Optical Analysis of Perovskite III-V Nanowires Interpenetrated Tandem Solar Cells.

Multi-junction photovoltaics approaches are being explored to mitigate thermalization losses that occur in the absorption of high-energy photons. However, the design of tandem cells faces challenges such as light reflection and parasitic absorption. Nanostructures have emerged as promising solutions due to their anti-reflection properties, which enhances light absorption. III-V nanowires (NWs) solar cells can achieve strong power conversion efficiencies, offering the advantage of potentially integrating tunnel diodes within the same fabrication process. Metal halide perovskites (MHPs) have gained attention for their optoelectronic attributes and cost-effectiveness. Notably, both material classes allow for tunable bandgaps. This study explores the integration of MHPs with III-V NWs solar cells in both two-terminal and three-terminal configurations. Our primary focus lies in the optical analysis of a tandem design using III-V semiconductor nanowire arrays in combination with perovskites, highlighting their potential for tandem applications. The space offered by the compact footprint of NW arrays is used in an interpenetrated tandem structure. We systematically optimize the bottom cell, addressing reflectivity and parasitic absorption, and extend to a full tandem structure, considering experimentally feasible thicknesses. Simulation of a three-terminal structure highlights a potential increase in efficiency, decoupling the operating points of the subcells. The two-terminal analysis underscores the benefits of nanowires in reducing reflection and achieving a higher matched current between the top and the bottom cells. This research provides significant insights into NW tandem solar cell optics, enhancing our understanding of their potential to improve photovoltaic performance.

Nano-optical designs for high-efficiency monolithic perovskite-silicon tandem solar cells.

Perovskite-silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite-silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. We show a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enable a greatly increased fabrication yield from 50% to 95%. Moreover, the open-circuit voltage is improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. Our optically advanced rear reflector with a dielectric buffer layer results in reduced parasitic absorption at near-infrared wavelengths. As a result, we demonstrate a certified power conversion efficiency of 29.80%.

Tripling the light extraction efficiency of a deep ultraviolet LED using a nanostructured p-contact.

Despite a wide array of applications, deep ultra-violet light emitting diodes offer relatively poor efficiencies compared to their optical counterparts. A contributing factor is the lower light extraction efficiency due to both highly absorbing p-contacts and total internal reflection. Here, we propose a structure consisting of a hexagonal periodic array of cylindrical nanoholes in the multi-layered p-contact which are filled with platinum. This nanostructure reduces the absorption of the p-contact layer, leading to a higher emission into the n-contact compared to a planar reference. An optimum geometry of the nanostructure allows a light extraction efficiency of 15.0%, much higher than the typical 4.6% of a planar reference. While the nanostructure strongly decreases the light absorption in the p-contact, it is still not able to considerably reduce the total internal reflection. Consequently, the nanostructured p-contact should be combined with other optical strategies, such as nanopatterned sapphire substrates to increase the efficiency even further. Despite this, the nanostructure described in this work provides a readily realizable path to enhancing the light extraction efficiency of state-of-the-art deep ultra-violet light emitting diodes.

Optimizing metal grating back reflectors for III-V-on-silicon multijunction solar cells.

Multi-junction solar cells allow to utilize sunlight more effectively than single junction solar cells. In this work, we present optical simulations of III-V-on-silicon solar cells with a metal grating at the back, which experimentally have reached more than 33% power conversion efficiency. First, we perform simulations with the finite element method and compare them with experimental data to validate our model. We find that accurately modeling the investigated geometrical structure is necessary for best agreement between simulation and experimental measurements. Then, we optimize the grating for maximized light trapping using a computationally efficient Bayesian optimization algorithm. The photo current density of the limiting silicon bottom cell is improved from 13.48 mA/cm2 for the experimental grating to 13.85 mA/cm2 for the optimized metal grating. Investigation of all geometrical optimization parameters of the grating (period, height,…) shows that the structure is most sensitive towards the period, a parameter highly controllable in manufacturing by inference lithography. The results show a pathway to exceed the current world record efficiency of the III-V-on-silicon solar cell technology.

Metasurface Enhanced Sensitized Photon Upconversion: Toward Highly Efficient Low Power Upconversion Applications and Nanoscale E-Field Sensors.

