Synthesis, Structure, and Characterization of 4,4'-(Anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium) Bismuth Iodide (C30H22N2)3Bi4I18, an Air, Water, and Thermally Stable 0D Hybrid Perovskite with High Photoluminescence Efficiency.

4,4'-(Anthracene-9,10-diylbis(ethyne-2,1-diyl))bis(1-methyl-1-pyridinium) bismuth iodide (C30H22N2)3Bi4I18 (AEPyBiI) was obtained as a black powder by a very simple route by mixing an acetone solution of BiI3 and an aqueous solution of C30H22N2I2. This novel perovskite is air and water stable and displays a remarkable thermal stability up to nearly 300 °C. The highly conjugated cation C30H22N2 2+ is hydrolytically stable, being nitrogen atoms quaternarized, and this accounts for the insensitivity of the perovskite toward water and atmospheric oxygen under ambient conditions. The cation in aqueous solution is highly fluorescent under UV irradiation (emitting yellow-orange light). AEPyBiI as well is intensely luminescent, its photoluminescence emission being more than 1 order of magnitude greater than that of high-quality InP epilayers. The crystal structure of AEPyBiI was determined using synchrotron radiation single-crystal X-ray diffraction. AEPyBiI was extensively characterized using a wide range of techniques, such as X-ray powder diffraction, diffuse reflectance UV-vis spectroscopy, Fourier transform infrared (FTIR) and Raman spectroscopies, thermogravimetry-differential thermal analysis (TG-DTA), elemental analysis, electrospray ionization mass spectroscopy (ESI-MS), and photoluminescence spectroscopy. AEPyBiI displays a zero-dimensional (0D) perovskite structure in which the inorganic part is constituted by binuclear units consisting of two face-sharing BiI6 octahedra (Bi2I9 3- units). The C30H22N2 2+ cations are stacked along the a-axis direction in a complex motif. Considering its noteworthy light-emitting properties coupled with an easy synthesis and environmental stability, and its composition that does not contain toxic lead or easily oxidable Sn(II), AEPyBiI is a promising candidate for environmentally friendly light-emitting devices.

Stabilizing lead halide perovskites with quaternary ammonium cations: the case of tetramethylammonium lead iodide.

Organoammonium lead halide perovskites, especially methylammonium lead iodide CH3NH3PbI3, are promising photovoltaic materials, but they are far from commercial applications due in particular to their thermal instability and moisture sensitivity. Here, we present a multitechnique study aimed at investigating the kinetic and thermodynamic stability of the simplest quaternary ammonium lead iodide, tetramethylammonium lead iodide N(CH3)4PbI3. The kinetics of thermal decomposition was studied by X-ray powder diffraction of samples treated in air at different temperatures combined with Rietveld quantitative phase analysis, and by the isoconversional analysis of differential thermal analysis measurements. Evidence for first order kinetics was obtained, with an activation energy of 280-290 kJ mol-1, suggesting that the breaking of the C-N bond is the rate determining step. The composition of the gas phase released under heating was investigated by Knudsen Effusion Mass Spectrometry, giving evidence for the occurrence of the process N(CH3)4PbI3(s) = PbI2(s) + N(CH3)3(g) + CH3I(g), consistent with the kinetic results. Decomposition pressures and thermodynamic properties were derived by Knudsen effusion mass loss experiments, obtaining values of 391.5 ± 2.0 kJ mol-1 and -577.4 ± 4.0 kJ mol-1 for the decomposition and formation enthalpies at 298 K, respectively. The reactivity towards water of N(CH3)4PbI3 was checked by XRD after total and prolonged immersion in water at room temperature. Overall, N(CH3)4PbI3 was found to be thermally much more stable than CH3NH3PbI3, both kinetically and thermodynamically, and much less prone to water-induced degradation, suggesting that the use of a quaternary ammonium cation may be an effective strategy in order to produce more stable materials.

Synthesis, physico-chemical characterization and structure of the elusive hydroxylammonium lead iodide perovskite NH3OHPbI3.

