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This study analyses thermomechanical stresses in silicon solar cells after the soldering process by finite element modeling. An experimentally validated model shows compressive and tensile stresses, longitudinal and transversal to a busbar or a pad row on the surface of a silicon solar cell. The impact of the interconnector segments at and in between two solder pads was investigated and characteristic locations of maximum stress were identified. In addition, the influence of the layout of the contact metallization on the thermomechanical stress was identified by geometry variations to reveal design guidelines that lead to reduced thermomechanical stress in a solar cell after the soldering process. The model results reveal maxima of the tensile stress located at the outermost contacts. Furthermore, a significant influence of the distance between the outermost contact areas and the solar cell edge was determined; with decreasing distance, the compressive stress maxima are higher, but in contrast the more critical tensile stress maxima decrease. For connected pad rows tensile stress maxima are larger compared to single pad connection, which shows the influence of the interconnector segments in between the solder joints of a pad row. After several stages of thermal cycling, electroluminescence measurements showed, in compliance with the model results, contact damages, mainly at the outermost contacts. Furthermore, connected pad rows revealed a steadily growing amount of damaged contacts, whereas single solder joints showed no defects up to 400 thermal cycles.

Understanding the origin of thermomechanical stress in solar cells is a key factor to extend the lifetime of photovoltaic modules. However, the methods to determine the stress are very limited. With the confocal micro-Raman spectroscopy, we present a contactless method, which is able to measure through the front glass and is well-known in the field of microelectronics. One major challenge for the measurement on crystalline silicon solar cells and modules is the surface texturization of the mono crystalline solar cell, which changes the topology from a plain (100) surface to pyramids with (111) flanks and (100) valleys. We develop a procedure to cover the challenges arising from this topology, namely the inhomogeneous stress distribution on the pyramid flanks and the different crystal planes of the phonon vibrations and the photon back scattering. By studying the procedure on a reference system, we determine a factor for the conversion of a micro-Raman peak shift to stress of Σ = − ( 833 ± 49 ) MPa / rel . cm − 1 . The presented measurements show that the factor holds for uniaxial stress, biaxial stress as well as the stress states occurring from the PV module production processes. We then apply the procedure to measure the stress from soldering 156 × 156 mm2 solar cells and the lamination. We obtain (− 21 ± 2) MPa for the stress in the unsoldered solar cells, which arise from the cell production steps, like metallization. After soldering, we measure (− 26 ± 3) MPa and after lamination (− 53 ± 6) MPa. Additionally we perform a line scan along the cell diagonal and area scans of the quarter cell as well as the end of one busbar. All results match well with a simulation of stress induced by the soldering process and lamination using the finite element method.

Li et al. (2020) reviewed and compiled worldwide loess distribution and identified three loess genesis modes (CR, MR and MRD), according to which Central Asian and Chinese Xinjiang loesses are generalized into MRD mode. Referring to Li et al. (2020), Li and Song (2020) discussed the loess genesis modes of several local sites in the said region on the grounds of geochemical data and modern dust storm observations and records. Concluding that the main dust sources are river systems rather than deserts, they averred that the loess genesis mode in Central Asia and Xinjiang region of China should be classified as MR mode. In reply to Li and Song (2020), the present article further discusses the main loess genesis modes in this region considering landform, near-surface wind over deserts, and loess distribution pattern and characteristics. We maintain that the primary genesis mode of the main loess bodies (accounting for approximately 80%) of this region is in MRD mode, although MR mode loesses (approximately 20%) exist in some small-scale basins and surrounding areas.

Raman spectroscopy is used for measuring stress in microelectronic devices [1] as well as in solar cells [2, 3]. However, on PV module level it has not been examined yet. We transfer the method in order to enable the experimental determination of thermomechanical stress in PV modules. For this purpose the stress in non-soldered, soldered and laminated solar cells is measured by a confocal Raman spectrometer. Additionally we simulate the thermomechanical stress induced by soldering and lamination by finite element modelling. Considering the initial stress state of the solar cells and a linear elastic material model of EVA, the results show a good agreement. By Raman spectroscopy we find the compressive stress in the solar cell after lamination to add up to 53 ± 6 MPa.

