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Within this study, we investigate the intrinsic photostability of thin‐film solar cells, here organic photovoltaic cells. Since degradation under natural sun light proceeds within the timeframe of months and years, the process needs to be speeded up for fast material analysis and screening, using high‐concentration accelerated lifetime testing (high‐C ALT). For this purpose, we established setups allowing irradiances of up to 730 sun equivalents (SE). One key finding of our study is that accelerating the testing procedure by such large intensities is possible but a precise measurement and control of the solar cell temperature is absolutely essential. Accordingly, we developed an innovative method of determining the temperature of the active layer which offers significant advantages over commonly used measurement methods. Furthermore, it was found that the degradation process under high illumination densities can be well described by a stretched exponential law. We demonstrate that the temperature kinetics of P3HT:PCBM was found to be Arrhenius governed with an activation energy of 27.2 kJ/mol under continuous illumination of 300 SE. Finally, it was shown that the velocity of light‐induced degradation of short‐circuit current depends linearly on the used irradiance dose at a given temperature starting from normal illumination conditions up to at least 300 SE. This makes high‐C ALT a very valuable tool for swift screening of the lifetime of novel thin‐film solar cells and materials.

Degradation of backsheets (BSs) of commercial silicon PV modules is currently recognized as a source of reduced module performance and module failure. Monitoring of the BS state in the field is possible by using non-destructive and highly informative near-infrared absorption (NIRA) spectroscopy. Application of NIRA for the analysis of multi-layer polyethylene terephtalate (PET) based BSs, which dominate the PV module market, is challenging due to a large variety of possible BS configurations that show only small differences in NIRA spectra. In the present work, a spectroscopic tool for the structural identification of PET-based BSs is introduced. The method is based on a principal component analysis of a database of 250 representative NIRA spectra of BSs of different types. It allows a BS with an unknown structure to be assigned to one of 12 different types based solely on its NIRA spectrum. The identification was successfully validated on a test collection of 45 selected BSs and shown to be feasible for the field deployment. Further automation of NIRA measurements and spectral analysis are expected to elevate the proposed tool to the level of a non-intrusive high-throughput field analysis of the BS composition and state in operating PV module grids.

A lot of effort is required in order to close the efficiency gap between laboratory record Cu(In,Ga)Se 2 (CIGS) solar cells and commercially produced modules. An obstacle easily overlooked is the fact that reduced module performance may have multiple root causes. Here, we show how to isolate two main factors that influence the open circuit voltage ( V oc ) of photovoltaic devices, the material composition and the local defects, here shunts in particular, i.e., regions of significantly lowered resistivity. In order to characterize the material composition, we used electroluminescence spectroscopy. Additionally, we investigated the effect of local defects on the V oc , by the use of thermography. Which of both factors dominates the resulting V oc depends on the insolation intensity under which the device is operated. We established a model in order to estimate the V oc as a function of the luminescence peak wavelength, the quantification of the thermal hot spots caused by local defects, and the insolation intensity. Subsequently, we investigated how these factors affect the electrical conversion efficiency of the device. The combination of these two measurement techniques results in a more conclusive evaluation of the electrical parameters, thereby enabling an improved quality assessment to allow a successive process optimization. This approach is also applicable to other thin film PV technologies such as perovskite and organic solar cells.

The annually produced quantity of solar modules has steadily increased over the past decades. Rising production speeds and the associated high throughput of wafers, cells, and modules will make an automatized quality inspection mandatory. In the case of visual optical inspection, automatized quality control by using machine vision is already possible. To localize cracks in solar cells, luminescence imaging is used, where several approaches for an automatized inspection exist, but a standard solution for an automatized inspection algorithm is not yet available. This is, in particular, true for multicrystalline solar cells, where the grainy structures in the luminescence images are hard to distinguish from small cracks. Another obstacle in automatic crack analysis is that reference segmentation algorithms are generally not publicly available. Accordingly, a new algorithm can hardly be compared by ranking it to an existing standard. In this paper, we adapted the vesselness algorithm for automatic processing of electroluminescence images of multicrystalline silicon solar cells. Segmentation of cracks in multicrystalline solar cells with the proposed enhanced crack segmentation algorithm shows very promising results on the used database compared with three different commonly used approaches. Furthermore, the segmentation code is made publicly available, and we propose that this algorithm may serve as a reference algorithm, sparking further progress in automatized crack segmentation for multicrystalline silicon solar cells.

