Importance of Interface Diffusion and Climate in Defect Dominated Moisture Ultrabarrier Applications

Area of Science:

• Materials Science
• Thin Film Technology
• Device Physics

Background:

• Organic electronic devices like OLEDs and organic photovoltaics (OPVs) need robust encapsulation against water vapor.
• Current water vapor transmission rate (WVTR) benchmarks are often insufficient as they don't account for diverse environmental aging conditions.
• Characterizing ultrahigh moisture barriers under varied temperature and humidity is critical but underexplored.

Purpose of the Study:

• To comprehensively characterize the performance of ultrahigh moisture barriers under diverse environmental conditions.
• To investigate the impact of temperature and relative humidity on barrier quality for sputtered Zinc-Tin-Oxide and atomic layer deposited AlOx.
• To understand the sorption and diffusion mechanisms within these barrier systems.

Main Methods:

• Utilized Calcium (Ca) testing to assess barrier performance.
• Exposed barrier samples (sputtered Zinc-Tin-Oxide and AlOx) to extensively varied climates, manipulating relative humidity at constant temperatures and temperatures at constant absolute humidity.
• Analyzed sorption and diffusion behaviors over time.

Main Results:

• Demonstrated that Henry's law accurately describes water vapor sorption in the tested barriers.
• Identified a significant, time-dependent change in the diffusion regime.
• Observed that this diffusion regime shift is intrinsically linked to the interface between the tested material and the barrier thin-film.

Conclusions:

• The water vapor transmission rate of ultrahigh moisture barriers is highly climate-dependent, necessitating advanced characterization beyond single WVTR values.
• Sorption follows Henry's law, but diffusion dynamics evolve over time, influenced by interfacial effects.
• These findings are crucial for developing reliable encapsulation strategies for sensitive organic electronic devices.