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Barium zirconium sulfide (BaZrS3) is an earth-abundant and environmentally friendly chalcogenide perovskite with promising properties for various energy conversion applications. Recently, sulfurization of oxide precursors has been suggested as a viable solution for effective synthesis, especially from the perspective of circumventing the difficulty of handling alkali earth metals. In this work, we explore in detail the synthesis of BaZrS3 from Ba-Zr-O oxide precursor films sulfurized at temperatures ranging from 700 {\deg}C to 1000 {\deg}C. We propose a formation mechanism of BaZrS3 based on a two-step reaction involving an intermediate amorphization step of the BaZrO3 crystalline phase. We show how the diffusion of sulfur (S) species in the film is the rate-limiting step of this reaction. The processing temperature plays a key role in determining the total fraction of conversion from oxide to sulfide phase at a constant flow rate of the sulfur-containing H2S gas used as a reactant. Finally, we observe the formation of stoichiometric BaZrS3 (1:1:3), even under Zr-rich precursor conditions, with the formation of ZrO2 as a secondary phase. This marks BaZrS3 quite unique among the other types of chalcogenides, such as chalcopyrites and kesterites, which can instead accommodate quite a large range of non-stoichiometric compositions. This work opens up a pathway for further optimization of the BaZrS3 synthesis process, straightening the route towards future applications of this material., Comment: Equal contribution from the first two authors

This article reports on studies of chlorine-substituted MAPbI3 using combined temperature-dependent XRD synchrotron and Pb-L3 edge EXAFS to analyze the anharmonicity of the lead halide bond. The EXAFS parameters were described in the orthorhombic phase by an Einstein or T2 type behavior, which was then compared with the experimental EXAFS parameters of the tetragonal/cubic phase. In the orthorhombic phase, it was observed that the asymmetry of the pair distribution function (cumulant C3) in MAPbCl3 is much lower than in MAPbI3. Compared with the behavior in the orthorhombic phase, the anharmonicity changed after the phase transition to the room temperature phase, with MAPbCl3 showing an increased anharmonicity and MAPbI3 a decrease. The differences between MAPbI3 and 2% chlorine substitution were small, both in the orthorhombic and tetragonal phases. By determining the structural parameters required to convert the effective force constants k0 and k3 resulting from the EXAFS analysis into the Morse potential parameters {\alpha} and D, we could establish that our results agree with other experimental findings. Moreover, by using XRD we found that the [PbX6] octahedra shrink slightly in the tetragonal phase of MAPbI3 and MAPbI2.94Cl0.06, towards increasing temperatures. This behavior in the tetragonal phase is related to the dominant negative tension effects observed by EXAFS.

Excellent conversion efficiencies of over 20 % and facile cell production have placed hybrid perovskites at the forefront of novel solar cell materials with CH3NH3PbI3 being its archetypal compound. The question why CH3NH3PbI3 has such extraordinary characteristics, particularly a hugely efficient light absorption, is hotly debated with ferroelectricity being a promising candidate. This does, however, afford the crystal structure to be non-centrosymmetric and we herein present crystallographic evidence as to how the symmetry breaking occurs on a crystallographic, and therefore long-scale, level. While the molecular cation CH3NH3+ is intrinsically polar, it is heavily disordered and cannot be the sole reason for ferroelectricity. We show that it, nonetheless, plays an important role as it distorts the neighboring iodide positions from their centrosymmetric positions.

