Extreme-ultraviolet to x-ray free-electron lasers (FELs) in operation for scientific applications are up to now single-user facilities. While most FELs generate around 100 photon pulses per second, ...FLASH at DESY can deliver almost two orders of magnitude more pulses in this time span due to its superconducting accelerator technology. This makes the facility a prime candidate to realize the next step in FELs-dividing the electron pulse trains into several FEL lines and delivering photon pulses to several users at the same time. Hence, FLASH has been extended with a second undulator line and self-amplified spontaneous emission (SASE) is demonstrated in both FELs simultaneously. FLASH can now deliver MHz pulse trains to two user experiments in parallel with individually selected photon beam characteristics. First results of the capabilities of this extension are shown with emphasis on independent variation of wavelength, repetition rate, and photon pulse length.
Organic/polymer semiconductors provide unique possibilities and flexibility in tailoring their optoelectronic properties to match specific application demands. One of the key factors contributing to ...the rapid and continuous progress of organic photovoltaics (OPVs) is the control and optimization of photoactive‐layer morphology. The impact of morphology on photovoltaic parameters has been widely observed. However, the highly complex and multilength‐scale morphology often formed in efficient OPV devices consisting of compositionally similar components impose obstacles to conventional morphological characterizations. In contrast, due to the high compositional and orientational sensitivity, resonant soft X‐ray scattering (R‐SoXS), and related techniques lead to tremendous progress of characterization and comprehension regarding the complex mesoscale morphology in OPVs. R‐SoXS is capable of quantifying the domain characteristics, and polarized soft X‐ray scattering (P‐SoXS) provides quantitative information on orientational ordering. These morphological parameters strongly correlate the fill factor (FF), open‐circuit voltage (Voc), as well as short‐circuit current (Jsc) in a wider range of OPV devices, including recent record‐efficiency polymer:fullerene solar cells and 12%‐efficiency fullerene‐free OPVs. This progress report will delineate the soft X‐ray scattering methodology and its future challenges to characterize and understand functional organic materials and provide a non‐exhaustive overview of R‐SoXS characterization and its implication to date.
Control and optimization of photoactive‐layer morphology is a key strategy to boost the device performance of organic photovoltaics (OPVs). Quantitative morphological parameters (domain characteristics and orientational ordering) resolved from resonant and polarized soft X‐ray scattering techniques are introduced and correlated well with the photovoltaic parameters in a wider range of OPV systems, including the record‐efficiency polymer:fullerene and nonfullerene systems.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Whereas the role of molecularly mixed domains in organic photovoltaic devices for charge generation is extensively discussed in the literature, the impact on charge recombination and thus fill factor ...is largely unexplored. Here, a combination of soft X‐ray techniques enables the quantification of phases at multiple length scales to reveal their role regarding charge recombination in a highly efficient solution processed small molecule system 7,7′‐(4,4‐bis(2‐ethylhexyl)‐4H‐silolo3,2‐b:4,5‐b′dithiophene‐2,6‐diyl)bis(6‐fluoro‐4‐(5′‐hexyl‐2,2′‐bithiophen‐5‐yl)benzoc1,2,5thiadiazole) (p‐DTS(FBTTh2)2) . A quantitative (linear) relationship between the average composition variations and the device fill‐factor is observed. The results establish the complex interrelationship between average phase purity, domain size, and structural order and highlight the requirement of achieving sufficient phase purities to diminish bimolecular and geminate recombination in solution processed small molecule solar cells.
Resonant soft X‐ray scattering reveals a correlation between average domain purity and device fill‐factor for an efficient solution processed small molecule 7,7′‐(4,4‐bis(2‐ethylhexyl)‐4H‐silolo3,2‐b:4,5‐b′dithiophene‐2,6‐diyl)bis(6‐fluoro‐4‐(5′‐hexyl‐2,2′‐bithiophen‐5‐yl)benzoc1,2,5thiadiazole):phenyl‐C71‐butyric acid methyl ester (p‐DTS(FBTTh2)2:PC71BM) system. The results show the requirement of an optimal combination of phase purities to diminish bimolecular as well as geminate recombination.
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The efficiency with which renewable fuels and feedstocks are synthesized from electrical sources is limited at present by the sluggish oxygen evolution reaction (OER) in pH-neutral media. We took the ...view that generating transition-metal sites with high valence at low applied bias should improve the activity of neutral OER catalysts. Here, using density functional theory, we find that the formation energy of desired Ni
sites is systematically modulated by incorporating judicious combinations of Co, Fe and non-metal P. We therefore synthesized NiCoFeP oxyhydroxides and probed their oxidation kinetics with in situ soft X-ray absorption spectroscopy (sXAS). In situ sXAS studies of neutral-pH OER catalysts indicate ready promotion of Ni
under low overpotential conditions. The NiCoFeP catalyst outperforms IrO
and retains its performance following 100 h of operation. We showcase NiCoFeP in a membrane-free CO
electroreduction system that achieves a 1.99 V cell voltage at 10 mA cm
, reducing CO
into CO and oxidizing H
O to O
with a 64% electricity-to-chemical-fuel efficiency.
Abstract
European XFEL is going to provide full polarization control in the soft X-ray SASE line (SASE3). For this purpose, four helical APPLE X undulators with 90 mm period are installed downstream ...with respect to the planar undulators of the SASE3 undulator line consisting of 21 planar undulators with 68 mm period. In this contribution, the measurement technique, as well as the results of the measurements and tuning of the APPLE X undulators performed at European XFEL are presented.
