Highly Sensitive and Selective Acetylene CuO/ZnO Heterostructure Sensors through Electrospinning at Lean O2 Concentration for Transformer Diagnosis.

Acetylene (C2H2) is a gas that can cause explosions in transformers even at low concentrations. Gas chromatography (GC) or photoacoustic spectroscopy (PAS) have been used to detect C2H2 during dissolved gas analysis (DGA), but they are not suitable for monitoring numerous transformers at substations. Even though metal oxide semiconductor (MOS) based C2H2 sensors have drawn much attention as a potential solution, existing MOS-based C2H2 sensors have low sensitivity toward C2H2 in the transformer environment (<2% O2 concentrations). This study develops high-performance C2H2 gas sensors for DGA using a heterostructure of CuO/ZnO (CZ) via the electrospinning process. Performance of various ratios of CZ composite nanofibers are compared in a transformer-like environment, and the optimal composition of CZ nanofibers for detection of C2H2 at 2% O2 concentration is proposed. The CuO:ZnO = 8:2 (CZ2) sensor achieves the highest response (Rg/Ra = 7.6 against 10 ppm of C2H2) toward low concentration of C2H2 at 200 °C with good stability (>10 h). In addition, the CZ2 sensor also shows a high selectivity (>5 times) to coexisting transformer oil gases which are H2, CH4, C2H4, C2H6, CO, and CO2. Overall, this study is the first to demonstrate a high performing DGA sensor under 2% O2 concentration that can provide a practical solution to monitoring the low concentration of C2H2 in transformers effectively.

Surface Reconstruction of a Perovskite Film by an Organic Salt for High-Performance Solar Cells with Improved Stability.

Organic-inorganic lead halide perovskites have undergone tremendous development due to their excellent optoelectrical properties, achieving exceptional photovoltaic performance up to over 25%. The interface engineering method has a significant role in further improving the perovskite solar cell performance to its limit. Herein, we fabricated a modified GA0.07MA0.93PbI3 perovskite film using the organic amine small molecule 3-(aminomethyl)pyridine (3AP), which increased the grain sizes and crystallinity through the modulated melting process as well as reacted with the surface component, especially the defect site of the PbI6 octahedral layer, resulting in a high-quality perovskite film. The perovskite films without (pristine) and with toluene were also fabricated to prove the significant role of the 3AP organic molecule. The 3AP-modified GA0.07MA0.93PbI3 perovskite film exhibits a long carrier lifetime and suppresses the charge recombination loss, resulting in an increased fill factor (FF) of 75.66% and a power conversion efficiency (PCE) of 17.28%, which are higher than those of pristine (FF, 66.36%; PCE, 14.06%) and toluene-treated perovskite devices (FF, 72.40%; PCE, 16.84%). More importantly, the 3AP-modified perovskite device shows remarkable environmental stability to the ambient conditions, with the PCE retaining 92% of the initial PCE for over 1000 h under ambient conditions.

Diammonium spacer-induced stable zigzag type 2D Dion-Jacobson lead/tin-based perovskite solar cells.

Hybrid halide two dimensional (2D) perovskites have attracted considerable attention because they exhibit an improvement in perovskite solar cells compared with their 3D analogs. However, their bulky organic space group, leading to higher bandgaps and exciton binding energy, limits the charge transport in solar cells. Herein, the 3-(aminomethyl)pyridinium (3API2, C6H10N2I2) dication is incorporated into FA(Pb0.5Sn0.5)I3 to develop zigzag type 2D Dion-Jacobson-phase perovskites, which have low band gaps in the range of 1.44 to 1.53 eV for concentrations from 5 mol% to 20 mol% due to structural distortion. The introduction of the 3API2 cation increases the carrier conductivity and produces a high-quality perovskite film with no pinhole and connected grains, which is favorable for efficient carrier transport. Consequently, solar cells employing FA(Pb0.5Sn0.5)I3 with 10 mol% 3API2 added as a light absorber achieve a power conversion efficiency of 5.46% with an open-circuit voltage of 0.47 V, a fill factor of 58.07% and a short-circuit current density of 20.18 mA cm-2. With this class of new 2D Dion-Jacobson perovskite compositions, this work suggests potential future directions for improving the performance and device stability of perovskite solar cells.

Long-lived spin-triplet excitons in manganese complexes for room-temperature phosphorescence.

