Double-Sided, Omnidirectional γ-AlOOH Hierarchical Nanostructures: Imparting Enhanced Antireflective Properties with Self-Cleaning Capacity for Optical Devices.

Abstract

Herein, we have successfully developed an integrated strategy to develop antireflective coatings with self-cleaning capabilities based on periodic double-sided photonic γ-AlOOH nanostructures to transmit maximum incident light photons. Interfacial reflections are instinctive and one of the fundamental phenomena occurring at interfaces owing to refractive index mismatch. The eradication of such undesirable light reflection is of significant consideration in many optical devices. A systematic approach was carried out to eradicate surface reflection and enhance optical transmission by tailored γ-AlOOH nanostructures. The γ-AlOOH photonic nanostructures with subwavelength features exhibited a gradient index, which almost eliminated the refractive index mismatch at the interface. Optical transmittance of 97% was achieved in the range of 350-800 nm at normal incidence compared to uncoated glass (89%). A multilayer model approach was adopted to extract the effective refractive index of the coating, which showed a graded index from the top to the bottom surface. Further, to fully comprehend the optics of these nanostructures, the omnidirectional (20-70°) antireflective property has been explored using variable-angle specular reflectance spectroscopy. The hierarchical γ-AlOOH nanostructures exhibited only ∼1.3% reflectance at the lower incident angle in the visible spectra and an average reflectance of ∼7.6% up to an incident angle of 70°. Moreover, the hierarchical nanostructures manifested contact angle (CA) >172° and roll-off angle (RA) <1° with excellent self-cleaning performance. Furthermore, the abrasion resistance of the coating is discussed in detail, which displayed a good resistance against sand erosion. Significantly, the photovoltaic performance of the coated modules exhibited a relative enhancement of ∼17% in efficiency, which is attributed to the efficient coupling of light rays. Thus, the integration of the antireflection (AR) property with self-cleaning ability can provide a cost-effective energy solution for optoelectronic devices, display devices, and thin-film optics.