Towards High Throughput Texturing of Polymer Foils for Enhanced Light Trapping in Flexible Perovskite Solar Cells using Roll‐to‐roll Hot Embossing

A path to further increase the power conversion efficiency of perovskite solar cells is maximizing sunlight absorption by using patterned substrates with enhanced light trapping capabilities. However, to be competitive with traditional solar cells, especially in niche markets, low cost texturing methods need to be developed. In this work, we present as a proof‐of‐concept a roll‐to‐roll hot embossing method to pattern flexible PET foils. The cylindrical mold for the embossing process was structured with periodic grooves by picosecond Direct Laser Interference Patterning (DLIP). The optical characterization of the textured PET shows a tenfold increase in the haze factor (diffuse to global transmittance ratio) compared to flat PET due to the high intensity diffracted beams. Flexible triple cation perovskite cells deposited onto these patterned substrates show on average an 8 % (relative) higher efficiency than similar devices deposited on a reference flat PET substrate. This enhancement can be attributed to the increase in the light trapping provided by the textured substrate. Finally, a cost analysis model shows that the additional cost of integrating the proposed hot embossing step into a perovskite solar module manufacturing facility would represent less than 0.35 % of the initial fabrication cost.Fil: Soldera, Marcos Maximiliano. Technische Universität Dresden; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Wang, Qiong. Helmholtz Zentrum Berlin für Materialien und Energie; AlemaniaFil: Soldera, Flavio Andres. Universitat Saarland; AlemaniaFil: Lang, Valentin. Technische Universität Dresden; AlemaniaFil: Abate, Antonio. Helmholtz Zentrum Berlin für Materialien und Energie; AlemaniaFil: Lasagni, Andrés Fabián. Technische Universität Dresden; Alemania. Fraunhofer Institute For Material And Beam Technology; Alemani

Investigations on micro-mechanical properties of polycrystalline Ti(C,N) and Zr(C,N) coatings

Micro-mechanical properties of Ti(C,N) and Zr(C,N) coatings deposited by chemical vapor deposition on a WC-Co cemented carbide substrate were examined by micro-compression testing using a nanoindenter equipped with a flat punch. Scanning Electron Microscopy, Focused Ion Beam, Electron Backscattered Diffraction and Finite Element Modeling were combined to analyze the deformation mechanisms of the carbonitride layers at room temperature. The results revealed that Ti(C,N) undergoes a pure intergranular crack propagation and grain decohesion under uniaxial compression; whereas the fracture mode of Zr(C,N) was observed to be inter/transgranular failure with unexpected plastic deformation at room temperature.Peer ReviewedPostprint (author's final draft

Tuning morphological features of lead iodide by low pressure vapor phase deposition

Lead iodide (PbI2) is a semiconductor with extensive use as an active layer for X-ray detectors and as a precursor for perovskite solar cells. Here we present a low vacuum method to obtain very uniform PbI2 films with full substrate coverage. This method consists in the sublimation of PbI2 inside a hot zone and its transport by an Ar flow to a substrate held at a controlled temperature. Using scanning electron microscopy combined with focused ion beam and X-ray diffraction we studied the morphology and crystallographic structure of the PbI2 films with different deposition parameters: substrate and source evaporation temperature, deposition time and substrate material. At high substrate temperature (80 °C) and low evaporation temperature (310 °C) onto a glass sample, we obtained dense and smooth PbI2 films showing hexagonal crystals, or platelets, stacked parallel to the substrate. The choice of the substrate material has a significant impact on the film morphology yielding porous-like structures with voids within the films for some substrates. A bandgap Eg = 2.42 eV and Urbach energy EU = 34.7 meV were obtained by absorbance measurements, which are comparable to films evaporated in high vacuum. Photoluminescence studies showed a dependence of the emission energies on the crystal orientation of the platelets which grow differently depending on the deposition conditions. The results show the ability of the low pressure vapor phase deposition technique to obtain good film properties, suitable for sensors and optoelectronic devices.Fil: Koffman Frischknecht, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Soldera, Marcos Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Soldera, Flavio Andres. Universitat Saarland; AlemaniaFil: Troviano, Mauricio Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Carlos, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Pérez, María Dolores. Comisión Nacional de Energía Atómica; ArgentinaFil: Taretto, Kurt Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; Argentin

