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8th World Conference on Photovoltaic Energy Conversion; 907-911, Solar cells with back-junction technology exhibit the metallization at the rear side of the solar cell thus gaining from a shading free sunny side. Electrical interconnections between the solar cells and ribbons in a string are exposed to various stresses during manufacturing of the module. Additionally, they are stressed by environmental conditions during field operation. We present a study of electrical-conductive adhesive (ECA) joints for back-junction (BJ) solar cell technology focusing on advanced defect diagnostics of the joints during and after climate stress. To assess the stability and prevent failures, advanced diagnostic methods for joints are needed which provide fast nondestructive and spatial-resolved information on the lateral current flow. Commonly, inspection techniques rely on electroluminescence imaging (EL) or visual inspection (VI). However, they are not sufficient since the information depends on indirect impacts. In this work, a comprehensive application by means of the magnetic-field imaging (MFI) and Lock-In Thermography (LIT) will be presented and compared to standard imaging techniques. MFI allows imaging of the lateral current paths or local current interruptions even inside a laminate while LIT is related to thermal power losses. The benefits of the combined MFI/LIT method for advanced failure diagnostics will be shown on selected defect ECA-joints. The MFI/LIT application offers the opportunity to improve the assessment of ECA-joints aging due to the spatial resolution and fingerprint defect signatures like single defective joints and current-stressed junctions. This will improve the risk assessment of process and design related late defects of interconnections of BJ-solar cells and other technologies. Furthermore, due to the defect localization, advanced material analysis on microscopic scale is applicable by target preparation allowing the determination of the underlying failure mechanism. This approach supports the detailed assessment of ECA to ribbon interconnection and allows a deeper understanding of root causes in terms of degradation mechanisms of different materials and processes.

8th World Conference on Photovoltaic Energy Conversion; 551-558, The successful industrialization of a solar cell technology must consider, beside technical and reliability aspects, also the competitiveness of process costs with respect to the main stream solar cell technologies. Since silver component is a considerable part of the cost of ownership of solar cells, the aim of this study is to push the boundaries of silver paste reduction at solar cell level, as well as at ECA interconnection process level. Through our approach we investigate the feasibility of the replacement of silver busbar of the IBC ZEBRA cell with the ECA interconnection line, as well as the interconnection through ECA pads. These variations were tested at established industrial process environments (qualified processes were implemented at TeamTechnik stringers: TT 1400ECA for ECA interconnection and TT2100 for soldered strings). The produced strings we investigated regarding extent of ECA curing, polymer compatibility, mechanical stability, electrical performance and reliability. Through this comprehensive investigation we obtain a clear identification for reliable configurations, which are worth following at further IBC ZEBRA interconnection process developments, as well as the experimentally determined material saving.

8th World Conference on Photovoltaic Energy Conversion; 187-190, Current motion and process sequences already lead to breakage in cell and module manufacturing under industry standard wafer cycle times. Increasing wafer throughput can lead to extreme handling challenges if the wafer needs to survive cell production undamaged. This investigation shows a method to analyze cell manufacturing processes regarding wafer damaging. A prototype handling process was developed, and damage was measured indirectly by the wafer strength. The statistical strength distributions of wafers are compared. The introduced procedure for wafer strength analysis was applied for the first time to evaluate high throughput manufacturing processes. Two handling operations modes, that means printing processes are compared to each other regarding the fracture stress distribution. The results show a decrease of wafer strength after handling by novel printing technologies. The rotary printing process and screen-printing was performed. Strength reduction was observed.

8th World Conference on Photovoltaic Energy Conversion; 811-815, A wide deployment of Photovoltaics (PV) in desert climate conditions requires overcoming the impact of the environmental factors on PV performance and reliability. High Ultra-violet (UV) irradiance, in combination with high module operating temperature that may reach over 70 C during summer months even for open rack installations, has shown to cause degradation of the PV module material. In this paper, we investigate the impact of UV irradiance on the properties of the PV module back sheet material. The data obtained from real outdoor testing conditions serves as a design guideline to develop a reliable PV module. For instance, FTIR (Fourier Transform Infrared) measurements on the polyamide-based back sheets confirmed the cracking and powdering of the back sheet material after 4 years of exposure in a desert climate.

