Photovoltaic (PV) module efficiency and reliability are two factors that have an important impact on the final cost of the PV electricity production. It is widely accepted that a good adhesion between the encapsulant and the different substrates of a PV module is needed to ensure long-term reliability. Several testing procedures exist that use a metric derived from the force at interface failure to characterize the adhesion. It has, however, not been demonstrated that those metrics relate directly to the interfacial adhesion (defined as the surface energy density needed to break interfacial bonds), and the obtained results usually relate to an apparent adhesion strength. In this work, we describe a new design for compressive-shear testing of polymer layers bonded to rigid substrates. We use it to characterize real interfacial adhesion of ethylene-vinyl acetate (EVA) and polyvinyl-butyral (PVB) to a glass substrate before and after degradation in damp-heat. Our results show that a peak-force based metric is unable to capture the evolution of adhesion through degradation, and a new metric based on the elastic strain energy of the encapsulant is proposed. Moreover, we show that PVB adhesion to glass is much more affected by damp-heat exposure where polymer saturation takes place, in comparison with the adhesion of EVA to glass. The presented characterization protocol is a powerful tool that can help in assessing the reliability of an encapsulant facing specific degradation conditions.

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In several countries, building‐integrated photovoltaics solutions could prospectively contribute to the growth of total installed photovoltaic (PV) capacity as they enable electricity production with minimal impact on free land. However, in some circumstances, the relatively high weight (≥15 kg/m2) of existing glass/glass building‐integrated photovoltaics modules may constitute a barrier to the diffusion of PV in the built environment. With the aim of limiting the weight while preserving excellent mechanical stability and durability properties, we propose a new design for lightweight crystalline‐silicon (c‐Si) PV modules in which the conventional polymer backsheet (or glass) is replaced by a composite sandwich structure, and the frontsheet by a transparent polymer foil. Since sandwich structures are generally realized using epoxy as a gluing material, requiring long processing times, we further investigate (1) the possibility of using standard polymers used in the solar industry as alternative adhesives in the sandwich and (2) the possibility to considerably simplify manufacturing, using conventional lamination processes. Mini‐modules are produced, characterized, and submitted to accelerated aging tests (thermal cycling and damp‐heat) to assess the stability of the product against environmental degradation. We show that, by using the reference epoxy adhesive, it is possible to manufacture a lightweight (~5 kg/m2) mini‐module in a 2‐step process, which successfully passes a selection of industry qualification tests, including thermal cycling, damp‐heat, and hail test. We further show that, by replacing epoxy by a PV adhesive, we are able to considerably simplify the manufacturing process, while preserving excellent mechanical and durability properties.

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