Solution-Processed Organic Solar Cells with High Open-Circuit Voltage of 1.3 V and Low Non-Radiative Voltage Loss of 0.16 V

Compared with inorganic or perovskite solar cells, the relatively large non-radiative recombination voltage losses (ΔV_non-rad) in organic solar cells (OSCs) limit the improvement of the open-circuit voltage (V_oc). Herein, OSCs are fabricated by adopting two pairs of D–π–A polymers (PBT1-C/PBT1-C-2Cl and PBDB-T/PBDB-T-2Cl) as electron donors and a wide-bandgap molecule BTA3 as the electron acceptor. In these blends, a charge-transfer state energy (E_CT) as high as 1.70–1.76 eV is achieved, leading to small energetic differences between the singlet excited states and charge-transfer states (ΔE_CT ≈ 0.1 eV). In addition, after introducing chlorine atoms into the π-bridge or the side chain of benzodithiophene (BDT) unit, electroluminescence external quantum efficiencies as high as 1.9 × 10⁻³ and 1.0 × 10⁻³ are realized in OSCs based on PBTI-C-2Cl and PBDB-T-2Cl, respectively. Their corresponding ΔV_non-rad are 0.16 and 0.17 V, which are lower than those of OSCs based on the analog polymers without a chlorine atom (0.21 and 0.24 V for PBT1-C and PBDB-T, respectively), resulting in high V_oc of 1.3 V. The ΔV_non-rad of 0.16 V and V_oc of 1.3 V achieved in PBT1-C-2Cl:BTA3 OSCs are thought to represent the best values for solution-processed OSCs reported in the literature so far.     

Tailoring Structure,Composition, and Energy Storage Properties of MXenes from Selective Etching of In‐Plane,Chemically Ordered MAX Phases

The exploration of 2D solids is one of our time's generators of materials discoveries. A recent addition to the 2D world is MXenes that possses a rich chemistry due to the large parent family of MAX phases. Recently, a new type of atomic laminated phases (coined i‐MAX) is reported, in which two different transition metal atoms are ordered in the basal planes. Herein, these i‐MAX phases are used in a new route for tailoriong the MXene structure and composition. By employing different etching protocols to the parent i‐MAX phase (Mo_2/3Y_1/3)₂AlC, the resulting MXene can be either: i) (Mo_2/3Y_1/3)₂C with in‐plane elemental order through selective removal of Al atoms or ii) Mo_1.33C with ordered vacancies through selective removal of both Al and Y atoms. When (Mo_2/3Y_1/3)₂C (ideal stoichiometry) is used as an electrode in a supercapacitor—with KOH electrolyte—a volumetric capacitance exceeding 1500 F cm^?3 is obtained, which is 40% higher than that of its Mo_1.33C counterpart. With H₂SO₄, the trend is reversed, with the latter exhibiting the higher capacitance (≈1200 F cm^?3). This additional ability for structural tailoring will indubitably prove to be a powerful tool in property‐tailoring of 2D materials, as exemplified here for supercapacitors.     

Isoindigo‐Based Polymers with Small Effective Masses for High‐Mobility Ambipolar Field‐Effect Transistors

So far, most of the reported high‐mobility conjugated polymers are p‐type semiconductors. By contrast, the advances in high‐mobility ambipolar polymers fall greatly behind those of p‐type counterparts. Instead of unipolar p‐type and n‐type materials, ambipolar polymers, especially balanced ambipolar polymers, are potentially serviceable for easy‐fabrication and low‐cost complementary metal‐oxide‐semiconductor circuits. Therefore, it is a critical issue to develop high‐mobility ambipolar polymers. Here, three isoindigo‐based polymers, PIID‐2FBT , P1FIID‐2FBT , and P2FIID‐2FBT are developed for high‐performance ambipolar organic field‐effect transistors. After the incorporation of fluorine atoms, the polymers exhibit enhanced coplanarity, lower energy levels, higher crystallinity, and thus increased µ _e. P2FIID‐2FBT exhibits n‐type dominant performance with a µ _e of 9.70 cm² V^?1 s^?1. Moreover, P1FIID‐2FBT exhibits a highly balanced µ _h and µ _e of 6.41 and 6.76 cm² V^?1 s^?1, respectively, which are among the highest values for balanced ambipolar polymers. Moreover, a concept “effective mass” is introduced to further study the reasons for the high performance of the polymers. All the polymers have small effective masses, indicating good intramolecular charge transport. The results demonstrate that high‐mobility ambipolar semiconductors can be obtained by designing polymers with fine‐tuned energy levels, small effective masses, and high crystallinity.     