Water ingress into the encapsulation of electronic devices is a serious issue, especially for organic and perovskite-based electronics. In order to guide the development of suitable barrier materials and design, a reliable, fast, and non-destructive analysis tool is required. In this work, an imaging setup is presented, which is based on selective infrared (IR) radiation sources and a mid- IR sensitive camera that uses the absorption band of water around 1920 nm and a reference band. This system enables us to monitor the distribution of water concentration inside the packaging of devices and its change over time. Our measurement is capable of detecting the local presence of water down to the mg/m2 concentration range in a wide variety of encapsulation materials. The new tool allows identifying the pathways of moisture ingress into the encapsulation along with the corresponding diffusion coefficient. Thus, it provides fast and reliable analysis of humidity related failure mechanisms, and consequently helps to improve the design of encapsulation materials and processes.

The crystallization of nanomaterials is a primary source of solid-state, photonic structures. Thus, a detailed understanding of this process is of paramount importance for the successful application of photonic nanomaterials in emerging optoelectronic technologies. While colloidal crystallization has been thoroughly studied, for example, with advanced in situ electron microscopy methods, the noncolloidal crystallization (freezing) of nanoparticles (NPs) remains so far unexplored. To fill this gap, in this work, we present proof-of-principle experiments decoding a crystallization of reconfigurable assemblies of NPs at a solid state. The chosen material corresponds to an excellent testing bed, as it enables both in situ and ex situ investigation using X-ray diffraction (XRD), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), atomic force microscopy (AFM), and optical spectroscopy in visible and ultraviolet range (UV–vis) techniques. In particular, ensemble measurements with small-angle XRD highlighted the dependence of the correlation length in the NPs assemblies on the number of heating/cooling cycles and the rate of cooling. Ex situ TEM imaging further supported these results by revealing a dependence of domain size and structure on the sample preparation route and by showing we can control the domain size over 2 orders of magnitude. The application of HAADF-STEM tomography, combined with in situ thermal control, provided three-dimensional single-particle level information on the positional order evolution within assemblies. This combination of real and reciprocal space provides insightful information on the anisotropic, reversibly reconfigurable assemblies of NPs. TEM measurements also highlighted the importance of interfaces in the polydomain structure of nanoparticle solids, allowing us to understand experimentally observed differences in UV–vis extinction spectra of the differently prepared crystallites. Overall, the obtained results show that the combination of in situ heating HAADF-STEM tomography with XRD and ex situ TEM techniques is a powerful approach to study nanoparticle freezing processes and to reveal the crucial impact of disorder in the solid-state aggregates of NPs on their plasmonic properties.

As the importance of electronics and software in automobiles grows, software maturity becomes an increasing challenge. To avoid the delays of production starts as well as recalls, new development processes are needed. To increase the testing abilities the compatibility between different development releases of electronic control units must be improved. To achieve this, we propose “hierarchical versioning”, a novel versioning scheme and set of rules how to handle compatible and incompatible modifications, using the hierarchical structure of vehicle networks. Data of the AUTOSAR (AUtomotive Open Software ARchitecture) based development history of a current model series automobile has been analyzed to gauge the applicability of hierarchical versioning. We found a worst case bandwidth increase of about 30% for intermittent development releases when using the scheme to introduce complete backward compatibility for an additional release cycle. The bandwidth of the final release is not affected. During this analysis we also noticed that less than 3% of changes cause incompatibilities in more than 100 communication connectors, while most of the changes only affect less than 10 communication connectors. This may further aide in increasing compatibility between releases and reduce the added bandwidth.

“The car is the ultimate mobile device” [1] and with its connectivity and a large number [2] of sensors and actuators an example for a cyber-physical system. The advantages of a service-oriented architecture (SOA) are shown in comparison to the classic signal-oriented design. A hybrid architecture which contains both static signal- and dynamic service-oriented elements is introduced. With an example we show how the benefits of a SOA can be achieved, even without migrating the whole vehicle away from the current static communication schemes. The “SuperTuxKart” application integrated into the Mercedes CLA as presented by Daimler on the Mobile World Congress 2019 [3] is an additional customer value application and used as our showcase. Its development and implementation can be greatly simplified if the target vehicle has an electric/electronic architecture, which is service-oriented. We introduce a new process to develop an application within a service-oriented vehicle and use software over the air (SOTA) updates to deploy it. The process is illustrated using a fictive, service-based application.

Cracks in silicon solar cells reduce cell efficiency and may lead to critical failures in cell and module production because of breakage. Detecting cracks in an early production stage is, therefore, advisable. Several approaches for crack detection systems have been developed in the past years. In order to compare the system performance, the rating done by the system has to be compared with a reference, i.e., a ground truth defining the crack's presence, position, and/or area. This information can also be used for training of detection algorithms based on supervised learning, e.g., convolutional neural networks. In the present article, we show that finding the ground truth is ambiguous and depends strongly on the operator and the applied metrology. For this end, we apply six crack detection tools to a set of 120 multicrystalline silicon passivated emitter and rear cells that were sorted out in industrial production because of cracks, and compare the human rating of six operators for every tool. The operators’ precision, i.e., the fraction of the contrasts detected as cracks that actually are cracks, ranges from 73% to 100% and their recall, i.e., the fraction of all actual cracks that have been found, from 30% to 92% for all tools and operators. To achieve the highest precision and recall, we suggest rating the images of an optical near-infrared system combined with luminescence imaging by three operators conjointly for the definition of ground truth for the present as well as for larger sample sets.

