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Recently, a record open-circuit voltage (1.1 V) is obtained for wide-bandgap Cu2ZnGeS4 (CZGS) thin-film solar cells with a Zn1-xSnxOy (ZTO) buffer grown by atomic layer deposition (ALD) (N. Saini et al. Sol. RRL 2021, 2100837). However, a low short-circuit current and a small variation in device performance with ZTO properties are observed, suggesting similar interface properties. Since the CZGS absorber cannot be etched due to peeling, it is suggested that the presence of an oxide interlayer can influence the device performance. Here, the chemical and electronic properties of the near-surface region of CZGS absorber and its interface with ZTO buffers with varying properties (bandgap and thickness) are studied nondestructively by employing excitation-dependent X-ray photoelectron spectroscopy. The formation of Ge oxide species is indicated at the absorber surface during device fabrication, which is preserved during ALD. Further, it is shown that the ZTO/CZGS interface properties are similar and not influenced by variations in ZTO properties, which can explain the small variation in device performance. Thus, attention shall be given to possible absorber surface cleaning treatment typically applied before the buffer deposition for Ge-containing CZGS, and an optimization of the ALD ZTO buffer layer growth shall be considered for a non-etched absorber.

This contribution studies the effect of ordered vacancy compounds (OVCs) on the minority carrier collection in wide-gap (Ag,Cu)(In,Ga)Se2 (ACIGS) solar cells. For this purpose, three samples with different ([Ag]+[Cu])/([In]+[Ga]) (I/III) values were processed: 1) a very off-stoichiometric absorber (I/III = 0.31), consisting of isolated chalcopyrite patches embedded in a major OVC bulk phase, 2) a moderately off-stoichiometric absorber (I/III = 0.77) with OVC patches at the front and back interfaces and 3) a close-stoichiometric absorber (I/III = 0.94) with only very few, isolated OVC patches. For each of these samples, synchrotron-based X-ray fluorescence (XRF) was measured on a nanoscale (55 nm resolution), while simultaneously recording the X-ray beam induced current (XBIC). The results, complemented by transmission electron microscopy and electron-beam induced current analyses, clearly indicate that the presence of the OVC phase reduces the carrier collection and thus the short-circuit current density of off-stoichiometric wide-gap ACIGS solar cells.

Two inorganic electron-selective layers (ESLs), Sn1-xGexOy (TGO) and Zn1-xGexOy (ZGO), were developed by using atomic layer deposition (ALD) with in situ quartz crystal monitoring. To ensure (Ag,Cu)(In,Ga)Se-2 (ACIGS) solar cell compatibility, a 120 degrees C ALD process was developed for GeOy using Ge(N(CH3)(2))(4) and H2O as precursors. In the ALD supercycle approach, the GeOy ALD cycle was interchanged with either ZnO or SnOy cycles to deposit TGO and ZGO with varying conduction band positions (Ec), respectively. The material properties were experimentally verified using X-ray photoelectron spectroscopy and optical absorption and by employing these films as ESLs in ACIGS solar cells. There, the open-circuit voltage initially increased as the Ge content of the TGO and ZGO films increased due to the ESL E-c simultaneously shifting up from the low position in ZnO or SnOy to match the ACIGS E-c. As the Ge content increased further, the fill factor (FF) of these devices decreased since the ESL E-c became positioned significantly above the ACIGS E-c, forming an energy barrier as seen from ACIGS. As a result, the efficiency of the ACIGS solar cell peaked for an intermediate Ge content for both TGO and ZGO. Using good TGO and ZGO compositions in ACIGS solar cells gave efficiencies of up to 14.8 and 17.0%, respectively, which were lower than the reference best cell efficiencies of up to 19.5% for CdS and 18.2% for Zn1-xSnxOy (ZTO). ZGO was, however, able to shift its Ec further up than ZTO, making it a potent ESL for high-band-gap absorbers. Based on the results, we listed a few key properties that are required for a good ACIGS solar cell ESL and gave a few suggestions on how they are linked to the previous success of ZTO.