Large-scale nanoimprinted metasurfaces based on silicon photonic crystal slabs were produced and coated with a NaYF4:Yb3+/Er3+ upconversion nanoparticle (UCNP) layer. UCNPs on these metasurfaces yield a more than 500-fold enhanced upconversion emission compared to UCNPs on planar surfaces. It is also demonstrated how the optical response of the UCNPs can be used to estimate the local field energy in the coating layer. Optical simulations using the finite element method validate the experimental results and the calculated spatial three-dimensional field energy distribution helps us to understand the emission enhancement mechanism of the UCNPs closely attached to the metasurface. In addition, we analyzed the spectral shifts of the resonances for uncoated and coated metasurfaces and metasurfaces submerged in water to enable a prediction of the optimum layer thicknesses for different excitation wavelengths, paving the way to applications such as electromagnetic field sensors or bioassays.

Detailed illumination model for bifacial solar cells.

We present a detailed illumination model for bifacial photovoltaic modules in a large PV field. The model considers direct light and diffuse light from the sky and treats the illumination of the ground in detail, where it discriminates between illumination of the ground arising from diffuse and direct light. The model calculates the irradiance components on arbitrarily many positions along the module. This is relevant for finding the minimal irradiance, which determines the PV module performance for many PV modules. Finally, we discuss several examples. The code for the model is available online (DOI: 10.5281/zenodo.3543570).

Nanopatterned sapphire substrates in deep-UV LEDs: is there an optical benefit?

Light emitting diodes (LEDs) in the deep ultra-violet (DUV) offer new perspectives for multiple applications ranging from 3D printing to sterilization. However, insufficient light extraction severely limits their efficiency. Nanostructured sapphire substrates in aluminum nitride based LED devices have recently shown to improve crystal growth properties, while their impact on light extraction has not been fully verified. We present a model for understanding the impact of nanostructures on the light extraction capability of DUV-LEDs. The model assumes an isotropic light source in the semiconductor layer stack and combines rigorously computed scattering matrices with a multilayer solver. We find that the optical benefit of using a nanopatterned as opposed to a planar sapphire substrate to be negligible, if parasitic absorption in the p-side of the LED is dominant. If losses in the p-side are reduced to 20%, then for a wavelength of 265 nm an increase of light extraction efficiency from 7.8% to 25.0% is possible due to nanostructuring. We introduce a concept using a diffuse ('Lambertian') reflector as p-contact, further increasing the light extraction efficiency to 34.2%. The results underline that transparent p-sides and reflective p-contacts in DUV-LEDs are indispensable for enhanced light extraction regardless of the interface texture between semiconductor and sapphire substrate. The optical design guidelines presented in this study will accelerate the development of high-efficiency DUV-LEDs. The model can be extended to other multilayer opto-electronic nanostructured devices such as photovoltaics or photodetectors.

Effects of whole plant brown algae (Laminaria japonica) on zootechnical performance, apparent total tract digestibility, faecal characteristics and blood plasma urea in weaned piglets.

Two trials were conducted with 48 newly weaned piglets (28 d old) each 8.6 ± 0.05 kg to study how Laminaria japonica plants (LJ) affect zootechnical performance, feed conversion and the apparent total tract digestibility (ATTD) of crude nutrients. All basal diets consisted of cereals, soybean meal, skim milk powder and premixes according to recommendations (no growth promoters or enzymes). For Trial 1, piglets from 16 litters (50% male-castrated, 50% female) were assigned to three treatment groups (n = 16) in a completely randomised block design. Groups received either 2.5% supplementation with sun dried (SD) or drum dried (DD) LJ powder or 2.5% of diatomaceous earth (control). For Trial 2, piglets from 12 litters received either 5% of diatomaceous earth (control) or one of three mixtures of diatomaceous earth + DD LJ powder (3.3%+1.7%, 1.7%+3.3% or 0.0%+5%; n = 12). Data collection included zootechnical performance, faecal consistency, blood plasma urea (Trial 1 and 2) and ATTD (Trial 2). Metabolisable energy (ME) of DD LJ and diets in Trial 2 was estimated using digestible nutrients. Statistical analysis included two-way ANOVA (treatment, block) and mixed linear regression. During both trials, LJ at dosages ≥2.5% significantly reduced feed:gain ratio compared to control (p ≤ 0.0001, = 0.01 for Trial 1, Trial 2) irrespective of the drying method. ATTD from Trial 2 significantly increased digestibilities of dry matter (DM) and crude ash (CA) (p ≤ 0.01) and significantly decreased digestibilities of organic matter and crude fibre in animals fed ≥3.33% DD LJ (p = 0.01). Fractional digestibility of the DD LJ resulted in limited ME of ~9.3 ± 2.5 MJ/kg DM. Dietary conversion ratios of ME and digestible DM of DD LJ diets from Trial 2 decreased linearly with increasing algal supplementation (R2 = 0.93, 0.94 and pslope = 0.002, 0.002 for MCR, DCR). In conclusion, dried LJ powder was included up to 5% into diets without impairing zootechnical performance. The improved feed conversion in the presence of LJ was partly due to slightly higher ME within the algae diets compared to control. However, piglets receiving LJ during Trial 2 needed significantly lower dietary ME and digestible DM to maintain growth performance. Thus, LJ exerted a performance enhancing effect on weaned piglets. The precise mode-of-action is yet unclear.