In typical power electronic modules several semiconductor dies such as MOSFET or IGBT are soldered to a DBC substrate. During module production the quality of the solder layers can be monitored by the use of X-ray inspection and the void rate can be determined. Recently, the more robust Ag-sinter technology is deployed for attaching the power dies to the substrate, especially for high reliability or high temperature requirements. Besides voiding also adhesion problems can occur during sintering due to multiple reasons (e.g. contamination). In contrast to volume defects, pure adhesion problems cannot be detected by means of X-rays. Accordingly, other methods have to be applied for process monitoring. The present investigation compares the advantages and disadvantages of different non-destructive imaging techniques towards the detection of defects in sinter layers. Besides X-ray, Scanning Acoustic Microscopy (SAM) and Lock-in Thermography methods (DLIT + ILIT) were studied and evaluated in terms of suitability for detecting different defect types, resolution (minimum defect sizes), inspection time and possible integration into the assembly process.

In proximity mask aligner photolithography, diffraction of light at the mask pattern is the predominant source for image shape distortions such as line end shortening and corner rounding. One established method to mitigate the impact of diffraction is optical proximity correction. This method relies on a deliberate sub-resolution modification of photomask features to counteract such shape distortions, with the goal to improve pattern fidelity and uniformity of printed features. While previously considered for masks featuring only rectangular shapes in horizontal or vertical orientation, called Manhattan geometries, we demonstrate here the capabilities of computational mask aligner lithography by extending optical proximity correction to non-Manhattan geometries. We combine a rigorous simulation method for light propagation with a particle-swarm optimization to identify suitable mask patterns adapt to each occurring feature in the mask. The improvement in pattern quality is demonstrated in experimental prints. Our method extends the use of proximity lithography in optical manufacturing, as required in a multitude of micro-optical devices. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Currently, certified lab scale organic photovoltaic (OPV) cells reach efficiencies of more than 12% and life times of 10 years. For commercialization, it is necessary to understand which performance can be reached in fully printed large scale products. Our investigations show that large area, semi-transparent organic photovoltaic modules based on industrially available materials can achieve power conversion efficiencies of more than 4.8% on rigid substrates and 4.3% on flexible ones. The modules processed with a combination of large area coating and laser patterning with an active area of 68.76 cm 2 for flexible modules and a total area of 197.4 cm 2 for glass modules offer exceptionally high geometric fill factors of more than 94% and a transparency of more than 10%. The processing recipe and the layout of the modules are based on indications of optical and electrical simulations which allow to produce devices with only negligible losses in comparison to small single cell devices. Losses due to imperfect coating or patterning are identified by thermal imaging.

It is well known that the performance of solar cells may significantly suffer from local electric defects. Accordingly, infrared thermography (i.p. lock-in thermography) has been intensely applied to identify such defects as hot spots. As an imaging method, this is a fast way of module characterization. However, imaging leads to a huge amount of data, which needs to be investigated. An automatized image analysis would be a very beneficial tool but has not been suggested so far for lock-in thermography images. In this manuscript, we describe such an automatized analysis of solar cells. We first established a robust algorithm for segmentation (or recognition) for both, the PV-module and the defects (hot spots). With this information, we then calculated a parameter from the IR-images, which could be well correlated with the maximal power (Pmpp) of the modules. The proposed automatized method serves as a very useful foundation for faster and more thorough analyses of IR-images and stimulates the further development of quality control on solar modules.

Superconducting nanowire single-photon detectors promise efficient (~100%) and fast (~Gcps) detection of light at the single-photon level. They constitute one of the building blocks to realize integrated quantum optical circuits in a waveguide architecture. The optical response of single-photon detectors, however, is limited to measure only the presence of photons. It misses the capability to resolve the spectrum of a possible broadband illumination. In this work, we propose the optical design for a superconducting nanowire single-photon spectrometer in an integrated optical platform. We exploit a cascade of cavities with different resonance wavelengths side-coupled to a photonic crystal bus waveguide. This allows to demultiplex different wavelengths into different spatial regions, where individual superconducting nanowires that measure the presence of single photons are placed next to these cavities. We employ temporal coupled-mode theory to derive the optimal conditions to achieve a high absorption efficiency in the nanowire with fine spectral resolution. It is shown that the use of a mirror at the end of the cascaded system that terminates the photonic crystal bus waveguide increases the absorption efficiency up to unity, in principle, in the absence of loss. The expected response is demonstrated by full-wave simulations for both two-dimensional and three-dimensional structures. Absorption efficiencies of about 80% are achieved both in two-dimensional structures for four cascaded cavities and in three-dimensional structures for two cascaded cavities. The achieved spectral resolution is about 1 nm. We expect that the proposed setup, both analytically studied and numerically demonstrated in this work, offers a great impetus for future quantum nanophotonic on-chip technologies., 10 pages, 9 figures

