We report on solid-state mesoscopic heterojunction solar cells employing nanoparticles (NPs) of methyl ammonium lead iodide (CH3NH3)PbI3 as light harvesters. The perovskite NPs were produced by reaction of methylammonium iodide with PbI2 and deposited onto a submicron-thick mesoscopic TiO2 film, whose pores were infiltrated with the hole-conductor spiro-MeOTAD. Illumination with standard AM-1.5 sunlight generated large photocurrents (JSC) exceeding 17 mA/cm2, an open circuit photovoltage (VOC) of 0.888 V and a fill factor (FF) of 0.62 yielding a power conversion efficiency (PCE) of 9.7%, the highest reported to date for such cells. Femto second laser studies combined with photo-induced absorption measurements showed charge separation to proceed via hole injection from the excited (CH3NH3)PbI3 NPs into the spiro-MeOTAD followed by electron transfer to the mesoscopic TiO2 film. The use of a solid hole conductor dramatically improved the device stability compared to (CH3NH3)PbI3 -sensitized liquid junction cells.

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Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%

Weyl and Dirac semimetals are three-dimensional phases of matter with gapless electronic excitations that are protected by topology and symmetry. As three-dimensional analogs of graphene, they have generated much recent interest. Deep connections exist with particle physics models of relativistic chiral fermions, and, despite their gaplessness, to solid-state topological and Chern insulators. Their characteristic electronic properties lead to protected surface states and novel responses to applied electric and magnetic fields. The theoretical foundations of these phases, their proposed realizations in solid-state systems, and recent experiments on candidate materials as well as their relation to other states of matter are reviewed.

Weyl and Dirac semimetals in three-dimensional solids

Highly efficient quantum-dot-sensitized solar cell is fabricated using ca. 2–3 nm sized perovskite (CH3NH3)PbI3 nanocrystal. Spin-coating of the equimolar mixture of CH3NH3I and PbI2 in γ-butyrolactone solution (perovskite precursor solution) leads to (CH3NH3)PbI3 quantum dots (QDs) on nanocrystalline TiO2 surface. By electrochemical junction with iodide/iodine based redox electrolyte, perovskite QD-sensitized 3.6 μm-thick TiO2 film shows maximum external quantum efficiency (EQE) of 78.6% at 530 nm and solar-to-electrical conversion efficiency of 6.54% at AM 1.5G 1 sun intensity (100 mW cm−2), which is by far the highest efficiency among the reported inorganic quantum dot sensitizers.

6.5% efficient perovskite quantum-dot-sensitized solar cell

Hollow micro-/nanostructures are of great interest in many current and emerging areas of technology. Perhaps the best-known example of the former is the use of fly-ash hollow particles generated from coal power plants as partial replacement for Portland cement, to produce concrete with enhanced strength and durability. This review is devoted to the progress made in the last decade in synthesis and applications of hollow micro-/nanostructures. We present a comprehensive overview of synthetic strategies for hollow structures. These strategies are broadly categorized into four themes, which include well-established approaches, such as conventional hard-templating and soft-templating methods, as well as newly emerging methods based on sacrificial templating and template-free synthesis. Success in each has inspired multiple variations that continue to drive the rapid evolution of the field. The Review therefore focuses on the fundamentals of each process, pointing out advantages and disadvantages where appropriate. Strategies for generating more complex hollow structures, such as rattle-type and nonspherical hollow structures, are also discussed. Applications of hollow structures in lithium batteries, catalysis and sensing, and biomedical applications are reviewed.