The synthesis of hydroxylammonium lead iodide NH3OHPbI3 was accomplished by means of the reaction between water solutions of HI and NH2OH with PbI2 in sulfolane in conjunction with either crystallization by CH2Cl2 vapor diffusion or sulfolane extraction with toluene. The appropriate choice of the solvent was found to be crucial in order to attain the desired material. The synthesized compound was extensively characterized by single crystal and powder X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, FT-IR spectroscopy, 1H-NMR spectroscopy, TG-DTA-QMS EGA (Evolved Gas Analysis), ESI-MS, and CHNS analysis. NH3OHPbI3 is an extremely reactive, deliquescent solid that easily oxidizes in air releasing iodine. Furthermore, it is the first reported perovskite to melt (m.p. around 80 °C) before decomposing exothermally at 103 °C. Such a chemical behavior, together with its optical absorption properties (i.e. yellow-colored perovskite), renders this material totally unsuitable for photovoltaic applications. The deliquescence of the material is to be ascribed to the strong hydrophilicity of hydroxylammonium ion. On the other hand, the relatively high Brønsted acidity of hydroxylammonium (pKa = 5.97) compared to other ammonium cations, promotes the reduction of atmospheric oxygen to water and the NH3OHPbI3 oxidation. The crystal structure, determined by single crystal X-ray diffraction with synchrotron radiation, is orthorhombic, but differs from the prototypal perovskite structure. Indeed it comprises infinite chains of face-sharing PbI6 octahedra along the c-axis direction with hydroxylammonium cations positioned between the columns, forming layers on the ac plane. The solvent intercalates easily between the layers. The crystal structure is apparently anomalous considering that the expected Goldschmidt's tolerance factor for the system (0.909) lies in the range of a stable prototypal perovskite structure. Therefore, the strong hydrogen bond forming tendency of hydroxylamine is likely to account for the apparent structural anomaly.

Screen Printed Pb3O4 Films and Their Application to Photoresponsive and Photoelectrochemical Devices.

A new and simple procedure for the deposition of lead (II, IV) oxide films by screen printing was developed. In contrast to conventional electrochemical methods, films can be also deposited on non-conductive substrates without any specific dimensional restriction, being the only requirement the thermal stability of the substrate in air up to 500 °C to allow for the calcination of the screen printing paste and sintering of the film. In this study, films were exploited for the preparation of both photoresponsive devices and photoelectrochemical cell photoanodes. In both cases, screen printing was performed on FTO (Fluorine-Tin Oxide glass) substrates. The photoresponsive devices were tested with I-V curves in dark and under simulated solar light with different irradiation levels. Responses were evaluated at different voltage biases and under light pulses of different durations. Photoelectrochemical cells were tested by current density⁻voltage (J-V) curves under air mass (AM) 1.5 G illumination, incident photon-to-current efficiency (IPCE) measurements, and electrochemical impedance spectroscopy.

Solid Solutions of Rare Earth Cations in Mesoporous Anatase Beads and Their Performances in Dye-Sensitized Solar Cells.

Solid solutions of the rare earth (RE) cations Pr(3+), Nd(3+), Sm(3+), Gd(3+), Er(3+) and Yb(3+) in anatase TiO2 have been synthesized as mesoporous beads in the concentration range 0.1-0.3% of metal atoms. The solid solutions were have been characterized by XRD, SEM, diffuse reflectance UV-Vis spectroscopy, BET and BJH surface analysis. All the solid solutions possess high specific surface areas, up to more than 100 m(2)/g. The amount of adsorbed dye in each photoanode has been determined spectrophotometrically. All the samples were tested as photoanodes in dye-sensitized solar cells (DSSCs) using N719 as dye and a nonvolatile, benzonitrile based electrolyte. All the cells were have been tested by conversion efficiency (J-V), quantum efficiency (IPCE), electrochemical impedance spectroscopy (EIS) and dark current measurements. While lighter RE cations (Pr(3+), Nd(3+)) limit the performance of DSSCs compared to pure anatase mesoporous beads, cations from Sm(3+) onwards enhance the performance of the devices. A maximum conversion efficiency of 8.7% for Er(3+) at a concentration of 0.2% has been achieved. This is a remarkable efficiency value for a DSSC employing N719 dye without co-adsorbents and a nonvolatile electrolyte. For each RE cation the maximum performances are obtained for a concentration of 0.2% metal atoms.