Photons produced in the SPDC process typically propagate through optical elements such as waveguides, lenses and beam splitters. We aim to exploit unconventional optical elements, whose fabrication has recently become possible due to the rapid development of nanotechnologies. Such miniaturized devices are typically integrated on microchips that may later become parts of larger quantum circuits. An example is provided by metamaterials, which are periodic arrays of metallic nanoparticles. These nanoparticles support surface plasmon polaritons - hybrid excitations that combine electromagnetic fields with coherent oscillations of valence-electron plasma. Here we experimentally characterize in free space a nanostructural beam splitter, which was designed to feature 25 % of reflection and transmission, and 50 % of absorption. Furthermore we experimentally show quantum interference in that device.

We apply a high-resolution interference microscope with spectral resolution to investigate the scattering response of isolated meta-atoms in real space. The final meta-atoms consist of core-shell clusters that are fabricated using a bottom-up approach. The meta-atoms are investigated with an increasing complexity. We start by studying silica and gold spheres and conclude with the investigation of the meta-atom, which consists of a silica core sphere onto which gold nanospheres are attached. Numerical simulations entirely verify the measured data. The measuring process involves recording the intensity and phase of the total field emerging from the scattering process of an incident light at the particle in the transmitted half-space with spectral and high spatial resolution. We show that spectrally resolved high-resolution interference microscopy can be used to differentiate between nanoparticles and characterize single meta-atoms, something that is rarely accomplished. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Photonic quantum technologies allow quantum phenomena to be exploited in applications such as quantum cryptography, quantum simulation and quantum computation. A key requirement for practical devices is the scalable integration of single-photon sources, detectors and linear optical elements on a common platform. Nanophotonic circuits enable the realization of complex linear optical systems, while non-classical light can be measured with waveguide-integrated detectors. However, reproducible single-photon sources with high brightness and compatibility with photonic devices remain elusive for fully integrated systems. Here, we report the observation of antibunching in the light emitted from an electrically driven carbon nanotube embedded within a photonic quantum circuit. Non-classical light generated on chip is recorded under cryogenic conditions with waveguide-integrated superconducting single-photon detectors, without requiring optical filtering. Because exclusively scalable fabrication and deposition methods are used, our results establish carbon nanotubes as promising nanoscale single-photon emitters for hybrid quantum photonic devices. Single photons are generated from electrically driven semiconducting single-walled carbon nanotubes embedded in a photonic circuit. Pronounced antibunching is observed when photon correlation is measured at cryogenic temperatures.

Commercial success of optoelectronical devices such as solar cells depend strongly on lifetime next to production costs and power conversion efficiency. While a steep decrease in production costs and significant increase in efficiency have been achieved, lifetime still plays often a limiting factor, in particular, in case of highly innovative new device types. Lifetime tests measuring the stability of devices without external influences (i. p. water) generally take very long time due to the required long lifetime of optoelectronical devices. We established a novel accelerated lifetime test (ALT) setup which may increase the test speed by a factor of several hundred. We verified the setup and the applicability of our ALT measurement routine with an experiment on a well-studied innovative thin-film solar cell type (P3HT:PCBM).

Local electric defects may result in considerable performance losses in solar cells. Infrared thermography is an essential tool to detect these defects on photovoltaic modules. Accordingly, IR-thermography is frequently used in R&D labs of PV manufactures and, furthermore, outdoors in order to identify faulty modules in PV-power plants. Massive amount of data is acquired which needs to be analyzed. An automatized method for detecting solar modules in IR-images would enable a faster and automatized analysis of the data. However, IR-images tend to suffer from rather large noise, which makes an automatized segmentation challenging. The aim of this study was to establish a reliable segmentation algorithm for R&D labs. We propose an algorithm, which detects a solar cell or module within an IR-image with large noise. We tested the algorithm on images of 10 PV-samples characterized by highly sensitive dark lock-in thermography (DLIT). The algorithm proved to be very reliable in detecting correctly the solar module. In our study, we focused on thin film solar cells, however, a transfer of the algorithm to other cell types is straight forward.