On accurate simulations of thin-film solar cells with a thick glass superstrate.

The optical response of periodically nanotextured layer stacks with dimensions comparable to the wavelength of the incident light can be computed with rigorous Maxwell solvers, such as the finite element method (FEM). Experimentally, such layer stacks are often prepared on glass superstrates with a thickness, which is orders of magnitude larger than the wavelength. For many applications, light in these thick superstrates can be treated incoherently. The front side of thick superstrate is located far away from the computational domain of the Maxwell solvers. Nonetheless, it has to be considered in order to achieve accurate results. In this contribution, we discuss how solutions of rigorous Maxwell solvers can be corrected for flat front sides of the superstrates with an incoherent a posteriori approach. We test these corrections for hexagonal sinusoidal nanotextured silica-silicon interfaces, which are applied in certain silicon thin-film solar cells. These corrections are determined via a scattering matrix, which contains the full scattering information of the periodically nanotextured structure. A comparison with experimental data reveals that higher-order corrections can predict the measured reflectivity of the samples much better than an often-applied zeroth-order correction.

Combining tailor-made textures for light in-coupling and light trapping in liquid phase crystallized silicon thin-film solar cells.

We present tailor-made imprinted nanostructures for light management in liquid phase crystallized silicon thin-film solar cells providing both, increased jsc by enhanced absorption and excellent electronic material-quality with Voc-values >640mV. All superstrate textures successfully enhance light in-coupling in 10-20µm thick liquid phase crystallized silicon thin-films. Moreover, the effect of combining imprinted textures at the front side with individually optimized light trapping schemes at the rear side of the absorber layers on the optical properties is analyzed. With a silicon absorber layer thickness of 17µm maximum achievable short-circuit current density of 37.0mA/cm2 is obtained, an increase by + 1.8mA/cm2 (or 5.1%) compared to the optimized planar reference.

Smooth anti-reflective three-dimensional textures for liquid phase crystallized silicon thin-film solar cells on glass.

Recently, liquid phase crystallization of thin silicon films has emerged as a candidate for thin-film photovoltaics. On 10 µm thin absorbers, wafer-equivalent morphologies and open-circuit voltages were reached, leading to 13.2% record efficiency. However, short-circuit current densities are still limited, mainly due to optical losses at the glass-silicon interface. While nano-structures at this interface have been shown to efficiently reduce reflection, up to now these textures caused a deterioration of electronic silicon material quality. Therefore, optical gains were mitigated due to recombination losses. Here, the SMooth Anti-Reflective Three-dimensional (SMART) texture is introduced to overcome this trade-off. By smoothing nanoimprinted SiO x nano-pillar arrays with spin-coated TiO x layers, light in-coupling into laser-crystallized silicon solar cells is significantly improved as successfully demonstrated in three-dimensional simulations and in experiment. At the same time, electronic silicon material quality is equivalent to that of planar references, allowing to reach V oc values above 630 mV. Furthermore, the short-circuit current density could be increased from 21.0 mA cm-2 for planar reference cells to 24.5 mA cm-2 on SMART textures, a relative increase of 18%. External quantum efficiency measurements yield an increase for wavelengths up to 700 nm compared to a state-of-the-art solar cell with 11.9% efficiency, corresponding to a j sc, EQE gain of 2.8 mA cm-2.

Effects of different iron supply to pregnant sows (Sus scrofa domestica L.) on reproductive performance as well as iron status of new-born piglets.

