Advanced methods for determining PV module process optimization potential

Published: March 24, 2014

By Gernot Oreski, Senior Researcher, Polymer Competence Center Leoben GmbH

Ethylene vinyl acetate (EVA) is still the dominant material used for encapsulation of solar cells. During PV module lamination, a three-dimensional network is formed by a chemical cross-linking of the polymer chains in order to increase the thermal stability of the material and to prevent the material from melting when exposed to application-relevant temperatures of up to 100°C. The cross-linking reaction, which is discontinuous and can take up to 30 min (depending on the EVA type), is the time-determining step in PV module lamination. The main objective of this paper is to gain a comprehensive understanding of the thermomechanical material behaviour during the PV module lamination process, and to develop a basis for the optimization of the PV module manufacturing process. The results presented will demonstrate that dynamic mechanical analysis (DMA) is a valuable and reliable characterization method for the investigation of the curing behaviour of EVA for solar cell encapsulation. DMA in shear mode allows a continuous measurement of the thermomechanical properties, even in the molten state, and therefore an in situ monitoring of the cross-linking reaction. Whereas it is possible to use temperature scans on partially cured EVA films to determine the state of cross-linking, isothermal scans on uncured samples allow the curing kinetics of EVA to be investigated. On the basis of an enhanced knowledge of the cross-linking reaction, the material-related process-parameter optimization potential of the PV module lamination process can be identified, and optimum processing temperature ranges and minimum cross-linking times can be derived.

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