The properties of organic photovoltaic devices (OPVs) with poly(3,4-ethylene dioxythiophene) : poly(styrene- sulfonate ) buffer layer modified by doping glycerol with different concentration have ...been investigated. The power conversion efficiency (PCE) of the device has been improved from 3.37% to 4.32% under AM 1.5 G (90 mW/cm 2 illumination) after the buffer layer was modified. The short-circuit current density also 24% increased with the modification. Surprisingly, as the doping concentration of glycerol was more than 30 mg/ml, PCE of the OPVs no longer increased even though the conductivity of buffer layer continually increased with doping concentration of glycerol. We particularly analyzed the effect of glycerol-modified buffer layer on performance of polymer photovoltaic devices by the contact angle and atomic force microscopy measurements, and the influence of surface morphology of buffer layer was also discussed.
A van der Waals heterostructure is a type of metamaterial that consists of vertically stacked two-dimensional building blocks held together by the van der Waals forces between the layers. This design ...means that the properties of van der Waals heterostructures can be engineered precisely, even more so than those of two-dimensional materials. One such property is the 'twist' angle between different layers in the heterostructure. This angle has a crucial role in the electronic properties of van der Waals heterostructures, but does not have a direct analogue in other types of heterostructure, such as semiconductors grown using molecular beam epitaxy. For small twist angles, the moiré pattern that is produced by the lattice misorientation between the two-dimensional layers creates long-range modulation of the stacking order. So far, studies of the effects of the twist angle in van der Waals heterostructures have concentrated mostly on heterostructures consisting of monolayer graphene on top of hexagonal boron nitride, which exhibit relatively weak interlayer interaction owing to the large bandgap in hexagonal boron nitride. Here we study a heterostructure consisting of bilayer graphene, in which the two graphene layers are twisted relative to each other by a certain angle. We show experimentally that, as predicted theoretically, when this angle is close to the 'magic' angle the electronic band structure near zero Fermi energy becomes flat, owing to strong interlayer coupling. These flat bands exhibit insulating states at half-filling, which are not expected in the absence of correlations between electrons. We show that these correlated states at half-filling are consistent with Mott-like insulator states, which can arise from electrons being localized in the superlattice that is induced by the moiré pattern. These properties of magic-angle-twisted bilayer graphene heterostructures suggest that these materials could be used to study other exotic many-body quantum phases in two dimensions in the absence of a magnetic field. The accessibility of the flat bands through electrical tunability and the bandwidth tunability through the twist angle could pave the way towards more exotic correlated systems, such as unconventional superconductors and quantum spin liquids.
The interlayer coupling in van der Waals heterostructures governs a variety of optical and electronic properties. The intrinsic dipole moment of Janus transition metal dichalcogenides (TMDs) offers a ...simple and versatile approach to tune the interlayer interactions. In this work, we demonstrate how the van der Waals interlayer coupling and charge transfer of Janus MoSSe/MoS2 heterobilayers can be tuned by the twist angle and interface composition. Specifically, the Janus heterostructures with a sulfur/sulfur (S/S) interface display stronger interlayer coupling than the heterostructures with a selenium/sulfur (Se/S) interface as shown by the low-frequency Raman modes. The differences in interlayer interactions are explained by the interlayer distance computed by density-functional theory (DFT). More intriguingly, the built-in electric field contributed by the charge density redistribution and interlayer coupling also play important roles in the interfacial charge transfer. Namely, the S/S and Se/S interfaces exhibit different levels of photoluminescence (PL) quenching of MoS2 A exciton, suggesting enhanced and reduced charge transfer at the S/S and Se/S interface, respectively. Our work demonstrates how the asymmetry of Janus TMDs can be used to tailor the interfacial interactions in van der Waals heterostructures.
Reactions of Ag(I) salt, NH4(E2P(OR)2) (R = iPr, Et; E = Se, S), and NaBH4 in a 7:6:1 ratio in CH2Cl2 at room temperature, led to the formation of hydride-centered heptanuclear silver clusters, ...Ag7(H){E2P(OR)2}6 (R = iPr, E = Se (3): R = Et; E = S(4). The reaction of Ag10(E){E2P(OR)2}8 with NaBH4 in CH2Cl2 produced Ag8(H){E2P(OR)2}6(PF6) (R = iPr, E = Se (1): R = Et; E = S(2)), which can be converted to clusters 3 and 4, respectively, via the addition of 1 equiv of borohydride. Intriguingly clusters 1 and 2 can be regenerated via adding 1 equiv of Ag(CH3CN)4PF6 to the solution of compounds 3 and 4, respectively. All complexes have been fully characterized by NMR (1H, 77Se, 109Ag) spectroscopy, UV–vis, electrospray ionization mass spectrometry (ESI-MS), FT-IR, thermogravimetric analysis (TGA), and elemental analysis, and molecular structures of 3 H and 4 H were clearly established by single crystal X-ray diffraction. Both 3 H and 4 H exhibit a tricapped tetrahedral Ag7 skeleton, which is inscribed within an E12 icosahedron constituted by six dialkyl dichalcogenophosphate ligands in a tetrametallic-tetraconnective (μ2, μ2) bonding mode. Density functional theory (DFT) calculations on the models Ag7(H)(E2PH2)6 (E = Se: 3′; E = S: 4′) yielded to a tricapped, slightly elongated tetrahedral silver skeleton, and time-dependent DFT (TDDFT) calculations reproduce satisfyingly the UV–vis spectrum with computed transitions at 452 and 423 nm for 3′ and 378 nm for 4′. Intriguingly further reactions of Ag7(H){E2P(OR)2}6 with 8-fold excess amounts of NaBH4 produced monodisperse silver nanoparticles with an averaged particle size of 30 nm, which are characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), and UV–vis absorption spectrum.
PDF
![[Ag7(H){E2P(OR)2}6] (E = Se...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0020-1669/small "[Ag7(H){E2P(OR)2}6] (E = Se, S): Precursors for the Fabrication of Silver Nanoparticles")