner. Here, we will report two types of DNA-based droplets technology: (i) DNA origami-based emulsion and (ii) DNA liquid droplet.
First, we will report a DNA origami nanoplate-based emulsion with designed nanopore function [1]. We constructed DNA-nanoplate-stabilized emulsion because DNA nanoplate produced by DNA origami method will have the design programmability. Here, we generated hexagonal DNA nanoplate using DNA origami technology. The DNA nanoplates were amphiphilized by the modification of the only one face of the hydrophilic DNA nanoplate with hydrophobic cholesterol groups. An aqueous solution of the amphiphilic DNA nanoplate was put into an oil phase of mineral oil, and then the two-phase solution was emulsified. By the microscopic observation, microemulsion stabilized with the amphiphilic DNA nanoplates was confirmed. Finally, we confirmed the ion transportation between contacted two droplets stabilized with the amphiphilic DNA nanoplates with a nanopore using a microdevice for ion current measurement. This result suggests that the integration of programmed function on DNA origami nanoplate-based emulsion.
Second, we will report a DNA droplet produced through liquid-liquid phase separation of a DNA nanostructure (named DNA Y-motif) solution [2]. In this study, we found that the phase behavior of DNA Y-motif could be controlled based on the sequence design of the terminal sticky end of the branches of DNA Y-motif. Also, we found that the fusion of the liquid-like DNA droplets could be controlled based on the sticky-end sequence and that the autonomous fission of DNA droplet could be achieved with enzymatic reaction. Finally, we demonstrated protein positioning in the DNA droplets based on the sequence. These results show that the condensed soft matter phase of DNA nanostructure can be used as a molecular robot body that has the integration ability of functional molecules such as proteins.
We believe that these technologies will promote the construction of molecular robots with integrated functions. Also, in the future, by the combination with biomembrane technology such as a DNA cytoskeleton [3] and the integration with electrical control device such as a computer-controlled artificial cell reactor [4], the functional molecular robots will be helpful in many fields mentioned above.

[1] Ishikawa, D., et al., Angew. Chem. Int. Ed., 58, 15299-15303 (2019).
[2] Sato, Y., et al., Science Advances, Vol. 6, no. 23, eaba3471, (2020).
[3] Kurokawa, C., et al., Proc. Natl. Acad. Sci. USA, 114(28), 7228-7233 (2017).
[4] Sugiura, H., et al., Nature Commun., 7, 10212 (2016).

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A particularly interesting application of diamond based quantum sensing is the detection of nuclear magnetic resonance on nanometer scales, including the detection of individual nuclear spins or small ensembles of external nuclear spins. Single nitrogen vacancy (NV) color centers in diamond currently have sufficient sensitivity for detecting single external nuclear spins and resolve their position within a few angstroms. The ability to bring the sensor close to biomolecules by implantation of single NV centers and attachment of proteins to the surface of diamond enabled the first proof of principle demonstration of proteins labeled by paramagnetic markers and label-free detection of the signal from a single protein. Single-molecule nuclear magnetic resonance (NMR) experiments open the way towards unraveling dynamics and structure of single biomolecules. However, for that purpose, NV magnetometers must reach spectral resolutions comparable to that of conventional solution state NMR. New techniques for this purpose will be discussed. Most of mentioned above results obtained so far with diamond centers are based on optical detection of single NV color centers. We will also show how photoelectrical detection of NV centers base on spin selective photoionization can provide robust and efficient access to spin state of individual color center.

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Layered topological materials such as topological insulators (TIs) and Weyl semimetals are a new class of quantum matters with large spin-orbit coupling. We reveal spin textures of such materials using the bilinear magneto-electric resistance (BMR) and photocurrent mapping. Topological surface states (TSS) dominated spin orbit torques are identified, and magnetization switching at room temperature is demonstrated in a topological material/ferromagnet (FM). Magnon-torque-driven magnetization switching is also demonstrated in the TI/NiO/FM devices at room temperature. In addition, topological materials can provide an alternative for rectification or frequency doubling. Looking towards the future, we hope that these studies will spark more works on harnessing spin currents at topological material/magnet interfaces and energy harvesting applications from topological materials.

