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Abstract: Optical spacer layers based on titaniumalkoxide precursor solutions were prepared by spin-coating on top of bulk heterojunction layers based on poly-3-hexylthiophene (P3HT) and phenyl-C61-butyric acid methylester (PCBM). Models and experiment have shown that the performance of polymer solar cells can improve upon application of an optical spacer by shifting the maximum of the electrical field vector of the incident light into the active layer. This avoids the so called “dead zone” close to the reflective electrode. We demonstrate a simple linear model that can be used to predict the intensity variations of the electrical field vector of the incident light through a multilayer structure. Central to our study is the thickness of the optical layer and we find that it is critical to control the optical spacer thickness on the actual active layer employed. X-ray reflectometry allows for the simultaneous determination of the active layer thickness and of the optical spacer layer. [Copyright &y& Elsevier]

Fiber-reinforced composites deliver lightweight but strong structures that are crucial in applications ranging from aerospace to the automotive industry. The advent of freeform injection molding has made the manufacturing of complex fiber-reinforced composites with full design freedom possible. Prediction of the mechanical properties, dictated by the local microfiber orientation, is essential for the performance characterization of fiber-reinforced composites. However, with conventional microtomography, the required microscale spatial resolution and the macroscopic field of view for full-size fiber-reinforced composite pieces cannot be effectively decoupled. X-ray scattering tensor tomography enables non-destructive macroscopic mapping of the local microfiber orientation as well as their degree of alignment. Recent advancements in X-ray optics have significantly increased the acquisition speed, making the tensor tomography attractive for industrial applications. Nonetheless, integration of the tensor tomography within production lines requires a flexible and robust implementation. In this work, we demonstrate the potential of X-ray scattering tensor tomography for industrial applications by characterizing the microstructure of a centimeter-sized industrially relevant freeform injection molding fiber-reinforced composite sample. We also show that the tensor tomography is compatible with robotic arms, which can position and orient objects in three dimensions with high flexibility and therefore are ideal sample manipulators for the tensor tomography in industrial settings. The results obtained with the robotic arm are compared to those obtained with the state-of-the-art 2-axis sample manipulation scheme. The retrieved information is highly consistent and shows agreement also with structure tensor analyses of conventional microtomography data taken at selected regions of the sample for additional validation. [ABSTRACT FROM AUTHOR]

• 3D X-ray diffraction yields per-grain strain, texture, twin relations and structure. • Applicable to a broad scope of functional polycrystalline materials. • Demonstrated by application to a kesterite (CZTS) thin film solar cell. • CZTS is a technologically interesting case with complex phase composition. • 3DXRD may detect and characterize secondary phases not otherwise distinguishable. [Display omitted] The non-destructive structural characterization of individual grains in thin-films photovoltaics based on polycrystalline materials is a powerful tool for revealing important details of the microstructure of solar cell absorbers. Here, we use three-dimensional X-ray diffraction (3DXRD) to obtain statistics on the phase, size, orientation and strain tensors of the grains, as well as their twin relations in Cu 2 ZnSnS 4 (CZTS) absorbers. Moreover, this powerful approach allows the non-ambiguous determination of phases with distinct optical and electrical properties but similar lattice parameters, such as CZTS and ZnS. Our analysis over cumulative statistics of nearly 600 grains in polycrystalline CZTS reveals that a fraction of 2.5% corresponds to the ZnS secondary phase. Statistics of the strain distribution in the polycrystalline CZTS layer indicate an average tensile stress in the plane of the film of ~70 MPa and a compressive stress along the normal to the film of ~145 MPa. We found that 41% of the total number of grains in CZTS absorbers are Σ3 twins. We calculate the frequency of the six types of Σ3 boundaries, revealing that the 180° rotation along the axis<221>is the most frequent. Accessing the microstructure opens the possibility to study its influence on the properties of the film, such as bandgap variations due to strain or the role of twin boundaries in the charge transport mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: Intrinsic polymer parameters such as regio-regularity, molecular weight, and crystallinity play an important role when studying polymer stability. 18 different batches of poly-3-hexyl-thiophene (P3HT) were degraded in a solar simulator (AM1.5G, 1000 W/m2) and the degradation kinetics were monitored. The results suggest that the radical reaction responsible for the photodegradation takes place at terminal thiophene rings exposed at points were the conjugation is broken. This proposed mechanism is supported by the fact that stability scales with regio-regularity following the ratio of head-to-tail connected thiophene units. Annealing was found to relax the P3HT films and increase conjugation length and, in turn, increase stability observed as a delayed spectral blueshift caused by photochemical degradation. Crystallinity was found to play a minor role in terms of stability. Oxygen diffusion and light shielding effects were shown to have a negligible effect on the photochemical degradation rate. The results obtained in this work advance the understanding of polymer stability and will help improve the design of materials used for polymer solar cells resulting in longer lifetimes, which will push the technology closer to large-scale applications. [Copyright &y& Elsevier]

