One-step synthesis of a mechanically robust, humidity-stable anti-reflective sub-micron coating with high transparency

Abstract

Interfacial light reflection often compromises the efficiency of optical systems, prompting the continuous demand for high-performance anti-reflective (AR) coatings. Porous silica or textured AR coatings usually offer excellent optical properties but suffer from poor adhesion to many organic substrates, especially under high humidity conditions, limiting their use in flexible device applications. To overcome the limitations, the AR coating should possess a low refractive index and mechanical robustness under highly humid conditions. Here, we report a crosslinked fluoropolymer for moisture-resistant, mechanically flexible AR coating fabricated via a single-step, solvent-free polymer deposition method, initiated chemical vapor deposition (iCVD). The 1H,1H,2H,2H-perfluorooctyl acrylate (C6FA) monomer, enabling a low refractive index and flexibility, was copolymerized with a 1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane (V3D3) monomer to impart mechanical durability against humid conditions. The resulting copolymer p(C6FA-co-V3D3) (pFV) exhibited a remarkably low refractive index (n < 1.38). Leveraging the nanometer-scale thickness control inherent to the iCVD process, the coating achieved a two-fold reduction in reflectance compared to the bare substrate across the entire visible spectrum. The compositional optimization enabled the pFV film to retain nearly 100% of its original thickness, refractive index, and smooth surface morphology even after the autoclave test (120 °C, 1 h, 0.3 bar). Optical transmittance exceeding 90% was retained over 10 000 bending cycles at a bending radius of 2 mm without crack or delamination. All these results collectively verified the pFV copolymer film as a promising candidate for next-generation AR coatings demanding simultaneous optical performance, moisture resistance, and mechanical robustness.