Br-Induced Suppression of Low-Temperature Phase Transitions in Mixed-Cation Mixed-Halide Perovskites.

Mixed-cation mixed-halide lead perovskites have been shown to be excellent candidates for solar energy conversion. However, understanding the structural phases of these mixed-ion perovskites across a wide range of operating temperatures, including very low temperatures for space applications, is crucial. In this study, we investigated the structure of formamidinium-based Cs FA Pb(Br I ) using low-temperature in situ synchrotron powder X-ray diffraction.

Disorder induced band gap lowering in kesterite type CuZnSnSeand AgZnSnSe: a first-principles and special quasirandom structures investigation.

Quaternary chalcogenides, i.e. CuZnSnS, crystallising in the kesterite crystal structure have already been demonstrated as potential building blocks of thin film solar cells, containing only abundant elements and exhibiting power conversion efficiencies of about 14.

Montmorillonite Exfoliation in LLDPE and Factors Affecting Its Orientation: From Monolayer to Multi-Nano-Layer Polymer Films.

The motivations of the present work are to investigate the exfoliation of montmorillonite within a linear low-density polyethylene matrix and to control its orientation during the cast extrusion process. The first part is focused on the exfoliation of the montmorillonite through the melt extrusion process. The accuracy and relevance of each method used to determine the exfoliation state of montmorillonite have been examined, thanks to X-ray diffraction, transmission electronic microscopy, and rheology.

Two-Channel Indirect-Gap Photoluminescence and Competition between the Conduction Band Valleys in Few-Layer MoS.

MoS is a two-dimensional layered transition metal dichalcogenide with unique electronic and optical properties. The fabrication of ultrathin MoS is vitally important, since interlayer interactions in its ultrathin varieties will become thickness-dependent, providing thickness-governed tunability and diverse applications of those properties. Unlike with a number of studies that have reported detailed information on direct bandgap emission from MoS monolayers, reliable experimental evidence for thickness-induced evolution or transformation of the indirect bandgap remains scarce.

Synergistic Role of Water and Oxygen Leads to Degradation in Formamidinium-Based Halide Perovskites.

Mixed-cation metal halide perovskites have shown remarkable progress in photovoltaic applications with high power conversion efficiencies. However, to achieve large-scale deployment of this technology, efficiencies must be complemented by long-term durability. The latter is limited by external factors, such as exposure to humidity and air, which lead to the rapid degradation of the perovskite materials and devices.

Atomic scale structure and bond stretching force constants in stoichiometric and off-stoichiometric kesterites.

The deviation from stoichiometry and the understanding of its consequences are key factors for the application of kesterites as solar cell absorbers. Therefore, this study investigates the local atomic structure of off-stoichiometric Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) and Cu2ZnGeSe4 (CZGSe) by means of Extended X-ray Absorption Fine Structure Spectroscopy. Temperature dependent measurements yield the bond stretching force constants of all cation-anion bonds in stoichiometric CZTS and CZTSe and nearly stoichiometric CZGSe.

Solvent and A-Site Cation Control Preferred Crystallographic Orientation in Bromine-Based Perovskite Thin Films.

Preferred crystallographic orientation in polycrystalline films is desirable for efficient charge carrier transport in metal halide perovskites and semiconductors. However, the mechanisms that determine the preferred orientation of halide perovskites are still not well understood. In this work, we investigate crystallographic orientation in lead bromide perovskites.

Interplay of Static and Dynamic Disorder in the Mixed-Metal Chalcohalide SnSbSI.

Chalcohalide mixed-anion crystals have seen a rise in interest as "perovskite-inspired materials" with the goal of combining the ambient stability of metal chalcogenides with the exceptional optoelectronic performance of metal halides. SnSbSI is a promising candidate, having achieved a photovoltaic power conversion efficiency above 4%. However, there is uncertainty over the crystal structure and physical properties of this crystal family.

Zinc germanium nitrides and oxide nitrides: the influence of oxygen on electronic and structural properties.

Zinc containing ternary nitrides, in particular ZnSnN and ZnGeN, have great potential as earth-abundant and low toxicity light-absorbing materials. The incorporation of oxygen in this system - may it be intentional or unintentional - affects the crystal structure of the materials as well as their optical band gaps. Herein, we explore the origins of structural changes between the wurtzite type and its hettotype, the β-NaFeO type, and highlight the effect of oxygen.

The kesterite-stannite structural transition as a way to avoid Cu/Zn disorder in kesterites: the exemplary case of the Cu(Zn,Mn)SnSe.

The solid solution series between CuZnSnSe, crystallizing in the kesterite type structure, and CuMnSnSe, adopting the stannite type structure, Cu(ZnMn)SnSe, was studied by a combination of neutron and X-ray powder diffraction. Powder samples with 0 ≤ ≤ 1 were synthesized by the solid state reaction of the pure elements and it was confirmed by wavelength-dispersive X-ray spectroscopy that each contained a homogeneous, off-stoichiometric quaternary phase. The lattice parameters and cation site occupancy factors were determined simultaneously by the Rietveld analysis of the neutron and X-ray powder diffraction data.

Elucidation of the reaction mechanism for the synthesis of ZnGeN through ZnGeO ammonolysis.

Ternary II-IV-N materials have been considered as a promising class of materials that combine photovoltaic performance with earth-abundance and low toxicity. When switching from binary III-V materials to ternary II-IV-N materials, further structural complexity is added to the system that may influence its optoelectronic properties. Herein, we present a systematic study of the reaction of ZnGeO with NH that produces zinc germanium oxide nitrides, and ultimately approach stoichiometric ZnGeN, using a combination of chemical analyses, X-ray powder diffraction and DFT calculations.

