Ultralow-dielectric transparent single-layer barrier coating based on photocrosslinkable hybrid aliphatic ladder-like polysilsesquioxanes

초록

Organic light-emitting diodes (OLEDs) deliver high color purities and wide viewing angles but are vulnerable to moisture and oxygen, requiring effective barrier coating layers. Although conventional thin-film encapsulation (TFE) methods use multilayer structures, issues related to pinholes and cost-effectiveness remain. Furthermore, touch panels applied to TFE layers to achieve low thicknesses can result in high electromagnetic interference and low touch sensitivity. Herein, we present an effective and facile fabrication strategy for constructing an ultralow-dielectric transparent barrier coating that effectively blocks moisture and oxygen and consequently achieves long lifetimes, even in a single-layer structure. Specifically, photocrosslinkable aliphatic ladder-like polysilsesquioxanes (LPSSQs) with low-dielectric alkyl chains and photoreactive methacrylate groups were employed in an ultralow-dielectric organic-inorganic hybrid encapsulation layer that simultaneously overcomes multilayer issues through high barrier properties and provides reduced signal interference through low dielectric properties. Photoreactive end-capped aliphatic LPSSQs with varying alkyl chains were synthesized via polycondensation and end-capping reactions and UV-cured without organic solvents, resulting in densely crosslinked and highly transmissive single-layer barrier coatings. The resulting LPSSQ-based barrier films exhibited a high optical transmittance of similar to 90%. Furthermore, the water contact angle increased with increasing alkyl chain length, indicating improved hydrophobicity of the barrier coating. A transparent single-layer barrier film comprising LPSSQs with optimal decyl chains providing the best volumetric free space achieved an ultralow dielectric constant of 2.16. This single-layer barrier approach achieved an improved lifetime compared to that of a bare OLED, ensuring its high potential as an effective encapsulation layer with excellent barrier properties.

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