8th World Conference on Photovoltaic Energy Conversion; 912-916, Shingled solar cells with Electrically Conductive Adhesive (ECA) interconnection represent a technological path to make very esthetic and efficient modules with lead free interconnection technology. The reliability assessment of the interconnection stability in shingled modules is one major aspect in the material qualification for selection of proper ECAs and process requirements. For shingle technology, commonly used electroluminescence (EL) image interpretation for string or module inspection gets more complex due to the lack of simple fingerprint-like clear features. The aim of this work is the evaluation of non-destructive proof, localization, and quantification of ECA failures in shingled solar cell modules. The Magnetic Field Imaging (MFI) technique has been applied to specifically detect defects in the interconnection. A simplified visualization scheme has been developed and successfully tested. A comparison between stressed shingled strings and their initial data allows the quantitative assessment of mechanical stress-related (bending and cycling) ECA-interconnection failures, their lateral distribution und occurrence frequency. With the application of the MFI-based imaging technique, it is feasible to detect and assess aged ECA interconnections as well as identify string-dependent inhomogeneities in aging. The applicability of the MFI-based approach has been successfully demonstrated and extends EL characterization with specific sensitivity to interconnection reliability assessment.

The inhibitory GABAergic system in the brain is involved in the etiology of various psychiatric problems, including autism spectrum disorders (ASD), attention deficit hyperactivity disorder (ADHD), and others. These disorders are influenced not only by genetic but also by environmental factors, such as preterm birth, although the mechanisms underlying are not known. In a translational hyperoxia model, exposing mice pups at age P5 to 80% oxygen for 48 hours to mimic a steep rise of oxygen exposure caused by preterm birth from in utero into room air, we documented a persistent reduction of cortical mature parvalbumin expressing interneurons until adulthood. Developmental delay of cortical myelin was observed together with decreased expression of oligodendroglial glial cell-derived neurotrophic factor (GDNF), a factor being involved in interneuronal development. Electrophysiological and morphological properties of remaining interneurons were unaffected. Behavioral deficits were observed for social interaction, learning, and attention. These results elucidate that neonatal oxidative stress can lead to decreased interneuron density and to psychiatric symptoms. The obtained cortical myelin deficit and decreased oligodendroglial GDNF expression indicate an impaired oligodendroglial-interneuronal interplay contributes to interneuronal damage.

38th European Photovoltaic Solar Energy Conference and Exhibition; 611-618, The metallization scheme of the back-junction back-contact “ZEBRA” cell, which is a configuration based on several metallization and insulation paste layouts, having all busbars located at rear side [1], require only process adaptation at already existing automated mass production interconnection equipment, as well as comprehensive qualification. By means of that, also based on previous research [2], two interconnection technologies were considered for investigation: soldering and gluing with electrically conductive adhesive for PV (ECA), whereby one is epoxy- and the other one acrylic-based, both with silver particle fillers. For these contacting media available industrial equipment was used, a teamtechnik TT2100 stringer for soldering process, with a new interdigitated back contact cell (IBC) process and a teamtechnik TT1600ECA stringer for gluing process, also with process adaptation for IBC cell type. Both these new processes implied trials and several characterization techniques for identification of capability and for optimization. For testing long-term reliability of the joints, a setup for investigation of interconnection susceptibility to ageing factors (UV, temperature cycling and damp heat) was defined for unprotected samples (strings) and for samples protected by encapsulation (laminated). A suitable testing tool for our approach was the peel force measurement, which is a direct measure for the quality of the joint. Main target was to identify the optimal characterization and features specific for an industrial ready process for the IBC “ZEBRA” cells.

