Solution-Processed Planar Perovskite Solar Cell Without a Hole Transport Layer

Solar cells with a structure of ITO/ZnO/CH₃NH₃PbI₃/graphite/carbon black electrode were fabricated by spin coating at ambient conditions. PbI₂ thin films were converted into CH₃NH₃PbI₃ perovskite by reacting with CH₃NH₃I in solution. The incorporation of electrochemically exfoliated graphite improved the fill factor, open circuit potential and short circuit current density. The best device yielded 10.2% power conversion efficiency

Three Unique Barium Manganese Vanadates from High-Temperature Hydrothermal Brines

Three new barium manganese vanadates, all containing hexagonal barium chloride layers interpenetrated by [V₂O₇]^4– groups, were synthesized using a high-temperature (580 °C) hydrothermal method. Two of the compounds were prepared from a mixed BaCl₂/Ba­(OH)₂ mineralizer, and the third compound was prepared from BaCl₂ mineralizer. An interesting structural similarity exists between two of the compounds, Ba₂Mn­(V₂O₇)­(OH)Cl and Ba₄Mn₂(V₂O₇)­(VO₄)₂O­(OH)­Cl. These two compounds crystallize in the orthorhombic space group <i>Pnma</i>, <i>Z</i> = 4, and are structurally related by a nearly doubled <i>a</i> axis. The first structure, Ba₂Mn­(V₂O₇)­(OH)Cl (<b>I</b>) (<i>a</i> = 15.097(3) Å, <i>b</i> = 6.1087(12) Å, <i>c</i> = 9.5599(19) Å), consists of octahedral manganese­(II) edge-sharing chains linked by pyrovanadate [V₂O₇] groups, generating a three-dimensional structure. Compound <b>II</b>, Ba₄Mn₂(V₂O₇)­(VO₄)₂O­(OH)Cl (<i>a</i> = 29.0814(11) Å, <i>b</i> = 6.2089(2) Å, <i>c</i> = 9.5219(4) Å), is composed of manganese­(III) edge-sharing chains that are coordinated to one another through pyrovanadate groups in a nearly identical way as in <b>I</b>, forming a zigzag layer. A key difference in <b>II</b> is that these layers are capped on either end by two monomeric [VO₄] groups that directly replace one [V₂O₇] group in <b>I</b>. The third compound, Ba₅Mn₃(V₂O₇)₃(OH,Cl)­Cl₃ (<b>III</b>), crystallizes in the trigonal space group <i>R</i>32 (<i>a</i> = 9.7757(4) Å, <i>c</i> = 22.4987(10) Å) and is composed of manganese­(II) trimeric units, [Mn₃O₁₂(OH,Cl)], coordinated to one another through pyrovanadate [V₂O₇] groups to form a three-dimensional structure. The unusual manganese trimers are built of three square pyramids all linked by a central (OH/Cl) atom. The key factor directing the formation of the different structures appears to be the identity and concentration of the halide brine mineralizer fluid. The ability of such brines to induce the formation of interpenetrated salt lattices in the present study is suggestive of a versatile realm of descriptive synthetic inorganic chemistry

Three Unique Barium Manganese Vanadates from High-Temperature Hydrothermal Brines

