Fogging occurs when moisture condensation takes the form of accumulated droplets with diameters larger than 190 nm or half of the shortest wavelength (380 nm) of visible light. This problem may be effectively addressed by changing the affinity of a material’s surface for water, which can be accomplished via two approaches: i) the superhydrophilic approach, with a water contact angle (CA) less than 5°, and ii) the superhydrophobic approach, with a water CA greater than 150°, and extremely low CA hysteresis. To date, all techniques reported belong to the former category, as they are intended for applications in optical transparent coatings. A well-known example is the use of photocatalytic TiO2 nanoparticle coatings that become superhydrophilic under UV irradiation. Very recently, a capillary effect was skillfully adopted to achieve superhydrophilic properties by constructing 3D nanoporous structures from layer-by-layer assembled nanoparticles. The key to these two “wet”-style antifogging strategies is for micrometer-sized fog drops to rapidly spread into a uniform thin film, which can prevent light scattering and reflection from nucleated droplets. Optical transparency is not an intrinsic property of antifogging coatings even though recently developed antifogging coatings are almost transparent, and the transparency could be achieved by further tuning the nanoparticle size and film thickness. To our knowledge, the antifogging coatings may also be applied to many fields that do not require optical transparency, including, for example, paints for inhibiting swelling and peeling issues and metal surfaces for preventing corrosion. These types of issues, which are caused by adsorption of moisture, are hard to solve by the superhydrophilic approach because of its inherently “wet” nature. Thus, a “dry”-style antifogging strategy, which consists of a novel superhydrophobic technique that can prevent moisture or microscale fog drops from nucleating on a surface, is desired. Recent bionic researches have revealed that the self-cleaning ability of lotus leaves and the striking ability of a water-strider’s legs to walk on water can be attributed to the ideal superhydrophobicity of their surfaces, induced by special microand nanostructures. To date, the biomimetic fabrication of superhydrophobic microand/or nanostructures has attracted considerable interest, and these types of materials can be used for such applications as self-cleaning coatings and stain-resistant textiles. Although a superhydrophobic technique inspired by lotus leaves is expected to be able to solve such fogging problems because the water droplets can not remain on the surface, there are no reports of such antifogging coatings. Very recently, researchers from General Motors have reported that the surfaces of lotus leaves become wet with moisture because the size of the fog drops are at the microscale—so small that they can be easily trapped in the interspaces among micropapillae. Thus, lotuslike surface microstructures are unsuitable for superhydrophobic antifogging coatings, and a new inspiration from nature is desired for solving this problem. In this communication, we report a novel, biological, superhydrophobic antifogging strategy. It was found that the compound eyes of the mosquito C. pipiens possess ideal superhydrophobic properties that provide an effective protective mechanism for maintaining clear vision in a humid habitat. Our research indicates that this unique property is attributed to the smart design of elaborate microand nanostructures: hexagonally non-close-packed (ncp) nipples at the nanoscale prevent microscale fog drops from condensing on the ommatidia surface, and hexagonally close-packed (hcp) ommatidia at the microscale could efficiently prevent fog drops from being trapped in the voids between the ommatidia. We also fabricated artificial compound eyes by using soft lithography and investigated the effects of microand nanostructures on the surface hydrophobicity. These findings could be used to develop novel superhydrophobic antifogging coatings in the near future. It is known that mosquitoes possess excellent vision, which they exploit to locate various resources such as mates, hosts, and resting sites in a watery and dim habitat. To better understand such remarkable abilities, we first investigated the interaction between moisture and the eye surface. An ultrasonic humidifier was used to regulate the relative humidity of the atmosphere and mimic a mist composed of numerous tiny water droplets with diameters less than 10 lm. As the fog was C O M M U N IC A IO N

The dry-style antifogging properties of mosquito compound eyes and artificial analogues prepared by soft lithography: a superhydrophobic state with high adhesive force

Degradation mechanisms of proton exchange membrane fuel cell under typical automotive operating conditions

Design of Nanostructured Solar Cells Using Coupled Optical and Electrical Modeling Michael G. Deceglie † , Vivian E. Ferry ‡ , A. Paul Alivisatos ‡ , and Harry A. Atwater* ,† Thomas J. Watson Laboratories of Applied Physics, California Institute of Technology, Pasadena, California 91125, United States Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States Abstract: Nanostructured light trapping has emerged as a promising route toward improved efficiency in solar cells. We use coupled optical and electrical modeling to guide optimization of such nanostructures. We study thin-film n-i-p a-Si:H devices and demonstrate that nanostructures can be tailored to minimize absorption in the doped a-Si:H, improving carrier collection efficiency. This suggests a method for device optimization in which optical design not only maximizes absorption, but also ensures resulting carriers are efficiently collected. Keywords: Thin film solar cells, plasmon, nanophotonic, light trapping, simulation, device physics, silicon, photovoltaics In order to maximize solar cell efficiency, it is necessary to optimize both the electrical device physics and the optical absorption of the device. Typically, these two problems are treated separately,