Hollow Micro-/Nanostructures: Synthesis and Applications**

基礎講座 電気泳動(Electrophoresis)

Nano‐embossed Hollow Spherical TiO2 as Bifunctional Material for High‐Efficiency Dye‐Sensitized Solar Cells

Size-dependent scattering efficiency in dye-sensitized solar cell

IO N We present a new class of electrically functional devices composed entirely of soft, liquid-based materials that display memristor-like characteristics. A memristor, or a “memory resistor”, is an electronic device that changes its resistive state depending on the current or voltage history through the device. Memristors may become the core of next generation memory devices because of their low energy consumption and high data density and performance. [ 1–3 ] Since the concept of memristors was theorized in 1971, [ 4 ] resistive switching memories have been fabricated from a variety of materials operating on magnetic, [ 5 ] thermal, [ 6 ] photonic, [ 7 ] electronic and ionic mechanisms. [ 3 , 8 , 9 ] Conventional memristive devices typically include metalinsulator-metal (M-I-M) junctions composed of rigid stacks of fi lms fabricated by multiple vacuum-deposition steps, often at high temperature. The most common “insulator” materials in M-I-M memristor junctions are inorganic metal oxides such as TiO 2 [ 10 ] and NiO. [ 11 ] Conducting pathways can form by current through such layers. Solid electrolytes between metal electrodes can also be used to create resistance switches (e.g., Ag/ Ag 2 S/Pt), in which conductive metal fi laments that bridge the two electrodes can be formed or annihilated on demand. [ 3 , 9 ] Memristive circuits composed of organic materials have some advantages over conventional metal oxides due to their ease of processing, light weight, and low cost. A variety of organic materials such as homogeneous polymers, small-molecule or nanoparticle doped polymers, and organic donor-acceptor complexes have been evaluated as components in memory switching devices. [ 12 ] We report new controllably bi-stable memristor-like devices fabricated entirely from liquid-based materials. These soft and fl exible devices are built from liquid metal and hydrogels that are used routinely in laboratories for hosting biological molecules and supporting cell growth. Hydrogels are soft, moldable and bio-compatible media similar to biological systems with high ion mobility due to the high water content ( > 90% water). [ 13 , 14 ] The ionic properties of the gels can be tuned by inclusion of polyelectrolytes that are immobilized via entanglement within the gel network. Hydrogels doped with polyelectrolytes have been utilized for fabricating electronic devices such as diodes and photovoltaic cells. [ 13 , 15 , 16 ] The electrodes of these devices, however, are rigid metals such as platinum and

Towards All‐Soft Matter Circuits: Prototypes of Quasi‐Liquid Devices with Memristor Characteristics

Selective wetting-induced micro-electrode patterning is used to fabricate flexible micro-supercapacitors (mSCs). The resulting mSCs exhibit high performance, mechanical stability, stable cycle life, and hold great promise for facile integration into flexible devices requiring on-chip energy storage.

Selective wetting-induced micro-electrode patterning for flexible micro-supercapacitors.

Eutectic gallium-indium alloy (EGaIn) liquid metal is highly conductive, moldable, and extremely deformable and has attracted significant attention for many applications, ranging from stretchable electronics to drug delivery. Even though EGaIn liquid metal is generally known to have low toxicity, the toxicity of the metal, rather than a salt form of Ga or In, has not been systematically studied yet. In this paper, we investigate the time-dependent concentration of the ions released from EGaIn liquid metal in an aqueous environment and their cytotoxicity to human cells. It is observed that only the Ga ion is dominantly released from EGaIn when no external agitation is applied, whereas the concentration of the In ion drastically increases with sonication. The cytotoxicity study reveals that all human cells tested are viable in the growth media with naturally released EGaIn ions, but the cytotoxicity becomes significant with sonication-induced EGaIn releasates. On the basis of the comparative study with other representative toxic elements, that is, Hg and Cd, it could be concluded that EGaIn is reasonably safe to use in an aqueous environment; however, it should be cautiously handled when any mechanical agitation is applied.

Hyung-Jun Koo

Papers

Nano‐embossed Hollow Spherical TiO2 as Bifunctional Material for High‐Efficiency Dye‐Sensitized Solar Cells

Size-dependent scattering efficiency in dye-sensitized solar cell

Towards All‐Soft Matter Circuits: Prototypes of Quasi‐Liquid Devices with Memristor Characteristics

Selective wetting-induced micro-electrode patterning for flexible micro-supercapacitors.

Cytotoxicity of Gallium–Indium Liquid Metal in an Aqueous Environment