Three new barium manganese vanadates, all containing hexagonal barium chloride layers interpenetrated by [V₂O₇]^4– groups, were synthesized using a high-temperature (580 °C) hydrothermal method. Two of the compounds were prepared from a mixed BaCl₂/Ba­(OH)₂ mineralizer, and the third compound was prepared from BaCl₂ mineralizer. An interesting structural similarity exists between two of the compounds, Ba₂Mn­(V₂O₇)­(OH)Cl and Ba₄Mn₂(V₂O₇)­(VO₄)₂O­(OH)­Cl. These two compounds crystallize in the orthorhombic space group <i>Pnma</i>, <i>Z</i> = 4, and are structurally related by a nearly doubled <i>a</i> axis. The first structure, Ba₂Mn­(V₂O₇)­(OH)Cl (<b>I</b>) (<i>a</i> = 15.097(3) Å, <i>b</i> = 6.1087(12) Å, <i>c</i> = 9.5599(19) Å), consists of octahedral manganese­(II) edge-sharing chains linked by pyrovanadate [V₂O₇] groups, generating a three-dimensional structure. Compound <b>II</b>, Ba₄Mn₂(V₂O₇)­(VO₄)₂O­(OH)Cl (<i>a</i> = 29.0814(11) Å, <i>b</i> = 6.2089(2) Å, <i>c</i> = 9.5219(4) Å), is composed of manganese­(III) edge-sharing chains that are coordinated to one another through pyrovanadate groups in a nearly identical way as in <b>I</b>, forming a zigzag layer. A key difference in <b>II</b> is that these layers are capped on either end by two monomeric [VO₄] groups that directly replace one [V₂O₇] group in <b>I</b>. The third compound, Ba₅Mn₃(V₂O₇)₃(OH,Cl)­Cl₃ (<b>III</b>), crystallizes in the trigonal space group <i>R</i>32 (<i>a</i> = 9.7757(4) Å, <i>c</i> = 22.4987(10) Å) and is composed of manganese­(II) trimeric units, [Mn₃O₁₂(OH,Cl)], coordinated to one another through pyrovanadate [V₂O₇] groups to form a three-dimensional structure. The unusual manganese trimers are built of three square pyramids all linked by a central (OH/Cl) atom. The key factor directing the formation of the different structures appears to be the identity and concentration of the halide brine mineralizer fluid. The ability of such brines to induce the formation of interpenetrated salt lattices in the present study is suggestive of a versatile realm of descriptive synthetic inorganic chemistry

Honeycomb-like S = 5/2 Spin–Lattices in Manganese(II) Vanadates

New complex manganese vanadate materials were synthesized as high-quality single crystals in multi-millimeter lengths using a high-temperature, high-pressure hydrothermal method. One compound, Mn₅(VO₄)₂(OH)₄, was grown from Mn₂O₃ and V₂O₅ in 3 M CsOH at 580 °C and 1.5 kbar. Changing the mineralizer to 1 M CsOH/3MCsCl leads to the formation of another product, Mn₆O­(VO₄)₂(OH). Both compounds were structurally characterized by single-crystal X-ray diffraction (Mn₅(VO₄)₂(OH)₄: <i>C</i>2/<i>m</i>, <i>Z</i> = 2, <i>a</i> = 9.6568(9) Å, <i>b</i> = 9.5627(9) Å, <i>c</i> = 5.4139(6) Å, β = 98.529(8)°; Mn₆O­(VO₄)₂(OH): <i>P</i>2₁/<i>m</i>, <i>Z</i> = 2, <i>a</i> = 8.9363(12) Å, <i>b</i> = 6.4678(8) Å, <i>c</i> = 10.4478(13) Å, β = 99.798(3)°), revealing interesting low-dimensional transition-metal features. Mn₅(VO₄)₂(OH)₄ possesses complex honeycomb-type Mn–O layers, built from edge-sharing [MnO₆] octahedra in the <i>bc</i> plane, with bridging vanadate groups connecting these layers along the <i>a</i>-axis. Mn₆O­(VO₄)₂(OH) presents a more complicated structure with both octahedral [MnO₆] and trigonal bipyramidal [MnO₅] units. A different pattern of planar honeycomb sheets are formed by edge-shared [MnO₆] octahedra, and these sublattices are connected through edge-shared dimers of [MnO₅] trigonal bipyramids to form corrugated sheets. Vanadate groups again condense the sheets into a three-dimensional framework. Infrared and Raman spectroscopies indicated the presence of OH groups and displayed characteristic Raman scattering due to vanadate groups. Temperature-dependent magnetic studies indicated Curie–Weiss behavior above 100 K with significant anti-ferromagnetic coupling for both compounds, with further complex magnetic behavior at lower temperatures. The data indicate canted anti-ferromagnetic order below 57 K in Mn₅(VO₄)₂(OH)₄ and below 45 K in Mn₆O­(VO₄)₂(OH). Members of another class of compounds, K₂M₃(VO₄)₂(OH)₂ (M = Mn, Co), also containing a honeycomb-type sublattice, were also synthesized to allow a comparison of the structural features across all three structure types and to demonstrate extension to other transition metals

