Cure state assessment of EVA-copolymers for PV-applications comparing dynamic-mechanical, dielectric and calorimetric properties

An ethylene vinyl acetate copolymer is widely used in photovoltaic industry as a pottant for crystalline solar cells. During solar module manufacturing the material undergoes a peroxide curing process which leads to elastomer like material properties. In this work, we applied a dielectric method using comb measuring electrodes for determination of EVA progress of cure. At first, we showed the direct correlation of calorimetric measurements, analyzing the consumption of peroxide cross linking agent, with dynamic viscosimetric measurements at different cure temperatures. In a second step, isothermal dielectric measurements have been chosen as a possible tool for direct cure monitoring in vacuum lamination processes. It was found that all methods show the same correlation and are powerful tools for cure monitoring. As we show in a final practical test, course of dielectric parameters can be monitored during a lamination procedure.