Perovskite solar cells consist of CH₃NH₃PbI₃ perovskite crystals. The purpose of this study is to improve the conversion efficiency and stability of the perovskite solar cells by adding a small amount of ethylammonium (EA) and rubidium (Rb) to the CH₃NH₃PbI₃ compounds. Addition of ethylamine hydrobromide and rubidium iodide provided an increase in carrier concentration and promotion of crystal growth, resulting in an improvement in conversion efficiencies and stability. First-principles calculations showed that the addition of Rb lowered the total energy and made the crystal stable. The band calculation also shows that the EA addition reduces the effective mass and improves the carrier mobility.

Fabrication and characterization of CH₃NH₃PbI₃ (MAPbI₃) perovskite solar cells using copper phthalocyanine complex (CuPc) and tetracyanoquinodimethane (TCNQ) with decaphenylpentacyclosilane were performed. Effects of chemical group such as carboxyl or amino group in CuPc on the photovoltaic properties were investigated by changing the concentration. Incorporation of carboxyl-CuPc and TCNQ on the perovskite layer improved the short circuit current density related to conversion efficiency. The photovoltaic performance depended on the (100) crystal orientation and the surface coverage. The stability of the conversion efficiency was maintained for 30 days by suppression of decomposition of the perovskite layer using carboxyl-CuPc and TCNQ. The molecular interaction between CuPc and TCNQ was discussed by the molecular orbital and density of states near highest occupied molecular orbital and lowest unoccupied molecular orbital.

The formation of quaternary compounds in the A^I₂X–B^IIX–C^IVX₂ systems where A^I–Cu, Ag; B^II–Zn, Cd, Hg; C^IV–Si, Ge, Sn; X–S, Se, Te is known for seven component combinations. The most common are the phases with the equimolar ratio of all three binary compounds described by the A^I₂B^IIC^IVX₄ formula. These quaternary compounds crystallize in non-centrosymmetric structures and may be of interest for nonlinear optics.

The boundary sides of the presented systems Ag₂Se–Zn(Cd, Hg, Pb)–SnSe₂ feature only two compounds, Ag₈SnSe₆ (Ag₂Se–SnSe₂ system) and Hg₂SnSe₄ (HgSe–SnSe₂ system).

The Ag₂Se–ZnSe–SnSe₂ and Ag₂Se–CdSe–SnSe₂ systems contain only one intermediate quaternary compound each, Ag₂Zn(Cd)SnSe₄, that form at the non-quasi-binary sections “Ag₂SnSe₃”–Zn(Cd)Se. The diffraction pattern of Ag₂ZnSnSe₄ was indexed in the tetragonal structure of the stannite type Cu₂FeSnS₄ (S.G. I2m) with the lattice parameters а=0.60434(2), с=1.13252(5) nm. The structure of the Ag₂CdSnSe₄ compound was determined in the orthorhombic symmetry, S.G. Cmc2₁. The Ag₈SnSe₆–Zn(Cd)Se sections of these systems are quasi-binary, of the eutectic type, with large solid solution ranges.

The Ag₂Se–HgSe–SnSe₂ system features at 670 K three intermediate phases, Ag₂HgSnSe₄, Ag₄Hg₃Sn₂Se₉, and Ag₆HgSnSe₆. Ag₂HgSnSe₄ crystallizes in the orthorhombic S.G. Pmn2₁. The Ag₄Hg₃Sn₂Se₉ compound crystallizes in the orthorhombic S.G. Imm2. This compound has a homogeneity region that is stretched to the ternary compound Hg₂SnSe₄. Тhe Ag₆HgSnSe₆ structure was not investigated.

No quaternary compounds were found in the Ag₂Sе–PbSе–SnSe₂ system. Ag₈SnSe₆–PbSe is the triangulating section in this system

Nanoparticles of magnetite have many biomedical applications: magnetic cell separation, DNA extraction, magnetic resonance, hyperthermia therapy, etc. Many of these properties depend of the particle size; therefore, methods able to control particle size are needed¹. Magnetotactic bacteria, like Magnetospirillum strains are able to produce magnetite crystals inside their magnetosomes with a perfect shape and size considered the ideal magnetic nanoparticle.² The particular and specie-specific morphologies of those magnetosomes are still not well understood, and some authors have pointed, as one of the possible cause, the confined space in which those crystals are produced. Crystallization in confinement occurs in a different manner compared to crystallization in bulk. During it, is possible to stabilize and study metastable polymorphs, to form crystals with preferred orientations, to modify morphologies, size and shape of crystals.³ To study the formation of magnetite crystals in a confined space we have created cross-linked protein crystals and used them as a matrix to promote the magnetite formation. Protein crystals are highly porous materials with a defined pore size that depends on the type of protein. In this work we have used two proteins (lysozyme and lipase), that have very different pore sizes.

