Interface effects on the moisture barrier properties of SiN_x/PMMA/SiN_x hybrid structure

Easily degradable organic photovoltaic (OPV) devices based on flexible polymer substrates require barrier films exhibiting extremely low permeation rates for water vapor. We report the barrier properties of hard/soft alternating layer structures where a soft PMMA layer is sandwiched between two hard SiN_x layers. The interfaces between the hard/soft layers hinder the propagation of pinholes from one single-layer to the other and thus have an effect on the overall barrier properties of the whole system. We focus our attention on the effect of increasing number of interfaces on the final barrier properties. The encapsulation barrier properties of these layers are assessed using the electrical calcium test. A minimum water vapor transmission rate (WVTR) of ~2×10^-4g/m²·day is reported for 7 hard/soft interfaces, which has also high potential for flexible barrier applications.