Cure Kinetics of Electrically Conductive Adhesives for Solar Cell Interconnection

Electrically conductive adhesives (ECA) provide an alternative lead-free interconnection technology for crystalline silicon solar cells with lower thermomechanical stress than standard soldering. They show high potential for use in emerging cell concepts like metal-wrap-through (MWT) or heterojunction technology. Obviously, curing of ECA is a critical step along the interconnection process. Understanding and predicting its cure kinetics is essential for cost-effective and reliable module manufacturing. The cure reaction of an ECA can be described by an autocatalytic reaction model. In order to determine the model parameters, empirical kinetic information of the ECA is needed, which we obtain with dynamic differential scanning calorimetry (DSC). With the use of isoconversional methods the activation energy in dependence of the degree of cure is determined. The model calculates the degree of cure for any given temperature profile. We validate the model with an arbitrary temperature profile in the DSC and find good agreement between experiment and simulation within 3-8% absolute difference in the degree of cure. As the methods given in this paper are easily adopted for the crosslinking reaction of ethylene-vinyl acetate (EVA), we simulate both the curing of ECA and the crosslinking of EVA during a typical lamination process.