Alloying a Cu(In,Ga)Se-2 (CIGS) solar cell absorber with silver to form (Ag,Cu)(In,Ga)Se-2 (ACIGS) is an effective route for improving the performance of CIGS-based thin-film solar cells by increasing the optical band gap and open-circuit voltage. While the role of Ag on the solar cell's performance and crystal structure has been analyzed, important gaps in our understanding remain, especially regarding the atomistic (short-range) structure. Previous X-ray absorption spectroscopy (XAS) results have shown that local atomic arrangements in Ag-free CIGS deviate from the long-range crystallographic structure deduced from X-ray diffraction (XRD). However, it is unclear how these structural deviations evolve with Ag alloying, particularly in the presence of Ga depth gradient. In this work, we employ angle-resolved XAS to probe the local environment of Se atoms within different depths of ACIGS absorbers with varying Ag content and Ga depth gradient. By complementing XAS results with X-ray diffraction measurements for long-range structures, glow discharge optical emission spectroscopy for elemental profiles, and scanning transmission electron microscopy for morphologies, changes in element-specific bond lengths, cell parameters, and anion displacement depending on compositions of Group [I] (Cu, Ag) and Group [III] (In, Ga) elements were mapped. The results suggest that the local atomic arrangement of the investigated ACIGS thin-film solar cell samples is depth-dependent and deviates from the long-range crystallographic structure. Possible reasons include tetragonal distortion or the presence of other phases or off-stoichiometry compounds. For the sample with the highest Ag content, increased bond lengths of Se-Group [I] atoms and Se-Ga are observed from the absorber bulk toward the near-absorber/buffer interface, whereas, in Ag-free CIGS, no significant changes are found. Results further indicate nonlinear anion displacement with Ag addition in the absorber bulk or with dep

Ag alloying and the introduction of alkali elements through a postdeposition treatment are two approaches to improve the performance of Cu(In,Ga)Se2 (CIGS) thin film solar cells. In particular, a postdeposition treatment of an alkali metal fluoride of the absorber has shown a beneficial effect on the solar cells performance due to an increase in the open circuit voltage (VOC) for both (Ag,Cu)(In,Ga)Se2 (ACIGS) and CIGS based solar cells. Several reasons have been suggested for the improved VOC in CIGS solar cells including absorber surface and interface effects. Less works investigated how the applied postdeposition treatment influences the ACIGS absorber surface and interface properties and the subsequent buffer layer growth. In this work we employed hard X-ray photoelectron spectroscopy to study the chemical and electronic properties at the real functional interface between a CdS buffer and ACIGS absorbers that have been exposed to different alkali metal fluoride treatments during preparation. All samples show an enhanced Ag content at the CdS/ACIGS interface as compared to ACIGS bulk-like composition, and it is also shown that this enhanced Ag content anticorrelates with Ga content. The results indicate that the absorber composition at the near-surface region changes depending on the applied alkali postdeposition treatment. The Cu and Ga decrease and the Ag increase are stronger for the RbF treatment as compared to the CsF treatment, which correlates with the observed device characteristics. This suggests that a selective alkali postdeposition treatment could change the ACIGS absorber surface composition, which can influence the solar cell behavior., Title in Web of Science: Surface/Interface Effects by Alkali Postdeposition Treatments of (Ag,Cu)(In,Ga)Se-2 Thin Film Solar Cells

Reciprocal interactions between endothelial cells (ECs) and adipocytes are fundamental to maintain white adipose tissue (WAT) homeostasis, as illustrated by the activation of angiogenesis upon WAT expansion, a process that is impaired in obesity. However, the molecular mechanisms underlying the crosstalk between ECs and adipocytes remain poorly understood. Here, we show that local production of polyamines in ECs stimulates adipocyte lipolysis and regulates WAT homeostasis in mice. We promote enhanced cell-autonomous angiogenesis by deleting Pten in the murine endothelium. Endothelial Pten loss leads to a WAT-selective phenotype, characterized by reduced body weight and adiposity in pathophysiological conditions. This phenotype stems from enhanced fatty acid beta-oxidation in ECs concomitant with a paracrine lipolytic action on adipocytes, accounting for reduced adiposity. Combined analysis of murine models, isolated ECs and human specimens reveals that WAT lipolysis is mediated by mTORC1-dependent production of polyamines by ECs. Our results indicate that angiocrine metabolic signals are important for WAT homeostasis and organismal metabolism. Endothelial cells in white adipose tissue are shown to produce polyamines, which regulate adipocyte lipolysis, thus demonstrating how local angiocrine signals contribute to healthy adipose tissue homeostasis.