For the comparative study with focus on mechanical long-term stability, we perform a temperature cycle (TC) test-to-failure for 1250 cycles according to IEC 61215 with laminated solar cell strings. The strings were produced with Multi Busbar (MBB) solar cells interconnected by wires and with solar cells with 3 busbars (3BB) interconnected by ribbons. One module sample comprises two electrically isolated 3-cell strings, one for each technology. The 3BB string displays a power loss of more than 5 % after 850 cycles, while the MBB string only exceeds 5% loss after 1250 cycles. After TC 1250 the 3BB string shows a degradation of -8.2 % in FF and -8.0 % in power, while the MBB string shows a degradation of -6.2 % in FF and of -5.3 % in power. In the second comprehensive comparative study we use for each interconnection technology 15 cells for isothermal storage (up to 130 °C, 42.8h) and 10 modules for TC (up to 400 cycles). Each reliability analysis includes IV and EL characterization as well as adhesion force measurements and microsection analysis. After TC 400 the MBB interconnection shows less than 1 % degradation in efficiency compared to 4-5 % degradation for 3BB ribbon interconnection in a common module setup. The cells and modules show that most of the electrical contacts are still intact with respect to the EL image after 42.8 h isothermal storage and TC 400, although the average peel forces degraded from about 2 N/mm to less than 0.5 N/mm. Both studies indicate a superior mechanical long-term stability for Multi Busbar technology compared to ribbon interconnection.

We propose an interconnection concept for solar cells that enables the soldering of solder coated copper wires directly on the contact fingers of the front side metallization without the need of busbars or contact pads. By reshaping the copper wires we realize a wave-shaped stress relief structure. This reduces the yield force, the force value where plastic deformation of the wire starts, up to 90 % compared to straight wires and therefore minimizes mechanical stresses in the joint after the soldering process essentially. Our experimental analysis demonstrates the mechanical long-term stability of the interconnection (ΔP

In order to achieve a fast and reliable qualification of promising conductive adhesives for solar cells, different accelerated ageing test sequences, accompanied with analyses on material level are conducted. Damp-heat followed by damp heat at a current range of 8 A; humidity freeze and thermal cycling. The testing procedure in the herein presented work is adapted to identify advantages and also weaknesses of the materials in combination with the entire design. The conductive adhesives replace the lead-based soldering thereby allowing a lower processing temperature. Another potential reduction of material costs is the use of double redundant fingers instead of busbars. In this way, a considerably smaller amount of silver is needed. The interconnectors are glued between theses double redundant fingers with the conductive adhesive. Another advantage of the gluing is the possibility of using groove structured interconnectors that allow an increase in power of the solar module by reflecting light back to the solar cell. As major degradation indicator the performance of the modules containing conductive adhesives, redundant fingers and groove structured interconnectors is measured before and after the exposition of the solar module to different accelerated ageing tests and compared to the reference solar module with flat interconnectors soldered on busbars. After the accelerating ageing test damp heat (DH), there was already a clear difference in viability of the conductive adhesives. For two conductive adhesives, module power losses were comparable to the reference, for a third one power losses amounted to 14 %. The loss in power is caused by an increase in serial resistance. Analyses of the adhesives indicate a relation between the degradation in damp-heat and the adsorption of humidity of the material. Different subsequent aging tests (after DH) showed the feasibility of this innovative technology, but also unveiled weaknesses compared to a traditional soldered busbar technology. Two of the three conductive adhesives have fulfilled the IEC 61215 criteria in terms of power loss after damp heat, humidity freeze and thermal cycling.

Acceptance of new technology is influenced by a number of situational and social factors. So far, only limited data are available on the influence of the teaching staff's gender on the acceptance of virtual dental implant planning by students. This study aimed at assessing the influence of the teaching staff's gender on the acceptance of a virtual implant planning course by male and female undergraduate dental students and their general attitude toward implantology. Two groups of third-year dental students (group 1, 9 males, 22 females; group 2, 12 males, 20 females) attended a virtual dental implant planning course. For the first group the teaching staff was all-male, while the teaching staff was all-female for the second group. After completion of the course the students filled in a technology acceptance questionnaire. An all-female teaching staff led to a degree of technology acceptance that did not differ significantly for male and female students. When the teaching staff was all-male, significant differences for technology acceptance occurred between male and female students. However, male as well as female students attributed the practice of implantology to both genders of dentists, equally, without statistically significant difference independent of the gender of the teaching staff. The more evenly distributed degree of technology acceptance of students of both genders being taught by a female staff is a favorable effect which may be explained by the more egalitarian style of women. Therefore, while feminization in dentistry proceeds, adequate measures should be taken to increase the number of female teachers.