Author(s): Vetter, A; Babbe, FS; Hofbeck, B; Kubis, P; Richter, M; Heise, SJ; Ohland, J; Riedel, I; Brabec, CJ | Abstract: Local electric defects may result in considerable performance losses in solar cells. Infrared (IR) thermography is one important tool to detect these defects on photovoltaic modules. Qualitative interpretation of IR images has been carried out successfully, but quantitative interpretation has been hampered by the lack of “calibration” defects. The aims of this study are to (i) establish methods to induce well-defined electric defects in thin-film solar cells serving as “calibration” defects and to (ii) assess the accuracy of IR imaging methods by using these artificially induced defects. This approach paves the way for improving quality control methods based on imaging in photovoltaic. We created ohmic defects (“shunts”) by using a focused ion beam and weak diodes (“interface shunts”) by applying a femto-second laser at rather low power on copper indium gallium selenide cells. The defects can be induced precisely and reproducibly, and the severity of the defects on the electrical performance can be well adjusted by focused ion beam/laser parameters. The successive assessment of the IR measurement (ILIT-Voc) revealed that this method can predict the losses in Pmpp (maximal power extractable) with a mean error of below 10%. Copyright © 2016 John Wiley a Sons, Ltd.

Single photon technology is enabling for quantum communication and processing. Combining single photon sources, routing circuitry and highly efficient detectors in a high yield, low-loss and scalable fashion represent today a major challenge. Nanophotonic devices allow for the realization of on-chip small footprint architectures for generating, manipulating and detecting single photons. Waveguide-integrated superconducting nanowire single photon detectors are today state-of-the art devices capable of detecting single photons propagating in an integrated photonic circuit with high efficiency, speed and low timing uncertainty. Their excellent metrics in the near-infrared allows to directly interface on-chip devices with existing C-Band communication technology systems. To move towards high communication speed, efficient detectors able to sustain Gcps count rate are desirable. Here we present the design process and the experimental characterization of a new generation of fast detectors, consisting of µm-long NbN superconducting nanowires embedded in a SOI two-dimensional photonic crystal cavity. Almost 70% efficiency at telecommunication wavelengths has been achieved with negligible dark counts and sub-ns recovery time, which could enable Gcps count rates.

We introduce a novel industrial grade 193nm continuous-wave laser light source for proximity mask-aligner lithography. A diode seed laser in master-oscillator power-amplification configuration is frequency-quadrupled using lithiumtriborate and potassium-uoro-beryllo-borate non-linear crystals. The large coherence-length of this monomodal laser is controlled by static and rotating shaped random diffusers. Beam shaping with imaging and non-imaging homogenizers realized with diffractive and refractive micro-optical elements is compared in simulation and measurement. We demonstrate resolution patterns offering resolutions

We present a mask-aligner lithographic system operated with a frequency-quadrupled continuous-wave diode laser emitting at 193 nm. For this purpose, a 772 nm diode laser is amplified by a tapered amplifier in the master-oscillator power-amplifier configuration. The emission wavelength is upconverted twice, using LBO and KBBF nonlinear crystals in second-harmonic generation enhancement cavities. An optical output power of 10 mW is achieved. As uniform exposure field illumination is crucial in mask-aligner lithography, beam shaping is realized with optical elements made from fused silica and CaF2 featuring a diffractive non-imaging homogenizer. A tandem setup of shaped random diffusers, one static and one rotating, is used to control speckle formation. We demonstrate first experimental soft contact and proximity prints for a field size of 1 cm2 with a standard binary photomask and proximity prints with a two-level phase mask, both printed into 120 nm layers of photoresist on unstructured silicon substrates.

The combination of efficient single-photon generation, manipulation, and detection on a single chip poses a major challenge for quantum photonics and all-optical quantum computing. Among a multitude of detection technologies, waveguide-integrated superconducting nanowire single-photon detectors stand out as they promise near-unity detection efficiencies at outstanding timing accuracy and speed. Here, by exploiting the concept of critical coupling, we present the integration of a short nanowire into a two-dimensional double heterostructure photonic crystal cavity to realize an integrated single-photon detector with excellent performance metric. The complete detector characterization reveals on-chip detection efficiencies of almost 70% at telecom wavelengths, recovery times of 480 ps, and vanishingly low dark count rates. Our design paves the way for the implementation of compact on-chip detector arrays and time-multiplexed single-detector schemes.

