High-quality and millimeter-sized perovskite single crystals of CsPbBr3 and Cs4PbBr6 were prepared in organic solvents and studied for correlation between photocurrent generation and photoluminescence (PL) emission. The CsPbBr3 crystals, which have a 3D perovskite structure, showed a highly sensitive photoresponse and poor PL signal. In contrast, Cs4PbBr6 crystals, which have a 0D perovskite structure, exhibited more than 1 order of magnitude higher PL intensity than CsPbBr3, which generated an ultralow photoresponse under illumination. Their contrasting optoelectrical characteristics were attributed to different exciton binding energies, induced by coordination geometry of the [PbBr6]4– octahedron sublattices. This work correlated the local structures of lead in the primitive perovskite and its derivatives to PL spectra as well as photoconductivity.

Photoresponse of CsPbBr3 and Cs4PbBr6 Perovskite Single Crystals

Cesium lead bromide (CsPbBr3) was recently introduced as a potentially high performance thin-film halide perovskite (HaP) material for optoelectronics, including photovoltaics, significantly more stable than MAPbBr3 (MA = CH3NH3+). Because of the importance of single crystals to study relevant material properties per se, crystals grown under conditions comparable to those used for preparing thin films, i.e., low-temperature solution-based growth, are needed. We show here two simple ways, antisolvent-vapor saturation or heating a solution containing retrograde soluble CsPbBr3, to grow single crystals of CsPbBr3 from a precursor solution, treated with acetonitrile (MeCN) or methanol (MeOH). The precursor solutions are stable for at least several months. Millimeter-sized crystals are grown without crystal-seeding and can provide a 100% yield of CsPbBr3 perovskite crystals, avoiding a CsBr-rich (or PbBr2-rich) composition, which is often present alongside the perovskite phase. Further growth is demonstrated t...

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Low-Temperature Solution-Grown CsPbBr3 Single Crystals and Their Characterization

Solution-Grown CsPbBr3 Perovskite Single Crystals for Photon Detection

Structural, electronic and optical properties of CsPbX3 (X=Cl, Br, I) for energy storage and hybrid solar cell applications

Despite the prevalence of alcohols and carboxylic acids as functional groups in organic molecules and the potential to serve as radical precursors, C–O bonds remain difficult to activate. We report a synthetic strategy for direct access to both alkyl and acyl radicals from these ubiquitous functional groups via photoredox catalysis. This method exploits the unique reactivity of phosphoranyl radicals, generated from a polar/SET crossover between a phosphine radical cation and an oxygen-centered nucleophile. We show the desired reactivity in the reduction of benzylic alcohols to the corresponding benzyl radicals with terminal H atom trapping to afford the deoxygenated products. Using the same method, we demonstrate access to synthetically versatile acyl radicals, which enables the reduction of aromatic and aliphatic carboxylic acids to the corresponding aldehydes with exceptional chemoselectivity. This protocol also transforms carboxylic acids to heterocycles and cyclic ketones via intramolecular acyl radic...

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Generation of Phosphoranyl Radicals via Photoredox Catalysis Enables Voltage–Independent Activation of Strong C–O Bonds

Acyl radicals were smoothly generated from acylsilanes under photoredox-catalyzed conditions. These radicals were formed upon ultraviolet B (UV-B), solar, or visible light irradiation by using decatungstate and acridinium salts as photocatalysts. Acylation of Michael acceptors and a few styrenes resulted in a smooth preparation of unsymmetrical ketones in yields up to 89%.

Acyl Radicals from Acylsilanes: Photoredox-Catalyzed Synthesis of Unsymmetrical Ketones

The phase diagrams of the systems PbBr2 + MeBr (Me = L i , Na, K, Rb, Cs, Tl) have been measured by visual and DTA methods. The structures and the thermal characteristics of the intermediate compounds have been pointed out by X-ray diffractometric technique and by DTA-calorimetric measurements, respectively. Moreover, the thermodynamic behaviour of these systems has been discussed

https://www.degruyter.com/downloadpdf/j/zna.1971.26.issue-8/zna-1971-0812/zna-1971-0812.xml

Binary Systems Formed by Lead Bromide with (Li, Na, K, Rb, Cs and Tl)Br: a DTA and Diffractometric Study

Abstract Miscibility gaps for the solid systems AgCl + NaCl and AgBr+NaBr have been measured by a high temperature X-ray technique. For the two studied systems the solubility curves are very nearly symmetrical in respect to the compositions xNaCl = .513 and xNaBr = .506, while the upper critical temperature are 198 °C for AgCl + NaCl and 285 °C for AgBr+NaBr. The thermodynamic properties of the two solid systems have been calculated using only experimental solubility data. Values of activity and of enthalpy of mixing were estimated and compared with those reported in literature.

Thermodynamic Properties of Solid Systems AgCl + NaCl and AgBr + NaBr from Miscibility Gap Measurements

By DTA and visual methods the phase diagrams of the ten binary systems formed by lithium, sodium, potassium, rubidium and cesium bromide with barium or strontium bromide have been drawn. Moreover, the fusion thermal effects regarding the eutectics and the congruent compounds singled out in the systems have been evaluated. The general thermodynamic behaviour of these systems is discussed in comparison with the ideal one.

Riccardo Riccardi

Papers

Acyl Radicals from Acylsilanes: Photoredox-Catalyzed Synthesis of Unsymmetrical Ketones

Binary Systems Formed by Lead Bromide with (Li, Na, K, Rb, Cs and Tl)Br: a DTA and Diffractometric Study

Thermodynamic Properties of Solid Systems AgCl + NaCl and AgBr + NaBr from Miscibility Gap Measurements

Binary Systems Formed by Alkali Bromides with Barium or Strontium Bromide

Characterization of the High Temperature Form of Fe2(MoO4)3