On March 6, 2025, Professor Kiyosato Toshiyuki and his team at Yamagata University's Organic Electronics Innovation Center announced a significant breakthrough in barrier technology by forming high-performance water vapor barrier films. By coating polysilazane (PHPS) and exposing it to high-intensity vacuum ultraviolet light (VUV), the research team successfully developed dense silicon nitride films, surpassing previous world records for water vapor barrier performance.
The enhanced PHPS film functions as an effective water vapor barrier film, achieving the remarkable water vapor transmission rate (WVTR) of 1.8 x 10-5 g/m2/day. This innovative method addresses the growing need for advanced barrier materials, particularly for next-generation organic electroluminescent (OLED) displays and perovskite solar cells, which are known for their sensitivity to moisture.
"This achievement not only enhances the performance of barrier materials but also addresses production efficiency," said Professor Kiyosato. The significance of this development lies not just in its performance but also the production processes, which have historically relied on inefficient vacuum processes leading to high costs. The new solution process enables large-scale manufacturing with lower costs, making it suitable for diverse applications.
The key to this advancement was the research team’s investigation of the reaction mechanisms influenced by the light intensity provided by the Xe excimer lamp, the source of VUV irradiation. By adjusting the lamp intensity between 103 and 309 mW/cm2, the researchers observed accelerated photo-densification reactions of the PHPS films under high-intensity VUV light, which could simultaneously shorten light irradiation times and improve barrier performance.
Previous techniques required approximately 2.5 minutes for light irradiation to achieve optimal barrier qualities. The breakthrough allows for this time to be drastically reduced to just 10 seconds, representing around 1/15th of the previous method's duration. Such efficiency is integral for commercial viability, particularly when mass production is concerned.
Following evaluations of the films irradiated at both lamp intensities, it was found these PHPS films exhibited significant absorption of VUV light at the irradiated surface. Measurements of the refractive index within the films revealed non-uniformity, with the surface displaying higher refractive indices. Focusing on the surface’s refractive index of 30 nm offered insights indicating its role as a water vapor barrier.
The findings also indicated the refractive index would increase with the integrated light amount applied. For example, films irradiated with 309 mW/cm2 at 3 J/cm2 exhibited higher refractive indices compared to those treated with lower intensities and higher total light amounts, demonstrating more effective densification.
By constructing barrier structures using three units (a total of six layers), researchers conducted water vapor transmission rate (WVTR) assessments, leading to the conclusion the developed solution-processed barrier structure outperformed previous records by 2.8 times. Even at lower irradiation conditions yielding only 3 J/cm2 of integrated light, the films achieved durability with WVTR = 3.8 x 10-5 g/m2/day, showcasing the enhanced barrier capabilities of the technology.
The current findings signal not just notable upgrades to barrier efficiency, but also the technological leap forward for industries reliant on moisture protection, including electronics and packaging sectors. "The substantial reduction of light irradiation time is key to making this process viable for mass production," Professor Kiyosato added, projecting hopes for broader applications beyond the immediate focus on solar cell technologies.
This research embodies the shift toward developing sustainable, efficient materials through innovative processes which, as it advances, promises to yield substantial impacts on manufacturing practices across various industries. The continued exploration of refining the barrier structures, as well as potential reductions in layer counts, indicates promising directions for future studies and commercial applications.