Using green energy or increase energy efficiency is the key to a sustainable world. I will introduce the potentials of 2D materials to build a sustainable world in terms of low-cost H2 generation, low-power-consuming devices, and IA enabled optimization of novel materials. Semiconducting catalysts are great candidates to replace noble metal to make green energy such as H2 due to their low cost. Using 2D materials as the model system, we have revisited the semiconductor-electrolyte interface and unraveled a universal self-gating phenomenon through micro-cell based measurements [1]. We unveiled a surface conductance mechanism that dominates the charge transport in semiconductor electrocatalysts. Based on this, we provided a guideline on how to design high-performance semiconductor electrocatalyst. Apart from the generation of green energy, we are also using 2D materials to build next-generation CMOS architecture, such as negative capacitance field-effect transistors, which may dramatically reduce the consumption of energy [2]. Finally, I will discuss our recent progress on the machine learning guided materials synthesis, as well as the novel design of neural networks hardware based on 2D materials [3].

[1] Yongmin He, et al., Self-gating in semiconductor electrocatalysis, Nature Materials, 2019.
[2] Xiaowei Wang, et al., Van der Waals negative capacitance transistors, Nature Communications 10, 3037, 2019
[3] Bijun Tang, et al., Machine learning-guided synthesis of advanced inorganic materials, Materials Today 2020. DOI: 10.1016/ j.mattod.2020.06.010

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Artificial Intelligence (AI) technology based on artificial neural networks is making a huge business and socioeconomic impact, changing our daily life. With an expectation of achieving a brain-like efficiency and large performance gain, there has been increasing interest to implement artificial neural networks using novel non-volatile memory devices. Novel cross-point array architectures based on resistive memory devices, which can be operated in a massively parallel manner, have shown potential to achieve a large acceleration in AI computation. For realization of such architectures in hardware, the specifications for synaptic devices are revealed to be different in many aspects with those for traditional memory devices, necessitating new material systems and device designs [1] for efficient AI computation. In this talk, I will overview the recent progress and effort to achieve ideal synaptic device characteristics for novel neuromorphic architectures, as exemplified in our recent experimental results on resistive memory devices (RRAM), capacitor-based approach, and 3-terminal ionic switching devices.

Optically-active defects in crystals can serve on-demand single photons and coherent spin qubits. Therefore, they provide important hardware for solid-state quantum architectures. However, limitation in optical interface and unwanted interaction in solid-state environment prevents efficient control and readout of the qubits states. Here, we present recent progress for high-resolution and high contrast optical interfaces for defect qubits as well as suppressed phonon interaction in point-planar defect complex in nanowire structures. Our approaches enable us to address defects with higher resolution and sensitivity, and therefore it will pave a new way of exploring solid-state quantum systems.

Quantum computer enables to solve complex problems faster than classical computer using quantum phenomena such as superposition and entanglement. Superconducting circuit is one of the leading platforms for realizing the quantum computer. The superconducting quantum computing systems including qubit can make circuit design with various parameters and are proper to expand to large-scale quantum system. In this talk, I introduce the superconducting quantum computing system in KRISS and present the latest progress on superconducting multi-qubit system. We characterized the qubit in the scalable quantum system and estimated the error rate of quantum gates. Also, we reconstructed various quantum states using single and two qubit gates.

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I will introduce and discuss about a new molecular computing chip, lipid nanotablet (LNT), that is based on a plasmonic nanoprobe-modified lipid bilayer. The LNT platform allows for reliably tracking and controlling the interactions between plasmonic nanoparticles in situ on a synthetic cell membrane surface. It will be shown that this LNT platform is versatile and powerful in providing a modular, scalable DNA computing platform for building a nanoparticle-based computing architecture and nanoparticle neural networks that can make autonomous logic decisions. The potential for using this LNT platform for next-generation smart biosensing applications will be also discussed.

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Nanocrystals exhibit a wide range of unique properties that depend sensitively on their size and shape. In this talk, I will elaborate several general and robust strategies for crafting a rich variety of functional 0D, 1D, shish-kebab, and Janus nanocrystals with precisely controlled dimensions, compositions, architectures, and surface chemistry by capitalizing on a set of judiciously designed unimolecular star-like, bottlebrush-like, worm-like, and Janus block copolymers, respectively, as nanoreactors. These strategies are effective and able to produce oil-soluble and water-soluble as well as stimuli-responsive monodisperse nanocrystals, including metallic, ferroelectric, magnetic, luminescent, semiconductor, perovskite, and their core/shell structures. The applications of these functional nanocrystals in self-assembly, control release, and energy conversion and storage (e.g., perovskite solar cells, LEDs, batteries, electrocatalysis, etc.) will also be discussed.