Herein, a new route of sulfur grading in CuInSe2 (CISe) thin-film solar absorbers by introducing an ultrathin (<50 nm) sacrificial sputtered CuInS2 (CIS) layer on top of the CISe. Different CIS top layer compositions (Cu-poor to Cu-rich) are analyzed, before and after a high-temperature treatment in selenium (Se)- or selenium+sulfur (SeS)-rich atmospheres. An [S]/([S] + [Se]) grading from the surface into the bulk of the Se- and SeS-treated samples is observed, and evidence of the formation of a mixed CuIn(S,Se)2 phase by Raman analysis and X-ray diffraction is provided. The optical bandgap from quantum efficiency measurements of solar cells is increased from 1.00 eV for the CISe reference to 1.14 and 1.30 eV for the Se- and SeS-treated bilayer samples, respectively. A ≈150 mV higher VOC is observed for the SeS-treated bilayer sample, but the cell exhibits blocking characteristics resulting in lower efficiency as compared with the CISe reference. This blocking is attributed to an internal electron barrier at the interface to the sulfur-rich surface layer. The difference in reaction routes and possible ways to improve the developed sulfurization process are discussed.

The Cu2ZnGe X Sn1-X S4 (CZGTS) thin-film solar cells have a limited open-circuit voltage (V OC) due to bulk and interface recombination. Since the standard CdS buffer layer gives a significant cliff-like conduction band offset to CZGTS, alternative buffer layers are needed to reduce the interface recombination. This work compares the performance of wide bandgap Cu2ZnGeS4 (CZGS) solar cells fabricated with nontoxic Zn x Sn1–x O y (ZTO) buffer layers grown by atomic layer deposition under different conditions. The V OC of the CZGS solar cell improved significantly to over 1 V by substituting CdS with ZTO. However, V OC is relatively insensitive to ZTO bandgap variations. The short-circuit current is generally low but is improved with KCN etching of the CZGS absorber before deposition of the ZTO buffer layer. A possible explanation for the device behavior is the presence of an oxide interlayer for nonetched devices., Title in thesis list of papers: Record 1.1 V open circuit voltage for Cu2ZnGeS4 based thin-film solar cells using atomic layer deposition Zn1-xSnxOy buffer layers

Zn1-xSnxOy (ZTO) deposited by atomic layer deposition has shown promising results as a buffer layer material for kesterite Cu2ZnSnS4 (CZTS) thin film solar cells. Increased performance was observed when a ZTO buffer layer was used as compared to the traditional CdS buffer, and the performance was further increased after an air annealing treatment of the absorber. In this work, we study how CZTS absorber surface treatments may influence the chemical and electronic properties at the ZTO/CZTS interface and the reactions that may occur at the absorber surface prior to atomic layer deposition of the buffer layer. For this, we have used a combination of microscopy and synchrotron-based spectroscopies with variable information depths (X-ray photoelectron spectroscopy, high-energy X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy), allowing for an in-depth analysis of the CZTS near-surface regions and bulk material properties. No significant ZTO buffer thickness variation is observed for the differently treated CZTS absorbers, and no differences are observed when comparing the bulk properties of the samples. However, the formation of SnOx and compositional changes observed toward the CZTS surface upon an air annealing treatment may be linked to the modified buffer layer growth. Further, the results indicate that the initial N2 annealing step integrated in the buffer layer growth by atomic layer deposition, which removes Na-COx species from the CZTS surface, may be useful for the ZTO/CZTS device performance.