A single quadrupole mass spectrometer coupled measuring setup was developed for the investigation of the helium transmission rate (HeTR) of SiOx-coated polyethylene terephthalate (PET) barrier films. The setup allows the pressure-less and time-resolved measurements of the helium permeation at transient and steady-state conditions. Whereas standard water vapour transmission rate (WVTR) experiments took extended test times (in the range of several days), HeTR measurements were finished after 1 h. For the material system investigated here, an excellent linear correlation of WVTR and HeTR was proven over two orders of magnitude (regarding WVTR). Experiments with application of different strain loads on the coated films revealed a significant increase of both, HeTR and WVTR. Scanning electron microscope (SEM) measurements evidenced multiple ruptures of the SiOx coating depending on the applied strain and initial thickness of the SiOx layer. Considering virgin barrier films and strain-ruptured barrier films, a good correlation of WVTR and HeTR was shown.

37th European Photovoltaic Solar Energy Conference and Exhibition; 474-477, Half-cell modules are a preferred technological option to produce high efficiency photovoltaic modules. In this work, we present results on different half-cell processes applied to state-of-the-art heterojunction solar cells. We show that for heterojunction solar cells, a well optimized cell separation process is necessary for reduced losses at the half-cell edge. The cell separation leads to additional depletion region recombination currents, which can be imaged and quantified by dark lock-in thermography (DLIT). To this end, we present a ‘Local I-V’ analysis that quantifies local electrical losses for different half-cell processes.

37th European Photovoltaic Solar Energy Conference and Exhibition; 302-304, Long term stability is a major quality criterion of solar cells. In particular, light exposure together with increased temperatures can lead to severe degradation losses. In this work, advanced cell technologies namely PERC and hetero-junction solar cells are investigated under illumination with white and UV light at moderate and elevated temperatures. The PERC solar cells showed a medium light induced degradation at elevated temperature. A similar trend is observed under UV illumination. Hetero-junction solar cells do not degrade under white light illumination. To the contrary, an efficiency improvement is observed under light exposure at increased temperatures. This improvement is mainly due to an increase in fill factor. The fill factor still increases during a treatment with pronounced UV amount. Even more, the elevated temperature treatment leads to a long-term stabilization of the HJT cells under UV exposure.

37th European Photovoltaic Solar Energy Conference and Exhibition; 853-860, Thermomechanical stress induced by interconnection process, which can cause cell bowing, is enhanced for interdigitated back contact ( IBC) solar cells. Efforts are made therefore at laboratory and industrial level to lower cell bowing in cell string, while targeting a reliable interconnection at fast, competitive production flow rates. Two widely available possibilities for interconnection of solar cells are considered in this research work: soldering versus gluing with electrically conductive adhesive (ECA). While soldering with widely used soldering alloys, like Sn60Pb40, is considered as a straight forward, well characterized and understood technique [1], utilization of conductive glues requires a far more specific and intensive analysis. Results from test setups and sample designs will be used in a detailed simulation tool (FEM) environment to obtain predictions for thermomechanical stress initially at cell string level; this will facilitate the qualification process, through a correlation between thermomechanical stress and cell bowing via simulation. Overall this study aims for defined feasible processes for soldering, respectively for gluing of cells, with focus on full cell format, which will ease the implementation of IBC ZEBRA cell in mass production at present competitive throughput level.

37th European Photovoltaic Solar Energy Conference and Exhibition; 305-307, Fine-line printing for metallic contact structures with high aspect ratios are preferred for modern solar cell metallization. The bleeding phenomenon of screen-printed pastes during the metallization can result in an impact on the solar cell performance by shading. In this work, we present an approach for the characterization of the bleeding of organic components of screen-printed metallization structures to assess the impact on the cell performance. Optical and hyperspectral imaging (HSI) have been applied for a fast assessment (affected area) and classification of organic bleeding. Microscopic structure revealed a local coverage of organics in pyramid valleys forming an effective optical layer. We show, that employing commercially available LBIC tools with measurement options for several wavelengths and spatial resolution of about 100 μm can be used for a quantitative current loss estimation. It was found that an EQE loss takes place at wavelength in the visual spectral range. Our multi-scale approach allows a deeper understanding of present organic bleeding and estimated the current loss to 0.2 %. However, narrow bleeding regions are challenging to measure and require a significantly higher spatial resolution which have been reached with a microscopic LBIC system.

