Electron beam cured acrylates as potential planarization layers

Abstract

In this study, electron beam (EB) curable acrylates are investigated for their use as planarization layers. Planarization layers can be used in multilayer thin film encapsulations for all kinds of flexible electronics, such as organic light emitting diodes (OLED), organic photovoltaics (OPV) and printed switching circuits, antennas, and sensors. Planarization layers cover particles and defects of the substrate and thus a plain smooth surface is created for optimized growing conditions of thin films, optimizing encapsulation properties. The thin film encapsulation prevents organic electronics from degradation due to invasive oxygen and water vapor. Several commercially available monomers and oligomers with different molar mass and number of reactive double bonds are investigated. The acrylates are deposited on polyethylene terephthalate (PET) web and glass substrates and cured by EB. The surfaces are analyzed using white light interferometry (WLI) and scanning electron microscopy (SEM). Density measurements and nanoindentation are also carried out to get information about the volume shrinkage and the elastic modulus. The correlation between chemical properties, degree of crosslinking, volume shrinkage and surface roughness are investigated. This work demonstrates that electron beam curing of acrylates is a promising method to generate smooth surfaces. It presents an increasing degree of crosslinking and volume shrinkage with decreasing molecular weight between crosslinks. Also, for comparable molecular weight between crosslinks, the volume shrinkage is higher for acrylates forming thermoplastics than for elastomers or duromers.