Abstract
Flexible organic electronic devices are often protected from degradation by encapsulation in multilayered films with very high barrier properties against moisture and oxygen. However, metrology must be improved to detect such low quantities of permeants. We therefore developed a modified ultra-low permeation measurement device based on a constant-flow carrier-gas system to measure both the transient and stationary water vapor permeation through high-performance barrier films. The accumulation of permeated water vapor before its transport to the detector allows the measurement of very low water vapor transmission rates (WVTRs) down to 2 × 10-5 g m-2 d-1. The measurement cells are stored in a temperature-controlled chamber, allowing WVTR measurements within the temperature range 23-80 °C. Differences in relative humidity can be controlled within the range 15%-90%. The WVTR values determined using the novel measurement device agree with those measured using a commercially available carrier-gas device from MOCON®. Depending on the structure and quality of the barrier film, it may take a long time for the WVTR to reach a steady-state value. However, by using a combination of the time-dependent measurement and the finite element method, we were able to estimate the steady-state WVTR accurately with significantly shorter measurement times.
Highlights
Recent developments in flexible organic electronic devices require flexible encapsulation materials with extremely high barrier properties against moisture and oxygen to protect the sensitive active and electrode materials
With a After standard deviation σWVTRzero of 1.0 this zeroing period, the relative humidity was set to 36%
The mean and standard deviation σWVTRsteady of the last five values, calculated using the same procedure applied during the zeroing period, were 6 × 10 5 and 1.6 × 10 5 g m 2 d 1, respectively
Summary
Recent developments in flexible organic electronic devices require flexible encapsulation materials with extremely high barrier properties against moisture and oxygen to protect the sensitive active and electrode materials. A current approach for the production of such encapsulation films is to coat polymeric substrate films such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) with alternating inorganic and organic layers.1,2 These materials have a long lag time before water penetration, in addition to a low steadystate water vapor transmission rate (WVTR), to ensure the long-term protection of the sensitive device layers. The WVTR values recorded before the water vapor permeation process reaches its steady-state are too low, producing inaccurate data that overestimate the performance of barrier materials. We developed an efficient and systematic approach for the measurement of water vapor permeation based on the accumulation of water vapor and an appropriate evaluation method. Same time independent of the barrier performance of the samples. (d) The combination of measurements and advanced theoretical calculations based on the finite element method (FEM) allows us to predict steady-state WVTR values accurately, long before steady-state conditions have been reached
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