Due to the unprecedented rapid increase of their power conversion efficiency, hybrid organic-inorganic perovskites CH 3 NH 3 PbX 3 (X = I, Br, Cl) can potentially revolutionize the world of solar cells. However, despite tremendous research activity, the origin of the exceptionally large diffusion length of their photogenerated charge carriers, that is, their low recombination rate, remains elusive. Using frequency and temperature-dependent dielectric measurements across the entire frequency spectrum, it is shown that the dielectric constant conserves very high values (>27) for frequencies below 1 THz in all three halides. This efficiently prevents photocarrier trapping and their recombination owing to the strong screening of charged entities. By combining ultrasonic and Raman spectroscopy with dielectric analysis, similarly large contributions to the dielectric constant are attributed to the dipolar disorder of the CH 3 NH 3 + cations as well as lattice dynamics in the gigahertz range yielding dielectric constants of ε stat = 62 for the iodide, 58 for the bromide, and about 45 for the chloride below 1 GHz at room temperature. Disorder continuously reduces for decreasing temperature. Dipole dynamics prevail in the intermediate tetragonal phase. The low-temperature orthorhombic state is antipolar. No indications of ferroelectricity are found.

Hybrid perovskite solar cells have been creating considerable excitement in the photovoltaic community. However, they still rely on toxic elements, which impose severe limits on their commercialization. Lead-free double hybrid perovskites in the form of Cs2AgBiBr6 have been shown to be a promising nontoxic and highly stable alternative. Nevertheless, device development is still in its infancy, and performance is affected by severe hysteresis. Here we realize for the first time hysteresis-free mesoporous double-perovskite solar cells with no s-shape in the device characteristic and increased device open-circuit voltage. This has been realized by fine-tuning the material deposition parameters, enabling the growth of a highly uniform and compact Cs2AgBiBr6, and by engineering the device interfaces by screening different molecular and polymeric hole-transporting materials. Our work represents a crucial step forward in lead-free double perovskites with significant potential for closing the gap for their market uptake.

Half antiperovskites were investigated within the series Sn2−xInxCo3S2 by X‐ray diffraction, thermal analysis, and DFT band structure calculations. The shandite type structure was confirmed from powder and single crystal diffraction for the studied compounds. Co orders like Ni in the previously studied InNi3/2S. SnCo3/2S is metrically pseudo cubic and can easily be deduced from the antiperovskite MgCo3C. The Curie temperature Tc = −97 °C of SnCo3/2S was confirmed by calorimetric data. Its electronic structure indicates a spin ${1 \over 2}$ type IA half metallic ground state. Upon In doping the crystal structure becomes hexagonally distorted towards a higher chex/ahex relation. The Curie temperature rapidly falls below −135 °C for x(In) = 0.4. A metal to semiconductor transition is predicted for ordered InSnCo3S2 from its electronic band structure. For InCo3/2S a non magnetic metallic ground state is found.

No abstract

The crystallographic and electronic structures of the ternary shandite type sulfides M 3 A 2 S 2 (M ϭ Co, Ni; A ϭ In, Sn) were investigated by X-ray diffraction, as well as density functional theory (DFT) band structure calculations with respect to superstructure and type-antitype relations. The crystal structure of Ni 3 In 2 S 2 (space group R3m, a ϭ 5.371 Å , c ϭ 13.563 Å ) was determined from a single crystal. The shandites show type-antitype relations to oxostannates(II) M 2 Sn 2 O 3 (M ϭ K, Rb) analogously to perovskite and antiperovskite. With a perovskite superstructure a group-subgroup relation is given to antiperowskites like Ni 3 MgC. Because of the ordered occupation of half of the M-positions the title compounds are described as half-antiperowskites M 3/2 AS. The occupation scheme causes the formation of Kagomé-nets. From

Halfantiperovskites II: on the Crystal Structure of Pd3Bi2S2 The crystallographic structure of Pd3Bi2S2 was determined from x‐ray diffraction data and compared to parkerite (Ni3Bi2S2), shandite (Ni3Pb2S2), and a high pressure form of laflammeite (Pd3Pb2S2). For Pd3Bi2S2 the structure type of corderoite, Hg3S2Cl2 (I213) was found that represents a cubic variant (a = 8,3097(9) Å) of the parkerite structure. It turns out to be a structural antitype of the low temperature cubic modification of K2Sn2O3, analogously to the previously investigated type‐antitype relation of shandit to high‐temperature K2Sn2O3. The crystal structures are derived from perovskites ABO3 and antiperovskites M3AX with only half of the O‐ and M‐sites being occupied. The M = Ni, Pd site ordering in shandite and parkerite type compounds is discussed in terms of ordered half antiperovskite (HAP) structures M3/2AS (A = Bi, Pb). The electronic band structure of Pd3Bi2S2 is calculated within the framework of density functional theory. The compound is found to behave metallic while K2Sn2O3 and corderoite are semiconductors. The bonding is analysed in terms of covalently bond [Pd3S2]δ− networks as proposed for [Sn2O3]2− and [Hg3S2]2+.

The lead free double perovskite Cs2AgBiBr6 is an upcoming alternative to lead based perovskites as absorber material in perovskite solar cells. So far, the majority of investigations on this interesting material have focused on polycrystalline powders and single crystals. We present vapor and solution based approaches for the preparation of Cs2AgBiBr6 thin films. Sequential vapor deposition processes starting from different precursors are shown and their weaknesses are discussed. Single source evaporation of Cs2AgBiBr6 and sequential deposition of Cs3Bi2Br9 and AgBr result in the formation of the double perovskite phase. Additionally, we show the possibility of the preparation of planar Cs2AgBiBr6 thin films by spin coating.

Explaining the time-dependent evolution of photoluminescence spectra of halide perovskite single crystals after pulsed excitation requires the consideration of a range of physical mechanisms, including electronic transport, recombination and reabsorption. The latter process of reabsorption and regeneration of electron-hole pairs from a photon created by radiative recombination in the single crystal itself is termed photon recycling and has been a highly controversial topic. We use photoluminescence experiments performed under different illumination conditions combined with numerical simulations that consider photon recycling to show which parameters affect temporal decays, spectral shifts and differences in the illumination direction. In addition, we use numerical simulations with and without photon recycling to understand the relative importance of chargecarrier transport and photon recycling. We conclude that under most relevant illumination conditions and times after the pulse, electronic transport is more important than photon recycling for the spectral behavior of the transients. However, inclusion of photon recycling is imperative for the understanding of the absolute density of electrons and holes present in the crystal during a certain time after the pulse.