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Stable Sb exhibits a rhombohedral structure, often referred to as distorted primitive cubic, with each Sb atom having three short and three longer first neighbor bonds. However, this crystal structure can also be interpreted as being layered, putting emphasis on only three short first neighbor bonds. Therefore, temperature-dependent extended X-ray absorption fine structure (EXAFS) spectroscopy is carried out at the Sb K-edge in order to obtain more detailed information on local structural and vibrational properties. Evaluation of the temperature-dependent bond lengths provides the temperature-dependent Peierls distortion while the temperature dependence of the variance of the interatomic distance distribution yields the EXAFS force constants. Ab initio density functional theory (DFT) calculations are used for determining projected force constants. Both EXAFS and DFT force constants are compared to those of other materials with different bonding characteristics, including two-center covalently bonded semiconductors, multicenter bonded IV-VI and V 2 VI 3 compounds, and metallic Cu. Clearly, Sb exhibits characteristics of both localized covalent bonding and delocalized multicenter bonding. This suggests a continuous transition between these two bonding scenarios and adds to the understanding of bonding in elemental Sb in particular and in IV-VI and V 2 VI 3 materials in general., (© 2025 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

The deviation from stoichiometry and the understanding of its consequences are key factors for the application of kesterites as solar cell absorbers. Therefore, this study investigates the local atomic structure of off-stoichiometric Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) and Cu2ZnGeSe4 (CZGSe) by means of Extended X-ray Absorption Fine Structure Spectroscopy. Temperature dependent measurements yield the bond stretching force constants of all cation-anion bonds in stoichiometric CZTS and CZTSe and nearly stoichiometric CZGSe. Low temperature measurements allow high precision analysis of the influence of off-stoichiometry on the element specific average bond lengths and their variances. The overall comparison between the materials is in excellent agreement with measures like ionic/atomic radii and bond ionicities. Furthermore, the small uncertainties allow the identification of systematic trends in the Cu-Se and Zn-Se bond lengths of CZTSe and CZGSe. These trends are discussed in context of the types and concentrations of certain point defects, which gives insight into the possible local configurations and their influence on the average structural parameters. The findings complement the understanding of the effect of off-stoichiometry on the local structure of kesterites, which affects their electronic properties and thus their application for solar cells., (© 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).)

A newly designed setup to perform steady-state X-ray excited optical luminescence (XEOL) spectroscopy and simultaneous XEOL and X-ray absorption spectroscopy characterization at beamline P65 of PETRA III is described. The XEOL setup is equipped with a He-flow cryostat and state-of-the-art optical detection system, which covers a wide wavelength range of 300-1700 nm with a high spectral resolution of 0.4 nm. To demonstrate the setup functioning, low-temperature XEOL studies on polycrystalline CuInSe 2 thin film, single-crystalline GaN thin film and single-crystalline ZnO bulk semiconductor samples are performed., (open access.)

Chalcogenide Cu(In,Ga)Se 2 solar cells yield one of the highest efficiencies among all thin-film photovoltaics. However, the variability of the absorber compositions and incorporated alkali elements strongly affect the conversion efficiency. Thus, effective strategies for spatially resolved tracking of the alkali concentration and composition during operation are needed to alleviate this limitation. Here, using a hard X-ray nanoprobe, we apply a synergistic approach of X-ray fluorescence analysis and X-ray beam-induced current techniques under operando conditions. The simultaneous monitoring of both compositional and functional properties in complete solar cells illustrates the exceptional capabilities of this combination of techniques in top-view geometry, where high spatial resolution resulted even underneath the electrical contacts. Our observations reveal Rb agglomerations in selected areas and compositional variations between different grains and their boundaries. The concurrent detection of the functionality exhibits negligible effects on the collection efficiency for Rb-enriched grain boundaries in comparison to their neighboring grains, which indicates the passivation of detrimental defects.

Thin-film solar cells based on Cu(In,Ga)Se 2 (CIGS) absorbers have achieved conversion efficiencies close to 23%. Such a high performance could be reached by incorporating heavy alkali elements into the CIGS absorber using an alkali fluoride post-deposition treatment (PDT). In order to improve the understanding of the effect of the PDT, we investigated a highly efficient CIGS solar cell whose absorber was subjected to a RbF-PDT. By applying synchrotron-based X-ray fluorescence analysis in combination with scanning transmission electron microscopy and electron backscatter diffraction to a cross-sectional lamella of the whole device, we were able to correlate the local composition of the absorber with its microstructure. The incorporated Rb accumulates at grain boundaries, with a random misorientation of the adjacent grains, at the p-n junction, and at the interface between the absorber and the MoSe 2 layer. The accumulation of Rb at the grain boundaries is accompanied by a reduced Cu concentration and slightly increased In and Se concentrations. Additionally, variations in the local composition of the absorber at the p-n junction indicate the formation of a secondary phase, which exhibits a laterally inhomogeneous distribution. The improved solar cell performance due to RbF-PDT can thus be expected to originate from a favorable modification of the back contact interface, the random grain boundaries, the p-n junction, or a combination of these effects.

The variation of atomic configurations and their corresponding structural parameters, such as first nearest neighbor distances, is a characteristic feature of ternary semiconductor alloys with zincblende structure. It has a strong influence on important material properties, most prominently the bandgap energy, and can contribute to a nonlinear behavior with changing alloy composition. Using (In,Ga)P as a model system, the atomic-scale structure has been modeled for all possible first nearest neighbor configurations based on experimentally determined structural parameters. While the average position of the P anion corresponds to the ideal lattice site, the average distance from this ideal lattice site does not vanish even in the random alloy. Based on this average anion displacement, the contribution to the bandgap bowing caused by structural relaxation of the alloy was calculated over the whole compositional range. Furthermore, the bowing contribution arising from the overall change of the In-P and Ga-P distances with respect to the binary values was determined. Thus, a clear distinction between the bandgap bowing caused by structural effects on the one hand and by charge redistribution on the other hand is possible.

The vibrational and thermal properties of embedded Pt nanocrystals (NCs) have been investigated with temperature-dependent extended x-ray absorption fine structure (EXAFS) spectroscopy. NCs of diameter 1.8-7.4 nm produced by ion implantation in amorphous SiO(2) were analysed over the temperature range 20-295 K. An increase in Einstein temperature (∼194 K) relative to that of a Pt standard (∼179 K) was evident for the smallest NCs while those larger than ∼2.0 nm exhibited values comparable to bulk material. Similarly, the thermal expansion of interatomic distances was lowest for small NCs. While the amorphous SiO(2) matrix restricted the thermal expansion of interatomic distances, it did not have a significant influence on the mean vibrational frequency of embedded Pt NCs. Instead, the latter was governed by finite-size effects or, specifically, capillary pressure.

We report on the observation of a fine structure in ion tracks in amorphous SiO2 using small angle x-ray scattering measurements. Tracks were generated by high energy ion irradiation with Au and Xe between 27 MeV and 1.43 GeV. In agreement with molecular dynamics simulations, the tracks consist of a core characterized by a significant density deficit compared to unirradiated material, surrounded by a high density shell. The structure is consistent with a frozen-in pressure wave originating from the center of the ion track as a result of a thermal spike.