The present study aimed to investigate the effects of different iron (Fe) supply to sows during gestation on their reproductive performance and placental Fe load. Additionally, the Fe status of the corresponding offspring was assessed. Twenty multiparous sows were fed from insemination to farrowing with isoenergetic and isonitrogenic balanced diets differing in Fe content. The diet low in Fe (Group -Fe) was mainly composed of soybean meal and maize meal and had a Fe content of 114 mg/kg DM. For the diet high in Fe (Group +Fe), the diet was supplemented with Fe(II)SO4 · 7H2O to a total Fe content of 256 mg/kg. Blood characteristics (haemoglobin, haematocrit, mean corpuscular haem concentration, total Fe-binding capacity, transferrin saturation) of all sows were measured at the beginning and at the end of gestation. Daily Fe retention was calculated at the day of farrowing. After birth, reproductive performance (litter size, piglet weight, litter weight), placental Fe content and Fe blood characteristics of the piglets were determined. Apparent daily Fe retention tended to be greater in Group +Fe (p < 0.1). Blood parameters of the sows did not show any variations between feeding groups, neither at the beginning nor at the end of pregnancy, whereas placental Fe content was lower in Group -Fe (p < 0.05). In addition, Fe supply during gestation improved litter size (p < 0.01) and litter weight (p < 0.05). Although all sows were supplied according to the current Fe recommendations, a significant decline in reproductive performance of Group -Fe was recognised. Therefore, it was concluded that the re-evaluation of the gross Fe requirements of pregnant sows is inevitable to accommodate the current feeding recommendations.

Deterministic composite nanophotonic lattices in large area for broadband applications.

Exotic manipulation of the flow of photons in nanoengineered materials with an aperiodic distribution of nanostructures plays a key role in efficiency-enhanced broadband photonic and plasmonic technologies for spectrally tailorable integrated biosensing, nanostructured thin film solarcells, white light emitting diodes, novel plasmonic ensembles etc. Through a generic deterministic nanotechnological route here we show subwavelength-scale silicon (Si) nanostructures on nanoimprinted glass substrate in large area (4 cm2) with advanced functional features of aperiodic composite nanophotonic lattices. These nanophotonic aperiodic lattices have easily tailorable supercell tiles with well-defined and discrete lattice basis elements and they show rich Fourier spectra. The presented nanophotonic lattices are designed functionally akin to two-dimensional aperiodic composite lattices with unconventional flexibility- comprising periodic photonic crystals and/or in-plane photonic quasicrystals as pattern design subsystems. The fabricated composite lattice-structured Si nanostructures are comparatively analyzed with a range of nanophotonic structures with conventional lattice geometries of periodic, disordered random as well as in-plane quasicrystalline photonic lattices with comparable lattice parameters. As a proof of concept of compatibility with advanced bottom-up liquid phase crystallized (LPC) Si thin film fabrication, the experimental structural analysis is further extended to double-side-textured deterministic aperiodic lattice-structured 10 µm thick large area LPC Si film on nanoimprinted substrates.

Symmetry-dependency of anticrossing phenomena in slab-type photonic crystals.

The optical properties of photonic crystals (PhCs) are strongly affected by their spatial symmetry characteristics. We observe anticrossing phenomena for large-area slab-type silicon PhCs sandwiched between a glass substrate and air. If a glass superstrate plus an index-matching fluid is added, thus establishing a mirror symmetry in z-direction, the anticrossing disappears. These characteristics are analyzed numerically using a finite-element Maxwell solver, and experimentally using large area samples made by nanoimprint lithography. We further discuss the findings by symmetry considerations.

Simulations of sinusoidal nanotextures for coupling light into c-Si thin-film solar cells.

We numerically study coupling of light into silicon (Si) on glass using different square and hexagonal sinusoidal nanotextures. After describing sinusoidal nanotextures mathematically, we investigate how their design affects coupling of light into Si using a rigorous solver of Maxwell's equations. We discuss nanotextures with periods between 350 nm and 1050 nm and aspect ratios up to 0.5. The maximally observed gain in the maximal achievable photocurrent density coupled into the Si absorber is 7.0 mA/cm2 and 3.6 mA/cm2 for a layer stack without and with additional antireflective silicon nitride layers, respectively. A promising application is the use as smooth anti-reflective coatings in liquid-phase crystallized Si thin-film solar cells.

Effect of a stroke support service in Germany: a randomized trial.

