Polysilazane‐Coated Films Achieving Record‐High Moisture Barrier Performance with Sub‐10 Seconds Densification Using High‐Power VUV Irradiation

An ultra-high moisture barrier compact SiN_X film can be achieved from solution-processed perhydropolysilazane (PHPS) through vacuum ultraviolet (VUV) light exposure. This study investigates the photochemical reactions and photo-densification of PHPS-based barrier films under varying VUV light intensities, focusing on their effects on barrier performance. Photo-dehydrogenation of PHPS, involving N─H and Si─H bond cleavage, is efficient and unaffected by light intensity. However, photo-densification shows a strong dependence on light intensity, particularly above 290 mW cm^-2. Higher intensities enhance Si─N bond cleavage, alter film dynamics, and reduce free volume through bond rearrangement, facilitating rapid network reconstruction essential for ultra-high barrier properties. High-power VUV light at 309 mW cm^-2 establishes a new benchmark for ultra-high barrier films via solution processing, achieving a record-low average water vapor transmission rate (WVTR) of 1.6 × 10^-5 g m^-2 day^-1. Films are produced in under 10 s per layer, maintaining a barrier property of 3.8 × 10^-5 g m^-2 day^-1. The optimal refractive index for the top 30 nm layer is 1.74-1.77, controlling WVTR within 10^-5 g m^-2 day^-1, ensuring superior barrier performance for flexible electronic devices, such as perovskite solar cells and organic photovoltaics.