36th European Photovoltaic Solar Energy Conference and Exhibition; 371-374, The market demands processes with high-throughput for the deposition of passivation layers for PERC solar cells. Inline PECVD tools are using multiple plasma sources with separately controllable process parameters in series for a stepwise controlled deposition of a layer, in example a silicon nitride layer. Accordingly, the final passivation layer consists of multiple sublayers with thicknesses in the range of several nanometers. The composition and thickness of these sublayers is crucial and define the properties of the full layer stack. A detailed time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) study has been conducted on a SixNy:H/AlxOy passivation layer stack. Samples with different deposition sequences of plasma sources have prepared to investigate the depth-resolved composition of sublayers in the SixNy:H layer. ToF-SIMS was evaluated as a fast technique with high sensitivity to depth-dependent composition variations. Slight changes in the Si/N-ratio correlate with respect to the location of the sample to the plasma source position. Differences in the sublayer’s chemical composition can be resolved and clearly attributed to a single plasma source. This analytical approach allows a detailed process monitoring of each plasma source and could help to improve sophisticated gradient layer systems.

36th European Photovoltaic Solar Energy Conference and Exhibition; 835-843, The aim of this work was to develop a PV module design with current components that is resistant to degradation mechanisms without increasing costs. A glass–foil module design with a 4 mm thick front glass with antireflective coating was chosen. The encapsulation material was varied (polyolefin and EVA from two manufacturers). The two test module series have different PERC cell types (multicrystalline with three busbars and monocrystalline with five busbars). We have developed a long sequential test sequence to evaluate the reliability of the modules according to the selected degradation modes. The test sequence included damp heat (3000 h), thermal cycling (200x) and UV light exposure (60 kWh/m²) with hail and mechanical stress testing. The performance of the polyolefin modules was better after the long test sequence. The second module series was better due to the better cells.

35th European Photovoltaic Solar Energy Conference and Exhibition; 266-269, The ZEBRA cell concept realizes low cost and large area interdigitated back contact (IBC) silicon solar cells. Furthermore, the concept allows a homogeneously distributed reverse bias breakdown at low voltages over the total cell area. Even without bypass diodes no severe hot spots will occur under partial shadings condition in a module. Hence, the homogeneity of the power dissipation is crucial for the reliability of the module under partial shading conditions. Root causes of non-uniform power generation under reverse condition must be understood and controlled. In this paper the macroscopic breakdown behavior and microscopic properties of the sample structure are compared by means of DLIT, reverse-bias EL and SEM/EBIC as well as ToF-SIMS. The microstructure and the local diffusion profiles of a IBC cell with non-uniform reverse breakdown have been analyzed separately in terms of correlation to the reverse breakdown. It is know that the local formation of high doping gradients at p+n+-junction leads to a low reverse breakdown voltage. Microscopic reverse-bias EL was used as a fast technique for identification of non-uniform p+n+-junction formation. On microscopic scales the structural roughness contributes to a spatially non-uniform generation of highly doped p+n+-junctions. However, on larger scales the breakdown behavior can be controlled through the dopant diffusion process. Our results show that this effect originates from different boron diffusion profiles which results in a variation of the boron sheet resistance on a cell.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1087-1091, In this paper, the reliability of copper indium gallium selenide (CIGS) photovoltaic (PV) technology under high temperature, high soiling rate and high UV exposure conditions of Doha (Qatar) was studied. Thin film delamination was found to be the main dominant failure mechanism that affects the module performance and reliability for CIGS modules installed in desert climate. Using both, non-destructive and destructive techniques, different aspects have been reported to contribute to the initiation and propagation of the interfacial failure. These are; the chemical surface modification of the transparent conductive oxide (TCO) and the ethylene vinyl acetate (EVA) encapsulant, the additives to EVA material and the ingress of moisture into the interface. As a result, a degradation of the module nominal power by 35% was measured after two years from installation.