Our preliminary data show the formation of small iron nanoparticles inside of both protein crystals and confirm penetration and accumulation of iron ions inside the protein crystals. Further studies will give more information about the role of protein crystals in the formation of magnetite nanoparticles.

References:

[1] Thomsen LB, Thomsen MS, Moos T. Targeted drug delivery to the brain using magnetic nanoparticles. Ther Deliv. 2015.

[2] Lovley, Derek R. Environmental Microbe-Metal Interactions. John Wiley & Sons, 2000.

[3] Meldrum, Fiona C, and O'Shaughnessy, Cedrick. "Crystallization in Confinement." Advanced Materials 2020

Bacterial methyl-accepting chemotaxis proteins (MCP) are the membrane bound receptors responsible for regulating swimming behavior in response to the extracellular chemicals ques. MCP forms a homodimer consisting of periplasmic ligand binding domain, a transmembrane domain, and a cytoplasmic signaling domain. Although their structural architecture and signaling mechanism are well conserved in many bacterial species, detailed structural information of the signaling domain has not been elucidated yet, especially, in the membrane lipid bilayer. In this study, Tsr, a serine chemoreceptor in Escherichia coli, has been used for the structural study of MCP in the lipid bilayer. The recombinant Tsr was overexpressed in E. coli and purified followed by the reconstitution into nanodiscs for providing the lipid bilayer environment. Structural characteristics of Tsr in nanodiscs were first investigated by the transmission electron microscopy (TEM) with negative staining followed by cryo-EM. EM studies revealed that Tsr was successfully reconstituted into nanodisc as one to three TSR dimers were identified in one nanodisc. However, while nanodiscs are well elucidated with strong intensity, Tsr was seen as thin tails embedded in the nanodics. Furthermore, cytoplasmic helical tails below HAMP domain showed high flexibility by displaying various conformation in the micrograph, which resulted in disappearance of the most of tail part during 2D classification and averaging steps. These results suggest that Tsr form a strong dimer with flexible conformation in the cytoplasmic signaling domain. However, trimer of dimer is not stable in the lipid bilayer environment although previous studies suggested that dimer forms trimer via interaction among cytoplasmic domains. Further cryoEM studies of Tsr in complex with other signaling mediators such as CheA ad CheW will elucidate the detailed protein interactions and their signaling mechanism.

Although silicon solar cells are currently the most common solar cells, they have a complicated fabrication process and are expensive. Recently developed CH₃NH₃PbI₃ (MAPbI₃)-based perovskite compounds have demonstrated numerous advantages, such as tunable band gaps, an easy fabrication process and high conversion efficiencies. However, MAPbI₃ compounds are unstable in air due to the migration of CH₃NH₃ (MA). MAPbI₃ crystals are known to be able to control their electronic states by the addition of other cations and anions, and this could be used to improve the stability of the perovskite photovoltaic devices. The purpose of this work is investigate the effects of addition of guanidinium [C(NH₂)₃; GA] on MAPbI₃ perovskite solar cells fabricated at a high temperature of 190 °C in atmospheric air. The addition of guanidinium iodide and the insertion of decaphenylpentasilane between the perovskite and hole transport layer improved the external quantum efficiency and short-circuit current density, and the conversion efficiencies were stable after 1 month. X-ray diffraction showed that the lattice constant of the perovskite crystals was increased by the addition of GA, and the GA addition also improved the surface morphology. First principles calculations on the density of states and band structures showed reduction of the total energy by the GA addition and the effectiveness of the nitrogen atoms in GA.

Recently, widely used method for recycling fly ash waste of coal collected from the electrostatic precipitators is the synthesis of zeolites from this waste material. Subsequently, zeolites can be used for a variety of purposes, but one that is attracting growing attention is the use of their porous structure for detection of volatile organic compounds. In this study fly ash of lignite coal collected from the electrostatic precipitators of one of the biggest TPPs in Bulgaria was used as a raw material for synthesis of zeolites of Na-X type by ultrasonic-assisted double stage fusion-hydrothermal alkaline conversion.

