A combined experimental and theoretical study on the side ingress of water into barrier adhesives for organic electronics applications

This paper presents a thorough experimental and theoretical analysis of a model system for the mechanism of cathode degradation in OLED and OPV devices due to lateral side ingress of water vapour into laminated thin film barrier structures. The experimental procedure allows for full quantitative control over layer dimensions of the laminate, as well as the buffer zone width of the lamination adhesive. The optical calcium test is used to monitor side ingress of water vapour both at ambient (20 °C/50% RH) and accelerated (60 °C/90% RH) weathering conditions. Three curable adhesive formulations with sorption and diffusion constants respectively in the range 0.03 < S < 0.4 mol m -3 Pa-1 and 5 × 10-14 < D < 2 × 10-12 m2 s-1 are benchmarked with respect to their capacity to retard ingress and calcium oxidation. A time-resolved 1D semi-analytical model is developed that simulates ingress and degradation. Extensive simulations involving a wide range of values for geometric, material-, and climate-related parameters allow for the derivation of scaling relations for the oxidation front displacement and break-through time as a function of the sorptivity and diffusivity of the lamination adhesive. It is demonstrated that the oxidation front position behaves as: ∼(DS) 1/2 and ∼D1/2Sn, n < 1/2 under permeation- and diffusion-controlled conditions respectively, whereas in those same regimes the break-through time behaves as: ∼d0 2D-1S-0.45 and ∼d0 2D-1Sn, -0.45 < n < 0, d0 indicating the width of the adhesive buffer zone. These insights demonstrate the fully predictive nature of the model and evidence its usefulness for both material development and barrier design for organic electronics applications. cop. the Partner Organisations 2014