Aluminium, thermally evaporated with physical vapor deposition (PVD), is considered a cost efficient rear metallization for crystalline silicon heterojunction or tunnel oxide passivated solar cells. Owing to the temperature-sensitivity of the solar cell structure, potential routes of low temperature interconnection methods for PV module integration are assessed. Textured wafers with a full area 2 μm PVD-Al metallization are divided into two groups: The first is capped with sputtered 100 nm Ti and 400 nm Ag for testing solderability. The second is capped with 400 nm Ag for electrically conductive adhesive (ECA) interconnection. Low temperature soldering with Sn43Bi57 and Sn41Bi57Ag2 coated ribbons and ribbon interconnection with two ECAs are evaluated in terms of peel strength, contact resistivity and accelerated aging properties. It is found that peel strength of soldered interconnections on the Al/Ti/Ag achieve between 1.5 N mm -1 to 2 N mm -1 whereas glued interconnections on Al/Ag between 0.5 N mm -1 to 1 N mm -1 . The contact resistivity is 2.6 × 10 -3 mΩ cm2 to 3.6 × 10 -1 mΩ cm2 for both interconnection technologies. Soldered samples show a stable contact resistivity when tested in 1000 h in damp heat conditions or 200 thermal cycles. The contact resistivity of glued interconnections increases to 1 mΩ cm2 to 10 mΩ cm2 along with an observed disintegration of the Al-layer and an ablation of the Ag-capping from the Al-layer.

In this paper, broad-band phase-based motion magnification (BPMM) is used to improve the modal parameter estimation from high-speed video of a structure undergoing low amplitude vibration. The authors use a novel application of the phase-based motion magnification technique to obtain improved results in the presence of image noise. A numerical simulation is performed to demonstrate and quantify the effect of broad-band motion magnification. A clear correlation is found between the magnification factor and the error in the motion obtained from 2-dimensional point tracking (2DPT). In a laboratory experiment, operational modal analysis is performed on a metallic nozzle with a 5.3 in exit diameter and a constant wall thickness of 0.03 inches. Fluorescent markers are painted on the nozzle lip. The nozzle is attached to a test stand and excited by pressurized air. The induced vibrations are captured by a single high-speed camera, which takes images of the nozzle lip. Using a 2DPT algorithm, the displacement history of the markers in the nozzle exit plane is extracted. As is typical for small and stiff structures, the resonant frequencies are quite high and the resulting vibration amplitudes are fairly low. This leads to low signal-to-noise ratio in the higher frequencies, which makes the following operational modal analysis much harder. By using BPMM as a preprocessor, the authors demonstrate that the outcome of modal analysis is greatly improved. Comparison with Finite Element analysis shows that the mode shapes agree much better with the experimental results when motion magnification is used. The modal parameters of the first six modes are found in the frequency range 0–1400 Hz using the new methodology, whereas without motion magnification only the first five modes are found.

The peel test of soldered/glued ribbons on solar cell metallizations is the critical test in the PV industry and research community to qualify the integrability of cells into modules. It has been shown that the peeling angle of the test setup strongly influences the measured peel forces [1,2], leading to higher forces for decreasing peeling angles < 90̊ and weakest forces for 135̊. Here, we apply the theory of Kinloch and Kawashita [3,4] to determine the adhesive fracture energies GA from 180̊ peel tests of three different ribbons which differ in compliance (softness) and thickness. The experiments show that the soft ribbon (σy = 62MPa) gives lower peel forces than the stiff ribbons (σy = 99MPa) while the adhesive fracture energies are higher. The thickness variation from 150 μm to 200 μm of the hard ribbon has no significant effect on the adhesive energy. Furthermore, our investigation confirms that switching from 90̊ peeling angles to 180̊ helps to reduce silicon fracture patterns at high forces. In conclusion, the adhesion does not only depend on the surface properties of cell metallization schemes and soldering conditions, but also on the choice of ribbon used for the peel test. We therefore recommend to use the adhesive fracture energy GA instead of the normalized peel forces to improve the consistency and comparability between different peel testing setups and ribbon materials as the peel test is essential for accepting (or rejecting) novel metallization concepts (plating, metallization pastes) and interconnection technologies (low melting solder alloys, conductive adhesives).