The hybrid halide perovskites MAPbI$_{3}$, MAPbI$_{2.94}$Cl$_{0.06}$, and MAPbCl$_{3}$ (MA - methylammonium) have been investigated using inelastic and quasielastic neutron scattering (QENS) with the aim of elucidating the impact of chloride substitution on the rotational dynamics of MA. In this context, we discuss the influence of the inelastic neutron scattering caused by low-energy phonons on the QENS resulting from the MA rotational dynamics in MAPbI$_{3-x}$Cl$_{x}$. Through a comparative temperature-dependent QENS investigation with different energy resolutions, which allow a wide Fourier time window, we achieved a consistent description of the influence of chlorine substitution in MAPbI$_{3}$ on to the MA dynamics. Our results show that chlorine substitution in the low temperature orthorhombic phase leads to a weakening of the hydrogen bridge bonds since the characteristic relaxation times of C$_{3}$ rotation at 70 K in MAPbCl$_{3}$ (135 ps) and MAPbI$_{2.94}$Cl$_{0.06}$ (485 ps) are much shorter than in MAPbI$_{3}$ (1635 ps). For the orthorhombic phase, we obtained the activation energies from the temperature-dependent characteristic relaxation times ${\tau}$C$_{3}$ by Arrhenius fits indicating lower values of E$_{a}$ for MAPbCl$_{3}$ and MAPbI$_{2.94}$Cl$_{0.06}$ compared to MAPbI$_{3}$. We also performed QENS analyses at 190 K for all three samples. Here we observed that MAPbCl$_{3}$ shows slower MA rotational dynamics than MAPbI$_{3}$ in the disordered structure., Comment: Corrected typos in Title and Abstract (

Hitting hard on the binary halides yields in the formation of Cs2[AgIn]Br6. The lead-free double perovskite marks, although not usable itself, a further step forward in finding sustainable and durable perovskite materials for photovoltaic applications. Cs2[AgIn]Br6 is one of the prominent examples of double perovskites materials that have been suggested to circumvent the use of lead compounds in perovskite solar cells. We herein report the successful synthesis of the material using a mechanochemical approach. It crystallizes in an elpasolite-type structure, an ordered perovskite superstructure, with a cell parameter of a = 11.00 {\AA}. However, the compound exhibits a relatively large optical bandgap of 2.36 eV and is unstable under illumination, which impedes its use as solar absorber material at this early stage. Still, substitution of lead and the potential of this synthesis method are promising as well as the fruitful combination of theoretical considerations with experimental materials discovery.

Organic or inorganic (A) metal (M) halide (X) perovskites (AMX3) are semiconductor materials setting the basis for the development of highly efficient, low-cost and multijunction solar energy conversion devices. The best efficiencies nowadays are obtained with mixed compositions containing methylammonium, formamidinium, Cs and Rb as well as iodine, bromine and chlorine as anions. The understanding of fundamental properties such as crystal structure and its effect on the band gap, as well as their phase stability is essential. In this systematic study X-ray diffraction and photoluminescense spectroscopy were applied to evaluate structural and optoelectronic properties of hybrid perovskites with mixed compositions., Comment: 4 pages, 3 figures, 2018 IEEE 45th Photovoltaic Specialists Conference

Single crystals of the methylammonium (MA) lead halides MAPbI3, MAPbBr3, and MAPbCl3 have been investigated using infrared spectroscopy with the aim of analyzing structural and dynamical aspects of processes that enable the ordering of the MA molecule in the orthorhombic crystal structure of these hybrid perovskites. Our temperature-dependent studies were focused on the analysis of the CH/NH rocking, C-N stretching, and CH/NH bending modes of the MA molecule in the 800-1750 cm-1 frequency range. They deliver a direct comparison of the behavior of the three halides on crossing the orthorhombic-tetragonal phase transition in MA lead halide single crystals. Drastic changes of all vibrational modes close to the phase transition were clearly observed. Additional spectral features that were not discussed previously are pointed out. The transformation of the 2-dimensional orthorhombic hydrogen bond layers into a more 3-dimensional arrangement in the tetragonal phase seems to be an important feature providing deeper insight into the mechanisms that lead to a free-rotating MA molecule in the inorganic host structure. The change of the molecules site symmetry in the tetragonal crystal structure seems to be an important feature of the orthorhombic-tetragonal phase transition. For low temperatures it can be stated that the iodide is stronger influenced by hydrogen bonding than the bromide and the chloride.