Symmetry relations in wurtzite nitrides and oxide nitrides and the curious case of Pmc2.

Binary III-V nitrides such as AlN, GaN and InN in the wurtzite-type structure have long been considered as potent semiconducting materials because of their optoelectronic properties, amongst others. With rising concerns over the utilization of scarce elements, a replacement of the trivalent cations by others in ternary and multinary nitrides has led to the development of different variants of nitrides and oxide nitrides crystallizing in lower-symmetry variants of wurtzite. This work presents the symmetry relationships between these structural types specific to nitrides and oxide nitrides and updates some prior work on this matter.

Hybrid Perovskite at Full Tilt: Structure and Symmetry Relations of the Incommensurately Modulated Phase of Methylammonium Lead Bromide, MAPbBr.

As energy-conversion materials, organic-inorganic hybrid perovskites remain a research- and finance-intensive topic. However, even for the arguably most iconic representatives, methylammonium and formamidinium lead halides, the crystal structures of several polymorphs have remained undetermined. Herein, we describe the incommensurately modulated structure of MAPbBr in (3+1)D superspace, as deduced from single-crystal X-ray diffractometry despite systematic twinning.

BaZrS Chalcogenide Perovskite Thin Films by HS Sulfurization of Oxide Precursors.

The earth-abundant ternary compound BaZrS, which crystallizes in the perovskite-type structure, has come into view as a promising candidate for photovoltaic applications. We present the synthesis and characterization of polycrystalline perovskite-type BaZrS thin films. BaZrO precursor layers were deposited by pulsed laser deposition and sulfurized at various temperatures in an argon-diluted HS atmosphere.

Cation distribution in CuZnSnSe, CuFeSnS and CuZnSiSe by multiple-edge anomalous diffraction.

Multiple-Edge Anomalous Diffraction (MEAD) has been applied to various quaternary sulfosalts belonging to the adamantine compound family in order to validate the distribution of copper, zinc and iron cations in the structure. Semiconductors from this group of materials are promising candidates for photovoltaic applications. Their properties strongly depend on point defects, in particular related to cation order-disorder.

Twinning in MAPbI at room temperature uncovered through Laue neutron diffraction.

The crystal structure of MAPbI, the signature compound of the hybrid halide perovskites, at room temperature has been a reason for debate and confusion in the past. Part of this confusion may be due to twinning as the material bears a phase transition just above room temperature, which follows a direct group-subgroup relationship and is prone to twinning. Using neutron Laue diffraction, we illustrate the nature of twinning in the room temperature structure of MAPbI and explain its origins from a group-theoretical point-of-view.

The influence of deuteration on the crystal structure of hybrid halide perovskites: a temperature-dependent neutron diffraction study of FAPbBr.

This paper discusses the full structural solution of the hybrid perovskite formamidinium lead tribromide (FAPbBr) and its temperature-dependent phase transitions in the range from 3 K to 300 K using neutron powder diffraction and synchrotron X-ray diffraction. Special emphasis is put on the influence of deuteration on formamidinium, its position in the unit cell and disordering in comparison to fully hydrogenated FAPbBr. The temperature-dependent measurements show that deuteration critically influences the crystal structures, i.

The Role of Bulk and Interface Recombination in High-Efficiency Low-Dimensional Perovskite Solar Cells.

2D Ruddlesden-Popper perovskite (RPP) solar cells have excellent environmental stability. However, the power conversion efficiency (PCE) of RPP cells remains inferior to 3D perovskite-based cells. Herein, 2D (CH (CH ) NH ) (CH NH ) Pb I perovskite cells with different numbers of [PbI ] sheets (n = 2-4) are analyzed.

The phase diagram of a mixed halide (Br, I) hybrid perovskite obtained by synchrotron X-ray diffraction.

By using synchrotron X-ray powder diffraction, the temperature dependent phase diagram of the hybrid perovskite tri-halide compounds, methyl ammonium lead iodide (MAPbI, MA = CHNH ) and methyl ammonium lead bromide (MAPbBr), as well as of their solid solutions, has been established. The existence of a large miscibility gap between 0.29 ≤ ≤ 0.

Determination of the miscibility gap in the solid solutions series of methylammonium lead iodide/chloride.

Perovskites are widely known for their enormous possibility of elemental substitution, which leads to a large variety of physical properties. Hybrid perovskites such as CHNHPbI (MAPbI) and CHNHPbCl (MAPbCl) are perovskites with an ABX-structure, where A is an organic molecule, B is a lead(II) cation and X is a halide anion of iodine or chlorine. Whereas MAPbCl crystallizes in the cubic space group Pm{\overline 3}m, MAPbI is in the tetragonal space group I4/mcm.

Facile Bulk Synthesis of π-Cubic SnS.

The cubic modification of binary tin sulfide (SnS) has gained significant interest as an earth-abundant, low-toxicity solar absorber material with a band gap close to the optimal value for the conversion of sunlight. We herein report a simple synthesis for the metastable material, which will allow more elaborate characterization methods to be used on this material, and present a full powder refinement of the material along with some preliminary results on the optical and thermal stability properties.

Microstrain distribution mapping on CuInSe2 thin films by means of electron backscatter diffraction, X-ray diffraction, and Raman microspectroscopy.

The investigation of the microstructure in functional, polycrystalline thin films is an important contribution to the enhanced understanding of structure-property relationships in corresponding devices. Linear and planar defects within individual grains may affect substantially the performance of the device. These defects are closely related to strain distributions.