Controlling stability, complexity and optical response of reversibly reconfigurable plasmonic nanocrystal superlattices is of critical importance for emergent optoelectronic technologies and can be achieved by engineering the chemical nature of the ligand shell. In this work, we experimentally explore how the design of surface ligands with semifluorinated alkyl chains impacts dynamic self-assembly of nanoparticles. A series of three promesogenic thiols was synthesized and grafted onto plasmonic nanocrystals via ligand exchange reaction. In all cases, after solvent evaporation, we obtained reversibly reconfigurable, thermally responsive assemblies. We examined these nanomaterials using a variety of techniques such as transmission electron microscopy, UV–vis, and small-angle X-ray scattering. We show that the number of aromatic rings and the length of the fluorinated chain strongly affects symmetry and reconfiguration temperatures of the assemblies. For an optimized material we show that it is possible to a...

Two-dimensional surface waves are a cornerstone for future integrated photonic circuits. They can also be beneficially exploited in sensing devices by offering dark-field illuminations of objects. One major problem in sensing schemes arises from the individual sensing objects: the interaction of surface waves with an object reduces the field amplitude, and the readout of other objects along the propagation path suffers from this reduced signal. Here we show in two experiments that nondiffracting and self-healing Bloch surface waves can be launched using a Fresnel axicon (i.e., fraxicon). First, we visualize the generation of an array of multiple focal spots by scanning near-field optical microscopy in the infrared. With a second device operating in the visible, we demonstrate the self-healing effect directly using a far-field readout method by placing metallic nanoantennas onto the multiple focal spots of the fraxicon. Our study extends the versatile illumination capabilities of surface wave systems. Two-dimensional surface waves play an important role in optical systems such as sensing devices. The authors experimentally and theoretically demonstrate a method for multiple self-healing surface wave beams which can help overcome issues related to reduction in signal strength when surface waves encounter obstacles during their propagation.

We present and discuss Talbot mask-aligner lithography, relying on a continuous wave laser emitting at 193nm for the illumination. In this source, a diode laser at 772nm is amplified by a tapered amplifier in master-oscillator power-amplifier configuration and frequency-quadrupled in two subsequent enhancement cavities using lithium triborate and potassium fluoro-beryllo-borate nonlinear crystals to generate the emission at 193 nm. The high coherence and brilliance of such an illumination source is predestined for plane wave mask-aligner illumination, crucial in particular for high-resolution lithographic techniques such as Talbot lithography and phase-shift masks. Talbot lithography takes advantage of the diffraction effect to image periodic mask features via self-replication in multiples of the Talbot distance behind the photomask when exposed by a plane wave. By placing a photoresistcoated wafer in one of the Talbot planes, the mask pattern is replicated in the resist. Periodic patterns with diverse shapes are required for wire grid polarizers, diffraction gratings, and hole arrays in photonic applications as well as for filters and membranes. Using an amplitude mask with periodic structures, we demonstrate here with such a technique sub-micron feature sizes for various designs at a proximity gap of 20 µm.

Selective absorbers for CSP plants to suppress thermal losses and to increase the efficiency is a promising topic and strong scientific efforts have been spent on how to design and realize such materials. However, there has been no comprehensive optimization analysis of the overall efficiency of CSP plants with selective absorbers. We performed a comprehensive computational parameter study of operation temperature and optical properties of the absorber and investigated their effect on the overall plant efficiency in dependence of sun light concentration up to C = 2000 suns. Optimal operation temperatures were shown not to exceed 1383 K. By using selective absorbers instead of a black body or currently used materials, our assessment yields a potential electrical power output gain of up to around 35%. Our investigations also provide the optical parameters of an ideal (perfect selective) absorber. Its optimal cut off wavelength λ cut lies around 2.4 μm for concentration factors below 120 and above 600 suns. For C in the range of 120–600 suns the value of the cut off wavelength is 1.79 μm. Simulating non-ideal (realistic) absorption properties, it was found that the strongest influence is caused by high absorption at low wavelengths. Low emittance at longer wavelengths plays a less important role. Also the sharpness of the transition from high absorption to low emittance plays a minor role regarding overall plant efficiency. As a rule of thumb, the cut-off wavelength should be at around 2.4 μm when assuming realistic (non-ideal) spectral selectivity. Finally, the theoretical maximum overall efficiency of a CSP plant achievable by an ideal selective absorber was calculated to up to 73% at 2000 suns and even up to 65% for a selective absorber with realistic optical properties.

We investigate how the bias current affects the hot-spot relaxation dynamics in niobium nitride. We use for this purpose a near-infrared pump-probe technique on a waveguide-integrated superconducting nanowire single-photon detector driven in the two-photon regime. We observe a strong increase in the picosecond relaxation time for higher bias currents. A minimum relaxation time of (22 ± 1) ps is obtained when applying a bias current of 50% of the switching current at 1.7 K bath temperature. We also propose a practical approach to accurately estimate the photon detection regimes based on the reconstruction of the measured detector tomography at different bias currents and for different illumination conditions.