Low-dimensional metal halide perovskites have become emerging candidates for applications in light emitting diodes due to the quantum confinement effect by tuning their composition and structure. However, they suffer from longstanding issues of environmental stability and lead toxicity. Herein, we report phosphorescent manganese halides, (TEM)2MnBr4 (TEM = HN(CH2CH3)3, triethylammonium) and (IM)6[MnBr4][MnBr6] (IM = C3H6N2, imidazolium) with a photoluminescence quantum yield (PLQY) of 50% and 7%, respectively. (TEM)2MnBr4 with a tetrahedral configuration exhibits brilliant green light emission centered at 528 nm, while the (IM)6[MnBr4][MnBr6] compound, in which octahedral and tetrahedral units coexist, exhibits red colored emission at 615 nm. The excited state of (TEM)2MnBr4 and (IM)6[MnBr4][MnBr6] is found to exhibit distinct photophysical emission characteristics consistent with triplet state phosphorescence. Efficient phosphorescence was achieved with a long lifetime of several milliseconds, 0.38 ms for (TEM)2MnBr4 and 5.54 ms for (IM)6[MnBr4][MnBr6], at room temperature. By studying the temperature dependent PL and single-crystal X-ray diffraction measurements and comparing our results with those of previously reported analogues, we have found a direct correlation between Mn⋯Mn distances and PL emission. Our study reveals that the long distance between the Mn centers has made a significant contribution to the long-lived phosphorescence with a highly emissive triplet state.

The red light emission in 2D (C4SH3CH2NH3)2SnI4 and (C4OH7CH2NH3)2SnI4 perovskites.

Two-dimensional (2D) perovskites have a large exciton binding energy due to the structure of the quantum confinement, which produces a faster radiative recombination, and so are promising potential materials for light-emitting diodes. However, most of the highly efficient hybrid halide perovskites are based on the toxic Pb-based materials, so the replacement of Pb with less toxic and suitable substitute elements has been investigated for environmental efficient materials. Herein, we report the Sn-based 2D perovskites, which include (TPM)2SnI4 (TPM = C4SH3CH2NH3) and (TFF)2SnI4 (TFF = C4OH7CH2NH3), as red emission materials. Structural characterization by single crystal X-ray diffraction reveals that (TPM)2SnI4 undergoes a structural evolution from the orthorhombic space group Cmc21 (100 K) to Pbca (298 K), while the (TFF)2SnI4 perovskite exhibits the monoclinic space group P21/c at 100 K and 298 K. The inorganic framework of (TFF)2SnI4 was separated by the bilayer TFF chains with an empty space, which is an effective structure to increase the quantum confinement effect. The band gaps of the (TPM)2SnI4 (1.80 eV) and (TFF)2SnI4 (1.73 eV) compounds indicate the direct band gap semiconductor materials. From the time-resolved photoluminescence results, it can be seen that (TPM)2SnI4 produces uniform short emission (0.73 ns) throughout the entire powder crystals, whereas (TFF)2SnI4 has a uniform and long emission life time (47 ns). Temperature-dependent photoluminescence (PL) studies indicate that the (TPM)2SnI4 and (TFF)2SnI4 perovskites have a strong split red emission at low temperature due to the vibration of the inorganic framework. As the temperature increases, the PL spectra shift to the high energy region and the emission intensity decreases. The PL spectra of (TPM)2SnI4 and (TFF)2SnI4 perovskites have maximum peak wavelengths at 622 nm and 640 nm, and show the photoluminescence quantum yields of 0.30% and 1.71%, respectively.

Formation of cubic perovskite alloy containing the ammonium cation of 2D perovskite for high performance solar cells with improved stability.

The perovskite solar cells have demonstrated to be strong competitors for conventional silicon solar cells due to their remarkable power conversion efficiency. However, their structural instability is the biggest obstacle to commercialization. To address these issues, we prepared (CH3NH3)1-x (HC(NH2)2) x PbI3 (CH3NH3 = MA, HC(NH2)2 = FA) perovskite alloys that contain ethylammonium (EA, CH3CH2NH3 +) and benzylammonium (BA, C6H5CH2NH3 +) cations with no new additional two-dimensional (2D) perovskite phases. The crystal structures of alloy perovskites exhibit the cubic phase, which decreased the cation disorder and the intrinsic instability compared to 3D MAPbI3 perovskite. The band gaps of the alloy perovskites are almost the same as the corresponding 3D perovskites, which exhibit a high refractive index, a large absorption coefficient, and paramagnetic properties for the production of high performance photovoltaic devices. After we constructed the solar cell with the configuration of regular (n-i-p) solar cells using the alloy perovskites, the power conversion efficiencies (PCE) of the MA0.83EA0.17PbI3 perovskite solar cell showed the highest efficiency, which was 10.22%, under 1 sun illumination.