Honeycomb-like S = 5/2 Spin–Lattices in Manganese(II) Vanadates

New complex manganese vanadate materials were synthesized as high-quality single crystals in multi-millimeter lengths using a high-temperature, high-pressure hydrothermal method. One compound, Mn₅(VO₄)₂(OH)₄, was grown from Mn₂O₃ and V₂O₅ in 3 M CsOH at 580 °C and 1.5 kbar. Changing the mineralizer to 1 M CsOH/3MCsCl leads to the formation of another product, Mn₆O­(VO₄)₂(OH). Both compounds were structurally characterized by single-crystal X-ray diffraction (Mn₅(VO₄)₂(OH)₄: <i>C</i>2/<i>m</i>, <i>Z</i> = 2, <i>a</i> = 9.6568(9) Å, <i>b</i> = 9.5627(9) Å, <i>c</i> = 5.4139(6) Å, β = 98.529(8)°; Mn₆O­(VO₄)₂(OH): <i>P</i>2₁/<i>m</i>, <i>Z</i> = 2, <i>a</i> = 8.9363(12) Å, <i>b</i> = 6.4678(8) Å, <i>c</i> = 10.4478(13) Å, β = 99.798(3)°), revealing interesting low-dimensional transition-metal features. Mn₅(VO₄)₂(OH)₄ possesses complex honeycomb-type Mn–O layers, built from edge-sharing [MnO₆] octahedra in the <i>bc</i> plane, with bridging vanadate groups connecting these layers along the <i>a</i>-axis. Mn₆O­(VO₄)₂(OH) presents a more complicated structure with both octahedral [MnO₆] and trigonal bipyramidal [MnO₅] units. A different pattern of planar honeycomb sheets are formed by edge-shared [MnO₆] octahedra, and these sublattices are connected through edge-shared dimers of [MnO₅] trigonal bipyramids to form corrugated sheets. Vanadate groups again condense the sheets into a three-dimensional framework. Infrared and Raman spectroscopies indicated the presence of OH groups and displayed characteristic Raman scattering due to vanadate groups. Temperature-dependent magnetic studies indicated Curie–Weiss behavior above 100 K with significant anti-ferromagnetic coupling for both compounds, with further complex magnetic behavior at lower temperatures. The data indicate canted anti-ferromagnetic order below 57 K in Mn₅(VO₄)₂(OH)₄ and below 45 K in Mn₆O­(VO₄)₂(OH). Members of another class of compounds, K₂M₃(VO₄)₂(OH)₂ (M = Mn, Co), also containing a honeycomb-type sublattice, were also synthesized to allow a comparison of the structural features across all three structure types and to demonstrate extension to other transition metals

Hydrothermal Synthesis and Characterization of Novel Brackebuschite-Type Transition Metal Vanadates: Ba₂M(VO₄)₂(OH), M = V³⁺, Mn³⁺, and Fe³⁺, with Interesting Jahn–Teller and Spin-Liquid Behavior

