• Jansen, Johan
• Durme, Kurt Van
• Ehrhardt, Dorothee
• Van Den Brande, Niko
• Mele, Bruno Van

Abstract

Photovoltaic modules typically contain a number of polymer layers, which may serve as encapsulant, back sheet, or (light-trapping) coating. Even though a variety of polymers is employed, all of them are facing the same challenge: the polymer layers must resist changing weather conditions and daily thermal cycling while maintaining their functionality during the whole module lifespan. However, thermal stress caused by mismatching thermal expansion coefficients of contiguous materials can lead to the formation of small fractures, which can grow into larger defects, and consequently reduce the module’s energy output. By introducing self-healing polymer layers (instead of conventional polymer materials), micro-defects can be autonomously repaired, i.e. without the need for an external intervention, before they start affecting module efficiency.<br/>In this work, Fourier transform infrared spectroscopy, (modulated temperature) differential scanning calorimetry and atomic force microscopy are employed to study the self-healing properties of partially reversible, UV-crosslinked polymer networks. Self-healing is achieved through thermally reversible Diels-Alder bonds, while structural integrity over the whole application temperature range (-40 °C to 85 °C) is maintained due to an irreversible polymer matrix, as demonstrated via dynamic mechanical analysis.<br/>It was recently shown that fully reversible furan/maleimide-based Diels-Alder systems are capable of room temperature healing [1] and that the Diels-Alder reaction even continues below the glass transition temperature (in diffusion-controlled conditions). [2] Hence, the partially reversible polymer layers developed in this work have the potential to exploit the daily temperature cycle of a photovoltaic module for self-healing, even during longer periods of moderate or cold temperatures.<br/><br/>[1] M. M. Diaz, J. Brancart, G. Van Assche, and B. Van Mele, “Room-temperature versus heating-mediated healing of a Diels-Alder crosslinked polymer network”, Polymer, vol. 153, pp. 453–463, 2018.<br/>[2] D. Ehrhardt, J. Mangialetto, R. Verhelle, J. Brancart, B. Van Mele, N. Van den Brande, K. Van Durme, J. Jansen, " The Effect of Vitrification on the Diels-Alder Reaction Kinetics", Central and Eastern European Committee for Thermal Analysis and Calorimetry (CEEC-TAC), p. 368 PS2.002, ISBN 978-3-940237-50-7.

Topics

• impedance spectroscopy
• polymer
• atomic force microscopy
• glass
• glass
• glass transition temperature
• thermal expansion
• defect
• differential scanning calorimetry
• Fourier transform infrared spectroscopy
• dynamic mechanical analysis