Stacking of Layered Halide Perovskite from Incorporating a Diammonium Cation into Three-Dimensional Perovskites.

Quasi two-dimensional (2D) layered perovskites have been emerging as promising candidates for photovoltaic cells because they exhibit intrinsic stability and a higher tunability of optical properties compared to three-dimensional (3D) perovskites. However, since most 2D perovskites have bulkier groups as an organic space group, they will inevitably have a van der Waals gap between the inorganic layers and their crystal growth directions orient in a lateral direction. It also interrupts carrier transport across the conducting inorganic layer in the solar cell. Here, we presents the new homologous 2D layered perovskites, (HA)(A)n-1PbnI3n+1, where HA stands for the histammonium ((C5N3H11)2+) as a diammonium cation and A stands for methylammonium (CH3NH3+) or formammonium (HC(NH2)2+). Since the ditopic HA has a diammoinium cation, it connects the inorganic slabs stacked in the vertical direction. The inorganic layer is stacked on the other layer to form a layered structure, which results in rigid and stable structures. These materials (1.64 eV for (HA)(FA)n-1PbnI3n+1 and 1.80 eV for (HA)(MA)n-1PbnI3n+1) have significantly lower band gaps than those of HAPbI4 (2.20 eV). Compared to the pure 2D and 3D perovskites, these perovskites have a longer electron lifetime due to the vertical crystal structure and show improved environmental stability for perovskite solar cell application.

Broadband white-light emission from supramolecular piperazinium-based lead halide perovskites linked by hydrogen bonds.

We demonstrate white-light emission using lead halide perovskites: (pip)2PbBr6 (pip = piperazine), (pip)2Pb4Cl12, (1mpz)2PbBr6 (1mpz = 1-methylpiperazine), and (2,5-dmpz)0.5PbBr3·2((CH3)2SO) (2,5-dmpz = trans-2,5-dimethylpiperazine, abbreviated as (2,5-dmpz)0.5PbBr3), in which the inorganic frameworks were connected by piperazinium dications through hydrogen bonds, forming a three-dimensional supramolecular network. From single-crystal X-ray diffraction measurements and Raman spectroscopy, we identified the crystal structures and local environmental vibrational modes in the inorganic framework, finding that (pip)2PbBr6 crystallized in the centrosymmetric orthorhombic space group Pnnm, whereas (pip)2Pb4Cl12 crystallized in the trigonal/rhombohedral space group R3. The zero-dimensional (1mpz)2PbBr6 structure crystallized in the centrosymmetric monoclinic space group P2/n, whereas the [PbBr6]4- octahedron was separated by a 1-methylpiperazine dication. (2,5-dmpz)0.5PbBr3·2((CH3)2SO) contained half a cation, which was completed by inversion symmetry, along with two dimethyl sulfoxide solvent molecules that crystallized in the monoclinic space group P21/c. Among the perovskites, (2,5-dmpz)0.5PbBr3·2((CH3)2SO) exhibited the longest carrier lifetime (42 ns), the lowest band gap (2.34 eV), and the highest photoluminescence quantum yield (58.02%). This is because it forms a 1D corner-sharing structure and has localized electronic states near the conduction band minimum, which contributes to the high photoluminescence quantum yield and white-light emission.

White-Light Emission from the Structural Distortion Induced by Control of Halide Composition of Two-Dimensional Perovskites ((C6H5CH2NH3)2PbBr4- xCl x).

Two-dimensional (2D) perovskites, which have a 2D orientation of the inorganic framework that determines largely the electronic characteristics and an organic cation in the interlayer that leads to a quantum well structure, have attracted a great deal of attention due to their superior stable optoelectronic properties. Especially, some of the greatest interest in 2D perovskites is their application in broad-band white-light emission for solid state lighting. We prepared (BZA)2PbBr4- xCl x (BZA= benzylammonium and x = 0, 1.5, 2, 3, 3.5, 4) to tune the white-light emission. In the (BZA)2PbBr4 perovskite structure, the bond lengths of Pb-Br for PbBr62- exhibit the same lengths of 2.98 and 3.00 Å, respectively. However, in PbCl6 octahedra the bridging Pb-Cl distances were 2.83/2.88 Å and 2.85/2.88 Å, respectively. The 2D perovskite (BZA)2PbCl4 exhibits a turquoise light emission due to its highly distorted structure, whereas (BZA)2PbBr4 emits a narrow blue emission. We controlled the white emission by mixing the two compounds in proportion and changed the color from blue to white using the intermediate compound (BZA)2PbBr4- xCl x ( x = 1.5, 2, 3, 3.5). The intermediate compound (BZA)2PbBr4- xCl x ( x = 1.5, 2, 3, 3.5) shifted in the white space of Commission Internationale de l'Éclairage coordinates, which were (0.324, 0.383), (0.312. 0.369), (0.319, 0.374), and (0.338, 0.396), respectively. The correlated color temperature of all compounds was observed above 5000 K, which suggests that these perovskites could be utilized as "cold" white-light-emitting materials.