Toward Activity Origin of Electrocatalytic Hydrogen Evolution Reaction on Carbon‐Rich Crystalline Coordination Polymers

The fundamental understanding of electrocatalytic active sites for hydrogen evolution reaction (HER) is significantly important for the development of metal complex involved carbon electrocatalysts with low kinetic barrier. Here, the MS_x N_y (M = Fe, Co, and Ni, x /y are 2/2, 0/4, and 4/0, respectively) active centers are immobilized into ladder‐type, highly crystalline coordination polymers as model carbon‐rich electrocatalysts for H₂ generation in acid solution. The electrocatalytic HER tests reveal that the coordination of metal, sulfur, and nitrogen synergistically facilitates the hydrogen ad‐/desorption on MS_x N_y catalysts, leading to enhanced HER kinetics. Toward the activity origin of MS₂N₂, the experimental and theoretical results disclose that the metal atoms are preferentially protonated and then the production of H₂ is favored on the M? N active sites after a heterocoupling step involving a N‐bound proton and a metal‐bound hydride. Moreover, the tuning of the metal centers in MS₂N₂ leads to the HER performance in the order of FeS₂N₂ > CoS₂N₂ > NiS₂N₂. Thus, the understanding of the catalytic active sites provides strategies for the enhancement of the electrocatalytic activity by tailoring the ligands and metal centers to the desired function.     

Crystal structure of β-Cs2Mo4O13

β-Modification of cesium tetramolybdate Cs₂Mo₄O₁₃ was prepared by hydrothermal reaction of lindgrenite Cu₃(MoO₄)₂(OH)₂ with a CsNO₃ solution. The compound crystallizes in the triclinic system, space group $P\bar 1β-Modification of cesium tetramolybdate Cs₂Mo₄O₁₃ was prepared by hydrothermal reaction of lindgrenite Cu₃(MoO₄)₂(OH)₂ with a CsNO₃ solution. The compound crystallizes in the triclinic system, space group P[`1]P\bar 1, a = 8.396(5), b = 8.655(5), c = 10.413(5) ?, α = 106.158(5)°, β = 103.686(5)°, γ = 109.761(5)°, V = 636.6(6) ?³. The Mo atoms are coordinated by O atoms to form strongly distorted MoO₆⁶⁻ octahedra. The Cs atoms coordinate nine O atoms each. Eight MoO₆⁶⁻ octahedra are combined in octamolybdate complexes by sharing common edges. These fragments, in turn, are linked in zigzag chains oriented along a-axis via peripheral octahedra sharing common edges. The compound is isostructural to the previously known alkali metal tetramolybdates A₂Mo₄O₁₃ (A = K, Rb), but differs essentially from α-Cs₂Mo₄O₁₃.     

Behavior of Anhydrous Uranyl Acetate at Heating in CH3CN. Crystal Structures of New Uranyl Acetates

Finely crystalline anhydrous uranyl acetate UO₂(OOCCH₃)₂ (I) was prepared by recrystallization from acetonitrile at 140-145°C. Its X-ray diffraction pattern was indexed in the monoclinic system: a = 7.4311(5), b = 12.6622(9), c = 4.1985(2) Å, = 92.01(1)°, V = 394.8(2) ų, Z = 2, _{c a l c} = 3.265 g cm^{- 3}; probable space group C2, Cm, or C2/m. Presumably, in structure I, the coordination polyhedra of U atoms (hexagonal bipyramids), sharing common equatorial edges, are linked to form infinite chains via bridging oxygen atoms of acetate ions. Under the same conditions, the presence of water in acetonitrile results in formation of crystalline [UO₂(OOCCH₃)₂·HOOCCH₃] (II) and (NH₄)₂[(UO₂)₅(₃-O)₂(OOCCH₃)₈] (III), whose composition and structure were determined by single crystal X-ray analysis. In the structure of II, one acetate ion is bidentate chelate and the other, bidentate bridging; the coordination number (CN) of the U atom is 7. In the structure of III, there are three crystallographically independent U atoms with CN 7 and 8. The coordination polyhedra of the U atoms, sharing common edges and vertices, are linked via bridging O^{2 -} ions and oxygen atoms of acetate ions.     