CuInGaSe2 (CIGS) thin film solar modules, despite their high efficiency, may contain three different kinds of macroscopic defects referred to as bulk defects, interface defects and interconnect defects. This occurs due to film's sensitivity to inhomogeneities during the manufacturing process. The result is a decrease of electrical power output from a cell or module. In this paper, we present the influence of macroscopic defects on the electrical behavior of CIGS thin film solar cells. To accomplish this, we investigated the relation between the IR-signal emitted of a defect in a cell (measured using illuminated lock-in thermography ILIT) and the respective open circuit cell voltage (Voc,cell) under low light conditions (

The German Adaptation Strategy launched a process to assess the consequences of climate change and identify key areas of adaptation measures. For its effective and efficient implementation it is important to set priorities based on generally recognized criteria. This paper proposes a cross-sectoral prioritization concept for asses sing and selecting federal adaptation measures. Based on a literature review, five key criteria could be distinguished (strategic importance, urgency, side-effects, no-regret, flexibility), which were supplemented with criteria to assess the technical and socioeconomic feasibility (economical aspects, acceptance). The multi-criteria approach enhances transparency and traceability of decision making in the adaptation process. Taking account of climate impacts (path 1) and prioritizing adaptation measures using the multi-criteria approach (path 2) constitute only a first step. Step 2 integrates the findings of path 1 and 2 to select appropriate measures for an Adaptation Action Plan.

Here we show our latest progress in the field of a single-photon spectrometer for the visible and infrared wavelengths ranges implementation. We consider three different on-chip approaches: a coherent spectrometer with a low power of the heterodyne, a coherent spectrometer with a high power of the heterodyne, and an eight-channel single-photon spectrometer for direct detection. Along with high efficiency, spectrometers show high detection efficiency and temporal resolution through the use of waveguide integrated superconducting nanowire single-photon detectors

In this short communication, we present a method which utilizes contactless ILIT (illuminated lock-in thermography) measurement of a photovoltaic (PV) module and image postprocessing in order to calculate the peak power Pmpp of the module and to study the influence of local defects on the module performance. In total, 103 Copper-Indium-Gallium-Diselenide (CIGS) modules were investigated and the results showed a good correlation (mean error less than 6%) between the calculated IR-signal and the measured Pmpp. We performed our study on CIGS modules but the presented approach is not restricted to CIGS modules. The method provides a valuable tool for PV quality control.

Ultrafast single-photon detectors with high efficiency are of utmost importance for many applications in the context of integrated quantum photonic circuits. Detectors based on superconductor nanowires attached to optical waveguides are particularly appealing for this purpose. However, their speed is limited because the required high absorption efficiency necessitates long nanowires deposited on top of the waveguide. This enhances the kinetic inductance and makes the detectors slow. Here, we solve this problem by aligning the nanowire, contrary to usual choice, perpendicular to the waveguide to realize devices with a length below 1 μm. By integrating the nanowire into a photonic crystal cavity, we recover high absorption efficiency, thus enhancing the detection efficiency by more than an order of magnitude. Our cavity enhanced superconducting nanowire detectors are fully embedded in silicon nanophotonic circuits and efficiently detect single photons at telecom wavelengths. The detectors possess subnanosecond decay (∼120 ps) and recovery times (∼510 ps) and thus show potential for GHz count rates at low timing jitter (∼32 ps). The small absorption volume allows efficient threshold multiphoton detection.

In Deutschland ist – wie in vielen Mitgliedstaaten der EU – Anpassung an den Klimawandel als eigenes Politikfeld mit einer nationalen Strategie, einem Masnahmenplan sowie fur die Umsetzung zustandigen Akteuren etabliert. Insbesondere bei physischen, raumwirksamen Masnahmen kommt dabei der kommunalen und regionalen Ebene eine masgebliche Rolle zu. Auf EU-Ebene kann die Umsetzung insbesondere durch einen geeigneten Forder- und Rechtsrahmen unterstutzt werden. Im Mittelpunkt des Kapitels stehen Klimaanpassungsstrategien auf den unterschiedlichen politischen Ebenen – von der EU bis zur Kommune –, Ansatze erfolgreicher Umsetzung und entsprechende Hemmnisse.

This paper investigates Dy3+-doped and Dy3+, Er3+-co-doped yttrium aluminum garnets (YAG) with the admixture of boron nitride with the aim of using them as efficient thermographic phosphors at high temperatures. The phosphors were synthesized using a conventional high-temperature solid-state method. The influence of two fluxes, B2O3 and LiF/NH4F, and the effect of activator and coactivator concentrations were investigated. Additionally, the effect of B3+ and N3− substituting for Al3+ and O2− ions, respectively, in the YAG:Dy3+ co-doped with Er3+ was studied for the first time. The changes in the host lattice led to a much stronger photoluminescence compared with the samples without B3+ and N3− substitution. The admixture of BN also improves the thermal sensitivity of the YAG:Dy and YAG:Dy, Er thermographic phosphors.