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Photoanodes that are effective in oxidizing water under visible light play an important role in construction of artificial photosynthesis systems such as overall water splitting, N2 fixation systems and so on.
In particular, gold nanoparticles (Au-NPs) loaded on titanium dioxide (TiO2) semiconductor system has been attracting much attention because it can absorb visible light due to localized surface plasmon resonance (LSPR) of Au-NPs. Such plasmonic Au-NPs not only function as a light-absorbing unit but also promote plasmon-induced hot carriers generation, and the charge separation of those hot carriers takes place at the Au-NPs/TiO2 interface, followed by reduction/oxidation reactions. However, the LSPR of a monolayer Au-NPs on a TiO2 substrate cannot achieve sufficient and broad-band light absorption, and the quantum yield of water oxidation reaction is still low.
Recently, we have developed a novel photoanode that utilized strong coupling between LSPR and Fabry–Pérot (FP) nanocavity to solve the issues of plasmonic water oxidation. In addition to increasing the absorption efficiency and broadening the absorption wavelength range, we also succeeded in improving the quantum yield of water oxidation reaction. The structure of the photoanode that exhibits strong coupling consists of Au-NPs/TiO2 thin film/Au-film (ATA). A component of the photoanode, TiO2 thin film/Au-film, act as a FP nanocavity. Strong coupling is induced when the resonant wavelengths of the nanocavity and the LSPR of Au-NPs match each other closely.
In my talk, the coupling strength of strong coupling system that depends on the number of Au-NPs per unit area will be introduced. In addition, using Au/Ag alloy NPs as a plasmonic component in the strong coupling photoanode to increase the coupling strength and the water oxidation reaction efficiency will also be talked.

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We demonstrate a new device architecture for flexible vertical Schottky barrier (SB) transistors and logic gates based on graphene–semiconductor–metal heterostructures and ion gel gate dielectrics. The vertical SB transistor structure was formed by (i) vertically sandwiching a semiconductor layer between graphene (source) and metal (drain) electrodes and (ii) employing a separate coplanar gate electrode bridged with the vertical channel through an ion gel. Various kinds of semiconductors such as transition mechanically-exfoliated metal dicharcogenides (MoS2 and WSe2), vacuum-deposited organic semiconductors (pentacene and PTCDI-C8), solution-processed indium-gallium-zinc-oxides, and polymer semiconductors were successfully applied as a vertical channel materials. The channel current was controlled by adjusting the SB height at the graphene/semiconductor heterojunction under application of an external gate voltage. The high intrinsic capacitance of the ion-gel gate dielectric facilitated modulation of the SB height at the source/channel heterojunction to around 0.5 eV at a gate voltage lower than 2 V. The resulting vertical SB transistors exhibited a high current density, a high on−off current ratio, and excellent operational and environmental stabilities. The simple structure of the unit transistor enables the successful fabrication of low-power logic gates based on device assemblies, such as the NOT, NAND, and NOR gates, prepared on a flexible substrate. The facile, large-area, and room-temperature deposition of both semiconductors and gate insulators integrates with transparent and flexible graphene opens up new opportunities for realizing graphene-based future electronics.

Supercapacitors (SCs) are an electrochemical energy storage device that can fill the gap between batteries and electrolytic capacitors. However, the widespread applications of commercialized carbonbased SCs are limited by their energy density, arising from their physical charge storage mechanism, which is by far lower than that of batteries. Moreover, the high-power applications of SCs are also limited by the slower kinetics than electrolytic capacitor due to the diffusion and distribution of ions onto the tortuous porous surface.
In this talk, I will introduce our recent progress on the rational design of 2D pseudocapacitive materials for high energy- and high power-oriented SCs applications. Firstly, I will address our contribution to the improvement of pseudocapacitance by the molecular level surface redox sites of 2D pseudocapacitive nanomaterials such as P-doped graphene and black phosphorus. In addition to energy aspect, we will focus on the kinetics feature of 2D MXenes, correlating with the multiscale structure and chemistry for ultrahigh power and high frequency response.

