Solvent-Free Mechanochemical Synthesis of a Systematic Series of Pure-Phase Mixed-Halide Perovskites MAPb(Ix Br1-x )3 and MAPb(Brx Cl1-x )3 for Continuous Composition and Band-Gap Tuning.

Hybrid perovskites have recently received much attention in optoelectronic applications. However, hybrid perovskites are unstable in a humid environment. Mixed halide perovskites (MHPs) show enhanced stability and band-gap tunability upon engineering of their halide composition. Here, MHPs are prepared through a solvent-free mechanochemical synthesis (MCS) route that allows superior control over halide compositions than the solvent synthesis routes (SS). The MCS route eliminates the problem in the preparation of MAPb(Ix Br1-x )3 with continuously varying x, while maintaining the material properties and suppressing phase segregation present in SS routes. UV-vis absorption and X-ray diffraction patterns confirm the production of the desired pure-phase MHPs. For MAPb(Ix Br1-x )3 (0≤x≤1), with increased ratio of halide (x), the cubic phase gradually transforms into the tetragonal phase and band-gap tunability is accomplished. The MCS route for the preparation of MHPs is a very promising and efficient technique for superior control in optoelectronic properties, leading to improved control in fabrication approaches.

Squeezed-Out Technique To Prepare High-Quality PbBr-Based Layered Perovskite Langmuir-Blodgett Films Applicable to Cavity Polariton Devices.

We propose a promising preparation technique to construct optically high-quality Langmuir-Blodgett (LB) films of lead bromide-based layered perovskites having an organic-inorganic quantum-well structure called "squeezed-out technique." Using this technique, we successfully prepared PbBr-based layered perovskite LB films whose average roughness is small enough to apply them for cavity polariton devices. The small roughness reveals that one can prepare microcavities having a high quality factor by using the technique. In addition, optical simulation of a cavity using the LB film demonstrated that the cavity polariton device has a large Rabi splitting of 116 meV, suggesting a stable polariton formation in the cavity even at room temperature.

PbBr-Based Layered Perovskite Organic-Inorganic Superlattice Having Carbazole Chromophore; Hole-Mobility and Quantum Mechanical Calculation.

We have successfully evaluated hole mobility in a spin-coated film of a lead-bromide based layered perovskite having carbazole chromophore-linked ammonium molecules as organic layer by using FET measurement. The values of hole mobility, threshold voltage and on/off ratio at room temperature were evaluated.to.be 1.7 x 10(-6) cm2 V-1 s-1, 27 V and 28 V, respectively. However, the spin-coated films on Si substrates were not so uniform compared with those on fused quartz substrates. To improve the film uniformity, we examined the relationship between substrate temperature during spin-coating and film morphology in the layered perovskite spin-coated films. The mean roughness of the spin-coated films on Si substrates was dependent on the substrate temperature. At 353 K, the mean roughness was minimized and the carrier mobility was enhanced by one order of magnitude; the values of hole mobility and threshold voltage were .estimated to be 3.4 x 10(-5) cm2 V-1 s-1, and 22 V at room temperature in a preliminary FET evaluation, respectively. In addition, we determined a crystal structure of the layered perovskite by X-ray diffraction analysis. To gain a better understanding of the observed hole transports, we conducted quantum mechanical calculations using the obtained crystal structure information. The calculated band structure of the layered organic perovskite showed that the valence band is composed of the organic carbazole layer, which confirms that.the measured hole mobility is mainly derived from the organic part of the layered perovskite. Band and hopping transport mechanisms were discussed by calculating the effective masses and transfer integrals for the 2D periodic system of the organic layer in isolation.

Enhancement of Exciton Emission in Lead Halide-Based Layered Perovskites by Cation Mixing.

Spin-coated films of a lead halide, PbX: X = I and Br, layered perovskites having cyclohexenylethyl ammonium molecule as an organic layer, which were mixed with other metal halide-based layered perovskites consisting of various divalent metal halides (for example, Ca2, Cdl2, FeI2, SnBr2 and so on), were prepared. The results of X-ray diffraction measurements exhibited that solid solution formation between PbX-based layered perovskite and other divalent metal halide-based layered perovskites was observed up to very high molar concentration of 50 molar% in the mixed film samples when divalent cations having ionic radius close to that of Pb2+ were employed. In the solid solution films, the exciton emission was much enhanced at room temperature. Exciton emission intensity of Pbl-based layered perovskite mixed with Cal-based layered perovskite (20 molar%) is about 5 times large that of the pristine Pbl-based layered perovskite, and that of PbBr-based layered perovskite mixed with SnBr-based layered perovskite (20 molar%) was also about 5 times large that of the pristine PbBr-based layered perovskite at room temperature.

Pyrene-cored blue-light emitting [4]helicenes: synthesis, crystal structures, and photophysical properties.

The synthesis, crystal structures and photophysical properties of two types of pyrene-cored blue-light emitting [4]helicenes (7 and 9) are reported. The chemical structures of all synthesized compounds were fully confirmed by 1H and 13C NMR spectra, mass spectroscopy as well as elemental analysis. Single-crystal X-ray analysis of these [4]helicenes revealed that there are two types of laterally naphthalene annulated helical architectures, which are clearly influenced by different R substituents. The photophysical properties of the [4]helicenes (7 and 9) were fully investigated in both solutions and films, along with the pre-cyclization products, 4,9- and 4,10-bis(phenylethenyl)pyrenes (6 and 8). Notable optical features were obtained in these compounds, which make them promising candidates for several important applications in modern electronic and optoelectronic devices, such as blue emitters in organic light-emitting devices (OLEDs), or as models for further exploring the development of a new generation of organic materials based on pyrene.

Highly emissive hand-shaped π-conjugated alkynylpyrenes: synthesis, structures, and photophysical properties.

Three alkynyl-functionalised, hand-shaped, highly fluorescent and stable emitters, namely, 2-tert-butyl-4,5,7,9,10-pentakis(p-R-phenylethynyl)pyrenes have been successfully synthesized via a Pd/Cu-catalysed Sonogashira cross-coupling reaction. The chemical structures of the alkynylpyrenes were fully characterized by their (1)H/(13)C NMR spectra, mass spectroscopy and elemental analysis. Synchrotron single-crystal X-ray analysis revealed that there is a 1-D, slipped, face-to-face motif with off-set, head-to-tail stacked columns, which are clearly influenced by the single, bulky, tert-butyl group in the pyrene ring at the 2-position. Detailed studies on the photophysical properties in both solutions and thin films strongly indicate that they might be promising candidates for optoelectronic applications, such as organic light-emitting devices (OLEDs) or as models for investigating the fluorescent structure-property relationship of the alkynyl-functionalised pyrene derivatives.

Formation of layered perovskite structure by folding monolayer during compression.

The morphology and layered structure of an alkyl ammonium bromide ultrathin film prepared on an aqueous solution of lead bromide were investigated on the basis of surface pressure-area curve measurements, reflection spectrum measurements, X-ray reflectivity measurements and atomic force microscopic observations. It became apparent that the layered structure sandwiched a two-dimensional inorganic layer between two organic monolayers was formed by folding the monolayer by compression on an aqueous PbBr2 solution.