Phase‐Controlled Synthesis of Monolayer Ternary Telluride with a Random Local Displacement of Tellurium Atoms

Alloying 2D transition metal dichalcogenides has opened up new opportunities for bandgap engineering and phase control. Developing a simple and scalable synthetic route is therefore essential to explore the full potential of these alloys with tunable optical and electrical properties. Here, the direct synthesis of monolayer WTe_2xS_2(1?x) alloys via one‐step chemical vapor deposition (CVD) is demonstrated. The WTe_2xS_2(1?x) alloys exhibit two distinct phases (1H semiconducting and 1T ′ metallic) under different chemical compositions, which can be controlled by the ratio of chalcogen precursors as well as the H₂ flow rate. Atomic‐resolution scanning transmission electron microscopy–annular dark field (STEM‐ADF) imaging reveals the atomic structure of as‐formed 1H and 1T ′ alloys. Unlike the commonly observed displacement of metal atoms in the 1T ′ phase, local displacement of Te atoms from original 1H lattice sites is discovered by combined STEM‐ADF imaging and ab initio molecular dynamics calculations. The structure distortion provides new insights into the structure formation of alloys. This generic synthetic approach is also demonstrated for other telluride‐based ternary monolayers such as WTe_2xSe_2(1?x) single crystals.     

W‐Based Atomic Laminates and Their 2D Derivative W1.33C MXene with Vacancy Ordering

Structural design on the atomic level can provide novel chemistries of hybrid MAX phases and their MXenes. Herein, density functional theory is used to predict phase stability of quaternary i‐MAX phases with in‐plane chemical order and a general chemistry (W_2/3M²_1/3)₂AC, where M² = Sc, Y (W), and A = Al, Si, Ga, Ge, In, and Sn. Of over 18 compositions probed, only two—with a monoclinic C2/c structure—are predicted to be stable: (W_2/3Sc_1/3)₂AlC and (W_2/3Y_1/3)₂AlC and indeed found to exist. Selectively etching the Al and Sc/Y atoms from these 3D laminates results in W_1.33C‐based MXene sheets with ordered metal divacancies. Using electrochemical experiments, this MXene is shown to be a new, promising catalyst for the hydrogen evolution reaction. The addition of yet one more element, W, to the stable of M elements known to form MAX phases, and the synthesis of a pure W‐based MXene establishes that the etching of i‐MAX phases is a fruitful path for creating new MXene chemistries that has hitherto been not possible, a fact that perforce increases the potential of tuning MXene properties for myriad applications.     

Metal‐Tuned Acetylene Linkages in Hydrogen Substituted Graphdiyne Boosting the Electrochemical Oxygen Reduction

Different from graphene with the highly stable sp²‐hybridized carbon atoms, which shows poor controllability for constructing strong interactions between graphene and guest metal, graphdiyne has a great potential to be engineered because its high‐reactive acetylene linkages can effectively chelate metal atoms. Herein, a hydrogen‐substituted graphdiyne (HsGDY) supported metal catalyst system through in situ growth of Cu₃Pd nanoalloys on HsGDY surface is developed. Benefiting from the strong metal‐chelating ability of acetylenic linkages, Cu₃Pd nanoalloys are intimately anchored on HsGDY surface that accordingly creates a strong interaction. The optimal HsGDY‐supported Cu₃Pd catalyst (HsGDY/Cu₃Pd‐750) exhibits outstanding electrocatalytic activity for the oxygen reduction reaction (ORR) with an admirable half‐wave potential (0.870 V), an impressive kinetic current density at 0.75 V (57.7 mA cm^?2) and long‐term stability, far outperforming those of the state‐of‐the‐art Pt/C catalyst (0.859 V and 15.8 mA cm^?2). This excellent performance is further highlighted by the Zn–air battery using HsGDY/Cu₃Pd‐750 as cathode. Density function theory calculations show that such electrocatalytic performance is attributed to the strong interaction between Cu₃Pd and C?C bonds of HsGDY, which causes the asymmetric electron distribution on two carbon atoms of C?C bond and the strong charge transfer to weaken the shoulder‐to‐shoulder π conjugation, eventually facilitating the ORR process.     