We report the first generation of coherent, tunable, variable-polarization, soft X-ray femtosecond pulses, generated by a seeded free-electron laser (FEL) operating in the fresh bunch, two-stage ...harmonic upshift configuration. Characterization of the radiation proves this FEL configuration can produce single-transverse-mode, narrow-spectral-bandwidth output pulses of several tens of microjoules energy and low pulse-to-pulse wavelength jitter at final wavelengths of 10.8 nm and below. The fresh bunch configuration enhances the FEL emission at high harmonic orders by avoiding a gain depression due to the energy spread induced by the first-stage FEL interaction. Coherent signals measured down to 4.3 nm suggest this configuration is directly scalable to photon energies that will enable scientific investigations below the carbon K-edge, including access to the L-edges of many magnetic materials, with an energy per pulse unlocking the gate for experiments in the soft X-ray region with close to Fourier-transform-limited pulses.A seeded free-electron laser with a two-stage harmonic upshift configuration provided tunable and coherent soft-X-ray pulses. The configuration produced single-transverse-mode, narrow-spectral-bandwidth femtosecond pulses with energies of several tens of microjoules and a low pulse-to-pulse wavelength jitter at wavelengths of 10.8 nm and below.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The ability to determine the electronic structure of catalysts during electrochemical reactions is highly important for identification of the active sites and the reaction mechanism. Here we ...successfully applied soft X-ray spectroscopy to follow in operando the valence and spin state of the Co ions in Li
Co
O
under oxygen evolution reaction (OER) conditions. We have observed that a substantial fraction of the Co ions undergo a voltage-dependent and time-dependent valence state transition from Co
to Co
accompanied by spontaneous delithiation, whereas the edge-shared Co-O network and spin state of the Co ions remain unchanged. Density functional theory calculations indicate that the highly oxidized Co
site, rather than the Co
site or the oxygen vacancy site, is mainly responsible for the high OER activity.
The ultrafast light-activated electrocyclic ring-opening reaction of 1,3-cyclohexadiene is a fundamental prototype of photochemical pericyclic reactions. Generally, these reactions are thought to ...proceed through an intermediate excited-state minimum (the so-called pericyclic minimum), which leads to isomerization via nonadiabatic relaxation to the ground state of the photoproduct. Here, we used femtosecond (fs) soft x-ray spectroscopy near the carbon K-edge (~284 electron volts) on a table-top apparatus to directly reveal the valence electronic structure of this transient intermediate state. The core-to-valence spectroscopic signature of the pericyclic minimum observed in the experiment was characterized, in combination with time-dependent density functional theory calculations, to reveal overlap and mixing of the frontier valence orbital energy levels. We show that this transient valence electronic structure arises within 60 ± 20 fs after ultraviolet photoexcitation and decays with a time constant of 110 ± 60 fs.
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BFBNIB, NMLJ, NUK, ODKLJ, PNG, SAZU, UL, UM, UPUK
Metal halide perovskites represent a family of the most promising materials for fascinating photovoltaic and photodetector applications due to their unique optoelectronic properties and much needed ...simple and low‐cost fabrication process. The high atomic number (Z) of their constituents and significantly higher carrier mobility also make perovskite semiconductors suitable for the detection of ionizing radiation. By taking advantage of that, the direct detection of soft‐X‐ray‐induced photocurrent is demonstrated in both rigid and flexible detectors based on all‐inorganic halide perovskite quantum dots (QDs) synthesized via a solution process. Utilizing a synchrotron soft‐X‐ray beamline, high sensitivities of up to 1450 µC Gyair−1 cm−2 are achieved under an X‐ray dose rate of 0.0172 mGyair s−1 with only 0.1 V bias voltage, which is about 70‐fold more sensitive than conventional α‐Se devices. Furthermore, the perovskite film is printed homogeneously on various substrates by the inexpensive inkjet printing method to demonstrate large‐scale fabrication of arrays of multichannel detectors. These results suggest that the perovskite QDs are ideal candidates for the detection of soft X‐rays and for large‐area flat or flexible panels with tremendous application potential in multidimensional and different architectures imaging technologies.
The direct detection of soft‐X‐ray‐induced photocurrent in both rigid and flexible detectors based on all‐inorganic halide perovskite quantum dots is reported. Utilizing inexpensive inkjet printing, perovskite film is printed homogeneously on various substrates to demonstrate large‐scale fabrication. These types of detectors are ideal candidates for applications in the detection of soft/hard X‐rays and for large‐area flat/flexible imaging technologies.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Soft X‐ray spectroscopy (SXS) techniques such as photoelectron spectroscopy, soft X‐ray absorption spectroscopy and X‐ray emission spectroscopy are efficient and direct tools to probe electronic ...structures of materials. Traditionally, these surface sensitive soft X‐ray techniques that detect electrons or photons require high vacuum to operate. Many recent in situ instrument developments of these techniques have overcome this vacuum barrier. One can now study many materials and model devices under near ambient, semi‐realistic, and operando conditions. Further developments of integrating the realistic sample environments with efficient and high resolution detection methods, particularly at the high brightness synchrotron light sources, are making SXS an important tool for the energy research community. In this progress report, we briefly describe the basic concept of several SXS techniques and discuss recent development of SXS instruments. We then present several recent studies, mostly in situ SXS experiments, on energy materials and devices. Using these studies, we would like to highlight that the integration of SXS and in situ environments can provide in‐depth insight of material's functionality and help researchers in new energy material developments. The remaining challenges and critical research directions are discussed at the end.
Recent instrumentation developments have advanced soft X‐ray spectroscopic tools for studying real‐world samples. Both photon‐in‐electron‐out and photon‐in‐photon‐out spectroscopy can be performed under semi‐realistic, and operando conditions through high‐efficiency and high‐resolution detection systems at high‐brightness synchrotron light sources. This Progress Report focuses on many recent advancements on in situ soft X‐ray spectroscopic tools and their applications in developing energy materials.
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