35th European Photovoltaic Solar Energy Conference and Exhibition; 557-560, The Black-Si method is a promising alternative technique to reduce the reflection of c-Si solar cells. However, drawbacks of this technique are (I) the ion bombardment of the silicon surface, (II) the plasma induced impurities and (III) the increase of the silicon roughness. The Black-SiN method bypasses these drawbacks by a maskless plasma texturing of a SiN-layer. This approach separates the optical properties of the SiN-layer and the electrical properties of the silicon bulk and p-n junction. The Black-SiN texture is etched by a capacitively coupled power supply with a SF6/O2 gas mixture in a direct glow discharge. First results show a parabolic like Black-SiN texture in a scale of approx. 100 nm. A simulation of the Black-SiN optical properties revealed a global reflection minimum of 7.40 % between 300-1200 nm wavelength with respect to the air mass 1.5 spectrum on a plane silicon surface. Hence, the Black-SiN method can contribute to an improved solar cell efficiency.

35th European Photovoltaic Solar Energy Conference and Exhibition; 825-831, In December 2014, the publicly funded project "AdmMo: Advanced multi-crystalline Modules" initiated by Hanwha Q-Cells started with the partners Heraeus, Frintrup, Innolas-Solutions, Meyer Burger Germany, Wavelabs, Karlsruhe Institute of Technology, Bergakademie Freiberg, Fraunhofer CSP and Fraunhofer ISE. The content of the project, which ended on April 30th, 2018, is a comprehensive and consistent further development of PERC cell and module technology. The overall project objective is a reduction of the “Levelized Cost of Electricity” (LCoE) to < 6 € ct / kWh in relation to the southern German region. For this purpose, a substantial cost reduction with simultaneous increase in performance of the cells and modules as well as a service life of the modules extended to 30 years was aspired. Our conference paper gives an overview of the most important results. Among other things, Cz-PERC solar cells with efficiencies > 22 % and based on this a module of 120 half-cells with a power output of 318 watts is demonstrated.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 413-417, Under illumination, multi-crystalline PERC solar cells may suffer from a severe efficiency loss up to 20 %rel induced by carrier injection at elevated temperatures which is known as LeTID. Our experiments reveal that LeTID degradation and regeneration occurs rather homogeneously throughout the cell. However, structural defects as grain boundaries are less affected by LeTID during the entire degradation and regeneration process. Based on these results, a gettering of impurities, which are involved in LeTID, during crystallization or cell processing is most likely. It is shown that this effect cannot be explained by a slower degradation at grain boundaries due a to locally reduced charge carrier density or a laterally inhomogeneous regeneration through defect gettering at grain boundaries during the LeTID. The getter range was determined to be around 200-250 μm based on conventional LBIC, supplemented by high-resolution μLBIC at an enhanced lateral resolution of 2-3μm. The maximum getter range of different impurities during the cooling after the firing step was estimated. The calculations indicated that if the LeTID impurity gettering occurs during the firing step then a fast diffuser in silicon (Cu, H, Ni, Co) has to be involved.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1705-1708, The rear side passivation of PERC (passivated emitter and rear) solar cells implies a modified contacting approach in comparison to Al back surface field cells. This substantial modification of the rear side leads to higher cell performance but can also imply new failure and degradation mechanisms. In our work, we present a systematic approach for a quantitative evaluation of individual components of the rear side metallization. We propose an experimental method to separate the major contributions to the series resistance of the rear side of PERC solar cells and show their impact on cell reliability during temperature cycling stress tests. The local contact between metallization and silicon, especially at voids, shows no degradation due to temperature cycling nor electromigration after high current injection. The degradation of the lateral resistance of the rear side metallization shows a good correlation with the measured series resistance increase.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 722-725, In this contribution, the wet chemical saw damage removal (SDR) and texturing of crystalline silicon wafers are replaced by maskless inductively coupled plasma (ICP) processes. For the SDR, an isotropic ICP process is applied with SF6 as etch gas leading to semicircle surface structures with few microns width. Subsequently, an anisotropic ICP texturing is performed with SF6/O2 forming parabolic like surface structures with lateral extent of approx. 500 nm. A superposition of nanotexture on the SDR microtexture is performed. Optical measurements reveal an average reflection of 3.71 %, transmission of 1.31 % and absorption of 94.98 % integrated from 200-1120 nm under a normal incidence of light after PECVD SiNx passivation. SEM images show a homogenous 70 nm SiNx deposition on the ICP textures. A sufficient passivation is achieved by ICP SF6 SDR with approx. 100 μs effective minority carrier lifetime at 1015 cm-3 minority carrier density (MCD). In combination with the ICP SF6/O2 texture, the samples have approx. 70 μs effective minority carrier lifetime at 1015 cm-3 MCD.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 354-357, Black silicon (b-Si) is of particular interest for the PV industry since it can significantly reduce reflection losses. A promising preparation method of b-Si surface textures is maskless plasma etching. However, the detailed mechanism of maskless plasma texturing in an SF6/O2 atmosphere is still unclear. In particular, the self-masking process is not well understood. For that reason, the change of the elemental composition of the Si surface caused by the plasma process is investigated by X-ray photoelectron spectroscopy (XPS) to discuss the formation of the self-masking layer. Evidence of a fluorine containing oxide layer was found on the surface of b-Si for the first time. Furthermore, it is shown that fluorine desorbs quickly out of the top layer under ambient air, which makes it challenging to characterize the self-masking layer. These results are an important contribution towards the understanding of the formation of plasma etched b-Si and the resulting oxide layer.