In order to reduce the size of the synthesized zeolites and thus to improve the quality of the composite thin films, as well as to study the influence of zeolites’ sizes on the sensing properties, the synthesized zeolites were wet-milled at three different durations. All zeolite powders were studied from the viewpoint of their surface morphology and structure via scanning electron microscopy and X-ray diffraction, respectively. The porosity and particle size of Na-X zeolites prior to and after milling were investigated by N₂-physisorption and Dynamic Light Scattering, respectively.

Zeolites thus obtained (milled and not-milled) were used to produce composite thin films based on sol-gel niobium pentoxide (Nb₂O₅). A complete optical characterization of the thin films was made and their sensing properties with respect to acetone vapor were studied. The change in the reflection coefficient ∆R of the films was calculated from measured reflectance spectra of the films prior and after exposure to the selected vapors.

Acknowledgments

Research equipment of Distributed Research Infrastructure INFRAMAT, part of Bulgarian National Roadmap for Research Infrastructures, supported by Bulgarian Ministry of Education and Science was used in this investigation.

The crystal structures of various types of perovskite halide compounds expected for solar cells were summarized and described. Atomic arrangements of these perovskite compounds can be investigated by X-ray diffraction and transmission electron microscopy. Based on the structural models, X-ray diffractions were calculated and discussed. Other halides such as elemental substituted or cation ordered double perovskite compounds were also described. In addition to the ordinary 3-dimensional perovskites, low dimensional perovskites with 2-, 1-, or 0-dimensionalities were summarized. The structural stabilities of the perovskite halides could be investigated by calculating the tolerance and octahedral factors, which can be useful for the guideline of elemental substitution to improve the structures and properties, and several low toxic halides were proposed. For the device conformation, highly crystalline-orientated grains and dendritic structures can be formed and affected the photovoltaic properties. The actual crystal structures of perovskite halides in the thin film configuration can be investigated by Rietveld analysis optimizing the atomic coordinates and occupancies. These results are useful for structure analysis of perovskite halide crystals, which are expected to be next-generation solar cell materials.

Many previous studies in the field of metamaterial absorbers have showed either wide or narrow absorption bandwidth. In this study, we propose a new electromagnetic metamaterial absorber with an appropriate bandwidth. In addition, the absorption turns out to be insensitive to the polarization of incident electromagnetic wave, and maintains a greatly high absorption even at a large incident angle such as 45 degrees. The absorption band can be adjusted easily with the parameters of structure, and the absorber itself is also flexible, which is good for the practical applications. We believe that the design concept provides a new candidate for some fields where the absorption bandwidth is required specifically, and this suggested absorber can be applied in many practical fields, additionally because of the low cost and superior performance.

Crystallization is a key purification technology adopted in more than 80% of all pharmaceutical products. However, the control of crystal shape and size can be very challenging particularly in the case of needle-like and plate-like crystals. The control of crystal shape and size distribution is critical to improve processability and physical properties of active pharmaceutical ingredients, such as dissolution, downstream processability and flowability. In recent years, spherical agglomeration (SA) received growing interest in the pharmaceutical industry as a shape modification technique, as an alternative to temperature cycling, shape modifiers, or wet milling. SA is commonly achieved in batch systems by adding a suitable bridging liquid (BL) to a system containing fully formed (after equilibrium) or growing (spherical crystallization) crystals. One of the major challenges in spherical agglomeration is to fine-tune particle size distribution, as most of the SA processes suffer from poor scalability and poor control of the droplet size of the BL.

In this study, two novel SA processes based on membrane systems were successfully implemented to produce spherical agglomerates of benzoic acid in a solvent: antisolvent crystallization process. Two membrane configurations were implemented; a flat disc mounted in a dispersion cell equipped with a mixing impeller, and a second one which was a cylindrical membrane equipped with a vibrating module which created shear with upward-downward vibration. To optimize the performance of the SA process, the impact of the BL flowrate, membrane pore size and pore arrangement, as well as agitation rate were investigated. Both systems were successfully used to generate spherical agglomerates with enhanced quality and size distribution. Smaller agglomerates were obtained with smaller pore size. In near future, the membrane systems will be scaled-up to investigate the scalability of the proposed SA system under the optimized operating conditions identified from the current study.