Surface topography quantification of super hard abrasive tools by laser scanning microscopy

Non-conventional super hard abrasive tools are made of composite materials containing super hard grains, e.g., diamond or cubic boron nitride (CBN) grains, bound by a metallic constitutive phase. These tools are usually produced by means of sintering, and are widely applied in the abrasive machining processes of modern manufacturing, especially in precision machining. The abrasive grains, which induce the material removal processes, are embedded in the metallic binder. They emerge as a consequence of self-dressing, resulting in a self-sharping effect. Therefore, the cutting surface of the tool displays an irregular topography. Quantification of surface topography scenario may supply valuable information to evaluate and understand its correlation to wear mechanisms. In this study, an experimental protocol consisting of five steps: specimen preparation, surface scanning, image assembly, image digital processing and surface quantification, was proposed and validated by characterizing two CBN honing tools used for precision machining: B151/L2/2010/50 (B151) and B91/128/x44/35 (B91) CBN honing stones. It involved the use of laser scanning microscopy and digital imaging processing for assessing significant dimensional, geometrical, and positional properties of CBN grains at the surface of super hard abrasive tools. It was shown that surface topography quantification is an effective method to evaluate and obtain the defined parameters. However, smaller grains may require images with higher resolution; thus, scanning must be refined. Finally, a critical comparative analysis of the experimental results attained for the studied tools pointed out honing stone B91 as more appropriated than B151 one for achieving a higher machining quality of the workpiece.Peer ReviewedPostprint (author's final draft

Thermomechanical Behavior of bulk Ni/MWNT composites produced via powder metallurgy

The thermal expansion behavior of Ni matrix composites reinforced with multiwalled carbon nanotubes (MWNT) fabricated by pressureless sintering and hot uniaxial pressing was studied in the range between 50 and 1050 °C and compared to that of pure Ni. The results show an active interaction between the MWNT and the Ni matrix by reducing the coefficient of thermal expansion (CTE) of pure Ni up to 76% between 50 and 400 °C. This reduction is due to the strong interfacial interaction between the matrix and the reinforcement and the low intrinsic CTE of the nanotubes. This outstanding behavior may be very useful in applications were low CTE is required as for example structural materials.Fil: Suárez, Sebastián. Universitat Saarland; AlemaniaFil: Soldera, Flavio. Universitat Saarland; AlemaniaFil: Gonzalez Oliver, Carlos Julian R.. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Acevedo, Diego Fernando. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mücklich, Frank. Universitat Saarland; Alemani

Atom Probe Tomography investigations on grain boundary segregation in polycrystalline Ti(C,N) and Zr(C,N) CVD coatings

Atom Probe Tomography (APT) was used to obtain a direct evidence of chlor segregation and cobalt diffusion at the grain boundaries (GBs) of polycrystalline coatings deposited by moderate temperature chemical vapor deposition (MT-CVD) on a WC-Co cemented carbide substrate. Reasons behind segregations are discussed, and its effects are correlated to the micromechanical properties of Ti(C,N) and Zr(C,N). It is concluded that chlorine segregation is a relevant factor for explaining the low cohesive strength at the GBs of Ti(C,N) leading to intergranular failure during micro-compression testing, while its absence in Zr(C,N) along with Co diffusion contribute to grain boundary strengthening.Peer ReviewedPreprin

Estudio de la microestructura de un cordón de soldadura de un acero P91 mediante microscopía electrónica de transmisión