Tumor growth in a 72-year-old male patient with malignant haemangiopericytoma in the left hemithorax could be followed radiologically for 4 years before symptoms of recurrent hypoglycaemia appeared. The endogenous insulin level in serum was maximally and serum IGF-1 and IGF-2 markedly reduced. An intravenous arginine load test showed a normal stimulation capacity of the pancreatic glucagon secretion but not that of insulin. After resection of the tumor, blood sugar metabolism was completely normalised. The insulin level, IGF-1 and IGF-2 in serum returned to normal.

Contains fulltext : 153534.pdf (Publisher’s version ) (Open Access) INTRODUCTION: Adults with end-stage kidney disease (ESKD) treated with haemodialysis experience mortality of between 15% and 20% each year. Effective interventions that improve health outcomes for long-term dialysis patients remain unproven. Novel and testable determinants of health in dialysis are needed. Nutrition and dietary patterns are potential factors influencing health in other health settings that warrant exploration in multinational studies in men and women treated with dialysis. We report the protocol of the "DIETary intake, death and hospitalisation in adults with end-stage kidney disease treated with HaemoDialysis (DIET-HD) study," a multinational prospective cohort study. DIET-HD will describe associations of nutrition and dietary patterns with major health outcomes for adults treated with dialysis in several countries. METHODS AND ANALYSIS: DIET-HD will recruit approximately 10,000 adults who have ESKD treated by clinics administered by a single dialysis provider in Argentina, France, Germany, Hungary, Italy, Poland, Portugal, Romania, Spain, Sweden and Turkey. Recruitment will take place between March 2014 and June 2015. The study has currently recruited 8000 participants who have completed baseline data. Nutritional intake and dietary patterns will be measured using the Global Allergy and Asthma European Network (GA(2)LEN) food frequency questionnaire. The primary dietary exposures will be n-3 and n-6 polyunsaturated fatty acid consumption. The primary outcome will be cardiovascular mortality and secondary outcomes will be all-cause mortality, infection-related mortality and hospitalisation. ETHICS AND DISSEMINATION: The study is approved by the relevant Ethics Committees in participating countries. All participants will provide written informed consent and be free to withdraw their data at any time. The findings of the study will be disseminated through peer-reviewed journals, conference presentations and to participants via regular newsletters. We expect that the DIET-HD study will inform large pragmatic trials of nutrition or dietary interventions in the setting of advanced kidney disease.

