Low-Dielectric Flexible Thin Film Encapsulation Materials Based on Molecular Engineering of Photoreactive Ladder-like Polysilsesquioxane

초록

Flexible organic light-emitting diodes (OLEDs) have attracted significant attention in the display industry owing to their unique self-emissive properties, high resolution, and various form factors. However, signal interference between adjacent capacitive touchscreen panels and high-speed, anode-dispersed OLED devices remains a challenge. Herein, we propose an unprecedented and effective strategy to minimize signal interference and distortion in OLEDs using low-dielectric flexible thin-film encapsulation materials based on photoreactive ladder-like polysilsesquioxanes (PSSQs). Although conventional thin-film encapsulation layers in flexible OLEDs may hinder the touch sensing performance owing to the high dielectric constant, our innovative approach of integrating a low-dielectric function into the flexible encapsulation layer can mitigate the signal interference of the OLEDs and simultaneously reduce the device thickness owing to the absence of an additional low-dielectric layer between the OLED and touchscreen panels. To this end, we synthesized photoreactive transparent PSSQs into ladder-like structures via a sol-gel reaction. The photoreactive acrylate groups of PSSQs formed a dense cross-linked structure in the thin encapsulation film upon ultraviolet (UV) exposure, achieving a remarkably low dielectric constant of 2.21 and a high optical transmittance of 99.5%. Furthermore, low-dielectric ladder-like PSSQs were blended with acrylate-based monomers to impart high flexibility to the thin encapsulation films. Incorporating acrylonitrile and methyl methacrylate effectively reduced the critical bending radius of the encapsulation films and improved the device lifetime by 243% relative to that of OLED devices encapsulated with conventional high-dielectric acrylate-based materials while maintaining low dielectric properties and high optical clarity. In addition, our low-dielectric flexible thin films effectively suppressed capacitive coupling between the finger and sensor electrodes, thereby satisfying the signal interference requirements of flexible, high-speed, OLED devices. By incorporation of a low dielectric function into the flexible encapsulation layer, the proposed strategy paves the way for the fabrication of flexible, lightweight, and thin optoelectronic devices with guaranteed lifetimes.

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