Fabrication of antireflective polymer films with subwavelength structures using Roll to Roll Nanoimprint Lithography

Anti-reflection based on the mimicking of moth eye subwavelength structures (SWSs) has several advantages over conventionally used multilayer thin film antireflective coatings like broad angular and spectral responses, polarization insensitivity and improved stability. In this study, we present the low cost fabrication of moth eye based SWSs on flexible polyethylene terephthalate (PET) substrate using Roll-to-Roll Ultraviolet Nanoimprint Lithography (UV-NIL). We have used a novel method to create a roller mold with embedded nanopores that can be used for easy replication of SWSs without demolding issues. Pure aluminum foil was wrapped around an acrylic cylinder (Ø = 90mm) and a multistep anodizing and pore widening scheme was employed to create well-ordered and periodic anodized aluminum oxide (AAO) nanopores with different aspect ratios. Optical characterization of the antireflective PET film shows a transmittance over 92 %, an increase of 3% as compared to bare PET, while reflectance can be reduced from 5.3% to 0.09% in the range of visible light. It was observed that higher aspect ratio SWSs is more effective in reducing reflections at higher incident angles. Consequently, we have demonstrated an economically feasible method for fabricating large area polymer films that can be used to reduce light reflections which impose severe limitations on the performance of many optoelectronic devices like solar cells, photodetectors and flat display panels.