To achieve a high solar-to-hydrogen (STH) conversion efficiency, strategies towards high photocurrent together with sufficient onset potential should be developed. Herein, we report a SnS semiconductor as a high-performance photocathode. Utilizing a sulfur precursor with a weak dipole moment generates high-quality dense SnS nanoplates with enlarged favorable crystallographic facets and suppress anisotropic growth. Furthermore, the introducing Ga2O3 layer between SnS and TiO2 in SnS photocathodes efficiently improves the charge transport kinetics without charge trapping. The SnS photocathode reveals the highest photocurrent density of 28 mA cm−2 at 0 V versus the reversible hydrogen electrode. In this study, for the first time, we demonstrated overall solar water splitting by combining an optimized SnS photocathode with a Mo:BiVO4 photoanode, achieving a STH efficiency of 1.7% and long-term stability of 24 h. The high-performance and low-cost SnS photocathode represents a promising new material in the field of photoelectrochemical solar water splitting. Solar water splitting directly converts solar energy into H2 fuel that is suitable for storage and transport. We further develop elaborate strategies yielding a high photocurrent in a tandem configuration along with sufficient photovoltage. Highly efficient solar water splitting devices based on emerging low-cost Sb2Se3 photocathodes coupled with semitransparent perovskite photovoltaics were demonstrated. A state-of-the-art Sb2Se3 photocathode exhibiting efficient long-wavelength photon harvesting enabled by judicious selection of junction layers was employed as a bottom absorber component. The top semitransparent photovoltaic cells, i.e., parallelized nanopillar perovskites using an anodized aluminum oxide scaffold, allowed the transmittance, photocurrent, and photovoltage to be precisely adjusted by changing the filling level of the perovskite layer in the scaffold. The optimum tandem device, in which similar current values were allocated to the top and bottom cells, achieved an STH conversion efficiency exceeding 10% by efficiently utilizing a broad range of photons at wavelength over 1000 nm.

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With increasing concern about air quality in the government, particulate matter (PM) is considered one of the most problematic pollutants for human health. The major source of PM in urban areas is particles from the exhaust emission of vehicles. As exhaust PM emissions, containing a variety of hydrocarbons, could lead to respiratory disease, the governments have restricted the concentration of vehicular emission via the Environmental Act. Additionally, in order to reduce air pollution, users of vehicles with internal combustion engines have been encouraged to switch to electric vehicles (EVs) by incentivizing purchase subsidies. While exhaust PM emissions will approach zero in EVs, the total emission level of PM by switching to EV may not reduce as expected. The emission factor of PM (3.7-7.2. mg/km) for EVs is almost the same as that for diesel engine vehicles (2.9-6.1. mg/km). Notably, there is another crucial source of PM apart from exhaust derived PM; namely, non-exhaust sources, such as tire-wear, break-wear, road surface wear, and dust resuspension, act as major airborne pollutants.
Major non-exhaust sources including tire-wear and break-wear were related to carbon black (CB) due to their use as reinforcing agents in tire and break-pads. Thus, CB could be considered as the main component of non-exhaust PM. Although several toxicological studies have been reported on lung-inflammation by non-exhaust PM, CB particles released from tire-wear were of no interest to toxicologists as it is considered to be tightly bound in the rubber tire matrices. Similar arguments can be found in government reports; exposure to free-bound CB does not occur during the use of products wherein CB is bound to other matrices, and CB is generally bound within the rubber of a tire. These reports insisted that unbound CB is not generally released into the environment from tire-wear. However, tire-wear particles (TWP) can become fragmented by weathering effects, such as continuous abrasion on the road, resuspension of road dust, and temperature changes. Therefore, additional wear could release the CB tightly bound within the tire rubber into the environment in a free-bound form.
Herein, we investigated the potential release of nano-CB and the formation of unbound CB from TWP through weathering. Ball milling is used as green technology to prepare the free-standing nanoparticles and de-agglomeration of nanoparticles. TWP was obtained through the surface abrasion of commercial passenger car tires using steel graters; the grinding work for the obtained particles was conducted for 14 days using ball milling instruments. Nano-sized particles were obtained from the parent TWP with increasing milling time, and the presence of CB was confirmed by conducting various characterizations of secondary particles. Additionally, the particle size was measured in real time around highways, and the samples collected on the highway were analyzed for the existence of free-bound CB in the environment.