Synergy of Ultrathin CoOx Overlayer and Nickel Single Atoms on Hematite Nanorods for Efficient Photo-Electrochemical Water Splitting

To solve surface carrier recombination and sluggish water oxidation kinetics of hematite (α-Fe₂O₃) photoanodes, herein, an attractive surface modification strategy is developed to successively deposit ultrathin CoO_x overlayer and Ni single atoms on titanium (Ti)-doped α-Fe₂O₃ (Ti:Fe₂O₃) nanorods through a two-step atomic layer deposition (ALD) and photodeposition process. The collaborative decoration of ultrathin CoO_x overlayer and Ni single atoms can trigger a big boost in photo-electrochemical (PEC) performance for water splitting over the obtained Ti:Fe₂O₃/CoO_x/Ni photoanode, with the photocurrent density reaching 1.05 mA cm⁻² at 1.23 V vs. reversible hydrogen electrode (RHE), more than three times that of Ti:Fe₂O₃ (0.326 mA cm⁻²). Electrochemical and electronic investigations reveal that the surface passivation effect of ultrathin CoO_x overlayer can reduce surface carrier recombination, while the catalysis effect of Ni single atoms can accelerate water oxidation kinetics. Moreover, theoretical calculations evidence that the synergy of ultrathin CoO_x overlayer and Ni single atoms can lower the adsorption free energy of OH* intermediates and relieve the potential-determining step (PDS) for oxygen evolution reaction (OER). This work provides an exemplary modification through rational engineering of surface electrochemical and electronic properties for the improved PEC performances, which can be applied in other metal oxide semiconductors as well.     

Seed Growth of Tungsten Diselenide Nanotubes from Tungsten Oxides

We report growth of tungsten diselenide (WSe₂) nanotubes by chemical vapor deposition with a two‐zone furnace. WO₃ nanowires were first grown by annealing tungsten thin films under argon ambient. WSe₂ nanotubes were then grown at the tips of WO₃ nanowires through selenization via two steps: (i) formation of tubular WSe₂ structures on the outside of WO₃ nanowires, resulting in core (WO₃)–shell (WSe₂) and (ii) growth of WSe₂ nanotubes at the tips of WO₃ nanowires. The observed seed growth is markedly different from existing substitutional growth of WSe₂ nanotubes, where oxygen atoms are replaced by selenium atoms in WO₃ nanowires to form WSe₂ nanotubes. Another advantage of our growth is that WSe₂ film was grown by simply supplying hydrogen gas, where the native oxides were reduced to thin film instead of forming oxide nanowires. Our findings will contribute to engineer other transition metal dichacogenide growth such as MoS₂, WS₂, and MoSe₂.     

X-ray photoelectron spectra and electronic structure of zirconium trisulfide and triselenide

X-ray photoelectron spectra of ZrS₃ and ZrSe₃ have been recorded. These compounds may be regarded as Zr(Ch₂)Ch (Ch=S,Se) with both (Ch₂) groups and isolated Ch atoms. An unambiguous assignment of the chalcogen core levels was made by comparing the spectra with those of ZrS₂ and ZrSe₂ (where all chalcogen atoms are isolated). The levels of the (Ch₂) groups are found at higher binding energies than those of the isolated Ch atoms, which is consistent with a larger negative charge on the isolated atoms. The structures of the valence bands of ZrS₃ and ZrSe₃ are discussed in terms of a molecular-orbital scheme for the (Ch₂) groups. The exciton peaks observed in the optical absorption spectra of ZrS₃ and ZrSe₃ are assigned as due to excitations of the (Ch₂) groups.     

