Importance of interface diffusion and climate in defect dominated moisture ultrabarrier applications

OLEDs and organic photovoltaic (OPV) devices require encapsulation from water vapor using a permeation barrier system. As a benchmark for barrier quality, often only a single number is provided as water vapor transmission rate. However, this value is highly dependent on the aging climate. So far, little scientific effort has been undertaken to characterize ultrahigh moisture barriers at different temperatures and relative humidities. We present Ca-test studies on sputtered Zinc-Tin-Oxide and atomic layer deposited AlOx barriers in extensively varied climates. Relative humidities are changed at constant temperatures, and temperatures are changed at constant absolute humidity. We find Henry's law to apply for sorption and discover a fundamental change of the diffusion regime with time related to the interface between the test and the barrier thin-film.