En el presente trabajo se llevó a cabo la caracterización microestructural de un cordón de pasada simple de unacero 9Cr1MoVNb P91 obtenido por el proceso de soldadura semiautomática bajo protección gaseosa(FCAW), en la condición “as welding” mediante microscopía electrónica de transmisión.El acero P91 tiene una buena soldabilidad, pero las propiedades mecánicas de las uniones soldadas son inferioresa las del material base. La zona afectada por el calor (ZAC) de este tipo de aceros es de 4 mm lo quedificulta extraer réplicas y láminas delgadas para el estudio de las distintas microestructuras generadas encada sub-zona de la ZAC: ZAC de grano grueso (ZACGG), ZAC de grano fino (ZACGF) y ZAC intercrítica(ZACIC). No obstante, fue posible extraer réplicas de cada región para identificar a los precipitados y pormedio de la utilización de un haz de iones focalizados (FIB-SEM) se pudieron extraer láminas delgadas de unárea específica para caracterizar la microestructura de la matriz.Se caracterizaron los precipitados presentes en cada sub-zona de la ZAC y cómo la disolución del M23C6afecta a la matriz que lo rodea. A bajas temperaturas pico y bajas velocidades de calentamiento/enfriamientotales como las que caracterizan a las zonas de grano fino (ZACIC y ZACGF) se encontró austenita retenidaen contacto de los carburos M23C6 parcialmente disueltos. Por otra parte, en las zonas con más altas temperaturaspico y altas velocidades de calentamiento/enfriamiento (ZACGG y zona fundida) se encontraron películasfinas de austenita retenida en los ex bordes de grano austenítico y en los listones de martensita.Palabras clave: acero 9Cr1Mo, cordón de soldadura, microscopía electrónica

Martensitic transformation in free-standing Cu-Al-Ni thin films with micrometric grain size

The martensitic transformation of polycrystalline thin films based on shape memory alloys is usually affected by the average grain size and by the thickness. We have carried out a study of the temperature driven martensitic transformation in micrometric grain size Cu-Al-Ni films with 18R structure. Thin films with a thickness of 6 μm were grown by sputtering on highly oriented pyrolytic graphite HOPG (0001) substrate at 873 K. After that, the samples were peeled-off from the substrate and annealed at 1123 K for 30 min. The observed microstructure shows an average grain size of 3.7 (± 0.2) μm. The martensitic start temperature (M s) for different films ranges from 170 K to 370 K due to small changes in the chemical concentration. The influence of surface oxides and changes in the atomic order produced by post-quench aging treatments is analyzed. The results show that while surface passivation has a weak influence, changes in the atomic order increase M s without impacting significantly on the hysteresis. Comparison with previous results of nanometric and micrometric grain size samples reveals that the barriers for the transformation are mainly given by plastic deformation at grain boundaries.Fil: Morán, Mauricio Javier. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Condo, Adriana Maria. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Bengió, Silvina. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Soldera, Flavio Andres. Universitat Saarland; AlemaniaFil: Sirena, Martin. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Haberkorn, Nestor Fabian. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

In Situ Analysis of the Phase Transformation Kinetics in the β-Water-Quenched Ti-5Al-5Mo-5V-3Cr-1Zr Alloy during Ageing after Fast Heating

Thermal treatments are the main route to achieve improvements in mechanical properties of β-metastable titanium alloys developed for structural applications in automotive and aerospace industries. Therefore, it is of vital importance to determine phase transformation kinetics and mechanisms of nucleation and precipitation during heat treatment of these alloys. In this context, the present paper focuses on the assessment of solid-state transformations in a β-water-quenched Ti-5Al-5Mo-5V-3Cr-1Zr alloy during the early stages of ageing treatment at 500 ◦C. In situ tracking of transformations was performed using high-energy synchrotron X-ray diffraction. The transformation sequence β + ω → α + α”iso + β is proposed to take place during this stage. Results show that isothermal α” phase precipitates from ω and from spinodal decomposition domains of the β phase, whereas α nucleates from ω, β and also from α” with different morphologies. Isothermal α” is considered to be the regulator of transformation kinetics. Hardness measurements confirm the presence of ω, although this phase was not detected by X-ray diffraction during the in situ treatment