29th European Photovoltaic Solar Energy Conference and Exhibition; 1759-1762, Transparent conductive oxide (TCO) layers for modern thin-film photovoltaic modules consist of several layers with different electric resistivity. In particular, SnO2-based TCOs exhibit a low resistive, consisting of an F-doped base layer (FTO) and a highly resistive interfacial layer. These interfacial layers are subject to process-induced degradation, which limits the performance of the thin film solar cell by modification of the specific resistance of the highly resistive interfacial layer between absorber material and FTO. This paper presents a method to measure the resistivity of the highly resistive interfacial layer by a modified transfer-length measurement (TLM).

29th European Photovoltaic Solar Energy Conference and Exhibition; 1395-1398, Laser processing of wafers for solar cell production is used i.e. for the application of local laser ablation of dielectric materials for PERC solar cell processing. In the present study 3 different laser-sources and parameters were used for local-contact openings (LCO) on the rear side of the wafer with subsequent metallization. For a microstructure analysis cross-sections have been prepared and investigated by means of scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). We detected in addition to the rear contacts with Al/Si-phase (filled contact) formed voids (void contact) at expected filled contact positions which are caused by the Kirkendall effect [6]. Filled and void contacts are found to be comparable in size and shape. Void contacts can be differentiated in total and intermediate void formations. Detailed measurements revealed information about local rear contact doping in according to the type of formed contact as well as microstructural details of the initial state of the void contact formation process.

29th European Photovoltaic Solar Energy Conference and Exhibition; 1371-1376, Sub-picosecond laser ablation was studied on different dielectric passivation layers. A residual in the high laser fluence ablation spot center was observed as already reported [1, 2, 3, 4], where it was identified to be remaining silicon nitride which was modified in its structure, but not completely removed [1, 2]. The existing theories assume silicon nitride to be present during the formation of this residual. This phenomenon has been confirmed in this work. The formation of this residual was also observed under conditions where no silicon nitride layer was present during the laser irradiation inside the laser irradiated region. It was shown, that there are two different residual formation types, one in the laser spot center and one in the overlapping region of two laser spots. We show that both types can be reproduced independently on several dielectric layers. The influence of the laser beam focus on the residual formation was tested to be irrelevant as well as a re-deposition from the laser generated plasma. In order to study the influence of the residual on the electrical cell parameters, PERC solar cells with different residual coverage were processed. IV measurements show that the series resistance of solar cells increases with increasing residual coverage of the openings.

28th European Photovoltaic Solar Energy Conference and Exhibition; 1231-1235, A wide range laser pulse duration experiment is carried out including pulse durations from 250 femtoseconds (fs) to 30 nanoseconds (ns) based on four different laser systems, two capable of visible (VIS) and ultra-violet (UV) wavelength. All laser systems are used to ablate PECVD SiO2/SiNX and PECVD-based nitride passivation stacks. Test structure samples for photoluminescence (PL) and scanning electron microscopy (SEM) analysis are ablated as well as typical line patterns for PERC solar cells and fluence test samples for all laser systems. In addition standard multi-crystalline (mc) solar cells are ablated on the front side as proposed in [1] to study laser damage effects due to the reduction of the pseudo fill factor (pFF). Thus a comparison of four different evaluation methods (SEM, pFF, PL, IV) for laser damage is carried out showing a good correlation between PL measurements and VOC and pseudo fill factor values from the IV characteristics on solar cell level. The pFF based method, although it is very reliable, does not provide full information for PERC rear side openings which is attributed to the dependence of the aluminum alloy formation on the surface structure remaining after laser ablation.