Kesterite Cu2ZnSnS4 (CZTS), used for thin film solar cells, has a band gap energy around 1.5–1.6 eV with possibilities for further increase through alloying. In some applications for wide band gap solar cells, reduced absorber thickness can be beneficial, to allow partial light transmission. Reduced thickness can also be beneficial to reduce bulk recombination, and so called ultrathin solar cells (<700 nm thick) have been studied for several materials systems. Here, we report performance for CZTS devices down to 250 nm thickness and show that performance loss from thickness reduction is relatively small, partly due to short minority carrier diffusion length. Insertion of thin passivation layers (Al2O3, SiO2 or HfO2) at the Mo/CZTS interface gives improved performance of ultrathin devices, from 4.7% to 5.6% efficiency for best performing cells having 250 nm thick CZTS with Mo as compared to Mo/Al2O3 back contact. The approach of NaF post deposition for making isolating passivation layers conductive is tested for the first time for CZTS and is shown to work. For fabrication of CZTS devices on transparent ITO back contact, the insertion of passivation layers can reduce diffusion of indium into CZTS, but device performance is lower than on Mo back contacts.

Multiplexed immunofluorescence provides an unprecedented opportunity for studying specific cell-to-cell and cell microenvironment interactions. We employ graph neural networks to combine features obtained from tissue morphology with measurements of protein expression to profile the tumour microenvironment associated with different tumour stages. Our framework presents a new approach to analysing and processing these complex multi-dimensional datasets that overcomes some of the key challenges in analysing these data and opens up the opportunity to abstract biologically meaningful interactions.

The Cu2ZnGe X Sn1-X S4 (CZGTS) thin-film solar cells have a limited open-circuit voltage (V OC) due to bulk and interface recombination. Since the standard CdS buffer layer gives a significant cliff-like conduction band offset to CZGTS, alternative buffer layers are needed to reduce the interface recombination. This work compares the performance of wide bandgap Cu2ZnGeS4 (CZGS) solar cells fabricated with nontoxic Zn x Sn1–x O y (ZTO) buffer layers grown by atomic layer deposition under different conditions. The V OC of the CZGS solar cell improved significantly to over 1 V by substituting CdS with ZTO. However, V OC is relatively insensitive to ZTO bandgap variations. The short-circuit current is generally low but is improved with KCN etching of the CZGS absorber before deposition of the ZTO buffer layer. A possible explanation for the device behavior is the presence of an oxide interlayer for nonetched devices., Title in thesis list of papers: Record 1.1 V open circuit voltage for Cu2ZnGeS4 based thin-film solar cells using atomic layer deposition Zn1-xSnxOy buffer layers

This contribution evaluates a sequential post‐deposition treatment of Cu(In,Ga)Se2 (CIGS) films, consisting of 1) a post‐sulfurization in elemental S‐atmosphere and 2) a subsequent treatment by heavy alkali fluorides (Alk‐PDT). First, the effect of the sulfurization step on the corresponding solar cell performance is investigated and optimum process parameters, leading to an efficiency improvement, are identified. Losses in carrier collection observed after S‐incorporation are attributed to an increased grain boundary (GB) recombination. It is found that the corresponding reduction in short‐circuit current density can be mitigated by a RbF‐ or KF‐PDT, supposedly by depleting GBs in Cu. However, in strong contrast to non‐sulfurized CIGS, the Alk‐PDT results in a lower open‐circuit voltage and distortions in the current–voltage (I –V ) characteristics for sulfurized absorbers. Possible explanations are the absence of a wide‐gap surface phase and/or air exposure between the post‐treatment steps. It is further proposed that a back contact barrier may be responsible for the distortions in I–V.