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In our previous study, we found that 20 nm-silica nanoparticles (SiNPs), but not 50 nm-SiNPs, induced an inflammatory response the lung of mice instilled repeatedly via the trachea for 90 days. To clarify the size-dependent response, we here compared the toxic mechanism of both sizes of SiNPs in vitro and in vivo. Cell viability decreased in cells exposed to both sizes of SiNPs compared with controls. The 20 nm- and 50 nm-SiNPs formed giant and autolysosome-like vacuoles in the cytosol, respectively, and structural damage of organelles, such as mitochondria, the endoplasmic reticulum (ER), lysosomes, and cell membranes, was more pronounced in cells exposed to 20 nm-SiNPs than in those exposed to 50 nm-SiNPs. While intracellular levels of reactive oxygen species were higher in cells exposed to both sizes of SiNPs compared with controls, intracellular calcium ions accumulated only in cells exposed to the smaller SiNPs. The total number of cells and the relative proportion of neutrophils were clearly elevated in the lungs of all mice exposed to 20 nm- and 50 nm-SiNPs compared with those in controls. Meanwhile, the levels of interleukin-6, macrophage inflammatory protein-1 alpha and monocyte chemoattractant protein-1 alpha significantly elevated only in the lungs of mice exposed to 20 nm-SiNPs. We also found that both sizes of SiNPs inhibited differentiation into M1 and M2 macrophages and decreased expression of adhesion molecules. Given that accumulation of giant vacuoles and dilation of the ER and mitochondria are key indicators of paraptosis, we suggest that 20 nm-SiNPs induce paraptosis-like cell death, leading to an inflammatory response.

Republic of Korea has established and promoted 「The Second Comprehensive Plan on Nano Safety Management (’17~’21)」at the governmental level in 2016, based on 「Mid-term plan for Nano Safety Management. In order to investigate the assessment of environmental exposure of nanomaterials in aqueous phase, we carried out following projects.
1. We have investigated the removal and release of NPs (TiO2 and ZnO) from field wastewater treatment plants
2. We have investigated the environmental monitoring of TiO2 NPs released from manufacturer.
3. We have monitored the environmental exposure of TiO2 and ZnO NPs released from cosmetic sunscreen in swimming pools.

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Nanomaterial development and research have precipitously increased recently, and engineered nano-related items are continuously introduced to the market. The use of nanomaterials extends to cosmetics, fabrics and clothing, personal care items, cleaning solutions, sporting equipment and electronics as well as toys for children; however, there are limited information of nanomaterials about the potential adverse effects in human health. In particular, potential adverse health effects of nanomaterials in developmental and reproductive function has been relatively less investigated in the nanotoxicology area. In this presentation, I will introduce the general overview of developmental and reproductive toxicities of nanomaterials and our toxicology study results with nanomaterials, including titanium dioxide, cerium oxide, zinc oxide, and silicon dioxide nanoparticles.

Plastic waste has been growing issue in environment and public health. There are various plastic depending on the chemical structure such as polyethylene (PE), polypropylene (PP), polystyrene (PS). Among them, PS nanoplastics were mainly used for risk assessment due to its commercial availability. However, PP is widely used plastics for packaging and mask and their risk assessment is rarely investigated due to the lack of reference materials. In this talk, I will present the synthetic methods of PP nano- and microplastics as reference materials and demonstrated their bioaccumulation study using zebrafish embryos. PP nanoplastics were prepared the modified non-solvent induced phase separation and fluorescently labeled by combined swelling-diffusion method. Their size was from hundreds nanometer to tens micrometer with spherical and fragmented shape. The red-fluorescent labeled nanoplastics were treated in zebrafish embroys for bioaccumulation study and found in mainly intestinal region of developing zebrafish with low mortality.

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For massive database-driven materials research, there are increasing demands for both fast and accurate quantum mechanical computational tools. Contemporary atomistic first-principles methods can be fast, sacrificing their accuracy, or be precise, consuming a significant amount of resources. Here, to overcome such a problem, we present a new first-principles computational method that exploits self-consistent determinations of the on-site and inter-site Hubbard interactions simultaneously and obtain band gaps of diverse materials in the accuracy of the GW method at a standard ab initio computational cost. We also obtain good agreements between computed and measured band gaps of low-dimensional systems, thus meriting this approach for large-scale as well as high-throughput calculations for various bulk and nanoscale materials with a higher accuracy.

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Display applications have become diverse and materials, device architecture and process should be selected considering resolution and area.
In this presentation, we will introduce multi-scale simulation approach for oxide TFT, OLED, and Quantum-Dot and discuss the key factors to enhance efficiency and reliability incorporating process variables. Additionally, we will introduce machine-learning technology for discovering new materials of OLED.