Characterisation of EVA encapsulant material by thermally stimulated current technique

The purpose of this investigation is to better define the thermal behaviour of EVA-based encapsulant during photovoltaic module encapsulation process and also in field exposure in desert climate using the thermally stimulated current (TSC) technique. TSC experiments were conducted on EVA in the temperature range from −150°C to 70°C, the measurements were carried out on uncured and cured specimens of EVA and on EVA samples especially prepared using the laminator equipment. When performing the measurements with the TSC instrument it was noted that the EVA exhibits two peaks assigned to dipole relaxation processes. The peak maximum current and the area under the TSC current peak were used for the determination of the glass transition temperature, activation energy and relaxation frequency. For original EVA, we found that glass transition temperature at constant polarisation voltage and under different polarisation temperatures remain unchanged and is located around −38°C. Also, the activation energy has been determined using initial rise method to be about 0.32 eV. At gel content of 70%, the cured EVA shows a reduced integrated area under the depolarisation peak, especially for the high temperature. The combined change in TSC peak parameters of EVA encapsulant is correlated with the degree of curing.