Robust operation of mesoporous antireflective coatings under variable ambient conditions

Antireflective coatings (ARCs) are important components in optical applications due to their ability to reduce reflection and maximize transmission of light across interfaces. Generating mesoporous films with adequate film thickness and refractive index is a common method to achieve amplitude and phase matching in low-cost single- layer interference-based ARCs. For high surface energy materials, pores on the 2 - 50 nm, i.e. the sub-wavelength scale, are subject to capillary condensation, and pore filling by surrounding gas phase water molecules at size-characteristic humidity values hampers their functioning. In this work, we examine the effect of relative humidity on mesoporous ARCs and present a simple method for the preparation of ARCs with robust operation under variable conditions. The materials route is based on the generation of well-defined porous aluminosilicate networks by block copolymer co- assembly with poly(isobutylene)block-poly(ethylene oxide) and post-synthesis grafting of trichloro(octyl)silane molecules to the pore walls. The functionalized films exhibited a maximum transmittance value of 99.8% with an average transmittance of 99.1% in the visible wavelength range from 400 nm to 700 nm. Crucially, the AR performance was maintained at high humidity values with an average transmittance decrease of only 0.2% and maximum values maintained at 99.7 %, which compared to maximum and average losses of 3.6% and 2.7 %, respectively, for non-functionalized reference samples. The ARCs were shown to withstand at least 50 humidity cycles, indicating long-term stability against fluctuating environmental conditions.