Mixed-ligand copper complexes with stable nitroxide — pseudotetrahedral tectons with the octahedral coordination core

The reaction of copper hexafluoroacetylacetonate (Cu(hfac)₂) with nitrile-substituted 3-imidazoline nitroxide enaminoketones (HL^R) or corresponding copper bis-chelates (CuL^R₂) yields asymmetric chelates Cu(hfac)L^R. Due to additional coordination of the nitrile and/or nitroxide groups to the copper atoms, the complexes form 3-D (R=i-Pr, Ph) and 2-D (R=n-Pr) coordination polymers. The key supramolecular feature of the complexes is that the Cu(hfac)L^R molecules having the octahedral metal ion behave as pseudotetrahedral tectons giving rise to 3-D structures. Cryomagnetic investigation of the complexes showed that due to weak interactions through the nitrile bridge the magnetic dimensionality of the materials is lower than the structural one: 1-D for Cu(hfac)L^i-Pr and 0-D for Cu(hfac)L^n-Pr and Cu(hfac)L^Ph.     

Effect of different catalyst supports on the (n,m) selective growth of single-walled carbon nanotube from Co–Mo catalyst

Co–Mo catalysts supported on four different high surface area oxides (SiO₂, Al₂O₃, MgO, and TiO₂) were evaluated to investigate the (n,m) selectivity control in single-walled carbon nanotube (SWCNT) synthesis. Results from Raman spectroscopy and thermogravimetric analysis showed that Co–Mo catalysts supported on SiO₂ and MgO possessed good selectivity toward SWCNTs, while photoluminescence and ultraviolet–visible–near-infrared spectroscopy results indicated that these two catalyst supports induced the same (n,m) selectivity to near-armchair tubes, such as (6,5) and (7,5) tubes. Catalysts supported on TiO₂ produced a mixture of multi-walled carbon nanotubes (MWCNTs) and SWCNTs, whereas catalysts supported on Al₂O₃ mainly grew MWCNTs. Characterization of catalysts by ultraviolet–visible diffuse reflectance spectroscopy suggested that the surface morphology of metal clusters over different supports was not directly responsible for the (n,m) selectivity. Analysis of monometallic (Co or Mo) and bimetallic (Co–Mo) catalysts using temperature program reduction demonstrated that catalyst supports changed the reducibility of metal species. The interaction between supports and Co/Mo metals perturbed the synergistic effect between Co and Mo, leading to the formation of different metal species that are responsible for the observed distinction in SWCNT synthesis.     

Effects of total gas flow rate and sputtering power on the critical condition for target mode transition in Al-O2 reactive sputtering

Reactive sputtering is one of the most commonly used techniques for the fabrication of compound thin films, and the critical condition for target mode transition from metal mode to oxide mode is very important. We investigated the effects of total gas flow rate and sputtering power on the critical condition in Al-O₂ reactive sputtering. It was found that the ratio of the number of sputtered Al atoms (N_Al) to the number of supplied O atoms (N_O) at the critical condition was almost constant, and the ratio of N_Al to N_O was close to the stoichiometric ratio of Al₂O₃ (2 to 3). It is thought that the introduced oxygen is gettered by Al atoms almost completely and the target remains in the metal mode below the critical condition. By increasing the amount of supplied O atoms above the stoichiometric ratio of Al₂O₃, the oxygen supply overcomes the gettering effect. Then, oxygen concentration in the plasma increases abruptly and the target mode changes from metal mode to oxide mode.     

The enhancement of spontaneous and induced transition rates by a Bose-Einstein condensate

Abstract

In this paper, an exactly solved model for the emission by N atoms is presented, the spontaneous and induced transition rates obtained, are enhanced by a factor which is proportional to the number of atoms n in the volume Λ³(2π²) (A is the transition wavelength of the atom) and dependent on the de-Broglie wavelength Λ_B in a more complicated way.     

