Hydrophobic surface modified HfO₂ antireflective coatings

Abstract

A multifunctional antireflective (AR) thin film is always a prerequisite for growing high-tech applications. Herein we proposed a surface modification technique to transform the hydrophilic behaviour of HfO2 AR nanofilms into hydrophobic without influencing the nanostructure, morphology, refractive index (η) or AR efficacy of HfO2 nanofilms. Our experimental results demonstrate that the fabricated HfO2 AR nanofilms retain its AR efficiency after surface modification to <1% in the visible wavelength range (450–700 nm) on FTO and sapphire. HfO2 AR nanofilms show hydrophilic behaviour before surface modification with a water contact angle (WCA) of 29° on FTO and 22° on sapphire. However, after surface treatment, they display hydrophobic nature θw > θ > 90° with a contact angle of (127°–130°). The experimental result demonstrates that the η of the thin layers fabricated at deposition angle 0°, 80°, and 88° before and after modification remains almost the same. HfO2 AR nanofilms exhibit long term AR permanency as AR efficiency measured within a year practically displays the equivalent reflectance curves similar to as deposit AR thin films, i.e. <1% in the wavelength range of 450–700 nm. We proposed a cost-effective procedure to make hydrophilic AR films to show non-wetting behaviour for its long-term exposure in a moist, damp environment without affecting the refractive index of AR thin film.

Superhydrophobic–Oleophobic Visible–Transparent Antireflective Nanostructured Anodic HfO2 Multifunctional Coatings for Potential Solar Panel Applications

“…Contrarily to the pronounced antireflection effect in the visible range, the nanostructured HfO 2 film obviously improves the reflection in the near-infrared region relative to the uncoated glass and the SiO 2 /Si wafer. Generally, the optical behavior of the present films in the visible range does not contradict the results published in the literature on optical properties of HfO 2 nanofilms prepared via different techniques on dissimilar substrates. − However, in the near-infrared region, the present films are apparently more reflective and less transparent than the reported films. Such a specific optical behavior, also revealed in the most recent work on spin-coated HfO 2 films, is considered advantageous for multifunctional superself-cleaning heat-protective dielectric HfO 2 coating with properties on demand for the solar energy industry, which will be discussed in section .…”