Amorphous tin-gallium oxide (a-SGO) grown with atomic layer deposition was evaluated as a buffer layer in (Ag,Cu)(In,Ga)Se2 thin-film solar cells in search for a new material that is compatible with a variety of absorber band gaps. Hard and soft X-ray photoelectron spectroscopy on absorber/a-SGO stacks combined with J–V characterization of solar cells that were fabricated, showed that the conduction band alignment at the absorber/a-SGO interface can be tuned by varying the cation composition and/or growth temperature. Here, the surface band gap was 1.1 eV for the absorber. However, optical band gap data for a-SGO indicate that a suitable conduction band alignment can most likely be achieved even for wider absorber band gaps relevant for tandem top cells. A best efficiency of 17.0% was achieved for (Ag,Cu)(In,Ga)Se2/a-SGO devices, compared to η = 18.6% for the best corresponding CdS reference. Lower fill factor and open-circuit voltage values were responsible for lower cell efficiencies. The reduced fill factor is explained by a larger series resistance, seemingly related to interface properties, which are yet to be optimized. Some layer constellations resulted in degradation in fill factor during light soaking as well. This may partly be explained by light-induced changes in the electrical properties of a-SGO, according to analysis of Al/SGO/n-Si metal-oxide-semiconductor capacitors that were fabricated and characterized with J–V and C–V. Moreover, the introduction of a 1 nm thick Ga2O3 interlayer between the absorber and a-SGO improved the open-circuit voltage, which further indicates that the absorber/a-SGO interface can be improved.

Surface treatments of Cu2ZnSnS4 have shown a beneficial effect on the solar cells performance due to a reduction in the open-circuit voltage (VOC) deficit. Several reasons have been suggested for the VOC deficit, including an unfavorable band alignment at the buffer/Cu2ZnSnS4 interface. Herein, the influence of Cu2ZnSnS4 surface treatment (air exposure and air anneal) on the electronic and chemical properties of Cu2ZnSnS4 and CdS/Cu2ZnSnS4 interfaces is investigated. Using hard X-ray photoelectron spectroscopy, it is shown that the band alignment at the CdS/Cu2ZnSnS4 interface is not significantly altered by the applied surface treatment. The device enhancement is instead connected to interface passivation for the surface-treated Cu2ZnSnS4 samples due to the formation of SnOx, which is shown to not be fully removed upon KCN etching prior to the buffer layer deposition. In addition, a surface treatment of the Cu2ZnSnS4 absorber prior to buffer layer deposition influences the growth of CdS buffer, as a thicker CdS-overlayer is observed to grow on a surface-treated Cu2ZnSnS4 sample as compared with a nontreated sample. This suggests that a reoptimization of the CdS thickness for a given Cu2ZnSnS4 surface treatment is required.

In situ structural and chemical state characterization of Rh/CeO2 and Ni/CeO2 catalysts during atmospheric pressure CO2 methanation has been performed by a combined array of time-resolved analytical techniques including ambient-pressure X-ray photoelectron spectroscopy, high-energy X-ray diffraction and diffuse reflectance infrared Fourier transform spectroscopy. The ceria phase is partially reduced during the CO2 methanation and in particular Ce3+ species seem to facilitate activation of CO2 molecules. The activated CO2 molecules then react with atomic hydrogen provided from H2 dissociation on Rh and Ni sites to form formate species. For the most active catalyst (Rh/CeO2), transmission electron microscopy measurements show that the Rh nanoparticles are small (average 4 nm, but with a long tail towards smaller particles) due to a strong interaction between Rh particles and the ceria phase. In contrast, larger nanoparticles were observed for the Ni/CeO2 catalyst (average 6 nm, with no crystallites below 5 nm found), suggesting a weaker interaction with the ceria phase. The higher selectivity towards methane of Rh/CeO2 is proposed to be due to the stronger metal–support interaction.

Catalytic CO oxidation is a seemingly simple reaction between CO and O-2 molecules, one of the reactions in automotive catalytic converters, and the fruit-fly reaction in model catalysis. Surprisingly, the phase responsible for the catalytic activity is still under debate, despite decades of investigations. We have performed a simple but yet conclusive study of single crystal Rh and Pd model catalysts, resolving this controversy. For Rh, the oxygen-covered metallic surface is more active than the oxide, while for Pd, thin oxide films are at least as active as the metallic surface, but a thicker oxide is less active. Apart from resolving a long-standing debate, our results pinpoint important design principles for oxidation catalysts as to prevent catalytic extinction at high oxygen exposures.

