Nanoindentation analysis of PV module polymeric components after accelerated aging

The degradation and failure of a PV module can be caused by mechanical property changes in the polymeric components during its lifetime. Previously most of the investigation of the mechanical changes, for example hardness, as well as the aging has been carried out with the polymeric materials as bulk. With nanoindentation the change in hardness of encapsulant and backsheet can be spatially resolved with a high lateral resolution. The nanoindentation tests were carried out on the cross-section of glass/encapsulant/backsheet laminates after sequential doses of 500 h damp-heat (DH) at 85 °C and 85 % r.h. Backsheets with different water vapor permeation rates were used. The results show an increase in hardness (up to 40 MPa from 500 h to 2000 h DH) for the PET-based backsheet (BS1) with the highest water vapor permeation rate, which suggests a high degree of hydrolysis of the PET core layer. The hardness values of the encapsulant in the PV laminate showed a uniform increase with a slightly depth-dependence after DH aging. Especially after 500 h DH exposure, the hardness values were slightly higher near the BSF/encapsulant interface.