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Design of Nanostructured Solar Cells Using Coupled Optical and Electrical Modeling - eScholarship

Despite the rapid increase of efficiency, perovskite solar cells (PSCs) still face some challenges, one of which is the current–voltage hysteresis. Herein, it is reported that yttrium-doped tin dioxide (Y-SnO2) electron selective layer (ESL) synthesized by an in situ hydrothermal growth process at 95 °C can significantly reduce the hysteresis and improve the performance of PSCs. Comparison studies reveal two main effects of Y doping of SnO2 ESLs: (1) it promotes the formation of well-aligned and more homogeneous distribution of SnO2 nanosheet arrays (NSAs), which allows better perovskite infiltration, better contacts of perovskite with SnO2 nanosheets, and improves electron transfer from perovskite to ESL; (2) it enlarges the band gap and upshifts the band energy levels, resulting in better energy level alignment with perovskite and reduced charge recombination at NSA/perovskite interfaces. As a result, PSCs using Y-SnO2 NSA ESLs exhibit much less hysteresis and better performance compared with the cells using pristine SnO2 NSA ESLs. The champion cell using Y-SnO2 NSA ESL achieves a photovoltaic conversion efficiency of 17.29% (16.97%) when measured under reverse (forward) voltage scanning and a steady-state efficiency of 16.25%. The results suggest that low-temperature hydrothermal-synthesized Y-SnO2 NSA is a promising ESL for fabricating efficient and hysteresis-less PSC.

Reducing Hysteresis and Enhancing Performance of Perovskite Solar Cells Using Low-Temperature Processed Y-Doped SnO2 Nanosheets as Electron Selective Layers.

Recent developments in catalyst-related PEM fuel cell durability

Fabrication of an Ionomer-Free Electrode Containing Vertically Aligned One-Dimensional Nanostructures for Alkaline Membrane Fuel Cells

Investigation of the correlation effects of catalyst loading and ionomer content in an anode electrode on the performance of polymer electrode membrane water electrolysis

Si-based magnetic tunnel transistor with high transfer ratio

Light Harvesting: Enhanced Light Harvesting in Mesoscopic Solar Cells by Multilevel Multiscale Patterned Photoelectrodes with Superpositioned Optical Properties (Adv. Funct. Mater. 36/2016)

Developing a method for fabricating high-efficient and low-cost fuel cells is imperative for commercializing polymer electrolyte membrane (PEM) fuel cells (FCs). This study introduces a mechanical and chemical modification technique using the oxygen plasma irradiation process for hydrocarbon-based (HC) PEM. The oxygen functional groups were introduced on the HC-PEM surface through the plasma process in the controlled area, and microsized structures were formed. The modified membrane was incorporated with plasma-treated electrodes, improving the adhesive force between the HC-PEM and the electrode. The decal transfer was enabled at low temperatures and pressures, and the interfacial resistance in the membrane-electrode assembly (MEA) was reduced. Furthermore, the micropillar structured electrode configuration significantly reduced the oxygen transport resistance in the MEA. Various diagnostic techniques were conducted to find out the effects of the membrane surface modification, interface adhesion, and mass transport, such as physical characterizations, mechanical stress tests, and diverse electrochemical measurements.

Segeun Jang

Papers

Fabrication of an Ionomer-Free Electrode Containing Vertically Aligned One-Dimensional Nanostructures for Alkaline Membrane Fuel Cells

Investigation of the correlation effects of catalyst loading and ionomer content in an anode electrode on the performance of polymer electrode membrane water electrolysis

Si-based magnetic tunnel transistor with high transfer ratio

Light Harvesting: Enhanced Light Harvesting in Mesoscopic Solar Cells by Multilevel Multiscale Patterned Photoelectrodes with Superpositioned Optical Properties (Adv. Funct. Mater. 36/2016)

Oxygen Plasma-Mediated Microstructured Hydrocarbon Membrane for Improving Interface Adhesion and Mass Transport in Polymer Electrolyte Fuel Cells.