**2.2. Loss of adhesion in backsheet films**

The multilayer composites that make up PV module backsheet films comprise three or more polymer layers. Outer layers provide resistance to weathering factors such as sunlight and humidity and are often made from fluoropolymers with polyvinyl fluoride (PVF), polyamide (PA), or polyethylene terephthalate (PET) [8] being popular choices.

Backsheet failures include yellowing, brittleness that leads to cracking, and delamination within the multilayer composite. Delamination and cracking allow water vapor and oxygen into the PV module and are considered to be the worst kind of failures within backsheets as they cause problems with isolation and subsequently can cause safety issues [9]. Water vapor critically affects degradation phenomena such as decomposition of the encapsulation, corrosion of the metal parts, and potential induced degradation (PID) of the PV modules. Such failures impact on the performance of a PV module and shorten its lifespan. Yellowing, on the other hand, has not been reported as having an influence on the electrical performance of modules.