Abstract: Large area polymer tandem solar cells completely processed using roll-to-roll (R2R) coating and printing techniques are demonstrated. A stable tandem structure was achieved by the use of orthogonal ink solvents for the coating of all layers, including both active layers. Processing solvents included water, alcohols and chlorobenzene. Open-circuit voltages close to the expected sum of sub cell voltages were achieved, while the overall efficiency of the tandem cells was found to be limited by the low yielding back cell, which was processed from water based ink. Many of the challenges associated with upscaling the multilayer tandem cells were identified giving valuable information for future experiments and development. [Copyright &y& Elsevier]

Abstract: Double slot-die coating using aqueous inks was employed for the simultaneous coating of the active layer and the hole transport layer (HTL) in fully roll-to-roll (R2R) processed polymer solar cells. The double layer film was coated directly onto an electron transport layer (ETL) comprising doped zinc oxide that was processed by single slot-die coating from water. The active layer comprised poly-3-hexylthiophene:Phenyl-C61-butyric acid methyl ester (P3HT:PCBM) as a dispersion of nanoparticles with a radius of 46nm in water characterized using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The HTL was a dispersion of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) in water. The films were analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS) as chemical probe and X-ray reflectometry as physical probe, confirming the identity of the layered structure. The devices were completed with a back electrode of either Cu tape or evaporated Ag. Under standard solar spectrum irradiation (AM1.5G), current–voltage characterization (J–V) yielded an open-circuit voltage (V oc ), short-circuit current (J sc ), fill factor (FF), and power conversion efficiency (PCE) of 0.24V, 0.5mAcm−2, 25%, and 0.03%, respectively, for the best double slot-die coated cell. A single slot-die coated cell using the same aqueous inks and device architecture yielded a V oc , J sc , FF, and PCE of 0.45V, 1.95mAcm−2, 33.1%, and 0.29%, respectively. [Copyright &y& Elsevier]

Abstract: By mapping the small-angle X-ray scattering (SAXS) from a looped poly-(para-phenylene terephtalamide) (aramid, PPTA) filament using a synchrotron X-ray microbeam, we investigate the effects of axially compressive and tensile strain on internal fibrillar structures. Unique observations of oscillations in the highly anisotropic SAXS patterns indicate a regular internal structure. Upon increase of the applied compressive strain, a significant decrease in oscillation frequency is observed in the scattering pattern. With an increase in imposed tensile strain an increase in oscillation frequency in the scattering pattern is observed. One model capable of describing the intensity is a model of stacked cylinders. These cylinders could be part of the fibrillar structure present in the PPTA fibres, which consist of cylinder- to tape-like objects, the presence of which is supported by SEM images. One hypothetical physical interpretation presented here for the appearance of a regular internal structure is the occurrence of fibrillar separation in regions undergoing axially compressive strain, and the appearance of strain relief/slip planes between packs of fibrils in regions undergoing tensile strain. Compaction of these packs upon increase of tensile strain could increase the repetition distance in the structure as multiple packs combine to form a single pack. [Copyright &y& Elsevier]

Abstract: The dehydrogenation kinetics of pure and nickel (Ni)-doped (2w/w%) magnesium hydride have been investigated by in situ time-resolved powder X-ray diffraction (PXD). Deactivated samples, i.e. air exposed, are investigated in order to focus on the effect of magnesium oxide (MgO) surface layers, which might be unavoidable for magnesium (Mg)-based storage media for mobile applications. A curved position-sensitive detector covering in and a rotating anode X-ray source provide a time resolution of 45s and up to 90 powder patterns collected during an experiment under isothermal conditions. A quartz capillary cell allowed the in situ study of gas/solid reactions. Three phases were identified: Mg, and MgO and their phase fractions were extracted by Rietveld refinement or integration of selected reflections from each phase. Dehydrogenation curves were constructed and analysed by the Johnson–Mehl–Avrami formalism in order to derive rate constants at different temperatures. The apparent activation energies for dehydrogenation of pure and Ni-doped magnesium hydride were and , respectively. Differential scanning calorimetry gave, for dehydrogenation of the Ni-doped sample. The relatively high activation energies are due to MgO surface layers, retarding the diffusion of hydrogen out of . The observed difference in of ca. 50kJ/mol is likely due to the catalytic effect of Ni on the recombination of H atoms to molecules verified by theoretical considerations. [Copyright &y& Elsevier]