PURPOSE: This trial investigated the effect of a stroke support service on physical functioning in post-stroke outpatients. METHODS: The randomized trial took place in two urban hospitals in Germany. The intervention covered a post-discharge stroke support service including following components: outreach work (via telephone contact and home-visit), informational events, training sessions, online portal, and written patient information. The control group received optimized standard care by written patient information. The primary outcome measure was physical function assessed by the physical scale of the stroke impact scale (SIS) 2.0 at baseline and after 12 months follow-up. Secondary outcomes covered health-related quality of life, depression, somatization, reinfarcts, and mortality. Use of health services was recorded. RESULTS: A total of 265 patients were randomized either to the intervention (n = 130) or to the control group (n = 135); n = 230 patients were analyzed after 12 months. The mean group difference on the physical SIS scale was - 2.7 points (95% CI, - 5.5-0.2) in favor of the control group. The overall risk of mortality in the control versus the intervention group was 11.6and 3.9%, respectively (hazard ratio 0.32, 95% CI, 0.12-0.88). All other outcomes were neither statistically nor clinically relevant, different between the two study groups. CONCLUSION: An additional stroke support service did not improve physical function, health-related quality of life, depression, somatization, or reinfarcts in stroke patients. Data suggest a lower overall risk of mortality in the intervention group.

Hfe and Hjv exhibit overlapping functions for iron signaling to hepcidin.

UNLABELLED: Functional inactivation of HFE or hemojuvelin (HJV) is causatively linked to adult or juvenile hereditary hemochromatosis, respectively. Systemic iron overload results from inadequate expression of hepcidin, the iron regulatory hormone. While HJV regulates hepcidin by amplifying bone morphogenetic protein (BMP) signaling, the role of HFE in the hepcidin pathway remains incompletely understood. We investigated the pathophysiological implications of combined Hfe and Hjv ablation in mice. Isogenic Hfe (-)/(-) and Hjv (-)/(-) mice were crossed to generate double Hfe (-)/(-) Hjv (-)/(-) progeny. Wild-type control and mutant mice of all genotypes were analyzed for serum, hepatic, and splenic iron content, expression of iron metabolism proteins, and expression of hepcidin and Smad signaling in the liver, in response to a standard or an iron-enriched diet. As expected, Hfe (-)/(-) and Hjv (-)/(-) mice developed relatively mild or severe iron overload, respectively, which corresponded to the degree of hepcidin inhibition. The double Hfe (-)/(-) Hjv (-)/(-) mice exhibited an indistinguishable phenotype to single Hjv (-)/(-) counterparts with regard to suppression of hepcidin, serum and hepatic iron overload, splenic iron deficiency, tissue iron metabolism, and Smad signaling, under both dietary regimens. We conclude that the hemochromatotic phenotype caused by disruption of Hjv is not further aggravated by combined Hfe/Hjv deficiency. Our results provide genetic evidence that Hfe and Hjv operate in the same pathway for the regulation of hepcidin expression and iron metabolism. KEY MESSAGES: Combined disruption of Hfe and Hjv phenocopies single Hjv deficiency. Single Hjv(-)/(-) and double Hfe(-)/(-)Hjv(-)/(-) mice exhibit comparable iron overload. Hfe and Hjv regulate hepcidin via the same pathway.

Iron metabolism in obesity: how interaction between homoeostatic mechanisms can interfere with their original purpose. Part II: epidemiological and historic aspects of the iron/obesity interaction.

The change from a mainly vegetarian fare to meat consumption went along with brain growth and increased insulin resistance to improve brain's glucose supply. Meat consumption increased iron bioavailability and, thus, physical and mental fitness. The "predation-release-hypothesis" proposes that group coordination, arms and fire abolished the survival advantage of lean individuals from predation. The "thrifty gene-hypothesis", in contrast, proposes that surviving repeated episodes of starvation increased efficiency of food utilization in the offspring; they learned to utilize every available calorie. As a consequence of either mechanism, improved food security will increase prevalence of obesity along with that of its fatal consequences, such as diabetes, hypertension, heart diseases, and cancer. Thus, improved food security collides with the biologically evolved mechanisms to store excessive calories in preparation for a famine that never came. The crash between homoeostatic mechanisms and human intervention caused the presently observed pandemia of obesity and explains why it is so difficult to avoid, in spite of its well known and often fatal consequences.