Temperature-dependent water vapour and oxygen permeation through different polymeric materials used in photovoltaic-modules

Most photovoltaic (PV)-modules have polymeric materials as encapsulants and back sheets. Usually these materials are not water vapour-tight and air-tight, but allow permeation of gases from the ambient atmosphere, especially oxygen and water vapour, which could contribute to degradation of the PV-modules.This work gives a short overview on how the permeation process through polymers takes place and how it is influenced by the material properties and ambient conditions. Results of permeation and diffusion measurements for water vapour as well as oxygen are shown for various encapsulation and back sheet materials with special focus on temperature dependence. The results demonstrate differences in permeability and temperature dependence for the investigated materials, but also show similarities for material groups. All investigated materials feature a Fickian behaviour within the measurement conditions even when crossing glass temperature or melting temperature. With these results, an Arrhenius-model was fitted to extrapolate permeation and diffusion values to a temperature range the PV-modules can be exposed to during lifetime.