Carbon-coated ZnO mat passivation by atomic-layer-deposited HfO2 as an anode material for lithium-ion batteries.

ZnO has had little consideration as an anode material in lithium-ion batteries compared with other transition-metal oxides due to its inherent poor electrical conductivity and large volume expansion upon cycling and pulverization of ZnO-based electrodes. A logical design and facile synthesis of ZnO with well-controlled particle sizes and a specific morphology is essential to improving the performance of ZnO in lithium-ion batteries. In this paper, a simple approach is reported that uses a cation surfactant and a chelating agent to synthesize three-dimensional hierarchical nanostructured carbon-coated ZnO mats, in which the ZnO mats are composed of stacked individual ZnO nanowires and form well-defined nanoporous structures with high surface areas. In order to improve the performance of lithium-ion batteries, HfO2 is deposited on the carbon-coated ZnO mat electrode via atomic layer deposition. Lithium-ion battery devices based on the carbon-coated ZnO mat passivation by atomic layer deposited HfO2 exhibit an excellent initial discharge and charge capacities of 2684.01 and 963.21mAhg-1, respectively, at a current density of 100mAg-1 in the voltage range of 0.01-3V. They also exhibit cycle stability after 125 cycles with a capacity of 740mAhg-1 and a remarkable rate capability.

Comparative experiments of graphene covalently and physically binding CdSe quantum dots to enhance the electron transport in flexible photovoltaic devices.

In this research, we prepared composite films via covalent coupling of CdSe quantum dots (QDs) to graphene through the direct binding of aryl radicals to the graphene surface. To compare the carrier transport with the CdSe aryl binding graphene film, we prepared CdSe pyridine capping graphene films through the pi-pi interactions of noncovalent bonds between the graphene and pyridine molecules. The photovoltaic devices were fabricated from the two hybrid films using the electrophoretic deposition method on flexible substrates. Even though the two hybrid films have the same amount of QDs and graphene, time-resolved fluorescence emission decay results show that the emission lifetime of the CdSe aryl group binding graphene film is significantly shorter than that of the pyridine capping CdSe-graphene. The quantum efficiency and photocurrent density of the device fabricated from CdSe aryl binding graphene were also higher than those of the device fabricated from pyridine capping CdSe-graphene. These results indicated that the carrier transport of the QD-graphene system is not related to the additive effect from the CdSe and graphene components but rather is a result of the unique interactions between the graphene and QDs. We could expect that these results can be useful in designing QD-graphene composite materials, which are applied in photovoltaic devices.

Fabrication of Ag nanoparticles embedded in TiO2 nanotubes: using electrospun nanofibers for controlling plasmonic effects.

Composites of electrospun poly(ethylene oxide) (PEO) fibers and silver nanoparticles (Ag NPs) were used as a soft template for coating with TiO2 by atomic layer deposition (ALD). Whereas the as-deposited TiO2 layers on PEO fibers and Ag NPs were completely amorphous, the TiO2 layers were transformed into polycrystalline TiO2 nanotubes (NTs) with embedded Ag NPs after calcination. Their plasmonic effect can be controlled by varying the thickness of the dielectric Al2 O3 spacer between Ag NPs and dye molecules by means of the ALD process. Electronic and spectroscopic analyses demonstrated enhanced photocurrent generation and solar-cell performance due to the intense electromagnetic field of the dye resulting from the surface plasmon effect of the Ag NPs.

TiO2 nanotube fabrication with highly exposed (001) facets for enhanced conversion efficiency of solar cells.

