Multiple-cation mixed-halide (Cs,FA,MA)Pb(I,Br)3 perovskites containing cesium, formamidinium (FA), and methylammonium (MA) possess excellent properties for a wide range of optoelectronic applications such as thin-film photovoltaics or lasers. We investigate the role of excitons and the exciton binding energy EB, relevant for the effectiveness of charge separation in solar cells, as well as the temperature-dependent bandgap energy Eg which is used as an indicator for crystal phase transitions. Generalized Elliott fits of absorption spectra offer the possibility to determine both EB and Eg. However, since excitonic effects are non-negligible even at room temperature, a careful and detailed analysis of the spectra is crucial for a correct interpretation. Therefore, an additional evaluation based on a so-called f-sum rule is applied to achieve an improved reliability of the results at higher temperatures. The obtained EB values of 20–24 meV for Cs-containing mixed perovskite compounds are below the ones of 24–32 meV and 36–41 meV for pure methylammonium lead iodide (MAPbI3) and bromide (MAPbBr3), respectively, and, thus, facilitate charge-carrier separation in photovoltaic applications. Furthermore, temperature-dependent (T = 5–300 K) studies of Eg in (Cs,FA,MA)Pb(I,Br)3 indicate a suppressed crystal phase transition by the absence of any phase-transition related signatures such as the well-known jump of about 100 meV in MAPbI3. We verify these results using temperature-dependent electroreflectance spectroscopy, which is a very reliable technique for the direct and non-destructive determination of optical resonances of the absorber layer in complete solar cells. Additionally, we confirm the suppression of the phase transition in Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3 by temperature-dependent X-ray diffraction.

Intercalation of organic cations in superconducting iron selenide can significantly increase the critical temperature (T c ). We present an electrochemical method using β-FeSe crystals (T c ≈ 8 K) floating on mercury as cathode to intercalate tetramethyl ammonium ions (TMA + ) quantitatively and yielding bulk samples of (TMA) 0.5 Fe 2 Se 2 with T c = 43 K. The layered crystal structure is closely related to the ThCr 2 Si 2 -type with disordered TMA + ions on the Th position between the FeSe layers. Although the organic ions are not detectable by X-ray diffraction, packing requirements as well as first principles DFT

A series of bis(pyrazolyl)methane copper complexes were found to catalyze a fast palladium‐free Sonogashira coupling reaction of several iodoarenes with terminal alkynes such as phenylacetylene, propargyl benzyl ether, and (tert‐butyl‐dimethyl)silylacetylene. These reactions proceed with CuCl2·2H2O (10 mol‐%) under aerobic conditions and the corresponding chelate ligand (10 mol‐%), with its tailored facial coordination mode, is crucial for the success of the reaction. The coupling can also be carried out in water with liquid aryl halides and a phase‐transfer catalyst.

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Red single crystals of β‐WO2 were synthesized under high‐pressure/high‐temperature conditions of 13.1 GPa and 1693 K in a Walker‐type multianvil apparatus. β‐WO2 crystallizes in the space group Pnma (Z=12) with the lattice parameters a=9.7878(5), b=8.4669(4), c=4.7980(2) Å, and V=397.62(3) Å3. The structure consists exclusively of WO6 octahedra, forming a twinned distorted rutile type structure. Temperature dependent X‐ray powder diffraction measurements at normal pressure conditions revealed an irreversible phase transition from β‐WO2 to α‐WO2 between 1173 and 1223 K. Magnetic measurements showed weakly positive susceptibility values which increase to lower temperatures. This is caused by traces of paramagnetic impurities. DFT calculations predict β‐WO2 to be a semiconductor with an indirect band gap of about 0.6 eV.