Indicators provide easy and quick information on the status or condition of an object of interest and are therefore widely used in policy-making. In recent years, policy interest in vulnerability research has increased and a growing number of studies have been aimed at developing vulnerability indicators. Some of these studies have been done within the social–ecological system (SES) framework, taking into account both social vulnerability and ecological vulnerability. A particular challenged faced, however, is with regard to the incorporation of indicators to capture the latter, especially as the concept of vulnerability as applied in ecology is relatively new and not yet well-explored. This paper expounds on this problem by answering the following questions: (1) How are the concept of vulnerability and thereby ecological vulnerability currently understood? (2) What are the challenges in the development and use of ecological vulnerability indicators? (3) What are the current efforts to overcome these challenges? One insight gathered is that due to the complexity, nonlinearity, and multiplicity of dynamics of natural systems, development of sufficiently general indicators of ecological vulnerability may not be realizable. Rather, ecological vulnerability assessment and the development of indicators thereof, whether done independent of the human system or within the SES, should be conducted at smaller scales and must be context-specific.

Although the energy codes or construction standards were considerably improved in the last decades, there are continuous reports on mold growth problems in buildings. Numerical prediction can be useful in assessing the risk of mold growth in new constructions and retrofit applications. Two well-known models exist and are widely used: the VTT model and the biohygrothermal IBP model. While the VTT model is an experimentally validated empirical model based on visual findings of mold growth, the biohygrothermal method models the growth of a mold hyphen in mm as a function of the transient ambient conditions. Since a hyphen is not visible to the naked eye it is not evident at what length the growth will become a nuisance. The VTT model uses a very clear six-step evaluation: the so-called mold index describing the intensity of growth on the surface. By comparing the results of the biohygrothermal and the VTT model it is possible to use the clear and acknowledged rating measure of the mold index also for the IBP model. For this purpose, a conversion function has been developed allowing the transformation of the calculated hyphen growth, in mm, into the mold index with a high level of correspondence. In collaboration of VTT and IBP a new postprocessor for the VTT model was developed which can be used to assess both: Results from hygrothermal numerical simulations or measured data. A classification employing a traffic light indicator helps to interpret the mold growth risk: green means no risk, red is not acceptable, while the yellow range indicates a possible risk and requires a specific evaluation.

Loess formation generally involves the four main stages of production, deflation, transportation, and deposition of loess particles. Traditionally, loesses are classified as glacial, desert, or other types based only on source area characteristics without taking into account provenance and transportation. Research on loess genesis is often local with only a few attempts at systematically overviewing worldwide loess distribution. Both the local and few global studies lack information on the variability in loess thickness, continuity, and areal extent. This review integrates a large body of information on loess source areas and transportation pathways and the existence of desert transition zones. Three modes of loess genesis, (1) continental glacier provenance-river transport, (2) mountain provenance-river transport, and (3) mountain provenance-river transport-desert transition, were identified. Global distribution maps of provenance and transport pathways of major loess areas and their different genesis modes were meticulously prepared. Maps showing the spatial distribution, thickness, and continuity of loess deposits were also composed and the sizes of loess-covered areas of each continent were re-estimated. The main features related to the distribution of the loess deposits on each continent are summarized for different regions or as a whole depending on the coverage of the source maps and references.

Foil metallized (FolMet) solar cells combine the high-efficiency PERC technology and a cost-efficient rear side metallization based on a 9 µm thin aluminum foil. Laser fired contacts are used to attach the foil to the rear side and allow for the mechanical and electrical contact to the cell. Direct soldering on aluminum is hampered by a native oxide film formed immediately when exposed to air. To realize the cell interconnection by a standard solder process the Al foil is coated by sputter deposition or roll cladding of solderable layers. This work evaluates the solderability of 200 µm thick coated Al foils with the common solder interconnection process established in photovoltaics using standard copper ribbons for module integration. Our analysis reveals for both coating approaches strong initial mechanical adhesion of > 4 N/mm after soldering and very low contact resistivities of < 1.6 µ∙cm2. The contact resistivity shows no degradation after isothermal aging within 1000 hours at 85 °C. The mechanical adhesion of the sputter coated Al foils remains at 3 N/mm under thermal aging of more than 1000 h at 85 °C whereas the adhesion for the Al foils coated by roll cladding drops strongly to values of < 1 N/mm already after 50 hours. SEM images indicate that this effect is caused by re-oxidation of the aluminum surface supported by micro cracks in the solderable top layer.

