Gernot Oreski

Encapsulants are vital for the structural integrity and protection of photovoltaic (PV) modules, yet the impact of processing history and crosslinking on their thermomechanical behaviour is often oversimplified in numerical simulations. This study experimentally investigates how lamination conditions affect six encapsulant types, including crosslinking (EVA, POE), noncrosslinking (TPO), and coextruded (EPE) materials. The crosslinking behaviour was characterized using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR), while thermomechanical properties were assessed via digital image correlation. Results indicate that conventional DSC‐based methods for the calculations of degree of crosslinking, while standard for EVA, have significant limitations when applied to multilayer encapsulants. Fourier transform infrared spectroscopy in attenuated total reflection mode combined with principal component analysis proved to be an effective, rapid method for qualitative clustering of crosslinked encapsulants. The findings reveal that manufacturing history strongly influences prelamination behaviour, even for the materials labelled under the same commercial nomenclature. Increased lamination duration drives encapsulants toward more isotropic coefficients of thermal expansion (CTE), with noncrosslinking materials reaching final CTE values faster. The presented dataset may support future investigations of stress development, thermomechanical interactions, and material selection in conventional and emerging PV module architectures.

Mass Customization (MC) in photovoltaic (PV) manufacturing enables the production of diverse, cost‐effective integrated PV products through the use of semi‐fabricates. This study evaluates the suitability of six commercially available polyolefin‐based encapsulants for roll‐to‐roll (R2R) lamination, a high‐throughput method essential for MC. Material properties such as melting behavior, viscosity, and crosslinking temperature were assessed alongside optical inspection before and after aging. Also creep behavior was investigated. Two materials exhibited good performance with minor encapsulation flaws and good stability, indicating their strong potential for R2R integration, whereas others showed limitations in curing or durability under thermal stress.

Polypropylene (PP) recyclates from mechanical recycling often contain mixtures of different PP types and grades and exhibit fluctuating material quality and variable property profiles. Since increasing amounts of recyclates must be incorporated into new products while maintaining product performance, the inconsistency can be particularly challenging. Therefore, reliable and rapid methods for material characterization and quality assessment are required to enable timely formulation adjustments. In this study, a PP homopolymer, block copolymer and random copolymer, together with two different PP recyclates, were compounded into binary and ternary blends. The materials and blends were characterized using melt flow rate (MFR) measurements, mechanical testing, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), Fourier-transform infrared (FTIR) and near-infrared (NIR) spectroscopy. Blending the virgin PP types altered the mechanical and thermal properties, generally resulting in intermediate property profiles. The recyclates differed clearly, with the commercial mixed recyclate showing higher MFR and lower ductility, whereas the recyclate from extrusion blow-molded PP bottles showed lower MFR and higher strain at break. FTIR and NIR spectroscopy captured systematic differences between PP types, recyclates and blends. Principal component analysis and correlation analyses showed that spectral data correlated with property changes. Exploratory partial least square regression models further suggested that selected properties can, in principle, be estimated from spectral data, although larger datasets are required for robust prediction. The results highlight the potential of FTIR and NIR spectroscopy for rapid screening, material ranking and quality assessment of PP blends and recyclate-containing materials.

Zusammenfassung: Die Qualität von Polyethylen (PE-)-Rezyklaten ist entscheidend für deren Einsatz in neuen Anwendungen. Der Eintrag gealterter PE-Produkte in den Recyclingstrom kann diese Qualität jedoch mindern. Um den Bedarf an Neumaterial oder zusätzlichen Stabilisatoren zur Kompensation dieser Qualitätsminderung zu reduzieren, ist eine zuverlässige Identifikation und Aussortierung stark gealterter Materialien erforderlich, um die Qualität von PE-Rezyklaten nachhaltig zu verbessern. In dieser Studie wurde das Potenzial der Alterungs- bzw. Degradationserkennung von PE mittels Nahinfrarot (NIR)-Hyperspektraltechnik untersucht. Hierfür wurden PE-Proben künstlich durch UV-Bestrahlung gealtert. Die Degradation wurde durch mechanische Prüfungen erfasst, wobei die Bruchdehnung als Kriterium zur Einteilung in die gewählten Degradationsklassen diente. Die NIR-Hyperspektraldaten wurden an einem NIR-Labor-Setup aufgenommen. Die Trennbarkeit wurde anhand von Klassifikationsmodellen bewertet, wobei sowohl multivariate Datenanalyse (Partial Least Squares Discriminant Analysis) als auch ein Verfahren des maschinellen Lernens (Support Vector Machine) eingesetzt und anschließend miteinander verglichen wurden. Die Ergebnisse zeigen, dass unter Verwendung von maschinellem Lernen hochgradig und weniger gealterte PE-Proben mit hoher Genauigkeit getrennt werden können. Damit eröffnet sich die Möglichkeit, bereits etablierte NIR-Sortiersysteme nicht nur zur Identifizierung von Polymertypen, sondern auch gezielt zur Degradationserkennung einzusetzen, was ein wichtiger Schritt hin zu qualitativ hochwertigeren Rezyklaten sowie Ressourcenschonung ist.

Permanent fluorescent labeling of polyethylene was achieved by covalent grafting of coumarin markers during reactive extrusion. The scalable method prevents marker leaching, while preserving polymer properties and enabling traceability.

In recent years, photovoltaic (PV) encapsulant films marketed as polyolefins (POs), more specifically as PO elastomers (POEs) and thermoplastic POs (TPOs), have gained significant market share and are projected to become the dominant encapsulation films by 2030. Relative to other industries, there are significant misconceptions about the term PO in the PV industry. Both in the scientific literature as well as in sales and advertising, the terms PO, POE, and TPO are often misused to describe the same type of material with comparable properties, while in reality these may each consist of separate material classes. This paper provides a comprehensive literature and market review, to showcase a broad range of PO and other ethylene copolymer encapsulants from recent studies, and discusses the materials' properties to clarify what constitutes a “polyolefin.” In addition, to promote a clearer comparison of encapsulant properties, we propose a two‐dimensional taxonomy to categorize polymers used in module manufacturing, including POs. In terms of improving the reliability of solar PV modules, PO‐based encapsulants have several advantages (including lower water uptake and ion diffusion), but might come with disadvantages too, such as a more complex processing and a higher sensitivity to the storage conditions and shelf life. All this might prospectively impact adhesion properties of the encapsulant to other materials' interfaces (glass, cells etc.) and end‐product quality. Because the track record of field‐deployed PV modules containing PO encapsulants is also limited, we hope to contribute to better material understanding and precision in communication in PV to secure quality.