Robust and Stable Atomically Precise Metal Nanoclusters Mediated Solar Water Splitting

Atomically precise metal nanoclusters (NCs) represent an emerging sector of light-harvesting antennas by virtue of peculiar atomic stacking fashion, quantum confinement effect, and molecular-like discrete energy band structure. Nevertheless, precise control of charge carriers over metal NCs has yet to be achieved by the short carrier lifetime and intrinsic instability of metal NCs, which renders the complexity of metal NCs-based photosystems with photoredox mechanisms remaining elusive. Herein, fine tuning of charge migration over metal NCs is demonstrated by constructing directional charge transfer channels in multilayered heterostructure enabled by a facile layer-by-layer (LbL) assembly approach, wherein oppositely charged branched poly-ethylenimine (BPEI) and glutathione (GSH)-capped gold NCs [Au_x NCs, Au₂₅(GSH)₁₈ NCs] are alternately deposited on the metal oxide (MOs: TiO₂, WO₃, Fe₂O₃) substrates. TheAu_x (Au₂₅) NCs layer serves as light-harvesting antennas for engendering charge carriers, andBPEI interim layer uniformly intercalated at the interface of Au_x NCs layer constitutes the tandem hole transport channel for motivating the charge transfer cascade, resulting in the considerably enhanced photoelectrochemical water oxidation performances. Besides, poor photo-stability of Au_x NCs is surmounted by stimulating the hole transfer kinetics process.     

Synthesis,crystal structure,and spectral properties of a complex of U(VI) with <Emphasis Type="Italic">m</Emphasis>-hydroxybenzoic acid

A new complex compound of U(VI) with m-hydroxybenzoic acid, K[(UO₂)(C₇H₅O₃)₃]·5H₂O, was prepared and characterized. A single crystal X-ray diffraction study showed that the coordination polyhedron of the U atom is a hexagonal bipyramid whose equatorial plane is formed by the O atoms of carboxy groups of three anions of m-hydroxybenzoic acid. The K atoms act as outer-sphere cations linking the adjacent anions [UO₂(C₇H₅O₃)₃]⁻ into neutral dimers {[UO₂(C₇H₅O₃)₃]K(H₂O)₃}₂. The structure also contains water molecules of crystallization, retained by hydrogen bonds.     

Correlation Between Tc and Crystal Chemical Parameters of Cation Sublattice An+1(Cu)n in Perovskite Layer of High-Tc Cuprate Superconductors

It was found the empirical dependence of T _c of high-temperature superconducting cuprates (HTSC) from the ratio (J) of such parameters as the distances between Cu atoms in CuO₂ plane and the distances from CuO₂ plane to adjacent ones of A cations (A – Ca, Sr, Ba, Y, La, and so on), also from the size and charge of A cations and doping atoms with effect on T _c is proved experimentally. All HTSC phases are divided only on two groups with an intrinsic dependence T _c (J): the phases formed by single CuO₂ plane and by several CuO₂ planes. The closer approximation of that dependence gives the equation of polynomial of third degree.     

Photoluminescence and Electrical Conductivity of As<Subscript>2</Subscript>S<Subscript>3</Subscript>〈Au〉 and As<Subscript>2</Subscript>S<Subscript>5</Subscript>〈Au〉 Glasses

The 77-K photoluminescence spectra of (As₂S₃)_{100 − x} Au_x and (As₂S₅)_{100 −x} Au_x (0 ≤ x ≤ 0.04) semiconducting glasses are measured for the first time. At low doping levels, the spectra of the (As₂S₅)_{100 − x} Au_x glasses are split into two components, one of which arises from the Au dopant. The temperature-dependent conductivity of the glasses shows two breaks at low Au concentrations and anomalous behavior in the range 300–360 K. Qualitative analysis of the conductivity data suggests that most of the impurity atoms have saturated valence bonds and form solid solutions with host atoms, changing the band gap of the material. A small fraction of the impurity atoms, those having unsaturated valence bonds, produce an electrically active level responsible for impurity conduction.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 876–880.Original Russian Text Copyright © 2005 by Babaev, Kamilov, Sultanov, Askhabov, Terukov.