The dynamic interaction of methanol and its derivatives with Cu-exchanged ZSM-5 during methanol temperature -programmed desorption from 30 to 450 degrees C has been investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy and first-principles calculations. The results emphasize that defects in the framework structure of the zeolite and Bronsted acid sites constitute ion-exchange sites for Cu ions. The Cu sites introduced in ZSM-S actively interact with methanol adsorbed at moderate temperature, i.e., below 250 degrees C, and take roles in further oxidation of the adsorbed species to formate and CO. Moreover, spectra recorded at higher temperatures, i.e., above 300 degrees C, after adsorption of methanol show strong interaction between methoxy groups and the zeolite framework, suggesting that, under mild conditions, proton extraction for methanol production during direct partial methane to methanol over Cu-ZSM-5 is necessary.

Density functional theory calculations are often used to interpret experimental shifts in core level binding energies. Calculations based on gradient-corrected (GC) exchange-correlation functionals are known to reproduce measured core level shifts (CLS) of isolated molecules and metal surfaces with reasonable accuracy. In the present study, we discuss a series of examples where the shifts calculated within a GC-functional significantly deviate from the experimental values, namely the CLS of C 1s in ethyl trifluoroacetate, Pd 3d in PdO and the O 1s shift for CO adsorbed on PdO(101). The deviations are traced to effects of the electronic self-interaction error with GC-functionals and substantially better agreements between calculated and measured CLS are obtained when a fraction of exact exchange is used in the exchange-correlation functional.

This PhD thesis reports on investigations of the atomic scale structure of model catalysts relevant for the catalytic oxidation of CO and methane over Pd, and NOx reduction over silver-alumina, important reactions in automotive catalysts. By using complementary experimental techniques such as X-ray Photoelectron Spectroscopy, High Pressure X-ray Photoelectron Spectroscopy, Surface X-ray Diffraction, Low Energy Electron Diffraction, Infrared Spectroscopy, and Scanning Tunneling Microscopy, combined with theoretical calculations, the work presented in this thesis aims at an atomistic characterization of the active sites for silver-alumina and Pd model catalysts which may help to the design of new and improved catalysts. The results highlight the complexity of the different structures that may form upon oxygen interaction with Ag and Pd single crystal surfaces. The gas adsorption studies (CO, NO) on clean and oxidized silver surfaces give insights into the chemical properties of the surfaces, information important for the understanding of the reaction mechanism for the NOx reduction. We have been able to propose models for the adsorption sites for CO and NO on oxidized Ag surface and to propose a model system for the NOx reduction over silver-alumina. A particular surface orientation of bulk Pd oxide, the PdO(101) was found to be active for the oxidation of methane. Our studies allow us to reveal the active sites on the surface, information important for the design of better catalysts. Moreover, the results from the CO oxidation over Pd(100) give new insights into the reaction mechanism. The active phase switches between a surface with chemisorbed oxygen to a surface oxide when the oxygen partial pressure is increased.

Density functional theory calculations and high-resolution core-level spectroscopy are used to explore the remarkable observation of decreased Ag 3d binding energy upon silver oxidation. The shift in Ag 3d binding energy is investigated at different degrees of oxidation and compared to results for Pd 3d, which exhibits a normal shift. Analysis of initial-state effects and valence electronic structure shows that the onsite Ag core potential is insensitive to oxidation despite a clear metal-to-oxygen charge transfer. The substantial negative shift for oxidized Ag is instead attributed to final-state effects as screening of the core-hole occurs in metal s states of bonding character.

Fullerenes are proposed as a precursor for preparation of nanocarbon materials using controlled collapse of cage structure by high temperature reaction with polycyclic aromatic hydrocarbons. The chemical modification of C60 by reaction with anthracene and coronene was studied over a broad temperature interval. The products of the reaction were characterized by X-ray diffraction, and Raman and IR spectroscopy. Mono- and multi-adducts of C60 with anthracene were obtained in the temperature interval 290–400 °C. Above 400 °C the C60 adducts are not stable and decompose back to C60 and anthracene. No chemical adducts of C60 with coronene were found below 500 °C. Above this temperature fullerite structure was found to expand reflecting interaction with coronene melt and vapor. The reactions of C60 with anthracene and C60 with coronene at temperatures above 650 °C resulted in fullerene cage collapse and formation of nanocarbons. These nanocarbons were found to store up to 0.45 wt% of hydrogen at ambient temperatures despite negligible surface area.