Hygrothermal and thermal cyclic stresses on thin-film Si photovoltaic modules

Degradation behavior of thin-film Si photovoltaic modules by hygrothermal and thermal cyclic stresses was studied. Degradation progresses along the scribe lines for integration and from the slit on back sheet for taking out interconnector ribbons. Not only acetic acid generated by hydrolysis reaction between ethylene-vinyl acetate encapsulant and penetrating water vapor but also water vapor itself is the origin of degradation. It is important that high-barrier ability back sheet with low water-vapor transmission rate is employed and also important how suppress the water-vapor ingress from the slit on the back sheet. On the other hand, thin-film Si photovoltaic modules show high tolerance to thermal cyclic stress since only a few interconnector ribbons are employed.