The idea to interconnect solar cells in a shingled manner like roof tiles dates back to the 1960’s. However, the standard interconnection technology in the PV industry nowadays is still the front to back series interconnection using solder coated copper ribbons. Shingle interconnection offers very high packing densities of solar cells and increases the module’s active area by eliminating busbars from the illuminated area. Direct interconnection of stripe-like solar cells by electrical conductive adhesives (ECA) replaces the front-to-back ribbon interconnection and therefore eliminates the interconnectors’ ohmic losses. Stripe-like solar cells additionally reduce the overall ohmic losses of the solar cell string by lower cell currents. In this work we provide an overview of the scientific state of the art and a summary of the most important features for shingled cell interconnection. We compare two calculation approaches for the joint deformation due to thermal expansion of the module materials and identify the most relevant parameters. The results show that the thickness of the joint material typically ranging from ~ 20-100 µm is crucial to reduce the shear deformation and therefore enabling sufficient long-term stability. Other geometrical parameters like the overlap width or number of solar cells per string only show a small effect on shear strain for cell widths >20 mm. First experimental prototypes of shingled mini-modules of bifacial pSPEER solar cells using low temperature soldering (Sn42Bi58) show a total power loss of < 5 % after accelerated TC200 testing.

Objectives Three-dimensional radiological imaging data play an increasingly role in planning, simulation, and navigation in oral and maxillofacial surgery. The aim of this study was to establish a new, highly precise, in vitro measurement technology for the evaluation of the geometric accuracy down to the micrometric range of digital imaging data. Material and methods A macerated human mandible was scanned optically with an industrial, non-contact, white light scanner, and a three-dimensional (3D) model was obtained, which served as a master model. The mandible was then scanned 10 times by cone beam computed tomography (CBCT), and the generated 3D surface bone model was virtually compared with the master model. To evaluate the accuracy of the CBCT scans, the standard deviation and the intraclass coefficient were determined. Results A total of 19 measurement points in 10 CBCT scans were investigated, and showed an average value of 0.2676 mm with a standard deviation of 0.0593 mm. The standard error of the mean was 0.0043 mm. The intraclass correlation coefficient (ICC) within the 10 CBCT scans was 0.9416. Conclusions This highly precise measuring technology was demonstrated to be appropriate for the evaluation of the accuracy of digital imaging data, down to the micrometric scale. This method is able to exclude human measurement errors, as the software calculates the superimposition and deviation. Thus inaccuracies caused by measurement errors can be avoided. This method provides a highly precise determination of deviations of different CBCT parameters and 3D models for surgical, navigational, and diagnostic purposes. Thus, surgical procedures and the post-operative outcomes can be precisely simulated to benefit the patient.

Background Lingual undercuts are common in the edentulous mandible and pose the risk of perforating the lingual cortical bone during insertion of dental implants, which may lead to hemorrhage or infections of the parapharyngeal space. The aim of our study was to determine the occurrence and extent of lingual undercuts in the molar and premolar/canine region of the mandible. Methods We analyzed 716 cross-sections of the edentulous molar region and 215 cross-sections of the edentulous first premolar/canine region. Mandibular morphology was classified into a U-configuration (undercut), P-configuration (parallel), and C-configuration (convex), depending on the shape of the alveolar ridge. Depth of the lingual concavity, concavity angle, and further parameters were measured to describe the mandibular morphology. Results Lingual undercuts had a prevalence of 68% in the molar region. The prevalence was significantly higher in the second molar region (90%) than in the first molar region (56%). A deep position of the inferior alveolar nerve close to the basal cortical bone was significantly associated with the presence of lingual undercuts. Conclusion Lingual undercuts are a frequent in the edentulous mandible. Cross-sectional analysis of three-dimensional radiographs provides the opportunity to determine a lingual undercut and to prevent complications of perforating the lingual cortical bone.

Electrically conductive adhesives as an alternative interconnection technology can potentially avoid the need for busbars on crystalline silicon solar cells. The adhesive is applied to the grid fingers and the ribbons for module integration can be directly attached to them. We analyze the interconnection related power losses by establishing an electrical model and validating the model with experimental I-V curve data. The maximum error is 7% for one-cell-minimodules. In the following, we select silver-reduced adhesives and tin-coated ribbons to build minimodules and perform environmental chamber tests. The interconnection related cell-to-module losses are higher by 0.5% compared to standard soldering on busbars. The minimodules with silver-reduced glues and tin-coated ribbbons are stable in 1000 h damp heat and degrade by a maximum of 3% after 200 thermal cycles. Only the highly Ag-filled acrylate failed the thermal cycling test.