Substrate-influenced water-resistant, optical, and ellipsometric properties of electron beam evaporated Ta2O5 transparent coatings

The current study offers a path toward the reliable and affordable manufacturing of high-performance dielectric surfaces consisting of tantalum pentoxide (Ta2O5) functional in the visible to near-infrared (NIR) spectrum. The article reports an in-depth analysis of its fabrication method and characterization for flat optical and photonic applications. Despite the inherent broadband gap of Ta2O5, films formed by conventional magnetron sputtering may unavoidably include flaws and show sub-bandgap absorption. The e-beam physical vapor deposition deposited Ta2O5 films show a high refractive index of nearly 2.2 to 2.1 across the visible wavelengths and a minimal absorption coefficient of k ≈ 0 down to λ0 ≈ 400 nm at an O2 flow rate and evaporation rate of 5 SCCM and 2.5 Å/s, respectively. In this work, Ta2O5 coating had a broadband gap of 3.87–3.91 eV, which permits low-loss and high-transmission functionality over the whole visible-NIR (400–1000 nm) and a portion of the near-ultraviolet (λ ∼ 320 nm) region. Complete oxidation of the annealed film was revealed by x-ray photoelectron spectroscopy, giving a stoichiometric ratio of Ta:O ∼ 2:5, a crucial parameter for lower optical absorbance. Moreover, optical investigations found high transparency (∼85%) in 350 nm ˂ λ ˂ 1000 nm, while the surface morphology exhibited uniform deposition with fairly flakelike grains having a size of 10–25 nm. As the developed coating resolves the issue of dust particle deposition on the solar-facing surface of photovoltaic components through the improved hydrophobic traits (water contact angle ∼ 114°), the coating has practical utility to realize self-cleaning ability of solar cells.