A new series of transition metal vanadates, namely, Ba₂M­(VO₄)₂(OH) (M = V³⁺, Mn³⁺, and Fe³⁺), was synthesized as large single crystals hydrothermally in 5 M NaOH solution at 580 °C and 1 kbar. This new series of compounds is structurally reminiscent of the brackebuschite mineral type. The structure of Ba₂V­(VO₄)₂(OH) is monoclinic in space group <i>P</i>2₁/<i>m</i>, <i>a</i> = 7.8783(2) Å, <i>b</i> = 6.1369(1) Å, <i>c</i> = 9.1836(2) Å, β = 113.07(3)°, <i>V</i> = 408.51(2) ų. The other structures are similar and consist of one-dimensional trans edge-shared distorted octahedral chains running along the <i>b</i>-axis. The vanadate groups bridge across edges of their tetrahedra. Structural analysis of the Ba₂Mn­(VO₄)₂­(OH) analogue yielded a new understanding of the Jahn–Teller effect in this structure type. Raman and infrared spectra were investigated to observe the fundamental vanadate and hydroxide vibrational modes. Single-crystal temperature-dependent magnetic studies on Ba₂V­(VO₄)₂(OH) reveal a broad feature over a wide temperature range with maximum at ∼100 K indicating that an energy gap could exist between the antiferromagnetic singlet ground state and excited triplet states, making it potentially of interest for quantum magnetism studies

Tuning Localized Surface Plasmon Resonance Wavelengths of Silver Nanoparticles by Mechanical Deformation

We describe a simple technique to alter the shape of silver nanoparticles (AgNPs) by rolling a glass tube over them to mechanically compress them. The resulting shape change in turn induces a red-shift in the localized surface plasmon resonance scattering spectrum and exposes new surface area. The flattened particles were characterized by optical and electron microscopy, single-nanoparticle scattering spectroscopy, and surface-enhanced Raman spectroscopy (SERS). Atomic force microscopy and scanning electron microscopy images show that the AgNPs deform into discs; increasing the applied load from 0 to 100 N increases the AgNP diameter and decreases the height. This deformation caused a dramatic red shift in the nanoparticle scattering spectrum and also generated new surface area to which thiolated molecules could attach, as evident from SERS measurements. The simple technique employed here requires no lithographic templates and has potential for rapid, reproducible, inexpensive, and scalable tuning of nanoparticle shape, surface area, and resonance while preserving particle volume

One-Pot Hydrothermal Synthesis of Tb^III₁₃(GeO₄)₆O₇(OH) and K₂Tb^IVGe₂O₇: Preparation of a Stable Terbium(4+) Complex

Two terbium germanates have been synthesized via high-temperature and high-pressure hydrothermal synthesis with 20 M KOH as a mineralizer using Tb₄O₇ as a starting material. Tb₁₃(GeO₄)₆O₇(OH) crystallizes in trigonal space group <i>R</i>3̅, is built up of isolated GeO₄ units, and contains a complex arrangement of terbium oxide polyhedra. K₂TbGe₂O₇ is a terbium­(4+) pyrogermanate that is isostructural with K₂ZrGe₂O₇ and displays a rare stable Tb⁴⁺ oxidation state in the solid state

Highly Conductive and Transparent Reduced Graphene Oxide Nanoscale Films via Thermal Conversion of Polymer-Encapsulated Graphene Oxide Sheets

Despite noteworthy progress in the fabrication of large-area graphene sheetlike nanomaterials, the vapor-based processing still requires sophisticated equipment and a multistage handling of the material. An alternative approach to manufacturing functional graphene-based films includes the employment of graphene oxide (GO) micrometer-scale sheets as precursors. However, search for a scalable manufacturing technique for the production of high-quality GO nanoscale films with high uniformity and high electrical conductivity is still continuing. Here we show that conventional dip-coating technique can offer fabrication of high quality mono- and bilayered films made of GO sheets. The method is based on our recent discovery that encapsulating individual GO sheets in a nanometer thick molecular brush copolymer layer allows for the nearly perfect formation of the GO layers via dip coating from water. By thermal reduction the bilayers (cemented by a carbon-forming polymer linker) are converted into highly conductive and transparent reduced GO films with a high conductivity up to 10⁴ S/cm and optical transparency on the level of 90%. The value is the highest electrical conductivity reported for thermally reduced nanoscale GO films and is close to the conductivity of indium tin oxide currently in use for transparent electronic devices, thus making these layers intriguing candidates for replacement of ITO films