High-sensitivity permeation measurements on flexible OLED substrates

摘要

We describe a novel method to measure permeation rates for oxidizing agents with very high sensitivity. The technique is based on monitoring the resistance of a degrading Ca sensor in situ, inside a climate chamber. A sensitivity limit below 10~(-6)g/m~2day is reported for accelerated measurement conditions of 38℃ and 90% relative humidity. The benefits of the method are demonstrated for single- and double-sided barrier foils, and the temperature and humidity dependence of the transport through PET is analyzed in detail. The method is also applied to obtain permeation rates for a barrier-coated substrate after as well as during bending. Theoretical simulations are used to evaluate the influence of a defect-dominated transport mechanism on the experimental results and to model the time evolution of the concentration profile in a double-barrier stack. Implications for the development of barrier-enhanced substrates for flexible OLED applications are discussed.