Near-field coupling to nanophotonic waveguides enables absorption engineering of superconducting nanowires for efficient single photon detection on chip. The direct compatibility with photonic circuitry allows for using such devices in the framework of integrated optics and thus for exploiting the rich toolbox of nanophotonics for device characterization and optimization. We integrate superconducting single photon detectors with photonic circuitry made from different transparent materials. Both single and multi-photon capability can be achieved through variation of the nanowire width, as well as ultra-fast single photon counting with high detection rates by reducing the nanowire length.

We report on the design, fabrication and measurement of travelling-wave superconducting nanowire single-photon detectors (SNSPDs) integrated with polycrystalline diamond photonic circuits. We analyze their performance both in the near-infrared wavelength regime around 1600 nm and at 765 nm. Near-IR detection is important for compatibility with the telecommunication infrastructure, while operation in the visible wavelength range is relevant for compatibility with the emission line of silicon vacancy centers in diamond which can be used as efficient single-photon sources. Our detectors feature high critical currents (up to 31 {\mu}A) and high performance in terms of efficiency (up to 74% at 765 nm), noise-equivalent power (down to 4.4*10^-19 W/(Hz^1/2) at 765 nm) and timing jitter (down to 23 ps)., Comment: 8 pages, 6 figures, Photonics West, Feb 2016, San Francisco, United States, SPIE Proceedings Volume 9750 - On-Chip Quantum Optics

Nanophotonic integrated circuits made from diamond-on-insulator templates are promising candidates for full-scale classical and quantum optical applications on a chip. For operation on a single photon level, both passive devices as well as light sources and single photon detectors co-implemented with a waveguide architecture are essential. Here, we present an in-depth investigation of the efficiency and timing characteristics of superconducting nanowire single-photon detectors (SNSPDs) situated directly atop diamond waveguides. Effects of nanowire length and critical current on the SNSPD performance are elaborated and true single-photon detection capability is confirmed by statistical measures.

During secondary bone healing, different tissue types are formed within the fracture callus depending on the local mechanical and biological environment. Our aim was to understand the temporal succession of these tissue patterns for a normal bone healing progression by means of a basic mechanobiological model. The experimental data stemmed from an extensive, previously published animal experiment on sheep with a 3 mm tibial osteotomy. Using recent experimental data, the development of the hard callus was modelled as a porous material with increasing stiffness and decreasing porosity. A basic phenomenological model was employed with a small number of simulation parameters, which allowed comprehensive parameter studies. The model distinguished between the formation of new bone via endochondral and intramembranous ossification. To evaluate the outcome of the computer simulations, the tissue images of the simulations were compared with experimentally derived tissue images for a normal healing progression in sheep. Parameter studies of the threshold values for the regulation of tissue formation were performed, and the source of the biological stimulation (comprising e.g. stem cells) was varied. It was found that the formation of the hard callus could be reproduced in silico for a wide range of threshold values. However, the bridging of the fracture gap by cartilage on the periosteal side was observed only (i) for a rather specific choice of the threshold values for tissue differentiation and (ii) when assuming a strong source of biological stimulation at the periosteum.

A simple approach to the mechanical modulation of layer-by-layer (LbL) films is through manipulation of the film assembly. Here, we report results based on altering the salt concentration during film assembly and its effect on film rigidity. Based on changes in film rigidity, cell adhesion characteristics and transfection activity were investigated in vitro. LbL films consisting of reducible hyperbranched poly(amide amine) (RHB) have been implemented along with DNA for investigating fibroblast adhesion on [RHB/DNA](n/2) films with varying rigidities. The rigidity was varied by changing the ionic concentration of the deposition solution between 0.01 m NaCl and 1.0 m NaCl. Molecular force probe (MFP) measurements were performed to measure the apparent Young's modulus, E(APP), of the films in situ. Cell adhesion and stress-fiber characteristics were investigated using total internal reflectance microscopy (TIRF-M). The average cell peripheral area, fiber density and average fiber length during 5 days of cell growth on films with either low (below 2.0 MPa) or high (above 2.0 MPa) film elastic modulus were investigated. Transfection studies were performed using gfpDNA and SEAP-DNA to investigate if changes in cell adhesion affect transfection activity. Furthermore, cell proliferation and cytotoxicity studies were used to investigate cellular viability over a week. The results have shown that surface modification of bioreducible LbL films of controlled thickness and roughness promotes cellular adhesion, stress-fiber growth and increased transfection activity without the need for an additional adhesive protein pre-coating of the surface or chemical cross-linking of the film.