Alternatives to lead- and tin-based perovskites for photovoltaics and optoelectronics are sought that do not suffer from the disadvantages of toxicity and low device efficiency of present-day materials. Here we report a study of the double perovskite Cs 2 TeI 6 , which we have synthesized in the thin film form for the first time. Exhaustive trials concluded that spin coating CsI and TeI 4 using an antisolvent method produced uniform films, confirmed as Cs 2 TeI 6 by XRD with Rietveld analysis. They were stable up to 250 °C and had an optical band gap of ∼1.5 eV, absorption coefficients of ∼6 × 10 4 cm –1 , carrier lifetimes of ∼2.6 ns (unpassivated 200 nm film), a work function of 4.95 eV, and a p-type surface conductivity. Vibrational modes probed by Raman and FTIR spectroscopy showed resonances qualitatively consistent with DFT Phonopy -calculated spectra, offering another route for phase confirmation. It was concluded that the material is a candidate for further study as a potential optoelectronic or photovoltaic material.

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This study is centered on the thermophysical characterization of different families of alkylammonium nitrate ionic liquids and their binary mixtures, namely the determination at atmospheric pressure of densities, electric conductivities and viscosities in the 288.15 < T/K < 353.15 range. First, measurements focusing on ethylammonium, propylammonium and butylammonium nitrate systems, and their binary mixtures, were determined. These were followed by studies involving binary mixtures composed of ethylammonium nitrate (with three hydrogen bond donor groups) and different homologous ionic liquids with differing numbers of hydrogen bond donor groups: diethylammonium nitrate (two hydrogen bond donors), triethylammonium nitrate (one hydrogen bond donor) and tetraethylammonium nitrate (no hydrogen bond donors). Finally, the behavior of mixtures with different numbers of equivalent carbon atoms in the alkylammonium cations was analyzed. The results show a quasi-ideal behavior for all monoalkylammonium nitrate mixtures. In contrast, the other mixtures show deviations from ideality, namely when the difference in the number of carbon atoms present in the cations increases or the number of hydrogen bond donors present in the cation decreases. Overall, the results clearly show that, besides the length and distribution of alkyl chains present in a cation such as alkylammonium, there are other structural and interaction parameters that influence the thermophysical properties of both pure compounds and their mixtures.

Mixing ionic liquids (as well as mixing an inorganic salt in an ionic liquid) constitutes an easy, elegant methodology to obtain new ionic materials. In this study, three ionic liquids (ILs) sharing a common cation were synthesized and mixed in nine different proportions giving rise to twentyseven binary mixtures. Specifically, 1-butyl-3-methylimidazolium nitrate, [C4C1Im][NO3], 1butyl-3-methylimidazolium chloride, [C4C1Im]Cl, and 1-butyl-3-methylimidazolium methanesulfonate, [C4C1Im][CH3SO3], were synthetized and characterized. They all share 1-butyl-3-methylimidazolium as the common, archetypal cation. None of them (or any of their binary mixtures) is liquid at the room temperature (T = 298.15 K) and two of them are only in the liquid state above temperatures of 343-353 K. Despite belonging to commonly used families of ILs, their handling and the study of their liquid properties (neat and mixtures) has become particularly difficult, mainly due to their tendency to solidify and their high viscosity (caused by hydrogenbonded networks). The main goal of this work is to evaluate the thermal, dynamic, and volumetric properties of these compounds and their mixtures, as well as the solid-liquid equilibria of their binary mixtures. Thermal properties, such as melting and glass transition temperatures were determined or calculated. Therefore, both density and viscosity have been measured, which were used for the calculation of the isobaric thermal expansion coefficient, molar volumes, excess molar volumes and viscosity deviations to linearity.