We demonstrate that the use of poly(vinyl pyrrolidone) (PVP) and acetic acid during the synthesis of TiO(2) nanotubes may result in the synthesis of single-crystal-like anatase TiO(2) with a mainly exposed and chemically active (001) facet. An enhancement in the overall conversion efficiency of dye-sensitized solar cells was observed in a photoanode consisting of TiO(2) single-crystal-like anatase exposed (001) facets.

Selective patterning of ZnO nanorods on silicon substrates using nanoimprint lithography.

In this research, nanoimprint lithography (NIL) was used for patterning crystalline zinc oxide (ZnO) nanorods on the silicon substrate. To fabricate nano-patterned ZnO nanorods, patterning of an n-octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) on SiO2 substrate was prepared by the polymer mask using NI. The ZnO seed layer was selectively coated only on the hydrophilic SiO2 surface, not on the hydrophobic OTS SAMs surface. The substrate patterned with the ZnO seed layer was treated with the oxygen plasma to oxidize the silicon surface. It was found that the nucleation and initial growth of the crystalline ZnO were proceeded only on the ZnO seed layer, not on the silicon oxide surface. ZnO photoluminescence spectra showed that ZnO nanorods grown from the seed layer treated with plasma showed lower intensity than those untreated with plasma at 378 nm, but higher intensity at 605 nm. It is indicated that the seed layer treated with plasma produced ZnO nanorods that had a more oxygen vacancy than those grown from seed layer untreated with plasma. Since the oxygen vacancies on ZnO nanorods serve as strong binding sites for absorption of various organic and inorganic molecules. Consequently, a nano-patterning of the crystalline ZnO nanorods grown from the seed layer treated with plasma may give the versatile applications for the electronics devices.

Anomalous bronchial artery originating from the right coronary artery in a patient with angina (2009: 4b).

Bronchial artery origins are subject to a wide range of anatomic variations, of which interventional radiologists should be aware. The authors report a patient with angina in whom an anomalous bronchial artery originated from the sinus node branch of the right coronary artery, causing a coronary steal phenomenon. The patient's symptom was successfully treated by transcatheter embolisation of the anomalous bronchial artery, which seems to be an effective alternative to surgery.

Patterning of conducting polymers using charged self-assembled monolayers.

We introduce a new approach to pattern conducting polymers by combining oppositely charged conducting polymers on charged self-assembled monolayers (SAMs). The polymer resist pattern behaves as a physical barrier, preventing the formation of SAMs. The patterning processes were carried out using commercially available conducting polymers: a negatively charged PEDOT/PSS (poly(3,4-ethylene-dioxythiophene)/poly(4-stylenesulphonic acid)) and a positively charged polypyrrole (PPy). A bifunctional NH 2 (positively charged) or COOH (negatively charged) terminated alkane thiol or silane was directly self-assembled on a substrate (Au or SiO 2). A suspension of the conducting polymers (PEDOT/PSS and PPy) was then spin-coated on the top surface of the SAMs and allowed to adsorb on the oppositely charged SAMs via an electrostatic driving force. After lift-off of the polymer resist, i.e., poly(methyl methacrylate, PMMA), using acetone, the conducting polymers remained on the charged SAMs surface. Optical microscopy, Auger electron spectroscopy, and atomic force microscopy reveal that the prepared nanolines have low line edge roughness and high line width resolution. Thus, conducting polymer patterns with high resolution could be produced by simply employing charged bifunctional SAMs. It is anticipated that this versatile new method can be applied to device fabrication processes of various nano- and microelectronics.

Surface treatment and characterization of ITO thin films using atmospheric pressure plasma for organic light emitting diodes.

Ar atmospheric pressure plasma (APP) was used to treat indium-tin-oxide (ITO). The plasma conditions were varied to treat the ITO surface, e.g., plasma treatment time, RF power, flow rate, and the plasma outlet-to-sample distance. The plasma effectiveness was measured by the contact angle. The change in the surface energy calculated with the Owens-Wendt method mainly arises from the polar component. The dynamic contact angle measurements show that APP-treated surface showed considerably lower hysteresis in the water and ethylene glycol but there was no change in hysteresis in methylene iodide compared with the untreated ITO. Atomic force microscopy showed that the Ar APP-treated surface sharply decreased the surface roughness and showed a similar morphology as the untreated ITO. X-ray photoelectron spectroscopy showed that the Ar APP treatment not only effectively removed carbon contamination from the surface but also introduced oxygen. Therefore, it is believed that the APP treatment modifies the physico-chemical properties of ITO, which can in turn improve the performance of the organic light-emitting diodes.